Physiology and clinical relevance of induced hypothermia

Modified intraoperative temperature management prevents prolonged length of stay after head and neck surgery with free flap reconstruction

The present study aimed to investigate the association between intraoperative body temperature and prolonged length of stay (PLOS) after free flap reconstruction. A total of 753 patients who underwent head and neck surgery with free flap reconstruction were collected and randomly assigned into primary and validation cohorts. In the primary cohort, univariable and multivariable analyses were conducted to evaluate associations between intraoperative time-weighted (TW) temperature (TW average [TWA] temperature, TW hypothermia and TW hyperthermia) and PLOS. Nomograms were developed with and without intraoperative TW temperature, and validated in the validation cohort. Severe intraoperative TW hypothermia (OR = 1.004; 95% CI: 1.000, 1.007; p = 0.032) was identified as an independent risk factor for PLOS. Intraoperative TWA temperature and TW hypothermia showed linear related predictive effect for PLOS. The nomogram incorporating intraoperative TW temperature showed higher C-index (0.652, 95% CI: 0.591, 0.713) and improved net reclassification improvement for non-event (0.277, 95% CI: 0.118, 0.435; p < 0.001). Lower TWA temperature with mild TW hypothermia had a preventive effect on PLOS with a linear association, which may provide a modified range for intraoperative temperature management. The proposed nomogram incorporating intraoperative TW temperature could be used to develop personalized preventive strategies for PLOS after free flap reconstruction. IRB NUMBER: SYSEC-KY-KS-2022-037. CLINICAL TRIAL REGISTRATION NUMBER: Not applicable.

Impact of Intraoperative Hypothermia on Microsurgical Free Flap Reconstructions

BACKGROUND

 Patients requiring microsurgical defect reconstruction are highly susceptible to intraoperative hypothermia, given oftentimes long operative times and exposure of large skin surface areas. While the impact of hypothermia has been extensively studied across various surgical fields, its role in the setting of microsurgical free flap reconstruction remains elusive. This study evaluates the effects of hypothermia on outcomes of free flap reconstructions.

METHODS

 Within 7 years, 602 patients underwent 668 microvascular free flap reconstructions. The cases were divided into two groups regarding the minimal core body temperature during free flap surgery: hypothermia (HT; < 36.0°C) versus normothermia (NT; ≥36.0°C). The data were retrospectively screened for patients' demographics, perioperative details, flap survival, surgical complications, and outcomes.

RESULTS

 Our data revealed no significant difference with regard to the rate of major and minor surgical complications, or the rate of revision surgery between both groups (p > 0.05). However, patients in the HT group showed significantly higher rates of total flap loss (6.6% [HT] vs. 3.0% [NT], p < 0.05) and arterial thrombosis (4.6% [HT] vs. 1.9% [NT], p < 0.05). This translated into a significantly longer hospitalization of patients with reduced core body temperature (HT: mean 16.8 days vs. NT: mean 15.1 days; p < 0.05).

CONCLUSION

 Hypothermia increases the risk for arterial thrombosis and total flap loss. While free flap transfer is feasible also in hypothermic patients, surgeons' awareness of core body temperature should increase. Taken together, we suggest that the mean intraoperative minimum temperature should range between 36 and 36.5°C during free flap surgery as a pragmatic guideline.

Neck cooling induces blood pressure increase and peripheral vasoconstriction in healthy persons

Introduction

Noninvasive temperature modulation by localized neck cooling might be desirable in the prehospital phase of acute hypoxic brain injuries. While combined head and neck cooling induces significant discomfort, peripheral vasoconstriction, and blood pressure increase, localized neck cooling more selectively targets blood vessels that supply the brain, spares thermal receptors of the face and skull, and might therefore cause less discomfort cardiovascular side effects compared to head- and neck cooling. The purpose of this study is to assess the effects of noninvasive selective neck cooling on cardiovascular parameters and cerebral blood flow velocity (CBFV).

