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The capnograph is in regular use as a respiratory monitor. From measurements of its trace, calculations of breathing rate and end-tidal carbon dioxide can be made. Unfortunately, the reliability of these calculations depends on the quality of the signal. In the case of cardiogenic oscillations, the averaged results may be grossly inaccurate and, therefore, misleading. This paper describes a method for detecting such cardiogenic oscillations and removing their effect from the final results of capnogram analysis. The algorithm used resulted in a sensitivity of 99.6% and a specificity of 99.2%, when compared with manual scoring. The criteria could easily be incorporated into equipment software and are a step in the direction of "intelligent" monitoring.

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Twelve recordings of overnight pulse oximetry representing a range of severity of obstructive sleep disturbance were evaluated by 7 experienced clinicians. Each recording was then scored by counting the number of minutes in each hour affected at any time by a fall in saturation to below 90%. Comparison of the clinical evaluation and the overall scores gave a clear level of 5 minutes per hour at and above which all the assessors agreed that the charts had clinically important desaturation. Overnight pulse oximetry was then performed on 25 children aged between 12 months and 10 years about to undergo adenotonsillectomy. The charts were scored by the method above with a score of 5 or more indicating a positive result for hypoxic episodes. The scores for shortened analysis periods of 1, 2, 3 and 4 hours duration were compared with the overall score and no cases which were negative, up to and including 4 hours, became positive in the overall result. Thus recording pulse oximetry for 4 hours provides sufficiently accurate information for clinical purposes.