Effect of severity of pulmonary disease on nitrous oxide washin and washout characteristics
Vichitvejpaisal, P.; Joshi, G.P.; Liu, J.; White, P.F.
Journal of the Medical Association of Thailand 80(6): 378-383
1997
ISSN/ISBN: 0125-2208 PMID: 9240012 Document Number: 938
The influence of chronic obstructive pulmonary disease (COPD) on the nitrous oxide (N-2O) 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 (FEV-1/FVC gt 80% predicted values; control group); Group II (n=30), patients with mild COPD (FEV-1/FVC = 65-79% of predicted values); and Group III (n=30), patients with moderate COPD (FEV-1/FVC = 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-2O), carbon dioxide (CO-2), and isoflurane. The duration of both N-2O washin (time from start of N-2O administration to equilibrium of inspired and expired N-2O concentrations) and 5 per cent washout (time from discontinuation of N-2O to an expired N-2O concentration of 5 per cent of the equilibrium value) were recorded. The duration of NO washin and washout were significantly prolonged in Groups II and III (P lt 0.001) as compared to the control group (Group I). The end-tidal CO-2 concentration decreased significantly during N-2O washout without causing oxygen desaturation (SpO-2 lt 90%). We conclude that the duration of N-2O washin and washout were significantly prolonged in anaesthetized patients with COPD which may delay the induction and recovery from N-2O anaesthesia.
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