Effect of lung recruitment on oxygenation in patients with acute lung injury ventilated in CPAP/pressure support mode

Introduction

One of the aims of lung recruitment is to improve oxygenation [1], but it has not yet been investigated in spontaneously breathing patients. Our objective was to evaluate the effects of recruitment maneuvers on oxygenation in patients ventilated in CPAP/ pressure support (CPAP/PS) mode.

Methods

In a prospective, observational study, 30 patients with a Lung Injury Score ≥2 were recruited. Following baseline measurements (t₀) PEEP was increased by 5 cmH₂O (t₁). Recruitment maneuver was applied for 40 seconds with 40 cmH₂O PS. Measurements were taken immediately after recruitment (t₂) then 15 minutes (t₃) and 30 minutes later (t₄).

Results

According to the difference of PaO₂/FiO₂ between t₂ and t₀, three groups were defined: nonresponders (NR: difference of PaO₂/FiO₂ ≤0%, n = 8), low responders (LR: difference of PaO₂/FiO₂ = 0 to 50%, n = 11) and high responders (HR: difference of PaO₂/FiO₂ >50%, n = 11). In the NR-group, PaO₂/FiO₂ decreased significantly: median (interquartile), PaO₂/FiO₂ = 178 (159 to 240) versus 165 (118 to 210) mmHg; in the LR-group and in the HR-group there was significant improvement: 119 (98 to 164) versus 161 (123 to 182) mmHg and 141 (130 to 183) versus 239 (224 to 369) mmHg, P < 0.05, respectively. Dynamic compliance (C_dyn) significantly dropped at t as compared with t in the NR-group, C_dyn = 62 (48 to 87) versus 53 (43 to 78) ml/cmH₂O, while there was no significant change in the LR- and HR-groups, P < 0.05. At the same time points the dead space to tidal volume ratio (Vds/Vte) significantly increased in the NR-group, Vds/Vte = 30 (23 to 37) versus 37 (26 to 42)%, but not in the LR- and HR-groups, P < 0.05.

Conclusion

Recruitment maneuvers improved PaO₂/FiO₂ in the majority of patients (73%) without affecting C_dyn or Vds/Vte; therefore it may be a safe approach to improve oxygenation in patients ventilated in CPAP/PS mode.