Methods

Eleven healthy persons (6 women, mean age 42 ± 11 years) underwent 90 min of localized dorsal and frontal neck cooling (EMCOOLS Brain.Pad™) without sedation. Before and after cooling onset, and after every 10 min of cooling, we determined rectal, tympanic, and neck skin temperatures. Before and after cooling onset, after 60- and 90-min cooling, we monitored RR intervals (RRI), systolic, diastolic blood pressures (BPsys, BPdia), laser Doppler skin blood flow (SBF) at the index finger pulp, and CBFV at the proximal middle cerebral artery (MCA). We compared values before and during cooling by analysis of variance for repeated measurements with post hoc analysis (significance: p < 0.05).

Results

Neck skin temperature dropped significantly by 9.2 ± 4.5 °C (minimum after 40 min), while tympanic temperature decreased by only 0.8 ± 0.4 °C (minimum after 50 min), and rectal temperature by only 0.2 ± 0.3 °C (minimum after 60 min of cooling). Index finger SBF decreased (by 83.4 ± 126.0 PU), BPsys and BPdia increased (by 11.2 ± 13.1 mmHg and 8.0 ± 10.1 mmHg), and heart rate slowed significantly while MCA-CBFV remained unchanged during cooling.

Conclusions

While localized neck cooling prominently lowered neck skin temperature, it had little effect on tympanic temperature but significantly increased BP which may have detrimental effects in patients with acute brain injuries.

Mild hypothermia is associated with improved outcomes in patients undergoing microvascular head and neck reconstruction

OBJECTIVE

Microvascular free tissue transfer has become the standard for reconstruction for large defects. With long operative times and an increased surface area exposed, transient hypothermia is common, but it is unclear how this impacts surgical outcomes. This study evaluated the impact of core body temperature on free tissue flap outcomes in patients undergoing microvascular reconstruction.

STUDY DESIGN

Retrospective data analysis.

SETTING

Mount Sinai Hospital; NYC, NY; 2007-2016.

SUBJECTS AND METHODS

Demographic information, mean/minimum/maximum body temperatures, and the presence of flap complications (venous thrombosis, arterial insufficiency, flap death, wound infection/dehiscence, fistula, chyle leak, hematoma/seroma) of 519 free tissue transfer patients were documented. Binomial logistic regression was used to examine associations between the presence of flap complications and mean temperature. Statistical analysis used SPSS, with p-values ≤0.05 deemed statistically significant.

RESULTS

393 soft-tissue and 125 osteocutaneous flaps were included. 19.8% (n = 103) patients had the presence of ≥1 flap complication, while 80.2% (n = 416) did not. Average temperature for all patients was 36.12 ± 0.84 °C, with minimum at 34.43 ± 0.97 °C and maximum at 37.24 ± 1.23 °C. After controlling for several factors including: tumor stage, radiation, diabetes, BMI, age, sex, and flap type, there was a significant association between flap complications and mean intraoperative temperature (Exp(B) = 1.559, p = 0.004).

CONCLUSION

Higher intraoperative temperatures were associated with worse outcomes. A mild relative hypothermia may improve flap outcomes in this population. This represents the largest study to date evaluating the impact of intraoperative temperature on free tissue transfer outcomes.

Selective brain hypothermia

Selective brain hypothermia is a powerful concept for neuroprotection that has been successfully investigated in a variety of animal models of global and focal ischemia. Its major advantages over systemic hypothermia include rapid induction of cooling, ability to achieve profound target brain temperatures, organ-selective cooling, and temperature control. Clinical systems and devices are available or are currently under development that utilize conductive (surface-cooling pads, closed-loop catheters), convective (transnasal coolant delivery), or mass and energy transport (cold intra-arterial infusion) methods to achieve and maintain selective brain hypothermia. The "ideal" brain-cooling system that is characterized by rapid cooling to profound hypothermia, its ability to maintain selective cooling over several days, and is noninvasive in nature, remains unrealistic. Instead, systems may be identified by their distinct advantages to meet a specific need in the care of a patient. This involves the consideration of the timing of ischemic injury (preischemic, intraischemic, postischemic), extent of ischemic damage (excitotoxicity, inflammation, necrosis, edema), and type and setting of therapeutic intervention (intensive care, interventional therapy, surgery). The successful translation of these systems into clinical practice will depend on smart engineering, safety and efficacy, and usability in current clinical work flow.

