Effect of PEEP levels on ventilation in prone position in patients suffering from acute lung injury

Objectives

Prone position (PP) improves oxygenation and respiratory mechanics in patients suffering from acute lung injury (ALI). Aim of our study was to better understand lung recruitment due to ventilation in PP.

Methods

4 sedated and paralysed suffering from ALI (3M/1F;mean age 59.8 ± 15.4; LIS: 2.30-3.15). Mechanical ventilation was done in volume-controlled mode with a computer controlled Servo Ventilator 900 C (Vt: 8-10 ml/kg; RR: 12-18 b/min; Ti: 33%; Tpaus: 5%; FiO₂ 0.4-0.6). Lung mechanics was studied during a computer controlled low sinusoidal flow oscillations inflation. Pressure and flow were read by the computer. Volume was calculated by integration of flow. The distending pressure (Pdist) was calculated by subtraction of resistive pressure drop in connecting tubes and airways. Compliance (Crs) was evaluated by plotting volume against Pdist. Each study breath was preceded by a 6 s long expiration during which PEEP was allowed to fall to zero and volume retained by PEEP (V_retPEEP) evaluated. Alveolar dead space (Yd_alv) was obtained by a single breath test for CO₂. Patients were studied in stable condition in supine position (SP) with a PEEP level of 5 cmH₂O. PEEP was then set at 10 cmH₂O and after 15 min the study repeated. The same procedure was followed after the patients were turned prone. The following parameters were analysed: EKG, blood pressure, blood gases, Crs, Vt, V_retPEEP.

Results

In the table the mean values are expressed. Patients were stable during the study, and no side effects were observed. One patients resulted non responder.

Conclusion

From our preliminary results, the improvement in oxygenation in PP seems to be due to a better lung recruitment and a reduction in Vd_alv.

Table