Effects of hypothermia on systemic and organ system metabolism and function

Avalanche burial pathophysiology - a unique combination of hypoxia, hypercapnia and hypothermia

For often unclear reasons, the survival times of critically buried avalanche victims vary widely from minutes to hours. Individuals can survive and sustain organ function if they can breathe under the snow and maintain sufficient delivery of oxygen and efflux of carbon dioxide. We review the physiological responses of humans to critical avalanche burial, a model which shares similarities and differences with apnoea and accidental hypothermia. Within a few minutes of burial, an avalanche victim is exposed to hypoxaemia and hypercapnia, which have important effects on the respiratory and cardiovascular systems and pose a major threat to the central nervous system. As burial time increases, an avalanche victim also develops hypothermia. Despite progressively reduced metabolism, reduced oxygen and increased carbon dioxide tensions may exacerbate the pathophysiological consequences of hypothermia. Hypercapnia seems to be the main cause of cardiovascular instability, which, in turn, is the major reason for reduced cerebral oxygenation despite reductions in cerebral metabolic activity caused by hypothermia. 'Triple H syndrome' refers to the interaction of hypoxia, hypercapnia and hypothermia in a buried avalanche victim. Future studies should investigate how the respiratory gases entrapped in the porous snow structure influence the physiological responses of buried individuals and how haemoconcentration, blood viscosity and cell deformability affect blood flow and oxygen delivery. Attention should also be devoted to identifying strategies to prolong avalanche survival by either mitigating hypoxia and hypercapnia or reducing core temperature so that neuroprotection occurs before the onset of cerebral hypoxia.

A century of exercise physiology: concepts that ignited the study of human thermoregulation. Part 3: Heat and cold tolerance during exercise

In this third installment of our four-part historical series, we evaluate contributions that shaped our understanding of heat and cold stress during occupational and athletic pursuits. Our first topic concerns how we tolerate, and sometimes fail to tolerate, exercise-heat stress. By 1900, physical activity with clothing- and climate-induced evaporative impediments led to an extraordinarily high incidence of heat stroke within the military. Fortunately, deep-body temperatures > 40 °C were not always fatal. Thirty years later, water immersion and patient treatments mimicking sweat evaporation were found to be effective, with the adage of cool first, transport later being adopted. We gradually acquired an understanding of thermoeffector function during heat storage, and learned about challenges to other regulatory mechanisms. In our second topic, we explore cold tolerance and intolerance. By the 1930s, hypothermia was known to reduce cutaneous circulation, particularly at the extremities, conserving body heat. Cold-induced vasodilatation hindered heat conservation, but it was protective. Increased metabolic heat production followed, driven by shivering and non-shivering thermogenesis, even during exercise and work. Physical endurance and shivering could both be compromised by hypoglycaemia. Later, treatments for hypothermia and cold injuries were refined, and the thermal after-drop was explained. In our final topic, we critique the numerous indices developed in attempts to numerically rate hot and cold stresses. The criteria for an effective thermal stress index were established by the 1930s. However, few indices satisfied those requirements, either then or now, and the surviving indices, including the unvalidated Wet-Bulb Globe-Thermometer index, do not fully predict thermal strain.

Autoregulation of Cerebral Blood Flow During 3-h Continuous Cardiopulmonary Resuscitation at 27°C

Introduction: Victims of accidental hypothermia in hypothermic cardiac arrest (HCA) may survive with favorable neurologic outcome if early and continuous prehospital cardiopulmonary resuscitation (CPR) is started and continued during evacuation and transport. The efficacy of cerebral autoregulation during hypothermic CPR is largely unknown and is aim of the present experiment. Methods: Anesthetized pigs (n = 8) were surface cooled to HCA at 27°C before 3 h continuous CPR. Central hemodynamics, cerebral O₂ delivery (DO₂) and uptake (VO₂), cerebral blood flow (CBF), and cerebral perfusion pressure (CPP) were determined before cooling, at 32°C and at 27°C, then at 15 min after the start of CPR, and hourly thereafter. To estimate cerebral autoregulation, the static autoregulatory index (sARI), and the CBF/VO₂ ratio were determined. Results: After the initial 15-min period of CPR at 27°C, cardiac output (CO) and mean arterial pressure (MAP) were reduced significantly when compared to corresponding values during spontaneous circulation at 27°C (-66.7% and -44.4%, respectively), and remained reduced during the subsequent 3-h period of CPR. During the first 2-h period of CPR at 27°C, blood flow in five different brain areas remained unchanged when compared to the level during spontaneous circulation at 27°C, but after 3 h of CPR blood flow in 2 of the 5 areas was significantly reduced. Cooling to 27°C reduced cerebral DO₂ by 67.3% and VO₂ by 84.4%. Cerebral VO₂ was significantly reduced first after 3 h of CPR. Cerebral DO₂ remained unaltered compared to corresponding levels measured during spontaneous circulation at 27°C. Cerebral autoregulation was preserved (sARI > 0.4), at least during the first 2 h of CPR. Interestingly, the CBF/VO₂ ratio during spontaneous circulation at 27°C indicated the presence of an affluent cerebral DO₂, whereas after CPR, the CBF/VO₂ ratio returned to the level of spontaneous circulation at 38°C. Conclusion: Despite a reduced CO, continuous CPR for 3 h at 27°C provided sufficient cerebral DO₂ to maintain aerobic metabolism and to preserve cerebral autoregulation during the first 2-h period of CPR. This new information supports early start and continued CPR in accidental hypothermia patients during rescue and transportation for in hospital rewarming.

Olanzapine-Induced Therapeutic Hypothermia Attenuates Renal Injury in Rats after Asphyxial Cardiac Arrest and Resuscitation

Return of spontaneous circulation (ROSC) through cardiopulmonary resuscitation (CPR) after cardiac arrest (CA) causes post-cardiac arrest syndrome (PCAS) due to dysfunction in various organs, which provokes acute kidney injury because of renal ischemia-reperfusion injury. Therapeutic hypothermia (TH) can reduce PCAS after CA and ROSC. However, it needs to be more sophisticated and effective. Hence, we aimed to elucidate the protective effects of olanzapine-induced TH against renal injury in asphyxial CA-induced rats. Every rat’s body temperature was maintained at 33 °C for 6 h after administering olanzapine post-CA and ROSC. Olanzapine-induced TH dramatically increased the survival rate of the rats and ameliorated renal tissue damage. Moreover, it suppressed oxidative stress responses through preservation of mitochondrial function and endoplasmic reticulum stress as the main contributor of oxidative stress. Notably, these actions of olanzapine-induced TH were mediated through the Sirt3-related signaling pathway, including the maintenance of Sirt3 and FOXO3a protein expression and the activation of AMPKα and superoxide dismutase 1 (SOD2, a mitochondrial antioxidant). This study is the first to disclose the protective effects of olanzapine-induced TH against renal injury after CA and ROSC, suggesting that olanzapine-induced TH could be utilized for treating CA followed by ROSC.

