Pulmonary volume recruitment manoeuvre restores pulmonary compliance and resistance after apnoea in anaesthetized lambs.

Abstract

We studied the effects of an episode of induced apnoea on the dynamic compliance (Crs) and resistance (Rrs) of the respiratory system in anaesthetized lambs and investigated the mechanisms underlying the effectiveness of a timed reexpansion inspiratory manoeuvre (TRIM). Following 2 min of apnoea, three manoeuvres were randomly performed: (i) control: reventilated without TRIM using initial settings and gas composition of 30% oxygen in 70% nitrous oxide; (b) T1: TRIM with 30% oxygen in 70% nitrous oxide, followed by reventilation with the initial settings; and (c) T2: preoxygenate with 100% oxygen, apnoea, then TRIM with 100% oxygen, then reventilation with 100% oxygen at the initial settings. The percentage change in Crs and Rrs was calculated at first breath, second breath, 10, 20, 40, 60, 90, 120 and 180 s postapnoea. Mean control decreased 15% and did not return to baseline during the study period. TRIM increased mean Crs in T1 and T2 by 8% and 9%, respectively, at first breath and returned to baseline and did not deteriorate for the remainder of the study period. Mean Rrs in the control group increased 20% and did not return to baseline during the study period. Mean Rrs in T1 and T2 initially increased 17% and 27%, respectively, at first breath and returned to baseline within 40 s. These results demonstrate that significant deterioration occurs in Crs and Rrs following 2 min of apnoea in anaesthetized lambs, which is not corrected with normal ventilation but is rapidly and completely reversed with a TRIM. This supports our hypothesis that volume recruitment of alveoli is an effective manoeuvre in restoring lung function. The practice of preoxygenation is also reinforced as the lambs maintained maximal oxygen saturation if they were ventilated with 100% oxygen prior to the 2 min of apnoea.