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Effect of baseline lung compliance on the subsequent response to positive end-expiratory pressure in ventilated
1Department of Clinical Investigation, Tripler Army Medical Center, Honolulu, HI.
Objective:
To determine the pulmonary function and hemodynamic effects of incremental positive end-expiratory pressure in two groups of normal ventilated newborn piglets with different baseline dynamic lung compliance.
Design:
Prospective, controlled, intervention study.
Setting:
Animal laboratory.
Interventions:
One group of piglets (inflation group) was prepared with 3 cm H2O (0.29 kPa) positive end-expiratory pressure and a maximal lung inflation to increase baseline lung compliance as compared with the other group (no-inflation group), prepared by 3 hrs of ventilation at zero end-expiratory pressure. Both groups were then subjected to a sequence of incremental positive end-expiratory pressures from 0 to 12 cm H2O (0 to 1.18 kPa) in 2-cm increments for 15-min periods at each level followed by a 60-min recovery period at zero end-expiratory pressure.
Measurements And Main Results:
Pulmonary function, hemodynamic and blood gas data were collected at each positive end-expiratory pressure value and at 15-min intervals during recovery. Baseline dynamic lung compliance was 5.2 +/- 0.3 mL/cm H2O (53.04 +/- 3.06 mL/kPa) in the inflation group and 2.5 +/- 0.1 mL/cm H2O (25.5 +/- 1.02 mL/kPa) in the no-inflation group. No differences were found in any other pulmonary function, hemodynamic or blood gas value at baseline. Incremental positive end-expiratory pressure resulted in a decrease in dynamic lung compliance and an increase in end-expiratory lung volume in both groups of piglets; dynamic lung compliance was greater in the inflation group at all times. No differences were found in end-expiratory lung volume between groups. Hemodynamic changes in both groups of piglets included: decreased cardiac output and increased pulmonary vascular resistance and systemic vascular resistance. The changes in cardiac output (-23% vs. -32%), pulmonary vascular resistance (+53% vs. +95%), and systemic vascular resistance (17% vs. 51%) were less in the inflation group as compared with the no-inflation group.
Conclusions:
Baseline dynamic lung compliance is an important determinant of the subsequent effect of positive end-expiratory pressure on pulmonary function and hemodynamics in the ventilated piglet with normal lungs.