Effects of hypothermia on inflammatory cytokine expression in rat liver following asphyxial cardiac arrest

Hypothermic treatment is known to protect against cardiac arrest (CA) and improve survival rate. However, few studies have evaluated the CA-induced liver damage and the effects of hypothermia on this damage. Therefore, the aim of the present study was to determine possible protective effects of hypothermia on the liver after asphyxial CA. Rats were subjected to a 5-min asphyxial CA followed by return of spontaneous circulation (ROSC). The body temperature was controlled at 37±0.5˚C (normothermia group) or 33±0.5˚C (hypothermia group) for 4 h after ROSC. Livers were examined at 6, 12 h, 1 and 2 days after ROSC. Histopathological examination was performed by H&E staining. Alterations in the expression levels of pro-inflammatory (TNF-α and interleukin IL-2) and anti-inflammatory cytokines (IL-4 and IL-13) were investigated by immunohistochemistry. Sinusoidal dilatation and vacuolization were observed after asphyxial CA by histopathological examination. However, these CA-induced structural alterations were prevented by hypothermia. In immunohistochemical examination, the expression levels of pro-inflammatory cytokines were reduced in the hypothermia group compared with those in the normothermia group while the expression levels of anti-inflammatory cytokines were increased in the hypothermia group compared with those in the normothermia group. In conclusion, hypothermic treatment for 4 h following asphyxial CA in rats inhibited the increase of pro-inflammatory cytokines and stimulated the expression of anti-inflammatory cytokines compared with the normothermic group. The results of the present study suggested that hypothermic treatment after asphyxial CA reduced liver damage via the regulation of inflammation.

DNA microarray analysis of hypothermia-exposed murine lungs for identification of forensic biomarkers

We used DNA microarray technology to analyze the pulmonary transcriptome of mice killed by hypothermia. This analysis identified significant differential regulation of 4094 genes; specifically, 1699 genes were upregulated, and 2395 were downregulated in response to hypothermia. The gene encoding cathelicidin antimicrobial peptide was the most upregulated gene, and that encoding BAI1-associated protein 2-like 1 was the most downregulated. Gene-set analysis identified significant hypothermia-induced variations in 101 pathways, and we discovered that pathways related to immunity are involved in the pulmonary pathogenesis of hypothermia. The present findings demonstrate some of the acute pulmonary responses to hypothermia and indicate several pulmonary genes as candidate forensic biomarkers of hypothermia. Furthermore, the present findings suggest that host defense is induced in hypothermic lungs. The present microarray data may facilitate the development of protein analyses for human forensics by immunohistochemistry, western blotting and enzyme-linked immunosorbent assay and may be beneficial in clinical research of hypothermia.

Study of the Effects of 3 h of Continuous Cardiopulmonary Resuscitation at 27°C on Global Oxygen Transport and Organ Blood Flow

Aims

Complete restitution of neurologic function after 6 h of pre-hospital resuscitation and in-hospital rewarming has been reported in accidental hypothermia patients with cardiac arrest (CA). However, the level of restitution of circulatory function during long-lasting hypothermic cardiopulmonary resuscitation (CPR) remains largely unknown. We compared the effects of CPR in replacing spontaneous circulation during 3 h at 27°C vs. 45 min at normothermia by determining hemodynamics, global oxygen transport (DO₂), oxygen uptake (VO₂), and organ blood flow.

Methods

Anesthetized pigs (n = 7) were immersion cooled to CA at 27°C. Predetermined variables were compared: (1) Before cooling, during cooling to 27°C with spontaneous circulation, after CA and subsequent continuous CPR (n = 7), vs. (2) before CA and during 45 min CPR in normothermic pigs (n = 4).

Results

When compared to corresponding values during spontaneous circulation at 38°C: (1) After 15 min of CPR at 27°C, cardiac output (CO) was reduced by 74%, mean arterial pressure (MAP) by 63%, DO₂ by 47%, but organ blood flow was unaltered. Continuous CPR for 3 h maintained these variables largely unaltered except for significant reduction in blood flow to the heart and brain after 3 h, to the kidneys after 1 h, to the liver after 2 h, and to the stomach and small intestine after 3 h. (2) After normothermic CPR for 15 min, CO was reduced by 71%, MAP by 54%, and DO₂ by 63%. After 45 min, hemodynamic function had deteriorated significantly, organ blood flow was undetectable, serum lactate increased by a factor of 12, and mixed venous O₂ content was reduced to 18%.

Conclusion

The level to which CPR can replace CO and MAP during spontaneous circulation at normothermia was not affected by reduction in core temperature in our setting. Compared to spontaneous circulation at normothermia, 3 h of continuous resuscitation at 27°C provided limited but sufficient O₂ delivery to maintain aerobic metabolism. This fundamental new knowledge is important in that it encourages early and continuous CPR in accidental hypothermia victims during evacuation and transport.

Mild Hypothermia Pretreatment Attenuates Liver Ischemia Reperfusion Injury Through Inhibiting c-Jun NH2-terminal Kinase Phosphorylation in Rats

BACKGROUND

Mild hypothermia is known to be protected against ischemia reperfusion (IR) injury. But the exact mechanisms of protection have not yet been fully understood and its usage has been limited. Mild hypothermia pretreatment (MHP) is used to investigate the mechanisms of the protective effects against liver IR injury.

METHODS

Anesthetized male Sprague-Dawley rats were randomly divided into five groups including the normal group (N), sham group (S), MHP group, normothermia pretreatment (NP) + IR group, and the MHP + IR group. In the pretreatment groups, mild hypothermia (32.2 ± 0.3°C) and normothermia (37 ± 0.5°C) pretreatment were applied for 2 hours, respectively. Then the IR groups suffered partial (70%) hepatic ischemia for 1 hour and reperfusion for 6 hours. At last, hepatic injury, apoptosis, and protein expression were assessed.

RESULTS

Levels of serum alanine transaminase, hepatic injury, hepatocyte apoptosis, and c-Jun N-terminal kinase (JNK) phosphorylation were significantly higher in the IR groups. But when compared to NP, all these changes induced by IR were markedly attenuated by MHP. Serum alanine transaminase levels were 383.4 ± 13.1U/L in the MHP + IR group and 951.3 ± 39.4 U/L in the NP + IR group. The histologic score of liver injury in the MHP + IR group was 4.83 ± 1.17, whereas in the NP + IR group it was 10.5 ± 1.05. The proportion of apoptotic cells in the MHP + IR group was 11.58 ± 0.60, but in the NP + IR group, it was 44.95 ± 1.61. The phosphorylation of JNK was also significantly reduced in the MHP + IR group. All these differences are statistically significant (P < .05).

CONCLUSIONS

MHP could markedly reduce liver IR injury, and these protective effects may be mainly exerted via inhibition of JNK phosphorylation.

Basis for the use of localized hypothermia during radical pelvic surgery

Controlled tissue cooling, or hypothermia, has been used therapeutically for decades to mitigate the negative effects of traumatic, ischemic, and surgical insults. When applied systemically, moderate hypothermia can attenuate or prevent the extent of neurologic sequelae. Localized hypothermia, on the other hand, has the capacity to reduce tissue edema, suppress inflammation, and minimize the severity of peripheral nerve injury. Therapeutic hypothermia has been used in critical care, neurosurgery, ophthalmology, otolaryngology, cardiothoracic surgery and most recently in urology. Nerve injury during radical pelvic surgery can result in urinary incontinence or retention, impotence and bowel dysfunction. Localized hypothermia during radical prostatectomy has demonstrated improved recovery of urinary continence and erectile function, and similar benefits might be observed in other types of radical pelvic surgery.

