The use of moderate therapeutic hypothermia for patients with severe head injuries: a preliminary report

Therapeutic hypothermia: past, present, and future

Cardiac arrest causes devastating neurologic morbidity and mortality. The preservation of the brain function is the final goal of resuscitation. Therapeutic hypothermia (TH) has been considered as an effective method for reducing ischemic injury of the brain. The therapeutic use of hypothermia has been utilized for millennia, and over the last 50 years has been routinely employed in the operating room. TH gained recognition in the past 6 years as a neuroprotective agent in victims of cardiac arrest after two large, randomized, prospective clinical trials demonstrated its benefits in the postresuscitation setting. Extensive research has been done at the cellular and molecular levels and in animal models. There are a number of proposed applications of TH, including traumatic brain injury, acute encephalitis, stroke, neonatal hypoxemia, and near-drowning, among others. Several devices are being designed with the purpose of decreasing temperature at a fast and steady rate, and trying to avoid potential complications. This article reviews the historical development of TH, and its current indications, methods of induction, and potential future.

Induced hypothermia and fever control for prevention and treatment of neurological injuries

Increasing evidence suggests that induction of mild hypothermia (32-35 degrees C) in the first hours after an ischaemic event can prevent or mitigate permanent injuries. This effect has been shown most clearly for postanoxic brain injury, but could also apply to other organs such as the heart and kidneys. Hypothermia has also been used as a treatment for traumatic brain injury, stroke, hepatic encephalopathy, myocardial infarction, and other indications. Hypothermia is a highly promising treatment in neurocritical care; thus, physicians caring for patients with neurological injuries, both in and outside the intensive care unit, are likely to be confronted with questions about temperature management more frequently. This Review discusses the available evidence for use of controlled hypothermia, and also deals with fever control. Besides discussing the evidence, the aim is to provide information to help guide treatments more effectively with regard to timing, depth, duration, and effective management of side-effects. In particular, the rate of rewarming seems to be an important factor in establishing successful use of hypothermia in the treatment of neurological injuries.

Selective hypothermia: an experimental study on traumatic brain injury in rats

OBJECTIVE: To evaluate the efficiency of selective hypothermia in the treatment of the traumatic brain injury in rats. METHOD: After the trauma produced for the model of cortical impact, a small craniectomy in the right frontoparietal region was carried through; after the procedure the animals had been divided in two groups of 15 each. Group A, without treatment with hypothermia (control group) and group B, treated with selective hypothermia for a period to 5 to 6 hours. After this time all the animals were sacrificed, their brains had been removed and histopathological analysis was carried through. RESULTS: Comparison between both groups was done using the counting of neurons injured for field. Counting in the control group n=15 had an average of 70.80 neurons injured for field against an average of 21.33 neurons injured for field in group B (submitted to the treatment with hypothermia), with n=15 also. The difference was statiscally significant. CONCLUSION: Based in the quantification of the neurons injured for field, the effectiveness of the treatment with selective hypothermia was demonstrated.

Use of induced hypothermia for neuroprotection: indications and application

Therapeutic temperature regulation has become an exciting field of interest. Mild-to-moderate hypothermia is a safe and feasible management strategy for neuroprotection and control of intracranial pressure in neurological catastrophies such as traumatic brain injury, subarachnoid and intracerebral hemorrhage, and large hemispheric stroke. Fever is associated with worse neurological outcome in patients with brain injury, normothermia may be of benefit in this patient population. The efficacy of mild-to-moderate hypothermia has been proven for neuroprotection after cardiac arrest with ventricular fibrillation as initial rhythm, and after neonatal asphyxia. Application of hypothermia and fever control in neurocritical care, available cooling technologies and systemic effects and complications of hypothermia will be discussed.

A prospective, observational clinical trial of fever reduction to reduce systemic oxygen consumption in the setting of acute brain injury

INTRODUCTION

Fever after acute brain injury appears to be a detrimental factor, associated with impaired neurological outcomes. This study assessed physiological changes in systemic oxygen consumption (VO2) during cutaneous cooling after severe brain injury.

METHODS

This prospective, observational, clinical study evaluated ten, critically ill, brain-injured patients requiring mechanical ventilation with a core body temperature of greater or equal to 38 degrees C. Febrile patients failing to defervesce after acetaminophen underwent indirect calorimetry for a 1-hour baseline period followed by a 4 h cooling period. The Arctic Sun(R) Temperature Management System (Medivance) directed core temperature to a goal of 36 degrees C.

RESULTS

The patients had a mean age of 32 years (95% CI 23, 40), Glasgow Coma Scale of 6 (95% CI 5,7), and APACHE 2 score of 19 (95% CI 15, 22), with 8 of 10 patients suffering traumatic brain injuries. The baseline 1-h core temperature was significantly reduced from 38.6 degrees +/- 0.9 to 36.3 degrees +/- 1.2 degrees C (P < 0.0001) over 4 h. Two cohorts were identified based upon the presence or absence of shivering. Within the non-shivering cohort, systemic VO2 was significantly reduced from 415 +/- 123 to 308 +/- 115 ml/min (-27 +/- 18%) (P < 0.05). In contrast, those with shivering showed no significant reduction in VO2, despite significantly decreasing core temperature. The overall percentage change of VCO2 correlated with VO2 (r (2) = 0.91).

CONCLUSION

Fever reduction in acute brain injury appears to significantly reduce systemic VO2, but is highly dependent on shivering control.

The acute care of traumatic brain injury

During the past few decades, management of acute traumatic brain injury has advanced substantially on several fronts. Implementation of rapid transport systems and the advent of trauma centres, together with advances in emergency medicine, critical care medicine and trauma neurosurgery, have improved outcome following head injury. Technological advances made during the past years in the field of invasive neuromonitoring that provide real-time information on brain oxygenation may further improve outcome by enabling individualized therapies for intracranial hypertension. Furthermore, these recent technological advances will provide insights into the pathophysiological processes that are active in traumatic brain injury and a better understanding of the biochemical effects of specific therapeutic regimens.

