Abstract
Rationale: Clinicians are often concerned that higher positive end-expiratory pressure (PEEP) will decrease cardiac index (CI). PEEP affects CI through multiple inter-related mechanisms. The adult Rhesus monkey is an excellent model to study cardiopulmonary interaction due to similar pulmonary and chest wall compliances to human infants.Objective: Our goal was to examine the impact of increasing PEEP on CI in Rhesus monkeys as a model for critically ill children.Methods: Prospective, experimental animal study. Nine healthy anesthetized, intubated Rhesus monkeys were allowed to breathe spontaneously at a PEEP of 0, 5, 10, and 15 cm H2O while CI was measured with an ultrasonic Doppler (USCOM).Measurements and main results: Cardiac index decreased between PEEP levels of 5 and 15 cm H2O. The mean decrease in CI for the entire cohort of monkeys was 18% (p < 0.01) with a range of −11 to 49%. Stroke volume and oxygen delivery also decreased between PEEP levels of 5 and 15 cm H2O (p < 0.01).Conclusion: Between PEEP levels of 5 and 15 cm H2O, there was a decrease in CI, stroke volume, and oxygen delivery in intubated Rhesus monkeys. A plausible mechanism is that over-distention of normally compliant lungs at increased PEEP resulted in decreased preload to the right ventricle, outweighing the potentially beneficial decrease in left ventricular afterload or pulmonary vascular resistance. Further investigation is warranted, particularly in children with lung injury, who have historically benefited from increased PEEP levels without over-distention.
Highlights
Clinicians are often concerned that higher positive end-expiratory pressure (PEEP) levels needed to achieve lung recruitment in patients with acute lung injury (ALI) will decrease cardiac index (CI) and potentially decrease oxygen delivery
Between PEEP levels of 5 and 15 cm H2O, there was a decrease in CI, stroke volume, and oxygen delivery in intubated Rhesus monkeys
A plausible mechanism is that over-distention of normally compliant lungs at increased PEEP resulted in decreased preload to the right ventricle, outweighing the potentially beneficial decrease in left ventricular afterload or pulmonary vascular resistance
Summary
Clinicians are often concerned that higher positive end-expiratory pressure (PEEP) levels needed to achieve lung recruitment in patients with acute lung injury (ALI) will decrease cardiac index (CI) and potentially decrease oxygen delivery. There are limited studies [1, 2] on the effect of PEEP on CI in children due to the perceived risk of invasive techniques required for direct CI measurement in the past. We used ultrasound Doppler to investigate the effect of PEEP on CI, stroke volume, and oxygen delivery in a controlled environment using a Rhesus monkey model that has significant physiological similarities to children. PEEP may increase CI by decreasing left ventricular afterload and if there is atelectasis by lung recruitment leading to decreased pulmonary vascular
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