Body temperature effects on lung injury in ventilated preterm lambs

AIMS

Mechanical ventilation causes lung injury in premature infants. Hypothermia may protect against and hyperthermia may augment lung injury. We tested the effects of hypo- and hyperthermia on ventilation induced acute lung injury in preterm lambs.

METHODS

Twin sheep fetuses at 128 d GA (term 150 d) were surgically delivered and randomized to unventilated control (UVC), normothermia (38-39 degrees C) without lung injury (NTNI), or to 1 of 3 injurious ventilation groups: hypothermic (33-34 degrees C, LT), normothermic (38-39 degrees C, NT) or hyperthermic (40-41 degrees C, HT). NT, LT and HT groups had 15 min of injurious ventilation (PEEP 0 cmH(2)O, V(T) escalation to 15 mL/kg) following delivery and prior to surfactant. The animals were then gently ventilated (PEEP 5cmH(2)O, V(T) 7.5 mL/kg) for 2h 45 min. NTNI lambs received surfactant at birth prior to gentle ventilation. The lambs were then euthanized, and bronchoalveolar lavage (BAL) fluid and lung tissue were used to evaluate lung injury, inflammatory cell counts, inflammatory markers and cytokine mRNA.

RESULTS

Target temperatures were achieved by 15 min of age and maintained for 3h. All ventilated groups had increased BAL protein, lung inflammation and increased cytokine mRNA. HT animals developed acidosis, premature death, pneumothoraces, impaired lung function and increased inflammatory mRNA expression. LT animals remained clinically stable without pneumothoraces or death, had improved ventilatory efficiency and trended toward lower inflammatory mRNA expression than NT animals.

CONCLUSION

Hyperthermia exacerbated ventilator induced lung injury, while hypothermia may protect against lung injury in the preterm lamb.

Mild hypothermia reduces the inflammatory response and hepatic ischemia/reperfusion injury in rats

BACKGROUND/AIMS

Hypothermia is known to protect against ischemia/reperfusion (I/R) injury. The mechanisms of protection are incompletely understood and a temperature threshold for protection has not been established.

METHODS

In anesthetized Wistar rats, partial (70%) hepatic ischemia was applied for 45 min. Three study groups were used. Group T31 (n = 6) spontaneously cooled to 31.3 +/- 0.8 degrees C, while group T34 (n = 6) spontaneously cooled to 34 degrees C and was then maintained at 34.0 +/- 0.1 degrees C using a heat lamp. The normothermic group (T37, n = 6) was maintained at 37.1 +/- 0.3 degrees C. Hepatic injury, inflammation, lipid peroxidation and metabolic function (using quantitative 1H-NMR) were assessed 24 h after reperfusion.

RESULTS

At 24 h following reperfusion, alanine aminotransferase and aspartate aminotransferase increased to 5101 +/- 2378 and 6409 +/- 4202 U/l in the normothermic T37 group (P < 0.05 vs. T34 and T31), whereas transaminases in hypothermic groups (T31 and T34) were significantly lower. Severe liver necrosis was only noted with T37. Myeloperoxidase activity was increased in the T37 group when compared with hypothermic groups (223 +/- 161 (T37) vs. 16 +/- 10 (T31) and 8 +/- 5 (T34) mU/min/mg of tissue, P<0.05 vs. T31 and T34). 1H-NMR analysis of the blood of normothermic animals revealed metabolic changes consistent with increased ischemic injury, which was almost completely ameliorated in T34 and T31 groups.

CONCLUSIONS

Mild hypothermia of 34 degrees C is sufficient to reduce I/R injury by inhibiting the inflammatory response. Further spontaneous cooling to 31 degrees C did not demonstrate any additional protective effect.

BRAIN COOLING CAUSES ATTENUATION OF CEREBRAL OXIDATIVE STRESS, SYSTEMIC INFLAMMATION, ACTIVATED COAGULATION, AND TISSUE ISCHEMIA/INJURY DURING HEATSTROKE

The purpose of the present study was to assess the therapeutic effect of hypothermic retrograde jugular vein flush (HRJVF) on heatstroke. HRJVF was accomplished by infusion of 4 degrees C isotonic sodium chloride solution via the external jugular vein (1.7 mL/100 g of body weight over 5 min). Immediately after the onset of heatstroke, anesthetized rats were divided into 2 major groups and given the following: 36 degrees C or 4 degrees C isotonic sodium chloride solution, i.v. They were exposed to ambient temperature of 43 degrees C to induce heatstroke. Another group of rats was exposed to room temperature (24 degrees C) and used as normothermic controls. When the 36 degrees C saline-treated rats underwent heat exposure, their survival time values were found to be 23 to 28 min. Immediately after the onset of heatstroke, resuscitation with an i.v. dose of 4 degrees C saline significantly improved survival during heatstroke (208-252 min). All heat-stressed animals displayed systemic inflammation and activated coagulation, evidenced by increased tumor necrosis factor alpha, prothrombin time, activated partial thromboplastin time, and d-dimer, and decreased platelet count and protein C. Biochemical markers evidenced cellular ischemia and injury/dysfunction: plasma levels of blood urea nitrogen, creatinine, glutamic oxaloacetic transaminase, glutamic pyruvic transaminase, and alkaline phosphatase; and striatal levels of glycerol, glutamate, and lactate/pyruvate; dihydroxy benzoic acid, lipid peroxidation, oxidized-form glutathione reduced-form glutathione, dopamine, and serotonin were all elevated during heatstroke. Core and brain temperatures and intracranial pressure were also increased during heatstroke. In contrast, the values of mean arterial pressure, cerebral perfusion pressure, and striatal levels of local blood flow, partial pressure of oxygen, superoxide dismutase, catalase, glutathione peroxidase, and glutathions reductase activities were all significantly lower during heatstroke. The circulatory dysfunction, systemic inflammation, hypercoagulable state, and cerebral oxidative stress, ischemia, and damage during heatstroke were all significantly suppressed by HRJVF. These findings demonstrate that brain cooling caused by HRJVF therapy may resuscitate persons who had a stroke by attenuating cerebral oxidative stress, systemic inflammation, activated coagulation, and tissue ischemia/injury during heatstroke.

Whole-body moderate hypothermia confers protection from wood smoke-induced acute lung injury in rats: The therapeutic window*

OBJECTIVE

Toxic smoke inhalation causes acute lung injury. We studied the efficacy and therapeutic window of whole-body hypothermia in rats with wood smoke-induced acute lung injury.

DESIGN

Randomized, controlled study.

SETTING

Research laboratory.

SUBJECTS

Anesthetized, paralyzed, and artificially ventilated rats (n = 100) were used.

INTERVENTIONS

Air or wood smoke (30 breaths) was delivered into the lung using a respirator. Immediately after challenge, the rat's colonic temperature was kept a) 37 degrees C (normothermia, NT) for 1 (NT-1-Air and NT-1-Smoke), 2.5 (NT-2.5-Air and NT-2.5-Smoke), or 5 hrs (NT-5-Air and NT-5-Smoke) in six groups; b) 30 degrees C (hypothermia, HT) for 2.5 (HT-2.5-Smoke) or 5 hrs (HT-5-Air and HT-5-Smoke) in three groups; c) 30 degrees C for the first 2.5 hrs followed by 37 degrees C for another 2.5 hrs (HT-NT-5-Smoke) in one group; or d) 37 degrees C for the first 2.5 hrs followed by 30 degrees C for another 2.5 hrs (NT-HT-5-Smoke) in on group.

