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F Dexter

Publications and source records attributed to F Dexter.

At least 109 records · Page 6Linked to original sources
PubMed1996

Estimate of the maximum absorption rate of microscopic arterial air emboli after entry into the arterial circulation during cardiac surgery.

Some clinicians place patients in the Trendelenburg position during aortic unclamping to decrease the incidence of microscopic cerebral air embolism. Experimental studies have shown that use of the Trendelenburg position does not prevent air emboli from reaching the brain. Nevertheless, the position can decrease the velocity at which bubbles approach the brain, giving more time for nitrogen in the bubbles to be absorbed. We applied a validated mathematical model to estimate that the maximum rate of absorption of microscopic air emboli in blood during and after cardiopulmonary bypass (CPB) equals 1.57 microns/s. This rate is very small, since clinically relevant microbubbles have radii 50-1500 microns, and travel from the aorta to the brain within seconds. The result holds for all usual conditions of CPB. We conclude that absorption does not affect the disposition of air introduced into the arterial circulation. Use of the Trendelenburg position cannot decrease neurologic injury from cerebral air embolism by permitting greater bubble absorption.

Cardiac Surgical Procedures↗
PubMed1996

Surgical ICU underutilization does not significantly discourage discharge.

An SICU must have sufficient capacity to handle peak weekly demand to prevent re-admission and/or poor quality of care. Excess capacity may, however, encourage unnecessary SICU utilization. The goal of this study was to assess the influence of availability of SICU beds on patient discharge and re-admission rates. The case series included 1,492 days, 36,816 patient days, 8,821 discharges, and 186 re-admissions within 3 days from a 24-bed multidisciplinary SICU at a tertiary care center. Census was defined to equal the total number of patients in the SICU each day. We found low census levels were not associated with significantly lower discharge rates. Decreasing the census from 19-24 to 13-18 patients per day decreased discharge rates from 31% to 30%. Odds ratio that a decrease in census by five from 24 decreased discharge rate equaled 1.01 (95% confidence interval 0.96 to 1.06). We conclude that when hospital managers choose an appropriate SICU capacity they need not be concerned that intermittent excess capacity will prompt physicians to significantly decrease their discharge rates.

Bed Occupancy↗
PubMed1996

Biomechanical evaluation of Caspar and Cervical Spine Locking Plate systems in a cadaveric model.

There exist two markedly different instrumentation systems for the anterior cervical spine: the Cervical Spine Locking Plate (CSLP) system, which uses unicortical screws with a locking hub mechanism for attachment, and the Caspar Trapezial Plate System, which is secured with unlocked bicortical screws. The biomechanical stability of these two systems was evaluated in a cadaveric model of complete C5-6 instability. The immediate stability was determined in six loading modalities: flexion, extension, right and left lateral bending, and right and left axial rotation. Biomechanical stability was reassessed following fatigue with 5000 cycles of flexion-extension, and finally, the spines were loaded in flexion until the instrumentation failed. The Caspar system stabilized significantly in flexion before (p < 0.05) but not after fatigue, and it stabilized significantly in extension before (p < 0.01) and after fatigue (p < 0.01). The CSLP system stabilized significantly in flexion before (p < 0.01) but not after fatigue, and it did not stabilize in extension before or after fatigue. The moment needed to produce failure in flexion did not differ substantially between the two plating systems. The discrepancy in the biomechanical stability of these two systems may be due to differences in bone screw fixation.

Adult↗
PubMed1995

Statistical analysis of drug interactions in anesthesia.

