Effect of halothane on the pulmonary vascular response to hypoxia in dogs

The pulmonary vascular response to alveolar hypoxia with and without halothane exposure was measured in dogs. Hypoxia increased pulmonary artery pressure (Ppa) and pulmonary vascular resistance (PVR) so that in each case inverse linear relationships were found with arterial oxygen saturation. These responses were highly significant and reproduceable but varied greatly between individuals. Halothane administration resulted in an increased slope of PVR against oxygen saturation due to the fact that reduction in cardiac output exceeded the reduction in Ppa. An analysis of variance showed that it was possible to predict accurately the hypoxic PVR and Ppa responses under halothane anaesthesia from the control hypoxic responses. Animals with low PVR responses showed the greatest arterial oxygen desaturation with hypoxia, whereas high responders showed least oxygen desaturation. Thus it was possible to predict those individuals at risk from severe arterial oxygen desaturation under halothane anaesthesia.