Clinical evaluation of a computer-controlled pressure support mode

We have designed a computerized system providing closed-loop control of the level of pressure support ventilation (PSV). The system sets itself at the lowest level of PSV that maintains respiratory rate (RR), tidal volume (VT), and end-tidal CO2 pressure (PETCO2) within predetermined ranges defining acceptable ventilation (i.e., 12 < RR < 28 cycles/min, VT) 300 ml [> 250 if weight < 55 kg], and PETCO2 < 55 mm Hg [< 65 mm Hg if chronic CO2 retention]). Ten patients received computer-controlled (automatic) PSV and physician-controlled (standard) PSV, in random order, during 24 h for each mode. An estimation of occlusion pressure (P-0.1) was recorded continuously. The average time spent with acceptable ventilation as previously defined was 66 +/- 24% of the total ventilation time with standard PSV versus 93 +/- 8% with automatic PSV (p < 0.05), whereas the level of PSV was similar during the two periods (17 +/- 4 cm H2O versus 19 +/- 6 cm H2O). The time spent with an estimated Po., above 4 cm H2O was 34 +/- 35% of the standard PSV time versus only 11 +/- 17% of the automatic PSV time (p < 0.01). Automatic PSV increased the time spent within desired ventilation parameter ranges and apparently reduced periods of excessive workload.