Anesthesiologists often use more than one drug in a patient to achieve a target response, such as a desired blood pressure. Isobolographic analysis is a standard mathematical method to test whether a drug-drug interaction exists and, if so, whether the interaction is synergistic or antagonistic. Several experimental protocols are suitable to collect data for interpretation by isobolographic analysis. Traditionally, each subject would receive a single dose of one or more drugs and the presence or absence of the target response in the subject at a specific time would be recorded. An alternative procedure is to infuse one or more drugs into each subject until the target response occurs. This procedure is clinically relevant to studies of anesthesia drugs, which are often titrated to achieve a target response. This latter method of testing for drug interaction requires fewer subjects than the traditional approach because more information is obtained from each subject. We present a statistical test for drug-drug interaction that uses the total doses of drugs given to each subject. This statistical test can be used as part of a complete analysis of drug-drug interaction. We consider (i) selection of appropriate sample sizes and doses; (ii) randomizing subjects to groups; (iii) effects of unequal group variances on the accuracy of the statistical test; (iv) appropriate methods to present the drug-drug interaction data graphically; and (v) tests to ensure that statistical assumptions are satisfied. Using the statistical methods described here, drug-drug interaction can be quantified and evaluated for statistical significance.

Anesthetics↗
PubMed1995

Mathematical analysis of haemodilution's direct effect on rate of brain cooling during cardiopulmonary bypass.

Cerebral hypothermia is the principal means of providing neurologic protection during cardiac surgery. Better understanding is needed of ways to improve brain cooling during bypass. The goal of this study is to find whether haemodilution has a significant direct effect on the rate of brain cooling, from changes in the blood's thermal properties. The brain is cooled during hypothermic cardiopulmonary bypass, almost exclusively, by the colder blood. We use the corresponding component of the bioheat transport model to predict the proportional direct effect of changing blood density and specific heat on the amplitude of the rate of brain cooling. We find that haemodilution can significantly change blood density and specific heat. For example, haemodilution with the fluorocarbon emulsion AF0104 from a haematocrit at 45% to a haematocrit at 22% increases blood density by 18%, and decreases specific heat by 21%. Nevertheless, the mathematical model predicts that the direct effect of haemodilution on the rate of brain cooling by the cold blood is small; +7%, +6% and -7% for normal saline, 5 g dl-1 albumin in normal saline, and AF0104 fluorocarbon emulsion, respectively. We conclude that, within the haemotocrit range used clinically during bypass, haemodilution with these substances has only a small direct effect on the rate of brain cooling.

Brain↗
PubMed1995

Interactions between NMDA and AMPA glutamate receptor antagonists during halothane anesthesia in the rat.

There is increasing evidence that pharmacologic antagonism of glutamatergic neurotransmission can potentiate the anesthetic effects of drugs such as halothane. The purpose of this study was to examine the anesthetic interaction between glutamate receptor antagonists. A competitive NMDA receptor antagonist (CGS 19755) and an AMPA receptor antagonist (NBQX) were administered either alone or in combination prior to determination of the minimum alveolar concentration (MAC) for halothane in the rat. CGS 19755 caused a dose-dependent maximum reduction in halothane MAC of approximately 80%. Doses of NBQX, which were low enough to cause no change in MAC when administered alone, substantially reduced MAC when administered with subanesthetic doses of CGS 19755. This effect decreased as the dose of CGS 19755 was increased. Finally, halothane MAC was reduced to zero when NBQX, in a dose sufficient to reduce halothane MAC by approximately 35% if given alone, was added to a pharmacodynamically similar dose of CGS 19755. Although MAC is believed to predominantly reflect nocioception at the spinal cord level, the results suggests that pharmacologic blockade of glutamatergic neurotransmission is sufficient to result in deep levels of anesthesia. Further, the effect of combinations of NMDA and AMPA receptor antagonists on halothane MAC is consistent with an in vivo physiologic interaction between the NMDA and AMPA receptors.

Anesthesia↗
PubMed1995

The cost efficacy of hypothetically eliminating adverse anesthetic outcomes from high-risk, but neither low- nor moderate-risk, surgical operations.

