Diagnostic Point-of-Care Ultrasound for the Cardiac Surgical Patient, From Head-to-Toe

In medicine, ultrasound has three broad applications: (1) procedural guidance (e.g., ultrasound-guided placement of a central venous catheter); (2) therapy (e.g., ultrasound lithotripsy); and (3) diagnostics¹. Diagnostic ultrasound can further be subdivided into two additional workflows: consultative and point-of-care^2,3. Consultative ultrasound refers to an ultrasound exam ordered by a patient's primary treating provider but performed by a separate specialist team. Whereas point-of-care ultrasound (POCUS) describes an ultrasound exam performed and interpreted by a patient's primary treating provider^2,3.

Over the past few decades, diagnostic POCUS has emerged as a useful bedside adjunct to narrow the differential diagnosis of organ dysfunction in a wide range of clinical contexts. One such clinical context is the care of patients undergoing cardiothoracic (CT) surgery, who suffer from dysfunction in a wide range of organ systems and for whom invasive pressure monitors (e.g., Swan-Ganz catheters) are being placed with less frequency. However, for most organ systems, proficiency with diagnostic POCUS remains variable among frontline clinicians, both in terms of image acquisition and interpretation^4,5,6,7,8,9. To address this unmet need, a recent JoVE Methods Collection on diagnostic POCUS describes and amalgamates a multitude of evidence-based image acquisition protocols. These protocols individually will be useful to a wide range of bedside clinical specialties. To illustrate their value in one specific context, this brief review focuses on the role of diagnostic POCUS in the care of patients undergoing CT surgery. For these CT surgery patients, we review how diagnostic POCUS can potentially facilitate their care from head to toe (Table 1).

Table 1: Diagnostic Point-of-Care Ultrasound applications relevant to the perioperative care of cardiothoracic surgery patients, from head to toe. Green: Strong evidence base in ICU settings, including evidence specifically in the CT ICU. Yellow: Moderate or less evidence in the CT ICU but with strong evidence in other settings. Orange: Low-quality evidence in all settings.

Head and neck
Patients undergoing CT surgery can suffer from a multitude of intracranial or cervical conditions that require rapid diagnosis and monitoring. Toward this end, POCUS of the head and neck may be helpful for evaluating the following datapoints: optic nerve sheath diameter, transcranial flow through the middle cerebral artery, airway anatomy, and carotid artery flow.

Patients undergoing CT surgery (especially those undergoing any aortic manipulation¹⁰ procedures) are at an increased risk of ischemic and hemorrhagic strokes. While computed tomography is the gold standard for diagnosis and serial assessment of intracerebral lesions, it usually requires resource-intensive transport of often unstable patients and thus cannot serve as a practical daily monitor of markers of important neurological parameters like intracranial pressure (ICP). In contrast, two diagnostic POCUS modalities can provide qualitative clues to elevated ICP and other intracerebral pathologies: optic nerve sheath diameter (ONSD) and transcranial color-coded Doppler (TCCD) of the middle cerebral artery (MCA).

Ultrasound measurement of ONSD has been extensively compared to invasive ICP monitoring and has been shown in many studies to be capable of discriminating between normal versus high ICP with high accuracy. However, reported diagnostic thresholds span roughly 4.1-6.3 mm depending on population and methods^11,12,13. Given this heterogeneity, it is possible that a three-category system would better reflect sensitivity-specificity trade-offs than a single dichotomous cutoff value. Toward this goal, future research could consider the following three-category sorting of ONSD: (1) <5.0 mm: likely normal ICP, (2) 5.0-5.5 mm: borderline / possibly elevated ICP, (3) 5.5 mm: likely elevated ICP. If future research is able to identify optimal cutoff(s) of ONSD, the modality would have a distinct advantage over existing alternatives. Most notably, compared to invasive methods of ICP monitoring, ONSD ultrasound might permit serial assessment with minimal risk to patients¹⁴, which can be especially useful in combination with the neurological exam to evaluate CT surgery patients who require therapeutic anticoagulation (i.e., for mechanical circulatory support, prosthetic valves, etc.). However, in isolation, ONSD is highly operator dependent and can be difficult to interpret when values fall in the borderline range.

