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Query: UMLS:C0020672 (hypothermia)
 17,327 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Although the environmental stresses to which man is subjected on the ground are less than those commonly encountered in aviation or under water, they may still exceed an individual's powers of adaptation. Extremes of temperature, commonly encountered in the Arctic or the tropics, may occur in regions of normally temperate climate and lead to failure of temperature regulation, resulting in hypothermia, frostbite, heat exhaustion, or heat stroke. High mountains impose additional hazards due to high winds and lack of oxygen, and deep mines are dangerous work-places because of high temperature and humidity. Some physiological acclimatization occurs in extreme natural environments and the dangers may be reduced by appropriate clothing, diet and behaviour.
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PMID:Adaptation and failure of adaptation to extreme natural environments. 113 66

Moderate hypothermia is one of the methods utilized for myocardial protection when the aortic root is cross-clamped but not opened. A combination of low-pressure, low-flow retrograde coronary sinus perfusion (RCSP) with oxygenated blood at moderate hypothermia (29 degrees C.) was demonstrated to yield significantly better protection to left ventricular function in dogs than does moderate hypothermia alone. Ventricular function was recorded before and after 1 hour of aortic cross-clamping at identical preloads and heart rates. Aortic pressure was returned to a level as close to base line as possible by constriction of the descending aorta. The average mean aortic pressure of the animals perfused retrograde at 29 degrees C. was returned to within 4 per cent of base line. By contrast, in the animals protected with moderate hypothermia alone, the pressure could be returned only to a level which was 37 per cent lower than base line. In animals protected with moderate hypothermia alone, cardiac output dropped 62 per cent, left ventricular stroke work (LVSW) 75 per cent, and peak dp/dt 44 per cent. In the animals protected with RCSP and moderate hypothermia, the cardiac output dropped 6 per cent, LVSW 9 per cent, and peak dp/dt 5 per cent. The differences in the changes noted between these two groups were significant for LVSW and dp/dt at a level of p less than 0.01 and for cardiac output and aortic pressure at a level of p less than 0.05. These results suggest that RCSP may be indicated when moderate hypothermia is otherwise chosen to be the sole source of myocardial protection.
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PMID:Drip retrograde coronary sinus perfusion for myocardial protection during aortic cross-clamping. 118 88

This work sums up several studies: clinical observation (electrocardiogram, cardiac rhythm, circulatory state), and biology (glycemia, blood oxygenation, acid-base balance) in 24 cases of accidental hypothermia, not related to poisoning by central nervous system depressive agents; haemodynamics in 18 of these cases; pathology of the myocardium in 11 cases; haemodynamics and microscopy of the myocardium in dogs with slowly induced or prolonged hypothermia; finally an electron microscope study in hypothermic rats. Electrocardiographic study and continuous monitoring of cardiac rhythm and tracing show, in addition to well known manifestations (bradycardia, lenghtening of QT, J wave), acute dysrhythmias, particularly circulatory arrests by asystole during or even 72 hours after rewarming. The clinical haemodynamic changes, measurable (cardiac output, mean arterial pressure, central venous pressure), or computable (stroke volume, peripheral resistances) are observed during rewarming. Several haemodynamic developments can be distinguished: --favourable evolution when the initial disturbances (decrease in cardiac output and in stroke volume, increase in peripheral resistances) disappear without any therapeutic support: --haemodynamic developments showing at a certain time evidence of hypovolemia requiring only moderate vascular replacement; --haemodynamic developments showing myocardial damage. In some cases, only hypothermia accounts for these. In circulatory arrests during or after rewarming, these haemodynamic disturbances raise the hypothesis of severe cardiac changes due to hypothermia itself.
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PMID:[Circulatory and metabolic disturbances in accidental hypothermia (author's transl)]. 121 94