A theoretical model of selective cooling using intracarotid cold saline infusion in the human brain

A three-dimensional mathematical model was developed to examine the transient and steady-state temperature distribution in the human brain during selective brain cooling (SBC) by unilateral intracarotid freezing-cold saline infusion. To determine the combined effect of hemodilution and hypothermia from the cold saline infusion, data from studies investigating the effect of these two parameters on cerebral blood flow (CBF) were pooled, and an analytic expression describing the combined effect of the two factors was derived. The Pennes bioheat equation used the thermal properties of the different cranial layers and the effect of cold saline infusion on CBF to propagate the evolution of brain temperature. A healthy brain and a brain with stroke (ischemic core and penumbra) were modeled. CBF and metabolic rate data were reduced to simulate the core and penumbra. Simulations using different saline flow rates were performed. The results suggested that a flow rate of 30 ml/min is sufficient to induce moderate hypothermia within 10 min in the ipsilateral hemisphere. The brain with stroke cooled to lower temperatures than the healthy brain, mainly because the stroke limited the total intracarotid blood flow. Gray matter cooled twice as fast as white matter. The continuously falling hematocrit was the main time-limiting factor, restricting the SBC to a maximum of 3 h. The study demonstrated that SBC by intracarotid saline infusion is feasible in humans and may be the fastest method of hypothermia induction.

Therapeutic hypothermia in acute ischemic stroke

Increased body temperatures are common in the acute phase of stroke. Experimental and clinical studies have suggested that increased body temperatures are related to poor outcome. In animal studies of focal cerebral ischemia, early hypothermia consistently reduced infarct volume. Based on these findings, several Phase II clinical trials have been performed to study physical methods to reduce body temperature in patients with acute stroke. The feasibility and safety of these methods have not yet been established with sufficient certainty. Pharmacological lowering of body temperature may be an attractive alternative approach. In guidelines for the treatment of acute stroke, antipyretics are generally recommended to reduce fever, although their effect on functional outcome is unknown. There is currently no evidence from randomized trials to support routine use of physical or pharmacological cooling in acute stroke. Large randomized clinical trials are needed to study the effect of both physical and medical cooling on functional outcome after stroke.

Successful Use of Prolonged Mild Hypothermia in a Patient With Severe Head Injury and Diffuse Brain Swelling-Case Report-

A 19-year-old female was admitted to our hospital after severe head injury in a traffic accident. On admission, she had no spontaneous respiration, but did have heart beat with a blood pressure of 100/60 mmHg. Neurological examination demonstrated that the Glasgow Coma Scale score was 3 and her pupils were fixed and dilated. Computed tomography (CT) showed diffuse brain swelling with disappearance of the perimesencephalic cistern. Chest CT showed bilateral lung contusions. Mild hypothermia with a target temperature of 33 degrees C was immediately induced, and was continued for 28 days to control the persistent increase in intracranial pressure (ICP). Subsequently, she recovered, and 20 months after admission, could speak and walk with slight hemiparesis on the left. Prolonged mild hypothermia may be effective to control persistent increase in ICP due to diffuse brain swelling.

Therapeutic effect of hypothermia and dizocilpine maleate on traumatic brain injury in neonatal rats

This study was undertaken to evaluate the therapeutic effect of hypothermia and dizocilpine maleate in traumatic brain injury (TBI) on newborn rats. After induction of TBI, physiologic and histopathological assessments were performed on both the control and therapeutic groups to evaluate the effects of both agents. Rats were assigned into four groups as follows: normothermic (n = 23), hypothermic (n = 18), normothermia plus dizocilpine maleate (n = 18) and hypothermia plus dizocilpine maleate (n = 18). All the rats were injured using a weight-drop head injury model, artificially ventilated with a 33% O(2) and 66% NO(2) mixture, and physiological parameters, intracranial pressure, and brain and rectal temperatures were recorded. Mortality, physiological, neurological parameters, and histopathological changes were assessed after 24 h. As a result, intracranial pressure, cerebral perfusion pressure, morbidity, weight loss, and microscopic changes were significantly worse in the normothermic group (p <0.05). There was no statistical difference between other groups (p > 0.05). Hypothermia and dizocilpine maleate displayed similar neuroprotective effects in TBI on newborn rats, but no additive effect was observed.

Temperature Management in Acute Neurologic Disorders

Temperature management in acute neurologic disorders has received considerable attention in the last 2 decades. Numerous trials of hypothermia have been performed in patients with head injury, stroke, and cardiac arrest. This article reviews the physiology of thermoregulation and mechanisms responsible for hyperpyrexia. Detrimental effects of fever and benefits of normalizing elevated temperature in experimental models are discussed. This article presents a detailed analysis of trails of induced hypothermia in patients with acute neurologic insults and describes methods of fever control.

Reliability and validity of the Pediatric Intensity Level of Therapy (PILOT) scale: a measure of the use of intracranial pressure-directed therapies

OBJECTIVE

To test the reliability and validity of the Pediatric Intensity Level of Therapy (PILOT) scale, a novel measure of overall therapeutic effort directed at controlling intracranial pressure (ICP) in the setting of severe (Glasgow Coma Scale of <or= 8) pediatric traumatic brain injury (TBI).

DESIGN

Case-control study via retrospective review of medical records.

SETTING

Tertiary-care, university-based children's hospital intensive care unit.

PATIENTS

Randomly selected patients <or=18 yrs old admitted to the intensive care unit in 2002-2003 with severe TBI (cases: group 1, n = 27), mild-moderate TBI (control: group 2, n = 30), extracranial trauma (control: group 3, n = 29), or nontraumatic illnesses (control: group 4, n = 27).

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

A 38-point scale was developed to quantify daily ICP-directed therapeutic effort. All currently recommended therapies are represented. Demographic and physiologic data were collected on all patients. A total of 24 of 27 patients with severe TBI received ICP-directed therapy; three did not because of judgments of futility. No control patients received ICP-directed therapy. The PILOT scale score was assessed for the first 7 days posttrauma or postadmission. Interrater reliability was 0.91 (intraclass correlation coefficient) and intrarater reliability was 0.94. The highest PILOT scale scores were in patients with severe TBI (11.7 +/- 5.6 vs. 1.3 +/- 1.7 vs. 2.0 +/- 2.1 vs. 1.9 +/- 1.8 for groups 1, 2, 3 and 4, respectively [mean +/- sd]; p < .001 by analysis of variance/Bonferroni). Patients with severe TBI who received ICP-directed therapy had higher PILOT scale scores (12.6 +/- 5.3 vs. 5.0 +/- 3.0, p = .001) than those who did not. Pearson's correlation coefficients of mean PILOT scale scores with measures of injury severity, outcome, and ICP were as follows: Glasgow Coma Scales score, -0.73 (p < .001); overall Injury Severity Score, 0.37 (p < .001); Injury Severity Score (head component only), 0.53 (p < .001); 6-month Glasgow Outcome Scale, -0.26 (p = .006); ICP burden (hours per day with ICP above treatment threshold), 0.59 (p = .002); and mean ICP, 0.41 (p = .044).

