Lack of effect of induction of hypothermia after acute brain injury

Current concepts in neurocritical care

The current concepts in neurocritical care including advancement in therapeutic interventions and monitoring modalities are covered for four entities: stroke, subarachnoid hemorrhage, traumatic brain injury and spinal cord injury. Although therapies were mainly supportive in the past, acute ischemic stroke may now be treated with tissue plasminogen activator if inclusion and exclusion criteria are met. The management of subarachnoid hemorrhage including cerebral vasospasm is discussed in detail. Traumatic brain injury and spinal cord injury with prevention of secondary injury to limit further sequelae are also covered. Medical complications which increase morbidity and mortality are also presented.

Anesthetic management of traumatic brain injury

The management of TBI remains an important and frustrating component of the practice of anesthesiology and critical care medicine. The difficulties in management of TBI as well as the poor response rates to medical therapy after TBI are not new. The following passage appeared in the introductory chapter of a text on TBI from 1897: "The manner of treatment is of importance in only a minority of cases, since many subjects of intracranial injury are fated to die whatever measures may be adopted for their relief, and a still greater number are destined to recover though left entirely to the resources of nature. It is probable that in by far the larger proportion of cases in which the issue is determined by treatment it is met in the initial stage, and by insuring restoration from primary shock" [111]. Although secondary insults from factors such as hypotension, hypoxemia, and hyperventilation increase morbidity and mortality, data are not yet available to indicate whether scrupulous prevention and prompt treatment of secondary injuries will reduce morbidity and mortality. In addition, no specific intervention to date has improved overall long-term outcome. With ongoing research, perhaps active interventions will become available. Until that time, thoughtful and careful attention to physiologic management provides the greatest opportunity for a good outcome.

Cerebral ischemia and trauma-different etiologies yet similar mechanisms: neuroprotective opportunities

Cerebral ischemia leads to brain damage caused by pathogenetic mechanisms that are also activated by neurotrauma. These mechanisms include among others excitotoxicity, over production of free radicals, inflammation and apoptosis. Furthermore, cerebral ischemia and trauma both trigger similar auto-protective mechanisms including the production of heat shock proteins, anti-inflammatory cytokines and endogenous antioxidants. Neuroprotective therapy aims at minimizing the activation of toxic pathways and at enhancing the activity of endogenous neuroprotective mechanisms. The similarities in the damage-producing and endogenous auto-protective mechanisms may imply that neuroprotective compounds found to be active against one of these conditions may indeed be also protective in the other. This review summarizes the pathogenetic events of ischemic and traumatic brain injury and reviews the neuroprotective strategies employed thus far in each of these conditions with a special emphasize on their clinical relevance and on future directions in the field of neuronal protection.

Fever: beneficial and detrimental effects of antipyretics

Although various forms of therapy have been used, since antiquity, to lower the temperature of febrile patients, it is still not known whether the benefits of antipyretic therapy outweigh its risks. Justifications for the use of antipyretic drugs, and the evidence pertaining to these rationales, are examined. Antipyretic therapy in sepsis, and adverse effects of antipyretic medications, are also reviewed.

Acute systemic administration of interleukin-10 suppresses the beneficial effects of moderate hypothermia following traumatic brain injury in rats

Traumatic injury to the central nervous system initiates inflammatory processes such as the synthesis of proinflammatory mediators that contribute to secondary tissue damage. Hence, administration of anti-inflammatory cytokines, such as interleukin-10 (IL-10) may be neuroprotective. Moderate hypothermia (30-32 degrees C) also decreases the pro-inflammatory response to traumatic brain injury (TBI). Thus, we hypothesized that the combination of IL-10 and hypothermia would provide synergistic neuroprotective effects after TBI. To test this hypothesis, fifty isoflurane-anesthetized rats underwent a controlled cortical impact (2.7 mm tissue deformation at 4 m/s) or sham injury and then were randomly assigned to one of five conditions (TBI/VEH Normothermia (37 degrees C), TBI/VEH Hypothermia (32 degrees C for 3 h), TBI/IL-10 Normothermia, TBI/IL-10 Hypothermia, and Sham/VEH Normothermia). Human IL-10 (5 microg) or VEH was administered (i.p.) 30 min after surgery. Function was assessed by established motor and cognitive tests on post-operative days 1-5 and 14-18, respectively. Cortical lesion volume and hippocampal CA(1)/CA(3) cell survival were quantified at 4 weeks. Brain sections from 15 additional rats were immunohistochemically assessed (MoAB RP-3) to determine neutrophil accumulation at 5 h after TBI. The administration of IL-10 after TBI produced an approximately 75% reduction in the number of RP-3-positive cells in both the normothermic and hypothermic groups vs. the normothermic vehicle-treated group (P<0.05), but did not improve functional outcome. In contrast, hypothermia alone enhanced both motor and cognitive function and increased CA(3) neuronal survival after TBI. Contrary to our hypothesis, systemic administration of IL-10 combined with hypothermia did not provide synergistic neuroprotective effects after TBI. Rather, IL-10 administration suppressed the beneficial effects produced by hypothermia alone after TBI. The mechanism(s) for the negative effects of IL-10 combined with hypothermia after TBI remain to be determined.

The importance of brain temperature in patients after severe head injury: relationship to intracranial pressure, cerebral perfusion pressure, cerebral blood flow, and outcome

Brain temperature was continuously measured in 58 patients after severe head injury and compared to rectal temperature, intracranial pressure, cerebral blood flow, and outcome after 3 months. The temperature difference between brain and rectal temperature was also calculated. Mild hypothermia (34-36 degrees C) was also used to treat uncontrollable intracranial pressure (ICP) above 20 mm Hg when other methods failed. Brain and rectal temperature were strongly correlated (r = 0.866; p < 0.001). Four groups were identified. The mean brain temperature ranged from 36.9 +/- 0.4 degrees C in the normothermic group to 38.2 +/- 0.5 degrees C in the hyperthermic group, 35.3 +/- 0.5 degrees C in the mild therapeutic hypothermia group, and 34.3 +/- 1.5 degrees C in the hypothermia group without active cooling. The mean DeltaT(br-rect) was positive for patients with a T(br) above 36.0 degrees C (0.0 +/- 0.5 degrees C) and negative for patients during mild therapeutic hypothermia (-0.2 +/- 0.6 degrees C) and also in those with a brain temperature below 36 degrees C without active cooling (0.8 +/- -1.4 degrees C) - the spontaneous hypothermic group. The cerebral perfusion pressure (CPP) was increased significantly by active cooling compared to the normothermic and hyperthermic groups. The mean cerebral blood flow (CBF) in patients with a brain temperature between 36.0 degrees C and 37.5 degrees C was 37.8 +/- 14.0 mL/100 g/min. The lowest CBF was measured in patients with a brain temperature <36.0 degrees C and a negative brain-rectal temperature difference (17.1 +/- 14.0 mL/100 g/min). A positive trend for improved outcome was seen in patients with mild hypothermia. Simultaneous monitoring of brain and rectal temperature provides important diagnostic and prognostic information to guide the treatment of patients after severe head injury (SHI) and the wide differentials that can develop between the brain and core temperature, especially during rapid cooling, strongly supports the use of brain temperature measurement if therapeutic hypothermia is considered for head injury care.

