26.3 Critical Care Point-of-Care Ultrasound (POCUS)

ABIM Critical Care Medicine Study Guide Exam

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1 Chapter 1: Exam Orientation: Format, Blueprint & Study Strategy

1.1 ABIM Critical Care Medicine Exam: Format, Blueprint & Study Strategy

2 Chapter 2: Acute Respiratory Failure & ARDS

2.1 ARDS Definition, Pathophysiology & Phenotypes 2.2 Lung-Protective Mechanical Ventilation 2.3 Refractory ARDS: Prone Positioning, Neuromuscular Blockade & VV-ECMO

3 Chapter 3: Obstructive Airways, Pulmonary Vascular & Pleural Emergencies

3.1 Severe Asthma & COPD Exacerbations in the ICU 3.2 Massive & Submassive Pulmonary Embolism 3.3 Pulmonary Hypertension & Right Ventricular Failure in the ICU 3.4 Massive Hemoptysis, Complex Pleural Effusions & Thoracic Drainage

4 Chapter 4: Airway, Parenchymal & Nonthrombotic Pulmonary Emergencies

4.1 Airway Management, Upper-Airway Obstruction & Artificial-Airway Complications 4.2 Diffuse Alveolar Hemorrhage, Interstitial Lung Disease, Pulmonary Vasculitis & Noncardiogenic Edema 4.3 Severe Community-Acquired & Viral Pneumonia 4.4 Nonthrombotic Embolism (Air, Fat, Amniotic Fluid, Tumor, Septic) & Acute Chest Syndrome

5 Chapter 5: Mechanical Ventilation Modes, Dyssynchrony & Liberation

5.1 Mechanical Ventilator Modes & Advanced Breath Delivery 5.2 Patient-Ventilator Dyssynchrony & Waveform Analysis 5.3 Ventilator Liberation, Spontaneous Breathing Trials & Post-Extubation Support

6 Chapter 6: Shock Syndromes & Hemodynamic Principles

6.1 Shock Classification, Cellular Pathophysiology & Biomarkers 6.2 Hemodynamic Monitoring: Arterial Lines, CVP & Pulmonary Artery Catheter 6.3 Dynamic Assessment of Fluid Responsiveness & Resuscitation Targets

7 Chapter 7: Vasoactive Therapies & Mechanical Circulatory Support

7.1 Vasopressors & Inotropes: Pharmacology & Clinical Titration 7.2 Temporary Mechanical Circulatory Support: IABP, Impella & TandemHeart 7.3 Venoarterial ECMO (VA-ECMO) & Differential Hypoxemia 7.4 Post-Cardiac Arrest Care, Targeted Temperature Management & Neuroprognostication

8 Chapter 8: Acute Kidney Injury & Renal Replacement Therapy

8.1 KDIGO AKI Classification, Etiologies & Diagnostic Evaluation 8.2 Continuous Renal Replacement Therapy (CRRT) vs Intermittent Hemodialysis 8.3 Indications & Timing for RRT in Critical Illness: AKIKI & STARRT-AKI

9 Chapter 9: Electrolyte, Acid-Base & Endocrine Emergencies

9.1 Severe Dysnatremias: Hyponatremia, Hypernatremia & Osmotic Demyelination 9.2 Potassium, Calcium, Magnesium & Phosphate Disorders 9.3 Complex & Mixed Acid-Base Disorders: Boston vs Copenhagen vs Stewart 9.4 Endocrine Crises: DKA, HHS, Thyroid Storm, Myxedema Coma & Adrenal Crisis

10 Chapter 10: Glycemic Control, Hyperammonemia, Pituitary & Adrenal Disorders

10.1 ICU Glycemic Control & Severe Hypoglycemia 10.2 Non-Hepatic Hyperammonemia & Metabolic Encephalopathy 10.3 Pituitary Emergencies, Adrenal Excess & Critical Illness-Related Corticosteroid Insufficiency

11 Chapter 11: Acute Coronary Syndromes & Cardiac Arrhythmias

11.1 Acute Coronary Syndromes & Mechanical Complications of Myocardial Infarction 11.2 Critical Tachyarrhythmias: Atrial Fibrillation with RVR, VT & VF 11.3 Critical Bradyarrhythmias, Conduction Blocks & Temporary Cardiac Pacing

