A recruitment maneuver improves apneic oxygenation

Apneic oxygenation (AO) is applied during surgery and in intensive care units. Even with AO, apnea is associated with progressive hypoxemia, limiting the tolerable amount of time in AO. This experimental study evaluates the effects of a recruitment maneuver (RM) on oxygenation, CO2 retention, and survival times during prolonged apnea, supported or not supported with intratracheal apneic oxygenation.

Following Ethic Committee approval, 15 male Sprague-Dawley rats were anesthetized and ventilated with PCV and FiO2:1 for 15 minutes. After obtaining a basal arterial blood-gas sample, the rats were randomized into 3 groups and disconnected from the ventilator: group (G) 1 (N.=6): AO with a cannula inserted into the carina; G2 (N=6): RM (40 cm H2O CPAP applied for 30 seconds) before AO; and G3 (N.=3): no application after disconnection (G3 was stopped after the first 3 subjects died within 3 minutes). Further arterial blood-gas samples were taken after 1, 3, and 6 minutes (T1, T3, and T6). Survival times after the start of AO were recorded.

G2 was associated with significantly higher values of PaO2 at T3 and T6 when compared to G1 (345±56 vs. 233±65 mm Hg at T3 and 258±31 vs. 180±31 mm Hg at T6, respectively, P<0.05). There were significant changes in PaO2, pH, and PaCO2 over time in all subjects, but no differences were observed between G1 and G2 in pH or PaCO2. Survival time in G2 was significantly longer as opposed to G1 (G1: 10.3±2.3 min; G2: 14.3±3.6 min; P<0.05).

RM prior to AO prolongs tolerance to apnea, probably by increasing the time before intolerable hypoxemia occurs, without a significant difference in PaCO2 levels.