
==== Front
Cureus
Cureus
2168-8184
Cureus
2168-8184
Cureus Palo Alto (CA)

10.7759/cureus.66908
Anesthesiology
Medical Education
Point-of-Care Ultrasound: A Vital Tool for Anesthesiologists in the Perioperative and Critical Care Settings
Muacevic Alexander
Adler John R
Dhir Ankita 1
Bhasin Dinkar 2
Bhasin-Chhabra Bhavna 3
Koratala Abhilash 4
1 Anesthesiology, Max Super Speciality Hospital, Chandigarh, IND
2 Cardiology, Postgraduate Institute of Medical Education and Research, Chandigarh, IND
3 Nephrology and Hypertension, Mayo Clinic Arizona, Scottsdale, USA
4 Nephrology, Medical College of Wisconsin, Milwaukee, USA
Bhavna Bhasin-Chhabra bhasin-chhabra.bhavna@mayo.edu
14 8 2024
8 2024
16 8 e669089 8 2024
Copyright © 2024, Dhir et al.
2024
Dhir 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 CC-BY 4.0., which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
This article is available from https://www.cureus.com/articles/260709-point-of-care-ultrasound-a-vital-tool-for-anesthesiologists-in-the-perioperative-and-critical-care-settings
Point-of-care ultrasound (POCUS) is an essential skill in various specialties like anesthesiology, critical care, and emergency medicine. Anesthesiologists utilize POCUS for quick diagnosis and procedural guidance in perioperative and critical care settings. Key applications include vascular ultrasound for challenging venous and arterial catheter placements, gastric ultrasound for aspiration risk assessment, airway ultrasound, diaphragm ultrasound, and lung ultrasound for respiratory assessment. Additional utilities of POCUS can include multi-organ POCUS evaluation for undifferentiated shock or cardiac arrest, ultrasound-guided central neuraxial and peripheral nerve blocks, focused cardiac ultrasound, and novel applications such as venous excess ultrasound. This review highlights these POCUS applications in perioperative and intensive care and summarizes the latest evidence of their accuracy and limitations.

gastric ultrasound
airway ultrasound
perioperative pocus
anaesthesiology
bedside ultrasound
pocus (point of care ultrasound)
==== Body
pmcIntroduction and background

Point-of-care ultrasound (POCUS) is increasingly being utilized across various acute specialties, including emergency medicine, critical care, and anesthesiology, as a diagnostic and therapeutic tool [1,2]. It includes focused, goal-directed bedside sonographic examinations of various organs, including the lungs, diaphragm, gastric antrum, heart, airway, pelvic organs, and vascular system [3]. Unlike consultative imaging, the physician performing POCUS is responsible for all aspects of image acquisition, interpretation, and formulating the management plan. Incorporating POCUS into routine bedside evaluation has gained substantial recognition, driven by a growing body of evidence demonstrating its superior diagnostic accuracy compared to traditional examination and assessment tools [4]. The perioperative period begins from the patient’s admission, through anesthesia and surgery, to the first 24 hours after the procedure [5]. Anesthesiologists are responsible for patient care and management during this time, making POCUS a vital skill for them. This narrative review summarizes the applications of POCUS in perioperative and intensive care settings, its relevance to anesthesiologists, and the latest evidence related to diagnostic accuracy and validity.

Review

Vascular ultrasound

Vascular ultrasound is employed for the placement of peripheral and central intravenous catheters and arterial catheters and to identify deep venous thrombosis intraoperatively as well as in critically ill patients.

Peripheral Venous Access and Arterial Line Placement

POCUS proves instrumental in locating deep-seated peripheral veins, which are not readily visible or palpable, including the cephalic, antebrachial, median cubital, and basilic veins [6]. In cases involving patients with difficult intravenous access, ultrasound-guided cannulation demonstrates an impressive success rate, consistently exceeding 90%, compared to the conventional technique, which typically achieves success rates of only 25-30% [7]. This reduces the need for more invasive central venous catheters [8]. These benefits also extend to the pediatric patient population, in whom obtaining peripheral venous access is particularly challenging [9]. Furthermore, POCUS also facilitates the insertion of arterial lines through real-time visualization of landmarks, improving first-pass success rates [10-12]. In a recent randomized controlled trial with 201 participants, arterial line placement was successful on the first attempt in 83.3% of patients in the ultrasound group compared to 55.6% in the digital palpation group (p-value 0.02) [12].

Central Venous Access

The traditional method of obtaining central venous access has been the use of anatomical landmarks to guide needle puncture. However, this method becomes challenging for certain patients with obesity, a history of intravenous drug abuse or chemotherapy, and chronic medical conditions like cancer and peripheral vascular diseases. However, POCUS-guided central venous cannulation is now considered the standard of care [11]. It provides numerous benefits, including preprocedural assessment of vein patency, real-time visualization of the targeted vessel during the procedure, reduced attempts at venipuncture, and the detection of complications such as malpositioned guidewire [13] (Figure 1).

Figure 1 Ultrasound of the internal jugular vein for guiding central venous access placement

(A) Needle tip in the vein (arrow). (B) Guidewire in the vein (arrow). (C) Thrombus (arrow) in the internal jugular vein detected prior to catheter placement.

Image credit: Abhilash Koratala

In a systematic review of 35 trials (involving 5,108 participants) comparing ultrasound-guided jugular venous catheter placement to landmark technique, ultrasound guidance increased the success rate from 91.7% to 97.6% (RR: 1.12, 95% CI: 1.08-1.17), enhanced the rate of successful first attempts from 50.1% to 82.2% (RR: 1.57, 95% CI: 1.36-1.82), reduced cannulation time, lowered complication rates from 13.5% to 3.4% (RR: 0.29, 95% CI: 0.17-0.52), and decreased inadvertent arterial punctures from 9.4% to 2.0% (RR: 0.28, 95% CI: 0.18-0.44) [14]. However, a few randomized controlled trials reported that the benefits of ultrasound-guided femoral and subclavian vein (SCV) cannulation did not parallel the improved outcomes seen with internal jugular vein cannulation [15]. Subsequently, a meta-analysis of six randomized controlled trials (953 patients) reevaluated the success and safety of ultrasound-guided SCV catheterization compared to the landmark technique. The real-time ultrasound-guided dynamic approach increased the overall success rate for SCV cannulation, improved the success rate at the first attempt, reduced the total number of attempts, lowered the complication rate, and shortened the time required for a successful procedure [16]. Similar improved outcomes have been shown with the use of ultrasound for femoral vein cannulation as well [11,16].

