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

The ability of the noninvasive continuous transcranial Doppler technique to reflect changes in cerebral blood flow during cardiac operations was evaluated in seven adults. Middle cerebral artery blood flow velocity changes were compared with simultaneous thermodilution measurements of venous blood flow in the ipsilateral internal jugular vein during 11 preset stages of the procedure. Cerebral blood flow was varied by changes in arterial carbon dioxide tension and temperature. High-dose fentanyl-droperidol anesthesia and alpha-stat pH management were employed. To facilitate comparisons between the two methods, the individual awake values of middle cerebral artery flow velocity (45.1 +/- 3.3 cm/sec, mean +/- standard error of the mean) and jugular venous blood flow (382 +/- 37 ml/min) were normalized (100%). Cerebral metabolic rate for oxygen was calculated as the product of jugular arteriovenous oxygen content difference and middle cerebral artery flow velocity or jugular venous blood flow, respectively. The individual correlations between the two flow estimates varied between 0.76 and 0.87 (median 0.83), and the correlation of the combined data from all seven patients was 0.77 (p less than 0.0001). Variations in arterial carbon dioxide tension induced significant changes in the two flow estimates both during normothermia before cardiopulmonary bypass and at deep hypothermia (20 degrees C) during cardiopulmonary bypass. The significant arterial carbon dioxide tension changes had no significant effects either on Doppler- or thermodilution-estimated cerebral metabolic rate for oxygen. Deep hypothermia (20 degrees C) reduced Doppler- and thermodilution-estimated cerebral metabolic rate for oxygen to 22.0% +/- 3.9% and 20.6% +/- 6.9% of the awake levels, respectively. The study supports the validity of using middle cerebral arterial flow velocity changes as an estimate of changes in volume flow through the brain during cardiac operations.
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PMID:Transcranial Doppler-estimated versus thermodilution-estimated cerebral blood flow during cardiac operations. Influence of temperature and arterial carbon dioxide tension. 190 62

Canine thyroid tissue (CTy) was subjected to hyperbaric oxygen culture (HOC) under conditions that affect immunoalteration in murine thyroid tissue (MTy). Survival of autografts and allografts implanted under the kidney capsule was determined after 21 days by 125I uptake and histology. Unlike MTy, autograft CTy subjected to normothermic HOC (95% O2, 5% CO2; 1.76 kg/cm2) for 48 h did not survive (0/8) whereas decrease of culture duration to 24 h resulted in autograft CTy survival (3/3). Under hypothermia (5 degrees C), HOC could be extended to 7 days with autograft CTy survival (3/3 after 4 days and 3/3 after 7 days). Allograft CTy after 24 h of normothermic HOC and 7 days of hypothermic HOC was rejected. Indicators of oxygen free radical injury were determined:catalase activity was comparable in MTy and CTy (means 14.82 and 6.3-10.8 mm/mg protein, respectively) but superoxide dismutase activity was low in CTy (means 0.01-0.29 and 4.75 U/mg protein, respectively). Malondialdehyde content after 48 h of normothermic HOC was higher in CTy than in MTy (means 2215 and 1275 nmol/g, respectively). The results show that CTy is injured by HOC under conditions tolerated by MTy, and that this difference is related to the greater sensitivity of CTy to oxygen free radical injury.
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PMID:A comparison of the effects of hyperbaric oxygen culture on survival of murine and canine thyroid gland grafts. 191 Apr 28

