Compliance versus dead space for optimum positive end expiratory pressure determination in acute respiratory distress syndrome

Objective:

To Compare compliance versus dead space (Vd) targeted positive end-expiratory pressure (PEEP) as regard its effect on lung mechanics and oxygenation.

Materials and Methods:

This study was carried out on 30 adult acute respiratory distress syndrome patients. The ventilator was initially set on volume controlled with tidal volume (Vt) 7 mL/kg predicted body weight (PBW), inspiratory plateau pressure (Ppl) <30 cm H₂ O. If the Ppl was >30 cm H₂ O with a TV of 6 mL/kg PBW, a step-wise Vt reduction of 1 mL/kg PBW to as low as 4 mL/kg/PBW was allowed. Respiratory rate adjusted to maintain pH 7.30-7.45. FiO₂ start at 100%. Best PEEP determined at 2 points, one by titrating PEEP until reaching the highest static compliance (Cst) (PEEP Cst) and the other one is at the lowest Vd/Vt (PEEP Vd/Vt). The following data measured before and 30 min after setting PEEP Cst and PEEP Vd/Vt. Cst, PaCO₂ - PetCO₂, Vd/Vt, PaO₂ /FiO₂, Ppl, heart rate, mean arterial pressure and oxygen saturation.

Results:

optimum PEEP determined by Vd/Vt was significantly (P < 0.05) lower than the optimum PEEP determined by Cst. Best PEEP Vd/Vt showed a significant decrease (P < 0.05) in Cst, PaCO₂ - PetCO₂, Vd/Vt and Ppl in comparison with best PEEP Cst. The PaO₂ /FiO₂ showed a significant increase (P < 0.05) with best PEEP Vd/Vt in comparison with best PEEP Cst.

Conclusion:

Vd guided PEEP improved compliance and oxygenation with less Ppl. Hence, its use as a guide for best PEEP determination may be useful.