Residency · Residency · Anesthesiology
Point-of-Care Ultrasound (POCUS) for the Anesthesiologist
Introduction
Point-of-care ultrasound has become an indispensable skill for anesthesiologists, extending far beyond vascular access and regional anesthesia. POCUS enables rapid, bedside assessment of cardiac function, volume status, pulmonary pathology, and airway anatomy. Mastery of focused ultrasound protocols improves diagnostic accuracy, procedural safety, and patient outcomes in the perioperative setting.
Ultrasound Physics Essentials
Key Principles
Higher frequency probes (10 to 15 MHz) provide better resolution but less penetration, while lower frequency probes (2 to 5 MHz) penetrate deeper. The three main transducer types are linear (used for vascular access and nerve blocks), curvilinear (used for abdominal and lung imaging), and phased-array (used for cardiac and lung imaging). The principal modes include B-mode (2D imaging), M-mode (motion over time), and Doppler (blood flow velocity and direction). Gain adjusts the brightness of received echoes, and time-gain compensation adjusts gain at specific depths. Tissue echogenicity describes the appearance: hyperechoic structures (bright, such as bone and pleura), hypoechoic structures (dark gray, such as muscle), and anechoic structures (black, such as fluid and blood).
Focused Cardiac Ultrasound (FoCUS)
Standard Views
The five standard views for focused cardiac ultrasound are the parasternal long-axis (PLAX), which assesses LV size and function, mitral and aortic valves, and pericardial effusion; the parasternal short-axis (PSAX), which evaluates LV wall motion at the papillary muscle level and RV assessment; the apical four-chamber (A4C), which allows biventricular comparison, valvular regurgitation assessment, and RV dilation evaluation; the subcostal four-chamber, which is useful when parasternal and apical windows are limited by obesity, PEEP, or surgical drapes; and the subcostal IVC view, which assesses volume status via IVC diameter and respiratory variation.
| FoCUS View | Probe Position | Key Structures Assessed | Primary Clinical Use |
|---|---|---|---|
| Parasternal long-axis (PLAX) | Left parasternal, 3rd–4th ICS | LV, MV, AV, pericardium | LV function, pericardial effusion, valve assessment |
| Parasternal short-axis (PSAX) | Left parasternal, 3rd–4th ICS (rotated 90°) | LV walls at papillary level, RV | Wall motion abnormalities, RV dilation |
| Apical four-chamber (A4C) | LV apex | All 4 chambers, MV, TV | Biventricular comparison, RV:LV ratio |
| Subcostal four-chamber | Subxiphoid | All 4 chambers | Alternative when parasternal/apical limited |
| Subcostal IVC | Subxiphoid, longitudinal | IVC diameter and collapsibility | Volume status assessment |
Critical Perioperative Findings
During the hypotension workup, POCUS differentiates hypovolemia (small hyperdynamic LV, collapsing IVC) from LV failure (dilated, poorly contracting LV), RV failure (dilated RV, D-shaped septum), tamponade (pericardial effusion with RA/RV diastolic collapse), and distributive shock (hyperdynamic LV, plethoric IVC). Visual estimation of ejection fraction correlates well with formal echocardiography for experienced operators. Regional wall motion abnormalities may indicate acute ischemia.
Lung Ultrasound
Normal Findings
The pleural line appears as a hyperechoic line that slides with respiration ("lung sliding"). A-lines are horizontal reverberation artifacts below the pleural line that indicate air-filled lung (normal or pneumothorax if no sliding is present). The bat sign describes ribs with acoustic shadowing flanking the pleural line.
Pathologic Findings
B-lines (lung rockets) are vertical hyperechoic artifacts extending from the pleural line to the bottom of the screen without fading. They indicate interstitial edema, pulmonary edema, or fibrosis, and three or more B-lines per intercostal space in two or more zones is pathological. Absent lung sliding combined with absent B-lines and a lung point is diagnostic of pneumothorax with a specificity approaching 100%. Consolidation or hepatization appears as tissue-like echotexture with air bronchograms, indicating atelectasis, pneumonia, or contusion. Pleural effusion appears as an anechoic collection above the diaphragm, and the spine sign (vertebral bodies visible above the diaphragm) confirms its presence.
