Pressure controlled inverse ratio ventilation is a recently described-2 ventilatory modality, in which the conventional inspiratory to expiratory (I:E) ratio is reversed, with the inspiratory phase becoming two to four times as long as the expiratory period. The PC-IRV has been reported to achieve improved oxygenation at lower peak airway pressures. Other advantages include lower minute volume and decreased levels of positive end expiratory pressure. In PC-IRY pressure control is used to change the inspiratory flow pattern so that each breath is initiated before expiratory flow from the previous breath reaches zero. A physiologic result of this ventilatory pattern is maintenance of end-expiratory pressures. The prolonged inspiratory phase, coupled with positive end-expiratory pressure, usually results in decreased peak inspiratory and increased mean airway pressures in patients receiving PC-IRV.
Respiratory modalities, such as PEEP, which result in increased peak and mean airway pressures have significant effects on hemodynamic and tissue oxygen metabolism parameters. With high levels of PEEP, although Pa02 is improved, cardiac output may be severely compromised, resulting in marked decreases in tissue Do2, deleteriously affecting tissue oxygen metabolism. Although PC-IRV is associated with auto-PEEP and increased mean airway pressures, its effects on hemodynamic variables have been studied in only a limited fashion. No changes were found in mean arterial pressure, mean pulmonary artery pressure, or pulmonary capillary wedge pressure before and after institution of PC-IRY The interaction between PC-IRV and cardiac output or parameters of tissue oxygen metabolism has not been reported. We initiated the present prospective study to better define the physiologic effects of PC-IRV on hemodynamic and cardiorespiratory variables.
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