CONCLUSIONS

The PILOT scale score can be obtained retrospectively and has good reliability. It can discriminate patients receiving ICP-directed therapy, even among patients with severe TBI, and correlates with measures of injury severity, outcome, and ICP in an expected way. Thus, it seems to be a valid measure of the use of ICP-directed therapy, although prospective, multiple-center validation is recommended.

Body temperature management after severe traumatic brain injury: methods and protocols used in the United Kingdom and Ireland

OBJECTIVE

To establish whether there is consensus in the management of body temperature in patients with severe traumatic brain injury (TBI) admitted to hospitals in the United Kingdom and Ireland for neurosurgical intensive care.

METHODS

Permission was granted from the Society of British Neurosurgeons (SBNS) and the Local Research Ethics Committee to undertake the survey. A senior member of nursing staff from all adult neurosurgical units, excluding our own, was contacted by telephone.

RESULTS

All 33 adult neurosurgical centres participated. Six units had a formal written protocol for the management of body temperature. For the remainder (27 units), interest was expressed in a protocol for temperature management particularly for those patients with intractable hyperthermia/fever. Administration of the antipyretic paracetamol was the most common 'first-line' treatment (13 units). Other 'first-line' methods were: circulating air-cooling blankets (9 units), water-filled cooling blankets (6 units), tepid sponging or wet soaks (2 units), convection fans (2 units) and administration of cold fluids via the gut or circulation (1 unit). When 'first-line' methods failed to bring about a fall in temperature, different combinations of these methods were used.

CONCLUSIONS

From this survey, it is evident that there is no consensus in the approach to temperature management in neurosurgical intensive care patients with severe TBI. Review and rationalisation of systems of care may be required in an effort to develop evidence-based nationwide guidelines.

Positive selective brain cooling method: a novel, simple, and selective nasopharyngeal brain cooling method

Brain damage is worsened by hyperthermia and prevented by hypothermia. Conventional hypothermia is a non-selective brain cooling method that employs cooling blankets to achieve surface cooling. This complicated method sometimes induces unfavorable systemic complications. We have developed a positive selective brain cooling (PSBC) method to control brain temperature quickly and safely following brain injury. Brain temperature was measured in patients with a ventriculostomy CAMINO catheter. A Foley balloon catheter was inserted to direct chilled air (8 to 12 L/min) into each side of the nasal cavity. The chilled air was exhaled through the oral cavity. In most patients, PSBC maintained normal brain temperature. This new technique provides quick induction of brain temperature control and does not require special facilities.

Pharmacological brain cooling with indomethacin in acute hemorrhagic stroke: antiinflammatory cytokines and antioxidative effects

We evaluated the effects of a novel pharmacological brain cooling (PBC) method with indomethacin (IND), a nonselective cyclooxygenase inhibitor, without the use of cooling blankets in patients with hemorrhagic stroke. Forty-six patients with hemorrhagic stroke (subarachnoid hemorrhage; n = 35, intracerebral hemorrhage; n = 11) were enrolled in this study. Brain temperature was measured directly with a temperature sensor. Patients were cooled by administering transrectal IND (100 mg) and a modified nasopharyngeal cooling method (positive selective brain cooling) initially. Brain temperature was controlled with IND 6 mg/kg/day for 14 days. Cerebrospinal fluid concentrations of interleukin-1beta (CSF IL-1beta) and serum bilirubin levels were measured at 1, 2, 4, and 7 days. The incidence of complicating symptomatic vasospasm after subarachnoid hemorrhage was lower than in non-PBC patients. CSF IL-1beta and serum bilirubin levels were suppressed in treated patients. IND has several beneficial effects on damaged brain tissues (anticytokine, free radical scavenger, antiprostaglandin effects, etc.) and prevents initial and secondary brain damage. PBC treatment for hemorrhagic stroke in patients appears to yield favorable results by acting as an antiinflammatory cytokine and reducing oxidative stress.

[Therapeutic hypothermia]

The benefit of therapeutic hypothermia after severe head injury is highly controversial. However, hypothermia is still used and studied in this context for multiple reasons. Efficacy of hypothermia is demonstrated after cerebral ischemia in numerous animal studies and after cardiac arrest in human studies. Hyperthermia is a major independent factor of outcome after cerebral ischemic or traumatic brain injury. Moreover, ICP is related to core temperature, and hypothermia may be used to decrease intracranial hypertension. However, many questions are still unresolved and can explain discrepancies between clinical studies: direct measurement of cerebral temperature, relationship between ICP, temperature and PaCO(2), level and duration of hypothermia and precise methods for cooling and particularly for rewarming.

Phase II clinical trial of moderate hypothermia after severe traumatic brain injury in children

OBJECTIVE

To determine whether moderate hypothermia (HYPO) (32-33 degrees C) begun in the early period after severe traumatic brain injury (TBI) and maintained for 48 hours is safe compared with normothermia (NORM) (36.5-37.5 degrees C).

METHODS

After severe (Glasgow Coma Scale score < or =8) nonpenetrating TBI, 48 children less than 13 years of age admitted within 6 hours of injury were randomized after stratification by age to moderate HYPO (32-33 degrees C) treatment in conjunction with standardized head injury management versus NORM in a multicenter trial. An additional 27 patients were entered into a parallel single-institution trial of excluded patients because of late transfer or consent (delayed in transfer >6 h but within 24 h of admission), unknown time of injury (e.g., child abuse), and adolescence (e.g., aged 13-18 yr). Assessments of safety included mortality, infection, coagulopathy, arrhythmias, and hemorrhage as well as ability to maintain target temperature, mean intracranial pressure (ICP), and percent time of ICP less than 20 mm Hg during the cooling and subsequent rewarming phases. Additionally, assessments of neurocognitive outcomes were obtained at 3 and 6 months of follow-up.

RESULTS

Moderate HYPO after severe TBI in children was found to be safe relative to standard management and NORM in children of all ages and in children with delay of initiation of treatment up to 24 hours. Although there was decreased mortality in HYPO in both studies, there was an increased potential for arrhythmias with HYPO, although they were manageable with fluid administration or rewarming. Additionally, there was a reduction in mean ICP during the first 72 hours after injury in both studies, although rebound ICP elevations in HYPO compared with those in NORM were noted for up to 10 to 12 hours after rewarming. Although functional outcome at 3 or 6 months did not differ between treatment groups, functional outcome tended to improve from the 3- to 6-month cognitive assessment in HYPO compared with NORM, although the sample size was too small for any definitive conclusions.

CONCLUSION

HYPO is likely a safe therapeutic intervention for children after severe TBI up to 24 hours after injury. Further studies are necessary and warranted to determine its effect on functional outcome and intracranial hypertension.

