Fuzzy logic for model adaptation of a pharmacokinetic-based closed loop delivery system for pancuronium.

In this paper, we investigate the ability of fuzzy to adapt the parameters of a pharmacokinetic and pharmacodynamic model-based controller for the delivery of the muscle relaxant pancuronium. The system uses the model to control the rate of drug delivery and uses feedback from a sensor which measures muscle relaxation level to adapt the model using fuzzy logic. The control strategy administers mini-bolus doses of pancuronium and modulates the magnitude and time interval between the bolus doses to maintain a patient's muscle relaxation within an allowable range specified by the user. Before each new dose is given, the fuzzy logic adaptation scheme uses the error between the predicted patient response and the measured response to adapt the model. The system was tested using computer simulation by varying the parameters of the model by 50% from their nominal values. It was also evaluated in a clinical trial of five patients undergoing surgical procedures lasting 5 h or longer.

A comparison of dynamic and isometric force sensors for train-of-four measurement using submaximal stimulation current.

OBJECTIVE: We studied the accuracy and repeatability of train-of-four (TOF) ratio measurements made from a dynamic piezoelectric sensor that records movement of the thumb in response to ulnar nerve stimulation compared with an isometric mechanomyogram that measures force of contraction of the adductor pollicis. METHODS: The study involved 10 patients whose level of neuromuscular block was held constant with an intravenous (IV) infusion of vecuronium bromide (0.4 to 1.0 micrograms/kg/min) (Organon, West Orange, NJ). The sensors were attached to opposite arms of each patient and simultaneous measurements of TOF ratio were taken at stimulation current levels of 50, 30, and 20 mA. RESULTS: In comparison to the TOF ratio measured at the maximal stimulation current (50 mA), the TOF ratio from the piezo sensor showed a bias and standard deviation of -0.13 +/- 0.24 when the stimulation current was reduced to 30 mA. At 20 mA, the bias and standard deviation was -0.24 +/- 0.28. The TOF ratio from the mechanomyogram showed a bias and standard deviation of 0.01 +/- 0.07 at 30 mA and 0.0 +/- 0.20 at 20 mA when compared with measurements made when the stimulation current was 50 mA. CONCLUSIONS: Both sensors showed diminished repeatability in TOF measurement with decreasing stimulation current. The data indicate that neither sensor is reliable for general monitoring of neuromuscular block at submaximal current levels. However, the individual patient results showed that some patients could be monitored accurately with both sensors, even at the lowest stimulation current levels.

Impact of the initial doses of rocuronium and pancuronium on subsequent maintenance for neuromuscular block.

PURPOSE: To determine the impact of the neuromuscular blocking agent given for intubation on the duration of effect of multiple maintenance doses of pancuronium and rocuronium. METHODS: Seventy-eight subjects were randomly assigned to receive one of four dosing combinations for intubation and neuromuscular maintenance: rocuronium for intubation and maintenance, rocuronium for intubation and pancuronium for maintenance, pancuronium for intubation and rocuronium for maintenance, or pancuronium for both. Each time that the first twitch response returned to 25% of the baseline value, the duration of the dose was determined and another maintenance dose was administered. The duration of action of the maintenance doses was compared between the groups. RESULTS: Twitch suppression from the first maintenance dose was shorter for subjects who received rocuronium for both doses (Group RR) compared with that for subjects that received pancuronium (Groups PR & PP) as their intubation dose (17.6 vs 34 & 59.8 min, respectively, P < 0.05). Subjects who received rocuronium followed by pancuronium (Group RP) showed a shorter duration of twitch suppression after the first maintenance dose than the group that received pancuronium for both doses (Group PP) (21.3 vs 59.8 min, P < 0.05). By the third maintenance dose, the influence of the intubating dose on the maintenance dose duration had essentially diminished. CONCLUSIONS: For combinations of rocuronium and pancuronium, the duration of twitch suppression after a maintenance dose is only dependent on the first agent given for the first two maintenance doses administered.