Hypotension After Protamine Administration
A 72-year-old woman, 65 kg, has just come off CPB after triple-vessel bypass. Her activated clotting time has returned toward baseline after a test dose of protamine, and the surgeon is giving the remaining protamine slowly through a central line. Within two minutes, the pump arterial pressure falls from 95/55 to 60/30 mmHg, the pulmonary artery pressure rises, and the patient becomes difficult to ventilate with increasing airway pressures. The perfusionist notes the venous reservoir is no longer in use, and the patient is still cannulated. The hematocrit is 30%, and there is no evidence of bleeding.
1. What is the most likely diagnosis, and what findings support it?
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The most likely diagnosis is a protamine reaction, possibly an anaphylactoid or catastrophic pulmonary vasoconstriction response. The timing within minutes of protamine administration, the abrupt hypotension, the rise in pulmonary artery pressure, and the difficulty ventilating with high airway pressures all fit. The combination of systemic hypotension and pulmonary hypertension suggests right ventricular failure from increased pulmonary vascular resistance. Other causes to consider include hemorrhage, pump failure, or anaphylaxis to another agent, but the absence of bleeding and the temporal relationship to protamine make a protamine reaction most likely. The findings of increased airway pressures and pulmonary hypertension are particularly suggestive of the pulmonary vasoconstriction variant, which can progress rapidly.
2. Outline your immediate management, including what you would stop and what you would give.
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Stop the protamine infusion immediately and call for help. Support oxygenation and ventilation, and increase inspired oxygen. Treat hypotension with volume and vasopressors, and consider pulmonary vasodilators if pulmonary hypertension is contributing. If the reaction is severe, consider reinstituting CPB for circulatory support, since the patient is still cannulated. Administer epinephrine or norepinephrine as needed for hemodynamic support, and consider antihistamines and corticosteroids for anaphylactoid features. Avoid further protamine; if heparin reversal is still needed, discuss alternatives with the surgeon. Monitor for right ventricular failure and arrhythmias. Document the reaction and ensure it is communicated for future procedures. The key judgment is to stop the drug and support circulation rather than continue the infusion.