Drugs that dissolve clots, such as streptokinase and rTPA, and drugs that promote vasodilation are undergoing clinical testing for the treatment of hyperacute stroke, but an adjuvant therapy that either prolongs temporal thresholds before irreversible injury occurs or actually protects the brain from ischemia would transform these trials. Mild hypothermia, either intraischemically or at the onset of reperfusion, provides us with a gold standard for cytoprotection against which new pharmacologic strategies can be measured. The cytoprotective effects of the voltage-sensitive calcium channel blockers and the NMDA antagonists have been relatively less compelling than more recent findings with non-NMDA or AMPA antagonists. Their ability to inhibit SINN or reduce neocortical infarction is remarkable. Future randomized clinical trials for both resuscitated cardiac arrest victims and patients sustaining embolic stroke are predicted by this major advance in the field of stroke medicine.
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PMID:Advances in cerebral ischemia: experimental approaches. 131 34

We examined the ability of phenyl-t-butyl-nitrone (PBN), an electron spin trapper, to attenuate ischemia-induced forebrain edema and hippocampal CA1 neuronal loss in gerbils, and to protect rat cerebellar neurons in primary culture from glutamate-induced toxicity. PBN, given i.p. at 75 or 150 mg/kg 30 min before ischemia (5 min occlusion), increased survival (at 7 days) of CA1 neurons from 60 +/- 14 (vehicle-treated, n = 17) to 95 +/- 15 (P less than 0.05, n = 15) and 145 +/- 3 (P less than 0.01, n = 15), respectively. When gerbils were treated with PBN (50 mg/kg, i.p.) immediately and 6 h after reperfusion, followed by b.i.d. for an additional 2 days, CA1 neurons survival improved from 35 +/- 9 (vehicle, n = 20, 6 min occlusion) to 106 +/- 17 (P less than 0.01, n = 13). In gerbils exposed to a more severe ischemia (10 min), pretreatment with 150 mg/kg PBN increased the survival of CA1 neurons from 6 +/- 6 (vehicle) to 27 +/- 10 (P less than 0.05, n = 11). Pretreatment with PBN, at 150 mg/kg, reduced forebrain edema (following 15 min ischemia) by 24.7% (P less than 0.01, n = 16). PBN at 50 mg/kg, i.p. had no hypothermic effect and at 75 or 150 mg/kg caused a transient hypothermia. The presence of PBN in the brain was confirmed in microdialysis samples and brain tissue extract using HPLC. In vitro, PBN protected rat cerebellar neurons against 100 microM glutamate-induced toxicity with an EC50 value of 2.7 mM. Our results further support the concept that free radicals contribute to brain injury following ischemia and suggest the potential therapeutic application of electron spin trappers in stroke.
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PMID:Neuroprotective effects of phenyl-t-butyl-nitrone in gerbil global brain ischemia and in cultured rat cerebellar neurons. 135 99

Composite valve graft replacement of the ascending aorta is being increasingly used, although it is not clear which technique, the Bentall, Cabrol, or button, is the best method for coronary artery ostial reattachment. We retrospectively analyzed our results with respect to these three techniques in 348 consecutive patients operated on between September 17, 1979, and January 29, 1991. Variables included aortic arch replacement in 88 patients (25%), need for deep hypothermia and circulatory arrest in 119 (34%), aortic dissection in 131 (38%), acute dissection in 34 (9.8%), reoperation in 79 (23%), and insertion of St. Jude prostheses in 270 (78%). The 30-day survival rate was 91% (316/348), the in-hospital survival rate was 90% (312/348), and the 30-day incidence of postoperative new transient (n = 6) and permanent (n = 6) stroke was 3% (12/348). The 30-day survival rates for each method were as follows: Cabrol, 92% (144/157); button, 91% (39/43); and Bentall, 91% (125/137). On stepwise multivariate logistic regression analysis with control for operative date and independent prognostic factors, operative technique was not an independent determinant of early mortality or stroke. On late follow-up, the Kaplan-Meier 5-year survival rate was 71% with no significant difference between the groups (3-year survival: Cabrol, 76%; Bentall, 79%; and button, 81%; p = 0.28). The 3-year freedom from reoperation was 95% (Cabrol, 97%; Bentall, 91%; and button, 100%; p = 0.17). We conclude that for patients undergoing reoperation or complicated repairs or when tension on the ostial anastomoses may occur, the Cabrol technique is preferable. If feasible, however, the button technique has better long-term results for both survival and rate of reoperation. An alternative technique is to use an interposition graft to reattach the left coronary artery and excise an aortic button for the right coronary artery reattachment. This has the advantages of technical ease in reattaching the left coronary artery, good results for reattachment of the right coronary artery, minimal tension on the anastomoses, and visualization of all anastomoses.
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PMID:Composite valve graft replacement of the proximal aorta: comparison of techniques in 348 patients. 151 May 9