| Lung Ultrasound Finding | Appearance | Diagnosis | Clinical Significance |
|---|---|---|---|
| A-lines + lung sliding | Horizontal reverberation artifacts | Normal lung | Air-filled lung, normal |
| A-lines + absent sliding | Horizontal artifacts, no pleural movement | Pneumothorax | Confirm with lung point (specificity ~100%) |
| B-lines (≥3 per space) | Vertical artifacts, pleural line to screen bottom | Pulmonary edema / interstitial disease | Bilateral = cardiogenic; focal = pneumonia/contusion |
| Consolidation (hepatization) | Tissue-like echotexture + air bronchograms | Atelectasis, pneumonia, contusion | Spine sign confirms effusion above diaphragm |
| Pleural effusion | Anechoic collection above diaphragm | Effusion | Spine sign positive; guide thoracentesis |
BLUE Protocol
The Bedside Lung Ultrasound in Emergency (BLUE) protocol uses three standardized points per hemithorax to rapidly diagnose the cause of acute respiratory failure. Its sensitivity and specificity exceed 90% for common diagnoses including pulmonary edema, pneumothorax, pneumonia, and COPD/asthma exacerbation.
Gastric Ultrasound
Gastric ultrasound is performed with a curvilinear probe in the right lateral decubitus or supine position, scanning the gastric antrum in the sagittal plane at the epigastrium. An empty stomach appears as a flat, "target-like" antrum, while a full stomach shows a distended antrum with solid or liquid content. Quantitative assessment using antral cross-sectional area correlates with gastric volume; a CSA greater than 340 mm squared suggests a volume greater than 1.5 mL/kg and aspiration risk. This technique is useful for emergency surgery, trauma, diabetic gastroparesis, and opioid-treated patients.
Vascular Access
Internal jugular vein cannulation uses short-axis and long-axis approaches with confirmation by compression, Doppler, and absence of arterial pulsation. Subclavian and axillary vein access requires identification of the vein in relation to the artery and pleura. Arterial cannulation of the radial and femoral arteries benefits from real-time guidance, which reduces attempts and complications. Ultrasound-guided central venous access is the standard of care and reduces mechanical complications by approximately 70%.
Airway Ultrasound
Ultrasound can identify the cricothyroid membrane for emergency front-of-neck access and is more reliable than palpation, especially in obese patients. Bilateral lung sliding confirms endotracheal tube ventilation, while absence on one side suggests endobronchial intubation. Subglottic diameter assessment in pediatric patients estimates appropriate ETT size. Identification of the tracheal midline and thyroid pathology that may complicate intubation is also possible.
Focused Assessment with Sonography in Trauma (FAST/eFAST)
The FAST exam includes four views: right upper quadrant (Morrison's pouch), left upper quadrant (splenorenal recess), suprapubic (pelvis), and subxiphoid (pericardium). The extended FAST (eFAST) adds bilateral anterior lung fields for pneumothorax detection. The exam detects free fluid (hemoperitoneum) with a sensitivity of approximately 85 to 95% when more than 200 mL is present.
Integration into Anesthetic Practice
Preoperatively, POCUS is used for cardiac function assessment, volume status evaluation, airway evaluation, and gastric content assessment. Intraoperatively, it assists with hemodynamic troubleshooting, confirmation of regional block success, ETT position, and volume responsiveness assessment. Postoperatively, it helps diagnose pneumothorax, pleural effusion, cardiac tamponade, or new cardiac dysfunction.
Clinical Pearls
POCUS is a screening and monitoring tool, not a replacement for formal echocardiography or radiology studies. The IVC assessment is most useful at extremes: a collapsing IVC suggests volume responsiveness, while a plethoric IVC with minimal variation suggests fluid overload or obstructive pathology. A systematic approach (such as the BLUE protocol or FoCUS) should always be used rather than ad hoc scanning to avoid confirmation bias. Gastric ultrasound can change anesthetic management in up to 10% of "NPO" patients who have unexpected gastric contents.
References
- Mahmood F, Matyal R, Skubas N, et al. Perioperative ultrasound training in anesthesiology: a call to action. Anesth Analg. 2016;122(6):1794-1804.
- Lichtenstein DA, Meziere GA. Relevance of lung ultrasound in the diagnosis of acute respiratory failure: the BLUE protocol. Chest. 2008;134(1):117-125.
- Perlas A, Arzola C, Van de Putte P. Point-of-care gastric ultrasound and aspiration risk assessment. Anesthesiology. 2018;128(6):1209-1215.
- Spencer KT, Kimura BJ, Korcarz CE, et al. Focused cardiac ultrasound: recommendations from the American Society of Echocardiography. J Am Soc Echocardiogr. 2013;26(6):567-581.