Similar to ONSD, TCCD of the MCA has also shown some ability to qualitatively detect elevated ICP¹⁵. This is performed by using pulse-wave Doppler to trace flow through the MCA and measuring the pulsatility index (PI) defined as follows: (systolic velocity - diastolic velocity) / mean velocity¹⁵. Elevated values of PI have correlated with elevated ICP in several studies, but the data are mixed. For example, PI values >1.2-1.3 predict ICP >= 20 cm H2O in studies of both adults and children¹⁶. However, in children with traumatic brain injury (TBI), the correlation only holds during the first 24 h after injury¹⁶. Further, PI is unreliable in the absence of pulsatile blood flow, which includes patients on mechanical circulatory support (MCS)^17,18.

Notably, there is evidence that combining ONSD and TCCD might increase diagnostic accuracy over either modality alone. For example, combining these modalities has been studied in adults and found to increase the area under the curve (AUC) for detection of elevated ICP to 0.91 from 0.78-0.86 for the modalities individually^19,20,21.

Beyond elevated ICP, TCCD of the MCA is also capable of detecting several other pathologies, including but not limited to: (1) cerebral vasospasm and (2) microemboli¹⁵. Whereas vasospasm monitoring is not routinely needed perioperatively in patients undergoing CT surgery, microemboli are occasionally a serious problem in patients with mechanical circulatory support (MCS) devices, such as intra-aortic balloon pumps (IABPs), extracorporeal pumps such as left ventricular assist devices (LVAD), and extracorporeal membrane oxygenation (ECMO). These microemboli can cause both hemorrhagic and ischemic neurological injuries. To attempt to mitigate these complications in any patients with forms of MCS that include an oxygenator (e.g., ECMO), serial TCDs can be used for microembolic monitoring²². Such monitoring is especially useful in situations where the membrane/circuit is aging and can help determine whether to perform a circuit exchange.

In the care of CT surgery patients, airway POCUS has potential utility to help answer several time-sensitive questions. First, airway POCUS can distinguish tracheal from esophageal intubation when capnography may be unreliable, such as in low-flow states (e.g., after induction on cardiopulmonary bypass or with massive pulmonary shunt)²³. Second, airway POCUS can facilitate pre-operative risk stratification by quantifying anterior neck soft-tissue and other sonographic metrics associated with difficult laryngoscopy, complementing standard bedside screening^24,25,26. And third, ultrasound mapping of the cricothyroid membrane before induction improves accuracy over palpation, especially in obese or anatomically challenging necks, facilitating faster rescue front-of-neck access if a "can't-intubate, can't-oxygenate" event occurs^27,28.

POCUS of the carotid artery presents a potential opportunity to gain insight into both global and regional bloodflow. In terms of global bloodflow, some studies have demonstrated that during cardiopulmonary resuscitation (CPR), carotid POCUS can be used semi-continuously to determine adequacy of CPR²⁹. The assumption is that the carotid artery is collapsible in the absence of a pulse and less compressible or pulsatile in the presence of it. In terms of regional perfusion, carotid POCUS is capable of detecting various forms of acute carotid occlusions, ranging from thrombosis to dissection^30,31. However, carotid POCUS remains in its infancy. In contrast to ultrasound of other organ systems, ultrasound of the carotid has proved challenging to shrink to a format compatible with point-of-care assessment because clinically useful carotid assessment requires comprehensive multi-segment imaging, precise velocity measurements, and rigorous quality assurance to verify compliance with validated interpretation standards³². Whereas POCUS excels at answering binary questions (e.g., "is the left ventricular function normal or impaired?"), carotid ultrasound requires graded quantification of stenosis and plaque morphology, which is hard to simplify. However, some of these barriers may be surmountable in the future by supplementing the skills of point-of-care providers with artificial intelligence.

Cardiothoracic
The two most common indications for POCUS in the cardiac surgical ICU are hypotension and management of mechanical circulatory support (MCS)³³. To narrow the differential diagnosis of hypotension, POCUS centers on evaluation of the heart and, depending on the cardiac findings, other organ systems as well^34,35. Cardiac-centric multi-organ POCUS helps to directly rule in cardiogenic and obstructive etiologies^35,36,37,38 and assists with identification of hypovolemia^39,40. Identification of distributive causes is usually a process of elimination, when multi-organ POCUS reveals no cardiogenic, obstructive, or hypovolemic explanation for hypotension^41,42.