Head and neck cooling decreases tympanic and skin temperature, but significantly increases blood pressure

BACKGROUND AND PURPOSE

Localized head and neck cooling might be suited to induce therapeutic hypothermia in acute brain injury such as stroke. Safety issues of head and neck cooling are undetermined and may include cardiovascular autonomic side effects that were identified in this study.

METHODS

Ten healthy men (age 35±13 years) underwent 120 minutes of combined head and neck cooling (Sovika, HVM Medical). Before and after onset of cooling, after 60 and 120 minutes, we determined rectal, tympanic, and forehead skin temperatures, RR intervals, systolic and diastolic blood pressures (BP), laser-Doppler skin blood flow at the index finger and cheek, and spectral powers of mainly sympathetic low-frequency (0.04-0.15 Hz) and parasympathetic high-frequency (0.15-0.5 Hz) RR interval oscillations and sympathetic low-frequency oscillations of BP. We compared values before and during cooling using analysis of variance with post hoc analysis; (significance, P<0.05).

RESULTS

Forehead skin temperature dropped by 5.5±2.2°C with cooling onset and by 12.4±3.2°C after 20 minutes. Tympanic temperature decreased by 4.7±0.7°C within 40 minutes, and rectal temperature by only 0.3±0.3°C after 120 minutes. Systolic and diastolic BP increased immediately on cooling onset and rose by 15.3±20.8 mm Hg and 16.5±13.4 mm Hg (P=0.004) after 120 minutes, whereas skin blood flow fell significantly during cooling. RR intervals and parasympathetic RR interval high-frequency powers increased with cooling onset and were significantly higher after 60 and 120 minutes than they were before cooling.

CONCLUSIONS

Head and neck cooling prominently reduced tympanic temperature and thus might also induce intracerebral hypothermia; however, it did not significantly lower body core temperature. Profound skin temperature decrease induced sympathetically mediated peripheral vasoconstriction and prominent BP increases that are not offset by simultaneous parasympathetic heart rate slowing. Prominent peripheral vasoconstriction and BP increase must be considered as possibly harmful during head and neck cooling.

Association of the Bedside Shivering Assessment Scale and derived EMG power during therapeutic hypothermia in survivors of cardiac arrest

INTRODUCTION

Shivering during therapeutic hypothermia (TH) after cardiac arrest (CA) is common, but the optimal means of detection and appropriate threshold for treatment are not established. In an effort to develop a quantitative, continuous tool to measure shivering, we hypothesized that continuous derived electromyography (dEMG) power detected by the Aspect A2000 or VISTA monitor would correlate with the intermittent Bedside Shivering Assessment Scale (BSAS) performed by nurses.

METHODS

Among 38 patients treated with TH after CA, 853 hourly BSAS measurements were compared to dEMG power measured every minute by a frontal surface electrode. Patients received intermittent vecuronium by protocol to treat clinically recognized shivering (BSAS>0). Mean dEMG power in decibels (dB) was determined for the hour preceding each BSAS measurement. dEMG and BSAS were compared using ANOVA.

RESULTS

The median dEMG power for a BSAS score of 0 (no shivering) was 27 dB (IQR 26-31 dB), BSAS 1 was 30.5 dB (IQR 28-35 dB), BSAS 2 was 34 dB (IQR 30-38 dB), and BSAS 3 was 34.5 dB (IQR 32-44.25). The dEMG for BSAS≥1 (shivering) was statistically different from BSAS 0 (p<0.0001). dEMG and BSAS correlated moderately (r=0.66, p<0.001).

