Influence of Intravenous Fentanyl Dose and Target Control (TCI) Infusion Protocols on Spontaneous Ventilation

Authors: S. Yamamoto, M.D.; M. Sakaguchi, M.D.; H. Yamaguchi, M.D.

Affiliation: Department of Anesthesia, Iwaki Kyoritsu General Hospital, Iwaki, Fukushima, 973-8555, Japan

Introduction: Fentanyl has small KeO and needs bolus injection to reach target concentration quickly. (1) However, fentanyl, 25-50 ug, bolus injection may induce respiratory depression and needs patients to be ventilated using positive pressure. TCI may be useful to give patients fentanyl with maintaining spontaneous ventilation (SV). We compared the effect of fentanyl on SV between effect site target control group (E-group) and blood concentration target control group (B-group).

Methods: After approval of the study protocol by the local ethical committee and obtained informed consent from each patient, 17 ASA I or II patient undergoing leg surgery were randomly assigned to one of the two groups; E-group (n=9), and B-group (n=8). Lumbar epidural anesthesia was given to minimize the alteration in ventilatory condition induced by pain. General anesthesia was induced using propofol, 2 mg/kg i.v., and laryngeal mask airway was placed. Anesthesia was maintained using O2 3L/min, N2O 3 L/min and 1 % sevoflurane under SV over 30 min. Then fentanyl was administered by TCI protocols, and the target concentration was started at 0.8-1.2ng/ml, and increased by 0.2 ng/ml stepwise every 20 min until respiratory rate (RR) < 10/min in both groups. RR, tidal volume, end-tidal CO2, predicted fentanyl effect site concentration, predicted fentanyl blood concentration were recorded every 5 min. Statistical analysis was done using ANOVA repeated measurement with significance level of p<0.05.

Results: RR decrement related to the increment of effect site fentanyl concentration, p<0.05. The mean target concentration of effect site was 1.47±0.20 ng/ml (E-group), and 1.2±0.6 ng/ml (B-group) at RR < 10/min. None of patients needs ventilatory assist during the study.

Conclusion: Degree of RR depression correlated with fentanyl's effect site concentration, but not with its blood concentration, especially during early phase of the study period. After the effect site concentration equilibrated with the blood concentration, either TCI protocol was not significant.

Reference: 1. Anesthesiology 74:53-63,1991