Deep Vein Thrombosis (DVT)

POCUS is a useful tool for the quick bedside diagnosis of lower and upper extremity DVT. This is particularly important in the context of catheter-associated thrombi and suspected cases of acute pulmonary embolism. In a meta-analysis of 43 studies, the sensitivity and specificity to diagnose cases of suspected DVT via proximal compression ultrasound were 90.1% (95% CI: 86.5-92.8) and 98.5% (95% CI: 97.6-99.1), respectively [17]. Figure 2 illustrates a common femoral vein DVT.

Figure 2 Compression ultrasound for evaluating lower extremity DVT

(A) Normal common femoral vein that is fully compressible with transducer pressure (B). (C) Common femoral vein with a hyperechoic thrombus in the lumen (arrow), which is non-compressible (D).

DVT: deep vein thrombosis

Image credit: Abhilash Koratala

Gastric ultrasound

Gastric POCUS facilitates individualized risk assessment of aspiration of gastric contents, which is a major factor contributing to anesthesia-related morbidity and mortality [18,19]. The risk assessment is based on a validated mathematical model established by Perlas et al., which measures the cross-sectional area of the gastric antrum in the right lateral decubitus position [20]. Figure 3 shows the view of the stomach in different states in axial and parasagittal views.

Figure 3 Gastric ultrasound for evaluation of gastric contents

(A, B) Ultrasound probe location and orientation for parasagittal and axial views of the gastric antrum. Parasagittal (C, E, G, I) and axial (D, F, H, J) views of the gastric antrum: empty stomach (C, D); one hour after ingestion of clear liquids (E, F); one minute after drinking approximately 500 mL (16 oz) of clear liquids, showing an expanded lumen with hypoechoic contents (G, H); immediately after a meal with a characteristic “ground-glass” appearance (I, J).

A: antrum; Ao: aorta; D: duodenum; IVC: inferior vena cava; L: liver; NPO: nil per os; P: pancreas; Py: pylorus; SMA: superior mesenteric artery

Created with BioRender.com.

Nguyen et al. (2023) [21]; Creative Commons Attribution (CC BY) license

Apart from healthy adults, this model has been tested in various patient populations, including morbidly obese individuals and pregnant patients [22-24]. Gastric POCUS has a sensitivity of 1.0 (95% CI: 0.925-1.0) and a specificity of 0.975 (95% CI: 0-0.072) to detect or rule out a full stomach [25]. POCUS is particularly valuable when the preoperative fasting status is uncertain or in the setting of high aspiration-risk conditions like gastroparesis, diabetic autonomic neuropathy, glucagon-like peptide 1 receptor agonist use, small bowel or gastric outlet obstruction, gastroesophageal reflux disease, increased intraabdominal pressure, and morbid obesity [26,27]. However, gastric ultrasound should only be used as an adjunct rather than a substitute for the standard recommendations for fasting. Further, the ultrasound findings may not be valid in patients with a large hiatus hernia and previous gastric surgery [19].

Gastric ultrasound may also be useful in the intensive care unit to evaluate gastric residual volume following enteral feeding, but it has not been well validated in this setting. While the Perlas mathematical model effectively estimates gastric volume after the intake of clear fluids, ongoing research is focused on developing new models for estimating gastric volume in patients receiving thick enteral feeds [28].

Airway ultrasound 

Identification of the Cricothyroid Membrane (CTM)

Surgical cricothyrotomy is a life-saving procedure performed to secure the airway after failed tracheal intubation [29]. Since this procedure is performed infrequently, the conventional method of digital palpation to locate the CTM has more chances of misidentification and failure. POCUS guidance can help improve the accuracy of this procedure [30] (Figure 4).

Figure 4 Airway ultrasound for identifying the CTM

Cricoid cartilage, thyroid cartilage, and CTM in a longitudinal plane.

Cc: cricoid cartilage; CTM: cricothyroid membrane; Tc: thyroid cartilage

Osman and Sum (2016) [31]; Creative Commons Attribution (CC BY) license

In a comprehensive meta-analysis conducted by Hung et al., the authors reported a significantly reduced failure rate in CTM identification when employing ultrasound guidance, with a pooled RR of 0.50 (95% CI: 0.33-0.76). Additionally, the study showed a reduced procedural time of 21.8 seconds (95% CI: -1.4 to 45.1), further supporting the efficacy of this technique [32].

Confirmation of Endotracheal Tube (ETT) Placement

Unrecognized esophageal intubation is not uncommon in emergency situations and can lead to serious patient harm [33]. Even when promptly detected, it is associated with a risk of severe hypoxemia, pulmonary aspiration, cardiac arrest, and, in rare instances, gastric or esophageal rupture [34]. Although capnography is considered a reference standard for the verification of ETT, airway POCUS allows easy detection of ETT tube location (Figure 5, Figure 6).

Figure 5 Airway ultrasound showing tracheal intubation

The arrow indicates the anterior aspect of the ETT.

ETT: endotracheal tube; T: trachea

Gottlieb et al. (2024) [35]; Creative Commons Attribution (CC BY) license

Figure 6 Airway ultrasound showing esophageal intubation

In the case of esophageal intubation, a curvilinear structure that mimics the trachea (T) is seen to the right of the trachea. This is the ETT within the esophagus (E) [35].

ETT: endotracheal tube

Gottlieb et al. (2024) [35]; Creative Commons Attribution (CC BY) license

This is particularly useful in certain emergency situations where capnography may become unreliable, like cardiopulmonary arrest, bronchospasm, and pulmonary thromboembolism [36].

Studies have confirmed the high accuracy of tracheal ultrasound in confirming the correct placement of an ETT. In adult patients, it has a sensitivity of 98.7% and a specificity of 97.1%. In pediatric patients, the sensitivity ranges from 92% to 100%, with a consistent specificity of 100% [36,37]. The accuracy remains consistent even in challenging scenarios, such as cardiac arrest [38,39]. In some patients, airway POCUS may be challenging, such as those with a cervical collar, a short neck, or subcutaneous emphysema that extends up to the head and neck [38].

Prediction of a Difficult Airway

Difficult intubation poses a challenge in perioperative management, affecting approximately 4.5-7.5% of cases in the operating room [18]. Predicting difficult intubation becomes particularly complex, and early identification of the risk factors for difficult intubation is crucial to minimizing adverse events.

Traditionally, physical examination of the airway has been the primary method for predicting difficult intubation. This involves evaluations like the modified Mallampati score (with a sensitivity of 53% and a specificity of 80%), the upper lip bite test (with a sensitivity of 67% and a specificity of 92%), and the thyromental distance (with a sensitivity of 37% and a specificity of 89%) [40,41]. Although these methods are valuable, they have their limitations. Airway ultrasound can be used as a complementary tool to clinical assessment in predicting a difficult airway.

