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 i f weight < 55 kg], and PETCO2 < 55 mm Hg [< 65 mm Hg if chronic CO2 retenti on]). Ten patients received computer-controlled (automatic) PSV and physici an-controlled (standard) PSV, in random order, during 24 h for each mode. A n estimation of occlusion pressure (P-0.1) was recorded continuously. The a verage time spent with acceptable ventilation as previously defined was 66 +/- 24% of the total ventilation time with standard PSV versus 93 +/- 8% wi th automatic PSV (p < 0.05), whereas the level of PSV was similar during th e 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 v ersus only 11 +/- 17% of the automatic PSV time (p < 0.01). Automatic PSV i ncreased the time spent within desired ventilation parameter ranges and app arently reduced periods of excessive workload.