A. Carollo et al., A RULE-BASED POSTOPERATIVE PAIN CONTROLLER - SIMULATION RESULTS, International journal of bio-medical computing, 33(3-4), 1993, pp. 267-276
We describe a system for controlling postoperative pain, a phenomenon
that is difficult to treat by conventional control methods due to inte
rpatient variability, interferences, non-linearity and the lack of a p
lausible, well-defined mathematical model. The system consists of two
phases. In Phase 1 a closed-loop fuzzy controller implementing a suita
ble control strategy brings the patient to a zero-pain state. In Phase
2, an open-loop computer-assisted continuous infusion controller main
tains a constant concentration of the analgesic (alfentanil) in plasma
, subject to an upper safety limit on infusion rate; the setpoint of t
his controller is periodically revised (either maintained or reduced)
on the basis of feedback on the duration of zero pain (setpoint reduct
ion is necessary because the open-loop system has no means of knowing
whether analgesic is accumulating in the patient). Pain is quantified
by the patient on a numerical scale of 1 to 10 at 1.5-min intervals du
ring Phase 1 and 9-min intervals during Phase 2. In simulation trials
in which a fixed approximate model was used for the effect of sedation
on pain while the pharmacokinetics of alfentanil were varied from one
simulated patient to another, zero pain was achieved in under 15 min
with minimal overshoot in plasma drug concentration and was maintained
, with only minor deviation, by means of low drug concentrations.