Mild therapeutic hypothermia (32 degrees C-34 degrees C) is the only therapy that improved neurological outcome after cardiac arrest in a randomized, controlled trial. Induced hypothermia after successful resuscitation leads to one additional patient with intact neurological outcome for every 6 patients treated. It protects the brain after ischemia by reduction of brain metabolism, attenuation of reactive oxygen species formation, inhibition of excitatory amino acid release, attenuation of the immune response during reperfusion, and inhibition of apoptosis. Potential side effects such as infections have to be kept in mind and treated accordingly. Mild hypothermia is a safe and effective therapy after cardiac arrest, even in hemodynamically compromised patients and in patients undergoing percutaneous coronary intervention. Its use is recommended by the American Heart Association and the International Liaison Committee on Resuscitation for unconscious adult patients with spontaneous circulation after out-of-hospital ventricular fibrillation cardiac arrest. Further research is needed to maximize its potential benefits.
This article is a support paper for the National Association of EMS Physicians' position paper on induced therapeutic hypothermia in resuscitated cardiac arrest patients. Induced hypothermia is one of the newest treatments aimed at increasing the dismal neurologically intact survival rate for out-of-hospital cardiac arrest patients. Two landmark studies published in 2002 by the New England Journal of Medicine led to the American Heart Association (AHA) Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care IIa recommendation of cooling unconscious adult patients with return of spontaneous circulation after out-of-hospital cardiac arrest due to ventricular fibrillation to 32 degrees C to 34 degrees C for 12 to 24 hours. Despite many limitations of those studies, the AHA also suggests that this therapy may be beneficial for patients with non-ventricular fibrillation arrests. However, the literature is lacking in answers with regard to the best methods to utilize in cooling patients. While avoiding delay in the initiation of cooling seems logical, the literature is also lacking evidence indicating the ideal time at which to implement cooling. Furthermore, it remains unclear as to which patients may benefit from induced hypothermia. Finally, the literature provides no evidence to support mandating induced hypothermia in the prehospital setting. Given limited prehospital resources, sometimes consisting of only two providers, attention first needs to be given to providing the basic care with the utmost skill. Once the basics are being delivered expertly, consideration can be given to the use of prehospital cooling for the resuscitated cardiac arrest patient in the setting of continued cooling in the hospital.
BACKGROUND: Local hypothermia induced by intravascular infusion of cold saline solution effectively reduces brain damage in stroke. We further determined the optimal temperature of local hypothermia in our study. METHODS: Seventy-eight adult male Sprague Dawley rats (260 - 300 g) were randomly divided into 3 groups: group A, ischemia/reperfusion without cold saline infusion (n = 26) (control group); group B, infusion with 20 degrees C saline before reperfusion (n = 26); group C: infusion with 10 degrees C saline before reperfusion (n = 26). In each group, we chose 15 rats for monitoring physical indexes and the temperature of the brain (cortex and striatum) and body (anus), measurement of brain infarction volume, assessment of neurological deficits and the survival rate of reperfusion at 48 hours. Another 8 rats from each group was chosen for examining brain edema, another 3 from each group for histological observation by electron microscopy (EM) and light microscopy (LM) at 48 hours after reperfusion. RESULTS: There was no significant difference among the 3 groups for physical indexes during the examination (F((2, 45)) = 0.577, P = 0.568; F((2, 45)) = 0.42, P = 0.78 for blood pressure and blood gas analysis, respectively). The brain temperature was significantly reduced in the group C compared to the other groups (F((2, 45)) = 37.074, P = 0.000; F((2, 45)) = 32.983, P = 0.000, for cortex and striatum temperature respectively), while the difference in rectal temperature between group A and B or C after reperfusion was not significant (F((2, 45)) = 0.17115, P = 0.637). And the brain infarct volume was significantly reduced in group C (from 40% +/- 10% in group A, 26% +/- 8% in group B, to 12% +/- 6% in group C, F((2, 45)) = 43.465, P = 0.000) with the neurological deficits improving in group C (chi(2) = 27.626, P = 0.000). The survival rate at 48 hours after 10 degrees C and 20 degrees C saline reperfusion was increased by 132.5% and 150%, respectively, as compared to the control group (chi(2) = 10.489, P = 0.005). The extent of the brain edema showed no significant difference (F((2, 21)) = 0.547, P = 0.587) after cold saline infusion compared to the control group. No obvious vascular injury was found by electron or light microscopy in either infusion group. CONCLUSIONS: Regional hypothermia with 10 degrees C cold saline infusion can significantly decrease the infarction volume, improve the neurological deficits, and 10 degrees C seems to be the optimal temperature in inducing a cerebral protection effect during stroke. This procedure could be adopted as a further treatment for acute stroke patients.
Hypothermia is considered nature's "gold standard" for neuroprotection, and its efficacy for improving outcome in patients with hypoxic-ischemic brain injury as a result of cardiac arrest is well-established. Hypothermia reduces brain edema and intracranial pressure in patients with traumatic brain injury. By contrast, only a few small pilot studies have evaluated hypothermia as a treatment for acute ischemic stroke, and no controlled trials of hypothermia for hemorrhagic stroke have been performed. Logistic challenges present an important barrier to the widespread application of hypothermia for stroke, most importantly the need for high-quality critical care to start immediately in the emergency department. Rapid induction of hypothermia within 3 to 6 hrs of onset has been hampered by slow cooling rates, but is feasible. Delayed cooling for the treatment of cytotoxic brain edema does not provide definitive or lasting treatment for intracranial mass effect, and should not be used as an alternative to hemicraniectomy. Sustained fever control is feasible in patients with intracerebral and subarachnoid hemorrhage, but has yet to be tested in a phase III study. Important observations from studies investigating the use of hypothermia for stroke to date include the necessity for proactive antishivering therapy for successful cooling, the importance of slow controlled rewarming to avoid rebound brain edema, and the high risk for infectious and cardiovascular complications in this patient population. More research is clearly needed to bring us closer to the successful application of hypothermia in the treatment for stroke.
OBJECTIVE: Hypothermia has long been known to be a potent neuroprotectant. In this mini-review, we highlighted clinical experience that hypothermia protects the brain from cerebral injury. We discussed the clinical practice of hypothermia in ischemic stroke. RESULTS: Multiple factors play a significant role in the mechanisms. Clinical application drew first from two clinical trials with comatose patients after cardiac arrest is attractive. The Australian and European study have led to renewed interest in these patients. More and more evidences bring the insight into its effects on cerebral ischemia. The type of cooling technique to be used, the duration of cooling and speed of rewarming appear to be key factors in determining whether hypothermia is effective in preventing or mitigating neurological injury. Although until now, there are no clear therapeutic standards of the parameters in therapeutic hypothermia, it is well accepted that cooling should be initiated as soon as possible. By combining hypothermia with other neuroprotectants, it may be possible to enhance protective effects, reduce side effects and lengthen the maximum time. CONCLUSION: In addition to its neuroprotective properties, hypothermia may extend the therapeutic window for other neuroprotective treatment. Thus, combination therapies with neuroprotective, anti-inflammatory and thrombolytic agents are likely to be investigated in the clinical setting in the future.