Ultrasound in Critical Care¶

Audrey White

Volume assessment¶

IVC measurements
Clinical Questions: Will the patient respond to fluid resuscitation? Is CVP low or high?
Protocol: See cardiology POCUS section
Limitations: Non applicable in patients with elevated abdominal pressure or abdominal contractions during measurement
Troubleshooting: Use the liver as a window to the IVC to avoid bowel gas. Start at the right mid-axillary line with the leading edge toward the head of the patient, and fan to view the IVC in longitudinal axis.

Lung Assessment¶

Lung ultrasound relies on recognition of ultrasound artifacts to identify normal and pathologic findings.
Normal findings
- “Bat sign”: Ultrasound cannot penetrate reflective rib surface, casting a vertical shadow
- A- lines: hyperechoic horizontal lines descending from the pleural line at regular intervals. This reverberation artifact occurs in normal aerated lung
Pathologic findings
- B-lines, comet tails: Vertical hyperechoic lines which (1) extend from the pleural line through the depth of the image, (2) move with lung sliding, and (3) obliterate A lines. Multiple B lines indicates excess interstitial fluid
- Lung rockets: >3 B lines indicates interstitial syndrome. Most common cause is acute pulmonary edema, also consider ARDS, PNA, pulmonary fibrosis, & pulmonary contusion. Helps distinguish CHF vs COPD exacerbation in patients with dyspnea
- Loss of lung sliding, barcode sign: The shimmering, twinkling appearance of the dynamic aerated lung is lost. Can confirm in M-mode with barcode sign- smooth homogenous lines indicating no movement of lung tissue. Lung sliding=suspicion for PTX but NOT specific unless can identify lung point
- Lung Point: The precise location where the lung detaches from the pleura can sometimes be identified. Can confirm in M-mode which will show “barcode” and “seashore” patterns adjacent. 100% specific for pneumothorax
- Pleural effusion, jellyfish sign: Anechoic fluid is visualized between the diaphragm and dynamic lung
Probe: linear or phased array
Protocol
- Adjust the depth to ~10cm to start. Position the probe vertically on the midclavicular line. Slide the probe so that the hyperechoic pleural line is visualized between rib shadows. Note presence/absence of A lines, B lines, lung sliding, and alveolar consolidation
- Repeat on the opposite side and lower anterior lung fields
- Repeat on the right and left mid-axillary line, upper and lower lung fields. Look for pleural effusion between the diaphragm and lung
- Repeat on the posterior lung fields if indicated to complete a 12-zone lung examination

Cardiovascular¶

Goal-directed echocardiography for acute shock

Pericardial tamponade
- Apical 4 chamber (A4C): pericardial effusion, may see end diastolic collapse of right atrium
- Parasternal long (PLAX): pericardial effusion will appear anterior to thoracic descending aorta, may see collapsing right ventricle
- False positives: pericardial cyst, pericardial fat pad, pleural effusion (posterior to thoracic descending aorta on PLAX)
Acute cor pulmonale
- PLAX, PSAX: paradoxical septal motion, D shaped left ventricle, dilated RV
- A4C: end-diastolic RV area : LV area > 1
- Subxiphoid (SUX): dilated IVC
LVEF- see cardiology section

Abdominal assessments¶

FAST exam
Clinical questions: Is there fluid in the peritoneal or pericardial spaces?
Probe: curvilinear or phased array
Protocol
- Start on abdominal mode at depth 21-25cm. Assess for pericardial effusion in SUX view
- Reduce depth to 12-16cm and place probe on the right anterior axillary line between ribs 8-12 with the indicator toward the patient’s head. Sweep medially to identify the right kidney. Assess for anechoic fluid in Morrison’s pouch between the kidney and liver, subdiaphragmatic space, and paracolic gutter. Rock the probe to assess for fluid cephalad to the diaphragm. Slide inferiorly to confirm no fluid around the inferior pole of the kidney
- Place probe on the left anterior axillary line between ribs 8-11 with the leading edge toward the patient’s head. Sweep medially to identify the left kidney. Assess for anechoic fluid in the splenorenal interface, subdiaphragmatic space, pleural space, paracolic gutter, and left kidney inferior pole
- Place probe midline just superior to the pubic symphysis. Identify the bladder in longitudinal and transverse view. Assess for fluid outside the bladder wall and in the pouch of Douglas (females) or rectovesicular space (males)
Limitations: Cannot detect retroperitoneal bleed. False positives from ascites, pleural effusion, subcapsular hematoma, ruptured cysts, physiologic fluid in pouch of Douglas, epicardial fat pad. Exam may be indeterminant if significant bowel gas or obesity
Small bowel obstruction assessment
- Overall SBO ultrasound has ~92% sensitivity and ~97% specificity to detect SBO and greater diagnostic accuracy than abdominal XR
- Probe: curvilinear
- Protocol: Have the patient lie supine and relax the abdominal wall. Place the probe vertically on the abdomen and sweep across all four quadrants in sagittal view. Repeat in transverse view. Measure small bowel wall thickness and diameter using the caliper tool
- Signs of SBO:
  - Diameter > 2cm • Decreased peristalsis
  - Wall thickness > 4mm • Back and forth stool movement
  - Tanga sign: In severe SBO, may see triangular pocket hypoechoic free fluid surrounding the small bowel near the obstruction
Renal ultrasound
- Protocol is similar to FAST exam. Fan the probe through each kidney in sagittal and transverse view to assess for dilation of the collecting ducts. To move the kidney inferiorly, ask the patient to take a deep breath
- Bilateral hydronephrosis and full bladder suggests urinary obstruction distal to the ureter
- Unilateral hydronephrosis suggests nephrolithiasis or ureteral obstruction
- Limitations: Renal US has a reported sensitivity of 70% and specificity of 75% to detect nephrolithiasis compared to CT

Last update: 2022-06-02 13:28:55