CONCLUSION

dEMG power measured from the forehead with the Aspect A2000 or VISTA monitor during therapeutic hypothermia correlated with the Bedside Shivering Assessment Scale. Given its continuous trending of dEMG power, the A2000 or VISTA may be a useful research and clinical tool for objectively monitoring shivering.

Brain temperature: heat production, elimination and clinical relevance

Neurological insults are a leading cause of morbidity and mortality, both in adults and especially in children. Among possible therapeutic strategies to limit clinical cerebral damage and improve outcomes, hypothermia remains a promising and beneficial approach. However, its advantages are still debated after decades of use. Studies in adults have generated conflicting results, whereas in children recent data even suggest that hypothermia may be detrimental. Is it because brain temperature physiology is not well understood and/or not applied properly, that hypothermia fails to convince clinicians of its potential benefits? Or is it because hypothermia is not, as believed, the optimal strategy to improve outcome in patients affected with an acute neurological insult? This review article should help to explain the fundamental physiological principles of brain heat production, distribution and elimination under normal conditions and discuss why hypothermia cannot yet be recommended routinely in the management of children affected with various neurological insults.

Effect of shivering on brain tissue oxygenation during induced normothermia in patients with severe brain injury

BACKGROUND

We analyzed the impact of shivering on brain tissue oxygenation (PbtO(2)) during induced normothermia in patients with severe brain injury.

METHODS

We studied patients with severe brain injury who developed shivering during induced normothermia. Induced normothermia was applied to treat refractory fever (body temperature [BT] > or =38.3 degrees C, refractory to conventional treatment) using a surface cooling device with computerized adjustment of patient BT target to 37 +/- 0.5 degrees C. PbtO(2), intracranial pressure, mean arterial pressure, cerebral perfusion pressure, and BT were monitored continuously. Circulating water temperature of the device system was measured to assess the intensity of cooling.

RESULTS

Fifteen patients (10 with severe traumatic brain injury, 5 with aneurysmal subarachnoid hemorrhage) were treated with induced normothermia for an average of 5 +/- 2 days. Shivering caused a significant decrease in PbtO(2) levels both in SAH and TBI patients. Compared to baseline, shivering was associated with an overall reduction of PbtO(2) from 34.1 +/- 7.3 to 24.4 +/- 5.5 mmHg (P < 0.001). A significant correlation was found between the magnitude of shivering-associated decrease of PbtO(2) (DeltaPbtO(2)) and circulating water temperature (R = 0.82, P < 0.001).

CONCLUSION

In patients with severe brain injury treated with induced normothermia, shivering was associated with a significant decrease of PbtO(2), which correlated with the intensity of cooling. Monitoring of therapeutic cooling with computerized thermoregulatory systems may help prevent shivering and optimize the management of induced normothermia. The clinical significance of shivering-induced decrease in brain tissue oxygenation remains to be determined.

The effects of temperature on cardiac pacing thresholds

BACKGROUND

Human core body temperature can fluctuate between 36 degrees C (sleep) and 42 degrees C (intense exercise). Also, efforts are underway to develop implantable pacing systems that minimize heating during magnetic resonance imaging (MRI) scans (i.e., MRI safe). Concerns exist that ventricular pacing capture thresholds (VPCT) are modified by changing cardiac temperatures. This project was designed to assess the effects of temperature on VPCT of the mammalian heart.

METHODS

Fresh ventricular specimens were obtained from healthy canine, healthy swine, and diseased human hearts. Isolated trabeculae were suspended in temperature-controlled tissue baths containing oxygenated Krebs buffer. Small active fixation pacing leads delivered pacing pulses to each specimen. Baseline strength-duration curves were determined at 37 degrees C, then at randomized temperatures ranging from 35 degrees C to 42 degrees C. Final thresholds were repeated at 37 degrees C to confirm baseline responses. All threshold data were normalized to a baseline average.

