What is the recommended treatment for vasoplegic shock in cardiac surgery?

Management of Vasoplegic Shock in Cardiac Surgery

First-line treatment for vasoplegic shock in cardiac surgery is α1-adrenergic agonist vasopressors, with norepinephrine as the preferred agent. 1, 2

Definition and Pathophysiology

Vasoplegic shock is characterized by:

• Severe hypotension
• Low systemic vascular resistance
• Normal or increased cardiac output
• Resistance to conventional vasopressors

This condition occurs in approximately 7.2% of cardiac surgery patients undergoing cardiopulmonary bypass and is associated with high morbidity and mortality 3.

Treatment Algorithm

First-Line Treatment:

1. Norepinephrine (0.05-0.1 μg/kg/min, titrated by 0.05-0.1 μg/kg/min every 5-15 minutes) 2
   • Target MAP: 50-80 mmHg during CPB 1
   • Avoid forcing MAP above 80 mmHg with vasopressors (Class III recommendation, Level B) 1

Second-Line Options (for refractory vasoplegic shock):

1. Vasopressin 1, 2, 4

   • Dosing: Start at 0.01 units/minute for septic shock
   • For post-cardiotomy shock: 0.03 units/minute
   • Maximum dose: 0.03 units/minute
   • Can be used alone or in combination with norepinephrine

2. Methylene Blue (Class IIa recommendation, Level B) 1, 5, 6

   • Dosing: 2 mg/kg IV bolus followed by same dose as continuous infusion
   • Mechanism: Inhibits guanylate cyclase, blocking nitric oxide-mediated vasodilation
   • Most effective when administered early in the course of vasoplegic shock
   • Benefits include:
     • Shorter ICU stay
     • Reduced need for hemodialysis
     • Lower serum lactate levels at 24 hours
     • Decreased norepinephrine requirements 3

3. Terlipressin (Class IIa recommendation, Level B) 1

   • Alternative vasopressin analog for refractory cases

4. Hydroxocobalamin (Class IIb recommendation, Level C) 1

   • May be considered in refractory cases

Monitoring Parameters

• Arterial line monitoring is essential when using vasopressors 2
• Assess adequacy of pump flow rate during CPB based on:
  • Mixed venous oxygen saturation (SvO₂)
  • Oxygen extraction ratio (O₂ER)
  • Near-infrared spectroscopy (NIRS)
  • Carbon dioxide production (VCO₂)
  • Lactate levels 1
• Maintain oxygen delivery (DO₂) at a minimum of 280 ml/min/m² to reduce risk of acute kidney injury 1

Important Considerations

• Timing matters: Evidence suggests a "window of opportunity" for methylene blue effectiveness, with better outcomes when administered early 5, 6, 3
• Safety profile: Methylene blue is safe at recommended doses (lethal dose is 40 mg/kg) 5, 6
• Mechanism clarification: Methylene blue is not a direct vasoconstrictor; it blocks the cGMP pathway, thereby enhancing the vasoconstrictive effects of catecholamines 5, 6

Pitfalls to Avoid

1. Delaying treatment of vasoplegic shock can lead to progression to multiorgan failure 7
2. Overuse of vasopressors to force MAP above 80 mmHg is not recommended and may be harmful 1
3. Failing to recognize that plasma concentrations of methylene blue decrease rapidly in the first 40 minutes, necessitating continuous infusion after the initial bolus 5, 6
4. Not considering alternative agents in truly refractory cases

By following this evidence-based approach to managing vasoplegic shock in cardiac surgery, clinicians can optimize outcomes and reduce the significant morbidity and mortality associated with this condition.