Clinical Evaluation of a Computer-controlled Pressure Support Mode

Abstract

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 (Pet CO₂ ) within predetermined ranges defining acceptable ventilation (i.e., 12 < RR < 28 cycles/min, Vt > 300 ml [ > 250 if weight < 55 kg], and Pet CO₂ < 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 P_0.1 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.