MEASUREMENTS AND MAIN RESULTS

Various acute lung injury indexes were assessed at 1, 2.5, or 5 hrs after challenge. In the air group, whole-body hypothermia did not affect the level of lung lipid peroxidation and the amount of proteins, total and differential cell counts, and concentrations of tumor necrosis factor-alpha and interleukin-1beta in bronchoalveolar lavage fluid. In the smoke groups, these acute lung injury indexes were increased showing that NT-5-Smoke > NT-2.5-Smoke > NT-1-Smoke. Whole-body hypothermia prevented increases in these acute lung injury indexes in the HT-2.5-Smoke and HT-5-Smoke groups. The efficacy of whole-body hypothermia in the HT-NT-5-Smoke group was superior to that in the NT-HT-5-Smoke group and similar to that in the HT-5-Smoke group. Whole-body hypothermia also alleviated smoke-induced poor gas exchange, pulmonary edema, and pathohistologic injurious signs.

CONCLUSIONS

Whole-body hypothermia confers protection from wood smoke-induced acute lung injury in rats by suppressing oxidant bronchoalveolar damage and pulmonary inflammation. Early and short-period (2 hrs) application of whole-body hypothermia provides favorable therapeutic effects.

End-point Temperature of Rewarming After Hypothermic Cardiopulmonary Bypass in Pediatric Patients

In an attempt to find an adequate end-point rewarming temperature after hypothermic cardiopulmonary bypass (CPB), 50 pediatric patients who underwent cardiac surgery were randomly assigned for the end-point rectal rewarming temperature at either 35.5 (Group 1) or 37.0 degrees C (Group 2). The patients' rectal temperature, with heart rate and blood pressure, was measured 0.5, 1.0, 4.0, 8.0, and 16.0 h after the arrival in the intensive care unit. For all patients, nonpulsatile perfusion with a roller pump and a membrane or bubble oxygenator was used for oxygenation. Age, sex, body surface area, total bypass time, and rewarming time were comparable in both groups. No afterdrop and no statistical differences in the rectal temperatures between the two groups were observed. Also, no statistical differences were observed between the two groups with respect to the heart rate and blood pressure. No shivering was noted in all patients. In conclusion, with the restoration of rectal temperature above 35.5 degrees C at the end of CPB in pediatric patients, the present study found no afterdrop.

The Role of Thermoregulation in Cardiac Resuscitation

Regulating a patient's body temperature has long been within the scope of practice of the critical care nurse. Different measures and modalities have been used to achieve normothermia in the past. Recent research has demonstrated how crucial body temperature can be, not only because of its potential for neuroprotection but also because of its effects on all body systems. The general consensus of current literature is that maintaining mild hypothermia at 32 degrees to 34 degrees C (89.6 degrees-93.2 degrees F) for 12 to 24 hours after cardiac arrest may provide optimal neuroprotection with minimal complications for patients.

Perioperative blood glucose control during adult coronary artery bypass surgery

Coronary artery bypass graft (CABG) procedures are among the most frequently performed surgical procedures in the United States. People with cardiovascular disease who also have diabetes have a greater risk of poor outcomes after CABG procedures than patients who do not have diabetes. This literature review examines current information regarding perioperative blood glucose (BG) control. It emphasizes BG control in adults during the hypothermic period of cardiopulmonary bypass. Hyperglycemia, not the diagnosis of diabetes, significantly increases the risk of adverse clinical outcomes, longer hospitalizations, and increased health care costs.

Metoprolol and coronary artery bypass grafting surgery: does intraoperative metoprolol attenuate acute beta-adrenergic receptor desensitization during cardiac surgery?

Cardiac surgery results in significant impairment of beta-adrenergic receptor (beta AR) function and is a cause of depressed myocardial function after surgery. We previously demonstrated that acute administration of beta AR blocker during cardiopulmonary bypass (CPB) in an animal model of coronary artery bypass grafting (CABG) surgery attenuates beta AR desensitization, whereas chronic oral beta-blockade therapy in patients undergoing CABG surgery does not prevent it. Therefore we hypothesized that acute administration of metoprolol during CABG surgery would prevent acute myocardial beta AR desensitization. A placebo-controlled initial phase (n = 72) was performed whereby patients were randomized to either metoprolol 10 mg or placebo immediately before CPB. Then a second dose-finding study was performed where patients received 20 mg (n = 20) or 30 mg (n = 20) of metoprolol. Hemodynamic monitoring, atrial membrane adenylyl cyclase activity, atrial beta AR density, and postoperative outcomes were measured. All groups showed similar decreases in isoproterenol-stimulated adenylyl cyclase activity (13%-24%). Cardiac output remained similar in all 4 groups throughout the intraoperative and postoperative period. In addition, patients receiving metoprolol 20 or 30 mg had less supraventricular arrhythmias 24 h postoperatively compared with patients receiving metoprolol 10 mg or placebo. Therefore, unlike our previous animal model of CABG surgery, metoprolol did not attenuate myocardial beta AR desensitization.

IMPLICATIONS

We investigated whether IV metoprolol given during cardiac surgery attenuates myocardial beta-adrenergic receptor (beta AR) desensitization. Although metoprolol did not reduce beta AR desensitization, the incidence of supraventricular arrhythmias was reduced by 75% in patients receiving 20 mg or 30 mg metoprolol.

Tissue-specific extravasation of albumin-bound Evans blue in hypothermic and rewarmed rats

The effects of hypothermia and rewarming on endothelial integrity were examined in intestines, kidney, heart, gastrocnemius muscle, liver, spleen, and brain by measuring albumin-bound Evans blue loss from the vasculature. Ten groups of twelve rats, normothermic with no pentobarbital, normothermic sampled at 2, 3, or 4 h after pentobarbital, hypothermic to 20, 25, or 30 degrees C, and rewarmed from 20, 25, or 30 degrees C, were cooled in copper coils through which water circulated. Hypothermic rats were cooled to the desired core temperature and maintained there for 1 h; rewarmed rats were cooled to the same core temperatures, maintained there for 1 h, and then rewarmed. Following Evans blue administration, animals were euthanized with methoxyflurane, tissues removed, and Evans blue extracted. Because hypothermia and rewarming significantly decrease blood flow, organ-specific flow rates for hypothermic and rewarmed tissues were used to predict extravasation. Hypothermia decreased extravasation in tissues with continuous endothelium (brain, muscle) and increased it in tissues with discontinuous endothelium (liver, lung, spleen). All tissues exhibited significant (p < 0.05) differences from normothermic controls. These differences are attributed to a combination of anesthesia, flow, and (or) change in endothelial permeability, suggesting that appropriate choice of organ and temperature would facilitate testing pharmacological means of promoting return to normal perfusion.

