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.