Osmotic therapy: fact and fiction

This review examines the available data on the use of osmotic agents in patients with head injury and ischemic stroke, summarizes the physiological effects of osmotic agents, and presents the leading hypotheses regarding the mechanism by which they reduce ICP. Finally, it addresses the validity of the following commonly held beliefs: mannitol accumulates in injured brain; mannitol shrinks only normal brain and can increase midline shift; osmolality can be used to monitor mannitol administration; mannitol should be not be administered if osmolality is >320 mOsm; and hypertonic saline is equally effective as mannitol.

Effect of Therapeutic Moderate Hypothermia on Multi-drug Resistance Protein 1-Mediated Transepithelial Transport of Drugs

To clarify the effect of therapeutic moderate hypothermia on drug distribution, transepithelial transport via multi-drug resistance protein 1 (MDR1) (also called P-glycoprotein or ABCB1) was evaluated at various temperatures in vitro using LLC-GA5-COL150 cells, which were established by transfecting human MDR1 complementary deoxyribonucleic acid into kidney epithelial LLC-PK(1) cells and express MDR1 on the apical membrane. MDR1 is expressed in the blood-brain barrier to limit drug distribution to the brain by exporting exogenous substances including calcium blockers and antiarrhythmic drugs. Digoxin was used as a typical substrate, as well as the non-substrate tetracycline and paracellular marker inulin. MDR1-mediated transport of digoxin decreased at lower temperatures. Transport of tetracycline also decreased at lower temperatures, probably due to changes in membrane fluidity. However, no change was found at over 32 degrees C, suggesting that passive diffusion does not change during moderate hypothermia. The distribution of MDR1 substrates should be considered during hypothermic conditions, as the clinical outcome could be affected.

The Effect of Hypothermia and Hyperthermia on Acute Brain Injury

The brain is extraordinarily susceptible to changes in temperature. Hyperthermia has been shown to exacerbate the biochemical cascade of secondary brain injury. Inversely, hypothermia limits the damaging effects of secondary brain injury. There has been a great deal of investigation regarding the detrimental effects of hyperthermia and the neuroprotection of hypothermia in animal studies. Within the last decade, clinical trials have begun to establish how the brain reacts to both temperature extremes. In the future, studies of hypothermia will continue in the quest of the optimal timing and degree of hypothermia. Hyperthermia will be examined in depth for its detrimental effects on an injured brain. Interventions for the prevention and treatment of hyperthermia will be explored. Nurses will implement cooling strategies to induce hypothermia, applying interventions to prevent complications, and they will also diagnose hyperthermia, deciding when and if to intervene pharmacologically and therapeutically. These advanced nursing actions will be guided by knowledge and understanding of available evidence. This article presents the pathophysiology of secondary brain injury and how it is affected by both hypothermia and hyperthermia. A review of the research leading up to clinical trials is explored, as well as a discussion of the future of temperature modulation for the brain injury patient. This information will help healthcare providers understand the effect that both hypothermia and hyperthermia have on the acutely injured brain.

Early Glasgow Outcome Scale Scores Predict Long-Term Functional Outcome in Patients with Severe Traumatic Brain Injury

Patients sustaining severe traumatic brain injury (TBI) have variable long-term outcomes. We examined the association between Glasgow Outcome Scale (GOS) assessed at 3 months and long-term outcomes at 12 months after TBI. We studied 159 patients with severe, closed traumatic brain injuries (Glasgow Coma Scale [GCS] <or= 8) who were treated at an academic medical center and survived for a minimum of 3 months after TBI. Demographics and admission clinical data and GOS at 3 and 12 months were analyzed. Multivariate logistic regression was used to asses the relationship between 3-month GOS, demographics, and clinical data and a poor outcome, defined as GOS 1-3 assessed at 12 months after injury. The patient population was predominantly male (77%), with a median age of 30 years and a median admission GCS of 6. The logistic regression model showed that the GOS at 3 months was the best predictor of 12-month outcomes (odds ratio = 15.22, p < 0.001). The presence of prolonged hypotension, diffuse axonal injury (DAI), and fixed and dilated pupils on admission were also significant independent predictors of poor 12-month outcome (for all, p <or= 0.047). The adjusted logistic model showed a steep gradient of long-term recovery potential depending upon GOS at 3 months, ranging from an 89.4% chance of poor outcome for patients with a GOS of 2, to a 0.11% chance of poor outcome for those with a GOS of 5. The 3-month GOS is a powerful independent predictor of long-term outcome for patients with severe TBI. Prolonged hypotension, DAI, and the presence of fixed and dilated pupils were also independent predictors of poor outcome.

Effect of hypothermia on transthoracic defibrillation in a swine model

BACKGROUND

Induced hypothermia (H) appears a promising intervention to protect the heart and brain after resuscitation from cardiac arrest. However, the influence of H on transthoracic defibrillation energy requirements is not well documented.

METHODS

In 39 swine (21.4+/-1.3(S.E.) kg) hypothermia was induced by surrounding the head, thorax and abdomen with ice. The swine were divided into four groups: (1) normothermia (N) followed by severe H (30 degrees C) (n=10), (2) severe H followed by N (n=10), (3) N followed by moderate H (33 degrees C) (n=10) and (4) moderate H followed by N (n=9). After 30s of electrically induced ventricular fibrillation (VF), the swine were defibrillated (biphasic waveform) at energies of 20J, 30J, 50J and 100J in random order in both N and H conditions.

RESULTS

For pigs in Group 1 (N followed by severe H), shock success in terminating VF was higher during hypothermia (odds ratio 4.09 (95% CI: 2.21, 5.58; p<0.0001), despite the fact that impedance rose from 39+/-3Omega (N) to 42+/-3Omega (H) (p<0.001) and current fell from 22+/-8 (N) to 21+/-7A (H) (p<0.001). There were no significant differences in the shock success between N and H for the other groups. Post-defibrillation ventricular asystole occurred less often during hypothermia compared to normothermia (p=0.0002).

CONCLUSION

Severe H facilitated transthoracic defibrillation in this swine model. Since impedance rose and current fell during H, the improved shock success must be due to a hypothermia-induced change in the mechanical or electrophysiologic properties of the myocardium. Moderate hypothermia did not alter the energy requirement for defibrillation.

Head injury therapies

The results of clinical trials in traumatic brain injury have to date been disappointing, despite promising results with animal models. Some of the agents which have been tested in clinical trials and some which are currently under evaluation are reviewed, and possible reasons for the lack of clinical benefit are discussed.