We tested whether hypothetical improvements in the quality of perioperative care can decrease hospital costs for elective surgical operations. Our case series was constructed retrospectively of consecutive patients who underwent one of the following elective operations at our tertiary care center: lung lobectomy (137), coronary artery bypass (339), kidney transplant (251), total hip replacement (305), laparoscopic cholecystectomy (203), or cesarean section (649). Only hospital costs were included in our study. Eliminating adverse anesthetic outcomes (identified by chart review) entirely would decrease total hospital costs (i.e., for all patients in that group) by less than 0.5% (95% confidence bound < 1.2%) for kidney transplant, 1.8% (< 3.5%) for total hip replacement, 0% for laparoscopic cholecystectomy, and 2.2% (< 6.2%) for cesarean section. In contrast, a hypothetical quality improvement that would have the effect of decreasing costs for the 10% most expensive patients just to the group median would decrease total costs by 30% (15%-44%) for lung lobectomy and 16% (10%-21%) for coronary artery bypass. We conclude that for low- and moderate-risk procedures, hypothetical improvements in the quality of anesthetic care will not reduce costs. However, improving the quality of perioperative care may be cost efficient for high-risk operations.

Anesthesia↗
PubMed1995

Decreases in anesthesia-controlled time cannot permit one additional surgical operation to be reliably scheduled during the workday.

We tested whether anesthesiologists can decrease operating room (OR) costs by working more quickly. Anesthesia-controlled time (ACT) was defined as the sum of 1) the time starting when the patient enters an OR until preparation or surgical positioning can begin plus 2) the time starting when the dressing is finished and ending when the patient leaves the OR. Case time was defined as the time starting when one patient undergoing an operation leaves an OR and ending when the next patient undergoing the same operation leaves the OR. An actual case series was constructed of 709 consecutive patients who underwent one of 11 elective operations at a tertiary care center. Statistical analysis of measured OR times showed that ACt would have to be decreased by more than 100% to permit one additional scheduled, short (30-min) operation to be performed in an OR during an 8-h workday after a prior series of cases, each lasting more than 45 min. Anesthesiologists alone cannot reasonably decrease case times sufficiently to permit one extra case to be reliably scheduled during a workday. Methods to decrease ACT (e.g., using preoperative intravenous catheter teams, procedure rooms, and/or shorter acting drugs) may simply increase costs.

Ambulatory Surgical Procedures↗
PubMed1995

Analysis of strategies to decrease postanesthesia care unit costs.

BACKGROUND: The goal of this study was to identify interventions that anesthesiologists can make to decrease total costs of a postanesthesia care unit (PACU). METHODS: Data were collected retrospectively from patients who underwent ambulatory surgery at our tertiary care center. RESULTS: Supplies and medications accounted for only 2% of PACU charges. Personnel costs, which depend on the peak number of patients in the PACU, accounted for almost all PACU costs. If nausea and vomiting could have been eliminated in each patient who suffered this complication, without causing sedation, the total time to discharge for all patients would have been decreased by less than 4.8% (95% confidence interval < 7.3%). Arrival rates to and times to discharge from the PACU followed triangular and log-normal distributions, respectively. Computer simulations, using published times to discharge for drugs with "faster recovery," such as propofol, showed that the use of these drugs would only decrease PACU costs if operating rooms were consistently scheduled to run later each day. Such earlier discharge also might be beneficial if used at night, but only if the PACU could close after a single patient leaves. However, reasonably achievable decreases in the times to discharge for all patients undergoing general anesthesia are unlikely to substantively decrease PACU costs. In contrast, arranging an operating room schedule to optimize admission rates would greatly affect the number of PACU nurses needed. CONCLUSIONS: Anesthesiologists have little control over PACU economics via choice of anesthetic drugs. The major determinant of PACU costs is the distribution of admissions.

Ambulatory Surgical Procedures↗
PubMed1995

Pulsatile versus nonpulsatile flow. No difference in cerebral blood flow or metabolism during normothermic cardiopulmonary bypass in rabbits.

