Reducing tidal volume and increasing positive end-expiratory pressure with constant plateau pressure during one-lung ventilation: effect on oxygenation

Background. It is no longer safe to use large tidal volumes (V-T) (>8 ml kg(-1)) for one-lung ventilation (OLV), and limiting plateau pressure should be a major objective. Due to the specificity of OLV, the use of positive end-expiratory pressure (PEEP) remains controversial. This study determined whether at the same low plateau pressure, reducing V-T and increasing PEEP were not inferior to larger V-T and lower PEEP ventilation in terms of oxygenation. Methods. This prospective, randomized, non-inferiority, cross-over trial included 88 patients undergoing open thoracotomy who received two successive ventilatory strategies in random order: V-T (8 ml kg 21 of ideal body weight) with low PEEP (5 cm H2O), or low V-T (5 ml kg 21) with a high PEEP. Respiratory rate and PEEP were, respectively, adjusted to maintain constant ventilation and plateau pressure. The primary endpoint was the Pa-O2/FIO2 ratio under each ventilatory strategy. Results. The non-inferiority of low-V-T ventilation could not be established. The mean adjusted Pa-O2/FIO2 ratio was lower overall during low-V-T ventilation, and differences between the two ventilatory modes varied significantly according to baseline (T0) Pa-O2/FIO2. Decreased oxygenation during low V-T was smaller when baseline values were low. Systolic arterial pressure was not lower during low-V-T ventilation. Conclusion. During OLV, lowering V-T and increasing PEEP, with the same low plateau pressure, reduced oxygenation compared with larger V-T and lower PEEP. This strategy may reduce the risk of lung injury, but needs to be investigated further.