Delivery performance of commercial TCI devices with Diprifusor module

S Schraag, J Flaschar, M Georgieff. Department of Anaesthesiology, University of Ulm, D-89070 Ulm, Germany

Introduction

Target controlled infusion (TCI) has become increasingly important in clinical anaesthetic routine. Currently there are three TCI syringe pumps commercially available and licensed which can be used with propofol pre-filled syringes (PFS), which are the ALARIS IVAC TIVA-TCI, the GRASEBY 3500 and the FRESENIUS VIAL MASTER TCI. All pumps incorporate the Diprifusor® pharmacokinetic module . Based on a previous study on prototype systems [1] we investigated the precision and accuracy of commercial pumps in comparison with the calculated values from the kinetic model [2].

Methods

We used a high precision scale (Sartorius MC 210C with windshield, range 210g ± 20µg ) and placed the pump on the same level as the scale, inserted a PFS (Diprivan® 1%-PFS, Zeneca) and connected a flexible tube (length 150cm) to the PFS. On the scale side we connected an i.v. cannula (diameter 1,2mm, length 45mm) to the flexible tube. The i.v. cannula passed perpendicularly through a little hole in the upper windshield of the scale and was inserted in a Propofol semi-filled vial on the scale. This vial had to be nearly closed to avoid inaccurate measuring in case of evaporation. We choose 6 clinically relevant target concentrations (1, 1,5, 2, 3, 5 and 8 µg/ml) and infusion was repeated 5 times for a 10 minutes interval with constant target. The amount of propofol delivered was obtained by weighing. We determined the calculated performance error of the model (cpe) and the predicted performance error of the pump (ppe).

Results

Data are presented as mean performance error (MPE) with 95% confidence interval (CI).

	Graseby CI		Alaris CI		FRES. VIAL	CI
Target	MPE	±95%	MPE	±95%	MPE	±95%
1,0 µg/ml	1,18	±1,40	4,15	±3,65	-0,48	±1,39
1,5 µg/ml	0,23	±1,25	2,01	±1,49	-0,51	±0,90
2,0 µg/ml	-0,45	±2,21	4,22	±1,37	-0,59	±0,65
3,0 µg/ml	0,83	±3,11	3,73	±1,06	-0,08	±0,60
5,0 µg/ml	-0,58	±0,56	-0,93	±0,31	-1,17	±0,07
8,0 µg/ml	-1,71	±0,21	-2,03	±0,19	-2,07	±0,38

All pumps worked well and precise during the measurements in a MPE bandwidth from –2% to +4,5% with a 95% confidence interval less than 4,5%.

Discussion and conclusion

The physical delivery performance is most precise and accurate with the FRESENIUS VIAL pump with little under-dosing. The ALARIS pump shows the highest variability and the GRASEBY has a trend in little over-dosing. However, all pumps seem to be accurate enough for practical use and the in between differences appear to have little clinical relevance.

References

1. Schraag S, Mohl, U Georgieff M, Proceedings of 24^th Central European Congress of Anaesthesiology, Vienna, Monduzzi Ed., p 339-342 1995.

2. Marsh B et al., Br J Anaest 1991; 67 : 41.