The effect of pentobarbital anaesthesia on spontaneous recovery from hypoxic apnoea (autoresuscitation) was investigated in SWR/J mice. Experiments were performed in 17 to 23 day old animals, in which the mechanism often fails, and in adults, in which it is usually successful. Mice, matched for age and weight, were injected with pentobarbital (62.5 mg/kg) or saline. Hypoxic apnoea was induced with 97% N2-3% CO2 and air given at its onset. To determine whether the effect of pentobarbital depended on hypothermia, we performed experiments in 17-23-day-olds with and without maintenance of body temperature. In the 'hypothermic' experiments one of 27 mice given pentobarbital died, compared with 10 of 22 controls (P less than 0.005). In the 'isothermic experiments', none of 15 mice given pentobarbital died, compared to 7 of 13 controls (P less than 0.005). All adults in both groups survived. Pentobarbital had a different effect on eupnoea and gasping: resting ventilation was depressed but gasp ventilation increased, and the duty cycle of gasps but not eupnoeic breaths was altered. Pentobarbital may facilitate autoresuscitation because gasping is unimpaired but oxygen consumption and lactate production are reduced, allowing cardiac function and cerebral survival until PO2 is restored.
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PMID:Effect of pentobarbital on spontaneous recovery from hypoxic apnoea in mice. 192 12

Differences in cerebral blood flow (CBF) between alpha-stat and pH-stat management depend on preserved responsiveness of the cerebral vasculature to changes in arterial carbon dioxide tension (PaCO2). We tested the hypothesis that hypothermia-induced reductions in CBF would decrease the CBF response to changing PaCO2 (delta CBF/delta PaCO2). Anesthetized New Zealand white rabbits were randomly assigned to one of three temperature groups--group 1 (37 degrees C, n = 9); group 2 (31 degrees C, n = 10); or group 3 (25 degrees C, n = 10)--and were cooled using cardiopulmonary bypass. After esophageal temperature equilibration (approximately 40 min), oxygenator gas flows were serially varied to achieve PaCO2 values of 20, 40, and 60 mm Hg (temperature-corrected). All animals were studied at all three PaCO2 levels in random order. At each level of PaCO2, CBF and masseter blood flow were determined using radiolabeled microspheres. There were no significant differences between groups with respect to mean arterial pressure (approximately 80 mmHg), central venous pressure (approximately 4 mmHg), or hematocrit (approximately 22%). Prior normothermic studies have found delta CBF/delta PaCO2 to be proportional to CBF. Nevertheless, in this study, with hypothermia-induced reductions in CBF, delta CBF/delta PaCO2 was not significantly different between temperature groups. Thus, hypothermia either increased the sensitivity of the cerebral vasculature to carbon dioxide and/or increased the effective level of cerebrospinal fluid respiratory acidosis produced by each increment of temperature-corrected PaCO2.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Cerebral blood flow response to PaCO2 during hypothermic cardiopulmonary bypass in rabbits. 192 75

Working rat hearts were perfused for 15 minutes at 37 degrees C before switching to a Langendorff perfusion (60 mm Hg aortic pressure) at 10 degrees C for 40 minutes of hypothermic arrest. Ventricular function was allowed to recover for 15 minutes at 37 degrees C by reestablishing the prehypothermic conditions. The perfusate was Krebs-Henseleit bicarbonate buffer containing 3% bovine serum albumin and either glucose (11 mmol/L) or glucose (11 mmol/L) plus palmitate (1.2 mmol/L) and gassed with 95% O2 and 5% CO2. In hearts receiving glucose alone as substrate, coronary flow was maintained constant during the 40 minutes of hypothermic arrest and returned to prehypothermic rates with rewarming. Ventricular function, as estimated by peak systolic pressure and heart rate, recovered to the prehypothermic level. When palmitate was added, coronary flow decreased continuously throughout the hypothermic perfusion (22% decrease by 40 minutes), and ventricular pressure development was lower throughout the rewarming perfusion. Tissue levels of adenosine triphosphate and creatine phosphate were well maintained and long-chain acyl coenzyme A and acyl carnitine decreased during hypothermia regardless of the substrate provided. With rewarming, tissue levels of adenosine triphosphate and creatine phosphate decreased in those hearts receiving palmitate. Omission of fatty acid either during hypothermia or during the first 5 minutes of rewarming improved recovery of function. Addition of oxfenicine to inhibit fatty acid oxidation, or inhibition of Ca2+ overload by verapamil and low perfusate Ca2+, prevented the effects of palmitate on ventricular function.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Fatty acids suppress recovery of heart function after hypothermic perfusion. 192 62