In patients undergoing CT Surgery, two common causes of obstructive shock that can be detected by POCUS are pericardial effusion causing tamponade physiology and dynamic LVOT obstruction^37,43,44,45. Cardiac tamponade in CT surgery patients is both an important use case of POCUS and a challenging one for several reasons. First, CT surgery patients typically have challenging transthoracic windows and non-existent subxiphoid windows due to tubes and drains^43,46. Second, in CT Surgery patients, the classic signs of tamponade (e.g., RV diastolic collapse, RA systolic collapse, etc.) may not be apparent because a compressive effusion is loculated or localized and compresses individual atria or ventricles^44,47. But even when POCUS does not definitively rule cardiac tamponade in or out, it can still help with decision-making in at least two ways: (i) integration of incomplete POCUS visualization of the heart with other findings (e.g., central venous pressure and tracing; chest tube output; clinical history; etc.) can change the overall suspicion for tamponade and (ii) in cases where the clinical context is indeterminate for tamponade and POCUS visualization of the heart is grossly inadequate, this inadequacy logically permits escalation to transesophageal echocardiography (TEE) as the next step in management. A second major cause of obstructive shock after cardiac surgery is dynamic LVOT obstruction. This can occur after specific types of surgery (e.g., mitral valve repair), in patients with certain anatomic findings (e.g., asymmetric upper septal hypertrophy and/or anterior mitral leaflet redundancy), or to any patient faced with specific hemodynamic circumstances (e.g., any combination of hypovolemia, low systemic vascular resistance, and/or excess inotropy)³⁶.

Cardiogenic shock is diagnosed by assessing the left and right ventricles for size and function⁴³. Because of subxiphoid drains, the typical views are parasternal long and short axes and apical views⁴³. Care must be taken to avoid foreshortening of the relevant cardiac chambers, especially in the apical views⁴⁶. Global or regional wall motion abnormalities of the left ventricle (LV) can also be determined in these views by providers with advanced training in echocardiography^43,46,48. Myocardial stunning can cause global dysfunction, whereas graft dysfunction usually presents with a regional change in contractility. Management options include institution of inotropic and/or mechanical support, as well as interrogation of the grafts in the newly revascularized patient. Right ventricular (RV) dysfunction is common in these patients and can occur due to poor myocardial protection^49,50. The dysfunctional right ventricle appears hypokinetic and enlarged on the parasternal long and short axis with a flattened or leftward deviated interventricular septum^49,50. The apical 4-chamber view can help quantify tricuspid annular plane systolic excursion (TAPSE) or associated functional tricuspid regurgitation (TR)^49,50. RV dysfunction is managed with inotropes and/or mechanical support^49,50.

In hypovolemic shock, cardiac POCUS may show certain intracardiac findings in the ventricles and inferior vena cava (IVC). First, in hypovolemia, the ventricles typically appear hyperdynamic and small in size throughout the cardiac cycle, including both systole and diastole due to inadequate preload⁴¹. Second, in hypovolemia, the IVC classically appears small (<2 cm in caliber) and easily collapsible (>50% respirophasic change in size). However, in practice, these IVC findings may not be present in many hypovolemic cardiac surgical patients who are mechanically ventilated and/or have varying degrees of right heart dysfunction. Further, the cutoff values for respiratory variability in IVC size in studies for volume responsiveness have varied from 14% for mechanically ventilated patients to 50% in spontaneously breathing patients⁵¹. One must hence use caution in interpreting volume-responsiveness based on IVC size and variation⁵². Finally, within these larger limitations, sonographers in the cardiac surgical ICU should also learn to image the IVC through the transhepatic window, since the subxiphoid space is routinely covered in dressings and drains⁵³.

Distributive shock is usually a diagnosis of exclusion when the three other shock mechanisms have been ruled out through a combination of POCUS and other clinical datapoints⁵⁴. However, cardiac POCUS does provide some clues to the presence of distributive shock: LV end-systolic collapse with relatively normal LV end-diastolic size being the principal one⁵⁵. Further, a combination of echo parameters (LVOT diameter, LVOT VTI, and estimation of CVP from IVC and/or VeXUS data - see Abdominal section below) can be used to estimate the systemic vascular resistance (SVR) quantitatively. However, these parameters are all subject to measurement error that amplifies when they are combined into multi-parameter calculations. Thus sonographic estimation of SVR should be thought of more as a trend monitor than a way of identifying the true SVR in absolute terms.

