| 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 CO(2) pressure (PET(CO(2))) within predetermined ranges defining
acceptable ventilation (i.e., 12 < RR < 28 cycles/min, VT > 300 ml [> 250 if weight < 55 kg], and
PET(CO(2)) < 55 mm Hg [< 65 mm Hg if chronic CO(2) 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 H(2)O versus 19 +/- 6 cm H(2)O). The time spent with an
estimated P(0.1) above 4 cm H(2)O 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. |