Abstract
Pressure support ventilation (PSV) is a mode of partial ventilatory support in which the breathing pattern can be easily affected by breath-by-breath interaction between the patient and a ventilator. Although propofol is advocated for sedation in the ICU, its effect on the breathing pattern during PSV is not well understood.
We studied seven postoperative patients on PSV during propofol sedation (Ramsay score: levels 4-5). Their breathing patterns were analyzed by a desktop computer equipped with a 16-bit AD board to process the flow and pressure signals of the ventilator (Bennet 7200) during and after propofol sedation for more than 30min.
After the termination of propofol sedation, the expiratory time decreased without any changes in the inspiratory time and mean inspiratory flow. This led to increases in respiratory frequency, duty cycle and minute ventilation. Respiratory cycles with a tidal volume of less than 50ml and with twice the mean tidal volume, respectively, appeared at 0% and 0.3% of all respiratory cycles. We concluded that propofol sedation at levels of 4-5 of Ramsay's score is associated with a decrease in minute ventilation due to prolongation of the expiratory time, without apparent changes in inspiratory drive in postoperative patients during PSV, and that it is effective for maintaining patients' adaptation to ventilators under PSV.
