Sodium nitroprusside ameliorates systemic but not pulmonary HBOC-201-induced vasoconstriction: an exploratory study in a swine controlled haemorrhage model.

BACKGROUND: Vasoconstriction is a side effect that may prevent the use of haemoglobin based oxygen carrier (HBOC) as blood substitute. Therefore, we tested the hypothesis that the NO donor, sodium nitroprusside (SNP), would mitigate systemic and pulmonary hypertension associated with HBOC-201 in a simple controlled haemorrhage swine model. METHODS: After 55% estimated blood volume withdrawal through a venous catheter, invasively anesthetized and instrumented animals were resuscitated with three 10 ml/kg infusions of either HBOC-201 or Hextend (HEX) with or without 0.8 µg/kg/min SNP (infused concomitantly via different lines). Haemodynamics, direct and indirect measures of tissue oxygenation, and coagulation were measured for 2h. RESULTS: Haemorrhage caused a state of shock manifested by hypotension and base deficit. HBOC-201 resuscitation resulted in higher systemic (p<0.0001) and pulmonary (p<0.002) blood pressure than with HEX. Elevation of systemic (p<0.0001) but not pulmonary (p>0.05) arterial pressure was attenuated by co-infusion of SNP, without significant group differences in haemodynamics, tissue oxygenation, platelet function, coagulation, methaemoglobin, or survival (p>0.05). CONCLUSION: In swine with haemorrhagic shock, co-administration of the NO donor, SNP, effectively and safely reduces HBOC-201-related systemic but not pulmonary vasoactivity. Interestingly, co-administration of the vasodilator SNP with HEX had no deleterious effects in comparison with HEX alone.