Early effects of acid-base management during hypothermia on cerebral infarct volume, edema, and cerebral blood flow in acute focal cerebral ischemia in rats

Effects of prenatal mobile phone radiation exposure on MMP9 expression: Implications for inflammation, oxidative stress, and sensory-motor impairment after neonatal hypoxia- ischemia in rats

Objective

Non-ionizing radiofrequency radiation, which finds application in various sectors such as industry, commerce, medicine, and particularly in mobile phone technology, has emerged as a topic of significant concern during pregnancy. The aim of this study was to investigate the effect of cell phone radio-frequency (RF) radiation during pregnancy on the Matrix metalloproteinase 2 (MMP-2) and (MMP-9) 9 expressions after neonatal hypoxia-ischemia (HI) in rats.

Materials and methods

Two groups were formed by randomly assigning female Wistar rats: Group 1 consisted of female rats that were not exposed to RF radiation during pregnancy, while Group 2 comprised female rats that were exposed to RF radiation during pregnancy. After delivery, male offspring were divided into four groups including: (a) SHAM, (b) Exposure (EXP), (c) hypoxia-ischemia (HI), (d) HI/Exposure (HI/EXP). Seven days after HI induction, neurobehavioral tests were performed, and then brain tissue was taken from the skull to measure MMP-2 and MMP-9 expressions, inflammation, oxidative stress, infarct volume and cerebral edema.

Results

MMP-9 mRNA expression in the HI/EXP group was significantly higher than the HI, SHAM and EXP groups. MMP-2 mRNA expression levels in the HI group were significantly higher than Sham and the EXP groups.TNF-α and Total oxidant capacity (TOC) levels in the HI/EXP group were significantly higher than HI, EXP and SHAM groups. Total antioxidant capacity (TAC) level in the HI/EXP group were significantly lower than HI, EXP and SHAM groups. Cerebral edema and infarct volume in the HI/EXP group were significantly greater than the HI group. Sensory-motor function was significantly weaker in HI/EXP as compared HI group.

Conclusion

Our findings indicate that during pregnancy, exposure to mobile phone RF radiation intensifies damage from HI in rat pups by elevating MMP-9 activity.

Physiological Changes in Subjects Exposed to Accidental Hypothermia: An Update

Background

Accidental hypothermia (AH) is an unintended decrease in body core temperature (BCT) to below 35°C. We present an update on physiological/pathophysiological changes associated with AH and rewarming from hypothermic cardiac arrest (HCA).

Temperature Regulation and Metabolism

Triggered by falling skin temperature, Thyrotropin-Releasing Hormone (TRH) from hypothalamus induces release of Thyroid-Stimulating Hormone (TSH) and Prolactin from pituitary gland anterior lobe that stimulate thyroid generation of triiodothyronine and thyroxine (T4). The latter act together with noradrenaline to induce heat production by binding to adrenergic β3-receptors in fat cells. Exposed to cold, noradrenaline prompts degradation of triglycerides from brown adipose tissue (BAT) into free fatty acids that uncouple metabolism to heat production, rather than generating adenosine triphosphate. If BAT is lacking, AH occurs more readily.

Cardiac Output

Assuming a 7% drop in metabolism per °C, a BCT decrease of 10°C can reduce metabolism by 70% paralleled by a corresponding decline in CO. Consequently, it is possible to maintain adequate oxygen delivery provided correctly performed cardiopulmonary resuscitation (CPR), which might result in approximately 30% of CO generated at normal BCT.

Liver and Coagulation

AH promotes coagulation disturbances following trauma and acidosis by reducing coagulation and platelet functions. Mean prothrombin and partial thromboplastin times might increase by 40–60% in moderate hypothermia. Rewarming might release tissue factor from damaged tissues, that triggers disseminated intravascular coagulation. Hypothermia might inhibit platelet aggregation and coagulation.

Kidneys

Renal blood flow decreases due to vasoconstriction of afferent arterioles, electrolyte and fluid disturbances and increasing blood viscosity. Severely deranged renal function occurs particularly in the presence of rhabdomyolysis induced by severe AH combined with trauma.

Conclusion

Metabolism drops 7% per °C fall in BCT, reducing CO correspondingly. Therefore, it is possible to maintain adequate oxygen delivery after 10°C drop in BCT provided correctly performed CPR. Hypothermia may facilitate rhabdomyolysis in traumatized patients. Victims suspected of HCA should be rewarmed before being pronounced dead. Rewarming avalanche victims of HCA with serum potassium > 12 mmol/L and a burial time >30 min with no air pocket, most probably be futile.