Separate from hypotension, a second major indication for cardiac POCUS in the perioperative care of CT Surgery patients is the management of MCS. Notably, a full discussion of cardiac POCUS in MCS is beyond the scope of this brief review and is covered extensively by another paper in this Methods Collection⁴³. But in a broad sense, POCUS can be used to help the management of patients with MCS in at least five ways: (1) Pre-implant evaluation: assessment of ventricular function, valvular lesions, and pericardial disease to guide device selection and predict support needs; (2) Cannulation and device positioning: using ultrasound to guide vascular access, confirm cannula or device placement, and detect malposition that could cause suction, recirculation, or obstruction; (3) Hemodynamic optimization: leveraging serial echo assessment of ventricular size, septal position, valve opening, and Doppler flow to titrate device speed or flow, balance LV/RV loading, and determine adequacy of decompression; (4) Complication detection: identifying tamponade, thrombus, aortic root stasis, worsening regurgitant lesions, or device malfunction (e.g., inlet obstruction, outflow graft kinking); (5) Weaning and recovery monitoring: using echo metrics such as LVOT VTI, aortic valve opening, ventricular dimensions, and valvular Doppler patterns to guide trial off and confirm myocardial recovery.

Of note, cardiac POCUS has important limitations in the postoperative patient. First, the presence of chest drains, sternal dressings, mediastinal air, and/or an open chest limits the views that can be obtained and the image quality in most transthoracic cardiac windows, so the threshold to perform rescue TEE in these scenarios should be quite low⁵⁶. Second, the tricuspid annular plane systolic excursion [TAPSE] - the most widely used quantitative tool to assess RV function - is frequently abnormal in the post-cardiotomy period even when the RV systolic function is normal by other parameters, and thus TAPSE cannot be solely relied upon to diagnose RV dysfunction^50,57,58. Third, like all other diagnostic ultrasound applications, cardiac POCUS is highly operator dependent^{4,35,39,59,60}.

While cardiac POCUS can help narrow the differential diagnosis of hypotension significantly, lung POCUS can assist by identifying specific pathologies such as tension pneumothorax, large pleural effusions causing hemodynamic compromise, and focal consolidations (such as in pneumonia or atelectasis)^54,61.

In addition to its role in refining the differential diagnosis of hypotension, lung point-of-care ultrasound (POCUS) serves as a valuable tool in the evaluation of respiratory dysfunction, including hypoxemia, hypercapnia, and respiratory distress^61,62. Lung POCUS can classify patients into five distinct sonographic phenotypes: (1) normal lung appearance; (2) focal absence of lung sliding; (3) focal B-lines; (4) bilateral B-lines; and (5) consolidation and/or effusion^61,62,63. Each of these phenotypes narrows the differential diagnosis of respiratory dysfunction to a focused set of clinical possibilities^61,62 (Table 2).

Table 2: five general sonographic patterns of lung ultrasound and differential diagnosis for each.

Phrenic nerve injury is common during cardiac surgery, due to excessive sternal retraction, harvesting of the left internal mammary artery, or direct injury during a clamshell incision for lung transplant^64,65. Thermal injury to the phrenic nerve is also a possibility during application of ice slushy during hypothermia on bypass⁶⁵. Diaphragmatic dysfunction can result postoperatively and POCUS of the diaphragm is a useful initial modality in diagnosis^66,67. Qualitative detection of asymmetric diaphragmatic excursion during vital capacity breathing raises suspicion for hemi-diaphragmatic dysfunction, which can be investigated with POCUS-based quantification and/or other imaging modalities such as fluoroscopy⁶⁶.

Abdominal
Patients undergoing CT surgery have the potential to develop intra-abdominal complications, several of which are potentially detectable with diagnostic POCUS: obstructive uropathy, cardio-renal congestion, gastrointestinal dilation/dysfunction, free peritoneal fluid, and possibly portal venous gas⁶⁸.

Obstructive uropathy is both a treatable cause of oliguria/acute kidney injury and amenable to rapid diagnosis by acute care providers with focused training in this modality^69,70. Specifically, studies have shown that intensivists and emergency medicine doctors can be taught to recognize both hydronephrosis and urinary distension^70,71,72. For instance, POCUS screening for hydronephrosis performed by non-radiologists has demonstrated a sensitivity ranging from 72%-93% and a specificity ranging from 66%-100%, depending on the operator experience and patient population^71,72.

