Upper Deflection Point Versus Lower Inflection Point on Pressure-Volume (P-V) Loop for Determination of Optimum Positive End Expiratory Pressure (PEEP) by Pressure-Volume (P-V) Loop in Acute Respiratory Distress Syndrome (ARDS) Patients: A Prospective Cohort Cross-Over Study

Abstract
Background: Lung-protective ventilation has the best outcome in ARDS. Therefore, low tidal volume (6ml/kg of predicted body weight), limitation of plateau pressure (less than 30cmH2O), and optimal PEEP are the key components of the lung protective ventilation. Pressure-Volume (P/V) loop is an important method to set PEEP, while the Lower Inflection Point (LIP) of the inflation limb is traditionally where PEEP is set; evidences suggest that the LIP does not correlate with the pressure at which recruited alveoli will begin to close. Setting PEEP slightly above the deflection point rather than the LIP may be more accurate in determining the optimum PEEP.
Aim: The aim is to compare two methods of optimum PEEP determination using Upper Deflection Point (UDP) versus Lower Inflection Point (LIP) on P-V loop in patients with ARDS, as regard lung mechanics, oxygenation and hemodynamics.
Patients and Methods: This study was carried out on 30 mechanically ventilated patients within 24 hours of fulfilling Berlin criteria for ARDS. All patients were ventilated with Low Tidal Volume Ventilation (LTVV). Pressure-Volume (P/V) loop was constructed using the quasistatic method with inspiratory flow rate of 3L/min and frequency 5 b/min. After (LIP) and (UDP) were determined on the (P/V) loop, the following parameters were measured before and 30 minutes after setting the optimum PEEP guided by (LIP) and (UDP): Peak airway pressure, mean airway pressure, plateau pressure, PaO2/FIO2 ratio, static compliance, Heart Rate (HR) and Mean Arterial Pressure (MAP).
Results: PEEP adjusted according to UDP showed signif-icant increase in static compliance and PaO2/FIO2 ratio and significant decrease in peak airway pressure, plateau pressure and mean airway pressure values in comparison with PEEP adjusted according to LIP.
Conclusions: PEEP adjusted according to UDP results in better oxygenation, lung mechanics and hemodynamic stability. So, it is recommended to adjust PEEP according to UDP.