Even during adequate general anesthesia, hypertension is a common phenomenon in patients undergoing aortocoronary bypass grafting (CABG). In such cases application of vasodilators is recommended in order to decrease myocardial oxygen consumption. This study was performed to compare two commonly used substances, i.e., nitrates and nifedipine, with regard to their influence on hemodynamics, renal blood flow, kidney function, and the requirement for homologous blood transfusions. METHODS. Forty-four patients gave their informed consent to the study. They were randomly divided into 2 groups: group 1 received nitroglycerin (3.0 micrograms/kg.min), group 2 nifedipine (Adalat, 0.5 microgram/kg.min) in order to prevent hypertension in the phase before onset of cardiopulmonary bypass (CPB). Anesthesia was induced by etomidate and succinylcholine and maintained as a modified neuroleptanalgesia with fentanyl (up to 50 micrograms/kg), midazolam (0.3 mg/kg.h), and pancuronium (0.1 mg/kg). Systolic blood pressure was kept within the range of 120-160 mm Hg; in case of higher values boluses of either 0.25 mg nitroglycerin or 0.5 mg nifedipine were administered. Cardiac index, stroke volume index, rate-pressure product, intrapulmonary shunt, and pulmonary and total peripheral resistances were evaluated at five predefined points: (1) after induction of anesthesia; (2) before incision; (3) before cannulating the aorta; (4) after decannulating the aorta; and (5) at the end of operation. Creatinine and free-water clearances as well as sodium and potassium excretion were calculated for three phases of the operation: (A) induction of anesthesia--onset of CPB; (B) during CPB; and (C) end of CPB--end of operation. CPB was performed using a membrane oxygenator (Sorin 51) and a nonpulsatile blood flow of 2.5 1/min.m2, which was reduced during mild hypothermia of 30-32 degrees C to 1.7 l/min.m2. Mean arterial pressure in both groups was kept at approximately 70 mm Hg. In case of lower pressures norepinephrine (50-100 micrograms/bolus) was administered; higher pressures were treated as described above. Volume substitution was performed initially by 500 ml hydroxyethyl starch and continued, if necessary, by homologous blood or 5% human albumin in order to keep the hematocrit greater than 30 in the phases before and after CPB. RESULTS. Group 2 showed significantly higher values of cardiac index and stroke volume index at point 3 while the rate-pressure product was clearly lower, indicating better myocardial performance and lower oxygen consumption than in group 1. Creatinine and free-water clearances in all three phases did not differ. However, sodium excretion during CPB was significantly higher in the nifedipine group while potassium excretion showed no differences. The average requirement for blood and blood substitutes was lower in group 2, but the difference could not be confirmed statistically because of the large dispersion of values. Nevertheless, 4 patients in the nifedipine group but no patient in group 1 did not need homologous blood transfusion. CONCLUSION. In comparison to nitrates, nifedipine showed some advantages in the treatment of hypertension during CABG: (1) it provided better myocardial performance; (2) it had a more reliable but not too long-lasting effect on elevated total peripherial resistance, leading to better hemodynamic stability; and (3) by not affecting the capacitance vessels it may necessitate fewer homologous blood transfusions.
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PMID:[Nifedipine versus nitroglycerin in aortocoronary bypass surgery. The effect on hemodynamics, kidney function and homologous blood requirement]. 153 39