We examined the relationship of changes in partial pressure of carbon dioxide on cerebral blood flow responsiveness in 20 pediatric patients undergoing hypothermic cardiopulmonary bypass. Cerebral blood flow was measured during steady-state hypothermic cardiopulmonary bypass with the use of xenon 133 clearance methodology at two different arterial carbon dioxide tensions. During these measurements there was no significant change in mean arterial pressure, nasopharyngeal temperature, pump flow rate, or hematocrit value. Cerebral blood flow was found to be significantly greater at higher arterial carbon dioxide tensions (p less than 0.01), so that for every millimeter of mercury rise in arterial carbon dioxide tension there was a 1.2 ml.100 gm-1.min-1 increase in cerebral blood flow. Two factors, deep hypothermia (18 degrees to 22 degrees C) and reduced age (less than 1 year), diminished the effect carbon dioxide had on cerebral blood flow responsiveness but did not eliminate it. We conclude that cerebral blood flow remains responsive to changes in arterial carbon dioxide tension during hypothermic cardiopulmonary bypass in infants and children; that is, increasing arterial carbon dioxide tension will independently increase cerebral blood flow.
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PMID:Cerebral blood flow response to changes in arterial carbon dioxide tension during hypothermic cardiopulmonary bypass in children. 200 99

There were presented operative technique and clinical results of extracorporeal circulation (ECG) with patients lungs utilization, instead of routinely applied artificial blood oxygenators. Auto-oxygenation method was applied in 12 patients with coronary artery disease treated by coronary artery bypass grafting (CABG). Operative procedure differs from the traditional one in two additional cannulations of pulmonary artery and left atrium. Two peristaltic pumps and incorporated in circulation blood reservoirs. Polystan 892910 allows for temporary substitution of cardiac function without lung disconnection. Lungs functioning during surgery do not render it difficult. Hypothermia enables to decrease respiration rate and tidal volume with no effect on physiological blood oxygenation and CO2 exhalation. Method assessment was based on results comparison with those obtained in patients treated by traditional method using bubble oxygenators-Venotherm 5,000. PO2, PCO2, platelets number and hemolysis extent were assessed before, in 10, 30, 60 min of ECG and just after it. Platelets activity and influence of the method on hemostatic disorders were evaluated based on clotting time by Ivy. Additionally hemostatic disorders were assessed by thoracic blood drainage volume calculated from the moment of protamine administration to drainage tubes withdrawal in average 18 hours after surgery. Laboratory parameters characteristically changing during ECG were also estimated. It was proved, that auto-oxygenation diminished negative effects of ECG. Increased platelets number, faster normalization of clotting time and decreased postoperative drainage were stated in the auto-oxygenation group. Postoperative drainage in this group was 260 +/- 60 ml in comparison with 800 +/- 100 ml of the control group. Authors consider that pulmonary function remaining during ECG positively affects on postoperative hemostasis. This method can be helpful in surgical management of coronary artery disease, especially in patients with primary coagulation disorders.
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PMID:[Personal observations with application of auto-oxygenation techniques in the surgical management of coronary disease]. 208 71

Eighty-six patients undergoing coronary artery bypass graft (n = 63) or intracardiac (n = 23) surgery were randomly assigned with respect to the target value for PaCO2 during cardiopulmonary bypass. In 44 patients the target PaCO2 was 40 mmHg, measured at the standard electrode temperature of 37 degrees C, while in 42 patients the target PaCO2 was 40 mmHg, corrected to the patient's rectal temperature (lowest value reached: mean 30.1, SD 1.9 degrees C). Other salient features of bypass management include use of bubble oxygenators without arterial filtration, flows of 1.8-2.4 l.min-1.m-2, mean hematocrit of 23%, and mean arterial blood pressure of approximately 70 mmHg, achieved by infusion of phenylephrine or sodium nitroprusside. Neuropsychologic function was assessed with series of tests administered on the day prior to surgery, just before discharge from the hospital (mean 8.0, SD 5.8 days postoperatively, n = 82), and again 7 months later (mean 220.7, SD 54.4 days postoperatively, n = 75). The scores at 8 days showed wide variability and generalized impairment unrelated to the PaCO2 group or to hypotension during cardiopulmonary bypass. At 7 months no significant difference was observed in neuropsychologic performance between the PaCO2 groups. Regarding cardiac outcome, there were no significant differences between groups in the appearance of new Q-waves on the electrocardiogram, the postoperative creatine kinase-MB fraction, the need for inotropic or intraaortic balloon pump support, or the length of postoperative ventilation or intensive care unit stay. These findings support the hypothesis that CO2 management during cardiopulmonary bypass at moderate hypothermia has no clinically significant effect on either neurobehavioral or cardiac outcome.
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PMID:A randomized study of carbon dioxide management during hypothermic cardiopulmonary bypass. 235 31