Preoperative bedside ultrasound involves measuring distances and ratios between reference points, including the hyomental distance in both neutral position and extension, the skin-to-epiglottis distance (SED), the distance from the skin to the hyoid bone, and the distance from the skin to the vocal cords [31]. A meta-analysis by Benavides-Zora et al. revealed that SED and the hyomental distance measured in extension position exhibited a sensitivity of 75% and 61% and a specificity of 86% and 88%, respectively. Notably, the ratio of the pre-epiglottic distance to the epiglottic distance at the center point of the vocal cords was most accurate in predicting difficult laryngoscopy, with a sensitivity of 82% and a specificity of 83% [42]. Another meta-analysis by Carsetti et al., involving 15 studies, highlighted SED as the most extensively studied parameter for predicting difficult intubation [43]. Hence, adding these tools to routine airway evaluation can significantly improve preoperative assessment.

Other Uses

Airway POCUS finds additional clinical applications, such as aiding in percutaneous tracheostomy by identifying suitable puncture sites and assessing blood vessels [44]. It also assists in determining the appropriate size of a double-lumen tube by measuring the width of the trachea at the sternoclavicular joint [45]. Further, it plays a role in assessing vocal cord function for identifying recurrent laryngeal nerve palsy, as well as detecting tracheal stenosis and tracheal invasion by thyroid cancer [46,47].

Diaphragm ultrasound

The diaphragm is the main inspiratory muscle [48]. Prolonged intubation, the use of muscle relaxants, and sepsis can lead to diaphragmatic muscle weakness in a critically ill patient. Diaphragmatic dysfunction (DD) is defined as a partial (weakness) or complete (paralysis) loss of muscle function, which leads to a reduction in inspiratory capacity and a decrease in respiratory muscle endurance [49]. DD can impact either the hemidiaphragm or both. DD frequently remains undiagnosed in clinical practice due to its nonspecific symptoms, and ultrasound can facilitate an easy bedside assessment of diaphragmatic function [50].

There are two approaches for assessing the diaphragm: the intercostal approach is used to measure parameters like muscle thickness and thickening fraction (TFDi), while the subcostal approach is utilized to gauge diaphragmatic excursion (DE) [51]. Diaphragm muscle weakness is established when DE of less than 10-15 mm during tidal breathing or a maximum TFDi of less than 20% is noted [52]. Diaphragm muscle weakness is a predictor of weaning failure in the ICU and can also be suggestive of increased work of breathing in chronic pulmonary conditions [53]. The diaphragm ultrasound is also useful in cardiac surgery, cervical spine procedures, and after the placement of upper limb blocks (e.g., interscalene blocks) to identify an iatrogenic phrenic nerve injury [51].

In a meta-analysis conducted by Parada et al., including 19 studies (1,204 participants), the sensitivity of diaphragm ultrasound for evaluating diaphragm excursion was 0.80 (95% CI: 0.77-0.83), while the specificity was 0.80 (95% CI: 0.75-0.84). Regarding the assessment of the diaphragm thickening fraction, the sensitivity was 0.85 (95% CI: 0.82-0.87), while the specificity was 0.75 (95% CI: 0.69-0.80) [54]. Although diaphragm ultrasound is reliable, there remain issues related to standardization because of the significant variability in image acquisition and methodology [55].

Lung ultrasound (LUS)

LUS is a valuable bedside diagnostic tool for assessing various respiratory pathologies [56,57]. Although LUS cannot directly image lung tissue as the air in the lungs scatters the ultrasound beam, the interpretation of artifacts and specific patterns can aid in the diagnosis [58]. It exhibits better diagnostic accuracy than auscultation and chest radiography in detecting pleural effusion, pneumothorax, acute respiratory distress syndrome (ARDS), and cardiogenic pulmonary edema [59]. According to a meta-analysis of nine studies, for detecting cardiogenic pulmonary edema, the sensitivity of LUS was 0.92 (95% CI: 0.84-0.97), and the specificity was 0.87 (95% CI: 0. 82-0.91) [60]. Another meta-analysis conducted by Ding et al. showed that LUS had more sensitivity (0.88) compared to chest X-rays (0.52) with the same specificity for the diagnosis of pneumothorax [61].

Normal LUS shows a shimmering (sliding) hyperechoic pleural line followed by horizontal reverberation artifacts, parallel to the pleural line, known as the A-lines [62,63]. Absent pleural sliding should raise suspicion for pneumothorax since the air in between the pleural layers abolishes sliding. However, visualizing the junction where the pleura transitions from normal sliding to absent sliding, known as the “lung point,” is more specific [62]. Effusions are identified as anechoic collections between the parietal and visceral pleura, first appearing in the dependent zone and then in other regions when extensive [64].

The presence of vertical hyperechoic artifacts, known as B-lines, that move with pleural sliding is the hallmark of interstitial syndrome. The interstitial syndrome includes any pathological condition leading to increased density in the interstitial space between alveoli. This includes pulmonary edema, pneumonia, ARDS, COVID-19, or pulmonary fibrosis [65]. In consolidation, the lung tissue appears like the liver (also called hepatization), often surrounded by some pleural effusion. Atelectasis appears similar to consolidation, and clinical context helps in differentiating these two conditions [64]. Some signs, such as mobile air in the airways (dynamic air bronchograms), favor consolidation over atelectasis. Some common ultrasonographic signs seen in lung pathologies are shown in Figure 7.

Figure 7 LUS

(A) Normal lung showing horizontal artifacts, i.e., A-lines (arrows). (B) Vertical artifacts (arrows) known as B-lines indicate interlobular septal thickening, typically seen in congestion. (C) Pleural effusion (asterisk) as seen on a lateral scan. (D) Right pleural effusion (asterisk) as seen from the subxiphoid scanning window.

IVC: inferior vena cava; LUS: lung ultrasound

Turk et al. (2023) [66]; Creative Commons Attribution (CC BY) license

POCUS for the evaluation of patients with undifferentiated shock and cardiac arrest

Perioperative cardiac arrest is a rare but potentially catastrophic event. According to the UK-wide prospective 7th National Audit Project (NAP7), the incidence of perioperative cardiac arrest is approximately three in 10,000, mostly occurring during non-elective, complex surgeries, while the incidence of potentially serious complications is one in 18 (6%) cases [67]. POCUS in undifferentiated shock or cardiac arrest can identify treatable causes (such as hypovolemia, hypoxia, cardiac tamponade, pneumothorax, and pulmonary embolism), assess the quality of chest compressions during CPR, and differentiate true pulseless electrical activity (PEA) from pseudo-PEA [68]. It can also provide prognostic information regarding the possibility of a return to spontaneous circulation and survival [69]. Established protocols like RUSH, POCUS-CA, SHoc-ED, and FATE offer algorithmic frameworks for sonographic assessment [68,70-72]. Yoshida et al. conducted a meta-analysis of 12 studies with 1132 patients and concluded that the sensitivity and specificity of POCUS in determining the type of shock were 0.82 and 0.98 for obstructive shock, 0.78 and 0.96 for cardiogenic shock, 0.90 and 0.92 for hypovolemic shock, and 0.79 and 0.96 for distributive shock, respectively [73]. The current cardiopulmonary resuscitation guidelines recommend that POCUS be considered an extra diagnostic tool in cases where experienced personnel can perform it without disrupting CPR, particularly when there is a clinical suspicion of a specific reversible cause [74].

