Arginine vasopressin improves cerebral perfusion following controlled haemorrhage in adult ewes.

Haemorrhagic shock causes significant morbidity and mortality. Novel pre-hospital therapy to improve haemodynamic stability and cerebral perfusion may improve outcomes but remains controversial. In an ovine model of controlled haemorrhagic shock, the effects of early intramuscular arginine vasopressin (AVP), adrenaline or placebo on haemodynamic stability and cerebral perfusion were compared. Carotid pressure and flow catheters were placed in healthy, anaesthetized adult ewes. Frontal cortex cerebral oxygenation was measured using near infrared spectroscopy. Controlled, rapid, haemorrhage (∼30% estimated blood volume) was induced. Five minutes post-bleed a 1 ml intramuscular dose of 0.9% saline, adrenaline 1 mg or AVP 20 IU was administered. Carotid blood pressure and flow improved significantly in the AVP group over the first 30 min post-intervention. To emulate standard trauma care, 1 L of 0.9% saline was infused 30 min post-bleed followed by re-transfusion of the sheep's own blood at 60 min post-bleed. Carotid blood pressure and flow in the AVP group remained significantly higher post-crystalloid infusion, but this difference was lost post-blood transfusion. Data were analysed by two-way ANOVA with time, group as the main factors. When compared to saline or adrenaline, a single dose of intramuscular AVP resulted in a progressive and sustained increase in carotid artery blood pressure and flow with commensurate increase in cerebral oxygenation. Intramuscular AVP has potential as an emergency pre-hospital therapy following exsanguinating haemorrhage; however, further studies are required to investigate whether the benefit of improved perfusion pressure outweighs the risks of exacerbating ongoing bleeding.