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

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

The new Travenol oxygenator is composed of 80 parallel blood pathways. Microporous membrane separates the blood and gas compartments. The membrane surface area is 3 m2, with a pore size of 0.01 microns. Venous blood drains directly from the patient through the oxygenator, then through an integral heat exchanger and into a reservoir, from which a single arterial pump returns the blood to the patient. The advantage of this configuration of membrane oxygenator is simplicity of setup and operation. A disadvantage that we have observed is an apparent variation in resistance to blood flow through the oxygenator during clinical perfusion. Construction changes in a later version of the oxygenator have reduced the resistance to flow through the blood pathway. This device has been used for 20 perfusions at moderate hypothermia (mean 31.8 degrees C) in patients up to 2.1 m2 body surface area for up to 313 minutes. Blood flow was 2.1 to 5.6 liters/min, partial arterial oxygen pressure 100 to 394 torr, partial arterial carbon dioxide pressure 19 to 57 torr (mean 37 torr) and, arterial pH 7.29 to 7.56 (mean 7.41). Oxygen transfer was as high as 230 ml/min. This integral oxygenator-heat exchanger-reservoir is operated like a bubble oxygenator, with direct venous drainage through the device and a single pump, but it uses a membrane oxygenator for gas exchange to eliminate the detrimental effects of bubbles.
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PMID:Initial clinical experience with a low pressure drop membrane oxygenator for cardiopulmonary bypass in adult patients. 642 87

The feasibility of clinical heart-lung transplantation requires a better understanding of the physiological consequences of the operation, heart-lung denervation, and the quality of graft preservation. An acute canine model was used to evaluate heart-lung function during the first 24 hours after transplantation. Measurements of cardiopulmonary dynamics were performed in 5 donor animals and compared sequentially after transplantation in the respective recipients. Orthotopic allotransplantation was performed on cardiopulmonary bypass with moderate hypothermia after perfusion of both the heart and lung with a clinical cardioplegic solution (4 degrees C; potassium chloride, 30 mEq/L; mannitol, 20 gm/L). Postoperatively, the animals were ventilated continuously and anesthetized. Hemodynamic variables were monitored, and measurements were made of arterial and venous oxygen, carbon dioxide, saturation, and pulmonary mechanics. Cardiac output and a derived measurement of lung water were determined. Pulmonary vascular resistance, arteriovenous shunt, resistance, and compliance were calculated. At the termination of the experiment, significant differences were observed between donor and recipient lung-water levels (7.7 +/- 0.9 ml/kg versus 12.0 +/- 3.1 ml/kg, respectively; p less than 0.05); 100% arterial oxygen tension (509 +/- 37 mm/Hg versus 227 +/- 114 mm/Hg, respectively; p less than 0.01); and pulmonary compliance (38 +/- 18 ml/cm H2O versus 11 +/- 4 ml/cm H2O, respectively; p less than 0.05). Arteriovenous shunt increased from 12.2 +/- 4 to 16.5 +/- 5% (p = 0.2). This model evaluates the technique currently employed clinically and will be used in the future to compare methods of heart-lung preservation with the goal of allowing distant heart-lung procurement.
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PMID:Acute physiological changes following heart-lung allotransplantation in dogs. 642 35

