ALI/ARDS: controlled mechanical ventilation + PEEP versus pressure controlled inverse ratio ventilation

ABSTRACT

In this prospective randomized clinical trial study, 40 patients requiring mechanical ventilation for ALI ARDS were divided into 2 groups [n=20 each]. Group I patients underwent mechanical ventilation with CMV+ PEEP and those in group 2 were ventilated with PC-IRV technique. The initial mode of ventilation for all patients was the conventional control mechanical ventilation [CMV+ PEEP] which was applied for 1 hour after which the mode of ventilation was changed over to PC-IRV in group 2 while the same mode of ventilation [CMV + PEEP] was continued in group 1. The ventilator parameters [tidal volume [VT]], respiratory rate [RR] minute ventilation [VE], fraction of inspired oxygen [FIO[2]], [PEEP] and inspiratory flow wave form were selected and adjusted according to patients needs in the one hour before start of the study protocol. Once the chosen ventilator mode was started the ventilalatory parameters were studied for 24 hours without interruption. The mean blood pressure [MAP], HR, CVP, Spo[2], mean airway pressure [Pmean], plateau pressure [Pplat], peak inspiratory pressure [PIP], ABG, and PaO[2]/FIO[2] were measured before start of the chosen ventilator mode [zero hour], 1 hour, 6 hour, 12 hours and 24 hours after initiation of ventilator mode and the results were compared to those obtained at zero hour and between groups. Despite a general trend toward a drop in MAP in group 1 [CMV + PEEP], the difference between groups was statistically insignificant regarding hemodynamic parameters. PaO[2] and SpO[2] were both increased at 1 and 6 hours of ventilatory support in both groups, and the PaO[2] results obtained at 6, 12 and 24 hours were significantly higher in patients in group 2 [PC-IRV] compared to patients on CMV + PEEP. The PIP and Pplat were lower through out the study period in PC -IRV group compared to CMV + PEEP group. The PaO[2]/ FIO[2] ratio was significantly higher at 12 and 24 hours in PC- IRV group compared to CMV + PEEP group. These data shows that PC-IRV improves oxygenation and allows the generation of a lower PIP and Pplat in patients with ALI/ARDS compared to CMV + PEEP