BACKGROUND: Although pulsatile and nonpulsatile cardiopulmonary bypass (CPB) do not differentially affect cerebral blood flow (CBF) or metabolism during hypothermia, studies suggest pulsatile CPB may result in greater CBF than nonpulsatile CPB under normothermic conditions. Consequently, nonpulsatile flow may contribute to poorer neurologic outcome observed in some studies of normothermic CPB. This study compared CBF and cerebral metabolic rate for oxygen (CMRO2) between pulsatile and nonpulsatile CPB at 37 degrees C. METHODS: In experiment A, 16 anesthetized New Zealand white rabbits were randomized to one of two pulsatile CPB groups based on pump systolic ejection period (100 and 140 ms, respectively). Each animal was perfused at 37 degrees C for 30 min at each of two pulse rates (150 and 250 pulse/min, respectively). This scheme created four different arterial pressure waveforms. At the end of each perfusion period, arterial pressure waveform, arterial and cerebral venous oxygen content, CBF (microspheres), and CMRO2 (Fick) were measured. In experiment B, 22 rabbits were randomized to pulsatile (100-ms ejection period, 250 pulse/min) or nonpulsatile CPB at 37 degrees C. At 30 and 60 min of CPB, physiologic measurements were made as before. RESULTS: In experiment A, CBF and CMRO2 were independent of ejection period and pulse rate. Thus, all four waveforms were physiologically equivalent. In experiment B, CBF did not differ between pulsatile and nonpulsatile CPB (72 +/- 6 vs. 77 +/- 9 ml.100 g-1.min-1, respectively (median +/- quartile deviation)). CMRO2 did not differ between pulsatile and nonpulsatile CPB (4.7 +/- 0.5 vs. 4.1 +/- 0.6 ml O2.100 g-1.min-1, respectively) and decreased slightly (0.4 +/- 0.4 ml O2.100 g-1.min-1) between measurements. CONCLUSIONS: During CPB in rabbits at 37 degrees C, neither CBF nor CMRO2 is affected by arterial pulsation. The absence of pulsation per se is not responsible for the small decreases in CMRO2 observed during CPB.

Anesthesia↗
PubMed1995

Glutamate release from the ovine fetal brain during maternal hemorrhage. A study using chronic in utero cerebral microdialysis.

BACKGROUND: Glutamate has been implicated in the pathophysiology of neuronal injury associated with cerebral hypoxia-ischemia. A model using chronic in utero microdialysis was developed to sample the extracellular space of the fetal brain. Using this model, we tested the hypothesis that glutamate efflux from the parasagittal parietal cortex of near-term fetuses would increase during maternal hemorrhage. METHODS: Twelve near-term fetal sheep were instrumented with vascular catheters, and a microdialysis probe(s) was implanted into the parasagittal parietal cortex. After a 3-day recovery period, the animals were subjected to maternal hemorrhage until either the fetal pH was < 7.00 or the fetus died. The extracellular glutamate concentration in the collected dialysate was determined by high pressure liquid chromatography (HPLC). RESULTS: Maternal hemorrhage resulted in an 80-90% decrease in uterine blood flow, a decrease fetal po2, and a mixed metabolic and respiratory fetal acidosis. There were two groups of fetuses, survivors (n = 5) and nonsurvivors (n = 7). The nonsurvivor group showed a large increase (10-30-fold) in peak glutamate release (P = 0.0015). Survivors demonstrated a small (threefold) increase that was not statistically significant (P = 0.065), unless one animal with very low probe recovery was excluded (P = 0.0048). CONCLUSIONS: Extracellular glutamate release from the fetal brain can occur during maternal hemorrhage with fetal acidemia. The pathophysiologic role (if any) of glutamate release in the survivors remains to be elucidated. Our results are consistent with the hypothesis that in utero release of glutamate occurs during periods of fetal asphyxia. This experimental preparation of chronic fetal brain microdialysis can be used to monitor the brain extracellular concentration of any dialyzable substance in response to stress, including maternal hemorrhage.

Animals↗
PubMed1995

Analysis of statistical tests to compare visual analog scale measurements among groups.