12 Chapter 12: Acute Heart Failure, Valvular & Pericardial Emergencies

12.1 Acute Decompensated Heart Failure & Cardiogenic Pulmonary Edema 12.2 Acute Valvular Regurgitation & Prosthetic Valve Emergencies 12.3 Pericardial Tamponade & Acute Aortic Syndromes

13 Chapter 13: Myocardial Disease, Hypertensive & Cardiac Device Emergencies

13.1 Fulminant Myocarditis, Stress & Peripartum Cardiomyopathy, and Hypertrophic Cardiomyopathy 13.2 Hypertensive Emergencies & Ruptured Abdominal Aortic Aneurysm 13.3 Implanted Cardiac Devices, LVAD Emergencies & Electrical Storm

14 Chapter 14: Sepsis & Systemic Infectious Diseases

14.1 Sepsis-3 Definitions & Surviving Sepsis Campaign 2026 Guidelines 14.2 Refractory Septic Shock & Adjunctive Therapies 14.3 Multidrug-Resistant Pathogens & Antimicrobial Stewardship in the ICU

15 Chapter 15: ICU-Acquired & Severe Focal Infections

15.1 Hospital-Acquired & Ventilator-Associated Pneumonia 15.2 Central Line-Associated Bloodstream Infections & Catheter-Associated UTIs 15.3 Intra-Abdominal Sepsis, Necrotizing Soft Tissue Infections & CNS Infections

16 Chapter 16: Focal, Special-Host & Systemic Infections

16.1 CNS Infections Beyond Bacterial Meningitis: Encephalitis, Brain Abscess & Epidural Abscess 16.2 Infections in the Immunocompromised Host, Tropical & Bioterror Infections 16.3 Infective Endocarditis, Device Infections & Other Focal Cardiovascular Infections 16.4 Antimicrobial Pharmacokinetics, Allergy, Toxicity & Infection Prevention 16.5 Gastrointestinal & Hepatobiliary Infections: Fulminant C. difficile, Typhlitis, CMV Colitis & Abscesses

17 Chapter 17: Neurocritical Care & Coma

17.1 Coma, Altered Mental Status & Acute Delirium in the ICU 17.2 Status Epilepticus & Non-Convulsive Status Epilepticus 17.3 Acute Ischemic Stroke & Intracranial Hemorrhage

18 Chapter 18: Cerebrovascular Syndromes, Encephalopathy & Withdrawal States

18.1 Cerebral Venous Sinus Thrombosis, PRES & Reversible Cerebral Vasoconstriction Syndrome 18.2 Alcohol & Sedative Withdrawal, Wernicke Encephalopathy & Drug-Induced Encephalopathy

19 Chapter 19: Intracranial Hypertension & Neuromuscular Weakness

19.1 Intracranial Pressure Monitoring, Cerebral Perfusion & Tiered ICP Management 19.2 Acute Neuromuscular Respiratory Failure, ICU-Acquired Weakness & Brain Death Determination

20 Chapter 20: Traumatic Brain Injury, Spinal Cord Injury & Toxin-Mediated Paralysis

20.1 Traumatic Brain Injury Management & Paroxysmal Sympathetic Hyperactivity 20.2 Acute Spinal Cord Injury, Neurogenic Shock & Autonomic Dysreflexia 20.3 Toxin-Mediated Paralysis & Neuromuscular Crises: Botulism, Tetanus, Tick Paralysis & Myasthenic Crisis

21 Chapter 21: Gastrointestinal, Hepatic & Abdominal Emergencies

21.1 Acute Upper & Lower Gastrointestinal Bleeding in the ICU 21.2 Acute Liver Failure & Severe Acute Pancreatitis 21.3 Abdominal Compartment Syndrome & Acute Mesenteric Ischemia

22 Chapter 22: Luminal GI Emergencies & Complications of Cirrhosis

22.1 Esophageal, Gastric & Bowel Emergencies: Perforation, Obstruction, Ogilvie Syndrome & Colonic Ischemia 22.2 Complications of Cirrhosis: Alcohol-Associated Hepatitis, Hepatorenal Syndrome & Pulmonary Vascular Syndromes