POCUS for regional anesthesia

Neuraxial Ultrasound 

Central neuraxial blocks (CNBs), such as spinal, epidural, and combined spinal epidural blocks, depend on surface anatomical landmarks, tactile perception, and optimal patient positioning for procedural success. Hence, these blocks can be challenging for certain patient subsets, such as obese patients, the elderly, pregnant patients, and those with spinal deformities like scoliosis [75,76].

Ultrasound has become a valuable tool for performing safe CNBs by providing real-time images of the spinal anatomy to guide the procedure. It is useful in pre-procedural scanning, aiding in midline localization, identification of intervertebral spaces, depth measurement, and anticipation of potential challenges [77-79]. It can also guide real-time needle placement, improve success rates, and enhance patient comfort [80]. However, image acquisition skills for neuraxial ultrasound have a steep learning curve and may be especially challenging in elderly patients with calcifications and obese patients [79]. Figure 8 and Figure 9 show the transverse and sagittal views of the spine required for conducting neuraxial ultrasound.

Figure 8 Sagittal views of the lumbar spine

(A) Sagittal transverse process view. (B) Sagittal articular process view. (C) Sagittal lamina view. (D) Sagittal spinous process view. (E) Parasagittal oblique view.

AC: anterior complex; AP: articular process; L: lamina; PC: posterior complex; SC: spinal canal (intrathecal space); SP: spinous process; TP: transverse process

Yoo et al. (2020) [79]; Creative Commons Attribution (CC BY) license

Figure 9 Transverse views of the lumbar spine

(A) Transverse spinous process view. (B) Transverse interspinous process view. (C) Tilted transverse interspinous process view.

AC: anterior complex; AP: articular process; L: lamina; PC: posterior complex; SC: spinal canal (intrathecal space); SP: spinous process

Yoo et al. (2020) [79]; Creative Commons Attribution (CC BY) license

Ultrasound-Guided Regional Nerve Blocks 

Ultrasound guidance for performing regional nerve blocks is now the standard of care. It facilitates real-time visualization of neural structures, monitoring needle placement, and assessing the spread of the local anesthetic agent. Compared to the traditional landmark method, ultrasound-guided blocks have higher success rates, decreased procedure times, a lesser anesthetic agent dose requirement, and a lower incidence of inadvertent vascular punctures and complications like pneumothorax [81-85].

In a comprehensive meta-analysis of 23 trials with more than 2,000 peripheral nerve blocks, the utilization of ultrasound guidance, either in isolation or in addition to nerve stimulation, showed a significant decrease in the incidence of vascular puncture, decreased procedural pain, and a lower requirement for additional analgesia or anesthesia [86]. However, there was no reduction in the occurrence of postoperative neurological complications. A recent consensus statement strongly advocates the utilization of ultrasound for regional anesthesia, supported by a high level of certainty in the available evidence [87].

Focused cardiac ultrasound (FoCUS) and hemodynamic assessment

FoCUS is a valuable tool in evaluating hemodynamically unstable patients in the perioperative period and intensive care [88,89]. Unlike formal transthoracic echocardiography (TTE), FoCUS aims at a point-of-care, limited cardiac evaluation that quickly recognizes specific ultrasound signs, which can help in narrowing down the differential diagnosis. The competence achieved in FoCUS can either be basic critical care echocardiography (CCE) or advanced CCE, depending on the training received [90].

Basic CCE utilizes standard two-dimensional TTE and generally excludes the use of spectral Doppler applications. Commonly used transthoracic views for this purpose are shown in Figure 10.

Figure 10 Basic echocardiographic views

(A) Parasternal long axis. (B) Parasternal short axis. (C) Apical four-chamber. (D) Subxiphoid; (E) IVC.

The green arrows indicate the direction of the transducer orientation marker.

IVC: inferior vena cava; LA: left atrium; LV: left ventricle; RA: right atrium; RV: right ventricle

Argaiz et al. (2021) [91]; reproduced with permission from Wolters Kluwer Health

It involves assessment of overall left ventricular (LV) function and size, appreciation of regional wall motion abnormalities, identification of pericardial effusion, evaluation of right ventricular (RV) function and size, and detection of significant valvular lesions based on color Doppler. Basic CCE is aimed at rapidly categorizing shock states and identifying life-threatening causes such as hypovolemic shock, cor pulmonale, possible aortic dissection, and cardiac tamponade [90,92] (Figure 11).

Figure 11 Ascending aortic dissection with cardiac tamponade

Transthoracic echocardiogram in a patient with ascending aortic dissection and cardiac tamponade: (A) Subcostal view showing a large pericardial effusion causing RV collapse. (B) A high-right parasternal view demonstrating the intimal dissection flap in the ascending aorta.

RV: right ventricular

Image credit: Dinkar Bhasin

Advanced CCE provides a more comprehensive and quantitative assessment of cardiac function, including parameters like cardiac output, valvular pathology, diastolic dysfunction, and pulmonary hypertension, for optimizing hemodynamics at the bedside (Figure 12).

Figure 12 Severe mitral stenosis in a patient with shock

(A) Apical four-chamber view demonstrates thickened mitral valve leaflets and a dilated left atrium (arrowheads). (B) Color Doppler imaging across the mitral valve shows turbulent flow across the mitral valve in diastole. (C) Parasternal short-axis view demonstrating thickened mitral valve leaflets (arrowheads) with commissural fusion giving a fish-mouth appearance. Mild pericardial effusion can also be appreciated. (D) Continuous-wave Doppler across the mitral valve demonstrates an elevated gradient. The valve area, as measured by pressure half-time, is 1 cm2.

Image credit: Dinkar Bhasin

In a meta-analysis of nine studies comparing the accuracy of clinical assessment with FOCUS for diagnosing various conditions, FoCUS-based examination was more sensitive (84% vs. 43%) and specific (89% vs. 81%) compared to clinical assessment for identifying LV dysfunction (LV ejection fraction <50%) [91]. Furthermore, FOCUS-based examination had a higher sensitivity (71% vs. 46%) for diagnosing aortic or mitral valve disease (of at least moderate severity) compared to clinical examination, with both having a similar specificity of 94% [93]. While not intended to replace existing diagnostic methods, FOCUS complements traditional tools and exams that may miss important cardiac diagnoses [94]. In patients with difficult transthoracic windows and during cardiopulmonary resuscitation, critical care transesophageal echocardiography (TEE) is emerging as a valuable bedside tool [95].

