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Impact of non-invasive oxygen reserve index versus standard SpO2 monitoring on peripheral oxygen saturation during endotracheal intubation in the intensive care unit: Protocol for the randomized controlled trial NESOI2
NESOI2
Hille Hugo Conceptualization Investigation Methodology Writing – original draft 1
Le Thuaut Aurélie Data curation Formal analysis Methodology 2
Asfar Pierre Investigation Writing – review & editing 3
Quelven Quentin Investigation Writing – review & editing 4
Mercier Emmanuelle Investigation Writing – review & editing 5
Le Meur Anthony Investigation Writing – review & editing 6
Quenot Jean-Pierre Investigation Writing – review & editing 7
Lemiale Virginie Investigation Writing – review & editing 8
Muller Grégoire Investigation Writing – review & editing 9 10
Cour Martin Investigation Writing – review & editing 11
Ferré Alexis Investigation Writing – review & editing 12
Berge Asael Investigation Writing – review & editing 13
Curtiaud Anaïs Investigation Writing – review & editing 14 15
Touron Maxime Investigation Writing – review & editing 16
Plantefeve Gaetan Investigation Writing – review & editing 17
Chakarian Jean-Charles Investigation Writing – review & editing 18
Ricard Jean-Damien Investigation Writing – review & editing 19
Colin Gwenhael Investigation Writing – review & editing 20
Orieux Arthur Investigation Writing – review & editing 21
Girardie Patrick Investigation Writing – review & editing 22
Jozwiak Mathieu Investigation Writing – review & editing 23 24
Rouaud Manon Conceptualization Methodology Project administration Supervision Validation Writing – review & editing 2
Juhel Camille Investigation Methodology Project administration Supervision Visualization Writing – review & editing 1
Reignier Jean Conceptualization Investigation Project administration Writing – review & editing 25
https://orcid.org/0000-0003-3706-078X
Lascarrou Jean-Baptiste Conceptualization Data curation Formal analysis Funding acquisition Investigation Methodology Project administration Resources Software Supervision Validation Visualization Writing – original draft Writing – review & editing 25 *
for the CRICS-TRIGGERSEP Network ¶
1 Medecine Intensive Reanimation, Nantes University Hospital, Nantes, France
2 Research and Innovation Department, Methodology and Biostatistics Platform, Nantes University Hospital, Nantes, France
3 Intensive Care Unit, Angers University Hospital, Angers, France
4 Intensive Care Unit, Rennes University Hospital, Rennes, France
5 Intensive Care Unit, Tours University Hospital, Tours, France
6 Intensive Care Unit, Cholet Hospital, Cholet, France
7 Intensive Care Unit, Dijon University Hospital, Dijon, France
8 Intensive Care Unit, Saint-Louis University Hospital, Assistance Publique-Hôpitaux de Paris (AP-HP), Paris, France
9 Centre Hospitalier Universitaire (CHU) d’Orléans, Médecine Intensive Réanimation, Université de Tours, MR INSERM 1327 ISCHEMIA, Université de Tours, Tours, France
10 Clinical Research in Intensive Care and Sepsis–Trial Group for Global Evaluation and Research in Sepsis (CRICS_TRIGGERSep) French Clinical Research Infrastructure Network (F-CRIN) Research Network, Orléans, France
11 Médecine Intensive-Réanimation, Edouard Herriot Hospital, University of Lyon, Lyon, France
12 Intensive Care Unit, Versailles Hospital, Le Chesnay, France
13 Intensive Care Unit, Haguenau Hospital, Haguenau, France
14 Department of Intensive Care (Service de Médecine Intensive—Réanimation), Hôpitaux Universitaires de Strasbourg, Strasbourg, France
15 INSERM (French National Institute of Health and Medical Research), UMR 1260, Regenerative Nanomedicine (RNM), University of Strasbourg, Strasbourg, France
16 Intensive Care Unit, Cochin University Hospital, Assistance Publique-Hôpitaux de Paris (AP-HP), Paris, France
17 Intensive Care Unit, Argenteuil Hospital, Argenteuil, France
18 Service de réanimation, Centre hospitalier de Roanne, CS 80511–42328 Roanne CEDEX, Roanne, France
19 Intensive Care Unit, Louis-Mourier Hospital, Assistance Publique-Hôpitaux de Paris (AP-HP), Colombes, France
20 Intensive Care Unit, Vendée District Hospital, La Roche-sur-Yon, France
21 Intensive Care Unit, Bordeaux University Hospital, Bordeaux, France
22 Intensive Care Unit, Lille University Hospital, Lille, France
23 Intensive Care Unit, Nice University Hospital, Nice, France
24 UR2CA, Unité de Recherche Clinique Côte d’Azur, Université Côte d’Azur, Nice, France
25 Nantes Université, Nantes University Hospital, Intensive Care Unit, Motion-Interactions-Performance Laboratory (MIP), UR 4334, Nantes, France
Yamamoto Ryo Editor
Keio University School of Medicine, JAPAN
Competing Interests: JBL has received lecturing fees from BD and Masimo. Alexis Ferré reports honoraria by Fisher & Paykel for a lecture during the 2022 SFMU Congress, which bears no relation to the submitted work. None of the other authors has any competing interests to disclose. This does not alter our adherence to PLOS ONE policies on sharing data and materials.

¶ The members of the CRICS-TRIGGERSEP Network are listed in the Acknowledgments section

* E-mail: jeanbaptiste.lascarrou@chu-nantes.fr
16 9 2024
2024
19 9 e03077238 2 2024
7 7 2024
© 2024 Hille et al
2024
Hille et al
https://creativecommons.org/licenses/by/4.0/ This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

In critically ill patients, endotracheal intubation (ETI) is lifesaving but carries a high risk of adverse events, notably hypoxemia. Preoxygenation is performed before introducing the tube to increase the safe apnea time. Oxygenation is monitored by pulse oximeter measurement of peripheral oxygen saturation (SpO2). However, SpO2 is unreliable at the high oxygenation levels produced by preoxygenation and, in the event of desaturation, may not decrease sufficiently early to allow preventive measures. The oxygen reserve index (ORI) is a dimensionless parameter that can also be measured continuously by a fingertip monitor and reflects oxygenation in the moderate hyperoxia range. The ORI ranges from 0 to 1 when arterial oxygen saturation (PaO2) varies between 100 to 200 mmHg, as occurs during preoxygenation. No trial has assessed the potential effects of ORI monitoring to guide preoxygenation for ETI in unstable patients. We designed a multicenter, two-arm, parallel-group, randomized, superiority, open trial in 950 critically ill adults requiring ETI. The intervention consists in monitoring ORI values and using an ORI target for preoxygenation of at least 0.6 for at least 1 minute. In the control group, preoxygenation is guided by SpO2 values recorded by a standard pulse oximeter, according to the standard of care, the goal being to obtain 100% SpO2 during preoxygenation, which lasts at least 3 minutes. The standard-of-care ETI technique is used in both arms. Baseline parameters, rapid-sequence induction medications, ETI devices, and physiological data are recorded. The primary outcome is the lowest SpO2 value from laryngoscopy to 2 minutes after successful ETI. Secondary outcomes include cognitive function on day 28. Assuming a 10% standard deviation for the lowest SpO2 value in the control group, no missing data, and crossover of 5% of patients, with the bilateral alpha risk set at 0.05, including 950 patients will provide 85% power for detecting a 2% between-group absolute difference in the lowest SpO2 value. Should ORI monitoring with a target of ≥0.6 be found to increase the lowest SpO2 value during ETI, then this trial may change current practice regarding preoxygenation for ETI.