Intestinal energy metabolism after ischemia-reperfusion: Effects of moderate hypothermia and perfluorocarbons

PURPOSE

This study investigated the roles of moderate hypothermia and extraluminal oxygenated perfluorcarbon (PFC) on intestinal metabolism after ischemia-reperfusion.

METHODS

A model of 30-minute intestinal ischemia followed by 60 minutes of reperfusion was used. The animals were maintained at either normothermia (36.5 to 37.5 degrees C) or moderate hypothermia (31 to 32 degrees C). Four groups of adult rats were studied (n = 8 per group): (A) sham at normothermia, (B) ischemia-reperfusion at normothermia, (C) ischemia-reperfusion at hypothermia and, (D) ischemia-reperfusion with extraluminal oxygenated PFC perfusion during ischemia at normothermia. Intestinal phosphocreatine, ATP and lactate levels were measured. Histologic changes in the intestine were evaluated.

RESULTS

Intestinal ischemia-reperfusion at normothermia caused a marked reduction in phosphocreatine and ATP with an increase in lactate. Moderate hypothermia exerted beneficial effects by attenuating the depletion of high-energy phosphates and the elevation of lactate. Extraluminal PFC perfusion during ischemia failed to produce a protective effect on high-energy phosphates, although it reduced lactate accumulation. Moderate hypothermia significantly decreased the degree of mucosal damage.

CONCLUSIONS

Whole-body moderate hypothermia protects the small intestine from reperfusion injury as measured both biochemically and histologically. Extraluminal oxygenated PFC administration during ischemia did not protect the intestine from reperfusion injury in this model.

Clinical trials in head injury

Traumatic brain injury (TBI) remains a major public health problem globally. In the United States the incidence of closed head injuries admitted to hospitals is conservatively estimated to be 200 per 100,000 population, and the incidence of penetrating head injury is estimated to be 12 per 100,000, the highest of any developed country in the world. This yields an approximate number of 500,000 new cases each year, a sizeable proportion of which demonstrate significant long-term disabilities. Unfortunately, there is a paucity of proven therapies for this disease. For a variety of reasons, clinical trials for this condition have been difficult to design and perform. Despite promising pre-clinical data, most of the trials that have been performed in recent years have failed to demonstrate any significant improvement in outcomes. The reasons for these failures have not always been apparent and any insights gained were not always shared. It was therefore feared that we were running the risk of repeating our mistakes. Recognizing the importance of TBI, the National Institute of Neurological Disorders and Stroke (NINDS) sponsored a workshop that brought together experts from clinical, research, and pharmaceutical backgrounds. This workshop proved to be very informative and yielded many insights into previous and future TBI trials. This paper is an attempt to summarize the key points made at the workshop. It is hoped that these lessons will enhance the planning and design of future efforts in this important field of research.

Management of large hemispheric strokes in the neurological intensive care unit

BACKGROUND

Patients with large hemispheric strokes frequently develop neurologic deterioration secondary to cerebral edema. Despite supportive care in the intensive care unit and traditional forms of therapy for cerebral edema, they have a high morbidity and mortality. New forms of therapy are being investigated to improve outcome in these patients.

REVIEW SUMMARY

This article begins with a discussion of the clinical and radiologic features of large hemispheric strokes. The role of increased intracranial pressure in neurologic deterioration and the predictors of outcome in these patients are reviewed. The various therapeutic options for management of cerebral edema in these patients, including the role of osmotic therapy, hypothermia, and hemicraniectomy, are explored.

CONCLUSIONS

Neurologic deterioration in patients with large hemispheric strokes necessitates admission to the intensive care unit for management of the airway, blood pressure, and cerebral edema. New promising therapies, such as hemicraniectomy and hypothermia, need to be further evaluated to define their role in the management of these patients.

Hypothermia and thiopentone sodium: individual and combined neuroprotective effects on cortical cultures exposed to prolonged hypoxic episodes

Because there are many conflicting reports on cerebroprotective effects of hypothermia and barbiturates, we examined the degree of neuroprotection at defined temperatures (normothermia, 37 degrees C; mild hypothermia, 32 degrees C; deep hypothermia, 22 degrees C; and profound hypothermia, 17 degrees C) and various concentrations (low, 4 microM; moderate, 40 microM; and high, 400 & microM) of thiopentone sodium (TPS), alone and in combination in cortical cultures exposed to prolonged hypoxia (24-48 hr). The survival rate of embryonic day (E)16 Wistar rat cortical neurons was evaluated on photomicrographs before and after experiments. During the 24-hr hypoxic period, the survival rate of neurons was maximal with combinations of mild hypothermia with 40 microM (91.6 +/- 0.7%) and 400 microM TPS (90.8 +/- 0.7%) or deep hypothermia combined with all concentrations of TPS (4 microM, 90.6 +/- 1.0%; 40 microM, 91.4 +/- 0.8%; 400 microM, 91.8 +/- 1.2%). During 48 hr hypoxia, the highest survival rate was seen with the combination of deep hypothermia and either 40 microM (90.9 +/- 0.6%) or 400 microM (91.1 +/- 1.4%) TPS. In the presence of profound hypothermia in combination with all concentrations of TPS, the survival rate was significantly reduced (P< 0.01) compared to combined application of either mild or deep hypothermia with TPS. In summary, maximal neuroprotection was attained with hypothermia and TPS in combination rather than applied individually, during prolonged hypoxic episodes (24- 48 hr). During a 24-hr hypoxic period, both mild and deep hypothermia combined with a clinically relevant concentration of TPS (40 microM) offered the highest neuroprotection. Only deep hypothermia provided maximal neuroprotection when combined with 40 microM TPS, during 48-hr hypoxia. Combination of profound hypothermia and TPS did not confer considerable neuroprotection during long lasting hypoxia.

