Foetal responses to acute haemorrhage under halothane anaesthesia

The effect of halothane anaesthesia on the foetal responses to acute haemorrhage was studied in chronically prepared ewes. An average of 27.9 ml X kg-1 of foetal blood was withdrawn resulting in an acute 20 per cent decrease in mean arterial pressure which returned toward the control value after 186 seconds. After the blood loss, cardiac output was reduced by 26.1 per cent and heart rate decreased by 26 per cent. Blood flows to the kidneys, placenta and musculoskeletal structures were reduced by 24.7, 38.2 and 35.3 per cent respectively but flow to the brain increased by 30 per cent. Reinfusion of lost blood, corrected flow reductions and the supply to the gastrointestinal organs increased above control values. This study showed that foetal lambs were able to tolerate an acute blood loss under halothane anaesthesia. An adequate perfusion pressure and blood flow to critical organs, such as the brain was maintained by increasing systemic vascular resistance. The compensation, however, was incomplete. Placental blood flow, maternal-foetal gas exchanges, and redistribution of cardiac output away from gastrointestinal tract and skin were impaired.