THE INFLUENCE OF CARDIAC OUTPUT ON ARTERIAL OXYGENATION: A THEORETICAL STUDY

Background Because maintaining arterial oxygenation (PaO2) during one-lung ventilation (OLV) can be a clinical problem, it is useful to be aware of factors that influence PaO2 in this situation and are under the control of the anesthesiologist. It is unknown whether, among the commonly used volatile anesthetic agents, one is associated with higher PaO2 levels. Clinical studies suggest that isoflurane provides superior PaO2 during OLV than does halothane. These have not been compared to enflurane. The authors studied PaO2 and hemodynamics during OLV with 1 MAC enflurane versus 1 MAC isoflurane. Methods Twenty-eight adults who had prolonged periods of OLV anesthesia with minimal trauma to the nonventilated lung (thoracoscopic or esophageal surgery) were studied in a cross-over design. Patients were randomized to two groups: Group 1 received 1 MAC enflurane in oxygen from induction until after the first 30 min of OLV, then were switched to 1 MAC isoflurane. In group 2, the order of the anesthetics was reversed. Results Isoflurane was associated with higher PaO2 values during OLV (P < 0.0001). Mean PaO2 (+/- SD) after 30 min OLV isoflurane was 231 (+/- 125) mmHg versus 184 (+/- 106) mmHg after 30 min OLV enflurane. The difference in PaO2 between the two anesthetics was most marked in the patients with the highest PaO2 during OLV: PaO2 isoflurane PaO2 enflurane varies; is directly proportional to PaO2 isoflurane (r = 0.65, P < 0.001). There were no other significant differences between anesthetic gases in the measured hemodynamic or respiratory variables. In the subgroup of patients with pulmonary artery catheters (n = 7), PaO2 correlated with cardiac output during OLV for both anesthetics (r = 0.81, P < 0.001). Conclusions During OLV, the PaO2 values with 1 MAC isoflurane were greater than those with enflurane. The dependence of PaO2 on cardiac output does not support the hypothesis that an increase in cardiac output will cause a decrease in hypoxic pulmonary vasoconstriction and a decrease in PaO2 during OLV.

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Effects of acetazolamide on aerobic exercise capacity and pulmonary hemodynamics at high altitudes

Journal of Applied Physiology ◽

10.1152/japplphysiol.00180.2007 ◽

2007 ◽

Vol 103 (4) ◽

pp. 1161-1165 ◽

Cited By ~ 31

Author(s):

Vitalie Faoro ◽

Sandrine Huez ◽

Sébastien Giltaire ◽

Adriana Pavelescu ◽

Aurélie van Osta ◽

...

Keyword(s):

Cardiac Output ◽

Aerobic Exercise ◽

Exercise Capacity ◽

Respiratory Exchange Ratio ◽

Hypoxic Pulmonary Vasoconstriction ◽

Arterial Oxygenation ◽

High Altitudes ◽

Pulmonary Hemodynamics ◽

Pulmonary Vasoconstriction ◽

Aerobic Exercise Capacity

Aerobic exercise capacity is decreased at altitude because of combined decreases in arterial oxygenation and in cardiac output. Hypoxic pulmonary vasoconstriction could limit cardiac output in hypoxia. We tested the hypothesis that acetazolamide could improve exercise capacity at altitude by an increased arterial oxygenation and an inhibition of hypoxic pulmonary vasoconstriction. Resting and exercise pulmonary artery pressure (Ppa) and flow (Q) (Doppler echocardiography) and exercise capacity (cardiopulmonary exercise test) were determined at sea level, 10 days after arrival on the Bolivian altiplano, at Huayna Potosi (4,700 m), and again after the intake of 250 mg acetazolamide vs. a placebo three times a day for 24 h. Acetazolamide and placebo were administered double-blind and in a random sequence. Altitude shifted Ppa/Q plots to higher pressures and decreased maximum O2 consumption (V̇o2max). Acetazolamide had no effect on Ppa/Q plots but increased arterial O2 saturation at rest from 84 ± 5 to 90 ± 3% ( P < 0.05) and at exercise from 79 ± 6 to 83 ± 4% ( P < 0.05), and O2 consumption at the anaerobic threshold (V-slope method) from 21 ± 5 to 25 ± 5 ml·min−1·kg−1 ( P < 0.01). However, acetazolamide did not affect V̇o2max (from 31 ± 6 to 29 ± 7 ml·kg−1·min−1), and the maximum respiratory exchange ratio decreased from 1.2 ± 0.06 to 1.05 ± 0.03 ( P < 0.001). We conclude that acetazolamide does not affect maximum exercise capacity or pulmonary hemodynamics at high altitudes. Associated changes in the respiratory exchange ratio may be due to altered CO2 production kinetics.

