A post-operative cardiac surgery patient develops distributive shock (MAP <65 mmHg) despite adequate fluid resuscitation. Norepinephrine is the first-choice vasopressor. According to the VASST trial, when should vasopressin be added?

• A As an initial vasopressor before norepinephrine
• B Only for cardiogenic shock
• C When norepinephrine dose exceeds 0.1-0.25 mcg/kg/min and MAP remains inadequate ✓
• D Vasopressin should not be used in post-cardiac surgery patients

Explanation

Vasopressin acts on V1 receptors causing vasoconstriction and is used as a vasopressor-sparing agent in septic shock. The VASST trial showed that vasopressin (0.03 U/min fixed dose) combined with norepinephrine was equivalent to norepinephrine alone overall, but a subgroup with less severe septic shock (norepinephrine <15 mcg/min) showed a survival benefit with vasopressin addition. Current Surviving Sepsis Campaign guidelines recommend adding vasopressin (0.03-0.04 U/min) when norepinephrine doses are high (>0.25 mcg/kg/min) to achieve MAP target or to reduce norepinephrine requirements, thereby limiting catecholamine toxicity.

Reference: Bailey & Love's Short Practice of Surgery, 27th ed.

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