Stimulus C50P CV (%) C50R CV (%) α CV (%) γ CV (%)
Probability of unconsciousness or sedation [12] (no response to OAA/S < 2) 2.16 19 19.0 9 2.13 16 7.94 33
Probability of adequate surgical analgesia [12] (no response to tracheal intubation, laryngoscopy) 5.63 22 19.0 9 2.13 16 7.94 33
Probability of adequate post-operative analgesia [9,10] (no response to pressure algometry) 4.16 - 8.84 - 8.2 - 8.34 -
Probability of intolerable ventilatory depression[11] (respiratory rate <= 4 breaths/minute) 7.0 26 4.1 24 3.0 38 3.2 25
C50P and C50R are effect site concentrations to produce a 50% probability of effect for propofol and remifentanil respectively. Alpha is the synergistic value for characterizing the interaction between remifentanil and propofol. Gamma is the slope of the response surface characterizing the dynamic range. CV indicates the coefficient of variation. OAA/S < 2 is the observers assessment of alertness score when a patient will respond to shaking and shouting, indicative of a patient’s responsiveness. Pressure algometry is defined as 50 PSI of tibial pressure, CV for pressure algometry was not available. They were assumed to be similar to the CV for tracheal intubation.
Table 2: Pharmacodynamic interaction model parameters for propofol and remifentanil with estimates of parameter variability for selected drug effects