Hypothermia cardiac arrest

The Hypothermia After Cardiac Arrest Study Group. Mild therapeutic hypothermia to improve the neurologic outcome after cardiac arrest. N Engl J Med 2002 346 549-556. 

Hypothermia should be implemented in unconscious adult patients with ROSC after out-of-hospital cardiac arrest when the initial rhythm was VF. These patients should be cooled to 32°C (89.6°F) to 34°C (93.2°F) for 12-24 hours. 

Hypothermia may be beneficial for patients with non-VF arrest out of hospital or for in-hospital cardiac arrest. 

Hypothermia can protect from cerebral injury by suppressing chemical reactions that occur after restoration of blood flow following cardiac arrest. Based on the results of two clinical trials, unconscious adult patients with spontaneous circulation after out-of-hospital cardiac arrest should be cooled to 32°C (89.6°F) to 34°C (93.2°F) for 12 to 24 hours when the initial rhythm is VF. Cooling may also benefit other rhythms or in-hospital cardiac arrest in adults there is insufficient evidence to recommend therapeutic hypothermia in children. 

Recently, two landmark prospective randomized controlled studies were published demonstrating the benefit of mild hypothermia in improving neurologic outcome in patients suffering cardiac arrest from ventricular fibrillation (73,74). 

The Australian study (73) randomly assigned 77 patients with ventricular fibrillation cardiac arrest to hypothermia (33°C) or normothermia. Patients were cooled within 2 h after return to spontaneous circulation and maintained at that temperature for 12 h. Forty-nine percent (21/43) of the hypothermia-treated patients had a good outcome, defined as di scharged home or to a rehabilitation facility compared with 26% (9/34) of the normothermia group (p = 0.046). There was no difference in the frequency of adverse effects between groups. 

Weinrauch V., Safar P., Tisherman S., Kuboyama K., and Radovsky A. (1992) Beneficial effect of mild hypothermia and detrimental effect of deep hypothermia after cardiac arrest in dogs. Stroke 23,1454-1462. 

Leonov Y., Sterz F., Safar P., et al. (1990) Mild cerebral hypothermia during and after cardiac arrest improves neurologic outcome in dogs. J. Cereb. Blood Flow Metab. 10, 57-70. 

Yli-Hankala A., Edmonds H. L., Jr., Jiang Y. D., Higham H. E., and Zhang P. Y. (1997) Outcome effects of different protective hypothermia levels during cardiac arrest in rats. Acta Anaesthesiol. Scand 41, 511-515. 

The aforementioned findings in rodents mirror results observed in dogs subjected to cardiac arrest with subsequent postischemic mild hypothermia of 1- to 12-h duration (38-44). For example, a 12-h period of 34°C hypothermia with hemodilution and elevated blood pressure reduced brain injury (e.g., hippocampus, neocortex, basal ganglia) and lessened functional deficits after cardiac arrest. However, in all of these studies the survival time was 4 d or less, and thus it has yet to be proven that postischemic hypothermia can permanently reduce ischemic brain injury in the dog. Based on the rodent literature, it would be useful to investigate more protracted bouts of mild hypothermia and assess longterm outcome in this intensive cardiac arrest model in the dog. 

Xiao F., Safar P., and Radovsky A. (1998) Mild protective and resuscitative hypothermia for asphyxial cardiac arrest in rats. Am. J. Emerg. Med. 16,17-25. 

Safar P., Xiao F., Radovsky A., et al. (1996) Improved cerebral resuscitation from cardiac arrest in dogs with mild hypothermia plus blood flow promotion. Stroke 27, 105-113. 

These are the first clinical trials to demonstrate improved outcomes using hypothermia in this population of cardiac arrest patients. However, it s possible that some of the beneficial outcome in these studies was related to the prevention of hyperthermia. Experimental data have shown that even mild hyperthermia contributes to ischemic injury. 

Deliberate mild hypothermia has been shown to be an extremely effective means of neuroprotection during periods of ischemia in experimental models. Intraoperative mild hypothermia has become a standard of practice for many neurosurgeons performing complex intracranial procedures. Recent findings of neurologic benefit in prospective, randomized, controlled clinical studies of cardiac arrest patients are encouraging, but more research is required to confirm and extend these positive results to other patients with stroke and traumatic insults. Further investigation must be completed to establish the optimal time and duration when treatment should be instituted to offer the optimal protection for patients with acute ischemic and traumatic injuries. 

LeiB., TanX., CaiH., XuQ., and Guo Q. (1994) Effect of moderate hypothermia on lipid peroxidation in canine brain tissue after cardiac arrest and resuscitation. Stroke 25,147-152. 

Neuroprotection by rapidly applied hypothermia following global brain ischemia was recently demonstrated in patients who had been resuscitated after cardiac arrest (55,56). In the study by Bernard et al. (55), patients randomly assigned to hypothermic treatment were cooled within 2 h (33°C) after the return of spontaneous circulation (12-h dura-... 

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