Effect of diazepam on survival of the immature pig in a confined atmosphere.

Diazepam is known to prolong survival in an atmosphere containing 5% oxygen, and to reduce cerebral metabolic rate and cerebral perfusion. It also depresses the arousal response to hypoxia and protects the optic nerve from anoxia. We hypothesised that diazepam might extend survival in a confined atmosphere with a limited amount of oxygen. Pigs consumed the oxygen in a sealed chamber until they reached the terminal state. The experimental pigs (n = 6) were sedated with diazepam 0.3 mg/kg i.v. and were compared with a control group (n = 5). We measured blood pressure, inspired O2 and CO2, minute ventilation, ECG, ambient and body temperatures, and PO2, PCO2, O2 content and pH in arterial and venous blood. In the diazepam-treated pigs, oxygen consumption was reduced in the hypoxic range (PIO2 below 60 torr) compared with the control pigs. Diazepam prevented the elevated hypoxic cardiac output found in the control pigs. There were almost no differences between the diazepam and control groups in the other parameters measured in the course of the exposure and in the terminal state. Terminal PIO2, PaO2, and PvO2 were 36.9 +/- 5.6, 27.9 +/- 8.6, 14.3 +/- 2.0 torr, and 36.9 +/- 5.7, 23.7 +/- 7.3, 15.7 +/- 7.6 torr in the diazepam and control groups, respectively. The survival time was 220 +/- 51 and 255 +/- 50 min in diazepam and control pigs, respectively. In spite of its anticonvulsant effect and the fact that it protects CNS white matter from anoxia, prolongs anoxic survival and eliminates the high oxygen demand in hypoxic arousal, diazepam failed to extend hypoxic survival in a confined atmosphere to a lower PIO2. However, diazepam had no deleterious effect on survival, and may therefore be used to ease stressful hypoxic conditions.