Hypothermia Improves Defibrillation Success and Resuscitation Outcomes From Ventricular Fibrillation

Background— Induced hypothermia is recommended to improve neurological outcomes in unconscious survivors of out-of-hospital ventricular fibrillation (VF) cardiac arrest. Patients resuscitated from a VF arrest are at risk of refibrillation, but there are few data on the effects of already existing hypothermia on defibrillation and resuscitation.

Methods and Results— Thirty-two swine (mean±SE weight, 23.0±0.6 kg) were divided into 4 groups: normothermia (n=8), mild hypothermia (35°C) (n=8), moderate hypothermia (33°C) (n=8), and severe hypothermia (30°C) (n=8). Hypothermia was induced by surrounding the animal with ice, and VF was electrically induced. After 8 minutes of unsupported VF (no CPR), the swine were defibrillated (biphasic waveform) with successive shocks as needed and underwent CPR until resumption of spontaneous circulation or no response (≥10 minutes). First-shock defibrillation success was higher in the moderate hypothermia group (6 of 8 hypothermia versus 1 of 8 normothermia; P =0.04). The number of shocks needed for late defibrillation (≥1 minute after initial shock) was less in all 3 hypothermia groups compared with normothermia (all P <0.05). None of the 8 animals in the normothermia group achieved resumption of spontaneous circulation compared with 3 of 8 mild hypothermia ( P =NS), 7 of 8 moderate hypothermia ( P =0.001), and 5 of 8 severe hypothermia ( P =0.03) animals. Coronary perfusion pressure during CPR was not different between the groups.

Conclusions— When VF was induced in the setting of moderate or severe hypothermia, resuscitative measures were facilitated with significantly improved defibrillation success and resuscitation outcome. The beneficial effect of hypothermia was not due to alteration of coronary perfusion pressure, which suggests that changes in the mechanical, metabolic, or electrophysiological properties of the myocardium may be responsible.

Therapeutic Hypothermia in Traumatic Brain Injury

Traumatic brain injury is a leading cause of death by trauma in adults in the United States and a major contributor to permanent physical, emotional, and psychological disabilities. Therapeutic hypothermia, defined as cooling of the body to less than 36 degrees C, has been shown to decrease mortality and morbidity and improve long-term outcomes by protecting the brain from secondary brain injury. The most commonly seen benefits of hypothermic temperatures of 32 degrees C to 33 degrees C are a significant reduction in intracranial hypertension and improved cerebral perfusion and oxygenation. Although evidence to date is insufficient to recommend the routine use of therapeutic hypothermia outside of the research setting, therapeutic hypothermia is used in multiple healthcare facilities in the world. The following article will define hypothermia and provide critical information necessary to provide care for the critically ill patient under therapeutic hypothermia. It will define the processes of brain injury and how hypothermia is thought to counteract those to protect the brain. Also included is a review of 2 major randomized, controlled trials of hypothermia for traumatic brain injury that have been instrumental in establishing guidelines and directing further research.

Gender associations with cerebrospinal fluid glutamate and lactate/pyruvate levels after severe traumatic brain injury

OBJECTIVE

Female sex hormones appear to be neuroprotective after traumatic brain injury by attenuating multiple mechanisms of secondary insult, including excitotoxicity and ischemia. The purpose of this study was to evaluate associations between gender and cerebrospinal fluid glutamate and lactate/pyruvate production and the role of hypothermia with gender in attenuating these markers.

DESIGN

Prospectively collected data were analyzed for adult patients with severe traumatic brain injury. Gender comparisons for cerebrospinal fluid glutamate and lactate/pyruvate production were determined using ventricular samples obtained over the first 48 hrs postinjury.

SETTING

University-based level I trauma center.

PATIENTS

There were 123 patients, male n = 93 and female n = 30 (n = 686 cerebrospinal fluid samples), with severe traumatic brain injury (Glasgow Coma Scale score < or =8).

INTERVENTIONS

A portion of these patients were part of a randomized controlled trial evaluating the effect of (48 hrs) therapeutic hypothermia after severe traumatic brain injury. The remainder received hypothermia (24 hrs) if they met clinical care criteria. Patients were cooled to 32-33 degrees C (within approximately 8 hrs) for either 24 or 48 hrs and then were rewarmed or remained normothermic.

MEASUREMENTS AND MAIN RESULTS

Regression analyses using generalized estimating equations for repeated measures showed significant increases in cerebrospinal fluid glutamate production for males compared with females (p = .0023) and a significant interaction between glutamate concentration, gender, and time (p = .0035) by 24 hrs postinjury. Females had lower lactate/pyruvate ratios than males (p = .0006), and there was a significant interaction between lactate/pyruvate, gender, and time (p = .0045) throughout the first 48 hrs postinjury. Hypothermia attenuated glutamate levels, particularly for males, over the time course studied.

CONCLUSIONS

These data suggest significant gender differences with glutamate and lactate/pyruvate production after severe traumatic brain injury. Gender- and hormone-mediated differences in central nervous system pathophysiology should be considered with clinical trials in traumatic brain injury.

Neurophysiological monitoring, magnetic resonance imaging, and histological assays confirm the beneficial effects of moderate hypothermia after epidural focal mass lesion development in rodents

OBJECTIVE

To assess the effects of moderate intraischemic hypothermia on neurophysiological parameters in an epidural balloon compression model in rats and to correlate the results with magnetic resonance imaging and histological findings.

METHODS

Neurophysiological monitoring included laser Doppler flow, tissue partial oxygen pressure, and intracranial pressure measurements and electroencephalographic assessments during balloon expansion, sustained inflation, and reperfusion. Moderate intraischemic cooling of animals was extended throughout the reperfusion period, and results were compared with those for normothermic animals. Moreover, histological morphometric and magnetic resonance imaging volumetric analyses of the lesions were performed.

RESULTS

Laser Doppler flow decreased slightly during ischemia (P < 0.05) in animals treated with hypothermia, and flow values demonstrated complete reperfusion, compared with incomplete flow restoration in untreated animals (P < 0.05). During ischemia, the tissue partial oxygen pressure was less than 4.3 mm Hg in both groups. After reperfusion, values returned to the normal range in both groups, but the tissue partial oxygen pressure in hypothermic animals was significantly higher (P = 0.042) and demonstrated 19% higher values, compared with normothermic animals, before rewarming. Moderate hypothermia attenuated a secondary increase in intracranial pressure (P < 0.05), and electroencephalographic findings indicated a trend toward faster recovery (P > 0.05) after reperfusion. Lesion size was reduced by 35% in magnetic resonance imaging volumetric evaluations and by 24.5% in histological morphometric analyses.