Some practical tips for performing FoCUS can be useful. For critically ill patients, particularly those on mechanical ventilation, obtaining good transthoracic views can be challenging. The subcostal window provides good alternative views for assessing ventricular function and valvular lesions. The plane of the subcostal four-chamber view is similar to the apical four-chamber view and gives an idea of the global LV function. Rotating the echo probe counter-clockwise from the subcostal four-chamber view yields short-axis views similar to the parasternal short-axis view and can help identify regional wall motion abnormalities. The subcostal four-chamber view is also good for identifying pericardial effusions and the RV collapse in cardiac tamponade. While TTE can facilitate early diagnosis of ascending aortic dissection by demonstrating a dissection flap, the diagnostic yield is poor, and aortic dissection should not be ruled out based on a negative TTE alone. The yield of TTE can be improved by employing high parasternal views, such as the right parasternal views, as illustrated in Figure 6. However, when clinical suspicion is high, TEE, or computed tomography, should be considered.

In recent times, there has been a growing awareness of the harmful effects of fluid overload, particularly in critical illness scenarios where the empirical use of intravenous fluids is prevalent [96]. A systematic review including 19,902 patients admitted to the intensive care unit revealed that non-survivors had a cumulative fluid balance 4.4 L higher than survivors after one week of ICU stay. Additionally, adopting a restrictive fluid management approach was linked to lower mortality rates compared to the outcomes associated with liberal fluid administration [97]. A novel sonographic assessment known as venous excess ultrasound (VExUS) is gaining prominence as a method to grade systemic venous congestion and monitor response to decongestive therapy [98-100]. The VExUS protocol combines the use of inferior vena cava (IVC) ultrasound with pulsed-wave Doppler assessment of the hepatic, portal, and intrarenal veins to generate a numerical score, as illustrated in Figure 13.

Figure 13 VExUS grading

When the diameter of the IVC is >2 cm, three grades of congestion are defined based on the severity of abnormalities on the hepatic, portal, and renal parenchymal venous Doppler. Hepatic vein Doppler is considered mildly abnormal when the systolic (S) wave is smaller than the diastolic (D) wave but still below the baseline; it is considered severely abnormal when the S-wave is reversed. Portal vein Doppler is considered mildly abnormal when the pulsatility is 30-50%, and severely abnormal when it is ≥50%. Asterisks represent points of pulsatility measurement. Renal parenchymal vein Doppler is mildly abnormal when it is pulsatile with distinct S and D components and severely abnormal when it is monophasic with a D-only pattern.

IVC: inferior vena cava; VExUS: venous excess ultrasound

Adapted from NephroPOCUS.com with permission

These IVC measurements and Doppler scans help assess the degree of venous congestion, categorizing it as mild, moderate, severe, or none. VExUS can be a valuable adjunct to bedside hemodynamic assessment as a noninvasive, individualized method to optimize fluid management in surgical and critically ill patients. In a group of post-cardiac surgery patients, the identification of flow abnormalities in two or more veins (among hepatic, portal, and kidney parenchymal veins) along with a full or dilated IVC (≥2 cm) has demonstrated the ability to predict the risk of acute kidney injury with greater accuracy (HR: 3.69; 95% CI: 1.65-8.24; p = 0.001) compared to relying solely on isolated central venous pressure measurements [101]. Clinical trials studying the utility of VExUS in various critically ill subgroups are currently underway [102].

Conclusions

POCUS is an essential skill for anesthesiologists in perioperative and critical care settings. It not only complements the traditional physical examination for accurate assessment of the patient but also enhances the procedural success rates of various invasive procedures where ultrasound guidance can be employed. In the preoperative period, airway ultrasound can be used to anticipate challenging airways, and gastric ultrasound can be utilized for aspiration risk assessment. During the intraoperative period, ultrasound can be utilized to perform procedures like peripheral and central vascular access, arterial line placement, and central neuraxial and peripheral nerve blocks. Multi-organ POCUS can provide useful clues in cases of perioperative emergencies or peri-arrest states. In the postoperative period or in intensive care, VExUS, FoCUS, and LUS may be helpful in the diagnosis of any pulmonary or cardiac complications and the assessment of fluid status. The latest evidence supports that POCUS leads to better quality of care and patient outcomes. As evidence of its benefits continues to grow, the use of POCUS in patient management is set to increase, making it essential to include POCUS in the training programs and curricula for anesthesiologists.

Disclosures

Author Contributions

Conflicts of interest: In compliance with the ICMJE uniform disclosure form, all authors declare the following:

Payment/services info: All authors have declared that no financial support was received from any organization for the submitted work.

Financial relationships: Abhilash Koratala declare(s) a grant from KidneyCure and the American Society of Nephrology’s William and Sandra Bennett Clinical Scholars Grant.

Other relationships: All authors have declared that there are no other relationships or activities that could appear to have influenced the submitted work.

Concept and design:  Ankita Dhir, Abhilash Koratala, Dinkar Bhasin, Bhavna Bhasin-Chhabra

Drafting of the manuscript:  Ankita Dhir, Dinkar Bhasin

Critical review of the manuscript for important intellectual content:  Abhilash Koratala, Bhavna Bhasin-Chhabra

