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

Sudden unexplained death may be seen with treatment of craniovertebral anomalies and surgery of the upper cervical spine. Death is due to sleep-induced apnea, premonitored by periods of confusion, lethargy, and asthenia. There may be associated hypotension, bradycardia, hyponatremia, hypothermia, inappropriate antidiuretic hormone secretion, and difficulty in micturition. The potential for respiratory failure may be predicted if a CO2 response test demonstrates an attenuated or abnormal response. Apnea during sleep may be reversed by arousal or may require ventilatory support for a period of time. The condition is self-limiting, but remains the major life-threatening complication. Both apnea and autonomic dysfunction are treatable and curable with appropriate diagnosis and management.
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PMID:Occult respiratory and autonomic dysfunction in craniovertebral anomalies and upper cervical spinal disease. 375 66

Survival following 3 hr of total circulatory arrest under profound hypothermic conditions was explored in 19 adult mongrel dogs. Thermoregulatory management included combined surface/perfusion hypothermia and azeotrope anesthesia in 95% O2/5% CO2. All animals were resuscitated and survived for at least 12 hr. During the last seven trials (Group II) the following principles were applied: uniform whole-body cooling where differences between rectal, esophageal, and pharyngeal temperatures averaged less than 1 degree C, induction of circulatory arrest at approximately 3 degrees C, constant lung inflation (10-12 cm H2O between 20 degrees C cooling and 20 degrees C rewarming, including the 3-hr arrest period) and ventilation assistance with positive end-expiratory pressure (4 cm H2O) after 20 degrees C rewarming, intraoperative maintenance of colloid osmotic pressure (COP) above 11 mm Hg, replacement of the cooling perfusate with a colloid-rich rewarming prime (COP = 15 mm Hg) and restoration of hemostasis with fresh whole blood transfusions. The application of these principles resulted in the long-term survival of five animals with four survivors displaying no clinically detectable neurological abnormalities. However, two animals developed optic impairment and one animal died from intusseption on the fourth postoperative day. Despite the improved results, it should also be noted that during pilot (Group I) studies (from which the aforementioned principles were derived) fatalities from complications attributed to systemic edema, central nervous system, or pulmonary or coagulation dysfunctions occurred in 9 out of 12 trials. We conclude that whole body protection following 3 hr of total circulatory arrest at a uniform temperature less than 5 degrees C can be successfully accomplished.
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PMID:Whole body protection during three hours of total circulatory arrest: an experimental study. 380 87

Previous studies have shown that organic bases, including some drugs, are secreted by renal proximal tubules. The present studies examined the transport of the organic bases cimetidine and procainamide by rabbit proximal straight tubules perfused in vitro. Both drugs were secreted into the tubule lumen. [3H]cimetidine secretion was reduced by quinidine, procainamide, and N-acetylprocainamide. Previous studies showed that cimetidine secretion was reduced by other organic bases. Hypothermia and ouabain inhibited [3H]procainamide secretion as was shown previously for cimetidine secretion. [3H]procainamide secretion was also reduced by quinidine, cimetidine, procainamide, and N-acetylprocainamide but not by probenecid. High concentrations of cimetidine (10(-3) M) had no effect on the rates of fluid or total CO2 absorption. When analyzed in terms of Michaelis-Menten kinetics, the effect of cimetidine on procainamide secretion and procainamide on cimetidine secretion was consistent with competitive inhibition. The results suggest that both cimetidine and procainamide are secreted into the lumen of proximal straight tubules predominately by an organic base transport mechanism. These studies raise the possibility that some of these drugs might compete for a common secretory mechanism in renal tubules and reduce the elimination of each other.
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PMID:Cimetidine and procainamide secretion by proximal tubules in vitro. 617 96

In 1975 H. Rahn put forward a new concept of hydrogen ions regulation which explains acid-base regulation in relation to body temperature and applies to all animal species. At the root of this concept is the finding that maintenance of intracellular neutrality is governed by water dissociation and regulated by imidazole-rich protein buffers. The pH of the extracellular fluid, which receives acid by-products of cell activity, is kept higher than that of the intracellular fluid (relative alkalinity). The difference between extracellular pH and neutrality is constant for each species and ranges from 0.6 to 0.8 pH units. It is unaffected by changes in temperature, and the total CO2 content of extracellular fluid remains constant. The authors were able to confirm the value of this new concept in man by experimental studies of in vitro and in vivo blood of patients undergoing aorto-coronary bypass under controlled hypothermia. They draw the following practical conclusions: (1) in subjects under moderate or deep hypothermia for surgical purposes, the acid-base status can be controlled and the extracellular pH adjusted by ensuring intracellular neutrality; this is done by keeping PCO 2 at such a level that the arterial blood pH measured at 37 degrees C remains around 7.40; (2) the problem of correcting acid-base values (pH-PCO 2) according to body temperature is solved simply by using pH and PCO 2 values measured at 37 degrees C and interpreting them, as usual, in terms of metabolic or respiratory acidosis or alkalosis.
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PMID:[Relations between acid-base equilibrium and body temperature. Physiological concepts and practical applications]. 622 30