Recent experimental and clinical studies from our institution have shown that the administration of cold, bicarbonate-buffered, hyperkalemic crystalloid cardioplegic solution resulted in a significant rise in intramyocardial pH. This rise could theoretically be caused by (1) the alkalinity of the solution administered (pH 8.2 at 25 degrees C), (2) the washout of acid metabolites with each administration, and (3) hypothermia per se. To investigate the relative effects of each of these three factors on intramyocardial pH, dogs on cardiopulmonary bypass received crystalloid cardioplegic solution either at 10 degrees C (n = 9) or at 37 degrees C (n = 8) every 30 min during 2 hr of aortic cross-clamping. Myocardial temperature, intramyocardial pH, and CO2 tension (Pmco2) were measured continuously. Needle biopsy specimens were taken every 30 min for biochemical and ultrastructural analysis. Before aortic cross-clamping, intramyocardial pH was 7.07 +/- 0.06 in both groups (+/- SEM). Upon each administration of cardioplegic solution, hearts in the 10 degrees C group cooled to 10 degrees to 15 degrees C and intramyocardial pH increased on the average by 0.31 +/- 0.03 units (p less than .001). In the 37 degrees C group intramyocardial pH was unaffected by cardioplegic solution. At the end of the cross-clamping period, intramyocardial pH had declined to 6.49 +/- 0.13 in the 10 degrees C group and to 5.60 +/- 0.08 in the 37 degrees C group, the fall in pH being significantly greater in the 37 degrees C group than in the 10 degrees C group (p less than .01).(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:The relative importance of alkalinity, temperature, and the washout effect of bicarbonate-buffered, multidose cardioplegic solution. 643 May 94

The effects of chronic naltrexone infusions on food intake and energy balance were examined in male rats. Animals were fed either Purina Chow, or chow plus a 32% sucrose solution. After one week of being maintained on these diets, animals were implanted (intrascapularly) with osmotic minipumps infusing either 200 micrograms/kg/hr naltrexone hydrochloride or saline. Sucrose + chow-fed animals exhibited increased O2 consumption, increased CO2 production and an elevation in the respiratory quotient (RQ) relative to chow-fed controls. When infused with naltrexone, sucrose + chow-fed animals decreased food intake and body weight gain. While chow-fed animals also suppressed food intake and body weight gain, these decreases were not as great as those observed in sucrose + chow-fed animals. As a function of naltrexone administration, both chow-fed and sucrose + chow-fed animals altered their metabolism as reflected by decreased RQ and adiposity as determined by skinfold measurements. In addition, sucrose feeding led to a hyperthermia which was reversed by naltrexone infusions. Thus, chronic naltrexone administration depressed appetite, reduced energy production and induced hypothermia in rats. As naltrexone is thought to block the endogenous opioid system, this suggests that the endorphins are involved in the regulation of food intake and thermogenesis.
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PMID:Modifications in food intake and energy metabolism in rats as a function of chronic naltrexone infusions. 643 49

In 28 children undergoing cardiopulmonary bypass with deep hypothermia for open heart surgery, an attempt was made to maintain pH at 7.4 not corrected for temperature by varying the CO2 concentration supplied to the oxygenator so that the PaCO2 was 5.33 kPa, not corrected for temperature. One to two percent CO2 gave satisfactory results. Five percent CO2 had previously been given. No adverse clinical side effects were noted, and the acid-base status remained stable for 24 hours in 16 patients. There are strong theoretical reasons for maintaining a pH of 7.4, uncorrected for temperature, during hypothermia and a clinical impression was gained of better myocardial function and improved systemic and cerebral perfusion.
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PMID:Acid-base control during hypothermia. Acid-base control in children during hypothermia without temperature correction of pH and PCO2. 643 44