Treadmill Exercise during Pregnancy Decreased Vulnerability to Neonatal Hypoxia-Ischemia through Reducing Inflammation and Increasing Antiapoptotic Gene Expressions and Antioxidant Capacity in Rats

Background

The purpose of present study was to assess the impact of maternal treadmill exercise during pregnancy on inflammation, oxidative stress, expression of Bax and Bcl-2 genes, and brain-derived neurotrophic factor (BDNF) level in neonatal rat brain after the hypoxia-ischemia injury. Material and Methods. A total of 24 female Wistar rats were utilized in this research. Two groups are randomly considered for rats: (1) not exercised through pregnancy and (2) exercised during pregnancy. Offsprings were divided into four groups including after delivery: (1) sham, (2) sham/exercise (sham/EX), (3) HI, and (4) HI+exercise. HI was induced in pups at postnatal day 8. Neurobehavioral tests were done seven days after HI induction. Then, the brain tissue was taken from the skull to estimate Bcl-2 and Bax gene expressions, BDNF, cerebral edema, infarct volume, inflammatory factors, oxidative stress, and neurological function.

Results

The BDNF level in the HI+exercise group was considerably higher than the HI, sham, and sham/EX groups. Tumor necrosis factor (TNF-α), C-reactive protein (CRP), and the whole oxidant capacity (TOC) levels in the HI group were significantly higher than the sham and sham/EX groups. TNF-α, CRP, and TOC levels in the HI+exercise group were significantly lower than the HI group. Total antioxidant capacity (TAC) level in the HI+exercise group was significantly higher than the HI group. Infarct volume and edema percent in the HI+exercise group were significantly lower than the HI group. Neurological function in the HI+exercise group was significantly better than the HI group. Bax expression in the HI+exercise group was significantly lower than the HI group. Bcl-2 expression in the HI+exercise group was significantly higher than the HI group. In the sham group, BDNF, TNF-α, CRP, TAC, TOC, edema levels, and neurological function had no significant difference with the sham/EX group.

Conclusion

It appears that the maternal treadmill exercise during pregnancy exerts a supportive impact against neonatal HI brain injury through increasing antioxidant capacity, Bcl-2 expression, and BDNF levels and decreasing inflammation that is resulted in the lower infarct volume and sensorimotor dysfunction.

Morphine consumption during pregnancy exacerbates neonatal hypoxia-ischemia injury in rats

OBJECTIVE

Hypoxia-Ischemia (HI) is the most common cause of death and disability in human infants. The use of opiate in pregnant women affects their children. The aim of this study was to evaluate the effect of morphine consumption during pregnancy and lactation on vulnerability to neonatal HI in rats.

MATERIALS AND METHODS

Female Wistar rats were randomly assigned into two groups: Group 1-Rats that did not receive any treatment during pregnancy and lactation and Group 2-Rats that received morphine during pregnancy and lactation. After delivery, male offspring were divided into four groups including: (a) SHAM, (b) SHAM/Morphine (SHAM/MO), (c) HI, (d) HI/Morphine (HI/MO). Seven days after HI induction, neurobehavioral tests were performed, and then, brain tissue was taken from the skull to measure cerebral edema, infarct volume, inflammatory factors, oxidative stress, and brain-derived neurotrophic factor (BDNF).

RESULTS

Total antioxidant capacity (TAC) and BDNF levels in the HI/MO group were significantly lower than HI and SHAM groups. TNF-α, C-reactive protein and total oxidant capacity levels in the HI/MO group were significantly higher than HI and SHAM groups. Cerebral edema and infarct volume in the HI/MO group were significantly higher than the HI group.

CONCLUSION

Based on the results, morphine consumption during pregnancy and lactation enhanced the deleterious effects of HI injury in pups.

