Nitrous oxide can enhance the hypnotic effect, but not the suppression of spinal motor neuron excitability by propofol in humans.
OBJECTIVE
We investigated whether nitrous oxide can enhance the suppressive effect of propofol on spinal motor neuron excitability in humans.


METHODS
Sixteen adult patients were prospectively randomly assigned to be given either propofol alone (group P; n = 8) or a supplement of 66% nitrous oxide with propofol (group PN; n = 8) for intraoperative sedation. Propofol was administered by a target-controlled infusion system to maintain sequentially increasing plasma propofol concentrations (Cpt) of 0.5, 0.8, 1.0, 1.3, 1.5 and 1.8 microg x ml(-1) in all patients. Assessment of the patient's level of sedation in both groups was performed with the Wilson Sedation Scale (WSS). F-wave analysis on the left abductor pollicis brevis muscle was carried out for the assessment of spinal motor neuron excitability at each plasma propofol concentration.


RESULTS
Significant differences in the WSS scores between group P and group PN were observed at 0.8, 1.0, 1.3, and 1.5 microg x ml(-1) of Cpt (group P < group PN; P < 0.01). Cpt greater than 1.0 microg x ml(-1) significantly reduced F-wave persistence in a concentration-dependent manner, and the ICpt 50 and ICpt 95 values for plasma propofol concentration (plasma propofol concentrations that produced 50% and 95% inhibition of the baseline, respectively) were 1.05 and 1.95 microg x ml(-1) in group P, and 1.07 and 2.14 microg x ml(-1) in group PN, respectively.


CONCLUSIONS
These results suggest that nitrous oxide can enhance the hypnotic effect, but not the suppression of spinal motoneuron excitability by propofol in humans at clinical levels of Cpt.
Kakinohana
Manabu
M
Division of Anesthesia, Okinawa Prefectural Miyako Hospital, Okinawa, Japan.
Miyata
Yuji
Y
Tomiyama
Hiroshi
H
Sugahara
Kazuhiro
K
D000328:Adult; D000704:Analysis of Variance; D018685:Anesthetics, Inhalation / Q000494:pharmacology*; D018686:Anesthetics, Intravenous / Q000097:blood / Q000494:pharmacology*; D016292:Procedural Sedation / Q000379:methods; D004357:Drug Synergism; D004558:Electric Stimulation / Q000379:methods; D004594:Electrophysiology / Q000379:methods; D005260:Female; D006801:Humans; D006991:Hypnosis, Anesthetic / Q000379:methods*; D008297:Male; D008875:Middle Aged; D009046:Motor Neurons / Q000187:drug effects*; D009609:Nitrous Oxide / Q000494:pharmacology*; D015742:Propofol / Q000097:blood / Q000494:pharmacology*; D011446:Prospective Studies; D013116:Spinal Cord / Q000187:drug effects*
D018685:Anesthetics, Inhalation; D018686:Anesthetics, Intravenous; D009609:Nitrous Oxide; D015742:Propofol