Physiologic characteristics of cold perfluorocarbon-induced hypothermia during partial liquid ventilation in normal rabbits

Because perfluorocarbon (PFC) liquid contacts closely with the alveolar capillaries during partial liquid ventilation (PLV), PLV with cold PFC may be used for the induction of hypothermia. Twenty rabbits were randomized to PFC-induced hypothermia (PH) (n = 7; core temperature 35 degrees +/- 1 degrees C), surface hypothermia (SH) (n = 7; 35 degrees +/- 1 degrees C), or normothermia (n = 6; 39 degrees +/- 1 degrees C). We induced PH by repeated in situ exchanges of 0 degrees C perfluorodecalin during PLV. At the establishment (0 min) of hypothermia in the PH group, oxygen consumption (P = 0.04) and oxygen extraction ratio (P = 0.01) decreased from normothermic condition. Metabolic (oxygen consumption, oxygen extraction ratio, serum lactate level) and hemodynamic variables (heart rate, blood pressure, cardiac output, pulmonary artery pressure) of the PH group were not different from those of the SH group at 0, 30, 60, 90, and 120 min of hypothermia. The difference in temperature between the pulmonary artery and rectum during the hypothermic period was smaller in the PH group compared with the SH group (P = 0.033). In conclusion, hypothermia may be induced during PLV by using cold PFC. This "pulmonary method" of cooling was comparable to a systemic method of cooling with regard to a few important physiologic variables, while maintaining a narrower interorgan temperature difference.

IMPLICATIONS

The induction of moderate hypothermia was feasible in rabbits by administrating cold perfluorocarbon liquid into the lung. Physiologic changes induced by this pulmonary cooling were comparable to those induced by systemic cooling. Our method may be regarded as a methodological advance in the field of therapeutic hypothermia.

Is hyperglycemia seen in children during cardiopulmonary bypass a result of hyperoxia?

OBJECTIVE

We sought to identify whether elevated PaO (2) itself can directly cause hyperglycemia in newborns and to document any additional effects of cardiopulmonary bypass on this response.

METHODS

Piglets were exposed to either normoxia (88 +/- 6 mm Hg) or hyperoxia (470 +/- 28 mm Hg) in the following studies. Anesthetized 3-day-old neonatal pigs were either ventilated for 2 hours of normoxia (n = 5) or hyperoxia (n = 5) or placed on normothermic, normoxic cardiopulmonary bypass (n = 6) and then randomly assigned to either undergo a 2-hour normoxic period or a 1-hour hyperoxic episode, followed by a return to normoxia for an additional hour. Blood glucose levels were measured in all animals.

RESULTS

No significant changes were observed in blood glucose levels in neonatal pigs that underwent 2 hours of normoxic ventilation (5.0 +/- 0.6 mmol/L) or cardiopulmonary bypass (6.6 +/- 1.6 mmol/L). However, the ventilatory model showed a significant and sustained (P <.001) hyperglycemic response after both 1 hour (8.6 +/- 1.0 mmol/L) and 2 hours (9.8 +/- 1.6 mmol/L) of hyperoxia. In the cardiopulmonary bypass model, exposure to 1 hour of hyperoxia elicited a significant (P <.05) hyperglycemic response (10.3 +/- 1.2 mmol/L), followed by a return to normal blood glucose levels (6.6 +/- 1.6 mmol/L) with a return to normoxia. This hyperoxia-mediated hyperglycemic response was confirmed when data examined from children undergoing cardiopulmonary bypass for primary repair of their congenital defects also identified a significant positive correlation (r = 0.72, P =.02) between oxygen levels and blood glucose levels measured before and at the end of cardiopulmonary bypass.

CONCLUSIONS

Hyperoxia triggers a hyperglycemic response in both ventilatory and bypass models. Cardiopulmonary bypass does not exacerbate this response, as shown by the similar levels of hyperglycemia sustained for the duration of the hyperoxic exposure in both experimental models. Therefore, not only may hyperoxia play a crucial role in the hyperglycemic response seen during neonatal cardiopulmonary bypass, but its effect on glucose homeostasis should be considered whenever children are exposed to hyperoxia.

Magnesium sulfate attenuates increased blood-brain barrier permeability during insulin-induced hypoglycemia in rats

Magnesium probably protects brain tissue against the effects of cerebral ischemia, brain injury and stroke through its actions as a calcium antagonist and inhibitor of excitatory amino acids. The effects of magnesium sulfate on cerebrovascular permeability to a dye, Evans blue, were studied during insulin-induced hypoglycemia with hypothermia in rats. Hypoglycemia was induced by an intramuscular injection of insulin. After giving insulin, each animal received MgSO4 (270 mg/kg) ip, followed by a 27 mg/kg dose every 20 min for 2.5 h. Plasma glucose and Mg2+ levels of animals were measured. Magnesium concentrations increased in the serum following MgSO4 administration (6.05 ± 0.57 vs. 2.58 ± 0.14 mg/dL in the Mg2+ group, and 7.14 ± 0.42 vs. 2.78 ± 0.06 mg/dL in the insulin + Mg2+ group, P < 0.01). Plasma glucose levels decreased following hypoglycemia (4 ± 0.66 vs. 118 ± 2.23 mg/dL in the insulin group, and 7 ± 1.59 vs. 118 ± 4.84 mg/dL in the insulin + Mg2+ group, P < 0.01). Blood-brain barrier permeability to Evans blue considerably increased in hypoglycemic rats (P < 0.01). In contrast, blood-brain barrier permeability to Evans blue was significantly reduced in treatment of hypoglycemic rats with MgSO4 (P < 0.01). These results indicate that Mg2+ greatly reduced the passage of exogenous vascular tracer bound to albumin into the brain during hypoglycemia with hypothermia. Mg2+ could have protective effects on blood-brain barrier permeability against insulin-induced hypoglycemia.Key words: blood-brain barrier, hypoglycemia, Mg2+, Evans-blue.

Effects of profound hypothermia on the blood–brain barrier permeability in acute and chronically ethanol treated rats

This study examines the effects of profound hypothermia on the blood-brain barrier (BBB) permeability in ethanol administrated rats. Vascular permeability to intravenously injected Evans blue (EB) was quantitatively examined in the brain regions of rats. Rats were treated with ethanol acute and chronically. Rectal temperature of rats was dropped into 20+/-1 degrees C during profound hypothermia. Mean arterial blood pressure in both acute and chronic ethanol treatments plus hypothermia significantly dropped into low levels as well as in hypothermia alone (P<0.01). Hypothermia led to a significant increase in the content of EB dye in the brain regions of rats (P<0.05). Both acute and chronic ethanol treatments plus hypothermia did not lead to a significant increase in the BBB permeability against intravenously injected EB dye. We conclude that ethanol intake protects the BBB against the effects of hypothermia.

Effects of induced hypothermia on renal sympathetic nerve activity and baroreceptor reflex in urethane-anesthetized rabbits

OBJECTIVE

To evaluate the role of the autonomic nervous system in hemodynamic changes during induced hypothermia.

DESIGN

Prospective, randomized animal study.

SETTING

An animal research laboratory in a medical university.

SUBJECTS

A total of 29 anesthetized rabbits.

INTERVENTIONS

Animals were anesthetized by intraperitoneal urethane. After tracheostomy and administration of gallamine, respiration was maintained by mechanical ventilatory support. The animals were divided into five groups (one control and the four experimental groups); animals were treated with an intact neuraxis and normothermia (control group), animals with an intact neuraxis (intact group), cervical vagotomized animals (vagotomy group), the carotid sinus and aortic nerves denervated animals (SAD group), and animals with SAD plus vagotomy (SADV group). The left renal sympathetic nerves were exposed by a retroperitoneal approach.

