Impact of positive end-expiratory pressure on cardiac index measured by ultrasound cardiac output monitor*

Abstract

Objectives: To evaluate the impact of different levels of positive end-expiratory pressure on cardiac index in children receiving mechanical ventilation. To explore the effect of lung recruitment on the relationship between positive end-expiratory pressure and cardiac output.

Design: Prospective, single center, and interventional.

Setting: PICU in a tertiary care children's hospital.

Patients: Fifty mechanically ventilated, hemodynamically stable children between 1 month and 20 years old.

Interventions: Positive end-expiratory pressure was altered to levels of 0, 4, 8, and 12 cm H2O in random order. Cardiac output was measured at different levels of positive end-expiratory pressure by continuous wave Doppler ultrasound (ultrasound cardiac output monitor). Baseline vital signs were recorded, as well as cardiac index and dynamic compliance of the respiratory system at each positive end-expiratory pressure level.

Measurements and main results: Median cardiac index decreased marginally as positive end-expiratory pressure increased, with a median change in cardiac index of 0.4 (< 10%) between positive end-expiratory pressure of 0 and 12 cm H2O (p < 0.001). There was no difference in heart rate or blood pressure as positive end-expiratory pressure increased (p > 0.5). For a subset of 29 patients (58%) in whom the highest dynamic compliance was at a positive end-expiratory pressure of 4 or 8 cm H2O, there was no difference in cardiac index between positive end-expiratory pressure 4 below versus positive end-expiratory pressure at highest dynamic compliance, or cardiac index between positive end-expiratory pressure 4 above versus positive end-expiratory pressure at highest dynamic compliance (p > 0.2). Regardless of optimal dynamic compliance, cardiac index decreased as positive end-expiratory pressure increased (p = 0.02).

Conclusions: In hemodynamically stable mechanically ventilated children, although there is a statistically significant decrease in cardiac output as positive end-expiratory pressure is increased between 0 and 12 cm H2O, the mean change is less than 10%, and this is likely not clinically significant. In the presence of lung disease, intensive care physicians should feel less reluctant in their use of positive end-expiratory pressure for hemodynamically stable patients.