[Neuroprotection in neurocritical care]

In intensive care medicine neuroprotection is understood mostly as various measures to avoid secondary brain damage after initial trauma, as in stroke, intracranial hemorrhage and resuscitation. Every brain trauma differs in the damage pattern and dynamics depending on the primary form of injury. Therefore, there are targeted treatment approaches depending on the pathophysiology of the medical condition. In addition, neuroprotective methods are desirable that are effective in the majority of patients with acute brain injury. In actual fact, in all forms of acute brain injury certain pathophysiological courses are encountered, which can lead to secondary brain damage depending on the intensity, e.g. reperfusion injury, damage to the blood-brain barrier and excitotoxicity. There is evidence to suggest that the creation of physiologically normal conditions leads to a favorable situation for the damaged brain. This article firstly describes the relevance of neuroprotective measures in neurocritical care medicine. Subsequently, general pathophysiological mechanisms in brain trauma are described. Following this, the pathophysiology and treatment options in brain pressure crises (reduction of intracranial pressure), anemia (transfusion management), hyperglycemia and hypoglycemia (adjustment of the blood sugar level) are dealt with. Finally, the use and benefits of therapeutic hypothermia are discussed. This has a special position as the only clinically effective individual measure for neuroprotection. The focus here is on the application following circulatory and cardiac arrest and resuscitation.

Hypocarbia and adverse outcome in neonatal hypoxic-ischemic encephalopathy

OBJECTIVE

To evaluate the association between early hypocarbia and 18- to 22-month outcome among neonates with hypoxic-ischemic encephalopathy.

STUDY DESIGN

Data from the National Institute of Child Health and Human Development Neonatal Research Network randomized, controlled trial of whole-body hypothermia for neonatal hypoxic-ischemic encephalopathy were used for this secondary observational study. Infants (n = 204) had multiple blood gases recorded from birth to 12 hours of study intervention (hypothermia versus intensive care alone). The relationship between hypocarbia and outcome (death/disability at 18 to 22 months) was evaluated by unadjusted and adjusted analyses examining minimum PCO(2) and cumulative exposure to PCO(2) <35 mm Hg. The relationship between cumulative PCO(2) <35 mm Hg (calculated as the difference between 35 mm Hg and the sampled PCO(2) multiplied by the duration of time spent <35 mm Hg) and outcome was evaluated by level of exposure (none-high) using a multiple logistic regression analysis with adjustments for pH, level of encephalopathy, treatment group (± hypothermia), and time to spontaneous respiration and ventilator days; results were expressed as odds ratios and 95% confidence intervals. Alternative models of CO(2) concentration were explored to account for fluctuations in CO(2).

RESULTS

Both minimum PCO(2) and cumulative PCO(2) <35 mm Hg were associated with poor outcome (P < .05). Moreover, death/disability increased with greater cumulative exposure to PCO(2) <35 mm Hg.

CONCLUSIONS

Hypocarbia is associated with poor outcome after hypoxic-ischemic encephalopathy.

Therapeutic hypothermia for acute ischemic stroke: ready to start large randomized trials?

Therapeutic hypothermia is a means of neuroprotection well established in the management of acute ischemic brain injuries such as anoxic encephalopathy after cardiac arrest and perinatal asphyxia. As such, it is the only neuroprotective strategy for which there is robust evidence for efficacy. Although there is overwhelming evidence from animal studies that cooling also improves outcome after focal cerebral ischemia, this has not been adequately tested in patients with acute ischemic stroke. There are still some uncertainties about crucial factors relating to the delivery of hypothermia, and the resolution of these would allow improvements in the design of phase III studies in these patients and improvements in the prospects for successful translation. In this study, we discuss critical issues relating first to the targets for therapy including the optimal depth and duration of cooling, second to practical issues including the methods of cooling and the management of shivering, and finally, of factors relating to the design of clinical trials. Consideration of these factors should inform the development of strategies to establish beyond doubt the place of hypothermia in the management of acute ischemic stroke.

Hypothermia reduces early hypoperfusion and metabolic alterations during the acute phase of massive subarachnoid hemorrhage: a laser-Doppler-flowmetry and microdialysis study in rats

Morbidity and mortality of subarachnoid hemorrhage (SAH) are correlated with the severity of the patient's acute neurological deficit. This initial presentation has been attributed to cerebral hypoperfusion in the acute phase, and we investigated the impact of moderate hypothermia on the early changes in perfusion and metabolism following massive experimental SAH. SAH was induced in 61 anesthetized rats by rapid injection of 0.5 mL of arterial blood into the cisterna magna. In normothermia (NT), animals were kept at 37 degrees C, while in the primary hypothermia (pHT) group, temperature was lowered to 32 degrees C prior to SAH, and in the secondary hypothermia (sHT) group, cooling was started immediately after SAH. From 30 min prior to 180 min after SAH, Laser-Doppler-flowmetry (LDF) probes allowed online recording of cerebral blood flow (CBF) while parenchymal dialysate was collected by microdialysis probes within the frontoparietal cortex. In NT, the acute phase was characterized by impaired autoregulation and prolonged hypoperfusion. In pHT and sHT, autoregulation was preserved and acute hypoperfusion rapidly improved. SAH also caused a highly significant reduction in glucose in NT only. pHT significantly reduced accumulation of lactate, glutamate, and aspartate. Comparable trends were present for histidine, GABA, and taurine, while glutamine consumption was ameliorated. Early perfusion deficits caused by acute hypoperfusion and disruption of cerebral autoregulation can be ameliorated by hypothermia. Also, the acute phase of experimental SAH is characterized by glucose depletion, lactate accumulation, and release of excitatory amino acids, which can be influenced favorably by hypothermia.