RESULTS

Both canine and swine trabeculae elicited significant decreases in thresholds (10-14%) at pacing stimulus durations (pulsewidths) of 0.02 ms (P < 0.01) and 0.10 ms (P < 0.05) between the temperatures of 38 degrees C and 41 degrees C, compared to baseline. Thresholds at 42 degrees C trended back to baseline for both canine (NS) and swine trabeculae (P < 0.05 compared to 38 degrees C-41 degrees C). Human trabeculae thresholds increased >35% (P < 0.05) at 42 degrees C relative to baseline with no significant differences at other temperatures.

CONCLUSIONS

Temperature is a significant factor on pacing thresholds for mammalian ventricular myocardium. Our data for the diseased human trabeculae indicate that cases where cardiac heating may occur (e.g., radiofrequency energy due to MRI scans, febrile events), patients without adequate VPCT safety margin may be at higher risk of loss of proper function of an implanted pacing or defibrillation system.

Neuroprotection for ischemic stroke: past, present and future

Neuroprotection for ischemic stroke refers to strategies, applied singly or in combination, that antagonize the injurious biochemical and molecular events that eventuate in irreversible ischemic injury. There has been a recent explosion of interest in this field, with over 1000 experimental papers and over 400 clinical articles appearing within the past 6 years. These studies, in turn, are the outgrowth of three decades of investigative work to define the multiple mechanisms and mediators of ischemic brain injury, which constitute potential targets of neuroprotection. Rigorously conducted experimental studies in animal models of brain ischemia provide incontrovertible proof-of-principle that high-grade protection of the ischemic brain is an achievable goal. Nonetheless, many agents have been brought to clinical trial without a sufficiently compelling evidence-based pre-clinical foundation. At this writing, around 160 clinical trials of neuroprotection for ischemic stroke have been initiated. Of the approximately 120 completed trials, two-thirds were smaller early-phase safety-feasibility studies. The remaining one-third were typically larger (>200 subjects) phase II or III trials, but, disappointingly, only fewer than one-half of these administered neuroprotective therapy within the 4-6h therapeutic window within which efficacious neuroprotection is considered to be achievable. This fact alone helps to account for the abundance of "failed" trials. This review presents a close survey of the most extensively evaluated neuroprotective agents and classes and considers both the strengths and weakness of the pre-clinical evidence as well as the results and shortcomings of the clinical trials themselves. Among the agent-classes considered are calcium channel blockers; glutamate antagonists; GABA agonists; antioxidants/radical scavengers; phospholipid precursor; nitric oxide signal-transduction down-regulator; leukocyte inhibitors; hemodilution; and a miscellany of other agents. Among promising ongoing efforts, therapeutic hypothermia, high-dose human albumin therapy, and hyperacute magnesium therapy are considered in detail. The potential of combination therapies is highlighted. Issues of clinical-trial funding, the need for improved translational strategies and clinical-trial design, and "thinking outside the box" are emphasized.

Possible stimulation of anti-tumor immunity using repeated cold stress: a hypothesis

Background

The phenomenon of hormesis, whereby small amounts of seemingly harmful or stressful agents can be beneficial for the health and lifespan of laboratory animals has been reported in literature. In particular, there is accumulating evidence that daily brief cold stress can increase both numbers and activity of peripheral cytotoxic T lymphocytes and natural killer cells, the major effectors of adaptive and innate tumor immunity, respectively. This type of regimen (for 8 days) has been shown to improve survival of mice infected with intracellular parasite Toxoplasma gondii, which would also be consistent with enhanced cell-mediated immunity.

Presentation of the hypothesis

This paper hypothesizes that brief cold-water stress repeated daily over many months could enhance anti-tumor immunity and improve survival rate of a non-lymphoid cancer. The possible mechanism of the non-specific stimulation of cellular immunity by repeated cold stress appears to involve transient activation of the sympathetic nervous system, hypothalamic-pituitary-adrenal and hypothalamic-pituitary-thyroid axes, as described in more detail in the text. Daily moderate cold hydrotherapy is known to reduce pain and does not appear to have noticeable adverse effects on normal test subjects, although some studies have shown that it can cause transient arrhythmias in patients with heart problems and can also inhibit humoral immunity. Sudden immersion in ice-cold water can cause transient pulmonary edema and increase permeability of the blood-brain barrier, thereby increasing mortality of neurovirulent infections.