MEASUREMENTS AND MAIN RESULTS

We examined the effects of surface cooling on HR, mean arterial pressure, central venous pressure, and renal sympathetic nerve activity (RSNA) in the animals. Changes of baroreflex sensitivity and plasma catecholamines were also measured simultaneously. Surface cooling caused progressive and profound decreases in HR in all experimental groups. In all groups, RSNAs increased at the early phase, which were followed by return to the precooling level.

CONCLUSIONS

Hemodynamics and RSNA during induced hypothermia are regulated by mechanisms other than the baroreceptor reflex system, possibly the dermal cold receptors. Suppression of the baroreflex occurred on HR but not on RSNA during hypothermia, which may indicate direct effects of hypothermia on the heart. RSNA responses may be activated earlier than systemic catecholamine responses during induced hypothermia.

Intravenous administration of levothyroxine for treatment of suspected myxedema coma complicated by severe hypothermia in a dog

A 7-year-old male English Coonhound with suspected myxedema coma complicated by severe hypothermia and metabolic abnormalities was treated with a combination of active external and core rewarming techniques, i.v. and oral administration of levothyroxine, supplemental oxygen, and administration of fluids (0.9% NaCl solution). Myxedema coma develops as a consequence of severe hypothyroidism and is characterized by a hypometabolic, stuporous state. Myxedema coma is associated with a high mortality rate, and most reported cases have involved Doberman Pinschers. Intravenous administration of levothyroxine can be used successfully in combination with oral administration to restore normal metabolic function and assist in warming and thermoregulation, although dosages should be conservative to avoid adverse cardiovascular effects.

Experimental studies on the endothelium ultrastructure of heart capillaries under moderate (28-30 degrees) and deep (22-24 degrees) hypothermia without perfusion

Ultrastructural changes in endothelial cells (EC) of myocardial capillaries were studied in 24 dogs which underwent hypothermia without perfusion. Biopsy specimens for electron microscopy were taken from the left ventricle of each dog in the control group, during anesthesia (prior to active cooling), and at the end of moderate (28-30 degrees ) and deep (22-24 degrees ) artificial body cooling. The following morphological types of the EC were identified both in the control group and in all test groups: those with moderately dense cytoplasm, light, dark, and irreversibly damaged cells. Dark cells showed increased numbers of plasmalemmal vesicles and appeared to be more transport-specialized as opposed to other types. In all stages of the experiment the amount of dark cells continuously increased (to 23.80, 34.62, and 47.17%, respectively). On cooling to 28-30 degrees, subcellular manifestation of reduced synthetic activity of organelles (nucleus, Golgi complex, and rough endoplasmic reticulum) was observed in all types of the EC. These changes persisted, or even increased, at the end of deep hypothermia. The transport activity of the EC changed differently in three experimental groups in all cell types. Micropinocytotic activity increased under spontaneous mild hypothermia (34-35 degrees ) during anesthesia and tended to decrease with subsequent artificial lowering of the temperature to 22-24 degrees. These ultrastructural changes seem to make up an integral part of the process of capillary endothelium adaptation to body surface cooling, and they might contribute to the development of tolerance to subsequent ischemic exposure during cardiac arrest.

Adenosine-triphosphate in trauma-related and elective hypothermia

BACKGROUND

In trauma patients, hypothermia is a frequent event. According to the literature, the majority of trauma patients are presenting a core temperature of less than 34 degrees C at admission. In contrast to the benefit of hypothermia in elective surgery, clinical experience with hypothermia in trauma patients has identified hypothermia to be one major cause of severe posttraumatic complications. It was hypothesized that this diverse effect of hypothermia is related to depletion of high-energy phosphates like adenosine triphosphate (ATP) in trauma patients. To verify this hypothesis, the relation of ATP plasma levels and hypothermia was examined in a clinical study.

METHODS

Three different groups of patients were under study. The first group (group A, normothermic control group) included patients (n = 15) undergoing elective surgery of the lower limb with a mean operation time of 113 minutes. The second study group (group B, hypothermic control) was composed of patients (n = 15) who were subjected to elective coronary artery bypass operation under hypothermia (31 degrees C for 48 minutes, mean total operation time being 205 minutes). The third study group (group C) included trauma patients (n = 23, mean Injury Severity Score [ISS] of 24.7). At the time of admission, 10 patients presented a core temperature more than or equal to 34 degrees C (group C1, mean ISS, 25.2; mean T(A), 34.5 degrees C), 13 patients presented a T(A) less than 34 degrees C (group C2, mean ISS, 26.0; mean T(A), 32.9 degrees C). In both groups of surgical patients, the ATP plasma level was measured preoperatively, at 2, 4, and 24 hours postoperatively. For trauma patients, this measurement was performed at admission and 24 hours later. Within the same schedule, body core temperature was recorded and the clinical course was documented as well.

RESULTS

Elective limb surgery in normothermic patients resulted only in a transient decrease in ATP plasma levels (preoperative, 87.8 micromol/dL; 4 hours postoperative, 52.0 micromol/dL). At 24 hours, the ATP plasma level (62.6 +/- 10.0 micromol/dL) has increased toward baseline level. Elective hypothermia in patients subjected to coronary bypass also resulted only in a transient decrease in ATP plasma levels. During the operation period, including hypothermia, the ATP plasma level was comparable (50.4 micromol/dL) to group A and also returned back toward normal values at 24 hours (58.2 micromol/dL). All trauma patients revealed a significant low ATP plasma level at admission compared with both control groups. Looking at subdivided groups the most significant drop in ATP plasma level (28.5 micromol/dL) was noted in patients presenting an initial core temperature less than 34 degrees C and ISS more than 30. Even 24 hours later, the ATP level of this subgroup was significantly diminished, despite a rise up to 44.4 micromol/dL. In contrast, only a moderate drop in ATP plasma concentration (59.2 micromol/dL) was noted in the group of T(A) more than or equal to 34 degrees C and ISS less than 20. This group revealed almost normal values (68.3 micromol/dL) 24 hours after trauma. In addition to hypothermia, the metabolic state, reflected by the plasma lactate levels, significantly influenced the ATP plasma levels, as high lactate levels were paralleled by low ATP levels. Also, the overall outcome was related to injury severity and hypothermia.

CONCLUSION

Hypothermia in elective surgery, established by active cooling, preserves the ATP storage and maintains an aerobic metabolism, which both contribute to the beneficial effect of hypothermia in ischemia/reperfusion in cardiovascular surgery. However, in trauma patients hypothermia is caused by insufficient heat production due to utilization of ATP under anaerobic metabolic conditions. Low ATP plasma levels combined with hypothermia seem to be a predisposition for post-traumatic complications like organ failure.