Pharmacological correction of hypothermic P(50) shift does not alter outcome from focal cerebral ischemia in rats

Hypothermia decreases the arterial PO(2) at which hemoglobin is 50% saturated (P(50)), increasing hemoglobin O(2)-binding affinity. We used RSR13, a synthetic allosteric modifier of hemoglobin that increases P(50), to study the role of altered hemoglobin O(2)-binding affinity in mild hypothermic neuroprotection. RSR13 (150 mg/kg iv) restored P(50) to normothermic values. Rats underwent 70 min of middle cerebral artery occlusion (MCAO) at 30.0, 34.0, or 37.5 degrees C with hemoglobin saturation held at 98-100%. The 34.0 degrees C group received RSR13 or vehicle before ischemia. After 7 days of recovery, infarct volumes were reduced in all hypothermic groups, without evidence of a detrimental effect on infarct size or neurological score as a result of P(50) correction. To examine for a beneficial effect of P(50) correction, ischemia duration was increased to 120 min in rats maintained at 34.0 degrees C. Correction of P(50) by RSR13 did not alter cerebral infarct sizes or neurological scores. The decrease in P(50), caused by mild hypothermia, could not be associated with infarct size or neurological deficit resulting from ischemic brain hypoxia in rats.

Management of childhood neurotrauma

A summary of some of the more important aspects of brain, spinal, peripheral nerve and sport injuries of childhood is presented. Guidelines for the treatment of severe brain injury have been developed for adults, are currently employed with success to treat children, but much information still needs to be acquired about childhood brain injury so that better age specific treatment modalities could be implemented. The unique anatomy of the spine during childhood predisposes to cervical spinal injury without radiographic abnormality; immobilization is the primary treatment and a minority of cases require surgery. Peripheral nerve injuries are uncommon, often missed, and require skillful evaluation and early treatment by physical therapy and oftentimes surgery. Appreciation of the sequelae of cerebral concussion, education on proper sport techniques, body conditioning, and equipment upkeep are the mainstay of vigilant sport injury treatment and prevention.

Moderate hypothermia in severe head injuries: the present and the future

The use of therapeutic moderate hypothermia for treating severe traumatic brain injury has been reported for more than 50 years. However, the most intense investigation of this treatment has occurred during the last 10 to 15 years. Virtually all preclinical studies have documented a robust treatment effect, not only in terms of reduced excitotoxicity and cerebral acidosis, but also in terms of histologic preservation and improved behavioral outcomes. Several single-center and small multicenter clinical trials conducted during the last decade also demonstrated benefit of early and late therapeutic hypothermia. However, a multicenter trial reported in February 2001 that included nearly 400 patients found no notable differences in neurologic outcomes in matched patients with head injuries who were treated with 48 hours of therapeutic moderate hypothermia compared with those kept at normal temperature. Findings from this study did suggest that rapid rewarming of patients with head injuries may be deleterious. A subgroup of young patients (less than 45 years of age) who were kept normovolemic showed a trend toward improved outcomes when treated with hypothermia. Current investigations, particularly in the preclinical arena, are focusing on combination therapy. To date, however, the addition of fibroblast growth factor, cyclosporine, or interleukin (IL)-10 to therapeutic moderate hypothermia has not been found to provide greater benefit than either therapy when used alone. Future investigations are aimed at further identifying the physiologic mechanisms responsible for secondary brain injury and ways in which other novel combination therapies may be expected to improve outcomes.

Adequate cerebral perfusion pressure during rewarming to prevent ischemic deterioration after therapeutic hypothermia

Ischemic deterioration during rewarming is one of the most notable clinical complications after successful therapeutic cerebral hypothermia, but the mechanism is not completely understood. Hypothermia may cause vasoconstriction and relative ischemia, especially with insufficient cerebral perfusion pressure (CPP). Various parameters were evaluated to determine the critical CPP threshold to avoid ischemia during rewarming. Cat experimental head injury was induced by inflating an epidural rubber balloon, and intracranial pressure was maintained at 30 mmHg. During rewarming after cerebral hypothermia, CPP was maintained at >120 mmHg (n = 16), 90 mmHg (n = 11), 60 mmHg (n = 11), and 40 mmHg (n=4) by controlling the blood pressure. Cerebral blood flow, cerebral metabolic rate for oxygen, arteriovenous difference of oxygen (AVDO2), cerebral venous oxygen saturation (ScvO2), and extracellular glutamate concentrations were monitored by glutamate oxidase electrode. After rewarming, the cerebral metabolic parameters were almost restored to the pre-injury level in animals with CPP of more than 90mmHg. However, in the animals with CPP= 60 mmHg, all parameters significantly deteriorated and indicated misery perfusion; ScvO2 was low (29.5+/-1.1%), AVDO2 was significantly high (9.9+/-0.8 ml 100 g(-1) min(-1)) (one-way analysis of variance, p<0.05), and electron microscopic features showed subcellular ischemic change. Extracellular glutamate significantly increased during the rewarming period only in the CPP= 40 mmHg group. CPP less than 60 mmHg during rewarming causes secondary ischemic insult, which might indicate continuation of cerebral vasoconstriction in hypothermia. CPP higher than 90 mmHg is required to avoid the potential risk of relative ischemia after hypothermia.

Management of hyperthermia in traumatic brain injury

Recently there has been much interest in the use of hypothermia in the management of the brain-injured patient and its effect on outcome. Most of these studies examine the use of hypothermia compared with normothermia of 37 degrees C and have failed to demonstrate a benefit in the treatment groups, but what is normothermia in the brain-injured patient? Good epidemiologic evidence suggests that the vast majority of patients admitted to an ICU environment will develop a fever. The development of fever is clearly associated with a worse prognosis. There is now a better understanding of the possible mechanism of harm of fever and the side effects of cooling. Several treatment options for controlling temperature are discussed. Despite a sound physiologic argument for controlling fever in the brain-injured patient, there is no evidence that doing so will improve outcome.

Fluid thresholds and outcome from severe brain injury

OBJECTIVE

To determine, by retrospective analysis, critical thresholds for intracranial pressure, mean arterial pressure, cerebral perfusion pressure, and fluid balance associated with poor outcome in patients with severe brain injury.

DESIGN

Retrospective review of patient data from the prospective, randomized, multicenter National Acute Brain Injury Study: Hypothermia, comparing outcome results at 6 months after injury with intracranial pressure, mean arterial pressure, cerebral perfusion pressure, and fluid balance measurements recorded during the 96-hr period after randomization.

