Cardiopulmonary effects of positive end-expiratory pressure in anesthetized, mechanically ventilated ponies

D. V. Wilson From the Department of Clinical Studies, University of Pennsylvania, School of Veterinary Medicine, New Bolton Center, Kennett Square, PA 19348 (Wilson, Soma).

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L. R. Soma From the Department of Clinical Studies, University of Pennsylvania, School of Veterinary Medicine, New Bolton Center, Kennett Square, PA 19348 (Wilson, Soma).

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Summary

To investigate the cardiopulmonary effects of positive end-expiratory pressure (peep), values of 10, 20, and 30 cm of H2O, were applied to anesthetized, dorsally recumbent, ventilated ponies. After iv induction of general anesthesia, peep was superimposed on controlled ventilation with 100% oxygen, and changes in gas exchange and cardiac function were measured. Increasing values of peep in these ponies caused a linear increase in the mean (± SEM) functional residual capacity, from a control value (zero end-expiratory pressure) of 1.7 ± 0.24 L to 2.2 ± 0.31, 2.9 ± 0.32 and 3.4 ± 0.3 L at peep of 10, 20, and 30 cm of H2O, respectively (P < 0.05). Paralleling these changes, intrapulmonary shunt fraction decreased significantly (P < 0.05) from a control value of 12.9 ± 0.5%, to 7.5 ± 1.1 and 2.1 ± 0.6%, at peep of 20 and 30 cm of H2O, respectively. Cardiac output was decreased by increasing values of peep, from control value of 11.7 ± 1.56 L/min to 9.9 ± 1.51, 8.8 ± 1.33 and 5.62 ± 0.56 L/min at peep of 10, 20, and 30 cm of H20, respectively. Related to decreasing cardiac output, tissue oxygen delivery also decreased as peep was increased, from control value of 2.0 ± 0.09 L/min to 1.8 ± 0.07, 1.6 ± 0.06, and 1.03 ± 0.04 L/min at peep of 10, 20, and 30 cm of H2O, respectively.

Thus, the effects of increasing values of peep in these ponies included increased functional residual capacity and arterial oxygenation, but marked reduction in cardiac output, resulting in no improvement or decrease in total oxygen delivery. Although peep is useful for improving arterial oxygenation, the deleterious cardiovascular effects should be anticipated or ameliorated by use of volume loading and/or inotrope administration.

Summary

To investigate the cardiopulmonary effects of positive end-expiratory pressure (peep), values of 10, 20, and 30 cm of H2O, were applied to anesthetized, dorsally recumbent, ventilated ponies. After iv induction of general anesthesia, peep was superimposed on controlled ventilation with 100% oxygen, and changes in gas exchange and cardiac function were measured. Increasing values of peep in these ponies caused a linear increase in the mean (± SEM) functional residual capacity, from a control value (zero end-expiratory pressure) of 1.7 ± 0.24 L to 2.2 ± 0.31, 2.9 ± 0.32 and 3.4 ± 0.3 L at peep of 10, 20, and 30 cm of H2O, respectively (P < 0.05). Paralleling these changes, intrapulmonary shunt fraction decreased significantly (P < 0.05) from a control value of 12.9 ± 0.5%, to 7.5 ± 1.1 and 2.1 ± 0.6%, at peep of 20 and 30 cm of H2O, respectively. Cardiac output was decreased by increasing values of peep, from control value of 11.7 ± 1.56 L/min to 9.9 ± 1.51, 8.8 ± 1.33 and 5.62 ± 0.56 L/min at peep of 10, 20, and 30 cm of H20, respectively. Related to decreasing cardiac output, tissue oxygen delivery also decreased as peep was increased, from control value of 2.0 ± 0.09 L/min to 1.8 ± 0.07, 1.6 ± 0.06, and 1.03 ± 0.04 L/min at peep of 10, 20, and 30 cm of H2O, respectively.

Thus, the effects of increasing values of peep in these ponies included increased functional residual capacity and arterial oxygenation, but marked reduction in cardiac output, resulting in no improvement or decrease in total oxygen delivery. Although peep is useful for improving arterial oxygenation, the deleterious cardiovascular effects should be anticipated or ameliorated by use of volume loading and/or inotrope administration.

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