Trial registration: Registered on ClinicalTrials.gov (NCT05867875) on April 27, 2023.

French Ministry of Health PHRC-21-0202 https://orcid.org/0000-0003-3706-078X
Lascarrou Jean-Baptiste The NESOI2 trial is funded by the 2021 Programme Hospitalier de Recherche Clinique National of the French Ministry of Health (grant number PHRC-21-0202). The funder had no role in designing the trial and will have no role in collecting, analyzing, or interpreting the data; writing the trial report; or deciding to submit the trial report for publication. The funder had no role in writing the present manuscript or in deciding to submit it for publication. Data AvailabilityNo datasets were generated or analysed during the current study. All relevant data from this study will be made available upon study completion.
Data Availability

No datasets were generated or analysed during the current study. All relevant data from this study will be made available upon study completion.
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pmcIntroduction

Endotracheal intubation (ETI) is performed as a lifesaving procedure in nearly a quarter of patients admitted to the intensive care unit (ICU) [1]. However, in this vulnerable population, complications occur during up to half of ETI procedures [2]. Severe complications consist of profound hypoxemia (26% of cases) and/or hypotension (25%), cardiac arrest (1%–3%), and death (0.5%–3%) [1,3,4]. Risk factors for severe hypoxemia include hypoxemia before ETI and difficult ETI [5]. Severe hypoxemia increases the risk of complications, including cardiac arrest, during ETI [3,6].

Preoxygenation is universally recommended to reduce the risk of hypoxemia by increasing the apneic time without desaturation [7,8]. However, the efficacy of preoxygenation is challenging to assess. Invasive PaO2 measurement is the reference standard but cannot be performed continuously in real time at the bedside [9]. Pulse oximetry estimation of peripheral oxygen saturation (SpO2) is the oxygenation-monitoring tool most widely used during ETI in the ICU but detects hypoxemia only with a delay. Predicting hypoxemia during ETI is essential to allow timely preventive action [5]. Importantly, SpO2 does not reliably reflect PaO2 in the moderate hyperoxia range achieved during preoxygenation. An end-tidal oxygen fraction (EtO2) greater than 90% has been suggested as a preoxygenation target [10]. However, EtO2 cannot be monitored in most ICUs and may be biased by leaks around the mask [9]. Moreover, in critically ill patients, notably those with acute hypoxemic respiratory failure, EtO2 does not reflect oxygen reserves and therefore the effectiveness of preoxygenation [9,11]. EtO2 and SpO2 may be high despite low PaO2 values. Finally, during acute respiratory failure, the functional reserve capacity decreases and intrapulmonary shunting bypasses alveolar-capillary exchanges, so that EtO2 does not reflect changes in PaO2 [12].

Preoxygenation is usually performed for 3 to 4 minutes, but whether this duration is optimal in all patients remains unclear. In one study, increasing the duration of preoxygenation did not seem to improve efficacy [13]. An additional parameter for optimizing the efficacy of preoxygenation and predicting hypoxemia during ETI would thus be welcome.

The oxygen reserve index (ORI) is a recently introduced parameter that can be continuously monitored using the Masimo Rad-97 finger monitor, which also monitors SpO2 (Masimo, Irvine, CA). This dimensionless index reflects oxygenation levels in the moderate hyperoxia range targeted by preoxygenation, defined as PaO2 between 100 and 200 mmHg. The ORI can range from 0.00 (PaO2 = 100 mmHg) to 1.00 (PaO2 = 200 mmHg). As indicated above, SpO2 does not reflect oxygenation within this range, since values ≥97% may indicate PaO2 levels between 90 and 600 mmHg [14]. In contrast, a preoxygenation ORI target corresponding to the desired level of hyperoxia can be defined. In addition, ORI monitoring may provide an early warning that desaturation is about to occur. The potential usefulness of the ORI for this purpose has only been evaluated in small observational studies of patients undergoing scheduled surgery. ORI values dropped below 0.4 a median of 30 [20–60] seconds before the onset of desaturation [15,16]. Our recent observational NESOI study showed that, in non-hypoxemic patients undergoing ETI, ORI fell below 0.4 a median of 81 [34–146] seconds before SpO2 decreased below 97% during the apnea following induction [17]. This time interval is sufficient to implement preventive measures such as mask ventilation or insertion of a supraglottic device. Interestingly, a high ORI value during preoxygenation independently predicted the absence of hypoxemia during ETI.

To assess the potential benefits of ORI monitoring during preoxygenation for ETI vs. the standard of care, we designed a multicenter randomized controlled trial in critically ill patients admitted to the ICU. The primary outcome is the lowest SpO2 value recorded during ETI.

Material and methods

This manuscript was written in accordance with Standard Protocol Items: Recommendations for Interventional Trials (SPIRIT) guidelines [18].

The first patient was recruited on August 1, 2023. On January 11, 2024, 203 patients had been included, i.e., 21.3% of the planned sample.

Design, objectives, and setting

This protocol is for a multicenter, parallel-group, two-arm, randomized, controlled, trial comparing preoxygenation with a target ORI ≥0.6 for 1 minute to standard pulse-oximeter SpO2 monitoring in critically ill patients undergoing ETI. The ORI is monitored using the Masimo Rad-97 monitor (Masimo, Irvine, CA, USA), which also measures SpO2.

The primary objective is to determine whether ORI monitoring during ETI with the above-described target (designated “ORI monitoring” hereafter) increases the lowest SpO2 value recorded by the Rad-97 monitor between the first introduction of the laryngoscope into the mouth and the end of the second minute following successful intubation. The secondary objectives are to determine whether ORI monitoring increases the lowest SpO2 value that is recorded by the standard pulse oximeter (sensitivity analysis of the primary outcome) and/or that is observed in the predefined sub-groups detailed below (subgroup analysis of the primary outcome), to assess the safety of ORI monitoring based on the occurrence of immediately life-threatening adverse events as described below, and to assess the efficacy of ORI monitoring based on the efficacy outcomes listed below.

Outcomes

The primary outcome is the lowest SpO2 value measured by the Rad-97 monitor between the first introduction of the laryngoscope into the mouth and the end of the second minute following successful intubation. One of the secondary outcomes is the lowest SpO2 value recorded by the standard pulse oximeter between the first introduction of the laryngoscope into the mouth and the end of the second minute following successful intubation; analysis of this outcome constitutes a sensitivity analysis of the primary outcome.

Additional secondary outcomes are the lowest SpO2 values in subgroups defined based on body mass index (BMI) <30 vs. ≥30 kg/m2, hypoxemia vs. other reason for ETI, presence vs. absence of shock at inclusion, difficult vs. non-difficult ETI, and highest ORI during preoxygenation <0.6 vs. or ≥0.6. The immediately life-threatening adverse events considered for assessing the safety of ORI monitoring are severe hypoxemia defined as SpO2<80%, severe hypotension defined as systolic blood pressure (SBP) <90 mmHg, cardiac arrest, and death. Finally, the efficacy outcomes are ICU mortality, day-28 mortality, ICU and hospital stay lengths, and cognitive status on day 28 as evaluated using the validated French version of the modified Telephone Interview for Cognitive Status (F-TICS-m) [19].

Patients

The patients are being recruited at 20 French ICUs. Recruitment started on August 1, 2023 and is expected to end in December 2025. Consecutive adults requiring ETI in the ICU are eligible if not included in another study of ETI with an oxygen-based outcome criterion. Follow-up data are collected from trial inclusion to day 28 or death, whichever occurs first. The SPIRIT figure “Schedule of enrolment, interventions, and assessment for patients” is Fig 1.