SETTING

Emergency departments and intensive care units in 11 metropolitan tertiary care university hospitals.

PATIENTS

A total of 392 patients, aged 16-65 yrs, with severe, nonpenetrating brain injuries and a Glasgow Coma Scale score of 3-8 after resuscitation, who were enrolled in a study designed to determine the treatment effect of moderate hypothermia in patients with severe brain injury.

INTERVENTION

Standard brain injury treatment for 193 randomly assigned patients and standard treatment plus hypothermia for 48 hrs for 199 patients.

MEASUREMENTS AND MAIN RESULTS

Intracranial pressure levels of 20, 25, and 30 mm Hg, mean arterial pressure levels of 70 and 80 mm Hg, cerebral perfusion pressure levels of 50, 60, and 70 mm Hg, and fluid balance levels in quartiles were examined for their effect on outcome as measured by the Glasgow Outcome Scale at 6 months after injury. When considered separately, any of the following-intracranial pressure >25 mm Hg, mean arterial pressure <70 mm Hg, or cerebral perfusion pressure <60 mm Hg and fluid balance lower than -594 mL-was associated with an increased percentage of patients with poor outcome. When the variables were combined into a stepwise logistic regression model, Glasgow Coma Scale score at admission, age, mean arterial pressure <70 mm Hg, fluid balance lower than -594 mL, and intracranial pressure > 25 mm Hg, in that order, were the most powerful variables in determining outcome.

CONCLUSIONS

Exceeding thresholds of intracranial pressure, mean arterial pressure, cerebral perfusion pressure, and fluid volume may be detrimental to severe brain injury outcome. Fluid balance lower than -594 mL was associated with an adverse effect on outcome, independent of its relationship to intracranial pressure, mean arterial pressure, or cerebral perfusion pressure.

Hypothermia on admission in patients with severe brain injury

Data from the "National Acute Brain Injury Study: Hypothermia" were examined to identify the impact of hypothermia on admission. In all patients, temperature was measured at randomization using bladder catheters with thermistors. Patients assigned to hypothermia were cooled using fluid-circulating pads. Outcome was assessed at 6 months using the dichotomized Glasgow Outcome Scale (good outcome = good recovery/moderate disability; poor outcome = severe disability/vegetative/dead). One-hundred and two patients (hypothermia, 62; normothermia, 40) were hypothermic on admission (< or =35.0 degrees C). Hypothermia-on-admission patients assigned to normothermia (n = 40) had a 78% poor outcome, and normothermia-on-admission patients assigned to normothermia had a 52% poor outcome (p < 0.004). Hypothermia-on-admission patients assigned to hypothermia had a lower percentage of poor outcomes than those assigned to normothermia (hypothermia, 61%; normothermia, 78%; p = 0.09). Patients over 45 years of age had an adverse effect of hypothermia regardless of admission temperature due to medical complications. Patients who were hypothermic on admission, age < or = 45 years (n = 81), and assigned to hypothermia had a significantly lower percentage of poor outcomes than those assigned to normothermia (hypothermia, 52%; normothermia, 76%; p = 0.02). Factors associated with hypothermia on admission were increased age, prehospital hypotension, smaller size, positive blood alcohol, larger volume of pre-hospital fluids, slightly higher injury severity, and winter enrollment The treatment effect was found in all of the four centers, which randomized the majority (80%) of the patients. It is unclear whether the improved outcome when hypothermia is maintained is a beneficial effect of very early hypothermia induction or an adverse effect of permitting the patients to rewarm passively.

Mild therapeutic hypothermia to improve the neurologic outcome after cardiac arrest

BACKGROUND

Cardiac arrest with widespread cerebral ischemia frequently leads to severe neurologic impairment. We studied whether mild systemic hypothermia increases the rate of neurologic recovery after resuscitation from cardiac arrest due to ventricular fibrillation.

METHODS

In this multicenter trial with blinded assessment of the outcome, patients who had been resuscitated after cardiac arrest due to ventricular fibrillation were randomly assigned to undergo therapeutic hypothermia (target temperature, 32 degrees C to 34 degrees C, measured in the bladder) over a period of 24 hours or to receive standard treatment with normothermia. The primary end point was a favorable neurologic outcome within six months after cardiac arrest; secondary end points were mortality within six months and the rate of complications within seven days.

RESULTS

Seventy-five of the 136 patients in the hypothermia group for whom data were available (55 percent) had a favorable neurologic outcome (cerebral-performance category, 1 [good recovery] or 2 [moderate disability]), as compared with 54 of 137 (39 percent) in the normothermia group (risk ratio, 1.40; 95 percent confidence interval, 1.08 to 1.81). Mortality at six months was 41 percent in the hypothermia group (56 of 137 patients died), as compared with 55 percent in the normothermia group (76 of 138 patients; risk ratio, 0.74; 95 percent confidence interval, 0.58 to 0.95). The complication rate did not differ significantly between the two groups.

CONCLUSIONS

In patients who have been successfully resuscitated after cardiac arrest due to ventricular fibrillation, therapeutic mild hypothermia increased the rate of a favorable neurologic outcome and reduced mortality.

Treatment of comatose survivors of out-of-hospital cardiac arrest with induced hypothermia

BACKGROUND

Cardiac arrest outside the hospital is common and has a poor outcome. Studies in laboratory animals suggest that hypothermia induced shortly after the restoration of spontaneous circulation may improve neurologic outcome, but there have been no conclusive studies in humans. In a randomized, controlled trial, we compared the effects of moderate hypothermia and normothermia in patients who remained unconscious after resuscitation from out-of-hospital cardiac arrest.

METHODS

The study subjects were 77 patients who were randomly assigned to treatment with hypothermia (with the core body temperature reduced to 33 degrees C within 2 hours after the return of spontaneous circulation and maintained at that temperature for 12 hours) or normothermia. The primary outcome measure was survival to hospital discharge with sufficiently good neurologic function to be discharged to home or to a rehabilitation facility.

RESULTS

The demographic characteristics of the patients were similar in the hypothermia and normothermia groups. Twenty-one of the 43 patients treated with hypothermia (49 percent) survived and had a good outcome--that is, they were discharged home or to a rehabilitation facility--as compared with 9 of the 34 treated with normothermia (26 percent, P=0.046). After adjustment for base-line differences in age and time from collapse to the return of spontaneous circulation, the odds ratio for a good outcome with hypothermia as compared with normothermia was 5.25 (95 percent confidence interval, 1.47 to 18.76; P=0.011). Hypothermia was associated with a lower cardiac index, higher systemic vascular resistance, and hyperglycemia. There was no difference in the frequency of adverse events.

