Ultrasound: in shock and hypotension

Background

• A bedside ultrasound paradigm for differentiating differentiating shock states (cardiogenic, obstructive, hypovolemic, distributive)
  • Tailor specific protocol to the patient at hand
• RUSH Protocol was conceived in 2008 and looks are 3 basic aspects of physiology

1. The Pump
   • RV:LV
   • Squeeze
   • Pericardial effusion and tamponade
2. The Tank
   • IVC
   • Pleural effusions
   • Pulmonary edema
   • Tension pneumothorax
3. The Pipes
   • AAA
   • Aortic dissection
   • DVT

The Protocol

Step 1: The Pump

Step 2: The Tank

Step 3: The Pipes

Rapid Ultrasound for Shock and Hypotension(RUSH) using the HI-MAP approach

• H - Heart (parasternal and four-chamber views)
• I - Inferior Vena Cava (for volume responsiveness)
• M - Morison’s pouch (i.e., FAST exam) and views of thorax (looking for free fluid)
• A - Aortic Aneurysm (ruptured abdominal aneurysm)
• P - Pneumothorax (i.e., Tension pneumothorax)

Heart

Technique: see Cardiac ultrasound

• Pericardial Effusion
  • May be most obvious with PLAX or subxiphoid views
    • In PLAX, pericardial fluid is anterior to descending aorta, while pleural fluid is posterior to it
  • Isolated anterior anechoic areas may be an anterior fat pad
  • Assess for tamponade physiology including diastolic collapse of RA or RV; see Pericardial effusion and tamponade
• LV squeeze
  • PLAX and PSAX are good views to estimate contractility
  • Change in size <30% between sys and dia = poor LV function
  • Hyperdynamicity, as determined by walls moving >90% or touching at end of systole, may indicate hypovolemia or sepsis
  • May direct fluid therapy
• RV strain
  • In 4-chamber view, RV should be <60% of LV; if dilated/larger think RV strain
  • While chronic RV strain (ex. cor pulmonale) may cause RVH, massive PE will not have time to cause RVH

IVC

Technique: see IVC ultrasound

• Measure 2cm caudally from RA-IVC junction
• If IVC <2.1cm and collapses >50% on inspiration then RAP/CVP is low
• If IVC >2.1cm and collapses <50% then RAP/CVP is high
  • Suggests fluid unresponsive; patient requires inotropes
• IVC measurements may be altered in patients receiving vasoactive medications or positive pressure ventilation

Morison's

Technique: see FAST exam

• Assess for free fluid
  • Morison's pouch (hepatorenal space)
  • Splenorenal
  • Bladder, including retrovesicular space
  • As part of E-FAST, when in hepatorenal or splenorenal views, aim/slide probe above diaphragm to assess for pleural effusion
• Note that while ascitic fluid often appears anechoic, blood may appear with mixed echogenicity due to the presence of clots

Aorta

Technique: see Aortic ultrasound

• Steady pressure with probe can displace bowel gas, improving view
• If >5cm assume ruptured AAA until proven otherwise
• In PLAX, aortic root >3.8cm may be seen in proximal aortic dissection or aortic aneurysm

Pulmonary

Technique: see Ultrasound: Lungs

• Assess for subpleural interstitial edema
  • Look for multiple comet tail artifacts or "B lines"(a few, 3-4, are OK)
    • If multiple found, there is interstitial pulmonary edema
• Assess for pneumothorax
  • Scan longitudinally in anterior 2nd-3rd IC space, mid-clavicular line, looking for echogenic pleural line
  • On M-mode, look for lack of pleural sliding, aka "Barcode sign"
  • Presence of lung point is highly specific for PTX

Other

Classic Ultrasound Findings For Critically Ill Patients

Disease	IVC	Cardiac	Lung (Phased Array)	Lung (Linear)
MI	↑	Focal WMA Mod/Poor squeeze	NL or B-lines	Sliding
Tamponade	↑	RA collapse with filling RV collapse with filling	NL	Sliding
PTX	↑	NL or Hyperdynamic	Lung point Consolidated lung	Absent lung sliding
Sepsis	↓	Hyperdynamic squeeze	NL (see pneumonia)	Sliding
Pneumonia	NL or ↓	Hyperdynamic squeeze	Unilateral B-lines	Sliding
Decompensated HF	↑	Mod/Poor squeeze	Bilateral B-lines	Sliding
PE	↑	RV > LV McConnell's sign	NL or Unilateral B-lines	Sliding

See Also

• Ultrasound (main)
• Undifferentiated shock