23 Chapter 23: Trauma, Burns & Perioperative Critical Care

23.1 Polytrauma Resuscitation, Damage Control & Massive Transfusion 23.2 Severe Burn Injury, Inhalation Injury & Environmental Emergencies 23.3 Perioperative Critical Care for High-Risk Surgical Patients

24 Chapter 24: Thoracic Trauma, Environmental Injury & Obstetric Critical Care

24.1 Thoracic Trauma: Flail Chest, Pulmonary Contusion, Great Vessel & Tracheobronchial Injury 24.2 Environmental Injury: Drowning, Diving, Altitude, Heat, Cold, Electrical & Radiation 24.3 Obstetric & Genitourinary Emergencies and the Physiology of Pregnancy

25 Chapter 25: Transplantation, Donor Management & Post-Cardiac Surgery Care

25.1 Solid Organ Transplant Recipients & Deceased Donor Management 25.2 Post-Cardiac Surgery Critical Care: Bleeding, Tamponade, Low Output & Vasoplegia

26 Chapter 26: Hematologic Emergencies, Toxicology, Critical Ultrasound & ICU Liberation

26.1 Hematologic Emergencies in the ICU: HIT, DIC, TMA & Anticoagulant Reversal 26.2 Critical Care Toxicology, Toxidromes & Specific Antidotes 26.3 Critical Care Point-of-Care Ultrasound (POCUS) 26.4 ICU Liberation, Analgosedation, Goals of Care & Critical Care Ethics

27 Chapter 27: Transfusion Medicine, Hematologic & Oncologic Disorders

27.1 Transfusion Medicine: Products, Thresholds, Reactions & Apheresis 27.2 Red and White Cell Disorders, Hemoglobinopathies, Factor Deficiencies & Hypercoagulable States 27.3 Oncologic Emergencies, Hematopoietic Cell Transplant Complications & Cellular Therapy Toxicity

28 Chapter 28: Clinical Pharmacology, Adverse Drug Reactions & Specific Poisonings

28.1 Pharmacokinetic Principles, Dose Adjustment & Drug Interactions in Critical Illness 28.2 Adverse Drug Reactions: Anaphylaxis, Severe Cutaneous Reactions & Hyperthermic Syndromes 28.3 Specific Poisonings: Sodium-Channel Blockers, Lithium, Valproate, Theophylline, Iron, Sulfonylureas & Methemoglobinemia

29 Chapter 29: Ethics, Research Methods, Administration & Abdominal Ultrasound

29.1 Advance Care Planning, Nonbeneficial Treatment, Informed Consent & Confidentiality 29.2 Critical Care Research Methods, Statistics, IRB Oversight & Quality Improvement 29.3 Abdominal, Vascular & Procedural Point-of-Care Ultrasound

26.3 Critical Care Point-of-Care Ultrasound (POCUS)

Key Takeaways Explain This Topic AI

Focused Cardiac Ultrasound (FoCUS) assesses left ventricular function, right ventricular strain, and pericardial effusion across five standard acoustic windows: PLAX, PSAX, A4C, subcostal 4-chamber, and subcostal IVC.

An E-point septal separation (EPSS) > 7 mm in the parasternal long-axis view indicates reduced left ventricular ejection fraction, with values > 15 mm correlating with severe systolic dysfunction.

Acute cor pulmonale on POCUS is identified by an RV/LV basal diameter ratio > 1.0, McConnell's sign (mid-free wall akinesia with apex sparing), and interventricular septal flattening ('D-shaped' LV) in both systole and diastole.

In lung ultrasound, the presence of even a single B-line unequivocally excludes pneumothorax at that acoustic interspace; the pathognomonic sign of pneumothorax is the Lung Point, which exhibits 100% specificity.

The RUSH protocol systematically evaluates undifferentiated shock across 'The Pump' (cardiac function and tamponade), 'The Tank' (IVC, thoracic and peritoneal fluid), and 'The Pipes' (aorta and femoral/popliteal veins).

Last updated: October 2026

Focused Cardiac Ultrasound (FoCUS)

Point-of-care focused cardiac ultrasound is a goal-directed examination performed to evaluate acute, life-threatening hemodynamic instability. Rather than providing a comprehensive structural evaluation, FoCUS addresses five binary clinical questions: severe left ventricular (LV) systolic dysfunction, acute right ventricular (RV) enlargement and strain, pericardial tamponade physiology, severe intravascular hypovolemia, and gross valvular catastrophes.