CONCLUSIONS

Our preliminary observations suggest that treatment with moderate hypothermia appears to improve outcomes in patients with coma after resuscitation from out-of-hospital cardiac arrest.

Effect of hypothermia on brain tissue oxygenation in patients with severe head injury

BACKGROUND

There is renewed interest in the use of induced hypothermia as a method of neuroprotection both intraoperatively and in the intensive care management of severe brain injury. In this study we have investigated the effects of hypothermia on brain tissue oxygenation in patients with severe head injury.

METHODS

Thirty patients with severe head injury (Glasgow coma score <8) were monitored with a multimodal sensor inserted into the brain which measures tissue PO2, PCO2, pH and temperature in addition to routine monitoring. Patients were cooled to a minimum of 33 degrees C when clinically indicated.

RESULTS

For all 30 patients brain and systemic temperature correlated well (r=0.96). Brain temperature was consistently higher than systemic temperature by 0.41 +/- 0.26 degrees C (confidence limits). Brain tissue PO2 decreased with hypothermia, with a significant reduction below 35 degrees C (P<0.05).

CONCLUSIONS

These results emphasize the advantage of measuring brain temperature directly, and suggest that decreasing brain temperature below 35 degrees C may impair brain tissue oxygenation.

Direct influence of mild hypothermia on cytokine expression and release in cultures of human peripheral blood mononuclear cells

Hypothermia is associated with elevated frequency of infectious complications. Dysfunction of the immune response caused by hypothermia has been demonstrated in both clinical and animal studies, but it still remains unclear to what extent immunocompetent cells are directly influenced by hypothermia. To estimate the direct influence of mild hypothermia on cytokine expression and release by human peripheral blood mononuclear cells (PBMC), primary cultures of PBMC were incubated at 34 degrees C or 32 degrees C activated by lipopolysaccharide (LPS), phytohemagglutinin (PHA), or tumor necrosis factor-alpha (TNF-alpha). The cytokine gene expression was evaluated by RT-PCR. Release of interleukin-2 (IL-2), IL-6, IL-10, and TNF-alpha was measured by ELISA. Mild hyperthermia significantly impaired IL-2 gene expression in PHA-stimulated cultures of PBMC and decreased IL-2 release in all variants of cultures. Secretion of IL-6, IL-10, and TNF-alpha was decreased in hypothermic cultures of PBMC stimulated with the T lymphocyte activator PHA. Slight suppression of IL-10 secretion was observed also in TNF-alpha-stimulated hypothermic cultures of PBMC. TNF-alpha release increased slightly in mild hypothermia control cultures. Our data demonstrate that the direct influence of hypothermia on cytokine expression and release from PBMC is not uniform. Reduction of IL-2 production might play a crucial role in the impairment of immune response in hypothermia.

Misclassification and treatment effect on primary outcome measures in clinical trials of severe neurotrauma

The power of clinical trials depends mainly on the choice of the primary outcome measure, the statistical test, and the sample size. The most widely used outcome measure has been the five-category Glasgow Outcome Scale (GOS). Contrary to intuition, we show that more categories do not necessarily increase the power of a trial and actually can decrease power. This is so for two reasons. The more categories of outcome measure used, the more the likelihood for misclassifications. The effect of 0%, 10%, and 20% misclassification rate upon power is illustrated. Misclassification rates in two completed trials are examined based on comparative overlap in GOS and Disability Rating Scale (DRS) categories. The outcome results of the "National Acute Brain Injury Study: Hypothermia" indicate that the ideal number of categories also depends upon the effect of study treatment. In the recently completed hypothermia trial, the use of a dichotomized GOS (good recovery/moderate disability versus severe disability/vegetative/dead) is shown to be more sensitive than use of three or more categories of the GOS. The results point to the importance of training study investigators who will collect the outcome data. The results also indicate that the number of categories should be carefully determined using the pilot data or the data from phase II trials.

Cooling-induced carotid artery dilatation: an experimental study in isolated vessels

BACKGROUND AND PURPOSE

Clinical and experimental studies seem to indicate that hypothermia may improve outcome in stroke victims and reduce experimental brain injury. The current interpretation is that cooling has a neuroprotective effect by reducing brain metabolism. The objective of our study was to test the hypothesis that hypothermia induces arterial vasodilatation and thereby increases cerebral blood flow.

METHODS

We recorded isometric tension in rabbit carotid artery strips in organ baths during stepwise cooling. The cooling responses were tested at basal tone, in noradrenaline-precontracted vessels, and after electric field stimulation.

RESULTS

Stepwise cooling from 37 degrees C to 4 degrees C induced reproducible graded relaxation, inversely proportional to temperature. The responses could be elicited at basal tone and in precontracted vessels. Cooling decreased the contractile responses to norepinephrine and potassium chloride. Cooling at 20 degrees C decreased the contractile responses to electric field stimulation, while at 10 degrees C these were totally abolished. Cooling-induced vasodilatation is not dependent on an endothelial mechanism.

CONCLUSIONS

Cooling of carotid artery preparations induced a reversible graded vasodilatation and decreased or abolished the effect of vasocontractile neurotransmitters. The effect of local hypothermia could increase cerebral blood flow and may constitute a positive therapeutic modality in stroke patients.

Mild hypothermia attenuates cytochrome c release but does not alter Bcl-2 expression or caspase activation after experimental stroke

Mild hypothermia protects the brain from ischemia, but the underlying mechanisms of this effect are not well known. The authors previously found that hypothermia reduces the density of apoptotic cells, but it is not certain whether temperature alters associated biochemical events. Mitochondrial release of cytochrome c has recently been shown to be a key trigger in caspase activation and apoptosis via the intrinsic pathway. Using a model of transient focal cerebral ischemia, the authors determined whether mild hypothermia altered expression of Bcl-2 family proteins, mitochondrial release of cytochrome c, and caspase activation. Mild hypothermia significantly decreased the amount of cytochrome c release 5 hours after the onset of ischemia, but mitochondrial translocation of Bax was not observed until 24 hours. Mild hypothermia did not alter Bcl-2 and Bax expression, and caspase activation was not observed. The present study provides the first evidence that intraischemic mild hypothermia attenuates the release of cytochrome c in the brain, but does not appear to affect other biochemical aspects of the intrinsic apoptotic pathway. They conclude that necrotic processes may have been interrupted to prevent cytochrome c release, and that the ameliorative effect of mild hypothermia may be a result of maintaining mitochondrial integrity. Furthermore, the authors show it is unlikely that mild hypothermia alters the intrinsic apoptotic pathway.

