Authors' reply to Moyle and Ashworth.

The recognised common causes of inaccurate oximetry in the context of home monitoring in virtual wards are listed in our article.1 Readers wanting to explore further can consult the British Thoracic Society’s emergency oxygen guidelines (section 7.1.2)2 or an excellent review on pulse oximetry from Chan and colleagues.3 As with all technologies, oximetry has limitations.\n\nThe effects of smoking and other activities on carboxyhaemoglobin (COHb) levels mentioned by Moyle4 are known, but they have not been of marked clinical significance in the context of patients managed in virtual wards. Schimmel and colleagues analysed non-invasively the effect of smoking outdoors on SpCO (an estimation of COHb) in smokers and non-smokers, noting that the mean level of COHb in smokers was 2.7% before smoking a cigarette and 3.1% after, compared with 1.3% in non-smokers.5 This rise was observed in minutes, and 80% of smokers had an SpCO of \u003c5%. A multicentre trial evaluating pulse oximeters against arterial gases found …