Shock & Undifferentiated Hypotension
Emergency evaluation and aggressive resuscitation of the hypotensive patient: differentiating hypovolemic, cardiogenic, obstructive, and distributive shock with the bedside RUSH exam and targeted inotropes.
Resuscitation Quick Ribbon (First 2 Minutes)
Bottom-Line Clinical Pearl
Shock is cellular hypoxia and impaired tissue perfusion, NOT a blood pressure number. Tachycardia, altered mentation, mottled extremities, oliguria, and serum lactate > 2 mmol/L precede hypotension. Execute the RUSH protocol (Pump, Tank, Pipes) immediately. In septic/distributive shock, start Norepinephrine early rather than drowning the patient in excessive crystalloids. In cardiogenic shock, inotropes (Dobutamine, Milrinone) combined with Norepinephrine are required; aggressive fluid boluses cause flash pulmonary edema.
1. Hemodynamic Profiles of the 4 Shock States
| Shock Category | Cardiac Output (CO) | Preload (PCWP/CVP) | Afterload (SVR) | Central Venous O2 (ScvO2) | Primary Etiologies |
|---|---|---|---|---|---|
| Hypovolemic | Decreased | Decreased | Increased | Decreased (< 70%) | Hemorrhage, dehydration, burns, third-spacing, DKA |
| Cardiogenic | Decreased | Increased | Increased | Decreased (< 60%) | Acute MI, end-stage HF, acute MR/VSD, myocarditis, arrhythmias |
| Obstructive | Decreased | Increased (or variable) | Increased | Decreased | Tension pneumo, cardiac tamponade, massive PE, aortic dissection |
| Distributive | Increased (early) / Variable | Decreased | Decreased (Vasodilation) | Increased (> 70%) | Sepsis, anaphylaxis, neurogenic (spinal cord transection), adrenal crisis |
2. The RUSH Protocol: Bedside Ultrasound for Undifferentiated Shock
| Component | Ultrasound Window | Look For | Key Findings & Diagnoses |
|---|---|---|---|
| The Pump | Parasternal Long & Short, Apical 4-Chamber, Subxiphoid | LV contractility, RV strain, Pericardial fluid | Pericardial effusion + RV collapse = Tamponade; Hyperdynamic LV = Sepsis/Hypovolemia; Dilated hypokinetic RV = Massive PE |
| The Tank | IVC, Lung Apices, Morison's Pouch, Splenorenal, Pelvis | Intravascular fullness, Pleural sliding, Free fluid | Collapsing IVC (< 1.5 cm) = Hypovolemia; Plethoric IVC (> 2.1 cm) = Cardiogenic/Obstructive; Absent lung sliding = Pneumothorax; Free peritoneal fluid = Hemoperitoneum / Ruptured ectopic |
| The Pipes | Abdominal Aorta, Femoral & Popliteal Veins | Aortic diameter, DVT compression | Abdominal aorta > 3 cm = AAA rupture; Non-compressible deep vein = DVT leading to massive PE |
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