BACKGROUND: A common type of study performed by anesthesiologists determines the effect of an intervention on pain reported by groups of patients. The goal of this study was to evaluate the effectiveness of t, analysis of variance (ANOVA), Mann-Whitney, and Kruskal-Wallis tests to compare visual analog scale (VAS) measurements between two or among three groups of patients. These results may be particularly helpful during the design of studies that measure pain with a VAS. METHODS: One VAS measurement was obtained from each of 480 nulliparous women in labor who were receiving oxytocin (149), nalbuphine (159), or epidural bupivacaine (172). Multiple simulated samples were then drawn from these data. These simulated samples were used in computer simulations of clinical trials comparing VAS measurements among groups. t and ANOVA tests were performed before and after an arcsin transformation was used, to make the data closer to a normal distribution. VAS measurements were also compared after they were divided into five ranked categories. RESULTS: The statistical distributions of VAS measurements were not normal (P < 10(-7)). Arcsin transformation made the distributions closer to normal distributions. Nevertheless, no statistical test incorrectly suggested that a difference existed among groups, when there was no difference, more often than the expected rate. t or ANOVA tests had a slightly greater statistical power than the other tests to detect differences among groups. Because arcsin transformation both decreased differences among means and reduced the variance to a lesser extent, it decreased power to detect differences among groups. Statistical power to detect differences among groups was not less for a five-category VAS than for a continuous VAS. CONCLUSIONS: We conclude that t and ANOVA, without an accompanying arcsin transformation, are good tests to find differences in VAS measurements among groups.

Analgesia, Epidural↗
PubMed1995

Glycine receptor antagonism. Effects of ACEA-1021 on the minimum alveolar concentration for halothane in the rat.

BACKGROUND: Glycine and glutamate binding sites are allosterically coupled at the N-methyl-D-aspartate (NMDA) receptor complex. Previous studies have shown that antagonism of glutamate at the NMDA receptor reduces the minimum alveolar concentration (MAC) for volatile anesthetics. 5-Nitro-6,7-dichloro-2,3-quinoxalinedione (ACEA-1021) is a competitive antagonist at the glycine recognition site of the NMDA receptor. The purpose of this study was to determine whether glycine receptor antagonism also reduces volatile anesthetic requirements in the rat. METHODS: In experiment 1, Sprague-Dawley rats were anesthetized with halothane in 50% O2-balance N2 and their lungs mechanically ventilated. They were randomly assigned to one of three groups according to the dose of ACEA-1021 administered (0, 20, or 40 mg/kg intravenously; n = 6). The bolus dose of ACEA-1021 was followed by a continuous intravenous infusion of vehicle or ACEA-1021 at 14 mg.kg-1.h-1. Halothane MAC was then determined by the tail-clamp method. In experiment 2, awake rats were randomly assigned to groups according to the same dosages of ACEA-1021 as in experiment 1. Arterial CO2 tension and mean arterial pressure were recorded before and 5 and 30 min after the start of the infusion. The infusion was then stopped, and the time to recovery of the righting reflex was recorded. RESULTS: In experiment 1, ACEA-1021 decreased halothane MAC (mean +/- SD) in a dose-dependent manner (control, 0.95 +/- 0.15 vol%; ACEA-1021 20 mg/kg, 0.50 +/- 0.14 vol%; ACEA-1021 40 mg/kg, 0.14 +/- 0.16 vol%; P < 0.01). In experiment 2, arterial CO2 tension was increased by ACEA-1021 (control, 38 +/- 3 mmHg; ACEA-1021 20 mg/kg, 43 +/- 3 mmHg; ACEA-1021 40 mg/kg, 48 +/- 2 mmHg; P < 0.01). Mean arterial pressure was not affected by any dose of ACEA-1021. The righting reflex was abolished in rats receiving ACEA-1021 40 mg/kg only and recovered 30 +/- 7 min after discontinuation of the infusion. CONCLUSIONS: Halothane MAC reduction by glycine receptor antagonism was greater than that previously observed for antagonism of glutamate at the NMDA or AMPA receptor. In rats receiving ACEA-1021 only, minimal hemodynamic depression and moderate hypoventilation were observed. Antagonism of glycine at the NMDA receptor recognition site offers a potential mechanism of action of anesthesia.

Animals↗
PubMed1995

pH-stat management reduces the cerebral metabolic rate for oxygen during profound hypothermia (17 degrees C). A study during cardiopulmonary bypass in rabbits.