Supervision:  Abhilash Koratala, Bhavna Bhasin-Chhabra
==== Refs
References

1 Perioperative point-of-care ultrasound: from concept to application Anesthesiology Ramsingh D Bronshteyn YS Haskins S Zimmerman J 908 916 132 2020 31977521
2 The utility of point of care ultrasonography (POCUS) Ann Med Surg (Lond) Hashim A Tahir MJ Ullah I Asghar MS Siddiqi H Yousaf Z 102982 71 2021 34840746
3 History of emergency and critical care ultrasound: the evolution of a new imaging paradigm Crit Care Med Kendall JL Hoffenberg SR Smith RS 0 30 35 2007
4 A systematic review of the cost-effectiveness of ultrasound in emergency care settings Ultrasound J Lentz B Fong T Rhyne R Risko N 16 13 2021 33687607
5 Stages and factors of the "Perioperative process": points in common with the aeronautical industry Arq Bras Cir Dig Davrieux CF Palermo M Serra E Houghton EJ Acquafresca PA Finger C Giménez ME 0 32 2019
6 Ultrasound-guided peripheral venous cannulation in critically ill patients: a practical guideline Ultrasound J Blanco P 27 11 2019 31624927
7 UltraSound guided PEripheral Catheterization increases first-atTempt success RAte in hospitalized patients when compared with conventional technique: SPECTRA - randomized clinical trial J Vasc Access Hansel LA Junges M Santos MS 11297298231162132 2023 36971377
8 Ultrasound-guided peripheral intravenous access program is associated with a marked reduction in central venous catheter use in noncritically ill emergency department patients Ann Emerg Med Shokoohi H Boniface K McCarthy M 198 203 61 2013 23141920
9 Difficult intravascular access in pediatric emergency department: the ultrasound-assisted strategy (DIAPEDUS study) J Intensive Care Med D'Alessandro M Ricci M Bellini T Chianucci B Calevo MG Piccotti E Moscatelli A 217 221 39 2024 37735884
10 Safety and feasibility of ultrasound-guided placement of peripherally inserted central catheter performed by neurointensivist in neurosurgery intensive care unit PLoS ONE Kim YO Chung CR Gil E Park CM Suh GY Ryu JA 0 14 2019
11 European Society of Anaesthesiology guidelines on peri-operative use of ultrasound-guided for vascular access (PERSEUS vascular access) Eur J Anaesthesiol Lamperti M Biasucci DG Disma N 344 376 37 2020 32265391
12 Arterial cannulation in adult critical care patients: a comparative study between ultrasound guidance and palpation technique Med Intensiva (Engl Ed) Gutte S Azim A Poddar B Gurjar M Kumar A 391 401 47 2023 36868961
13 How to improve the efficiency and the safety of real-time ultrasound-guided central venous catheterization in 2023: a narrative review Ann Intensive Care Boulet N Muller L Rickard CM 46 25 2023 https://pubmed.ncbi.nlm.nih.gov/37227571/
14 Ultrasound guidance versus anatomical landmarks for internal jugular vein catheterization Cochrane Database Syst Rev Brass P Hellmich M Kolodziej L 6962 9 2015
15 Ultrasound guidance versus anatomical landmarks for subclavian or femoral vein catheterization Cochrane Database Syst Rev Brass P Hellmich M Kolodziej L Schick G Smith AF 0 1 2015
16 Real-time ultrasound guidance as compared with landmark technique for subclavian central venous cannulation: a systematic review and meta-analysis with trial sequential analysis Crit Care Med Zawadka M La Via L Wong A 642 652 51 2023 36861982
17 Diagnosis of deep vein thrombosis of the lower extremity: a systematic review and meta-analysis of test accuracy Blood Adv Bhatt M Braun C Patel P 1250 1264 4 2020 32227213
18 Major complications of airway management in the UK: results of the Fourth National Audit Project of the Royal College of Anaesthetists and the Difficult Airway Society. Part 1: anaesthesia Br J Anaesth Cook TM Woodall N Frerk C 617 631 106 2011 21447488
19 Ultrasound assessment of gastric content and volume Anesthesiology Perlas A Chan VW Lupu CM Mitsakakis N Hanbidge A 82 89 111 2009 19512861
20 Validation of a mathematical model for ultrasound assessment of gastric volume by gastroscopic examination Anesth Analg Perlas A Mitsakakis N Liu L 357 363 116 2013 23302981
21 Rapid evaluation of gastric content with ultrasound: an educational tool Cureus Nguyen H Paluska MR Falcon R Petersen TR Soneru C 0 15 2023
22 Ultrasound assessment of gastric volume in severely obese individuals: a validation study Br J Anaesth Kruisselbrink R Arzola C Jackson T Okrainec A Chan V Perlas A 77 82 118 2017 28039244
23 Intra- and interrater reliability of ultrasound assessment of gastric volume Anesthesiology Kruisselbrink R Arzola C Endersby R Tse C Chan V Perlas A 46 51 121 2014 24595113
24 Gastric ultrasound in the third trimester of pregnancy: a randomised controlled trial to develop a predictive model of volume assessment Anaesthesia Arzola C Perlas A Siddiqui NT Downey K Ye XY Carvalho JC 295 303 73 2018 29265187
25 Diagnostic accuracy of point-of-care gastric ultrasound Anesth Analg Kruisselbrink R Gharapetian A Chaparro LE 89 95 Chan 128 2019 29624530
26 Aspiration under anaesthesia: risk assessment and decision-making Contin Educ Anaesth Crit Care Pain Robinson M Davidson A 171 175 14 2014
27 Clinical significance of pulmonary aspiration during the perioperative period Anesthesiology Warner MA Warner ME Weber JG 56 62 78 1993 8424572
28 Ultrasound assessment of gastric volumes of thick fluids: validating a prediction model Eur J Anaesthesiol Tacken MC van Leest TA van de Putte P Keijzer C Perlas A 1223 1229 38 2021 33606419
29 Cricothyrotomy in difficult airway management: a narrative review Trends Anaesth Crit Care Gaitini L Gómez-Ríos MÁ Hochman O 101249 2023
30 Structured approach to ultrasound-guided identification of the cricothyroid membrane: a randomized comparison with the palpation method in the morbidly obese Br J Anaesth Kristensen MS Teoh WH Rudolph SS 1003 1004 114 2015 25991744
31 Role of upper airway ultrasound in airway management J Intensive Care Osman A Sum KM 52 4 2016 27529028
32 Comparison between ultrasound-guided and digital palpation techniques for identification of the cricothyroid membrane: a meta-analysis Br J Anaesth Hung KC Chen IW Lin CM Sun CK 0 11 126 2021
33 Oesophageal intubation: an analysis of 2000 incident reports Anaesth Intensive Care Holland R Webb RK Runciman WB 608 610 21 1993 8273883
34 Intubation practices and adverse peri-intubation events in critically ill patients from 29 countries JAMA Russotto V Myatra SN Laffey JG 1164 1172 325 2021 33755076
35 Point-of-care ultrasound for airway management in the emergency and critical care setting Clin Exp Emerg Med Gottlieb M O'Brien JR Ferrigno N Sundaram T 22 32 11 2024 37620036
