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

Oxygen availability during cardiopulmonary bypass was assessed in 22 patients under hypothermic and relatively normothermic conditions. The patients were divided into two groups, 17 of whom received ACD blood and 5, CPD blood. The mean P50 for all patients fell from a preoperative value of 25.9 +/- 2.4 (SD) to 15.6 +/- 2.1 during hypothermia confirming a leftward shift of the oxyhemoglobin dissociation curve. Oxygen uptake, calculated from a-v oxygen content differences (avDO2) and flow, was significantly lower during hypothermic bypass (65 +/- 27 ml/min) than during rewarming (121 +/- 41 ml/min). The increase in oxygen affinity during hypothermia was influenced also by changes in acid base and 2,3-DPG concentrations, the changes being similar in both the ACD and CPD groups of patients. During rewarming, however, oxygen availability was increased in the CPD group presumably from significantly increased 2,3-DPG concentrations. A "functional" value of hemoglobin, based upon the effects of the shift of the oxyhemoglobin dissociation curve and, therefore, reflecting the true capacity of hemoglobin to unload oxygen at the tissue level, was calculated. During the hypothermic phase of bypass, this functional hemoglobin was only 4.2 g/100 ml blood, suggesting that, in spite of reduced metabolic demands, oxygenation reserves are minimal.
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PMID:Oxygen availability during hypothermic cardiopulmonary bypass. 1 30

The well known effects of the lowering of the intraerythrocyte 2, 3, diphosphoglycerate (2, 3, DPG) level and hypothermia, on the affinity of oxygen for hemoglobin, lead the authors to study the influence of these parameters on this affinity during general anesthesia. The following observations were made in 15 adult subjects, undergoing prolonged general anaesthesia (average time: 3 hrs. 10 minutes): the dissociation curve of oxyhemoglobin (DCO) by the method of mixing, the intraerythrocyte 2,3, DPG level, the hemoglobin concentration and arterial blood parameters (PO2, PCO2, pH). These measurements were recorded before and after the general anaesthesia. The results were the following: a significant reduction of P50, measured under standard conditions (from 27.64 +/- 1.74 torr to 25.57 +/- 2.28, p less than or equal to 0.01) associated with a decrease in 2,3, DPG (from 0.94 +/- 0.31 mol/mol Hb at 0.64 +/- 0.24 p less than 0.01). Among the factors responsible for this variation in the affinity, it was proved that the volume of blood transfused was of importance as well as a decrease in body temperature during the operation. When the temperature is made to vary from 37 degrees C to 35 degrees C. the P50 ranges from 25.57 +/- 2.28 to 22.86 +/- 0.97 (p less than 0.01). To conclude the authors underline the importance of hypothermia and the volume of blood transfused (average time of preservation = 15 days) on the effects of the affinity of oxygen for hemoglobin.
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PMID:[Changes in the affinity of oxygen for hemoglobin during general anesthesia]. 2 19

Acid-base terminology including the sue of SI units is reviewed. The historical reasons why nomograms have been particularly used in acid-base work are discussed. The theoretical basis of the Henderson-Hasselbalch equation is considered. It is emphasized that the solubility of CO2 in plasma and the apparent first dissociation constant of carbonic acid are not chemical constants when applied to media of uncertain and varying composition such as blood plasma. The use of the Henderson-Hasselbalch equation in making hypothermia corrections for PCO2 is discussed. The Astrup system for the in vitro determination of blood gases and derived parameters is described and the theoretical weakness of the base excess concept stressed. A more clinically-oriented approach to the assessment of acid-base problems is presented. Measurement of blood [H+] and PCO2 are considered to be primary data which should be recorded on a chart with in vivo CO2-titration lines (see below). Clinical information and results of other laboratory investigations such as plasma bicarbonate, PO2,P50 are then to be considered together with the primary data. In order to interpret this combined information it is essential to take into account the known ventilatory response to metabolic acidosis and alkalosis, and the renal response to respiratory acidosis and alkalosis. The use is recommended of a chart showing the whole-body CO2-titration points obtained when patients with different initial levels of non-respiratory [H+] are ventilated. A number of examples are given of the use of this [H+] and PCO2 in vivo chart in the interpretation of acid-base data. The aetiology, prognosis and treatment of metabolic alkalosis is briefly reviewed. Treatment with intravenous acid is recommended for established cases. Attention is drawn to the possibility of iatrogenic production of metabolic alkalosis. Caution is expressed over the use of intravenous alkali in all but the severest cases of metabolic acidosis. The role of 2,3-diphosphoglycerate on tissue oxygenation is stressed and use of intravenous sodium phosphate as an alternative to intravenous bicarbonate is mentioned.
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PMID:The physiological assessment of acid-base balance. 23 27