Cerebral autoregulation: the role of CO2 in metabolic homeostasis

In this review the role of PaCO2 in regulating cerebral blood flow and flow/metabolism coupling, as well as its impact on intracellular metabolic processes are discussed. Starting with a discussion of alpha-stat versus pH-stat ventilatory management, the apparently contradictory finding of exacerbation of ischemic injury by extracellular acidosis in some experimental models versus others in which neuroprotection is evidenced is discussed and contrasted with the conclusion that the relatively small degree of change in pH associated with clinical changes in PaCO2 is unlikely to directly impact ischemia/reperfusion processes. However, examples of susceptible patients in whom relatively small changes in PaCO2 can produce adverse effects on cerebral perfusion are also illustrated re-emphasizing the necessity for individualization rather than generalization of care.

Hypothermia effects on neurovascular coupling and cerebral metabolic rate of oxygen

Neuronal activation is accompanied by a local increase in cerebral blood flow (CBF) and in cerebral metabolic rate of oxygen (CMRO(2)), caused by neurovascular and neurometabolic coupling. Hypothermia is used as a neuroprotective approach in surgical patients and therapeutically after cardiac arrest or stroke. The effect of hypothermia on neurovascular coupling is of interest for evaluating brain function in these patients, but has not been determined so far. It is not clear whether functional hyperaemia actually operates at subnormal temperatures. In addition, decreasing brain temperature reduces spontaneous CMRO(2) following a known quantitative relationship (Q(10)). Q(10) determination may serve to validate a recently introduced CMRO(2) measurement approach relying on optical measurements of CBF and hemoglobin concentration. We applied this method to investigate hypothermia in a functional study of the somatosensory cortex. Anesthetized Wistar rats underwent surgical implantation of a closed cranial window. Using laser Doppler flowmetry and optical spectroscopy, relative changes in CBF and hemoglobin concentration were measured continuously. At the same time, an electroencephalogram (EEG) was recorded from the measurement site. By the application of ice packs, whole-body hypothermia was induced, followed by rewarming. Spontaneous EEG, CBF and CMRO(2) were measured, interleaved by blocks of electrical forepaw stimulation. The Q(10) obtained from spontaneous CMRO(2) changes of 4.4 (95% confidence interval 3.7-5.1) was close to published values, indicating the reliability of the CMRO(2) measurement. Lowering brain temperature decreased functional changes of CBF and CMRO(2) as well as amplitudes of somatosensory evoked potentials (SEP) to the same degree. In conclusion, neurovascular and neurometabolic coupling is preserved during hypothermia.

Therapeutische Hypothermie und Säure-Basen-Management

Moderate hypothermia is being increasingly advocated for acute neurological clinical situations. In case of proved clinical success, however, it is relatively time consuming and requires personal and structural resources. In addition, profound knowledge and a sound understanding of the physiology of hypothermia are necessary prerequisites. In particular, the variety of untoward effects, which increase with decreasing temperature, underline the need for specific diagnostic and therapeutic skills. A further challenge is associated with the adaptation of the parameters of homoeostasis to a basically altered temperature. Among these, management of acid-base balance is a managerial cornerstone. In principle, two different regimens may be used, i.e. the pH-stat and the alpha-stat regimes. Applying pH-stat during hypothermia means keeping the pH constant, whereas the H(+)/OH(-) quotient is held constant when relying on the alpha-stat regime. Because of the lack of prospective clinical data any comparative evaluation of the two alternatives actually remains a matter of speculation. However, experimental data as well as physiological considerations may support an illness-oriented differentiated approach (e.g. increased cerebral pressure vs. cardiac arrest vs. stroke). Prospective studies are required to allow an evidence-based and substantiated clinical decision regarding the management of pCO(2) and pH during therapeutic hypothermia.

