Post-Operative Hypotension (Circulatory Shock) Lecture

Overview

• Focus: Post-operative hypotension or circulatory shock
• Objective: Simplifying the differential diagnosis of shock in post-op patients
• MAP Definition: Mean arterial pressure < 65 mm Hg

Types of Shock

1. Distributive Shock

• Most Common: Sepsis (most common post-op cause), Anaphylaxis, Neurogenic shock
• Mechanism: Vessel dilation and leakiness, causing insufficient fluid distribution
• Post-Op Application: Think sepsis first

2. Hypovolemic Shock

• Causes: Lack of fluids (e.g., from surgery, open abdomen) or bleeding
• Mechanism: Insufficient fluid in normal-sized blood vessels
• Post-Op Application: Ensure adequate fluid resuscitation and monitor for internal bleeding

3. Cardiogenic Shock

• Causes: Heart's inability to pump blood (e.g., heart failure, valvular disease, arrhythmia)
• Mechanism: Bad heart function despite normal/clamped down blood vessels
• Post-Op Application: Less common, but still possible

4. Obstructive Shock

• Causes: Pulmonary embolism, pneumothorax, cardiac tamponade
• Mechanism: Physical obstruction impeding blood flow
• Post-Op Application: Rare and often over-emphasized but important to consider if clinical signs suggestive

Clinical Approach

Immediate Actions

1. Initial Assessment: Check blood pressure and confirm its correctness
2. Physical Findings: Look at urine output, mental status, etc.
3. Stabilizing Treatments:
   • Fluids: Administer isotonic fluids (e.g., lactated ringers, normal saline)
   • IV Access: Ensure good intravenous access
   • Vasopressors: Initiate norepinephrine if fluids aren’t sufficient
   • Ventilation: Consider intubation if critically ill
4. Concurrent Workup:
   • Laboratory Tests: CBC, basic metabolic panel, lactate, blood gas (arterial/venous)
   • Infection Workup: Blood cultures, urinalysis, chest x-ray
   • Imaging: Based on suspicion (e.g., CTA abdomen for bleeding, CXR for infection)
   • Other Diagnostics: EKG, focused cardiac ultrasound if indicated

Data and Evidence

• Prevalence: Distributive shock is the most common in ICU settings; particularly sepsis in post-op patients
• Statistics:
  • Distributive shock: >50% of cases
  • Hypovolemic shock: Roughly equal to cardiogenic shock but more relevant in surgical patients
  • Cardiogenic shock: Possible but less common in surgical patients
  • Obstructive shock: Extremely rare (approx. 2% of all patients)

Strategy for Effective Management

1. Empirical Treatment: Initiate fluids and pressors while identifying the cause
2. Focused Differential: Prioritize sepsis and bleeding in post-op patients
3. Higher Level of Care: Consider ICU for severe hypotension requiring pressors
4. Review and Reassess: Regularly reassess the diagnosis based on response to initial treatments and ongoing data

Educational Disclaimer

• Purpose: For educational purposes only; not for diagnosing or treating diseases
• Next Steps: Follow up with further educational content