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Effects of gravity on lung diffusing capacity and cardiac output in prone and supine humans

Journal of Applied Physiology ◽

10.1152/japplphysiol.01154.2002 ◽

2003 ◽

Vol 95 (1) ◽

pp. 3-10 ◽

Cited By ~ 27

Author(s):

M. Rohdin ◽

J. Petersson ◽

P. Sundblad ◽

M. Mure ◽

R. W. Glenny ◽

...

Keyword(s):

Cardiac Output ◽

Normal Subjects ◽

Arterial Oxygenation ◽

Diffusing Capacity ◽

Alveolar Volume ◽

Pulmonary Capillary Blood Flow ◽

Pulmonary Capillary ◽

Supine Posture ◽

Pulmonary Capillary Blood ◽

Residual Capacity

Both in normal subjects exposed to hypergravity and in patients with acute respiratory distress syndrome, there are increased hydrostatic pressure gradients down the lung. Also, both conditions show an impaired arterial oxygenation, which is less severe in the prone than in the supine posture. The aim of this study was to use hypergravity to further investigate the mechanisms behind the differences in arterial oxygenation between the prone and the supine posture. Ten healthy subjects were studied in a human centrifuge while exposed to 1 and 5 times normal gravity (1 G, 5 G) in the anterioposterior (supine) and posterioanterior (prone) direction. They performed one rebreathing maneuver after ∼5 min at each G level and posture. Lung diffusing capacity decreased in hypergravity compared with 1 G (ANOVA, P = 0.002); it decreased by 46% in the supine posture compared with 25% in the prone ( P = 0.01 for supine vs. prone). At the same time, functional residual capacity decreased by 33 and 23%, respectively ( P < 0.001 for supine vs. prone), and cardiac output by 40 and 31% ( P = 0.007 for supine vs. prone), despite an increase in heart rate of 16 and 28% ( P < 0.001 for supine vs. prone), respectively. The finding of a more impaired diffusing capacity in the supine posture compared with the prone at 5 G supports our previous observations of more severe arterial hypoxemia in the supine posture during hypergravity. A reduced pulmonary-capillary blood flow and a reduced estimated alveolar volume can explain most of the reduction in diffusing capacity when supine.

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The Influences of three Intraoperative Ventilatory Strategies on Arterial Oxygenation in Morbid Obese Patients Undergoing Laparoscopic Bariatric Surgery

Journal of Advances in Medicine and Medical Research ◽

10.9734/jammr/2021/v33i1630995 ◽

2021 ◽

pp. 1-16

Author(s):

Shaimaa E. Shaban ◽

Reda S. Salama ◽

Mohamed M. Abu Elyazed ◽

Abdelraheem M. Dowidar

Keyword(s):

Bariatric Surgery ◽

Cardiac Output ◽

Respiratory Mechanics ◽

Recruitment Maneuver ◽

Conventional Ventilation ◽

Laparoscopic Bariatric Surgery ◽

Obese Patients ◽

Arterial Oxygenation ◽

Morbid Obese ◽

The Mean

Background: Maintaining satisfactory ventilation for obese patients undergoing bariatric surgery frequently poses a challenge for anesthetists. The optimal ventilation strategy during pneumoperitoneum remains obscure in obese patients. In this study, we investigated the effect of conventional ventilation, inverse ratio ventilation (IRV) and alveolar recruitment maneuver (RM) on arterial oxygenation, lung mechanics and hemodynamics in morbid obese patients undergoing laparoscopic bariatric surgery. Methods: 105 adult obese patients scheduled for elective laparoscopic bariatric surgery were randomly allocated into three groups: Conventional ratio ventilation (I:E ratio was 1:2, PEEP 5 cmH2O and no RM), Inverse Ratio Group (IRVG) (I:E ratio was 2:1 and PEEP 5 cmH2O and No RM ) and Recruitment Maneuver Group (RMG) ( RM was done and I:E ratio was 1:2). Arterial blood gases and respiratory mechanics were recorded after induction of anesthesia (T1), 5 minutes (T2), 30 minutes (T3), 60 minutes (T4) after the beginning of pneumoperitoneum and at the end of the surgery (T5). Cardiac output was recorded at (T1), (T2), (T3) and (T5). Results: At T3, T4 and T5, arterial oxygen tension was higher in RMG than IRVG than CG (P ˂ 0.05). At T3, T4 and T5, the mean airway pressure and dynamic compliance (Cdyn) were significantly higher in IRVG and RMG compared with CG (P ˂ 0.05) while at those times, the mean air way pressure and Cdyn in IRVG and RMG were comparable. Cardiac output result were comparable between all groups throughout the study period (P ˃ 0.05). Conclusions: RM and IRV had provided better arterial oxygenation and respiratory mechanics compared to conventional ventilation in morbid obese patients undergoing laparoscopic bariatric surgery. However, RM had better gas exchange than IRV.

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