Dying pattern in volume-controlled hemorrhagic shock in awake rats

We previously determined that in awake, unmonitored Sprague-Dawley rats, bleeding of 2.5 ml/100 g over 20 min resulted in hemorrhagic shock (HS) with about a 75% survival rate over 24 h, and bleeding of 3.0 ml/100 g in about 25% survival to 24 h. In the present study, we monitored systolic and mean arterial pressure (MAP), central venous pressure (CVP), breathing movements, electroencephalogram (EEG), and arterial blood gases to 3 h in order to study dying patterns. After cannulation under light anesthesia and awakening for 2 h, the rats were bled over 20 min. Ten rats in each of four groups were studied. Shed blood volume (SBV) in group I was 2.0 ml/100 g; in group II, 2.5 ml; in group III, 3.0 ml; and in group IV, 3.5 ml. Three hour survival rates were 100% for group I, 80% for group II (survival time 149 +/- 65 [106-180] min), 40% for group III (survival time 116 +/- 72 [93-180] min), and 0% for group IV (survival time 32 +/- 38 [5-69] min). MAP decreased at end of bleeding, increased transiently to moderately hypotensive levels (attempted self-resuscitation), and then either recovered to normotension or declined to cardiac arrest (death), which was defined as simultaneous apnea, systolic arterial pressure less than or equal to 30 mmHg without pulsations, and isoelectric EEG. EEG depression began with hypotension to MAP less than or equal to 50 mmHg. During HS, PaO2 increased, and PaCO2, pHa, and Hct all decreased. The results suggest that this model with SBV of 3.25 ml/100 g would give a low, but not zero 3 h survival, and therefore would be suitable for the study of responses to field resuscitation potentials.