36 Bedside ultrasound for tracheal tube verification in pediatric emergency department and ICU patients: a systematic review Pediatr Crit Care Med Lin MJ Gurley K Hoffmann B 0 76 17 2016
37 Ultrasonography for the confirmation of endotracheal tube intubation: a systematic review and meta-analysis Ann Emerg Med Gottlieb M Holladay D Peksa GD 627 636 72 2018 30119943
38 Endotracheal tube placement confirmation by ultrasonography: a systematic review and meta-analysis of more than 2500 patients J Emerg Med Sahu AK Bhoi S Aggarwal P 254 264 59 2020 32553512
39 Ultrasonography for confirmation of endotracheal tube placement: a systematic review and meta-analysis Resuscitation Chou EH Dickman E Tsou PY 97 103 90 2015 25711517
40 Bedside predictors of difficult intubation: a systematic review Minerva Anestesiol Vannucci A Cavallone LF 69 83 82 2016 https://pubmed.ncbi.nlm.nih.gov/25990431/ 25990431
41 Predicting difficult intubation in apparently normal patients: a meta-analysis of bedside screening test performance Anesthesiology Shiga T Wajima Z Inoue T Sakamoto A 429 437 103 2005 16052126
42 Diagnostic performance of airway ultrasound for the assessment of difficult laryngoscopy: a systematic review and meta-analysis J Cardiothorac Vasc Anesth Benavides-Zora D Jaramillo MC Townsley MM 1101 1109 37 2023 37012134
43 Airway ultrasound as predictor of difficult direct laryngoscopy: a systematic review and meta-analysis Anesth Analg Carsetti A Sorbello M Adrario E Donati A Falcetta S 740 750 134 2022 34914641
44 Real-time ultrasound guided percutaneous dilatational tracheostomy with and without bronchoscopic control: an observational study Minerva Anestesiol Chacko J Gagan B Kumar U Mundlapudi B 166 174 81 2015 https://pubmed.ncbi.nlm.nih.gov/25057932/ 25057932
45 Can ultrasound be useful for predicting the size of a left double-lumen bronchial tube? Tracheal width as measured by ultrasonography versus computed tomography J Clin Anesth Sustić A Miletić D Protić A Ivancić A Cicvarić T 247 252 20 2008 18617120
46 Ultrasonography as a method of screening for tracheal invasion by papillary thyroid cancer Surg Today Tomoda C Uruno T Takamura Y 819 822 35 2005 16175461
47 Vocal cord dysfunction: ultrasonography-aided diagnosis during routine airway examination Saudi J Anaesth Kumar A Sinha C Singh AK Bhadani UK 370 371 11 2017 28757854
48 The respiratory muscles Clin Sci (Lond) Green M Moxham J 1 10 68 1985 3155450
49 Diaphragmatic dysfunction is characterized by increased duration of mechanical ventilation in subjects with prolonged weaning Respir Care Lu Z Xu Q Yuan Y Zhang G Guo F Ge H 1316 1322 61 2016 27682813
50 Diaphragm and peripheral muscle thickness on ultrasound: intra-rater reliability and variability of a methodology using non-standard recumbent positions Respirology Baldwin CE Paratz JD Bersten AD 1136 1143 16 2011 21645172
51 Sonographic evaluation of the diaphragm in critically ill patients. Technique and clinical applications Intensive Care Med Matamis D Soilemezi E Tsagourias M 801 810 39 2013 23344830
52 Measuring diaphragm thickness with ultrasound in mechanically ventilated patients: feasibility, reproducibility and validity Intensive Care Med Goligher EC Laghi F Detsky ME 642 649 41 2015 25693448
53 Mechanical ventilation and diaphragmatic atrophy in critically ill patients: an ultrasound study Crit Care Med Zambon M Beccaria P Matsuno J 1347 1352 44 2016 26992064
54 Effectiveness of diaphragmatic ultrasound as a predictor of successful weaning from mechanical ventilation: a systematic review and meta-analysis Crit Care Parada-Gereda HM Tibaduiza AL Rico-Mendoza A 174 27 2023 37147688
55 Methodological and clinimetric evaluation of inspiratory respiratory muscle ultrasound in the critical care setting: a systematic review and meta-analysis Crit Care Med Truong D Abo S Whish-Wilson GA 0 36 51 2023
56 The sound of air: point-of-care lung ultrasound in perioperative medicine Can J Anaesth Goffi A Kruisselbrink R Volpicelli G 399 416 65 2018 29411300
57 Lung ultrasound for critically ill patients Am J Respir Crit Care Med Mojoli F Bouhemad B Mongodi S 701 714 15 2019
58 Point-of-care lung ultrasound in adults: image acquisition J Vis Exp Pereira RO Convissar DL Montgomery S Herbert JT Reed CR Tang HJ Bronshteyn YS 2023
59 Lung ultrasound for the emergency diagnosis of pneumonia, acute heart failure, and exacerbations of chronic obstructive pulmonary disease/asthma in adults: a systematic review and meta-analysis J Emerg Med Staub LJ Mazzali Biscaro RR Kaszubowski E Maurici R 53 69 56 2019 30314929
60 Diagnostic efficacy of lung ultrasound in cardiogenic pulmonary edema: a systematic review and meta-analysis Eur Rev Med Pharmacol Sci Dong LJ Li J Liu W Ankaerjiang AW Li B Chen YT Yu ZX 6947 6955 27 2023 37606105
61 Diagnosis of pneumothorax by radiography and ultrasonography: a meta-analysis Chest Ding W Shen Y Yang J He X Zhang M 859 866 140 2011 21546439
62 International evidence-based recommendations for point-of-care lung ultrasound Intensive Care Med Volpicelli G Elbarbary M Blaivas M 577 591 38 2012 22392031
63 Lung ultrasound in the critically ill Ann Intensive Care Lichtenstein DA 1 4 2014 24401163
64 Fluid administration limited by lung sonography: the place of lung ultrasound in assessment of acute circulatory failure (the FALLS-protocol) Expert Rev Respir Med Lichtenstein D 155 162 6 2012 22455488
65 Relevance of lung ultrasound in the diagnosis of acute respiratory failure*: the BLUE protocol Chest Lichtenstein DA Mezière GA 117 125 134 2008 http://134 18403664
66 Point-of-care ultrasound in diagnosis and management of congestive nephropathy World J Crit Care Med Turk M Robertson T Koratala A 53 62 12 2023 37034023
67 The incidence of potentially serious complications during non-obstetric anaesthetic practice in the United Kingdom: an analysis from the 7th National Audit Project (NAP7) activity survey Anaesthesia Kane AD Cook TM Armstrong RA 43 53 79 2024 37944508
68 Point-of-care ultrasound in cardiorespiratory arrest (POCUS-CA): narrative review article Ultrasound J Ávila-Reyes D Acevedo-Cardona AO Gómez-González JF Echeverry-Piedrahita DR Aguirre-Flórez M Giraldo-Diaconeasa A 46 13 2021 34855015
69 Echocardiography for prognostication during the resuscitation of intensive care unit patients with non-shockable rhythm cardiac arrest Resuscitation Flato UA Paiva EF Carballo MT Buehler AM Marco R Timerman A 1 6 92 2015 25891961
70 Transthoracic echocardiography for cardiopulmonary monitoring in intensive care Eur J Anaesthesiol Jensen MB Sloth E Larsen KM Schmidt MB 700 707 21 2004 15595582