Therapeutic temperature modulation in neurocritical care

The ability to effectively achieve and maintain long-term temperature control is an important goal that has been previously unachievable in the neurocritical care setting. Previous attempts have been limited by the inability to overcome physiologic defense mechanisms, short duration of action, or significant adverse effects. Recent advances in technology have made therapeutic temperature modulation feasible. In this review, current concepts of therapeutic temperature modulation are presented. New advances in technology may provide an important breakthrough in the ability to reduce fever-associated morbidity in neurocritically ill patients. What remains to be seen is whether the advantages of these technologies will outweigh the risks associated with therapeutic temperature modulation.

Astrocytic contributions to bioenergetics of cerebral ischemia

Astrocytes are multifunctional cells that interact with neurons and other astrocytes in signaling and metabolic functions, and their resistance to pathophysiological conditions can help restrict loss of tissue after an ischemic event provided adequate nutrients are supplied to support their requirements. Astrocytes have substantial oxidative capacity and mechanisms to upregulate glycolytic capability when respiration is impaired. An astrocytic enzyme that synthesizes a powerful activator of glycolysis is not present in neurons, endowing astrocytes with the ability to sustain ATP production under restrictive conditions. The monocarboxylic acid transporter (MCT) isoforms predominating in astrocytes are optimized to facilitate very large increases in lactate flux as lactate concentration increases within (1-3 mM) and above (>3 mM) the normal range. In sharp contrast, the major neuronal MCT serves as a barrier to increased transmembrane transport as lactate rises above 1 mM, restricting both entry and efflux. Lactate can serve as fuel during recovery from ischemia but direct evidence that lactate is oxidized by neurons (vs. astrocytes) to maintain synaptic function is lacking. Astrocytes have critical roles in regulation of ionic homeostasis and control of extracellular glutamate levels, and spreading depression associated with ischemia places high demands on energy supplies in astrocytes and contributes to metabolic exhaustion and demise. Disruption of Ca2+ homeostasis, generation of oxygen free radicals and nitric oxide, and mitochondrial depolarization contribute to astrocyte death during and after a metabolic insult. Novel pharmaceutical agents targeted to astrocytes and hyperoxic therapy that restores penumbral oxygen level during energy failure might improve postischemic outcome.

Combination therapy of moderate hypothermia and thrombolysis in experimental thromboembolic stroke--an MRI study

Thrombolysis (T) is limited by reperfusion-associated injury and the short therapeutic window after stroke onset. The present study investigates whether hypothermia alone or in combination with thrombolysis has beneficial effects after experimental thromboembolic stroke. Wistar rats (n = 60) were subjected to thromboembolic occlusion (TE) of the middle cerebral artery (MCA). Thrombolysis (T) was performed with intravenous recombinant tissue-plasminogen activator (rt-PA) 1 h (early T) or 3 h (late T) after TE. Hypothermia (Hy) was applied for 4 h at 33 degrees C started 1 h after TE. Experimental groups included control (C), early thrombolysis (ET), late thrombolysis (LT), hypothermia (Hy), early thrombolysis plus hypothermia (ET+Hy), and late thrombolysis plus hypothermia (LT+Hy). Animals were investigated by MRI and silver infarct staining (SIS) to assess the cerebral infarct size. All animals of group Hy survived, in contrast to 40% in group C (P < 0.05). ET+HY and LT+Hy showed a trend towards better survival as compared to ET and LT alone. PWI parameters were not significantly different between ET versus ET+HY and LT versus LT+Hy, but rt-PA administration led to improved cerebral perfusion in MRI. Significant differences in infarct volumes (T2/SIS) were found after 24 h in all treatment groups versus the control group (P < 0.05). The lesion volume calculated from T2 was significantly smaller in ET (16% +/- 5%), ET+Hy (10 +/- 4%), and LT+Hy (20% +/- 9%) after 5.5 h (10.8% +/- 4.8%) versus C (42% +/- 15%), (P < 0.05). These data indicate that hypothermia improves survival and decreases infarct volume. However, there were no significant differences between the use of rt-PA alone or in combination with hypothermia. Further studies are needed to confirm these effects, also several days after stroke onset.