Testing the hypothesis

The proposed procedure is an adapted cold swim (5–7 minutes at 20 degrees Celsius, includes gradual adaptation) to be tested on a mouse tumor model. Mortality, tumor size, and measurements of cellular immunity (numbers and activity of peripheral CD8+ T lymphocytes and natural killer cells) of the cold-exposed group would be compared to those of control groups (warm swim and no treatment). Cold-water stress would be administered twice a day for the duration of several months.

Implications of the hypothesis

If the hypothesis is supported by empirical studies and the method is shown to be safe, this could lead to the development of an adjunctive immunotherapy for some (non-lymphoid) cancers, including those caused by viral infections.

Possible use of repeated cold stress for reducing fatigue in chronic fatigue syndrome: a hypothesis

BACKGROUND

Physiological fatigue can be defined as a reduction in the force output and/or energy-generating capacity of skeletal muscle after exertion, which may manifest itself as an inability to continue exercise or usual activities at the same intensity. A typical example of a fatigue-related disorder is chronic fatigue syndrome (CFS), a disabling condition of unknown etiology and with uncertain therapeutic options. Recent advances in elucidating pathophysiology of this disorder revealed hypofunction of the hypothalamic-pituitary-adrenal axis and that fatigue in CFS patients appears to be associated with reduced motor neurotransmission in the central nervous system (CNS) and to a smaller extent with increased fatigability of skeletal muscle. There is also some limited evidence that CFS patients may have excessive serotonergic activity in the brain and low opioid tone.

PRESENTATION OF THE HYPOTHESIS

This work hypothesizes that repeated cold stress may reduce fatigue in CFS because brief exposure to cold may transiently reverse some physiological changes associated with this illness. For example, exposure to cold can activate components of the reticular activating system such as raphe nuclei and locus ceruleus, which can result in activation of behavior and increased capacity of the CNS to recruit motoneurons. Cold stress has also been shown to reduce the level of serotonin in most regions of the brain (except brainstem), which would be consistent with reduced fatigue according to animal models of exercise-related fatigue. Finally, exposure to cold increases metabolic rate and transiently activates the hypothalamic-pituitary-adrenal axis as evidenced by a temporary increase in the plasma levels of adrenocorticotropic hormone, beta-endorphin and a modest increase in cortisol. The increased opioid tone and high metabolic rate could diminish fatigue by reducing muscle pain and accelerating recovery of fatigued muscle, respectively.

TESTING THE HYPOTHESIS

To test the hypothesis, a treatment is proposed that consists of adapted cold showers (20 degrees Celsius, 3 minutes, preceded by a 5-minute gradual adaptation to make the procedure more comfortable) used twice daily.

IMPLICATIONS OF THE HYPOTHESIS

If testing supports the proposed hypothesis, this could advance our understanding of the mechanisms of fatigue in CFS.

The feasibility of a regional cardiac arrest receiving system

BACKGROUND

Patients suffering out-of-hospital cardiac arrest (OOHCA) are generally transported to the closest ED, presumably to expedite a hospital level of care and improve the chances of return for spontaneous circulation (ROSC) or provide post-resuscitative care for patients with prehospital ROSC. As hospital-based therapies for survivors of OOHCA are identified, such as hypothermia and emergency primary coronary interventions (PCI), certain hospitals may be designated as cardiac arrest receiving facilities. The safety of bypassing non-designated facilities with such a regional system is not known.

OBJECTIVES

To explore the potential ED contribution in OOHCA victims without prehospital ROSC and document the relationship between transport time and outcome in patients with prehospital ROSC.

METHODS

This was a prospective, observational study conducted in a large, urban EMS system over an 18-month period. Data were collected using the Utstein template for OOHCA. The incidence of prehospital ROSC was calculated for patients who were declared dead on scene, transported but died in the ED, died in the hospital, and survived to hospital discharge. The relationship between transport time and survival was also explored for patients with prehospital ROSC.

