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Open Access Open Badges Research article

Residual sleepiness after N2O sedation: a randomized control trial [ISRCTN88442975]

J Lance Lichtor1*, Bradford S Lane2 and M Bridget Zimmerman3

Author Affiliations

1 University of Iowa, Department of Anesthesia, 200 Hawkins Drive, 6 JCP, Iowa City, IA 52242-1079

2 University of Chicago, Department of Anesthesia and Critical Care, 5841 S. Maryland Ave, Chicago, IL 60637

3 University of Iowa, Department of Biostatistics, 200 Hawkins Drive, C22-E GH, Iowa City, IA 52242

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BMC Anesthesiology 2004, 4:5  doi:10.1186/1471-2253-4-5

Published: 12 May 2004



Nitrous oxide (N2O) provides sedation for procedures that result in constant low-intensity pain. How long do individuals remain sleepy after receiving N2O? We hypothesized that drug effects would be apparent for an hour or more.


This was a randomized, double blind controlled study. On three separate occasions, volunteers (N = 12) received 100% oxygen or 20% or 40% N2O for 30 min. Dependent measures included the multiple sleep latency test (MSLT), a Drug Effects/Liking questionnaire, visual analogue scales, and five psychomotor tests. Repeated measures analysis of variance was performed with drug and time as factors.


During inhalation, drug effects were apparent based on the questionnaire, visual analogue scales, and psychomotor tests. Three hours after inhaling 100% oxygen or 20% N2O, subjects were sleepier than if they breathed 40% N2O. No other drug effects were apparent 1 hour after inhalation ceased. Patients did not demonstrate increased sleepiness after N2O inhalation.


We found no evidence for increased sleepiness greater than 1 hour after N2O inhalation. Our study suggests that long-term effects of N2O are not significant.