Standard Acoustic Windows and Views

Parasternal Long Axis (PLAX) : Probe placed in the 3rd or 4th left intercostal space adjacent to the sternum with the orientation marker pointing toward the patient's right shoulder. Visualizes the right ventricular outflow tract (anteriorly), the interventricular septum, the LV cavity, the posterior LV wall, the mitral valve, the left atrium, the aortic valve, the aortic root, and the descending thoracic aorta in cross-section.

Effusion Differentiation : Pericardial effusions track anterior to the descending thoracic aorta; pleural effusions track posterior to the descending thoracic aorta.

Parasternal Short Axis (PSAX) : Probe rotated 90 degrees clockwise from PLAX with the marker directed toward the patient's left shoulder. Sweeping from base to apex evaluates the aortic valve level ("Mercedes-Benz" sign), mitral valve level ("fish mouth"), papillary muscle level (mid-ventricular "doughnut"), and apical level. Assesses regional LV contractility and interventricular septal geometry.

Apical Four-Chamber (A4C) : Probe positioned at the cardiac apex (typically 5th intercostal space, anterior axillary line) with marker pointing toward the left axilla. Demonstrates the LV, RV, left atrium, right atrium, mitral valve, and tricuspid valve. Ideal for evaluating RV-to-LV size ratio and tricuspid annular displacement.

Subcostal (Subxiphoid) Four-Chamber : Probe positioned below the xiphoid process with the marker directed to the patient's left, angled flat toward the left shoulder using the liver as an acoustic window. The primary rescue window in mechanically ventilated patients with hyperinflated lungs.

Subcostal Inferior Vena Cava (IVC) : Probe rotated 90 degrees sagittal from the subcostal four-chamber view with the marker directed cephalad. Visualizes the longitudinal entry of the IVC into the right atrium, measured 1 1 1 to 2 cm 2\text{ cm} 2 cm caudal to the junction of the hepatic veins.

Left Ventricular Systolic Assessment

Qualitative Visual Estimation : LV contractility is categorized as hyperdynamic (ejection fraction > 70 % > 70\% > 70% , with end-systolic cavity obliteration), normal ( 50 % − 70 % 50\% - 70\% 50% − 70% ), mildly reduced ( 40 % − 49 % 40\% - 49\% 40% − 49% ), moderately reduced ( 30 % − 39 % 30\% - 39\% 30% − 39% ), or severely reduced ( < 30 % < 30\% < 30% ).

E-Point Septal Separation (EPSS) : Measured in the PLAX view using M-mode cursor alignment across the tip of the anterior mitral valve leaflet. EPSS represents the minimum distance between the peak early diastolic opening of the anterior leaflet (the E-point) and the interventricular septum. In a normal ventricle, the leaflet approaches or touches the septum (normal EPSS < 7 mm \text{EPSS} < 7\text{ mm} EPSS < 7 mm ). When LV dilation or systolic impairment occurs, ventricular filling is reduced and the septum dilates away from the leaflet, widening the gap. An EPSS > 7 mm \text{EPSS} > 7\text{ mm} EPSS > 7 mm indicates reduced ejection fraction, and an EPSS > 15 mm \text{EPSS} > 15\text{ mm} EPSS > 15 mm strongly correlates with severe systolic dysfunction ( LVEF < 30 % \text{LVEF} < 30\% LVEF < 30% ). Note: Mitral stenosis or aortic regurgitation (aortic jet deflecting the leaflet) cause false-positive EPSS elevations independent of LV function.

Right Ventricular Strain and Acute Cor Pulmonale

Under normal physiological conditions, the RV is triangular and its volume is significantly smaller than the LV. In the A4C view, the normal end-diastolic RV-to-LV basal diameter ratio is < 0.6 < 0.6 < 0.6 . Signs of RV strain include:

RV Dilation : An RV/LV basal diameter ratio > 0.6 > 0.6 > 0.6 indicates RV enlargement; an RV/LV ratio > 1.0 \text{RV/LV ratio} > 1.0 RV/LV ratio > 1.0 indicates severe RV dilation and acute cor pulmonale.