Fundamental physicochemical characteristics of the acid-base related constituents of extracellular and intracellular fluid spaces of vertebrates in relation to changes in temperature have been reviewed. Emphasis has been placed upon the dissociation constant of water, the solubility constant of CO2, the dissociation constant of histidine imidazole, the hydroxyl-hydrogen ion ratio, the protein charge state and the alpha-imidazole regulation concept. Because pN and pKIm change in parallel when temperature varies, the OH/H ratio and the alpha-imidazole value for any sample of blood or plasma held anaerobically in vitro are invariant with changing temperature, since a constant CO2 content is maintained. Thus, when blood or plasma cools, pH increases and PCO2 decreases, but relative alkalinity and the protein charge state remain constant. These responses are solely the consequence of physical constants, that is, equilibrium constants and gas solubility, changing with temperature. In vivo, the set of PCO2 is established in each poikilothermic species by its normal ventilatory pattern designed to maintain constant CO2 content. Regulation in vivo in poikilotherms consists of adjustments of ventilation per unit metabolism (VA/VCO2) appropriate to every temperature. When the ventilatory and renal mechanisms of human beings are suppressed by anesthesia and hypothermia, their extracellular and intracellular responses mimic those of poikilotherms. Clinical management of hypothermia in humans requires ventilatory control using oxygen-augmented room air without added CO2 monitored by pH measurements of arterial blood warmed anaerobically to 37 degrees C. Finally, the need for new techniques to measure intracellular pH as temperature is lowered and some areas for further investigation are suggested.
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PMID:The hydroxyl-hydrogen ion concentration ratio during hypothermia. 629 7

Intraoperative hypothermia has become a common occurrence. Postoperative rewarming often is accompanied by shivering and results in increased metabolic and circulatory demands. We examined the metabolic, hemodynamic, and biochemical variables in 2 groups of hypothermic (greater than 35.8 degrees C) patients requiring mechanical ventilation after a major operation. One was observed during routine medical management whereas the other group received 40 mg of metocurine iodide and then observed during routine medical management. All patients were allowed to rewarm passively. O2 consumption (VO2, ml/min, STPD), CO2 production (VCO2, ml/min, STPD) and respiratory quotient (RQ) measurements were made every 15 min using a Beckman Metabolic Measurement Cart. Esophageal temperature, arterial blood pressure, heart rate (HR), rate pressure product, CVP, arterial blood gases, serum lactate concentration, and duration of shivering also were recorded. Suppression of the shivering by metocurine increased rewarming time significantly and decreased VCO2, VO2, HR, rate pressure product, mean arterial pressure (MAP), and the O2 cost of rewarming. Thus, the elimination of shivering during postoperative rewarming is associated with a decrease in caloric, metabolic demands and myocardial work (as assessed by the rate pressure product) while rewarming time is prolonged. In the postoperative, hypothermic, critically ill patient, suppression of the shivering response in selected patients may be indicated.
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PMID:Physiologic requirements during rewarming: suppression of the shivering response. 640 3

The present study examined the effects of exposure of rats to elevated environmental levels of CO2 on norepinephrine metabolism in the hypothalamus and other regions of the brain. In confirmation of previous findings by others CO2 at 10 or 15% was found to elevate both dopa accumulation after dopa decarboxylase inhibition and norepinephrine utilization after tyrosine hydroxylase inhibition. These effects however were found to be transient occurring only during the first 30 min of 2.5 h exposure. In this regard CO2 differs from another form of stress, restraint which produces a sustained 2.5 h increase of dopa accumulation and NE accumulation. Restraint was also more effective than CO2 in depleting endogenous stores of hypothalamic NE. The factor responsible for the adaptation of the catecholamine response to CO2 was not identified although it was shown not to be hypothermia and it was reversed by a 2 h CO2-free recovery period.
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PMID:Rapid adaptation of the stimulatory effect of CO2 on brain norepinephrine metabolism. 642 Jul 12