Acetaminophen for altering body temperature in acute stroke: a randomized clinical trial

BACKGROUND AND PURPOSE

Mild alterations in temperature have prominent effects on ischemic cell injury and stroke outcome. Elevated core body temperature (CBT), even if mild, may exacerbate neuronal injury and worsen outcome, whereas hypothermia is potentially neuroprotective. The antipyretic effects of acetaminophen were hypothesized to reduce CBT.

METHODS

This was a randomized, controlled clinical trial at 2 university hospitals. Patients were included if they had stroke within 24 hours of onset of symptoms, National Institutes of Health Stroke Scale (NIHSS) score > or =5, initial CBT <3 8.5 degrees C, and white blood cell count < 12 600 cells/mm(3); they were excluded if they had signs of infection, severe medical illness, or contraindication to acetaminophen. CBT was measured every 30 minutes. Patients were randomized to receive acetaminophen 650 mg or placebo every 4 hours for 24 hours. The primary outcome measure was mean CBT during the 24-hour study period; the secondary outcome measure was the change in NIHSS.

RESULTS

Thirty-nine patients were randomized. Baseline CBT was the same: 36.96 degrees C for acetaminophen versus 36.95 degrees C for placebo (P=0.96). During the study period, CBT tended to be lower in the acetaminophen group (37.13 degrees C versus 37.35 degrees C), a difference of 0.22 degrees C (95% CI, -0.08 degrees C to 0.51 degrees C; P=0.14). Patients given acetaminophen tended to be more often hypothermic <36.5 degrees C (OR, 3.4; 95% CI, 0.83 to 14.2; P=0.09) and less often hyperthermic >37.5 degrees C (OR, 0.52; 95% CI, 0.19 to 1.44; P=0.22). The change in NIHSS scores from baseline to 48 hours did not differ between the groups (P=0.93).

CONCLUSIONS

Early administration of acetaminophen (3900 mg/d) to afebrile patients with acute stroke may result in a small reduction in CBT. Acetaminophen may also modestly promote hypothermia <36.5 degrees C or prevent hyperthermia >37.5 degrees C. These effects are unlikely to have robust clinical impact, and alternative or additional methods are needed to achieve effective thermoregulation in stroke patients.

Neurotensin analog NT69L induces rapid and prolonged hypothermia after hypoxic ischemia

OBJECTIVE

To determine whether the neurotensin analog NT69L, administered systemically, could induce mild brain hypothermia after asphyxial cardiac arrest (ACA) in rats.

METHODS

The study design was experimental, blinded, randomized, and approved by the animal use committee. All rats had continuous monitoring of brain temperature and sustained 8 minutes of ACA, resuscitation, and either saline or NT69L intravenously after return of spontaneous circulation (ROSC). Rats surviving 14 days after ACA had a neurological deficit score (NDS) and a Morris Water Maze (MWM) test.

RESULTS

Seven of eight rats in each group survived 14 days. Brain temperature was less than 35 degrees C 13.1 +/- 3 minutes (mean +/- standard deviation) after NT69L vs controls that remained 37.5 degrees C at the same ambient temperature (p < 0.05 ANOVA). The NT69L group remained below 35 degrees C for 300 +/- 100 minutes while the controls remained at 37.5 +/- 0.5 degrees C. The NDS in the NT69L rats was 3 +/- 3% vs controls 26 +/- 8% (p < 0.05, Kruskal-Wallis, 0% = normal, 100% = brain dead). The NT69L rats performed better on the MWM vs the controls (22 +/- 8 sec vs 45 +/- 26 sec, respectively, p < 0.05 ANOVA).

CONCLUSIONS

NT69L induced rapid and prolonged mild brain hypothermia after ACA in this rat model and reduced neurological deficits.

Treatment window for hypothermia in brain injury

OBJECT

The goal of this study was to evaluate the therapeutic window for hypothermia treatment following experimental brain injury by measuring edema formation and functional outcome.

METHODS

Traumatic brain injury (TBI) was produced in anesthetized rats by using cortical impact injury. Edema was measured in the ipsilateral and contralateral hemispheres by subtracting dry weight from wet weight, and neurological function was assessed using a battery of behavioral tests 24 hours after TBI. In injured rats, it was found that brain water levels were elevated at I hour postinjury, compared with those in sham-injured control animals, and that edema peaked at 24 hours and remained elevated for 4 days. Hypothermia (3 hours at 30 degrees C) induced either immediately after TBI or 60 minutes after TBI significantly reduced early neurological deficits. Delay of treatment by 90 or 120 minutes postinjury did not result in this neurological protection. Immediate administration of hypothermia also significantly decreased the peak magnitude of edema at 24 hours and 48 hours postinjury, compared with that in normothermic injured control animals. When delayed by 90 minutes, hypothermia did not affect the pattern of edema formation.

CONCLUSIONS

When hypothermia was administered immediately or 60 minutes after TBI, injured rats showed an improvement in functional outcome and a decrease in edema. Delayed hypothermia treatment had no effect on functional outcome or on edema.

Prehospital and resuscitative care of the head-injured patient

The ultimate neurologic outcome following severe head trauma depends on the extent of primary brain insult sustained at the time of the trauma itself, and the subsequent neurochemical and neurophysiologic pathologic changes occurring as a result of the injury. Although there are currently no specific therapies that have proven to be consistently effective in reversing the devastating consequences of primary brain insult, the reduction or prevention of secondary brain insult is possible. The emergent resuscitation and care of the severely head injured patient can therefore impact the patient's final neurologic outcome. As new data are accumulated, traditional and new therapies for severe head injury have come under scrutiny. While no absolute standards have been advanced, guidelines have been established that can help direct the acute stabilization of severely head injured patients.

Current controversies in shock and resuscitation

Many controversies and uncertainties surround resuscitation of hemorrhagic shock caused by vascular trauma. Whereas the basic pathophysiology is better understood, much remains to be learned about the many immunologic cascades that lead to problems beyond those of initial fluid resuscitation or operative hemostasis. Fluid therapy is on the verge of significant advances with substitute oxygen carriers, yet surgeons are still beset with questions of how much and what type of initial fluid to provide. Finally, the parameters chosen to guide therapy and the methods used to monitor patients present other interesting issues.

