British Journal of Anaesthesia, Vol 82, Issue 4 580-585, Copyright © 1999 by The Board of Management and Trustees of the British Journal of Anaesthesia
MCO. van den Nieuwenhuyzen, FHM. Engbers, AGL. Burm, A. A. Vletter, J. W. van Kleef and J. G. Bovill
We have examined the influence of plasma protein binding on inter-
individual and intra-individual variability in the effective postoperative
analgesic concentration (EAC) of alfentanil and on the performance of the
target-controlled infusion system used. Ten patients received standardized
anaesthesia and target-controlled alfentanil for postoperative analgesia.
Analgesia was assessed using a visual analogue scale (VAS). Plasma protein
binding of alfentanil was assessed at four different times (on arrival in
the recovery room, at 21:00 on the day of surgery and at 09:00 and 21:00 on
the first postoperative day). Bias and inaccuracy were examined on the day
of surgery and on the first postoperative day. Unbound fractions of
alfentanil varied from 5 to 15% and varied in time. In general, the unbound
fractions on the day of surgery were higher than those on the first
postoperative day. Thirty- nine percent of inter-individual variability in
the EAC of alfentanil (range 33-140 ng ml-1) at the onset of therapy could
be explained by protein binding. At the other observation times,
correlations between unbound fraction and EAC were only moderate. Bias on
the day of surgery was -19% and 12% on the first postoperative day (ns).
Inaccuracy was 23% and 18%, respectively (ns). We conclude that
inter-individual variations in plasma protein binding can explain a
significant portion of inter-individual variability in the EAC of
alfentanil in the early postoperative phase.
CLINICAL INVESTIGATIONS
Target-controlled infusion of alfentanil for postoperative analgesia: contribution of plasma protein binding to intra-patient and inter- patient variability
Department of Anaesthesiology, Leiden University Medical Centre, PO Box 9600, 2300 RC Leiden, The Netherlands
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