Clinical Study Of Lung Recruited Volume To Select Positive End Expiratory Pressure In Patients With Acute Respiratory Distress Syndrome

Objective: To access the effect on alveolar recruitment of positive endexpiratory pressure (PEEP) and to investigate lung recruited volume directing PEEPin acute respiratory distress syndrome(ARDS).Methods: Thirty ventilated patients with stable hemodynamics satisfyingcriteria of ARDS were included in the study group. Pressure volume (P-V) curveswere traced using the low flow technique and the low inflection point (LIP) wasdetermined. Recruited volume of three different PEEP levels 5cm H₂O,10cm H₂O,15cm H₂O (1cm H₂O=0.098 kPa) were measured by pressure-volume curvemethod. Effects of different PEEP levels on lung mechanics, hemodynamics and gasexchange were compared.Results: (1) The change of lung recruited volume: Lung recruited volumeelevated when PEEP increased from 5 cm H₂Oto 15 cm H₂O [(39.6±13.8)m 1 vs.120.6±39.7) ml vs. (180.5±40.8)ml, all P＜0.05). LIP can be measured withtwenty-three of all P-V curves, LIP (9.8±2.9).Others cannot be measured. Allpatients were separated into two groups:LIP group and without LIP group. Recruitedvolume at PEEP 15 cm H₂O in the patient group with lower inflection point (LIP)was larger than the group without LIP. (2)The change of oxygenation and gasexchange: partial pressure of arterial oxygen (PaO₂) and arterial oxygen saturation(SaO₂)increased with PEEP. Arterial oxygenation index (PaO₂/FiO₂) increased withPEEP. A positive correlation was found between recruited volume and arterialoxygenation index (r=0.452, P＜0.01). With same PEEP, there was no significantdifference on PaO₂/FiO₂ between LIP group and without LIP group(P＞0.05). (3)Thechange ofhemodynamics: There was no significant difference on heart rate(HR),mean artery pressure (MAP),cardiac index(CI),pulmonary artery pressure(PAP), pulmonary arterial wedge pressure (PAWP) and the central venous pressure (CVP)when PEEP increased from 5 cm H₂O to 15 cm H₂O. (4) The change of pulmonarymechanics: peak inspiratory pressure(PIP),plateau airway pressure(Pplat) and meanairway pressure(Pm) all increase significantly with PEEP(all P＜0.01). There was nosignificant difference during the static pulmonary compliance(Cst) at different PEEPlevels (P＞0.05).Conclusion: Recruited volume increases with PEEP, and the PEEP-inducedincrease in arterial oxygenation is significantly correlated to recruited volume.