McConnell's Sign : Severe hypokinesis or akinesia of the RV mid-free wall with preserved or hyperdynamic contraction of the RV apex. Highly specific ( 94 % − 96 % 94\% - 96\% 94% − 96% ) for acute pulmonary embolism.

Interventricular Septal Flattening ("D-Shaped" LV) : Evaluated in the PSAX view at the papillary muscle level:

Isolated Diastolic Flattening : Indicates RV Volume Overload (e.g., tricuspid regurgitation, atrial septal defect).

Systolic and Diastolic Flattening : Indicates RV Pressure Overload (e.g., massive pulmonary embolism, acute respiratory distress syndrome with severe pulmonary vascular dysfunction).

Tricuspid Annular Plane Systolic Excursion (TAPSE) : M-mode measurement of the longitudinal excursion of the lateral tricuspid valve annulus toward the apex in A4C. A TAPSE < 17 mm \text{TAPSE} < 17\text{ mm} TAPSE < 17 mm confirms RV systolic dysfunction.

Cardiac Tamponade Evaluation

Pericardial fluid appears as an anechoic space between the epicardium and parietal pericardium. Hemodynamic compromise progresses through specific ultrasound stages:

Early Diastolic RV Collapse : Indentation of the RV anterior free wall into the RV cavity during ventricular diastole (when RV pressure is lowest). This finding is highly specific for tamponade.

Late Diastolic / Systolic Right Atrial (RA) Collapse : Inversion of the RA free wall lasting for more than one-third ( > 33 % > 33\% > 33% ) of the cardiac cycle. This is the earliest and most sensitive ultrasound sign of tamponade.

Plethoric, Non-Collapsible IVC : IVC diameter > 2.1 cm > 2.1\text{ cm} > 2.1 cm with < 50 % < 50\% < 50% respiratory collapse (collapsibility index). An uncompromised, collapsing IVC virtually excludes cardiac tamponade (sensitivity approaching 100 % 100\% 100% ), except in rare "low-pressure tamponade" in hypovolemic patients.

Doppler Respiratory Variation (Pulsus Paradoxus) : Mitral inflow Doppler E E E -wave velocity variation > 25 % > 25\% > 25% or tricuspid inflow variation > 40 % > 40\% > 40% across the respiratory cycle.

Lung Ultrasound: The BLUE Protocol

Lung ultrasound is governed by acoustic artifacts created by the interface of acoustic sound waves with air, water, and pleural membranes. The BLUE Protocol (Bedside Lung Ultrasound in Emergency) standardizes this evaluation in acute respiratory failure.

Ultrasound Artifact / Sign Physical Origin & Sonographic Appearance Clinical Significance & Associated Pathology

Pleural Line ("Bat Sign") Hyperechoic horizontal line located 0.5 cm 0.5\text{ cm} 0.5 cm deep to the rib shadows. Fundamental anatomical landmark representing the visceral and parietal pleural interface.

Lung Sliding Glistening, back-and-forth horizontal shimmer of visceral pleura against parietal pleura ("ants marching on a line"). Confirms visceral and parietal pleura are in direct contact and dynamic apposition. Rules out pneumothorax at that specific site.

Seashore Sign (M-Mode) Linear horizontal lines in superficial chest wall ("waves") transitioning to a homogeneous granular pattern below the pleural line ("beach"). Normal lung sliding in M-mode, confirming movement of aerated pulmonary parenchyma.

A-Lines Horizontal, parallel, hyperechoic reverberation lines occurring at exact integer multiples of the probe-to-pleural-line distance. Repetitive reflection of sound between probe and pleura. Indicates normal aerated lung (when sliding is present) or pneumothorax (when sliding is absent).

B-Lines ("Comet Tails") Vertical, hyperechoic, laser-like reverberation artifacts arising strictly from the pleural line, extending to the bottom of the screen without fading, erasing A-lines, and moving with sliding. Arise from fluid-filled subpleural interlobular septa. ≥ 3 \ge 3 ≥ 3 B-lines per intercostal space defines interstitial syndrome (pulmonary edema, ARDS, pneumonitis).

Stratosphere / Barcode Sign (M-Mode) Continuous, parallel horizontal lines extending throughout the entire depth of the ultrasound field, completely replacing the sandy granular pattern. Demonstrates absence of lung sliding, which is sensitive but not specific for pneumothorax : pleural adhesions or pleurodesis, apnea, mainstem intubation, and severe bullous disease also abolish sliding.