10.1371/journal.pone.0307723.g001 Fig 1 SPIRIT schedule of enrolment, interventions, and assessments.

Inclusion criteria

The inclusion criteria are ICU admission and a need for ETI and oxygen therapy (regardless of the device and flow rate) to obtain SpO2>97%.

Non-inclusion criteria

The non-inclusion criteria are age younger than 18 years, need for fiberoptic intubation (as determined by the attending intensivist), contraindication to laryngoscopy (e.g., unstable spinal-cord injury), insufficient time to include and randomize the patient (e.g., due to cardiac arrest), pregnancy, breastfeeding, being a correctional facility inmate, being under guardianship, not being covered by the French statutory health insurance system, and refusal of the patient (if competent) or next of kin to participate in the trial.

Randomization

Blocked randomization in a 1:1 ratio is achieved using a computer-generated random sequence of numbers, via the secure Ennov Clinical website (https://nantes-lrsy.ennov.com/EnnovClinical). At each center, the investigators will use their identification number and password to log into the site to enroll patients. The investigators will not be aware of the blocking details. Randomization is stratified based on center, intubating intensivist experience with ETI (expert vs. non-expert as defined below), and preoxygenation device used (NIV vs. other) (Fig 2).

10.1371/journal.pone.0307723.g002 Fig 2 Patient flowchart.

The Rad-97 monitor is used in both groups but the display is masked and invisible to the intubating intensivist in the control group. Blinding of the intubating physician to trial group allocation is not feasible as the Rad-97 monitor itself is visible in both groups. However, Rad-97 ORI and SpO2 values are recorded for the trial by a clinical research nurse not involved in the ETI procedure or in any other components of patient management.

Intervention and control arms

Intervention arm

The trial intervention consists in monitoring the ORI to achieve a value ≥0.6 for 1 minute during preoxygenation. The end of preoxygenation is defined as the start of induction, which occurs when the preoxygenation duration is at least 3 minutes and the ORI has been ≥0.6 for at least 1 minute. Thus, if ORI is ≥0.6 after 90 seconds of preoxygenation, induction is started 90 seconds later, after 3 minutes of preoxygenation. If ORI is ≥0.6 after 2.5 minutes of preoxygenation, induction is started 1 minute later, after 3.5 minutes of preoxygenation. In patients whose ORI remains <0.6 after 3 minutes of preoxygenation, the preoxygenation device is changed and preoxygenation continued until ORI is ≥0.6 for at least 1 minute. When this goal is not achieved, no maximal preoxygenation duration is specified given the pragmatic trial design; however, the investigators have been informed than 6 to 8 minutes of preoxygenation are expected to maximize benefits) (Fig 3). The ORI threshold of 0.6, corresponding to an estimated PaO2 value of 160 mmHg, was chosen based on unpublished personal data (JBL). The SpO2 values recorded by the standard pulse oximeter are also communicated to the intubating intensivist.

10.1371/journal.pone.0307723.g003 Fig 3 Details of the intervention.

Control arm

In the control group, oxygenation is monitored according to the standard of care, that is, using the standard pulse oximeter available in each ICU (Fig 4A and 4B). The intubating intensivist will not be aware of the SpO2 and ORI values provided by the Rad-97 monitor throughout the ETI procedure, which are recorded by the clinical research nurse. The Rad-97 monitor is masked and its alarms turned off. Preoxygenation lasts at least 3 minutes, with no maximum duration.

10.1371/journal.pone.0307723.g004 Fig 4 Details of endotracheal intubation management in the control and intervention arms

(A) Control arm. (B) Intervention arm.

Standard of care applied in both arms

The other components of the standard of care are applied in both arms. Two intensivists are present throughout the entire ETI procedure, including at least one ETI expert defined as having at least 5 years of ICU experience or at least 1 year of ICU experience plus at least 2 years of operating-room experience [20]. At least one of the two intensivists is trained in ORI monitoring. One of the two intensivists is the physician in charge of the patient. Preoxygenation is not started until the standard pulse oximeter and Rad-97 monitor are in place, on different fingers (ideally the forefinger for the standard pulse oximeter and the middle finger for the Rad-97 monitor) of the hand on the side contralateral to the arm equipped with the non-invasive blood-pressure cuff.

Selection of the preoxygenation device is at the discretion of the intubating intensivist. The options are a bag-valve mask with a flow rate of 60 L/min [21–23], non-rebreather mask with a flow rate of 60 L/min [23,24], NIV with 100% fraction of inspired oxygen (FiO2) [25], and high-flow nasal cannula oxygen with 100% FiO2 and a flow rate of 60 L/min [26,27]. However, the protocol recommends NIV in patients with hypoxemia defined as a need for >8 L/min of supplemental oxygen to maintain SpO2 ≥95%. Additional apneic oxygenation or/and apneic ventilation are allowed [28].

The choice of induction drugs and their dosages is at the discretion of the intubating intensivist. However, the intubating intensivists are encouraged to follow international [7] and French [8] recommendations that etomidate (0.2–0.3 mg/kg) and ketamine (1–2 mg/kg) be used as hypnotics, succinylcholine (1 mg/kg) as the first-line muscle relaxant, and rocuronium (1 mg/kg) as the alternative muscle relaxant.

Selection of the intubation device (laryngoscope or videolaryngoscope) and of blade type and size is at the discretion of the intubating intensivist. If the first attempt fails, the intubating intensivist is free to choose between repeating the same technique or switching to a different technique. The choice of this alternative technique is at the discretion of the intubating intensivist, who follows recommendations [7,8]. Each insertion of the laryngoscope into the mouth is counted as an intubation attempt. Correct tube position is confirmed based on examination of four consecutive capnography cycles. Immediately after successful ETI, the balloon is inflated and the tube connected to the ventilator.

Data collection

At each participating ICU and for each patient, the trial data are entered into an electronic case report form (Ennov, Paris, France), in real time, by a clinical nurse not involved in patient management. The collected baseline data include demographics, medical history, reason for ICU admission, reason for ETI, BMI, skin color scale score (Fitzpatrick score [29]), criteria predicting difficult ETI and difficult mask ventilation [30], MACOCHA score [30], Knaus chronic disease score [31], and Charlson Comorbidity Index [32]. The Sequential Organ Failure Assessment (SOFA) score [33] and Simplified Acute Physiology Score version II (SAPS II) [34] are recorded at ICU admission. The following are collected at inclusion and throughout the ETI procedure: hemodynamic data (SBP, diastolic blood pressure [DBP], mean arterial pressure [MAP], heart rate, and need for vasopressor therapy) and respiratory data (SpO2, ORI, respiratory rate, expiratory EtCO2, FiO2, positive end-expiratory pressure, and tidal volume). The data collection timepoints during ETI are inclusion, start of preoxygenation, end of preoxygenation (which coincides with start of induction, i.e., of hypnotic administration), start of laryngoscopy defined as the first introduction of the laryngoscope into the mouth, confirmation of successful intubation by capnography, and end of the second minute after successful intubation. ETI duration runs from induction initiation to confirmation of successful intubation (Fig 5). SpO2 values are recorded from both the standard pulse oximeter and the Rad-97 monitor. The lowest SpO2 values recorded by each device during the ETI procedure, the highest ORI value during preoxygenation, and the lowest SBP value during the ETI procedure are collected. Other routinely collected data are the preoxygenation device used; oxygenation device used between induction initiation and beginning of laryngoscopy, if any; duration of preoxygenation; drugs and doses used; intubation device used; need to perform a Sellick maneuver and/or re-ventilation (via a face mask or supraglottic device); Cormack-Lehane grade [35], POGO [36], and VIDIAC scores [37]; number of attempts before successful intubation (each attempt being defined as laryngoscope insertion into the mouth), with details; and adverse events during ETI.