CONCLUSION

Intraischemic hypothermia improves cerebral microcirculation, attenuates a secondary increase in intracranial pressure, facilitates electroencephalographic recovery, and reduces the lesion size.

Cerebral pathophysiology and critical care neurology: basic hemodynamic principles, cerebral perfusion, and intracranial pressure

Pediatric neurologic intensive care differs from standard pediatric intensive care in two important respects. First, the diagnosis, monitoring, and management of problems related to disorders of cerebral perfusion and intracranial pressure (ICP) are central to nearly all of pediatric neurologic and neurosurgical intensive care. Second, various clinical problems normally encountered in the intensive care unit (ICU) have additional implications when associated with neurologic disease. Regardless of the cause, treatment should be undertaken as expeditiously as possible and should be based on the principles of resuscitation, reducing the volume of the intracranial contents, and reassessment. This chapter aims to outline some basic principles underlying the diagnosis and management of elevated ICP in children.

Is keeping cool still hot? An update on hypothermia in brain injury

PURPOSE OF REVIEW

The purpose of this review is to examine recent research results for hypothermia as a treatment for brain injury.

RECENT FINDINGS

One potential application for hypothermia is as a means of control of elevated intracranial pressure in which hypothermia is induced when intracranial pressure becomes uncontrollable by conventional means. A second application is as a neuroprotectant in which hypothermia is induced very early and maintained for a specified period as a means of diminishing the biochemical cascade that produces secondary brain injury. The clinical data indicate that hypothermia reduces elevated intracranial pressure, but no conclusion can be drawn as to whether this improves outcome over existing techniques (eg, mannitol and barbiturates). There is little evidence that hypothermia acts as a neuroprotectant in trials, all of which used treatment windows of over 4 hours.

SUMMARY

Hypothermia is a useful adjunct to barbiturates and mannitol to control elevated intracranial pressure. The results of trials that have tested systemic hypothermia as a neuroprotectant have been negative or equivocal, and cooling may have been induced outside the treatment window.

Brain temperature in patients with chronic hydrocephalus after subarachnoid hemorrhage

The relationships between temperature indices and clinical condition on admission or improvement after ventriculoperitoneal (VP) shunting were evaluated in patients with subarachnoid hemorrhage (SAH). Brain temperatures were measured at intervals of 1 cm from the brain surface to the lateral ventricle at shunt operation. Rectal temperature was also measured. The difference between intraventricular and rectal temperatures was correlated with age (p = 0.0486), Glasgow Coma Scale (p = 0.0129), Hunt and Hess grade (p = 0.0101), and improvement score after VP shunting (p = 0.0104). Measurement of brain temperature may predict the outcome of VP shunting in patients with SAH.

Post-traumatic moderate systemic hypothermia reduces TUNEL positive cells following spinal cord injury in rat

STUDY DESIGN

A standardized animal model of contusive spinal cord injury (SCI) with incomplete paraplegia was used to test the hypothesis that moderate systemic hypothermia reduces neural cell death. Terminal deoxynucleotidyl transferase [TdT]-mediated deoxyuridine triphosphate [dUTP] nick-end labeling (TUNEL) staining was used as a marker of apoptosis or cell damage.

OBJECTIVE

To determine whether or not moderate hypothermia could have a neuroprotective effect in neural cell death following spinal cord injury in rats.

SETTING

Kagawa Medical University, Japan.

METHODS

Male Sprague-Dawley (SD) rats (n=39) weighing on average 300 g (280-320 g) were used to prepare SCI models. After receiving contusive injury at T11/12, rats were killed at 24 h, 72 h, or 7 days after injury. The spinal cord was removed en bloc and of examined at five segments: 5 and 10 mm rostral to the center of injury, center of injury, and 5 and 10 mm caudal to the center of injury. Rats that received hypothermia (32 degrees C/4 h) were killed at the same time points as those that received normothermia (37 degrees C/3 h). The specimens were stained with hematoxylin and eosin, and subjected to in situ nick-end labeling (TUNEL), a specific method for visualizing cell death in the spinal cord.

RESULTS

At 24 h postinjury, TUNEL positive cells (TPC) decreased significantly 10 mm rostral to center of injury in hypothermic animals compared to the normothermia group. At 72 h post-SCI, TPC also decreased significantly at 5 mm rostral, and 5 and 10 mm caudal to the lesion center compared to normothermic animals. At 7 days postinjury, a significant decrease of TPC was observed at the 5 mm rostral and 5 mm caudal sites compared to normothermic animals.

CONCLUSION

These results indicate that systemic hypothermia has a neuroprotective effect following SCI by attenuating post-traumatic TPC.

Technical refinements and drawbacks of a surface cooling technique for the treatment of severe acute ischemic stroke

PURPOSE

To describe a technique for the induction of hypothermia and its complications for the treatment of acute ischemic stroke.

METHODS

Adults with acute (<8 hours), severe (National Institutes of Health Stroke Scale>14) ischemic stroke of the anterior circulation were enrolled. Patients were intubated, sedated, and paralyzed. Surface cooling to 32 degrees+/-1 degrees C was performed with a cooling blanket and an alcohol/ice bath. Hypothermia was maintained for 12-72 hours. Physiological parameters were measured continuously. A computed tomography scan of the brain was obtained at 24 hours. Rewarming was initiated 12 hours after middle cerebral artery recanalization at a rate of 0.25 degrees C/hour. All complications and adverse outcomes were documented from initiation of hypothermia until hospital discharge.

RESULTS

Eighteen patients with a mean National Institutes of Health Stroke Scale=21.4+/-5.6 were treated. The goal temperature was reached within 3.2+/-1.5 hours. Cooling time was proportional to body weight (p=0.009) and decreased with immediate paralysis to prevent shivering (p=0.033). Maintenance and rewarming were characterized by fluctuations in core temperature. All patients developed a decrease in blood pressure, heart rate, and potassium values that were proportional to temperature (p<0.05). Complications were generally mild, but pneumonia and myocardial infarction or both occurred in five patients. There were trends for increased risk of complications with longer duration of hypothermia (p=0.08) and increasing age (p=0.0504). Rewarming was well-tolerated with rebound cerebral edema occurring in only one patient.

CONCLUSION

Surface cooling for the treatment of acute ischemic stroke can be performed rapidly with early neuromuscular paralysis. Advanced age and prolonged hypothermia may be associated with an increased risk of complications.

