title: The effect of nitrous oxide on the measurement of single-breath transfer factor.
abstract: One hour after a bone marrow biopsy and inhalation of Entonox gas (50% nitrous oxide (N2O) and 50% oxygen), a patient had a markedly reduced transfer factor of the lung for carbon monoxide (TL,CO). Three hours after Entonox, the patient had a normal TL,CO. Since carbon monoxide (CO) and N2O have similar spectral wavelengths, it was proposed that residual N2O in the lungs was interfering with the infra-red analysers used to detect CO concentrations. Experiments were performed to verify the "interference" effect and its duration. Five healthy volunteers performed serial triplicate TL,CO measurements over 3 h on two randomized days (Control vs N2O). The first triplicate TL,CO on each day served as a baseline measurement. Following the baseline measurement on the N2O day, each subject inhaled Entonox for 10 min. To serve as a control for the infrared effect, the identical protocol was repeated using a gas chromatography method for TL,CO determination. The infra-red method showed a marked reduction (> 50%) in TL,CO 30 min after N2O inhalation. This reduction did not return to baseline levels for at least 2 h. In comparison, the gas chromatography method showed no significant reduction in TL,CO. In a group of healthy nonsmoking subjects, N2O markedly affected the measurement of the transfer factor of the lungs for carbon monoxide using infra-red analysers. The time course over which the measurement was reduced was at least 2 h for a 10 min inhalation period. The effect was entirely due to a measurement error associated with infra-red technology.
authors.affiliation: Dept of Respiratory Medicine, Royal North Shore Hospital, St Leonards, NSW, Australia.
authors.forename: C L
authors.initials: CL
authors.lastname: Phillips
authors.forename: R
authors.initials: R
authors.lastname: Simmul
authors.forename: A I
authors.initials: AI
authors.lastname: Smith
authors.forename: N
authors.initials: N
authors.lastname: Berend
mesh_terms: D000328:Adult; D019162:Anesthetics, Combined / Q000097:blood / Q000378:metabolism / Q000494:pharmacology*; D018685:Anesthetics, Inhalation / Q000097:blood / Q000378:metabolism / Q000494:pharmacology*; D016477:Artifacts; D002248:Carbon Monoxide / Q000097:blood; D002263:Carboxyhemoglobin / Q000032:analysis; D002849:Chromatography, Gas; D004338:Drug Combinations; D005260:Female; D006801:Humans; D008168:Lung / Q000378:metabolism; D008297:Male; D008875:Middle Aged; D009609:Nitrous Oxide / Q000097:blood / Q000378:metabolism / Q000494:pharmacology*; D010100:Oxygen / Q000097:blood / Q000378:metabolism / Q000494:pharmacology*; D011653:Pulmonary Diffusing Capacity / Q000187:drug effects*; D012119:Respiration / Q000187:drug effects; D013055:Spectrophotometry, Infrared; D013997:Time Factors
chemical_list: D019162:Anesthetics, Combined; D018685:Anesthetics, Inhalation; D004338:Drug Combinations; C001147:Entonox; D002248:Carbon Monoxide; D002263:Carboxyhemoglobin; D009609:Nitrous Oxide; D010100:Oxygen