10.1371/journal.pone.0307723.g005 Fig 5 Data collection timepoints.

Each patient is followed up until death or day 28, whichever occurs first. The following are recorded: SOFA score every day from day 1 to day 7, vital status at ICU discharge and on day 28, ICU and hospital stay lengths, and cognitive status on day 28 assessed during a telephone interview using the F-TICS-m [19].

Interim analysis

No interim analysis is planned.

Ethics and dissemination

Ethics

The NESOI-2 protocol was approved by the appropriate ethics committee (Comité de Protection des Personnes Ouest III) on March 20, 2023 (#2023-A00114-41) and was registered on ClinicalTrials.gov on April 27, 2023 (#NCT05867875). Before trial inclusion, the patient, or next of kin if the patient is incompetent, is given an information document. Written or oral consent is then sought. If the patient is incompetent and no next of kin is available, trial inclusion is performed according to the emergency procedure set forth by French law, and informed consent is then sought as soon as a relative is available then when the patient recovers competency.

Dissemination

The policy for publishing the trial findings will comply with international recommendations [38] and the CONSORT statement (http://www.consort-statement.org). The findings will be published in peer-reviewed journals and presented during national and international scientific meetings. Communications and scientific reports relevant to the trial will be under the responsibility of the study coordinator (JBL), who will first obtain the approval of the other investigators. Guidelines for authorship issued by the International Committee of Medical Journal Editors will be followed.

Patient and public involvement

Neither the patients nor the public were involved in designing this protocol. They will not be involved in disseminating the findings.

Statistics

Sample size

Assuming a standard deviation of 10% for the lowest SpO2 value in the control group [1], no missing data, and crossover of 5% of patients, with the bilateral alpha risk set at 0.05, the inclusion of 950 patients provides 85% power for detecting a 2% absolute between-group difference in the lowest SpO2 value.

The recruitment rate predicted based on data from each participating center was 5 patients per month. The observed recruitment rate from trial initiation on August 1, 2023, to January 11, 2024, is consistent with this prediction.

Statistical analyses

The baseline characteristics of the overall population and each randomization group will be described as absolute number (%) for categorical variables and as mean±SD, range, and interquartile range for quantitative variables. No statistical tests will be performed to compare the two groups at baseline.

The main analysis will be based on the modified intention-to-treat population defined as all randomized patients who meet the legal criteria. Patients with SpO₂ values below 98% at the end of preoxygenation will be included in the modified intention-to-treat population. An analysis will also be performed in the per-protocol population obtained by excluding patients with ORI recording failure or ORI<0.6 at the end of preoxygenation.

The primary outcome will be compared between groups using a mixed-effects linear regression model to account for the stratification variables (center as a random effect and operator experience and preoxygenation device as fixed effects). In the event of non-normality of the residuals observed graphically (Q-Q plot), the usual transformations of the variables will be tested to improve the fit.The analyses of the effect of ORI monitoring on the primary outcome will be repeated in sub-groups defined by BMI (< or ≥30 kg/m2), reason for ETI (hypoxemia vs. other), presence vs. absence of shock at inclusion, difficult vs. non-difficult ETI, and ORI<0.6 vs. ≥0.6. For each subgroup analysis, the statistical model described for the main analysis will be used, with incorporation of the interaction terms (subgroup variable by randomization group). The same statistical model will also be used to compare the groups regarding the lowest SpO2 value recorded by the standard pulse oximeter.

The proportions of patients with at least one serious adverse event threatening short-term survival will be compared using a mixed-effects linear regression model. ICU and day-28 mortality will be evaluated by plotting Kaplan-Meier curves and compared between groups using a Cox proportional hazards model. Goodness of fit of the model will be assessed using Schoenfeld residuals to study the proportional hazard assumption and Martingale residuals to study linearity of continuous covariates. A Fine-and-Gray model will be used to compare ICU and hospital stay lengths. Cognitive status on day 28 will be compared between groups using a mixed-effects linear regression model in the population of day-28 survivors. All analyses will be adjusted on the stratification criteria.

For all analyses, P values ≤0.05 will be taken to indicate significant differences. The statistical analyses will be performed using SAS software v9.4 (SAS Institute, Cary, NC).

In case of missing data for the primary outcome, multiple imputation will be performed. No imputation will be performed for missing data about secondary outcomes.

Harms

Adverse events are recorded into the electronic case report form for each patient. Patients who experience one or more adverse events possibly related to ETI may be temporarily withdrawn from the trial, if deemed appropriate by the attending intensivist.

Discussion

Several recent trials have assessed the efficacy of various interventions for improving the safety of ETI in highly unstable patients [4,28,39–41]. Promising results have been obtained [17]. Videolaryngoscopy is gaining in popularity [42,43]. The intervention in our trial consists in ORI monitoring as a means of limiting desaturation during ETI. The trial thus assesses a single component of the ETI procedure, which involves many more. Whether focusing on a single component will allow the detection of a significant effect is the main issue raised by our protocol.

SpO2 monitoring is widely used in the ICU despite the absence of randomized controlled trials demonstrating that this practice decreases mortality. We believe it would be unacceptable to abstain from using SpO2 monitoring. Thus, all patients will have their SpO2 values monitored using a standard pulse oximeter throughout the ETI procedure, and the results will be communicated to the intubating intensivists in both trial arms. Mean SpO2 values obtained using standard pulse oximeters correlated well with those obtained using the Rad-97 monitor. It should be noted that relying solely on SpO2 values for monitoring oxygenation remains controversial [44]. The primary outcome (lowest SpO2) is recorded from the beginning of laryngoscopy to the end of the second minute after successful intubation. This duration was chosen to avoid interactions with ventilator setting changes, in accordance with a previous study [28]. Preoxygenation devices are important to the safety of intubation [45]. Randomization will occur before preoxygenation. Therefore, for patients in the ORI-monitoring group whose ORI does not reach 0.6, the protocol allows a change to another preoxygenation device.

We chose an ORI cutoff of 0.6 as the preoxygenation target for several reasons. First, in an intraoperative study, 96.6% of PaO2 values were ≥150 mmHg when ORI was over 0.55 [46]. Second, in the NESOI1 study, 0.6 was the median ORI value at the end of preoxygenation (0.62 [0.26–0.83]) [17]. In the NESOI2 study, the median ORI in patients without an SpO2 drop below 90% during intubation was close to 0.6 (0.68 [0.27–0.89]). Moreover, 0.6 is midway between values in patients without vs. with SpO2<97% in NESOI1 (0.77 [0.59–1.00] vs. 0.49 [0.22–0.77]). Thus, an ORI of 0.6 indicates an effective level of hyperoxia while also probably being achievable in a large-scale clinical study.

Contact for public queries

General queries including information about current recruitment status can be addressed to Ms. Florance Pasquier, florane.pasquier@chu-nantes.fr

Contact for scientific queries

The primary investigator is Jean-Baptiste Lascarrou, who will deal with any scientific enquiries.

Dr. Jean-Baptiste Lascarrou, Médecine Intensive Réanimation, CHU de Nantes, 30 Bd Jean Monet, 44093 Nantes Cedex 9, FRANCE

Telephone: +33 240 087 376

jeanbaptiste.lascarrou@chu-nantes.fr

Public title

New non-invasive oxygenation parameter compared to standard non-invasive pulse oximetry for preventing low oxygenation during endotracheal intubation

Supporting information

S1 Checklist SPIRIT 2013 checklist: Recommended items to address in a clinical trial protocol and related documents*.

(DOC)

S1 File (DOCX)

We are indebted to Antoinette Wolfe, MD, for assistance in preparing and reviewing the manuscript; Joseph Herault for managing the database; Manon Rouaud for coordinating the trial; and Emmanuel Billaud and Alban Jauffrit, both at Masimo Corporation, for providing details on how the Rad-97 monitor works.

Members of the CRICS-TRIGGERSEP Network:

Hugo Hille, Médecine Intensive Reanimation, Nantes University Hospital, Nantes, France

Pierre Asfar, Intensive Care Unit, Angers University Hospital, Angers, France

Emmanuelle Mercier, Intensive Care Unit, Tours University Hospital, Tours, France

Jean-Pierre Quenot, Intensive Care Unit, Dijon University Hospital, Dijon, France

Grégoire Muller, Médecine Intensive Réanimation, Orléans University Hospital, MR INSERM 1327 ISCHEMIA, Université de Tours, Tours, France

Asael Berge, Intensive Care Unit, Haguenau Hospital, Haguenau, France

Anaïs Curtiaud, Médecine Intensive Réanimation), Strasbourg University Hospital, Strasbourg, France; INSERM (French National Institute of Health and Medical Research), UMR 1260, Regenerative Nanomedicine (RNM), Strasbourg University, Strasbourg, France

Maxime Touron, Intensive Care Unit, Cochin University Hospital, Assistance Publique-Hôpitaux de Paris (AP-HP), Paris, France

Gaetan Plantefeve, Intensive Care Unit, Argenteuil Hospital, Argenteuil, France

Gwenhael Colin, Intensive Care Unit, Vendée District Hospital, La Roche-sur-Yon, France

Jean Reignier, Intensive Care Unit, Nantes University Hospital, Motion-Interactions-Performance Laboratory (MIP), UR 4334, Nantes, France

Jean-Baptiste Lascarrou, Intensive Care Unit, Nantes University Hospital, Motion-Interactions-Performance Laboratory (MIP), UR 4334, Nantes, France (contact for the Network)

10.1371/journal.pone.0307723.r001
Decision Letter 0
Yamamoto Ryo Academic Editor
© 2024 Ryo Yamamoto
2024
Ryo Yamamoto
https://creativecommons.org/licenses/by/4.0/ This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Submission Version0
6 Mar 2024

PONE-D-24-03563Impact of non-invasive oxygen reserve index versus standard SpO2 monitoring on peripheral oxygen saturation during endotracheal intubation in the intensive care unit: Protocol for the randomized controlled trial NESOI2

PLOS ONE

Dear Dr. Lascarrou,

Thank you for submitting your manuscript to PLOS ONE. After careful consideration, we feel that it has merit but does not fully meet PLOS ONE’s publication criteria as it currently stands. Therefore, we invite you to submit a revised version of the manuscript that addresses the points raised during the review process.

Please submit your revised manuscript by Apr 20 2024 11:59PM. If you will need more time than this to complete your revisions, please reply to this message or contact the journal office at plosone@plos.org. When you're ready to submit your revision, log on to https://www.editorialmanager.com/pone/ and select the 'Submissions Needing Revision' folder to locate your manuscript file.

Please include the following items when submitting your revised manuscript:

A rebuttal letter that responds to each point raised by the academic editor and reviewer(s). You should upload this letter as a separate file labeled 'Response to Reviewers'.

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If you would like to make changes to your financial disclosure, please include your updated statement in your cover letter. Guidelines for resubmitting your figure files are available below the reviewer comments at the end of this letter.

If applicable, we recommend that you deposit your laboratory protocols in protocols.io to enhance the reproducibility of your results. Protocols.io assigns your protocol its own identifier (DOI) so that it can be cited independently in the future. For instructions see: https://journals.plos.org/plosone/s/submission-guidelines#loc-laboratory-protocols. Additionally, PLOS ONE offers an option for publishing peer-reviewed Lab Protocol articles, which describe protocols hosted on protocols.io. Read more information on sharing protocols at https://plos.org/protocols?utm_medium=editorial-email&utm_source=authorletters&utm_campaign=protocols.

We look forward to receiving your revised manuscript.

Kind regards,

Ryo Yamamoto

Academic Editor

PLOS ONE

Journal requirements:

When submitting your revision, we need you to address these additional requirements.

1. Please ensure that your manuscript meets PLOS ONE's style requirements, including those for file naming. The PLOS ONE style templates can be found at

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When you resubmit, please ensure that you provide the correct grant numbers for the awards you received for your study in the ‘Funding Information’ section.

3. Thank you for stating the following financial disclosure:

“French Ministry of Health.

PHRC 2021.”

Please state what role the funders took in the study.  If the funders had no role, please state: "The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript."

If this statement is not correct you must amend it as needed.

Please include this amended Role of Funder statement in your cover letter; we will change the online submission form on your behalf.

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“JBL has received lecturing fees from BD and Masimo. Alexis Ferré reports honoraria by Fisher & Paykel for a lecture during SFMU Congress 2022, outside the submitted work. All other authors reports not competing interests.”

Please confirm that this does not alter your adherence to all PLOS ONE policies on sharing data and materials, by including the following statement: "This does not alter our adherence to  PLOS ONE policies on sharing data and materials.” (as detailed online in our guide for authors http://journals.plos.org/plosone/s/competing-interests).  If there are restrictions on sharing of data and/or materials, please state these. Please note that we cannot proceed with consideration of your article until this information has been declared.

Please include your updated Competing Interests statement in your cover letter; we will change the online submission form on your behalf.

5. One of the noted authors is a group or consortium [CRICS-TRIGGERSEP Network]. In addition to naming the author group, please list the individual authors and affiliations within this group in the acknowledgments section of your manuscript. Please also indicate clearly a lead author for this group along with a contact email address.

6. We note that Figure 4 in your submission contain copyrighted images. All PLOS content is published under the Creative Commons Attribution License (CC BY 4.0), which means that the manuscript, images, and Supporting Information files will be freely available online, and any third party is permitted to access, download, copy, distribute, and use these materials in any way, even commercially, with proper attribution. For more information, see our copyright guidelines: http://journals.plos.org/plosone/s/licenses-and-copyright.

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In the figure caption of the copyrighted figure, please include the following text: “Reprinted from [ref] under a CC BY license, with permission from [name of publisher], original copyright [original copyright year].”

2. If you are unable to obtain permission from the original copyright holder to publish these figures under the CC BY 4.0 license or if the copyright holder’s requirements are incompatible with the CC BY 4.0 license, please either i) remove the figure or ii) supply a replacement figure that complies with the CC BY 4.0 license. Please check copyright information on all replacement figures and update the figure caption with source information. If applicable, please specify in the figure caption text when a figure is similar but not identical to the original image and is therefore for illustrative purposes only.

7. We note that the original protocol that you have uploaded as a Supporting Information file contains an institutional logo. As this logo is likely copyrighted, we ask that you please remove it from this file and upload an updated version upon resubmission.

Additional Editor Comments:

Thank you for submitting the protocol of interesting study.

Please see reviewer's comment.

[Note: HTML markup is below. Please do not edit.]

Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. Does the manuscript provide a valid rationale for the proposed study, with clearly identified and justified research questions?

The research question outlined is expected to address a valid academic problem or topic and contribute to the base of knowledge in the field.

Reviewer #1: Yes

Reviewer #2: Yes

**********

2. Is the protocol technically sound and planned in a manner that will lead to a meaningful outcome and allow testing the stated hypotheses?

The manuscript should describe the methods in sufficient detail to prevent undisclosed flexibility in the experimental procedure or analysis pipeline, including sufficient outcome-neutral conditions (e.g. necessary controls, absence of floor or ceiling effects) to test the proposed hypotheses and a statistical power analysis where applicable. As there may be aspects of the methodology and analysis which can only be refined once the work is undertaken, authors should outline potential assumptions and explicitly describe what aspects of the proposed analyses, if any, are exploratory.

Reviewer #1: Partly

Reviewer #2: Yes

**********

3. Is the methodology feasible and described in sufficient detail to allow the work to be replicable?

Descriptions of methods and materials in the protocol should be reported in sufficient detail for another researcher to reproduce all experiments and analyses. The protocol should describe the appropriate controls, sample size calculations, and replication needed to ensure that the data are robust and reproducible.

Reviewer #1: Yes

Reviewer #2: Yes

**********

4. Have the authors described where all data underlying the findings will be made available when the study is complete?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception, at the time of publication. The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.

Reviewer #1: Yes

Reviewer #2: Yes

**********

5. Is the manuscript presented in an intelligible fashion and written in standard English?

PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here.

Reviewer #1: Yes

Reviewer #2: Yes

**********

6. Review Comments to the Author

Please use the space provided to explain your answers to the questions above and, if applicable, provide comments about issues authors must address before this protocol can be accepted for publication. You may also include additional comments for the author, including concerns about research or publication ethics.

You may also provide optional suggestions and comments to authors that they might find helpful in planning their study.

(Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: Thank you for sharing the manuscript titled "Impact of Non-Invasive Oxygen Reserve Index Versus Standard SpO2 Monitoring on Peripheral Oxygen Saturation During Endotracheal Intubation in the Intensive Care Unit: Protocol for the Randomized Controlled Trial NESOI2" for review.

The paper outlines a research protocol assessing the impact of preoxygenation guided by the Oxygen Reserve Index (ORI) on the severity of desaturation during orotracheal intubation in ICU settings.

The manuscript is well-written and largely unambiguous. The methodology is thoroughly described and detailed. I have no significant comments.

Abstract

Line 85: "ORI target for preoxygenation of at least 0.6 for at least 1 minute." Please explain the rationale for selecting this specific target.

Line 85: "Preoxygenation is guided by SpO2 values recorded by a standard pulse oximeter, according to the standard of care." Could you describe how SpO2 guides preoxygenation? (Is it aiming for a SpO2 of 100% for a specific duration?).

Main Manuscript

• Line 189: Please explain the relevance of reference 19 in the methodology. Does it describe a study with a similar methodology? Or is it related to another aspect? In any case, if the reference is cited to justify methodological choices (such as the rationale behind the decision to monitor saturation 2 minutes post-intubation), it would be more appropriate to include it in the discussion section.

• Line 190: "The secondary outcome includes the sensitivity analysis of the primary outcome." This analysis pertains to alternative statistical presentations of the primary endpoint. I suggest relocating this alongside the calculations for the primary endpoint.

• Line 257: "Chosen based on unpublished personal data (JBL)." Please provide a brief description of what these data have shown.

• Line 264: "The intensivist will not be aware of the SpO2 and ORI values..." If the intensivist is unaware of these monitors, on what basis will he determine the duration of preoxygenation?

• Line 291: "Intubating intensivist..." If the choice of drugs is left to the discretion of the intensivist, I see no value in citing recommendations.

• Line 322: The various phases, durations, and definitions could be graphically represented on a timeline, enhancing understanding.

• The choice of alternative devices for initial preoxygenation should be controlled. Suppose the distribution of alternatives to preoxygenation differs between groups. In that case, it might raise questions about whether the difference in preoxygenation quality is related to the monitoring or the preoxygenation tool.

Reviewer #2: Impact of non-invasive oxygen reserve index versus standard SpO2 monitoring on peripheral oxygen saturation during endotracheal intubation in the intensive care unit: Protocol for the randomized controlled trial NESOI

Thank you for considering me for this review.

This is a protocol for a multicenter, two-arm, 83 parallel-group, randomized, superiority, open trial in 950 critically ill adults requiring endo tracheal intubation (ETI) aiming at monitoring ORI values and using an oxygen reserve index (ORI) target for 85 preoxygenation of at least 0.6 for at least 1 minute as compared to a standard of care SpO2 monitoring.

The protocol is well written and could have significant implications on the care of this vulnerable patient group by potentially preventing desaturations.

Here are my comments:

• ICU patients needing intubation are a heterogenous population. I think including a respiratory failure patient or a congestive cardiac patient with a trauma or septic patient would skew the results. The study would benefit from a more homogenous study population.

• Since ORI values represent a PaO2 of >100mmHg none of the patients with SpO2 <98%, will have a measurable ORI value. Therefore, I would suggest explicitly excluding patients who do not reach an SpO2 of 99-100% after 3-5 min of preoxygenation.

• P 9, first paragraph – the primary outcome measurement time (lowest SpO2 value, first introduction of the laryngoscope into the mouth and the end of the second 189 minute following successful intubation) seems too short to me. Two minutes after intubation could be too short for SpO2 to recover after apnea in critically ill patients.

• P 9, R 197 – As mentioned above, ORI will be 0 at SpO2 >98%, thus it can’t assess severe hypoxic events

**********

7. PLOS authors have the option to publish the peer review history of their article (what does this mean?). If published, this will include your full peer review and any attached files.

If you choose “no”, your identity will remain anonymous but your review may still be made public.

Do you want your identity to be public for this peer review? For information about this choice, including consent withdrawal, please see our Privacy Policy.

Reviewer #1: Yes: Issam Tanoubi

Reviewer #2: No

**********

[NOTE: If reviewer comments were submitted as an attachment file, they will be attached to this email and accessible via the submission site. Please log into your account, locate the manuscript record, and check for the action link "View Attachments". If this link does not appear, there are no attachment files.]

While revising your submission, please upload your figure files to the Preflight Analysis and Conversion Engine (PACE) digital diagnostic tool, https://pacev2.apexcovantage.com/. PACE helps ensure that figures meet PLOS requirements. To use PACE, you must first register as a user. Registration is free. Then, login and navigate to the UPLOAD tab, where you will find detailed instructions on how to use the tool. If you encounter any issues or have any questions when using PACE, please email PLOS at figures@plos.org. Please note that Supporting Information files do not need this step.

Attachment Submitted filename: 2024_ORI_ICU_PlosOne.docx

10.1371/journal.pone.0307723.r002
Author response to Decision Letter 0
Submission Version1
25 Apr 2024

Please find enclosed Reviewer Answer.

Attachment Submitted filename: Editor and Reviewer Answer(aw).docx

10.1371/journal.pone.0307723.r003
Decision Letter 1
Yamamoto Ryo Academic Editor
© 2024 Ryo Yamamoto
2024
Ryo Yamamoto
https://creativecommons.org/licenses/by/4.0/ This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Submission Version1
29 May 2024

PONE-D-24-03563R1Impact of non-invasive oxygen reserve index versus standard SpO2 monitoring on peripheral oxygen saturation during endotracheal intubation in the intensive care unit: Protocol for the randomized controlled trial NESOI2PLOS ONE

Dear Dr. Lascarrou,

Thank you for submitting your manuscript to PLOS ONE. After careful consideration, we feel that it has merit but does not fully meet PLOS ONE’s publication criteria as it currently stands. Therefore, we invite you to submit a revised version of the manuscript that addresses the points raised during the review process.

