Effects of sevoflurane and propofol on the nociceptive withdrawal reflex and on the H reflex.
BACKGROUND
The predominant target of anesthetics to suppress movement responses to noxious stimuli is located in the spinal cord. Although volatile anesthetics appear to produce immobility by actions on the ventral rather than the dorsal horn, the site of action of propofol remains unclear.


METHODS
In a crossover design, the authors compared in 13 volunteers the effects of sevoflurane and propofol on the amplitudes of the H reflex, which is mediated exclusively in the ventral horn and a withdrawal reflex (RIII Reflex), which integrates dorsal and ventral horn function. The concentrations were adjusted according to a Dixon up-and-down approach, depending on movement responses to tetanic stimulation.


RESULTS
Sevoflurane and propofol concentrations ranged from 1.2 to 1.6 Vol% and 3 to 6 mg/l, respectively. Sevoflurane reduced the H reflex amplitude significantly to 66 +/- 17% (mean +/- SD) of its control values. Propofol did not significantly reduce the H reflex. The reductions under the two drugs differed significantly. The RIII reflex amplitude was significantly reduced to 19 +/- 10% and 27 +/- 12% (mean +/- SD) of the control values by sevoflurane and propofol, respectively. The reductions did not differ between the drugs.


CONCLUSIONS
Probably because of the polysynaptic relay, the attenuation of the withdrawal reflex exceeds the attenuation of the H reflex. Sevoflurane produces a larger inhibitory effect on the H reflex than propofol, which confirms that the ventral horn is a more important target for volatile anesthetics, whereas effects of propofol on this site of action are rather limited. Our findings indirectly suggest for propofol a relatively stronger effect within the dorsal horn.
Baars
Jan H
JH
Department of Anesthesiology, Charité, Universitätsmedizin Berlin, Germany. jan.baars@charite.de
Mager
René
R
Dankert
Katharina
K
Hackbarth
Mark
M
von Dincklage
Falk
F
Rehberg
Benno
B
D000328:Adult; D018592:Cross-Over Studies; D004359:Drug Therapy, Combination; D006181:H-Reflex / Q000187:drug effects* / Q000502:physiology; D006801:Humans; D008297:Male; D008738:Methyl Ethers / Q000008:administration & dosage*; D010147:Pain Measurement / Q000187:drug effects* / Q000379:methods; D015742:Propofol / Q000008:administration & dosage*; D012018:Reflex / Q000187:drug effects / Q000502:physiology; D000077149:Sevoflurane; D055815:Young Adult
D008738:Methyl Ethers; D000077149:Sevoflurane; D015742:Propofol