To evaluate the effects of 5% carbon dioxide (CO2) administration for hypothermic circulatory arrest, neurological evaluation and pathological studies were carried out on the canine brain. Twenty-two dogs were assigned to five groups: Group 1: Three dogs without hypothermia were sacrificed as the control group. Group 2: Nine dogs were subjected to surface hypothermia (20 degrees C) under deep ether anesthesia with 100% oxygen (O2) and hyperventilation. Circulatory arrest time was 30 min in Group 2A and 60 min in Group 2B. Group 3: Ten dogs were surface cooled (20 degrees C) under deep ether anesthesia with a 95% O2 and 5% CO2 mixture. Thirty minutes of circulatory arrest was instituted in Group 3A and 60 min in Group 3B. Dogs in Groups 2 and 3 were surface rewarmed and kept alive until they were sacrificed electively 6 or more months later. Results were as follows: (i) Postoperative neurological disturbance was detected in only two dogs in Group 2B. (ii) The percentage of damaged nerve cells among the total nerve cells counted in the cerebral cortex of the frontal lobe was significantly greater in Groups 2A (22.4%), 2B (30.1%), 3A (19.6%), and 3B (22.2%) compared with Group 1 (7.1%). (iii) The number of glia cells per nerve cell in the cerebellar dentate nucleus was significantly higher in Group 2B (27.2) than in Groups 1 (11.8), 2A (16.7), 3A (17.9), and 3B (18.6). (iv) The number of Purkinje cells in a 10-mm length of the cerebellum was markedly reduced to 89 in Group 2B compared with 122, 134, and 117 in Groups 1, 2A, and 3A, respectively. In conclusion, the results of quantitative pathological brain analysis reflected the incidence of postoperative neurological disturbance and suggested that the administration of 5% CO2 could prolong the time limit for circulatory arrest.
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PMID:The effects of 5% carbon dioxide on the quantitative analysis of long-term pathology of the brain after surface hypothermia. 210 59

During surgery under pentobarbital sodium anesthesia, 20 rats had heat exchange devices implanted into their abdominal cavity. After recovery, 14 rats underwent two sets of trials, one in which body core temperature (Tbc) was lowered to 34.5-35.5 degrees C and another in which Tbc was raised to 40.5-41.5 degrees C. Rats breathed air and hypoxic (15, 11, and 7% O2 in N2) and hypercapnic (2, 4, and 6% CO2 in air) gas mixtures. Respiratory responses were measured using a barometric method and compared with data from the same rats breathing the gas mixtures at normal Tbc (37.5-38.5 degrees C) before surgery. The six remaining rats served as controls (Tbc unchanged). Lowering Tbc increased respiration in air, whereas heating had no effect. Hypothermia and severe hypoxia combined to inhibit respiration when compared with breathing air at lowered Tbc or low O2 at normal Tbc. The CO2 response slope became steeper when Tbc was raised, suggesting an increased CO2 sensitivity. Possible sites for the hypothermia-hypoxia interaction and the hyperthermia-hypercapnia interaction are discussed.
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PMID:Body temperature effects on hypoxic and hypercapnic responses in awake rats. 211 31


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