Traumatic injury in the developing brain–effects of hypothermia

Little is known about the underlying mechanisms of head trauma in the developing brains, despite considerable social and economic impact following such injuries. Age has been shown to substantially influence morbidity and mortality. Children younger than 4 years of age had worse cognitive, motor, and brain atrophy outcomes than children 6 years of age and older. Younger children tend to more frequently suffer from diffuse cerebral swelling compared to adults. Typical autoptic findings also include axonal injury and ischemic neurodegeneration. These differences impact not only the primary response of the brain to injury but the secondary response as well. The complexity of damaging mechanisms in traumatic brain injury contributes to the problem of determining effective therapy. As an alternative/ adjunct to pharmacological approaches, hypothermia has been shown to be cerebroprotective in traumatized adult brains. Although a large number of animal studies have shown protective effects of hypothermia in a variety of damaging mechanisms after TBI, little data exist for young, developing brains. The injury mechanisms of TBI in the immature, effects of hypothermia following resuscitation on adult and immature traumatized brains, and some possible mechanisms of action of hypothermia in the immature traumatized brain are discussed in this review.

Les variations thermiques modifient les paramètres des gaz du sang : quelles conséquences en pratique clinique ?

OBJECTIVE

To understand changes in blood gases results with core temperature.

METHODS

Analysis from two case reports.

RESULTS

Hypothermia induces a decrease in PaCO(2) with a related increase in pH, thus a physiologic alkalosis. Decrease in PaCO(2) is due to an increase of gas solubility and a decrease of peripheral consumption that can be estimated from comparison between corrected and non-corrected for temperature blood gases. For O(2), variations of temperature induce variations of solubility but also of haemoglobin affinity for O(2). During hyperthermia, haemoglobin affinity for O(2) is decreased with a decreased SvO(2) for a same PvO(2). SvO(2) ischemic or therapeutic thresholds are thus modified with core temperature.

CONCLUSION

Blood gases cannot be understood without patient core temperature. Physiologic variations of PaCO(2) and pH must probably be tolerated. Ischemic threshold should be estimated on PvO(2), not only on PvO(2).

Hypothermia and stroke: the pathophysiological background

Hypothermia to mitigate ischemic brain tissue damage has a history of about six decades. Both in clinical and experimental studies of hypothermia, two principal arbitrary patterns of core temperature lowering have been defined: mild (32-35 degrees C) and moderate hypothermia (30-33 degrees C). The neuroprotective effectiveness of postischemic hypothermia is typically viewed with skepticism because of conflicting experimental data. The questions to be resolved include the: (i) postischemic delay; (ii) depth; and (iii) duration of hypothermia. However, more recent experimental data have revealed that a protected reduction in brain temperature can provide sustained behavioral and histological neuroprotection, especially when thermoregulatory responses are suppressed by sedation or anesthesia. Conversely, brief or very mild hypothermia may only delay neuronal damage. Accordingly, protracted hypothermia of 32-34 degrees C may be beneficial following acute cerebral ischemia. But the pathophysiological mechanism of this protection remains yet unclear. Although reduction of metabolism could explain protection by deep hypothermia, it does not explain the robust protection connected with mild hypothermia. A thorough understanding of the experimental data of postischemic hypothermia would lead to a more selective and effective clinical therapy. For this reason, we here summarize recent experimental data on the application of hypothermia in cerebral ischemia, discuss problems to be solved in the experimental field, and try to draw parallels to therapeutic potentials and limitations.

Induced hypothermia in critical care medicine: a review

BACKGROUND

Clinical trials of induced hypothermia have suggested that this treatment may be beneficial in selected patients with neurologic injury.

OBJECTIVES

To review the topic of induced hypothermia as a treatment of patients with neurologic and other disorders.

DESIGN

Review article.

INTERVENTIONS

None.

MAIN RESULTS

Improved outcome was demonstrated in two prospective, randomized, controlled trials in which induced hypothermia (33 degrees C for 12-24 hrs) was used in patients with anoxic brain injury following resuscitation from prehospital cardiac arrest. In addition, prospective, randomized, controlled trials have been conducted in patients with severe head injury, with variable results. There also have been preliminary clinical studies of induced hypothermia in patients with severe stroke, newborn hypoxic-ischemic encephalopathy, neurologic infection, and hepatic encephalopathy, with promising results. Finally, animal models have suggested that hypothermia that is induced rapidly following traumatic cardiac arrest provides significant neurologic protection and improved survival.

CONCLUSIONS

Induced hypothermia has a role in selected patients in the intensive care unit. Critical care physicians should be familiar with the physiologic effects, current indications, techniques, and complications of induced hyperthermia.