The primary purpose of this study was to determine the effects of different positive end-expiratory pressure in the lung protective strategy on ventilation-perfusion distribution measured by the multiple inert gas elimination technique.
All patients were on pressure-controlled mode with the inspiratory pressure, FiO2 and PEEP adjusted to provide a tidal volume of 6-8 ml/kg, an oxygen saturation > 90% and a plateau pressure ≤ 35 cm H2O. Six levels of PEEP were studied in an incremental manner: 0 cmH2O (ZEEP), PLIP-4, -1, +2, +5, +8 cmH2O. All physiological parameters were measured at the end of each 30-min PEEP trial. If the patient showed signs of hemodynamic instability or desaturation to < 88% during trials at lower PEEP, that trial was terminated and PEEP was increased to the next higher level.
Eleven patients were ventilated with low tidal volume and PEEP from 0 to 8 cmH2O above the lower inflection point pressure. These patients had a large intrapulmonary shunt and dead space with an additional mode at the high ventilation-perfusion regions. Intrapulmonary shunt and dead space improved with increasing positive end-expiratory pressure up to 2-5 cmH2O above the lower inflection point pressure. Higher positive end-expiratory pressure increased dead space without further reduction in intrapulmonary shunt.
The dispersion of ventilation and perfusion also followed a similar trend. Other endpoints commonly used for titrating positive end-expiratory pressure, such as oxygenation, alveolar recruitment and lung compliance, all increased with increasing positive end-expiratory pressure while hemodynamic parameters were unaffected. Thus based on ventilation-perfusion matching, positive end-expiratory pressure of 2-5 cmH2O above the lower inflection point pressure appears optimalduring protective lung ventilation.
We determined PEEP effects during protective lung ventilation using ventilation-perfusion (VA/Q) distribution as an endpoint.This method of adjusting PEEP was used because it has been shown that the recruiting potential of lung tissues with PEEP varied significantly among individual ARDS patients. Our goal was to determine if there was a PEEP level that gave the most optimal VA/Q distribution.
Chin-Pyng Wu, None.