Importance of model fitting when a non-commercial TCI system was used: taking Kataria’s parameter as an example

Abstract

To the Editor: When using a non-commercial target-controlled infusion (TCI) system, it is important to confirm that the patient matches the population in the study on which the pharmacokinetic parameters were determined. The anesthesiologist who operates the system is responsible for the proper functioning of that system, and we should not expect a fail-safe system such as that provided by a commercial TCI pump with a built-in Diprifusor (AstraZeneca, London, UK). In this letter, we wish to alert the readers of the Journal of Anesthesia to the importance of this point, using Kataria’s parameter as an example [1]. We were planning anesthetic management using propofol TCI for a 2-year and 11-month-old boy (weight 11 kg, height 85 cm) because his father was suspected to have had malignant hyperthermia. TCI using a syringe pump (Graseby 3500; Graseby Medical Ltd, Watford, Herts, UK) operated by STANPUMP software (available at http://opentci.org/doku.php; accessed 1 Mar 2010) with Kataria’s parameter can be easily used because the parameter is preinstalled in the free software, in contrast to the necessity of a special device [2] or new programming for ‘‘Paedfusor’’ [3] or other parameters. The day before the surgery we performed a test run to determine whether the TCI system would work properly because two physical characteristics of the patient did not match those of the population on which the previous study had been based, although the values were near the lowest values. We were able to input the physical characteristics without any rejection; however, when it was assumed that administration of propofol would start at the concentration of 5 lg/mL, the simulation showed an abnormal infusion rate and concentration of propofol, and the syringe pump started operating at a very high speed. The infusion rate after the initial dose was 776 lg/kg/min; it increased quickly, exceeding the initial dose 180 s after the initial administration, reached 15,000 lg/kg/min by 190 s after starting administration, and then remained constant. The predicted concentration of propofol reached 5 lg/mL 10 s after starting administration and remained constant until 190 s but started decreasing 200 s after starting administration, eventually falling below zero, and kept decreasing (Fig. 1). The reason for this phenomenon is that the rapid peripheral volume (V2) was calculated as a minus quantity (-0.72). V2 was calculated by the following equation [1]: