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Indian J Crit Care Med
Indian J Crit Care Med
IJCCM
Indian Journal of Critical Care Medicine : Peer-reviewed, Official Publication of Indian Society of Critical Care Medicine
0972-5229
1998-359X
Jaypee Brothers Medical Publishers

10.5005/jp-journals-10071-24742
Letter to the Editor
Author Response: The Evolution of Central Venous-to-arterial Carbon Dioxide Difference (PCO2 Gap) during Resuscitation Affects ICU Outcomes: A Prospective Observational Study
Tiwari Anand M 1https://orcid.org/0000-0002-9791-8365

Zirpe Kapil G 2https://orcid.org/0000-0002-8140-727X

Kulkarni Atul P 3https://orcid.org/0000-0002-5172-7619

1,2 Department of Neuro Trauma Unit, Ruby Hall Clinic, Pune, Maharashtra, India
3 Department of Anaesthesia, Critical Care and Pain, Tata Memorial Hospital, Homi Bhabha National Institute, Mumbai, Maharashtra, India
Anand M Tiwari, Department of Neuro Trauma Unit, Ruby Hall Clinic, Pune, Maharashtra, India, Phone: +91 7798255626, e-mail: dranandtiwari@gmail.com
7 2024
29 6 2024
28 7 710710
Copyright © 2024; The Author(s).
2024
https://creativecommons.org/licenses/by-nc/4.0/ © The Author(s). 2024 Open Access. This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (https://creativecommons.org/licenses/by-nc/4.0/), which permits unrestricted use, distribution, and non-commercial reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.
How to cite this article: Tiwari AM, Zirpe KG, Kulkarni AP. Author Response: The Evolution of Central Venous-to-arterial Carbon Dioxide Difference (PCO2 Gap) During Resuscitation Affects ICU Outcomes: A Prospective Observational Study. Indian J Crit Care Med 2024;28(7):710.

Keywords

Intensive care unit outcome
PCO2 gap
Shock
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pmc Dear Editor,

We thank the authors Vijay S, Manoj K, and Pramela R for their interest in our article.1 We appreciate this opportunity to further elaborate about our study about the evolution of PCO2 gap in patients with shock, by addressing their concerns.

We acknowledge that 2D echocardiography is an operator-dependent procedure. It is imperative to minimize inter-observer and intraobserver variability. In the present study, 2D echocardiography was performed by a single well-trained observer with certification. Additionally, an average of 3 readings of the cardiac index was taken for each study participant at all prespecified time intervals before evaluation, which took care of intraobserver variability.

In our study, 110 adult patients with shock, [MAP (±SD) 55.5 ± 5.7 mm Hg] were included. Those with impaired cardiac function (EF < 40%) were excluded. We resuscitated these patients as per the surviving sepsis guidelines to maintain uniformity.2 Dynamic measures were used to guide fluid resuscitation, rather than physical examination or static parameters alone. The type of shock was categorized as per the clinician's decision, including distributive (40%) and combined (14.5%), and they diagnosed 64.5% of patients as having septic shock.

All study participants at the time of inclusion had a high PCO2 gap (PCO2 > 6 mm Hg) with a mean (± SD) PCO2 gap 10 (± 3.7) mm Hg. After 6 hours of resuscitation, the PCO2 gap decreased in 61 patients, while it continued to be high in the remaining (49) patients.

The authors of the letter suggest comparing data with differences in severity of illness, vasopressor requirement, type of shock and acid base status between the two groups after 6 hours. With respect to the severity of illness score, i.e., acute physiology and chronic health evaluation II (APACHE-II), in our population the median score was 15 (12–20). Available evidence from meta-analysis and systematic review by Kriswidyatomo et al.3 reported no difference between high gap group and low gap group. With respect to suggestion on comparison of shock types, vasopressor requirement and acid base status, we have shown trends of appropriate surrogates such as the cardiac index, urine output and serum lactate between the two groups in Figure 3.1

We formulated a null hypothesis that a persistently high PCO2 gap during resuscitation in patients with shock is associated with poor outcomes. We estimated Spearman's rank correlation coefficient with a p-value of significance for correlating the pCO2 gap with lactate and cardiac index. To advance our understanding of PCO2 gap validity, a multicenter randomized larger study sample is warranted. We concur with the reader's suggestion regarding the need to evaluate the strength of correlation for the validity of the PCO2 gap.

Orcid

Anand M Tiwari https://orcid.org/0000-0002-9791-8365

Kapil G Zirpe https://orcid.org/0000-0002-8140-727X

Atul P Kulkarni https://orcid.org/0000-0002-5172-7619

Source of support: Nil

Conflict of interest: None
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References

1. Zirpe KG Tiwari AM Kulkarni AP Vaidya HS Gurav SK Deshmukh AM et al. The evolution of central venous-to-arterial carbon dioxide difference (PCO2 Gap) during resuscitation affects ICU outcomes: A prospective observational study Indian J Crit Care Med 2024 28 4 349 354 10.5005/jp-journals-10071-24680 38585325
2. Evans L Rhodes A Alhazzani W Antonelli M Coopersmith CM French C et al. Surviving sepsis campaign: International guidelines for management of sepsis and septic shock 2021 Crit Care Med 2021 49 11 e1063 e1143 10.1097/CCM.0000000000005337 34605781
3. Kriswidyatomo P Pradnyan Kloping Y Guntur Jaya M Adrian Nugraha R Prognostic value of PCO2 gap in adult septic shock patients: A systematic review and meta-analysis Turk J Anaesthesiol Reanim 2022 50 5 324 331 10.5152/TJAR.2021.21139 36301280
