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Suppression of the human spinal H‐reflex by propofol: a quantitative analysis
Author(s) -
Baars J. H.,
Dangel C.,
Herold K. F.,
Hadzidiakos D. A.,
Rehberg B.
Publication year - 2006
Publication title -
acta anaesthesiologica scandinavica
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.738
H-Index - 107
eISSN - 1399-6576
pISSN - 0001-5172
DOI - 10.1111/j.1399-6576.2006.00923.x
Subject(s) - propofol , medicine , anesthesia , reflex , withdrawal reflex , pharmacodynamics , spinal cord , bispectral index , pharmacokinetics , pharmacology , psychiatry
Background: The spinal cord is an important site of anaesthetic action because it mediates surgical immobility. During anaesthesia with volatile anaesthetics, it has been shown that the suppression of the spinal H‐reflex correlates with surgical immobility. To evaluate whether the H‐reflex could also be a possible candidate for monitoring immobility during propofol anaesthesia, this study assessed the concentration‐dependent suppression of the H‐reflex by propofol. To discriminate different effect sites, the individual concentration response‐curves and the t 1/2ke0 of the H‐reflex have been compared with those of two EEG parameters. Methods: In 18 patients, anaesthesia was induced and maintained with propofol infused using a target‐controlled infusion pump at stepwise increasing and decreasing plasma concentrations between 0.5 and 4.5 mg/l. The H‐reflex of the soleus muscle was recorded at a frequency of 0.1 Hz. Calculated propofol concentrations and H‐reflex amplitude were analysed in terms of a pharmacokinetic‐pharmacodynamic (PKPD) model with a sigmoid concentration‐response function. Results: For slowly increasing propofol concentrations, computer fits of the PKPD model for H‐reflex suppression by propofol yielded the following median parameters: EC 50 1.1 (0.8–1.7) mg/l, slope parameter 2.4 (2.0–3.7), and a t 1/2ke0 of 6.7 (2.8–7.5, 25–75% quantiles) min. For the bispectral index, the t 1/2ke0 was 2.2 (1.8–3.1) min and for the spectral edge frequency at the 95th percentile of the power spectrum 2.8 (1.9–3.2) min. Conclusions: Propofol, unlike sevoflurane, suppresses the spinal H‐reflex at concentrations far lower than the C 50 skin incision. The differences in t 1/2ke0 ‐values indicate the presence of different effect compartments for effects on the H‐reflex and the EEG.