BACKGROUND: Greater cerebral metabolic suppression may increase the brain's tolerance to ischemia. Previous studies examining the magnitude of metabolic suppression afforded by profound hypothermia suggest that the greater arterial carbon dioxide tension of pH-stat management may increase metabolic suppression when compared with alpha-stat management. METHODS: New Zealand White rabbits, anesthetized with fentanyl and diazepam, were maintained during cardiopulmonary bypass (CPB) at a brain temperature of 17 degrees C with alpha-stat (group A, n = 9) or pH-stat (group B, n = 9) management. Measurements of brain temperature, systemic hemodynamics, arterial and cerebral venous blood gases and oxygen content, cerebral blood flow (CBF) (radiolabeled microspheres), and cerebral metabolic rate for oxygen (CMRO2) (Fick) were made in each animal at 65 and 95 min of CPB. To control for arterial pressure and CBF differences between techniques, additional rabbits underwent CPB at 17 degrees C. In group C (alpha-stat, n = 8), arterial pressure was decreased with nitroglycerin to values observed with pH-stat management. In group D (pH-stat, n = 8), arterial pressure was increased with angiotensin II to values observed with alpha-stat management. In groups C and D, CBF and CMRO2 were determined before (65 min of CPB) and after (95 min of CPB) arterial pressure manipulation. RESULTS: In groups A (alpha-stat) and B (pH-stat), arterial pressure; hemispheric CBF (44 +/- 17 vs. 21 +/- 4 ml.100 g-1.min-1 [median +/- quartile deviation]; P = 0.017); and CMRO2 (0.54 +/- 0.13 vs. 0.32 +/- 0.10 ml O2 x 100 g-1.min-1; P = 0.0015) were greater in alpha-stat than in pH-stat animals, respectively. As a result of arterial pressure manipulation, in groups C (alpha-stat) and D (pH-stat) neither arterial pressure (75 +/- 2 vs. 78 +/- 2 mmHg) nor hemispheric CBF (40 +/- 10 vs. 48 +/- 6 ml.100 g-1.min-1; P = 0.21) differed between alpha-stat and pH-stat management, respectively. Nevertheless, CMRO2 was greater in alpha-stat than in pH-stat animals (0.71 +/- 0.10 vs. 0.45 +/- 0.10 ml O2 x 100g-1.min-1, respectively; P = 0.002). CONCLUSIONS: At 17 degrees C, CMRO2 with pH-stat management is 35-40% less than that with alpha-stat management and is independent of CBF or arterial pressure differences between the techniques.

Acid-Base Equilibrium↗
PubMed1995

Comparisons between desflurane and isoflurane or propofol on time to following commands and time to discharge. A metaanalysis.

BACKGROUND: Anesthesiologists can best decide whether to use desflurane based on the magnitudes of its effects compared to other general anesthetics. The goal of this study was to estimate the mean decrease in times to following commands when desflurane was being used instead of isoflurane or propofol. The mean decrease in time to hospital discharge after ambulatory surgery when desflurane was used instead of propofol also was examined. METHODS: Published studies that met entry criteria were collected up to November 1994. Included are studies in which patients were randomly assigned to groups, extubation was planned at the end of surgery, and general anesthesia was induced with an intravenous agent. We used random-effects metaanalysis to calculate confidence intervals for pooled mean differences. RESULTS: Six studies (with 229 patients) that compared desflurane to propofol met the inclusion criteria. Eight studies (with 316 patients) compared desflurane to isoflurane. A statistically significant difference in the time to following commands after discontinuation of desflurane versus propofol (mean difference 0.7 min (propofol minus desflurane), 95% confidence interval -0.2 to 1.7 min) was not found. Patients who received propofol were discharged to home a mean of 17 min (4-30 min) more quickly than patients who received desflurane. Patients who received desflurane followed commands a mean of 4.4 min (3.3-5.4 min) more quickly than did patients who received isoflurane. CONCLUSIONS: There are only minor clinically important differences between desflurane and isoflurane or propofol with respect to time to following commands and time to discharge.