The treatment of hypothermia associated with hemorrhage, exposure, or intraoperative intervention continues to represent a challenge for trauma care teams. An innovative technique for combining microwave heating with continuous temperature monitoring into a feedback-controlled system for blood warming has been developed. The effect of microwave warming on the structure and function of blood was compared with that in nonheated controls. Erythrocyte structural integrity (hemolysis) was evaluated by comparing levels of lactate dehydrogenase (LDH), potassium (K+), and plasma hemoglobin (PHGB), and hematocrit (HCT) in heated and nonheated (control) samples of banked red blood cells. Hemoglobin function was evaluated in fresh blood by comparing the P50 and hemoglobin electrophoresis of experimental and control samples. Prewarming temperatures were 3 degrees or 23 degrees C; temperatures after warming were 35 degrees, 37 degrees, or 39 degrees C. The results reflect the percentage of changes for 84 heated and 24 unheated blood samples. There were no statistical differences in any of the biochemical variables measured. The P50 for three heated and three unheated samples was 30.7 +/- 1.2 and 30.5 +/- 0.9 mm Hg (p greater than 0.05). There were no changes in the hemoglobin electrophoretic patterns in experimental or control samples. This system is designed to deliver microwave energy in a uniform and controlled manner, overcoming the limitations of conventional microwave ovens that in the past caused local overheating and subsequent hemolysis when used for blood warming. The structural and functional integrity of erythrocytes after microwave warming indicate the safety and effectiveness of this technique.
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PMID:The effect of in-line microwave energy on blood: a potential modality for blood warming. 163 11

The effects of temperature on oxygenation and metabolism in perfused rat hindlimb was studied at 35 degrees C and 15 degrees C. Oxygenation of myoglobin and oxidation of cytochrome aa3 in the thigh (quadriceps) muscle were estimated from the difference spectra measured with a rapid-scanning spectrophotometer. Simultaneously, oxygen uptake and release of lactate and pyruvate were measured. (1) In hypothermia, glycolysis played a major role in energy metabolism even though Cyt aa3 was maintained in a more oxidized state than in normothermia. (2) P50 of myoglobin in perfused rat hindlimb was 5.0 mmHg at 35 degrees C, 2.3 mmHg at 25 degrees C and 1.1 mmHg at 15 degrees C. The delta H degree was -13.0 kcal/mol. (3) When about 30% of myoglobin was deoxygenated at both 35 degrees C and 15 degrees C, the oxygen uptake started to decrease and lactate release increased. (4) At 35 degrees C, the oxidation level of cytochrome aa3 was same as the oxygenation level of myoglobin. At 15 degrees C, however, the oxidation level of cytochrome aa3 was clearly higher than the oxygenation level of myoglobin. The oxygen uptake at 15 degrees C was about one third that at 35 degrees C. In conclusion, in order to maintain the aerobic condition of cytochrome aa3 in mitochondria of rat skeletal muscle, a tissue oxygen tension higher than 12 mmHg at 35 degrees C, and higher than 3 mmHg at 15 degrees C is required.
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PMID:Temperature effect on oxygenation and metabolism of perfused rat hindlimb muscle. 196 61

The oxyhemoglobin dissociation curve was quantified in 15 patients subjected to hypothermic cardiopulmonary bypass under opiate-benzodiazepine anesthesia using the alpha-stat approach to control blood acid-base status. The P50 was calculated from a single measurement of oxygen tension and hemoglobin saturation in blood obtained from the pulmonary artery or the venous line from the cardiopulmonary bypass circuit. In addition, the P50 was directly determined at the registered patient temperature. The P50 decreased from 3.87(+/- 0.15) kPa (mean, SEM) before anesthesia to 1.55(+/- 0.16) kPa during hypothermic (25.43 +/- 1.99 degrees C) cardiopulmonary bypass (p less than 0.001). On rewarming, the P50 increased to 4.89 +/- 0.27 kPa (at 36.14 +/- 0.14 degrees C, p less than 0.001 compared to the preinduction and hypothermic values). Eight hours after cardiopulmonary bypass the P50 returned to the preinduction value (3.72 +/- 0.22 kPa). The relationship between temperature and P50 is described by the regression equation: P50 = 0.22(+/- 0.02).Temperature--3.78(+/- 0.62). The correlation was 0.78 (p less than 0.001). It is concluded that (1) the leftward shift of the oxyhemoglobin dissociation curve during hypothermia may be detrimental to oxygen delivery and (2) the oxygen saturation of the venous blood should not be used indiscriminately to evaluate cellular oxygen status.
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PMID:The oxyhemoglobin dissociation curve before, during and after cardiac surgery. 208 10