Lung Point Dynamic, pathognomonic junction where normal sliding lung and absent sliding (stratosphere pattern) alternate within the exact same ultrasound view during respiration. Near-100% specificity for pneumothorax , but sensitivity is only about 66 % 66\% 66% : the lung point is absent when the lung is completely collapsed away from the chest wall, as in large or tension pneumothorax.

Tissue-Like Sign (Hepatinization) Consolidated, non-aerated lung parenchyma taking on the acoustic appearance of solid abdominal organs (liver/spleen), often with air bronchograms. Diagnostic of alveolar consolidation (bacterial pneumonia, dense atelectasis, pulmonary contusion, or infarct).

Dynamic vs. Static Air Bronchograms Dynamic: Punctate/linear hyperechoic air foci moving with respiration within consolidation. Static: Non-moving hyperechoic branched air foci. Dynamic bronchograms confirm active ventilation within pneumonia . Static bronchograms indicate non-ventilated resorptive atelectasis.

Spine Sign Continuation of the hyperechoic vertebral line cephalad past the diaphragm into the thoracic cavity. Fluid or dense consolidation conducts sound to the posterior thorax. Diagnostic of pleural effusion or dense lower lobe consolidation.

Note

The Absolute B-Line Rule : The presence of even a single definitive, laser-like B-line conclusively rules out a pneumothorax at that exact intercostal location because a B-line requires acoustic transmission through the visceral pleura into pulmonary parenchyma.

Vascular Compression Ultrasound for DVT

Vascular POCUS for deep vein thrombosis (DVT) relies exclusively on complete mechanical coaptation (compressibility) of the vein lumen under gentle downward probe pressure. The evaluation employs either a 2-point protocol (examining the common femoral vein at the saphenofemoral junction and the popliteal vein down to its trifurcation) or an extended 3-point protocol (incorporating the deep femoral vein and the proximal femoral vein). A vein is normal if the anterior and posterior walls completely collapse and touch, completely obliterating the lumen. Non-compressibility is the diagnostic criterion. Acute thrombus is often hypoechoic or even anechoic, so absence of visible clot does not exclude DVT; venous distension and low echogenicity only support acuity.

Multi-Organ Shock Protocol: The RUSH Exam

The Rapid Ultrasound in Shock (RUSH) protocol provides a rapid, physiological evaluation of undifferentiated hypotension categorized into "The Pump", "The Tank", and "The Pipes":

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Distributive (Septic) Shock Profile : Hyperdynamic LV contractility (end-systolic cavity obliteration), collapsing IVC (low central venous pressure), lung sliding with A-lines, and negative FAST. Septic cardiomyopathy can instead depress LV or RV function, so a normal-to-low ejection fraction does not exclude sepsis.

Cardiogenic Shock Profile : Severely depressed LV systolic function (dilated LV, EPSS > 15 mm \text{EPSS} > 15\text{ mm} EPSS > 15 mm ), plethoric non-collapsing IVC, diffuse bilateral B-lines (pulmonary edema), and negative FAST.

Obstructive Shock Profile :

Pulmonary Embolism : Severely enlarged RV ( RV/LV > 1.0 \text{RV/LV} > 1.0 RV/LV > 1.0 ), McConnell's sign, D-shaped septum in systole and diastole, plethoric IVC, normal lung sliding, and lower extremity DVT.

Cardiac Tamponade : Anechoic pericardial effusion, diastolic RV collapse, systolic RA collapse, and plethoric IVC.

Tension Pneumothorax : Complete absence of lung sliding, absent B-lines, stratosphere sign in M-mode, absent lung pulse, and plethoric IVC (impaired venous return). A lung point is often absent because the lung is fully collapsed; tension physiology is a clinical diagnosis that calls for immediate decompression.

Hypovolemic / Hemorrhagic Shock Profile : Hyperdynamic LV, flat or completely collapsing IVC ("kissing walls"), bilateral lung sliding with normal A-lines, and positive FAST (free anechoic fluid in Morison's pouch, splenorenal recess, or retrovesical pouch) or leaking abdominal aortic aneurysm ( > 3 cm > 3\text{ cm} > 3 cm ).