Temperature dependency of the vagal chronotropic response in the young puppy: an 'environmental-autonomic interaction'

We investigated the effects of mild hypothermia (34.3 +/- 0.2 degrees C [mean +/- SD]), hyperthermia (40.8 +/- 0.2 degrees C) and hypoxia (PaO2 = 43 +/- 4 mmHg) on the response to heart rate to continuous right vagus nerve stimulation (the 'vagal chronotropic response') in young puppies, aged 5-22 days. Puppies were anesthetized with alpha-chloralose, vagotomized and pre-treated with propranolol (1 mg/kg i.v.) and phentolamine (1 mg/kg, 1-2 mg/kg/h i.v.). Hypoxia (n = 9) did not significantly alter the resting sinus cycle length and did not alter the response of sinus cycle to a 30 s train of 8 Hz right vagal stimulation. Mild hypothermia (n = 8) increased the resting sinus cycle length by 16 +/- 4% and greatly augmented the vagal chronotropic response (from 76 +/- 27% change in the sinus cycle length (normothermia) to 155 +/- 38% (hypothermia)). Both the sinus cycle length and the vagal chronotropic response turned towards pre-hypothermia values with rewarming. Mild hypothermia also increased the negative chronotropic response to 20 micrograms/kg/min i.v. of methacholine (12 +/- 2% change in the sinus cycle length (normothermia) versus 24 +/- 14% (hypothermia)), suggesting that a postsynaptic mechanism is involved in the hypothermia-induced augmentation of the cardiac vagal chronotropic response. In contrast to hypothermia, mild hyperthermia (n = 8) decreased the resting sinus cycle length slightly (-5 +/- 5% change) and significantly attenuated the cardiac vagal chronotropic response (from 88 +/- 28% change in sinus cycle length (normothermia) to 50 +/- 26% (hyperthermia)). These changes were also reversible with the re-establishment of normothermia. This demonstrates that clinically relevant, environmentally-induced changes in body temperature can directly and reversibly modify parasympathetic efferent responses.

Triage of critically ill patients: an overview of interventions

The recognition of tissue hypoxia or cumulative oxygen debt is of fundamental importance for triage and resuscitation of critically ill patients during the ¿golden hour¿ in the emergency department (ED). The measurement of central venous blood oxygen saturation, plasma lactate concentration, cardiac output, systemic oxygen transport and use, and non-vital organ oxygenation and function can enhance the detection of systemic and regional hypoperfusion and tissue hypoxia. Systemic and organ-specific oxygenation indices may guide the choice of therapy to optimize resuscitation of the macrocirculation and microcirculation in critically ill ED patients.

The effect of profound hypothermia on blood-brain barrier permeability during pentylenetetrazol-induced seizures

The changes in the permeability of the blood-brain barrier during pentylenetetrazol (PTZ)-induced seizures were investigated in normothermic and hypothermic rats. Six groups of rats were studied: (I) normothermic control; (II) hypothermic control; (III) normothermia plus PTZ (80 mg/kg); (IV) normothermia plus PTZ (160 mg/kg); (V) hypothermia plus PTZ (80 mg/kg); (VI) hypothermia plus PTZ (160 mg/kg). The rats were anesthetized with diethyl ether. In the hypothermic animals, colonic temperature was reduced to 20 +/- 1 degree C by submerging the animals in ice water. In normothermic animals, distinct Evans-blue leakage was observed in the occipital cortex, thalamus, hypothalamus, substantia nigra, corpus striatum, and medulla oblongata in both PTZ groups. However, hypothermic animals which received a high dose of PTZ showed the most severe blood-brain barrier breakdown. Mean levels of Evans blue in the brains of low-dose (80 mg/kg) PTZ-treated animals were 8.7 +/- 2.2 micrograms/g and 5.7 +/- 1.4 micrograms/g in the normothermic and hypothermic groups, respectively. This difference was significant (P < 0.01). The levels in the high dose (160 mg/kg) PTZ-treated animals were 10.2 +/- 3.5 micrograms/g and 15.9 +/- 3.6 micrograms/g in the normothermic and hypothermic groups, respectively (P < 0.02). In conclusion, deep hypothermia prevents the blood-brain barrier disruption induced by 80 mg/kg pentylenetetrazol and aggravates the increase in permeability after 160 mg/kg pentylenetetrazol.

Hyperglycemia increases cerebral intracellular acidosis during circulatory arrest

Phosphorus 31 nuclear magnetic resonance spectroscopy was used to assess cerebral high-energy phosphate metabolism and intracellular pH in normoglycemic and hyperglycemic sheep during hypothermic circulatory arrest. Two groups of sheep (n = 8 per group) were placed in a 4.7-T magnet and cooled to 15 degrees C using cardiopulmonary bypass. Spectra were acquired before and during circulatory arrest and during reperfusion and rewarming. Intracellular pH and adenosine triphosphate levels decreased during circulatory arrest. Compared with the normoglycemic animals, the hyperglycemic group was significantly more acidotic with the greatest difference observed during the first 20 minutes of reperfusion (6.40 +/- 0.08 versus 6.08 +/- 0.06; p < 0.001). Intracellular pH returned to baseline after 30 minutes of reperfusion in the normoglycemic group but did not reach baseline until 1 hour of reperfusion in the hyperglycemic animals. Adenosine triphosphate levels were significantly higher in the hyperglycemic group during circulatory arrest. Repletion of adenosine triphosphate during reperfusion was similar for both groups. These results support the hypothesis that hyperglycemia during cerebral ischemia drives anaerobic glycolysis and thus leads to increased lactate production and an increase [corrected] in the intracellular acidosis normally associated with ischemia.

Continuous central venous oximetry and shock index in the emergency department: use in the evaluation of clinical shock

Initial therapy of shock in the emergency department (ED) emphasizes the normalization of physiologic variables such as heart rate (HR), mean arterial pressure (MAP), and central venous pressure (CVP) rather than restoration of adequate tissue oxygenation. After hemodynamic stabilization of MAP, CVP, and HR, the authors examined tissue oxygenation as indicated by continuous central venous oximetry (SCVO2), lactic acid concentration, and shock index (SI). Sixteen consecutive nonrandomized patients presenting to the ED of a large urban hospital in shock (MAP < 60 mm Hg, HR > 120 beats/min, and altered sensorium) were initially resuscitated with fluid, blood, inotropes, and/or vasoactive drug therapy to normalize MAP, CVP, and HR. In addition, SCVO2, arterial lactate concentration, and SI were measured after completion of resuscitation in the ED. Eight patients (group no. 1) had inadequate tissue oxygenation reflected by low SCVO2 (less than 65%). Four patients in group no. 1 had elevated arterial lactic acid concentration. All group no. 1 patients had an elevated SI (> 0.7) suggesting persistent impairment of left ventricular stroke work. Eight patients (group no. 2) had normal or elevated SCVO2 (> 65%). In group no. 2, arterial lactic acid concentration was elevated in six and SI in seven patients. Normalization of hemodynamic variables does not adequately reflect the optimal endpoint of initial therapy in shock in the ED. Most (94%) of these patients continue to have significant global ischemia and cardiac dysfunction as indicated by reduced SCVO2 and elevated lactic acid concentration and SI. Systemic tissue oxygenation should be monitored and optimized in the ED in these critically ill patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Changes in human intracerebral temperature in response to different methods of brain cooling

The rectal, epidural, and intraventricular temperatures were continuously monitored in 10 seriously injured and unconscious patients admitted for neurosurgical intensive care. Different attempts were made to lower their brain temperatures. Isolated head cooling, whether with frozen liquid (Hypotherm Gel Kap; Flexoversal, Hilden, Germany) or a cooling helmet, had very limited effect. Nasopharyngeal cooling had no effect. During barbiturate coma, a considerable increase in brain temperature was observed. The administration of paracetamol was the single most effective method by which to lower brain temperature, at times by 2 degrees C and usually with a concomitant decrease in the temperature gradient between the rectum and the brain. However, in order to achieve a lasting reduction of brain temperature to 35 degrees C, we had to use a combination of head cooling and intensive whole-body cooling.

