M12.3 Intravenous Delivery of Anesthetic Drugs
Traditionally, most anesthetics have been vapor-phase, such as isoflurane. In recent years there has been a move toward the intravenous (IV) delivery of drugs for anesthesia. One of the more popular IV anesthetics is propofol. For a particular population of subjects, the following kinetic values have been determined: k10 = 0.152, k12 = 0.207, k13 = 0.040, k21 = 0.092, and k31 = 0.0048, all with units of min-1. Also, assume that the volume of the blood plasma compartment is V1 = 12 liters.
What is the required steady-state propofol infusion rate to maintain a desired blood concentration of 2 mg/ml? Develop the state space model, based on Equations (M12.2) and (M12.3 or M12.4), assuming that the plasma volume is 12 liters. What are the units of the manipulated input (propofol infusion rate) and measured output (blood concentration)? Develop the process transfer function model, if the manipulated drug infusion rate has units of mg/hr, and the blood concentration has units of mg/ml. Develop a feedback-control strategy to control blood concentration by manipulating the propofol infusion rate. Make a setpoint change from 1 to 2 mg/ml. Are the closed-loop response and drug infusion rate feasible?
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