An isolated dog heart preparation was used to study the effect of left-shifting the O2 dissociation curve by carbamylation or hypothermia. The two interventions had a similar effect on the variables of O2 delivery. There were significant decreases in myocardial O2 consumption, coronary sinus PO2, and O2 extraction. There was no compensatory increase in O2 transport. Coronary flow autoregulation was somewhat blunted by hypothermia but not by carbamylation. We conclude that an increase in hemoglobin-O2 affinity is capable of limiting myocardial O2 delivery and that increases in convective O2 transport play a minor role at best in the coronary adaptation to small decreases in P50.
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PMID:Myocardial oxygen transport during leftward shifts of the oxygen dissociation curve by carbamylation or hypothermia. 278 56

Blood may provide superior cardioplegia compared with crystalloid cardioplegic solution. However, the results are controversial. This may be due to a leftward shift of the hemoglobin (Hb)-O2 dissociation curve induced by hypothermia, increasing the oxygen affinity for Hb. This effect may negate the potential benefit of blood cardioplegia. The oxygen affinity for Hb can be decreased by increasing the red cell 2,3-diphosphoglycerate (2,3-DPG), and hence, more oxygen can be delivered to the myocardium. The present investigation was undertaken to study the effects of 2,3-DPG-enriched blood cardioplegia on the functional recovery of the myocardium and changes in the coronary sinus red blood cell (RBC) adenosine-triphosphate (ATP), lactate, and RBC DPG after one and a half hours of reperfusion following one hour of ischemic cardiac arrest in dogs. The dogs were divided into three groups: crystalloid (CR); stored blood (SB), and high 2,3-DPG blood (HDPG) cardioplegic groups. Incubation of canine RBC in phosphoenal pyruvate (PEP) led to a 36% increase in DPG and a rightward shift in the Hb-O2 dissociation curve. There was a 4 mm Hg shift in the P50. When compared with the CR group, there was a significant decrease in the cardiac index (CI) and left ventricular work index (LVWI) and a significant increase in the total systemic vascular resistance (TSVR) in the SB group. The CI and LVWI of the HDPG group were similar to those of the CR group, but the TSVR was significantly greater in the former group. The LVWI was significantly greater and the TSVR smaller in the HDPG group as compared with those in the SB group.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:High 2,3-DPG blood cardioplegia and myocardial preservation during cardiopulmonary bypass. 334 90

Oxygen transport and delivery to peripheral tissues during hypothermia are analyzed theoretically, taking into consideration various conditions observed both in nature and clinically. With decreasing temperature, P50 (the oxygen tension [PO2] at 50% hemoglobin saturation with oxygen) decreases, thereby leading to low mixed venous oxygen tension (PvO2) and thus low tissue PO2 values. On cooling from 37 degrees C to 25 degrees C at pH 7.4, the P50 decreases from a normal 26.8 mm Hg to 13.2 mm Hg. In the intact animal, as well as in a patient on cardiopulmonary bypass, oxygen consumption (Vo2) and cardiac output (QT, or recommended pump flow rate) decrease. If the ratio of Vo2/QT remains constant, then the arteriovenous O2 content difference, C(a-v)O2, must remain constant. If C(a-v)O2 is 5 ml/dl, we calculate that the PvO2 must decrease from a normal 40 mm Hg to 26.8 mm Hg at 25 degrees C. Clinically induced hypothermia is usually accompanied by hemodilution of the patient's blood to 50% normal hematocrit, which would reduce PvO2 to 13.7 mm Hg. Use of constant relative alkalinity (pH = 7.58 at 25 degrees C) further reduces the P50 to 10.8 mm Hg and the PvO2 to 10.9 mm Hg. Other clinical situations are also discussed. Sensitivity analysis predicts that during hypothermia PvO2 (and thus tissue PO2) is very dependent on P50, hemoglobin concentration, and QT, and less dependent on oxygen solubility and arterial PO2. We conclude that monitoring of mixed venous or tissue PO2 might be advisable, and that blood flow is the component of oxygen transport most amenable to manipulation by the clinician to ensure adequate tissue oxygenation during induced hypothermia.
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PMID:Theoretical analysis of oxygen transport during hypothermia. 371 43

The influence of temperature on the oxygen affinity of hemoglobin, expressed as half saturation tension P50, was investigated in male Sprague Dawley rats, which had been exposed to a cold environment for about 12 h. P50-values were determined by equilibrating blood samples to a known PO2 at different temperatures. The well known increase in oxygen affinity at low temperatures was observed, but after a longer hypothermic period this effect was diminished. This reduction of the temperature effect is manifested in a change of the ratio delta log P50/delta T from 0.022 in control experiments to 0.0115 in hypothermia. In cold adapted rats such an effect means a better oxygen supply to tissue at low body temperatures than in control animals. These changes in oxygen delivery after cold acclimatisation may partially be interpreted as the result of the decreased intraerythrocytic pH and elevated concentration of ATP found in the present study.
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PMID:Diminution of the temperature effects on the oxygen affinity of hemoglobin after prolonged hypothermia. 719 Jun 74


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