Buspirone and meperidine synergistically reduce the shivering threshold

Mild hypothermia (i.e., 34 degrees C) may prove therapeutic for patients with stroke, but it usually provokes shivering. We tested the hypothesis that the combination of buspirone (a serotonin 1A partial agonist) and meperidine synergistically reduces the shivering threshold (triggering tympanic membrane temperature) to at least 34 degrees C while producing little sedation or respiratory depression. Eight volunteers each participated on four randomly-assigned days: 1) large-dose oral buspirone (60 mg); 2) large-dose IV meperidine (target plasma concentration of 0.8 microg/mL); 3) the combination of buspirone (30 mg) and meperidine (0.4 microg/mL); and 4) a control day without drugs. Core hypothermia was induced by infusion of lactated Ringer's solution at 4 degrees C. The control shivering threshold was 35.7 degrees C +/- 0.2 degrees C. The threshold was 35.0 degrees C +/- 0.8 degrees C during large-dose buspirone and 33.4 degrees C +/- 0.3 degrees C during large-dose meperidine. The threshold during the combination of the two drugs was 33.4 degrees C +/- 0.7 degrees C. There was minimal sedation on the buspirone and combination days and mild sedation on the large-dose meperidine day. End-tidal PCO2 increased approximately 10 mm Hg with meperidine alone. Buspirone alone slightly reduced the shivering threshold. The combination of small-dose buspirone and small-dose meperidine acted synergistically to reduce the shivering threshold while causing little sedation or respiratory toxicity.

IMPLICATIONS

Mild hypothermia may be an effective treatment for acute stroke, but it usually triggers shivering, which could be harmful. Our results indicate that the combination of small-dose buspirone and small-dose meperidine acts synergistically to reduce the shivering threshold while causing little sedation or respiratory toxicity. This combination may facilitate the induction of therapeutic hypothermia in stroke victims.

Intercenter variance in clinical trials of head trauma--experience of the National Acute Brain Injury Study: Hypothermia

OBJECT

In a recently conducted trial of hypothermia in patients with severe brain injury, differences were found in the effects of hypothermia treatment among various centers. This analysis explores the reasons for such differences.

METHODS

The authors reviewed data obtained in 392 patients treated for severe brain injury. Prerandomization variables, critical physiological variables, treatment variables, and accrual methodologies were investigated among various centers. Hypothermia was found to be detrimental in patients older than the age of 45 years, beneficial in patients younger than 45 years of age in whom hypothermia was present on admission, and without effect in those in whom normothermia was documented on admission. Marginally significant differences (p < 0.054) in the intercenter outcomes of hypothermia-treated patients were likely the result of wide differences in the percentage of patients older than 45 years of age and in the percentage of patients in whom hypothermia was present on admission among centers. The trial sensitivity was likely diminished by significant differences in the incidence of mean arterial blood pressure (MABP) less than 70 mm Hg (p < 0.001) and cerebral perfusion pressure (CPP) less than 50 mm Hg (p < 0.05) but not intracranial pressure (ICP) greater than 25 mm Hg (not significant) among patients in the various centers. Hours of vasopressor usage (p < 0.03) and morphine dose (p < 0.001) and the percentage of dehydrated patients varied significantly among centers (p < 0.001). The participation of small centers increased intercenter variance and diminished the quality of data.

CONCLUSIONS

For Phase III clinical trials we recommend: 1) a detailed protocol specifying fluid and MABP, ICP, and CPP management: 2) continuous monitoring of protocol compliance; 3) a run-in period for new centers to test accrual and protocol adherence; and 4) inclusion of only centers in which patients are regularly randomized.

Posttraumatic hypothermia is neuroprotective in a model of traumatic brain injury complicated by a secondary hypoxic insult

OBJECTIVE

Human traumatic brain injury frequently results in secondary complications, including hypoxia. In previous studies, we have reported that posttraumatic hypothermia is neuroprotective and that secondary hypoxia exacerbates histopathologic outcome after fluid-percussion brain injury. The purpose of this study was to assess the therapeutic effects of mild (33 degrees C) hypothermia after fluid-percussion injury combined with secondary hypoxia. In addition, the importance of the rewarming period on histopathologic outcome was investigated.

DESIGN

Prospective experimental study in rats.

SETTING

Experimental laboratory in a university teaching hospital.

INTERVENTION

Intubated, anesthetized rats underwent normothermic parasagittal fluid-percussion brain injury (1.8-2.1 atmospheres) followed by either 30 mins of normoxia (n = 6) or hypoxic (n = 6) gas levels and by 4 hrs of normothermia (37 degrees C). In hypothermic rats, brain temperature was reduced immediately after the 30-min hypoxic insult and maintained for 4 hrs. After hypothermia, brain temperature was either rapidly (n = 6) or slowly (n = 5) increased to normothermic levels. Rats were killed 3 days after traumatic brain injury, and contusion volumes were quantitatively assessed.

MEASUREMENTS AND MAIN RESULTS

As previously shown, posttraumatic hypoxia significantly increased contusion volume compared with traumatic brain injury-normoxic animals (p <.02). Importantly, although posttraumatic hypothermia followed by rapid rewarming (15 mins) failed to decrease contusion volume, those animals undergoing a slow rewarming period (120 mins) demonstrated significantly (p <.03) reduced contusion volumes, compared with hypoxic normothermic rats.

CONCLUSIONS

These data emphasize the beneficial effects of posttraumatic hypothermia in a traumatic brain injury model complicated by secondary hypoxia and stress the importance of the rewarming period in this therapeutic intervention.

Hypothermia after cardiac arrest: feasibility and safety of an external cooling protocol

BACKGROUND

No proven neuroprotective treatment exists for ischemic brain injury after cardiac arrest. Mild-to-moderate induced hypothermia (MIH) is effective in animal models.

METHODS AND RESULTS

A safety and feasibility trial was designed to evaluate mild-to-moderate induced hypothermia by use of external cooling blankets after cardiac arrest. Inclusion criteria were return of spontaneous circulation within 60 minutes of advanced cardiac life support, hypothermia initiated within 90 minutes, persistent coma, and lack of acute myocardial infarction or unstable dysrhythmia. Hypothermia to 33 degrees C was maintained for 24 hours followed by passive rewarming. Nine patients were prospectively enrolled. Mean time from advanced cardiac life support to return of spontaneous circulation was 11 minutes (range 3 to 30); advanced cardiac life support to initiation of hypothermia was 78 minutes (range 40 to 109); achieving 33 degrees C took 301 minutes (range 90 to 690). Three patients completely recovered, and 1 had partial neurological recovery. One patient developed unstable cardiac dysrhythmia. No other unexpected complications occurred.