Clinical Trials in Traumatic Brain Injury: Lessons for the Future

Thus far, none of the neuroprotective drugs that have been tested to reduce or prevent secondary ischemic brain damage have been shown clear benefit. We will attempt to identify factors that may be responsible for some of these failures. We also will give our thoughts on how to prevent these pitfalls in the usefulness and criteria for use of animal models for traumatic brain injury to depict human head injury are discussed. Clearly, mechanism-driven trials, in which individual pathophysiological mechanisms are targeted, are more likely to show benefit in this heterogeneous patient population. Other factors, such as the effect of brain penetration, safety and tolerability of the compound, and the interface between the pharmaceutical industry and academics are a major influence in the success of these trials. Furthermore, the way trials have been analyzes in the past may not always have been be the most appropriate to show benefits. It is clear that a multi-targeted approach is necessary to address the complicated and closely related mechanisms seen after traumatic and or ischemic brain damage.

The importance of gender on the beneficial effects of posttraumatic hypothermia

The authors studied the importance of gender on the consequences of mild posttraumatic hypothermia following parasagittal fluid-percussion (F-P) brain injury in rats. After traumatic brain injury (TBI), brain temperature was maintained at normothermia (37 degrees C) or reduced to 33 degrees C for 4 h starting 30 min after the insult followed by a 1.5-h slow rewarming period. Animals (n = 48) were allowed to survive for 3 days before quantitative histopathological and immunocytochemical examination. As previously reported, contusion volume in normothermic animals (37 degrees C) was smaller (P < 0.05) in intact females compared to males. In addition, numbers of NeuN-positive cortical neurons were greater in females versus males after TBI. Posttraumatic hypothermia significantly reduced overall contusion volume in males (P < 0.05), while not significantly reducing contusion volume in females. Likewise, hypothermia protected against the loss of cortical neurons in males but had no effect in females. Ovariectomized females showed contusion volumes and neuronal cell counts comparable to those seen in males as well as a significant reduction in contusion volumes and greater neuronal counts following posttraumatic hypothermia. These data are the first to demonstrate that posttraumatic hypothermia (4 h) does not affect short-term histopathological outcomes in female rats. Potential mechanisms underlying this gender difference are discussed. Finally, these experimental findings may have important implications in terms of clinical trials using therapeutic hypothermia targeting patients with central nervous system (CNS) injury.

Therapeutic hypothermia

Hypothermia is common during anaesthesia and surgery owing to anaesthetic-induced inhibition of thermoregulatory control. Perioperative hypothermia is associated with numerous complications. However, for certain patient populations, and under specific clinical conditions, hypothermia can provide substantial benefits. Lowering core temperature to 32-34 degrees C may reduce cell injury by suppressing excitotoxins and oxygen radicals, stabilizing cell membranes, and reducing the number of abnormal electrical depolarizations. Evidence from animal studies indicates that even mild hypothermia provides substantial protection against cerebral ischaemia and myocardial infarction. Mild hypothermia has been shown to improve outcome after cardiac arrest in humans. Randomized trials are in progress to evaluate the potential benefits of mild hypothermia during aneurysm clipping and after stroke or acute myocardial infraction. However, as hypothermia can cause unwanted side-effects, further research is needed to better quantify the risks and benefits of therapeutic hypothermia.

Mild Hypothermia Inhibits Exogenous Glutamate-Induced Increases in Nitric Oxide Synthesis

The purpose of this study was to investigate changes in nitric oxide (NO) synthesis induced by exogenous glutamate perfusion into the cerebral cortex, and the effects of mild hypothermia on this glutamate-induced NO synthesis. Glutamate-induced cortical lesions were produced by perfusion of 0.5 M glutamate solution via a microdialysis probe, and the extracellular concentrations of NO end-products (nitrite and nitrate) were measured by microdialysis in normothermic (37 degrees C) and hypothermic (32 degrees C) rats. The levels of NO end-products in the normothermia group were elevated markedly by glutamate perfusion, and this change was completely attenuated by the induction of hypothermia. The glutamate-induced increases were also attenuated markedly by both Nomega-nitro-L-arginine methyl ester (L-NAME) and 7-nitroindazole (7-NI). These results suggest that the perfusion of exogenous glutamate into the cortex induces NO synthesis, that is derived primarily from the activity of neuronal NO synthase. These results also demonstrate that hypothermia prevents this glutamate-induced increase in NO, suggesting that the protection afforded by the hypothermic condition is most likely linked to its inhibition of the glutamate-induced NO synthesis.

Hypothermia in the management of traumatic brain injury. A systematic review and meta-analysis

OBJECTIVE

Brain injury remains the leading cause of death in cases of trauma in North America and Europe. This article critically appraised and summarised all published and peer-reviewed, randomised, controlled trials of the use of hypothermia in traumatic brain injury.

DESIGN

To be included, a study had to be a published, randomised, controlled trial of the use of hypothermia in the management of traumatic brain injury. Pooling of data and meta-analysis of results occurred.

SETTING

Conducted at a tertiary level Canadian teaching hospital.

PATIENTS AND PARTICIPANTS

Patients were combined from eight randomised, controlled trials to generate a population of 748 severely head-injured patients.

MEASUREMENTS AND RESULTS

Eight studies provided data on the efficacy of hypothermia in the management of traumatic brain injury. The pooled odds ratio of mortality in the hypothermic group was 0.81 (95%CI =0.59-1.13, p=0.22). The OR of a poor neurological outcome (GOS 1,2 or 3) was 0.75 (95% CI=0.56-1.01, p=0.06). The odds ratio for pneumonia in the normothermic group was 0.42 (95%CI =0.25-0.70, p=0.001).

CONCLUSIONS

Although meta-analysis suggests that iatrogenic hypothermia may confer a marginal benefit in neurological outcome, there does not appear to be clear evidence of lower mortality rates in unselected traumatic brain injury patients. Prolonged hypothermia may confer a benefit, particularly in patients with elevated intracranial pressure refractory to conventional manipulations. Conclusions regarding the use of hypothermia are controversial and not strongly supported by the available evidence.

Ultrarapid, convection-enhanced intravascular hypothermia: a feasibility study in nonhuman primate stroke

BACKGROUND AND PURPOSE

Hypothermia has been shown to be neuroprotective in a variety of clinical settings. Unfortunately, poor delivery techniques and insufficient data in appropriate preclinical models have hampered its development in human stroke. To address these limitations, we have devised a 10F intravascular catheter capable of rapid systemic cooling of nonhuman primates.

METHODS

Placed in the inferior vena cava via a transfemoral approach, the catheter was used to induce mild systemic hypothermia 3 hours after the onset of hemispheric stroke in baboons.

