[The value of nitrogen washout/washin method in assessing alveolar recruitment volume in acute lung injury patients].

Objective: To evaluate the precision and feasibility of nitrogen washout/washin method in assessing lung recruitment of acute lung injury (ALI) patients.

Methods: Fifteen ALI patients underwent mechanical ventilation were involved. Two positive end-expiratory pressure (PEEP) levels (high and low) were adjusted according to ARDSnet recommendations or measurement of transpulmonary pressure, each for 30 minutes. Tidal volume (Vt), plateau of airway pressure (Pplat), other respiratory mechanics, gas-exchange and hemodynamics were measured. End expiration lung volume (EELV) was measured at different PEEP levels through nitrogen washout/washin method, and formula (EELVhighPEEP-EELVlowPEEP)-VtlowPEEP/(PplatlowPEEP-PEEPlowPEEP)×(PEEPhigh-PEEPlow) was used as recruitment (Rec-N2). Alveolar recruitment was measured using pressure-volume (P-V) curves (Rec-mes). Correlation and consistency of Rec-N2 and Rec-mes were compared by correlation analysis and Bland-Altman technique.

Results: PEEP titrated by ARDSnet recommendations or transpulmonary pressure were (7 ± 2) cm H2O (1 cm H2O = 0.098 kPa) vs (14 ± 5) cm H2O (P = 0.008); and there were significant differences in peak pressure (23 ± 5) cm H2O vs (28 ± 6) cm H2O, plateau of airway pressure (17 ± 4)cm H2O vs (22 ± 6) cm H2O, esophageal pressure, transpulmonary pressure and other respiratory mechanics between the two PEEP levels (P < 0.05). The P-V curve technique gave Rec-mes a value of 100 (-25 ∼ 185)ml. The nitrogen washout/washin technique gave Rec-N2 a value of 180 (-19 ∼ 255) ml, which showed a good correlation with a bias of 46 (8 ∼ 80) ml (R(2) = 0.755, P < 0.0001).

Conclusion: Nitrogen washout/washin technique can be used to determine lung recruitment volume of ALI patients.