ACCURACY OF THE “PAEDIFUSOR” - A NEW PROPOFOL TCI SYSTEM FOR CHILDREN

 

D Amutike*, A Lal*, A Absalom, GNC Kenny

University Dept of Anaesthesia, Glasgow Royal Infirmary & HCI Hospital

 

Introduction: Target Controlled Infusion (TCI) systems are commonly used in adults but seldom in children. A prototype paediatric TCI system, the “Paedifusor” has been developed. This system is similar to the commercially available adult system (“Diprifusor”), but uses a set of pharmacokinetic parameters and algorithms specific for children. The aim of our study was to assess the predictive performance of the “Paedifusor”.

 

Method: Following approval by the hospital ethics committee, 29 children undergoing either cardiac catheterisation or cardiac surgery were recruited into the study after informed and written consent was obtained from the parents or guardian. Induction and maintenance of anaesthesia was performed using the system. Arterial blood samples (0.5 ml) were obtained at the following times: 3 and 8 minutes after induction, 60 – 90 seconds after a decrease of the propofol target, during stable anaesthesia, during cardiopulmonary bypass, on stopping the TCI pump, 3 and 8 minutes after stopping the TCI pump and on eye opening. Samples were stored and assays for whole blood propofol concentration (C_m) were performed at a later date. The predicted propofol concentration (C_pred) was recorded every time a blood sample was collected. For each sampling point, prediction error (PE) has been calculated, as follows:

 

PE (%) = C_m – C_pred   X 100

                     C_pred

The PE was then used to calculate the median prediction error (MDPE), median absolute prediction error (MDAPE) and wobble. MDPE and MDAPE are measures of bias and precision respectively.

 

Results: The mean age and weight of the patients were 6.85 years and 21.18 kg respectively. MDPE, MDAPE and wobble for the Paedifusor are shown in the Table 1.

 

Table 1: performance of “Paedifusor”

 

		MDPE (%)	MDAPE (%)	Wobble (%)
Non-bypass (N=8)		5.5	12.6	9.1
	Before	3.1	7.9	6.9
Bypass (N=21)	During	-5.5	7.6	5.2
	After	7.9	17.5	14.1
All patients		4.1	9.7	8.3

 

The values for bias and precision of the Paedifusor compare very favourably with the results obtained in the study using the modified paediatric microconstants which showed bias 2.8% and precision of 16.2%[1]. The Paedifusor performance indices, MDPE and MDAPE are much better than those found in adult patients using the Diprifusor (MDPE of 16% and MDAPE 24%)[2] 

 

References

1.     Marsh B et al. Br J Anaesth 1991;67:41 - 48

2.     Swinhoe, C.F et al. Anaesthesia 1998; 53(Suppl. 1): 61-67