Haemodynamic effects of effect site targeted propofol TCI. comparison to Diprifusor^®

L. Hollos, N. Moony. Dept. of Anaesthetics, Kettering General Hospital, Kettering, NN16 8UZ, UK

Background and goal of study

Commercially available computerized target-controlled infusions of propofol control the blood concentration of the drug but targeting the effect site may give better control of anaesthesia. It is not known whether targeting the effect site is associated with higher cardiovascular instability (1) and therefore we designed this study to investigate the cardiovascular parameters during effect site targeted propofol anaesthesia.

Materials and Methods

Following Ethics Committee approval, 20 ASA grade I or II patients scheduled for total knee replacement under subarachnoid block were randomly ascribed to two groups. General anaesthesia was induced in both groups with propofol infusion. (Group B - Diprifusor®) used to target the blood levels of propofol and Group E – STELPUMP computer programme connected to a syringe driver used to target the effect site). Initial concentration of 5 ug/ml was decreased to 4 ug/ml by 0.25 ug/ml in a stepped fashion. Heart rate, systolic, diastolic and mean blood pressure was recorded before commencement of propofol infusion and when target concentrations were reached. Time of loosing verbal command was also recorded. The results were analysed statistically using ANOVA and regression analysis.

Results

Time of loosing verbal command was significantly reduced in Group E when compared to Group B, 58.0 ±5.96 sec. to 80.0 ±10.67 sec. (p<0.05), respectively. We found no significant difference in heart rate when compared to baseline values in both groups. The systolic blood pressure decreased significantly in both groups when compared to baseline values. Comparing the diastolic and mean blood pressure we found a significant difference in Group B, but no difference in Group E. There was also no significant difference between the groups (table).

		Target propofol concentration (ug/ml)
	Baseline	5.0	4.75	4.5	4.25	4.0
HR gr. B	77.0 ± 13.8	80.5 ± 10.7	78 ± 8.2	75.5 ± 8.1	72.5 ± 8.1	72.5 ± 8.6
gr. E	75 ± 11.35	72.5 ± 18.45	69 ± 15.6	68.5 ± 16.34	67 ± 17.26	65 ± 18.07
SBP gr. B	158 ± 12.33	108 ± 21.33*	109.5 ± 15.04*	113 ± 15.46*	119 ± 13.49*	134 ± 19.56*
gr. E	153.5 ± 20.29	116 ± 17.38*	117.5 ± 24.21*	120 ± 25.43*	113 ± 31.16*	118 ± 29.93
DBP gr. B	83 ± 9.62	72 ± 11.79*	70.5 ± 10.66*	68.5 ± 13.48*	66 ± 8.76*	73 ± 11.41
gr. E	75.5 ± 13.34	69.5 ± 8.08	68 ± 11.78	71 ± 13.91	67 ± 12.14	66.5 ± 10.5
MBP gr. B	104 ± 10.65	88 ± 15.69*	88 ± 12.15*	82 ± 14.22*	83.5 ± 9.43*	91 ± 15.5
gr. E	97.6 ± 15.8	85.5 ± 11.4	84.5 ± 17.53	90.5 ± 17.54	83.5 ± 17.29	80.5 ± 13.96

p<0.05 vs. baseline, HR: heart rate (1/min.), SBP: systolic, DBP: diastolic,

MBP: mean BP (mmHg)

Conclusion

When the effect site is targeted there is a more rapid onset of anaesthesia than in the blood targeting group, this is to be expected because of the higher bolus dose delivered at the start of infusion. However, this group of patients seems also to have more cardiovascular stability than the blood-targeted group. This could be explained by the fact that when the effect site is targeted there is a pause between the large bolus dose and the commencement of the background infusion. (There is no similar pause of the infusion in the blood-targeted pump.) This pause in the infusion may explain the greater cardiovascular stability even though the patients lose conscious more rapidly.

It is concluded that effect site-targeting results in more rapid onset of anaesthesia and cardiovascular stability than blood-targeted infusions.

References

1. White PF: Intravenous anaesthesia and analgesia: What is the role of target-controlled infusion? J. Clin. Anaesthesia 8:26S-28S, 1996