We present a surgical technique that we believe provides superior cerebral protection for simultaneous correction of carotid and cardiac pathology with low operative mortality and stroke rate. Our study population consists of 23 consecutive patients undergoing cardiac operation between August 1989 and April 1991 who also had associated critical (greater than 85%) carotid artery stenosis. Using 20 degrees C systemic hypothermia for cerebral protection, we performed simultaneous correction of both lesions during the aortic cross-clamp period, using continuous retrograde blood cardioplegia for myocardial protection. Mean patient age was 69.4 years; 83% were 65 years or older. Eighty-seven percent had angina, 35% had recent myocardial infarctions (within 30 days), and 52% had congestive heart failure. Asymptomatic bruit was found in 39%, and 61% had previous strokes, neurologic symptoms, or both. All had 85% or greater luminal narrowing on cerebral angiography, with 65% having severe or critical contralateral disease as well. Sixty-one percent had associated other vascular pathology, including peripheral vascular occlusive disease, renal artery stenosis, or abdominal aortic aneurysm. There were no postoperative strokes or neurologic events. One early vein graft occlusion resulted in postoperative myocardial infarction and subsequent death (4.3%).
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PMID:Combined cardiac operation and carotid endarterectomy during aortic cross-clamping. 843 Oct 83

The cases of 100 consecutive patients who underwent coronary artery bypass grafting with coronary sinus (retrograde) cardioplegia (group R) without the antegrade-retrograde approach were reviewed. To evaluate the safety and the efficacy of this technique, another 100 consecutive patients who underwent a similar procedure but with conventional aortic root (antegrade) cardioplegia (group A) were used as a comparison. The two groups were similar with respect to age, male to female ratio, associated medical problems, extent of coronary artery disease, mean preoperative ejection fraction (0.56 +/- 0.13 versus 0.53 +/- 0.18), pump time (113.1 +/- 43 versus 111.7 +/- 38 minutes), aortic cross-clamp time (57.4 +/- 20 versus 60.8 +/- 23 minutes), number of grafts per patient, level of hypothermia, complication rate, rate of postoperative myocardial infarction (4% versus 3%), and mortality rate (2% versus 2%). Hemodynamic measurements were made 6 hours after operation in 59 patients in group R and 47 patients in group A. The cardiac index, left ventricular stroke work index, and right ventricular stroke work index were better in group R but not significantly so (p greater than 0.05). However, only 27% of patients in group R required a temporary pacemaker, and only 9% needed inotropic agents after 6 hours of operation in contrast to 51% and 42%, respectively, in group A (p less than 0.05). There were no complications from catheter intubation. In group R, right ventricular wall temperature (11 degrees +/- 3.6 degrees C) was higher than the septal (10.8 degrees +/- 3.2 degrees C) and left ventricular wall temperatures (9.1 degrees +/- 2.8 degrees C) (p greater than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Coronary sinus cardioplegia: clinical trial with only retrograde approach. 159 57

31-Phosphorus magnetic resonance spectroscopy was used in a rat model of 10 min severe incomplete forebrain ischaemia (2-vessel occlusion with hypotension) to assess the effect of mild brain hypo- and hyperthermia (+/- 2 degrees C) on intracellular pH and high energy phosphates. In three experimental groups intracerebral temperature was maintained at levels of 34, 36 and 38 degrees C during ischaemia and early reperfusion. The steady level of intracellular pH during ischaemia was 6.63, 6.58 and 6.53 in the 34, 36, and 38 degrees C groups, respectively. The rate of initial recovery of intracellular pH in reperfusion was 0.046 +/- 0.012 pH units per min (+/- s.d.) in the 36 degrees C group compared to 0.056 +/- 0.010 (+/- s.d., P less than 0.05) in the 34 degrees C group and 0.032 +/- 0.009 (+/- s.d., P less than 0.01) in the 38 degrees C group. The recovery in early reperfusion of phosphocreatine and ATP was slower in the 38 degrees C group compared to the other groups. The findings were consistent with recent studies, suggesting that even mild hypothermia may afford protection to the ischaemic brain, and furthermore indicate that mild hyperthermia as fever or even subfebricity may be deleterious for the outcome in stroke patients.
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PMID:The effects of brain temperature on temporary global ischaemia in rat brain. A 31-phosphorous NMR spectroscopy study. 163 61


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