RESULTS

Cooling was achieved at a rate of 6.3+/-0.8 degrees C/h. Target brain temperatures (32.2+/-0.2 degrees C) were reached at the same time (47.7+/-6.32 minutes) as target esophageal temperatures (32.0+/-0.0 degrees C). Hypothermia was maintained for 6 hours in all animals. Animals did not experience the infections, coagulopathy, or cerebral edema commonly seen with surface cooling methods in human stroke.

CONCLUSIONS

These data suggest that a brief episode of mild core hypothermia instituted at a clinically relevant time point can be achieved in primate stroke and that our intravascular cooling technique provides safe, rapid, and reproducible hypothermia.

Neuroprotection in hypothermia linked to redistribution of oxygen in brain

Hypothermia improves the outcome of acute ischemic stroke, traumatic injury, and inflammation of brain tissue. We tested the hypothesis that hypothermia reduces the energy metabolism of brain tissue to a level that is commensurate with the prevailing blood flow and hence allows adequate distribution of oxygen to the entire tissue. To determine the effect of 32 degrees C hypothermia on brain tissue, we measured the sequential changes of physiological variables by means of PET in pigs. Cerebral blood flow and oxygen consumption (cerebral metabolic rate of oxygen) declined to 50% of the baseline in 3 and 5 h, respectively, thus elevating the oxygen extraction fraction to 140% of the baseline at 3 h. The results are consistent with the claim that cooling of the brain to 32 degrees C couples both energy metabolism and blood flow to a lower rate of work of the entire tissue.

Moderate hypothermia improves neurobehavioral deficits after an epidural focal mass lesion in rodents

The objective of this study was to evaluate the effects of a moderate, intraischemic hypothermia on the behavorial deficits up to 4 weeks after induction of a focal mass lesion. A focal epidural mass lesion was induced by an epidural balloon. The severity of the trauma was defined by the balloon volume and flattening of electroencephalography. Hypothermia (32 degrees C) was induced as soon as maximum balloon infIation was reached. Ischemia was extended over 30 min. After reperfusion, normothermic (n = 24) and hypothermic animals (n = 25) were monitored for 3 h followed by a rewarming of the cooled animals. Results were compared to sham-operated animals (n = 10). Behavioral deficits were assessed by postural reflex (PR), open field (OF), beam balance (BB), beam walking (BW), and water maze tests (WMT). MRI follow-up and histology was evaluated. Sham-operated rats showed normal test results. Rats with normothermia showed worsening of test performance (PR, p < 0.05; OF, p < 0.05; BB, p < 0.05; BW, p < 0.05; WMT, p < 0.05) compared to controls over the whole observation period. A significantly better behavioral outcome was observed in animals treated with hypothermia which showed no differences from controls 3-4 days after injury (PR, OF, BB, BW, WMT, p > 0.05). Lesion induced mortality was reduced in cooled animals but overall mortality rates were not influenced by this therapeutic measure. Neuronal cell loss in the CA1-CA4 region (p < 0.05) was reduced and the lesion size smaller (21%/p > 0.05) in hypothermic animals. Magnetic resonance imaging revealed that the lesion was more pronounced in the cortical grey matter after normothermia, whereas hypothermic animals showed more subcortical brain lacerations. In conclusion, intraischemic hypothermia significantly improved the behavioral outcome, and decreased lesion-induced mortality and the size of the lesion after an epidural focal mass lesion.

Role of hypothermia in the management of severe cases of subarachnoid hemorrhage

Mild hypothermia is thought to have a brain protective effect to pathophysiological conditions, which are caused by severe brain damage including brain injury and cerebral stroke. In this paper, general aspects of this treatment as history, pathophysiological effect, and problems are summarized. Also, the clinical effects of hypothermic therapy for a subarachnoid hemorrhage are reviewed. Main targets of the therapy for this disease are severe primary brain damage caused by the attack itself and secondary ischemic brain damage after delayed vasospasm. But even now, there are no fully established data about the effect of hypothermia at such conditions after subarachnoid hemorrhage. The results of our study of cerebral blood flow and cerebral oxygen metabolism using positron emission tomography are presented to show the physiological effect of hypothermia on human brain after severe brain damage caused by subarachnoid hemorrhage. In conclusion, effect of hypothermia on subarachnoid hemorrhage is not confirmed yet and reported data is limited, so that additional studies, especially controlled studies, would be recommended.

The use of mild hypothermia for patients with severe vasospasm: a preliminary report

The purpose of this study was to determine the effect of mild hypothermia on cerebral ischaemia due to severe vasospasm, which was refractory to medical and intravascular treatments and to assess the brain protection of this treatment in patients who underwent delayed aneurysm clipping after presenting with ischaemic neurological deficits. Mild hypothermia (32-34 degrees C of brain temperature) was employed in two groups: (1) Patients (Hunt and Kosnik grades I to II) who showed progressive neurological deficits due to vasospasm and did not respond to conventional therapy (Group 1) and (2) Patients who received delayed aneurysm clipping after presenting with ischaemic neurological deficits due to vasospasm (Group 2). Seven of 8 patients in both Groups showed a favorable outcome with mild hypothermia (good recovery in 5 and moderate disability in two patients). Mild hypothermia is considered to be effective on critical cerebral ischaemia due to vasospasm even after failure to response the conventional therapies and to provide brain protection in delayed aneurysm clipping.

Effects of moderate hypothermia on proinflammatory cytokine production in a rat model of caerulein-induced pancreatitis

INTRODUCTION

Proinflammatory cytokines act as mediators of the local and systemic manifestations of acute pancreatitis (AP).

AIMS

To investigate whether moderate hypothermia (MH) (32 degrees C) can reduce the severity of AP by inhibiting cytokine production in a rat model of caerulein-induced pancreatitis.

METHODOLOGY

Rats were divided into three groups: control rats (Group I), AP rats treated with normothermia (38 degrees C) (Group II), and AP rats treated with MH (Group III). AP was induced by intramuscular injection of caerulein and intraperitoneal infusion of lipopolysaccharide. MH was induced 4 hours after the first caerulein injection. Serum interleukin (IL)-1beta, tumor necrosis factor (TNF)-alpha, IL-6, amylase, and lipase levels were determined 8 hours after the first injection. The pancreas and lung were examined histologically.

RESULTS

MH in comparison with normothermia significantly reduced serum levels of IL-1beta, TNF-alpha, IL-6, amylase, and lipase. Histologically, the MH group showed less vacuolization of the acinar cells and cellular infiltration into the interacinar areas of the pancreas than were shown in the normothermia group, but these effects were not evident in the lung.

CONCLUSION

Our results suggest that MH may be clinically applicable for reducing the severity of AP.