The gaseous microemboli (GME) production and gas transfer characteristics of two series of bubble oxygenators (Harvey H-1500 and Bentley BOS-10) were evaluated during clinical perfusion in 33 adult patients during open heart surgery for acquired valvular and ischaemic heart disease. For each oxygenator series, patients were divided into two groups, depending upon the method of measurement (intermittent or continuous) of the arterial PO2(PaO2). Using the data available, the perfusionist altered the gas:blood flow ratio in an attempt to maintain the PaO2 within the normal range. In the first group (I = intermittent), where PaO2 data were available only intermittently, the PaO2 values were well above normal, and large numbers of GME were detected in the arterial blood. In the second group (C = continuous), where the PaO2 data were available continuously, there was significantly better control of the PaO2 (P less than 0.001 and P less than 0.01 for the H-1500 and BOS-10, respectively) and significantly fewer GME (P less than 0.01 and P less than 0.05 for the H-1500 and BOS-10, respectively). The Bentley BOS-10 oxygenator used a lower gas:blood flow ratio to achieve physiological levels (range 9 to 13 kPa at 37 degrees C) of PaO2 than did the Harvey H-1500 oxygenator, but there was no difference in the number of GME detected. The lower gas:blood flow ratios for the BOS-10 oxygenators in group C resulted in significantly higher PaCO2 values well outside the physiological range (4 to 6 kPa at 37 degrees C) during the rewarming phase (mean PaCO2 = 7.6 +/- 0.8 kPa) of cardiopulmonary bypass than did the H-1500 oxygenator (mean PaCO2 = 6.3 +/- 0.7 kPa). Mean values for the PaCO2 for both oxygenators during other phases of bypass (cooling and hypothermia) were within the physiological range. If the CO2 retention was corrected by increasing the gas:blood flow ratio the PaO2 values and GME counts became elevated.
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PMID:A clinical evaluation of the gas transfer characteristics and gaseous microemboli production of two bubble oxygenators. 644 73

The relative effects of temperature and CO2 on the blood flow in the common carotid artery (CCBF) were investigated in vagotomized, paralyzed rabbits under urethane-chloralose general anaesthesia with artificial ventilation. During hypothermia a 52% fall of CCBF was observed in rabbits ventilated by the classic method. Administration of a hyperkapnic mixture for breathing caused a further 16% CCBF fall, with a simultaneous rise in PaCO2 by 23%. During ventilation with a respirator triggered by phrenic nerve activity hypothermia caused a 30% CCBF fall without changes in PaCO2 value. Administration of the hyperkapnic mixture for breathing caused, in these circumstances, a 9% CCBF fall with a 7% PaCO2 increase. Hyperthermia caused during ventilation by the classic method a 42% rise in CCBF and a 22% PaCO2 rise. The hyperkapnic mixture given for breathing decreased the CCBF by 9% and increased the PaCO2 by 15%. On the other hand, during ventilation with the respirator triggered by phrenic nerve activity no changes were observed in these parameters. This suggests that the thermic stimulus exerts a direct effect on the regulation of the blood flow to the brain, and during hypothermia it prevails over the stimulus produced by CO2.
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PMID:"Paradoxical" effect of carbon dioxide on common carotid artery blood flow in rabbits during hypothermia and hyperthermia. 644 50

A technique of reversible cold blockade was applied in decerebrate and vagotomized rabbits that were immobilized and artificially ventilated to study the modulation of spontaneous respiratory rhythms. Respiratory discharges were recorded from vagal and phrenic efferents before and during cold blockade at the second cervical segment (C2) with a coolant-circulated thermode (-15 degrees C). Measurement of the cooling profile demonstrated that there was significant hypothermia in the regions of the phrenic nucleus (+25 degrees C) and obex of the medulla (+26 degrees C). Arterial pressure was maintained by continual norepinephrine infusion, end-tidal carbon dioxide tension was held at hypercapnic levels, and rectal temperature was regulated near 38 degrees C. The cold blockade of descending respiratory drives to the cervical phrenic nucleus inhibited the spontaneous activity in the phrenic nerve for more than 90 min. Phrenic activity could be induced by the intravenous injection of strychnine, but not doxapram, although this was not of respiratory quality. These results show that in the absence of descending and pharmacologic drives, but in the presence of phrenic hypothermia, spinalized rabbits are incapable of generating rhythmic patterns of discharge. C2 cold blockade also significantly slowed the spontaneous central respiratory rhythm with no change in integrated vagal amplitude, presumably due to a direct cooling effect on brainstem oscillators for breathing.
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PMID:Respiratory effects of high cervical cord cold blockade on efferent vagal and phrenic discharges in the rabbit. 650 90


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