The differential diagnosis of oliguria and acute kidney injury (AKI) in CT surgery patients also includes cardio-renal congestion, which can be screened for using the Venous Excess in Ultrasound Score (VeXUS)⁷³. VeXUS evaluates four intra-abdominal veins (inferior vena cava, portal vein, hepatic veins, and interlobar renal veins) with 2-dimensional (2-D) and pulse-wave Doppler (PWD) to assign patients a 0-3 score, with 0 indicating zero congestion and 3 indicating severe congestion⁷³. Although VeXUS remains in its infancy as a diagnostic tool, there is emerging evidence supporting its use. For example, in one study of 150 patients presenting to the Emergency Department with AKI, VeXUS had a sensitivity of 78% and specificity of 81% for the detection of cardio-renal congestion, with the gold standard being a comprehensive chart review of clinical data⁷⁴. Further, when studies have used right atrial pressure (RAP) measured by heart catheterization as the gold standard, they have found that VeXUS has an AUC of 0.9 (95% CI 0.83-0.97) for predicting RAP > 10 mm Hg and AUC 0.99 for (95% CI 0.96-1) for RAP >= 12 mm Hg^75,76.

Another emerging intra-abdominal application of POCUS is evaluation of the stomach and intestines for dilation and/or dysfunction⁷⁷. POCUS of the stomach alone has grown within the field of anesthesiology as an accurate method of screening for "full stomach" - i.e., stomachs that have either solids or excess thick liquids beyond what is expected in fasted adults⁷⁸. Such pre-operative screening for a full stomach can be helpful in the perioperative care of CT Surgery patients who have risk factors for delayed gastric emptying (e.g., diabetes, end-stage renal disease, use of glucagon-like peptide-1 [GLP-1] receptor agonists, etc.) or unclear fasting history (e.g., unreliable historian, etc.)^79,80. Gastric POCUS can further be helpful in the care of CT Surgery patients postoperatively to screen for gastroparesis⁸¹. Detection of gastroparesis can be performed from either the subxiphoid or the left upper quadrant (LUQ) windows in the general population. But in the post-CT Surgery population, the subxiphoid region is routinely occupied by multiple drains/tubes that obscure the underlying sonoanatomy, requiring use of the LUQ window specifically to visualize a fluid-filled gastric body/fundus^82,83. Although the LUQ window is capable of qualitatively detecting a stomach grossly dilated, the view is often indeterminate due to air in the body/fundus of the stomach that is present across a wide range of gastric contents. Thus, currently the LUQ window does not permit quantitative estimation of stomach volume and can only sort gastric state into two broad categories: (1) full of liquids or solids, or (2) indeterminate gastric contents.

Separate from evaluation of the stomach, POCUS can also be used to screen for small bowel pathology that can afflict CT surgery patients perioperatively: ileus, obstruction, and bowel perforation^77,83. While intestinal POCUS remains very much in its infancy as a diagnostic tool, there is evidence that systematic POCUS evaluation of the abdomen can identify the combined entity of ileus and/or small bowel obstruction with moderate specificity (80%), high sensitivity (93%), and overall high diagnostic accuracy (AUC 0.96)⁸⁴. Similarly, meta-analysis level data suggests that ultrasound for detection of pneumoperitoneum has high sensitivity (91%), specificity (96%), and overall high diagnostic accuracy (AUC 0.92)⁸⁵.

More broadly, screening for free peritoneal fluid is sometimes useful in CT Surgery patients who develop unexplained hypotension. As part of the workup for undifferentiated hypotension, the peritoneal views of the Focused Assessment with Sonography in Trauma can be performed⁴⁵. This consists of screening for free peritoneal fluid in the right upper quadrant (RUQ), LUQ, and pelvis⁴⁵. If free peritoneal fluid is unexpectedly found in any of these locations in a hypotensive patient, the differential diagnosis of hypotension should be broadened to include acute intra-abdominal pathology, such as injury to the liver/spleen or a hollow viscus, as can occur during insertion of trocars or chest tubes through the upper abdominal wall during CT surgeries⁸².