Please submit your revised manuscript by Jul 13 2024 11:59PM. If you will need more time than this to complete your revisions, please reply to this message or contact the journal office at plosone@plos.org. When you're ready to submit your revision, log on to https://www.editorialmanager.com/pone/ and select the 'Submissions Needing Revision' folder to locate your manuscript file.

Please include the following items when submitting your revised manuscript:A rebuttal letter that responds to each point raised by the academic editor and reviewer(s). You should upload this letter as a separate file labeled 'Response to Reviewers'.

A marked-up copy of your manuscript that highlights changes made to the original version. You should upload this as a separate file labeled 'Revised Manuscript with Track Changes'.

An unmarked version of your revised paper without tracked changes. You should upload this as a separate file labeled 'Manuscript'.

If you would like to make changes to your financial disclosure, please include your updated statement in your cover letter. Guidelines for resubmitting your figure files are available below the reviewer comments at the end of this letter.

If applicable, we recommend that you deposit your laboratory protocols in protocols.io to enhance the reproducibility of your results. Protocols.io assigns your protocol its own identifier (DOI) so that it can be cited independently in the future. For instructions see: https://journals.plos.org/plosone/s/submission-guidelines#loc-laboratory-protocols. Additionally, PLOS ONE offers an option for publishing peer-reviewed Lab Protocol articles, which describe protocols hosted on protocols.io. Read more information on sharing protocols at https://plos.org/protocols?utm_medium=editorial-email&utm_source=authorletters&utm_campaign=protocols.

We look forward to receiving your revised manuscript.

Kind regards,

Ryo Yamamoto

Academic Editor

PLOS ONE

Journal Requirements:

Please review your reference list to ensure that it is complete and correct. If you have cited papers that have been retracted, please include the rationale for doing so in the manuscript text, or remove these references and replace them with relevant current references. Any changes to the reference list should be mentioned in the rebuttal letter that accompanies your revised manuscript. If you need to cite a retracted article, indicate the article’s retracted status in the References list and also include a citation and full reference for the retraction notice.

[Note: HTML markup is below. Please do not edit.]

Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. Does the manuscript provide a valid rationale for the proposed study, with clearly identified and justified research questions?

The research question outlined is expected to address a valid academic problem or topic and contribute to the base of knowledge in the field.

Reviewer #1: Yes

Reviewer #2: Yes

**********

2. Is the protocol technically sound and planned in a manner that will lead to a meaningful outcome and allow testing the stated hypotheses?

The manuscript should describe the methods in sufficient detail to prevent undisclosed flexibility in the experimental procedure or analysis pipeline, including sufficient outcome-neutral conditions (e.g. necessary controls, absence of floor or ceiling effects) to test the proposed hypotheses and a statistical power analysis where applicable. As there may be aspects of the methodology and analysis which can only be refined once the work is undertaken, authors should outline potential assumptions and explicitly describe what aspects of the proposed analyses, if any, are exploratory.

Reviewer #1: Yes

Reviewer #2: Yes

**********

3. Is the methodology feasible and described in sufficient detail to allow the work to be replicable?

Descriptions of methods and materials in the protocol should be reported in sufficient detail for another researcher to reproduce all experiments and analyses. The protocol should describe the appropriate controls, sample size calculations, and replication needed to ensure that the data are robust and reproducible.

Reviewer #1: Yes

Reviewer #2: Yes

**********

4. Have the authors described where all data underlying the findings will be made available when the study is complete?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception, at the time of publication. The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.

Reviewer #1: Yes

Reviewer #2: Yes

**********

5. Is the manuscript presented in an intelligible fashion and written in standard English?

PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here.

Reviewer #1: Yes

Reviewer #2: Yes

**********

6. Review Comments to the Author

Please use the space provided to explain your answers to the questions above and, if applicable, provide comments about issues authors must address before this protocol can be accepted for publication. You may also include additional comments for the author, including concerns about research or publication ethics.

You may also provide optional suggestions and comments to authors that they might find helpful in planning their study.

(Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: Thank you for your revisions and for addressing the initial comments on your manuscript. Upon further review, I have two additional suggestions that could strengthen your submission:

Responses to comments 1, 5, and 9 from Reviewer #1 should be incorporated into the discussion section of the article to better justify and explain the methodological choices made.

Concerning Reviewer #2’s Comments: I understand that the authors prefer not to exclude patients with SpO₂ below 98% at the end of preoxygenation due to their rarity. However, it is essential to clearly describe in the statistical section how their data will be analyzed should this issue arise.

Reviewer #2: The responses to my initial review have been answered. I accept the author's comments and I agree with the publication

**********

7. PLOS authors have the option to publish the peer review history of their article (what does this mean?). If published, this will include your full peer review and any attached files.

If you choose “no”, your identity will remain anonymous but your review may still be made public.

Do you want your identity to be public for this peer review? For information about this choice, including consent withdrawal, please see our Privacy Policy.

Reviewer #1: Yes: Issam Tanoubi

Reviewer #2: Yes: Peter Szmuk, M.D.

**********

[NOTE: If reviewer comments were submitted as an attachment file, they will be attached to this email and accessible via the submission site. Please log into your account, locate the manuscript record, and check for the action link "View Attachments". If this link does not appear, there are no attachment files.]

While revising your submission, please upload your figure files to the Preflight Analysis and Conversion Engine (PACE) digital diagnostic tool, https://pacev2.apexcovantage.com/. PACE helps ensure that figures meet PLOS requirements. To use PACE, you must first register as a user. Registration is free. Then, login and navigate to the UPLOAD tab, where you will find detailed instructions on how to use the tool. If you encounter any issues or have any questions when using PACE, please email PLOS at figures@plos.org. Please note that Supporting Information files do not need this step.

10.1371/journal.pone.0307723.r004
Author response to Decision Letter 1
Submission Version2
4 Jun 2024

Please find enclosed Reviewer Answers.

Attachment Submitted filename: Reviewer Answer R2(aw).docx

10.1371/journal.pone.0307723.r005
Decision Letter 2
Yamamoto Ryo Academic Editor
© 2024 Ryo Yamamoto
2024
Ryo Yamamoto
https://creativecommons.org/licenses/by/4.0/ This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Submission Version2
2 Jul 2024

PONE-D-24-03563R2Impact of non-invasive oxygen reserve index versus standard SpO2 monitoring on peripheral oxygen saturation during endotracheal intubation in the intensive care unit: Protocol for the randomized controlled trial NESOI2PLOS ONE

Dear Dr. Lascarrou,

Thank you for submitting your manuscript to PLOS ONE. After careful consideration, we feel that it has merit but does not fully meet PLOS ONE’s publication criteria as it currently stands. Therefore, we invite you to submit a revised version of the manuscript that addresses the points raised during the review process.

An additional statistical reviewer suggest some minor revisions.

Please respond to them.

Please submit your revised manuscript by Aug 16 2024 11:59PM. If you will need more time than this to complete your revisions, please reply to this message or contact the journal office at plosone@plos.org. When you're ready to submit your revision, log on to https://www.editorialmanager.com/pone/ and select the 'Submissions Needing Revision' folder to locate your manuscript file.