Anesthetics, Inhalation↗
PubMed1995

Theoretical analysis of cerebral venous blood hemoglobin oxygen saturation as an index of cerebral oxygenation during hypothermic cardiopulmonary bypass. A counterproposal to the "luxury perfusion" hypothesis.

BACKGROUND: Jugular venous catheters and near-infrared spectroscopy can measure cerebral venous blood hemoglobin oxygen saturation (SvO2). We used computer simulation to characterize the relation between Sv02 and cerebral metabolic rate for oxygen (CMR02) during hypothermic cardiopulmonary bypass (CPB). METHODS: We developed a theoretical model of cerebral oxygen consumption and blood-brain oxygen transfer. Our model included the temperature dependence of blood and brain oxygen solubility; the temperature, age, and acid-base dependence of hemoglobin oxygen dissociation; and the temperature and age dependence of CMRO2. We simulated cerebral blood flow reductions that decreased Sv02 and CMR02. RESULTS: Our model predicts the relation between CMR02 and Sv02 to be dependent on temperature, because of a shift of the oxygen partial pressure at which hemoglobin oxygen saturation equals 0.50. For example, during normothermic CPB, Sv02 can decrease to 30% before CMR02 will decrease to less than 90% of normal. In contrast, for alpha-stat management of infants at 17 degrees C, Sv02 must be maintained at greater than 95% to maintain CMR02 at greater than 90% of its temperature appropriate value. CONCLUSIONS: High Sv02 observed during hypothermic CPB may indicate impaired oxygen transfer from hemoglobin to brain, not "luxury perfusion." The relation between Sv02 and CMR02 depends dramatically on the temperature of the patient. Sv02 per se may not be reliable index of normal CMR02 during hypothermic CPB.

Animals↗
PubMed1995

Diaspirin cross-linked hemoglobin does not increase brain oxygen consumption during hypothermic cardiopulmonary bypass in rabbits.

BACKGROUND: Decreased erythrocyte deformability due to cardiopulmonary bypass (CPB) and/or hypothermia, may result in brain capillary beds that have decreased erythrocyte transit, resulting in a generalized impairment of brain oxygenation during CPB. Because brain capillary plasma flow continues even when erythrocyte flow is absent, the authors' hypothesized augmentation of plasma oxygen content with a non-erythrocyte-associated oxygen transport molecule would increase brain oxygen uptake during hypothermic CPB. METHODS: Anesthetized New Zealand white rabbits, maintained on CPB at 27 degrees C, were randomized to one of three groups. In group 1 (n = 13), plasma oxygen content was increased by administration of alpha-alpha diaspirin cross-linked hemoglobin. In this group, pretreatment with 0.5 mg/kg verapamil was necessary to prevent hypertension. In group 2 (n = 13), alpha-alpha diaspirin cross-linked hemoglobin was not administered, but verapamil was given as before (control). In group 3 (n = 13), neither alpha-alpha diaspirin cross-linked hemoglobin nor verapamil was administered (control). At 60 min of CPB, cerebral blood flow (microspheres) and cerebral metabolic rate for oxygen (Fick) were determined. RESULTS: Systemic physiologic variables did not differ among groups. Although total arterial oxygen content was equivalent in all groups (approximately 12.1 ml O2/dl), the alpha-alpha diaspirin cross-linked hemoglobin group had a much greater proportion of the total arterial oxygen content present in a non-erythrocyte-associated form, 29 +/- 5% versus 6 +/- 2% and 5 +/- 3%, in groups 2 and 3, respectively. Nevertheless, neither cerebral blood flow (approximately 34 ml.100g-1.min-1) nor cerebral metabolic rate for oxygen (approximately 1.2 ml O2.100g-1.min-1) differed among groups. CONCLUSIONS: Because oxygen was equally available to the brain in all groups, independent of whether oxygen was associated with erythrocytes or not, it was concluded that erythrocyte/capillary interactions do not limit oxygen transfer from blood to brain during moderately hypothermic CPB. The hypertensive response to alpha-alpha diaspirin cross-linked hemoglobin during CPB is probably a result of nitric oxide scavenging.

Animals↗