Experimental Study Of Recruitment Maneuver In The Management Of Acute Respiratory Distress Syndrome

Part 1: The effect of various methods of lung recruitment maneuvers on hemodynamics and lung status of canines ARDS modelObjective: To investigate the effect of recruitment maneuver with sustained inflation (SI) and Pressure-controlled ventilation (PCV) on oleic acid induced canine ARDS model.Methods: Measurements were made in 12 healthy male outbreed dogs. They were equally randomized to SI group and PCV group. Each dog was anesthetized with pentobarbital given intravenously (30 mg/kg), orally intubated with an endotracheal tube, and mechanically ventilated with Servo-i Ventilator ( basic setting: volume control ventilation, initial rate 30 min^-1 and tidal volume 8 ml/kg, I: E=1: 2, inspiratory pause time 10%, PEEP 6 cm H₂O, FiO₂ 100%). A pulmonary artery catheter was inserted through the external jugular vein, and PiCCO hot dilated catheter was inserted via femoral cut-down and connected to the PiCCO monitor. After stabilized for 30 minutes, 0.1-0.15 ml/kg oleic acid was intravenously injected to induce ARDS. In SI group, the ventilator setting was changed to CPAP, 40cm H₂O for 40 seconds. In PCV group, the ventilator setting was changed to PCV, pressure above PEEP: 14 cm H₂O, I: E=1:1, PEEP 26 cm H₂O for 120 seconds. After the RM was finished, the ventilator was changed back to basic setting,PEEP began from 24 cm H₂O (T24) and decreased by 2 cm H₂O each 10 minutes. After reaching 6 cm H2O (T6) for 10 minutes, the PEEP was adjusted to 0 cm H2O immediately. The parameters of hemodynamics and mechanics of lung were recorded, and arterial blood was drawn for blood gas analysis. Cold saline was injected to measure EVLW, ITBV and GEDV before RM (Tb) and 100 minutes after RM (T6). After the experiments were finished, the pathologic changes in the lung were evaluated at sacrifice.Results: After the lung recruitment, both groups have dramatically increased oxygenation and thereis no difference between two groups. During RM, SI group cardiac index (CI) and mean arterial pressure (MAP) were statistically significant lower than PCV group (P<0.05). After the lung injury, the EVLW dramatically increased and there was no significant difference before or after RM, or between SI group and PCV group. Conclusions:1, SI and PCV both could increase the oxygenation in the oleic acid induced canine ARDS model. 2, When conducting lung recruitment, comparing to SI, PCV results in more stable hemodynamics.3, There was no effect for recruitment maneuvers on EVLW.Part2: Use of dynamic compliance for optimal PEEP titration after recruitment maneuver in canines ARDS modelObjective: To tested whether the continuous monitoring of dynamic compliance could become a useful bedside tool for detecting the beginning of collapse of a fully recruited lung. Methods: Measurements were made in 6 healthy male outbreed dogs in accordance with part 1.The animals were randomized to undergoing recruitment maneuver with SI (n=4) or PCV (n=2). The PEEP titration was from 24 cm H2O (T24) and decreased by 2 cm H2O every 10 minutes in accordance with part 1. During each stage, Ppeak, Cdyn and EIP were continually measured by Servo-i monitor, and the variation trends were calculated (Open Lung Tool software). Arterial blood was drawn for blood gas analysis. The time that lung collapse begin was defined as >10% decrease of oxygenation index.Results: In all the 6 dogs, when PEEP= 16 cm H2O, the oxygenation index decreased for more than 10%. Simultaneously, the lung compliance reached its peak value. This suggests that PEEP at this moment indicates the beginning of lung collapse. Therefore, the optimal PEEP should be 2 cm H2O, which is 18 cm H2O.Conclusions: During the titration of PEEP after lung recruitment, the beginning of lung collapse could be inferred from the dynamic compliance, therefore the optimal PEEP could also be determined.