Please include the following items when submitting your revised manuscript:

A rebuttal letter that responds to each point raised by the academic editor and reviewer(s). You should upload this letter as a separate file labeled 'Response to Reviewers'.

A marked-up copy of your manuscript that highlights changes made to the original version. You should upload this as a separate file labeled 'Revised Manuscript with Track Changes'.

An unmarked version of your revised paper without tracked changes. You should upload this as a separate file labeled 'Manuscript'.

If you would like to make changes to your financial disclosure, please include your updated statement in your cover letter. Guidelines for resubmitting your figure files are available below the reviewer comments at the end of this letter.

If applicable, we recommend that you deposit your laboratory protocols in protocols.io to enhance the reproducibility of your results. Protocols.io assigns your protocol its own identifier (DOI) so that it can be cited independently in the future. For instructions see: https://journals.plos.org/plosone/s/submission-guidelines#loc-laboratory-protocols. Additionally, PLOS ONE offers an option for publishing peer-reviewed Lab Protocol articles, which describe protocols hosted on protocols.io. Read more information on sharing protocols at https://plos.org/protocols?utm_medium=editorial-email&utm_source=authorletters&utm_campaign=protocols.

We look forward to receiving your revised manuscript.

Kind regards,

Ryo Yamamoto

Academic Editor

PLOS ONE

Journal Requirements:

Please review your reference list to ensure that it is complete and correct. If you have cited papers that have been retracted, please include the rationale for doing so in the manuscript text, or remove these references and replace them with relevant current references. Any changes to the reference list should be mentioned in the rebuttal letter that accompanies your revised manuscript. If you need to cite a retracted article, indicate the article’s retracted status in the References list and also include a citation and full reference for the retraction notice.

[Note: HTML markup is below. Please do not edit.]

Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. Does the manuscript provide a valid rationale for the proposed study, with clearly identified and justified research questions?

The research question outlined is expected to address a valid academic problem or topic and contribute to the base of knowledge in the field.

Reviewer #1: Yes

Reviewer #3: Yes

**********

2. Is the protocol technically sound and planned in a manner that will lead to a meaningful outcome and allow testing the stated hypotheses?

The manuscript should describe the methods in sufficient detail to prevent undisclosed flexibility in the experimental procedure or analysis pipeline, including sufficient outcome-neutral conditions (e.g. necessary controls, absence of floor or ceiling effects) to test the proposed hypotheses and a statistical power analysis where applicable. As there may be aspects of the methodology and analysis which can only be refined once the work is undertaken, authors should outline potential assumptions and explicitly describe what aspects of the proposed analyses, if any, are exploratory.

Reviewer #1: Yes

Reviewer #3: Yes

**********

3. Is the methodology feasible and described in sufficient detail to allow the work to be replicable?

Descriptions of methods and materials in the protocol should be reported in sufficient detail for another researcher to reproduce all experiments and analyses. The protocol should describe the appropriate controls, sample size calculations, and replication needed to ensure that the data are robust and reproducible.

Reviewer #1: Yes

Reviewer #3: Yes

**********

4. Have the authors described where all data underlying the findings will be made available when the study is complete?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception, at the time of publication. The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.

Reviewer #1: Yes

Reviewer #3: Yes

**********

5. Is the manuscript presented in an intelligible fashion and written in standard English?

PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here.

Reviewer #1: Yes

Reviewer #3: Yes

**********

6. Review Comments to the Author

Please use the space provided to explain your answers to the questions above and, if applicable, provide comments about issues authors must address before this protocol can be accepted for publication. You may also include additional comments for the author, including concerns about research or publication ethics.

You may also provide optional suggestions and comments to authors that they might find helpful in planning their study.

(Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: I thank the authors for adequately addressing the reviewers' comments. I have no further comments to add.

Reviewer #3: On the overall, the manuscript addresses previously raised questions. My additional comments are as follows:

1. A linear mixed model will be fitted, which is based on Gaussian assumptions of the random terms (random effects & errors). What would be the recourse, when the Gaussian assumptions fail (which can certainly happen)?

2. Cox regression will be employed, but necessary goodness of fit statistics and tests of the proportional hazards assumptions need to be mentioned.

**********

7. PLOS authors have the option to publish the peer review history of their article (what does this mean?). If published, this will include your full peer review and any attached files.

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10.1371/journal.pone.0307723.r006
Author response to Decision Letter 2
Submission Version3
3 Jul 2024

Please find enclosed Letter.

Attachment Submitted filename: Reviewer Answer R3(aw).docx

10.1371/journal.pone.0307723.r007
Decision Letter 3
Yamamoto Ryo Academic Editor
© 2024 Ryo Yamamoto
2024
Ryo Yamamoto
https://creativecommons.org/licenses/by/4.0/ This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Submission Version3
10 Jul 2024

Impact of non-invasive oxygen reserve index versus standard SpO2 monitoring on peripheral oxygen saturation during endotracheal intubation in the intensive care unit: Protocol for the randomized controlled trial NESOI2

PONE-D-24-03563R3

Dear Dr. Lascarrou,

We’re pleased to inform you that your manuscript has been judged scientifically suitable for publication and will be formally accepted for publication once it meets all outstanding technical requirements.

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Academic Editor

PLOS ONE

Additional Editor Comments (optional):

Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. Does the manuscript provide a valid rationale for the proposed study, with clearly identified and justified research questions?

The research question outlined is expected to address a valid academic problem or topic and contribute to the base of knowledge in the field.

Reviewer #3: Yes

**********

2. Is the protocol technically sound and planned in a manner that will lead to a meaningful outcome and allow testing the stated hypotheses?

The manuscript should describe the methods in sufficient detail to prevent undisclosed flexibility in the experimental procedure or analysis pipeline, including sufficient outcome-neutral conditions (e.g. necessary controls, absence of floor or ceiling effects) to test the proposed hypotheses and a statistical power analysis where applicable. As there may be aspects of the methodology and analysis which can only be refined once the work is undertaken, authors should outline potential assumptions and explicitly describe what aspects of the proposed analyses, if any, are exploratory.

Reviewer #3: Yes

**********

3. Is the methodology feasible and described in sufficient detail to allow the work to be replicable?

Descriptions of methods and materials in the protocol should be reported in sufficient detail for another researcher to reproduce all experiments and analyses. The protocol should describe the appropriate controls, sample size calculations, and replication needed to ensure that the data are robust and reproducible.

Reviewer #3: Yes

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4. Have the authors described where all data underlying the findings will be made available when the study is complete?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception, at the time of publication. The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.

Reviewer #3: Yes

**********

5. Is the manuscript presented in an intelligible fashion and written in standard English?

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Reviewer #3: Yes

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6. Review Comments to the Author

Please use the space provided to explain your answers to the questions above and, if applicable, provide comments about issues authors must address before this protocol can be accepted for publication. You may also include additional comments for the author, including concerns about research or publication ethics.

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Reviewer #3: The authors were able to address my previous round of questions. I have no further questions this round.

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Reviewer #3: No

**********

10.1371/journal.pone.0307723.r008
Acceptance letter
Yamamoto Ryo Academic Editor
© 2024 Ryo Yamamoto
2024
Ryo Yamamoto
https://creativecommons.org/licenses/by/4.0/ This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
1 Aug 2024

PONE-D-24-03563R3

PLOS ONE

Dear Dr. Lascarrou,

I'm pleased to inform you that your manuscript has been deemed suitable for publication in PLOS ONE. Congratulations! Your manuscript is now being handed over to our production team.

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on behalf of

Dr. Ryo Yamamoto

Academic Editor

PLOS ONE
==== Refs
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