The role of central venous oximetry, lactic acid concentration and shock index in the evaluation of clinical shock: a review

Initial therapy of shock in the emergency department emphasizes the normalization of hemodynamic variables e.g. heart rate (HR), mean arterial pressure (MAP), central venous pressure (CVP) rather than optimization of systemic and regional oxygenation. Central venous oximetry (ScvO2), arterial lactic acid concentrations (Lact) and the shock index (SI) were examined during initial hemodynamic stabilization of clinical shock in the emergency room. Although initial therapy normalized MAP, CVP and HR; ScvO2, Lact and SI continued to be abnormal indicating inadequate systemic oxygenation and left ventricular (LV) performance. Measurement of ScvO2, Lact and SI may provide valuable additional information on the adequacy of systemic oxygenation and LV function during initial therapy of shock. This may identify patients who require further monitoring and intervention to optimize systemic oxygen transport and cardiac performance and reduce their morbidity and mortality.

Conservative treatment of stress ulcer bleeding: a new approach

Stress ulcer prophylaxis diminishes but does not eliminate the risk of severe bleeding from this complication. In 70-80% of the cases the source of bleeding is hemorrhagic gastritis. No controlled studies exist which have in particular investigated conservative therapy in patients with stress-induced hemorrhage. Even effective measures to suppress gastric acid secretion or to reduce splanchnic blood flow are ineffective in 10-40% of intensive care unit patients with stress-induced bleeding. In these cases total gastrectomy has so far often been the only therapeutic approach. We report our experience with a new approach in treating severe stress-induced hemorrhagic gastritis after ineffective primary treatment with H2-receptor antagonists, pirenzepine and somatostatin. Continuous gastric lavage with 5-10 l ice-cold Ringer's solution was used until complete cessation of bleeding, as evident from clear lavage. Repeated administration of 12 g sucralfate (60 ml) at 2-h intervals for 24 h through a gastric tube was used to prevent recurrence of bleeding and to promote healing. Sucralfate was reduced on the 2nd and 3rd day to 20 ml 2-hourly and later to 10 ml 4-hourly. In four patients this treatment was used as an ultima ratio when the patients were already scheduled for total gastrectomy. A total of 23 patients were treated during a 7-year period; all of them responded successfully, and no patient required surgery.

Cell metabolism response to cardiopulmonary bypass in patients undergoing aorto-coronary grafting

The main parameters of muscle acid-base, water and energy metabolism were studied in ten patients undergoing low-flux (1.5 l/min/m2), low-pressure (40 to 60 mmHg) hypothermic (26 degrees C) cardiopulmonary bypass (CPB) for aortocoronary grafting; absolute gas exchange and haemodynamic data were also measured throughout the entire CPB period. At the end of CPB a substantial preservation of water and energy metabolic indexes was found; a condition of extracellular metabolic acidosis was apparently sustained by muscle cell anaerobic glycolysis enhancement with a consequent increase of both muscle and plasma lactate content. Subnormal cell phosphocreatine levels as well as reduced bicarbonate buffer stores and decreased intracellular pH, were detected. Direct limiting effects of hypothermia on tissue O2 delivery and muscle oxidative metabolism as well as vasoconstriction and arteriovenous shunting associated with CPB procedures are likely to be involved in the above mentioned alterations of cell metabolism.

Sensitivity of isovolumic relaxation to hypothermia during myocardial infarction

Effects of moderate spontaneous hypothermia on left ventricular systolic and diastolic function during acute myocardial infarction were documented in 17 anesthetized dogs with micromanometric pressure and ventriculographic dimension recordings acquired at baseline and at 1 and 3 h after coronary occlusion. In Group 1 (n = 5), core temperature was allowed to decline spontaneously. In Groups 2 (n = 6) and 3 (n = 6), core temperature was maintained at normothermic levels. Hypothermia impaired isovolumic relaxation markedly despite its lack of effect on ventricular volumes or ejection fraction. At 32.3 degrees C, tau 1/2, defined as the time needed for the left ventricular pressure at the time of peak negative rate of change of left ventricular pressure (dP/dt) to fall by 50%, was increased by 129% 3 h after occlusion. In addition, at this temperature significant changes were found in heart rate, cardiac output, minute work, peak positive and peak negative dP/dt, systolic ejection time, mean velocity of circumferential fiber shortening, mean aortic pressure and end-diastolic pressure. Thus, hypothermia evolving under conditions of general anesthesia profoundly alters left ventricular function in the setting of acute myocardial infarction, a phenomenon that requires consideration and control in studies of myocardial ischemia and left ventricular function in experimental animals.

Multicenter hypothermia survey

A multicenter survey evaluated the clinical presentation, treatment, and outcome of accidental hypothermia. Data were collected from 13 emergency departments, with 401 of the 428 cases presenting during a two-year study period. Core temperatures ranged from 35 C to 15.6 C (mean, 30.57 C +/- 3.53) with 272 cases (63.6%) less than or equal to 32.2 C. There were no significant differences by age in presenting temperature, rewarming strategies, or mortality. The first hour rewarming rate was significantly (P less than .05) faster in the population less than or equal to 59 years (1.08 +/- 1.39 C/hr) than in those greater than or equal to 60 years (0.75 +/- 1.16 C/hr). Male core temperatures averaged 30.27 +/- 3.44 C versus female temperatures of 31.1 +/- 3.61 C. There were no clinically significant differences in male (N = 296) versus female (N = 132) profiles. High ethanol levels (315 to 800 mg%) did not affect outcome. Nine of 27 (33%) patients who received CPR initiated in the field survived, versus six of 14 (43%) with CPR begun in the ED. The profile of the CPR versus non-CPR population differed significantly (P less than .05) in location (outdoors), initial temperature (24.8 +/- 3.77 C vs 30.94 +/- 3.12 C), third-hour rewarming rate (2.28 +/- 1.53 C vs 1.17 +/- 1.18 C/hr), and numerous laboratory parameters. Tracheal intubation was performed without incident in 117 cases, of which 97 were less than or equal to 32.2 C. There were 73 fatalities (17.1%). Of these, 84.9% (N = 62) were less than or equal to 32.2 C. Predisposing conditions in this group included "serious" illness (30), systemic infection (28), trauma (15), immersion (ten), frostbite (seven), and overdose (two). The initial pulse, hemoglobin, and first-hour rewarming rate was lower in the deceased population, while the potassium, urea nitrogen, creatinine, and phosphorus were elevated. Excluding treatment combinations, outcome with exclusive use of a single rewarming strategy was passive external rewarming, 14 deaths below 32.2 C, 13 above; active external rewarming, six deaths below 32.2 C, two above; active core rewarming, 38 deaths below 32.2 C, none above. Refinements of the American Heart Association's CPR standards in hypothermia and a Hypothermia Survival Index are proposed.