The effect of experimental hypothermia on changes of the electrophysiological equivalent of minute ventilation (Veq) was studied in rabbits under urethane-chloralose general anaesthesia with muscle relaxation and artificial ventilation. The animals were subjected to bilateral vagotomy prior to the experiment. During normothermia (37.5 +/- 0.7 degree C) and hypothermia (29.9 +/- 1.7 degrees C) the animals were given for breathing a hypercapnic mixture of gases (CO2 5% with O2 95%) and asphyxia was produced by switching off the respirator. The arterial blood pressure, blood flow in the common carotid artery, end-expiratory CO2 concentration, "integrated" phernic nerve activity and brain-stem temperature were recorded. The partial pressure of carbon dioxide and oxygen, hydrogen ion concentration and arterial acid-base balance were determined with correction for temperature changes. The equivalent of minute ventilation (being the product of the frequency and amplitude of "integrated" phrenic nerve activity) decreased in hypothermia by 91%, with a simultaneous fall of PaCO2 from 33,48 +/- 3.84 mmHg to 23.40 +/- 3.59 mmHg (by 30%). The hypercapnic stimulus applied during hypothermia produced a fivefold lower Veq value than in normothermia and under control conditions (despite a similar value of PaCO2 of 28.89 +/- 3.12 mmHg). The Veq value approaching that found under normal conditions in normothermia was observed during hypothermia only when asphyxia was induced when the value of PaCO2 was 37.07 +/- 8.74 mm Hg and that of PaO2 was 37.41 +/- 29.11 mmHg. During hypothermia the blood flow in the common carotid artery decreased by 16% when the animals were breathing the hypercapnic mixture. The analysis of the obtained results showed a direct effect of temperature on respiratory activity generation and regulation of arterial blood flow to the brain. It may be supposed also that hypothermia raises the response threshold to CO2 level in the breathed air.
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PMID:Minute ventilation changes in rabbits during experimental hypothermia. 642 Oct 87

Thirty adult mongrel dogs were divided into 3 equal groups and studied to define the optimal PCO2 level with azeotrope (halothane-diethyl ether) anesthesia under surface hypothermia (Groups I, II and III = F1CO2 0%, 5% and 10%, respectively). All animals were cooled to 18-20 degrees C and were subjected to 30 (Group I) or 60 minutes (Groups II and III) of total circulatory arrest. Group I animals had frequent arrhythmic episodes during cooling and postoperative motor disturbances occurred in 80% despite only 30 minutes of circulatory arrest. By contrast Group II animals were less arrhythmic during cooling; were easily resuscitated following 60 minutes of arrest and only 30% developed moderate reversible motor disturbances postoperatively. Hemodynamics were similar between Groups II and III during cooling but resuscitation using an F1CO2 of 10% (Group III) was extremely difficult and required massive cardiotonic support throughout rewarming. Furthermore, two dogs in Group III died within the first two postoperative days. However, none of the 8 survivors displayed neurological abnormalities. On balance, a ventilatory regimen utilizing 5% CO2 during surface-induced hypothermia under azeotrope anesthesia resulted in optimum intraoperative management and a satisfactory postoperative course and although some CNS disturbance (high-stepping gait) was noted, all animals recovered completely.
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PMID:The importance of appropriate concentrations of inspired carbon dioxide on induced hypothermia under halothane-ether azeotrope anesthesia. 642 47

The basic physiologic characteristics of acid-base equilibria during hypothermia were briefly reviewed. By graphic analysis, four possible clinical strategies for managing the acid-base status of the patient undergoing H-CPB were documented. The effect of hemodilution on buffer capacity was charted in a manner applicable to common current operative procedures. During hypothermia for cardiac operations as presently conducted, the perfusionist is in control of the temperature of the body and the perfusion preservation of the body and brain; the surgeon must assume responsibility for preservation of the heart. The literature pertinent to the relationship of the acid-base state to the functions and structural preservation of the heart and brain during the conditions of cooling to and rewarming from deep hypothermia associated with cardiopulmonary bypass, aortic cross clamping, cardioplegia and total circulatory arrest have been reviewed. The evidence is overwhelming that myocardial anoxia caused by aortic occlusion or total circulatory arrest at any temperature to 15 degrees C. result in progressive acidosis which, of itself, is myotoxic. In contrast, alkalinity is ionotropic. Myocardial ischemia, in both adults and infants, should be prevented and treated by alkaline perfusion cooling and by frequent coronary perfusion of a cardiopreservative solution which is extremely cold (4 to 8 degrees C.), oxygenated, has a pH of 7.8, slightly hyperosmolar and which has a hematocrit of 20 per cent (imidazole, erythrocytes and plasma protein colloid), a cardioplegic ionic pattern and energy substrates. Reperfusion of the heart should begin at a 37 pH of 7.8. Evidence is strong that the use of CO2 added to any gas mixture is harmful. It increases myocardial acidosis; it does not increase cerebral blood flow during hypothermia. Protection of the unperfused brain of an infant should emphasize prevention of circulatory arrest prolonged to more than 40 minutes. Temporary reperfusion at that time limit should be used. Probably the best general management of the body for H-CPB is alpha-stat, which preserves biologic neutrality. The uncorrected analyzer reads pH 7.4 and Pco2 at any temperature. However, the need for preservation of the hypoxic heart is overwhelming and, thus, the best acid-base management for cardiac hypothermic operations is significant respiratory alkalosis. The most appropriate sites for the collection of blood samples for gas analysis and measuring temperatures were discussed; "body temperature" is the most unreliable parameter measured. The major characteristics of an "ideal" cardiopreservative solution were described.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:The importance of acid-base management for cardiac and cerebral preservation during open heart operations. 642 51


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