Beneficial effect of mild hypothermia and detrimental effect of deep hypothermia after cardiac arrest in dogs.

Abstract

Background and Purpose: Mild cerebral hypothermia (34°C) induced immediately after cardiac arrest improves outcome. Deep postarrest hypothermia (15°C) has not been studied.Methods: We used our dog model of normothermic ventricular fibrillation (no blood flow) of 12.5 minutes, reperfusion by brief cardiopulmonary bypass, controlled ventilation to 20 hours, and intensive care to 72 hours. Head surface cooling and bypass cooling were performed from start of reperfusion to 1 hour. Five groups of six dogs each were compared: group I, normothermic controls; group II, deep hypothermia (15°C); group III, moderate hypothermia (30°C); group IV, mild hypothermia (34°C); and group V, mild hypothermia with head surface cooling begun during no flow.Results: In control group I, five dogs remained comatose (overall performance category [OPC] 4) and one severely disabled (OPC 3). In group II, four dogs achieved OPC 4 and two dogs OPC 3 (NS versus group I). Compared with group I, OPCs were better in group III (p<0.05), group IV (p<0.05), and group V (p<0.05). Neurological deficit scores were also better in groups III, IV, and V than in groups I or II (p<0.05). Total brain histological damage scores were better in group III (p-0.02), group IV (p=0.06), and group V (p<0.05) than in group I. In group II, OPC and neurological deficit scores were the same and histological damage scores numerically worse than in group I and all were worse than in groups III, IV, and V (p<0.05). Cardiovascular complications and myocardial morphological damage in groups II and III were worse than in groups I, IV, and V (p<0.05).Conclusions: Mild or moderate cerebral hypothermia induced immediately after cardiac arrest improves cerebral outcome, more likely when initiated during arrest, whereas deep postarrest hypothermia can worsen cerebral and cardiac outcome. (Stroke 1992;23:1454-1462 KEY WORDS • anoxia • cerebral ischemia • hypothermia • dogs

Hypothermic neuroprotection

“…Supporting this logic, in the adult dog, deep hypothermia (to a rectal temperature of 15°C) after cardiac arrest was detrimental, whereas mild hypothermia (34 to 36°C), from 10 minutes until 12 hours after cardiac arrest was beneficial. 86 Overall, subsequent studies suggest that a reduction in cerebral temperature to between 32 and 34°C is required for effective neuronal rescue. In fetal sheep cooled from 90 minutes after ischemia, substantial neuroprotection was seen only in fetuses in whom there was a sustained decrease in the extradural temperature to less than 34°C (normal temperature in the fetal sheep is 39.5°C).…”

Therapeutic heat and cold in cardiac rehabilitation

“…The use of moderate hypothermia after cardiac arrest was initially reported in the late 1950s and early 1960s [75,76]. There were no further investigations conducted on hypothermia as a resuscitative measure until the 1990s, when laboratory studies demonstrated the benefit of mild hypothermia [77][78][79][80]. These studies led to the preliminary clinical research on mild hypothermia.…”

Prehospital Therapeutic Hypothermia for Cardiac Arrest

“…It is very important to avoid overcooling below the target range because adverse events likely increase when patients are cooled to < 32°C. [73,74] In a retrospective review, investigators showed that unintentional overcooling below target temperature is common, and concluded that improved mechanisms for temperature control are required to prevent potentially deleterious complications of more profound hypothermia. [75] I also add that effective and accurate methods for prehospital temperature monitoring is important, such as tympanic or esophageal temperature monitors.…”