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Deterimental effect of prolonged hypothermia in cats and monkeys with and without regional cerebral ischemia
Abstract:
In a previous study occlusion of a middle cerebral artery (MCA) followed by 48 h of hypothermia (29 degrees) was lethal in 5 of 5 monkeys as compared to only 3 of 9 normothermic animals. The present study extended these observations in monkeys and cats with or without MCA occlusion. In monkeys MCA occlusion plus 48 h of hypothermia was consistently lethal. Without MCA occlusion of 2 of 3 monkeys survived, but were comatose the first 12 h post-hypothermia. In normothermic cats, MCA occlusion was lethal in only one of 5 animals whereas hypothermia was lethal in 20 of 21 cats with or without MCA occlusion. The detrimental effects of hypothermia were not favorably influenced either by hemodilution or by deliberate alterations in PaCO2. The effect of 48 h of hypothermia and rewarming on cerebral blood flow (CBF) and cerebral metabolites was evaluated in 6 normal monkeys. CBF was reduced 60 to 70 percent at 29 degrees C and returned to only a maximum of 50 percent of control with re-warming. Prior to re-warming distribution of CBF was inhomogeneous. Cerebral metabolites were borderline normal prior to re-warming but energy stores decreased while lactate increased with re-warming.
Insights
Hypothermia combined with middle cerebral artery occlusion is lethal in most monkeys. Hypothermia alone also proved detrimental to cats, impacting cerebral blood flow and metabolites.
Area of Science:
- Neuroscience
- Physiology
- Critical Care Medicine
Background:
- Previous studies indicated high mortality in monkeys with middle cerebral artery (MCA) occlusion and hypothermia.
- The current study aimed to further investigate the effects of hypothermia and MCA occlusion in animal models.
Purpose of the Study:
- To evaluate the lethality and physiological consequences of hypothermia and MCA occlusion in monkeys and cats.
- To assess the impact of hypothermia on cerebral blood flow (CBF) and cerebral metabolites during and after rewarming.
Main Methods:
- Monkeys and cats underwent MCA occlusion and/or 48-hour hypothermia (29°C).
- Hemodilution and PaCO2 alterations were tested as potential protective measures.
- Cerebral blood flow and metabolite levels were measured in normal monkeys during and after hypothermia and rewarming.
Main Results:
- MCA occlusion plus hypothermia was consistently lethal in monkeys.
- Hypothermia alone was highly lethal in cats (20/21), regardless of MCA occlusion.
- Hypothermia significantly reduced CBF (60-70%) in monkeys, with incomplete recovery post-rewarming.
- Cerebral metabolites showed decreased energy stores and increased lactate with rewarming.
Conclusions:
- Combined MCA occlusion and hypothermia pose a significant lethal risk in primates.
- Prolonged hypothermia is detrimental to cats, irrespective of cerebral ischemia.
- Hypothermia severely impairs CBF and alters cerebral metabolism, with potential negative consequences during rewarming.