RESULTS

A total of 1141 cardiac arrest patients were enrolled over the 18-month period. A strong association between prehospital ROSC and final disposition was observed (chi-square test for trend p<0.001). Only two patients who survived to hospital discharge did not have prehospital ROSC. Mean transport times were not significantly different for patients with prehospital ROSC who were declared dead in the ED (8.3min), died following hospital admission (7.8min), and survived to hospital discharge (8.5min). Outcomes in patients with prehospital ROSC who had shorter (7min or less) versus longer transport times were similar, and receiver-operator curve analysis indicated no predictive ability of transport time with regard to survival to hospital admission (area under the curve=0.52).

CONCLUSIONS

In this primarily urban EMS system, the vast majority of survivors from OOHCA are resuscitated in the field. A relationship between transport time and survival to hospital admission or discharge was not observed. This supports the feasibility of developing a regional cardiac arrest system with designated receiving facilities.

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.

Effects of intrathecal bupivacaine in conjunction with hypothermia on neuronal protection against transient spinal cord ischemia in rats

BACKGROUND

Excitotoxic neuronal injury from ischemia may be reduced by local anesthetics. We investigated the neuroprotective effects of intrathecally administered bupivacaine and hypothermia in a rat model of transient spinal cord ischemia.

METHODS

PE-10 intrathecal catheter-implanted male Sprague-Dawley rats were randomly assigned to one of four groups: normothermia (NT) and hypothermia (HT) groups (given 15 microl of normal saline) and bupivacaine (B) and bupivacaine-hypothermia (BHT) groups (given 15 mul of 0.5% bupivacaine). Transient spinal cord ischemia was induced by inflation of a 2F Fogarty catheter placed in the aortic arch for 12 min. The rectal temperature was maintained at 37.0 +/- 0.5 degrees C for the NT and B groups, and at 34.5 +/- 0.5 degrees C for the HT and BHT groups. Motor and sensory deficit scores were assessed 2 and 24 h after reperfusion. Lumbar spinal cords were harvested for histopathology and immunoreactivity of heat shock protein 70 (HSP70).

RESULTS

After reperfusion, the motor and sensory deficit scores of the NT group were significantly higher than those of the HT (P < 0.05) and BHT (P < 0.001) groups. Significant differences were evident in the motor and sensory deficit scores between the HT and BHT groups at 24 h (P < 0.05). Neuronal cell death and immunoreactivity of HSP70 were frequently observed in the NT and BT groups, but not in the HT and BHT groups.

CONCLUSIONS

These results collectively suggest that intrathecal bupivacaine does not provide neuroprotection during normothermic transient spinal cord ischemia in rats, but enhances the neuroprotective effects of hypothermia.

Modern treatment options for intracerebral hemorrhage

Spontaneous intracerebral hemorrhage (ICH) is a devastating neurological event with a 30-day mortality of approximately 40%. Recent research provides new insights into the pathophysiology of ICH-associated edema, with potential molecular and cellular targets for future therapy. Neuroimaging techniques such as gradient echo MRI are yielding insights into cerebral microbleeds and the microangiopathies associated with hypertension and cerebral amyloid angiopathy. Recent literature provides new medical treatment strategies for fever, acute hypertension, and perihematomal edema, and methods of reducing intracranial pressure. Two randomized controlled trials have provided crucial evidence regarding surgical and medical intervention for acute ICH intervention. Recombinant factor VIIa appears to lessen growth of ICH when administered within 4 hours of ictus. Further study of potential efficacy and safety is underway in an international phase III trial. In addition, the Surgical Trial in Intracerebral Hemorrhage reported results from an international randomized trial of 1033 patients who did not show benefit for surgical evacuation of ICH, compared with medical therapy alone. Less invasive surgical methods for hematoma evacuation, studied previously over the past decade, continue to be investigated.