EFFECT OF BASE-LINE LUNG COMPLIANCE ON THE SUBSEQUENT RESPONSE TO POSITIVE END-EXPIRATORY PRESSURE IN VENTILATED PIGLETS WITH NORMAL LUNGS

Objective: To determine the pulmonary function and hemodynamic effects of incremental positive end-expiratory pressure in two groups of norm al ventilated newborn piglets with different baseline dynamic lung com pliance. Design: Prospective, controlled, intervention study. Setting: Animal laboratory. Interventions: One group of piglets (inflation gro up) was prepared with 3 cm H2O (0.29 kPa) positive end-expiratory pres sure 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 t hen subjected to a sequence of incremental positive end-expiratory pre ssures from 0 to 12 cm H2O (0 to 1.18 kPa) in 2-cm increments for 15-m in periods at each level followed by a 60-min recovery period at zero end-expiratory pressure. Measurements and Main Results: Pulmonary func tion, hemodynamic and blood gas data were collected at each positive e nd-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 basel ine. Incremental positive end-expiratory pressure resulted in a decrea se in dynamic lung compliance and an increase in end-expiratory lung v olume in both groups of piglets; dynamic lung compliance was greater i n the inflation group at all times. No differences were found in end-e xpiratory lung volume between groups. Hemodynamic changes in both grou ps of piglets included: decreased cardiac output and increased pulmona ry vascular resistance and systemic vascular resistance. The changes i n 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. Conclusi ons: Baseline dynamic lung compliance is an important determinant of t he subsequent effect of positive end-expiratory pressure on pulmonary function and hemodynamics in the ventilated piglet with normal lungs.