Open Lung Strategy in a Lamb Model of Respiratory Distress Syndrome

Abstract

We tested the hypothesis that an open lung strategy with recruitment maneuvers will improve oxygenation and decrease lung injury in comparison with a permissive hypercapnia strategy in preterm lambs. Preterm lambs born by operative delivery at 131 ± 1 days of gestational age (term = 150 days) were randomized to an open lung group (OLG, n = 5) or a permissive hypercapnia group (PHG, n = 4). In the OLG, ramp recruitment maneuvers were performed by increasing and then decreasing peak inspiratory pressure and positive end-expiratory pressure (adjusting for expiratory tidal volume [V(T)] 6 to 8 mL/kg). In the PHG, lambs received ventilation with V(T) of 6 to 8 mL/kg, adapting pressures and respiratory rate according to arterial blood gases results. Fraction of inspired oxygen was adjusted for oxygen saturation 88 to 93%. Lambs were ventilated for 6 hours. Lung pathology was assessed by masked examiners. There were no significant differences for arterial to alveolar oxygen tension ratio, partial pressure of arterial carbon dioxide, blood pressure, compliance, resistance, and other variables between groups. Gas leaks were noted in four of five lambs in the OLG and one of four in the PHG (relative risk 3.2; 95% confidence interval 0.5 to 18). By histological examination, lung areas were overdistended (49% in the OLG, 37% in the PHG). Open lung ventilation following ramp recruitment maneuvers did not offer advantages and might increase lung injury compared with a permissive hypercapnia strategy in preterm lambs with lung immaturity.