CONCLUSIONS

Mild-to-moderate induced hypothermia after cardiac arrest is feasible and safe. However, external cooling is slow and imprecise. Efforts to speed the start of cooling and to improve the cooling process are needed.

Brain temperature, body core temperature, and intracranial pressure in acute cerebral damage

OBJECTIVES

To assess the frequency of hyperthermia in a population of acute neurosurgical patients; to assess the relation between brain temperature (ICT) and core temperature (Tc); to investigate the effect of changes in brain temperature on intracranial pressure (ICP).

METHODS

The study involved 20 patients (10 severe head injury, eight subarachnoid haemorrhage, two neoplasms) with median Glasgow coma score (GCS) 6. ICP and ICT were monitored by an intraventricular catheter coupled with a thermistor. Internal Tc was measured in the pulmonary artery by a Swan-Ganz catheter.

RESULTS

Mean ICT was 38.4 (SD 0.8) and mean Tc 38.1 (SD 0.8) degrees C; 73% of ICT and 57.5% of Tc measurements were > or =38 degrees C. The mean difference between ICT and Tc was 0.3 (SD 0.3) degrees C (range -0.7 to 2.3 degrees C) (p=0. 0001). Only in 12% of patients was Tc higher than ICT. The main reason for the differences between ICT and Tc was body core temperature: the difference between ICT and Tc increased significantly with body core temperature and fell significantly when this was lowered. The mean gradient between ICT and Tc was 0.16 (SD 0.31) degrees C before febrile episodes (ICT being higher than Tc), and 0.41 (SD 0.38) degrees C at the febrile peak (p<0.05). When changes in temperature were considered, ICT had a profound influence on ICP. Increases in ICT were associated with a significant rise in ICP, from 14.9 (SD 7.9) to 22 (SD 10.4) mm Hg (p<0.05). As the fever ebbed there was a significant decrease in ICP, from 17.5 (SD 8.62) to 16 (SD 7.76) mm Hg (p=0.02).

CONCLUSIONS

Fever is extremely frequent during acute cerebral damage and ICT is significantly higher than Tc. Moreover, Tc may underestimate ICT during the phases when temperature has the most impact on the intracranial system because of the close association between increases in ICT and ICP.

Neuroprotective adaptations in hibernation: therapeutic implications for ischemia-reperfusion, traumatic brain injury and neurodegenerative diseases

Brains of hibernating mammals are protected against a variety of insults that are detrimental to humans and other nonhibernating species. Such protection is associated with a number of physiological adaptations including hypothermia, increased antioxidant defense, metabolic arrest, leukocytopenia, immunosuppression, and hypocoagulation. It is intriguing that similar manipulations provide considerable protection as experimental treatments for central nervous system injury. This review focuses on neuroprotective mechanisms employed during hibernation that may offer novel approaches in the treatment of stroke, traumatic brain injury, and neurodegenerative diseases in humans.

Increased Intracerebral Pressure Following Stroke

Increased intracerebral pressure with lethal herniation still accounts for high mortality rates in patients with massive strokes. Patients that are likely to develop increased intracranial pressure can often be identified within the first few hours after stroke onset. Although medical management seems to fail in most of these patients, early hemicraniectomy and induced moderate hypothermia (32;C to 33;C) represent two novel therapeutic approaches to improve neurologic outcomes and decrease mortality rates.

Hypothermia for the management of intracranial hypertension in acute liver failure

Increased intracranial pressure in patients with acute liver failure remains a major cause of mortality. Treatment options are limited, and without urgent liver transplantation, mortality rates of up to 90% are common in those who fulfill criteria for poor prognosis. Several studies in animal models of acute liver failure set the stage for the clinical application of moderate hypothermia in humans. Few patients are treated with hypothermia for increased intracranial pressure. However, data indicate that moderate hypothermia is a safe and effective method of treatment for increased intracranial pressure that is unresponsive to other medical therapies, and that this treatment can be used as a successful bridge to liver transplantation. Recent data also suggest that increases in intracranial pressure can be prevented during the dissection and reperfusion phases of liver transplantation for acute liver failure if patients are kept hypothermic during the surgical procedure. This article focuses on the use of moderate hypothermia for the treatment of increased intracranial pressure in patients with acute liver failure.

Cooling for acute ischemic brain damage (cool aid): an open pilot study of induced hypothermia in acute ischemic stroke

BACKGROUND AND PURPOSE

Hypothermia is effective in improving outcome in experimental models of brain infarction. We studied the feasibility and safety of hypothermia in patients with acute ischemic stroke treated with thrombolysis.

METHODS

An open study design was used. All patients presented with major ischemic stroke (National Institutes of Health Stroke Scale [NIHSS] score >15) within 6 hours of onset. After informed consent, patients with a persistent NIHSS score of >8 were treated with hypothermia to 32+/-1 degrees C for 12 to 72 hours depending on vessel patency. All patients were monitored in the neurocritical care unit for complications. A modified Rankin Scale was measured at 90 days and compared with concurrent controls.

RESULTS

Ten patients with a mean age of 71.1+/-14.3 years and an NIHSS score of 19.8+/-3.3 were treated with hypothermia. Nine patients served as concurrent controls. The mean time from symptom onset to thrombolysis was 3.1+/-1.4 hours and from symptom onset to initiation of hypothermia was 6.2+/-1.3 hours. The mean duration of hypothermia was 47.4+/-20.4 hours. Target temperature was achieved in 3.5+/-1.5 hours. Noncritical complications in hypothermia patients included bradycardia (n=5), ventricular ectopy (n=3), hypotension (n=3), melena (n=2), fever after rewarming (n=3), and infections (n=4). Four patients with chronic atrial fibrillation developed rapid ventricular rate, which was noncritical in 2 and critical in 2 patients. Three patients had myocardial infarctions without sequelae. There were 3 deaths in patients undergoing hypothermia. The mean modified Rankin Scale score at 3 months in hypothermia patients was 3.1+/-2.3.

CONCLUSION

Induced hypothermia appears feasible and safe in patients with acute ischemic stroke even after thrombolysis. Refinements of the cooling process, optimal target temperature, duration of therapy, and, most important, clinical efficacy, require further study.