71 Rapid cardiac ultrasound of inpatients suffering PEA arrest performed by nonexpert sonographers Resuscitation Niendorff DF Rassias AJ Palac R Beach ML Costa S Greenberg M 81 87 67 2005 16199290
72 Point-of-care multiorgan ultrasonography for the evaluation of undifferentiated hypotension in the emergency department Intensive Care Med Volpicelli G Lamorte A Tullio M 1290 1298 39 2013 23584471
73 Diagnostic accuracy of point-of-care ultrasound for shock: a systematic review and meta-analysis Crit Care Yoshida T Yoshida T Noma H Nomura T Suzuki A Mihara T 200 27 2023 37231510
74 2022 international consensus on cardiopulmonary resuscitation and emergency cardiovascular care science with treatment recommendations: summary from the basic life support; advanced life support; pediatric life support; neonatal life support; education, implementation, and teams; and first aid task forces Circulation Wyckoff MH Greif R Morley PT 0 557 146 2022
75 Factors associated with difficult neuraxial blockade Local Reg Anesth Ružman T Gulam D Haršanji Drenjančević I Venžera-Azenić D Ružman N Burazin J 47 52 7 2014 25336987
76 Vertebral level of Tuffier's line measured by ultrasonography in parturients in the lateral decubitus position Korean J Anesthesiol Kim SH Kim DY Han JI Baik HJ Park HS Lee GY Kim JH 181 185 67 2014 25302094
77 Lumbar neuraxial ultrasound for spinal and epidural anesthesia: a systematic review and meta-analysis Reg Anesth Pain Med Perlas A Chaparro LE Chin KJ 251 260 41 2016 25493689
78 Real-time ultrasound-guided paramedian spinal anaesthesia: evaluation of the efficacy and the success rate of single needle pass Br J Anaesth Chong SE Mohd Nikman A Saedah A Wan Mohd Nazaruddin WH Kueh YC Lim JA Shamsul Kamalrujan H 799 801 118 2017 28510752
79 Ultrasonography for lumbar neuraxial block Anesth Pain Med (Seoul) Yoo S Kim Y Park SK Ji SH Kim JT 397 408 15 2020 33329842
80 Comparative efficacy of ultrasound guidance or conventional anatomical landmarks for neuraxial puncture in adult patients: a systematic review and network meta-analysis Br J Anaesth Kamimura Y Yamamoto N Shiroshita A 1097 1111 132 2024 37806932
81 Comparison of ultrasound-guided and traditional localisation in intraspinal anesthesia: a systematic review and network meta-analysis BMJ Open Zhang Y Peng M Wei J Huang J Ma W Li Y 0 13 2023
82 Did ultrasound fulfill the promise of safety in regional anesthesia? Curr Opin Anaesthesiol Barrington MJ Uda Y 649 655 31 2018 30004951
83 Analgesic efficacy of ultrasound-guided regional anesthesia: a meta-analysis J Clin Anesth Gelfand HJ Ouanes JP Lesley MR 90 96 23 2011 21377070
84 Adverse outcomes associated with nerve stimulator-guided and ultrasound-guided peripheral nerve blocks by supervised trainees: update of a single-site database Reg Anesth Pain Med Orebaugh SL Kentor ML Williams BA 577 582 37 2012 22996199
85 Effects of ultrasound guidance on the minimum effective anaesthetic volume required to block the femoral nerve Br J Anaesth Casati A Baciarello M Di Cianni S 823 827 98 2007 17478453
86 A systematic review and meta-analysis of ultrasound versus electrical stimulation for peripheral nerve location and blockade Anaesthesia Munirama S McLeod G 1084 1091 70 2015 25989611
87 The second American Society of Regional Anesthesia and Pain Medicine evidence-based medicine assessment of ultrasound-guided regional anesthesia: executive summary Reg Anesth Pain Med Neal JM Brull R Horn JL 181 194 41 2016 26695878
88 Focused cardiac ultrasonography: current applications and future directions J Ultrasound Med Luong CL Ong K Kaila K Pellikka PA Gin K Tsang TS 865 876 38 2019 30146784
89 Perioperative applications of focused cardiac ultrasound Int Anesthesiol Clin Hollon MM Bradley C McCullough I Borgmeier E 24 33 60 2022
90 American College of Chest Physicians/La Société de Réanimation de Langue Française statement on competence in critical care ultrasonography Chest Mayo PH Beaulieu Y Doelken P 1050 1060 135 2009 19188546
91 Comprehensive assessment of fluid status by point-of-care ultrasonography Kidney360 Argaiz ER Koratala A Reisinger N 1326 1338 2 2021 35369665
92 Recommendations for core critical care ultrasound competencies as a part of specialist training in multidisciplinary intensive care: a framework proposed by the European Society of Intensive Care Medicine (ESICM) Crit Care Wong A Galarza L Forni L 393 24 2020 32620166
93 Comparative accuracy of focused cardiac ultrasonography and clinical examination for left ventricular dysfunction and valvular heart disease: a systematic review and meta-analysis Ann Intern Med Marbach JA Almufleh A Di Santo P 264 272 171 2019 https://www.acpjournals.org/doi/abs/10.7326/M19-1337?journalCode=aim 31382273
94 Reliability of focused cardiac ultrasound by novice sonographer in preoperative anaesthetic assessment: an observational study Cardiovasc Ultrasound Andruszkiewicz P Sobczyk D Gorkiewicz-Kot I Kowalik I Gelo R Stach O 45 13 2015 26589140
95 Critical care transesophageal echocardiography Chest Mayo PH Narasimhan M Koenig S 1323 1332 148 2015 26204465
96 Diagnosis of fluid overload: from conventional to contemporary concepts Cardiorenal Med Koratala A Ronco C Kazory A 141 154 12 2022 36096121
97 Fluid overload, de-resuscitation, and outcomes in critically ill or injured patients: a systematic review with suggestions for clinical practice Anaesthesiol Intensive Ther Malbrain ML Marik PE Witters I Cordemans C Kirkpatrick AW Roberts DJ Van Regenmortel N 361 380 46 2014 25432556
98 Venous excess doppler ultrasound for the nephrologist: pearls and pitfalls Kidney Med Koratala A Reisinger N 100482 4 2022 35707749
99 Point of care venous Doppler ultrasound: exploring the missing piece of bedside hemodynamic assessment World J Crit Care Med Galindo P Gasca C Argaiz ER Koratala A 310 322 10 2021 34888157
100 Bedside ultrasound in the management of cardiorenal syndromes: an updated review Cardiorenal Med Argaiz ER Romero-Gonzalez G Rola P Spiegel R Haycock KH Koratala A 372 384 13 2023 37980889
101 Quantifying systemic congestion with point-of-care ultrasound: development of the venous excess ultrasound grading system Ultrasound J Beaubien-Souligny W Rola P Haycock K Bouchard J Lamarche Y Spiegel R Denault AY 16 12 2020 32270297
102 Doppler identified venous congestion in septic shock: protocol for an international, multi-centre prospective cohort study (Andromeda-VEXUS) BMJ Open Prager R Argaiz E Pratte M 0 13 2023
