Effect of Severity of Pulmonary Disease on Nitrous Oxide Washin and Washout Characteristicst
PHONGTHARA VICHITVEJPAISAL, M.D.*, JIN LIU, M.D.*, GIRISH P. JOSHI, M.B., B.S., M.D., F.F.R.C.S.I*, PAUL F. WHITE, M.D., Ph.D., F.A.N.Z.C.A.*
Affiliation : * Department of Anesthesiology and Pain Management, The University of Texas Southwestern Medical Center at Dallas, Texas, U.S.A. t Presented at the 1994 Annual Meeting of the American Society of Anesthesiologists, San Francisco, October 1994.
Abstract The influence of chronic obstructive pulmonary disease (COPD) on the nitrous oxide (Np) washin and washout characteristics was evaluated in 90 (ASA II-III) males undergoing elective peripheral surgery under general anaesthesia with controlled ventilation. Patients were classified by preoperative bedside pulmonary function testing into three groups. Group I (n=30), patients without COPD (FEVJFVC > 80% predicted values; control group); Group II (n=30), patients with mild COPD (FEVJFVC = 65-79% of predicted values); and Group III (n=30), patients with moderate COPD (FEVJFVC = 50-64% of predicted values). The anaesthetic technique was standardized for all patients. The Datex Capnomac Ultima™ monitor was used to measure the inspired and expired concentrations of nitrous oxide (N,O), carbon dioxide (C02), and isoflurane. The duration of both Np washin (time from start of :Np administration to equilibrium of inspired and expired Np concentrations) and 5 per cent washout (time from discontinuation of Np to an expired Np concentration of 5 per cent of the equilibrium value) were recorded. The duration of N20 washin and washout were significantly prolonged in Groups II and III (P < 0.001) as compared to the control group (Group I). The end-tidal C02 concen- tration decreased significantly during Np washout without causing oxygen desaturation (Sp02 < 90%). We conclude that the duration of N20 washin and washout were significantly prolonged in anaesthetized patients with COPD which may delay the induction and recovery from Np anaesthesia.
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