While imaging the abdomen from multiple views, one can, in principle, encounter acoustic shadowing within the portal venous system suggestive of portal venous gas (PVG). While PVG was classically thought to be pathognomonic for bowel ischemia, more recent studies suggest that only about half of cases of PVG are due to ischemia, with the rest being due to other causes such as gastrointestinal obstruction, infection, or perforation^{86,87,88,89,90}. While all of these causes of PVG are potentially life-threatening, there are conditions that can mimic PVG on ultrasound that are chronic and/or benign "incidentalomas" (e.g., hepatic granulomas, atherosclerotic disease in adjacent arteries, etc.)⁹¹. Thus, sonographic identification of PVG, like all imaging findings, needs to be interpreted in the context of the patient's clinical presentation and severity of illness with awareness of PVG's full differential diagnosis.

Extremity and/or musculoskeletal
CT Surgery patients tend to have limited mobility and underlying frailty. As a result, they have a higher predisposition towards developing deep vein thrombosis (DVT), which can result in limb swelling, pain, and further reduction in mobility. In addition, large clots can travel towards the IVC, right atrium, and pulmonary vasculature, resulting in hemodynamically significant pulmonary emboli (PE). To expedite the diagnosis of venous thrombo-embolic (VTE) disease, a simplified version of the consultative lower extremity venous exam performed by sonographer-radiologist teams has been proposed and validated^92,93. This exam consists of venous compression ultrasound of 5-6 specific points between the groin and knee on each leg, focusing on the following three veins: common femoral, femoral, and popliteal⁹³. Identification of a non-compressible vein in any of the scanning locations rules in a DVT with 96% specificity, 86% sensitivity, and overall 95% diagnostic accuracy⁹³. Further, there is evidence that combining focused DVT ultrasound with POCUS of the heart and lungs can significantly increase the accuracy of the traditional Well's scoring system to estimate the probability of VTE^94,95.

Another CT surgery-relevant application of POCUS for the lower extremities is sonographic screening for sarcopenia as a surrogate for overall frailty. Sonographic frailty screening employs a linear high-frequency transducer on the anterior thigh to measure the antero-posterior thickness of the rectus femoris (RF) muscle⁹⁶. This measurement of RF thickness has predictive value in patients undergoing surgery, both pre- and postoperatively. Pre-operatively, RF thickness identifies frailty in a way that is not captured by other routine metrics like the Society of Thoracic Surgery (STS) score^97,98,99. The addition of frailty to STS may permit more accurate pre-op risk stratification and identification of at-risk patients most in need of prehabilitation^97,98,99. Postoperatively, sonographic frailty screening identifies patients anticipated to have longer duration requirements for mechanical ventilation and intensive care unit (ICU) length of stay and need for subsequent placement to skilled nursing facilities¹⁰⁰.

Diagnostic POCUS offers a powerful, bedside extension of the physical examination for patients undergoing cardiothoracic surgery. These patients are particularly vulnerable to complex neurological, pulmonary, cardiovascular, and hemodynamic complications, and traditional diagnostic modalities often require transport, specialized resources, or invasive monitoring that may not be feasible in unstable settings. From assessment of intracranial pressure with optic nerve sheath diameter and transcranial Doppler, to evaluation of lung pathology, cardiac function, and intravascular volume status, POCUS can help clinicians obtain actionable information in real time. Further, the ability to perform serial examinations at the bedside enhances the utility of POCUS for monitoring dynamic disease processes and guiding interventions.

However, utilization of diagnostic POCUS in any setting (including the ICU) must be done with caution. First, diagnostic POCUS is highly operator dependent, and for most diagnostic POCUS applications, there is limited learning curve data to identify a minimum number of training studies needed to achieve proficiency61. In practice, this means that hospital credentialing/privileging bodies must ascertain competence by coming up with ad hoc criteria or relying on national certificates/certifications61. Second, diagnostic POCUS ideally requires both documentation of findings in the medical record and durable image archiving. Whereas documentation of findings is relatively easy to achieve (either within existing ICU progress notes or in separate standalone notes), in many (perhaps most ICUs), image archiving for POCUS is not yet established. But achieving image archiving is a critical step toward permitting quality assurance, log-keeping, and medico-legal compliance.

Despite these limitations of diagnostic POCUS, growing evidence suggests that combining modalities might increase diagnostic accuracy. Broader adoption will depend on standardized protocols, robust training, and integration with advanced technologies, ultimately positioning POCUS as a fundamental tool in perioperative critical care.