Current clinical methods of measurement of respiratory rate give imprecise values

Abstract

BackgroundRespiratory rate is a basic clinical measurement used for illness assessment. Errors in measuring respiratory rate are attributed to observer and equipment problems. Previous studies commonly report rate differences ranging from 2 to 6 breaths·min−1 between observers.MethodsTo study why repeated observations should vary so much, we conducted a virtual experiment, using continuous recordings of breathing from acutely ill patients. These records allowed each breathing cycle to be precisely timed. We made repeated random measures of respiratory rate using different sample durations of 30, 60 and 120 s. We express the variation in these repeated rate measurements for the different sample durations as the interquartile range of the values obtained for each subject. We predicted what values would be found if a single measure, taken from any patient, were repeated and inspected boundary values of 12, 20 or 25 breaths·min−1, used by the UK National Early Warning Score, for possible mis-scoring.ResultsWhen the sample duration was nominally 30 s, the mean interquartile range of repeated estimates was 3.4 breaths·min−1. For the 60 s samples, the mean interquartile range was 3 breaths·min−1, and for the 120 s samples it was 2.5 breaths·min−1. Thus, repeat clinical counts of respiratory rate often differ by >3 breaths·min−1. For 30 s samples, up to 40% of National Early Warning Scores could be misclassified.ConclusionsEarly warning scores will be unreliable when short sample durations are used to measure respiratory rate. Precision improves with longer sample duration, but this may be impractical unless better measurement methods are used.

Classifying signals from a wearable accelerometer device to measure respiratory rate

“…A previous analysis of the nasal cannula signals obtained from this study showed that repeated estimates of respiratory rate, made from the same record, but at different times, could vary substantially. [6] The performance after signal selection is superior to results reported in previous studies. [11-13, 24, 25] The study has several strengths: a medically appropriate cohort of patients, studied in clinical circumstances, using an appropriate and accurate comparison signal.…”

“…Ischaemic heart disease or venous thromboembolism was suspected in 14 patients, and 13 had either sepsis or urinary tract infection. The remainder had neurological conditions such as stroke (9), gastrointestinal disease (6), and other conditions (4). Many patients had comorbid conditions: these were cardiovascular in 32, respiratory in 20, diabetes in 11, and renal impairment in 12.…”

“…[5] Current measurements of respiratory rate need to be improved. Breaths are counted for a limited time, [6] values recorded by different observers often differ, [7] and charted values are not trustworthy. [8] Accurate measurement of respiratory rate with a wearable device has practical difficulties.…”

“…Repeating observations made over one minute gives results with an interquartile range of 3 breaths/minute. [6] When comparing methods, exactly the same breaths should be sampled, but previous studies failed to do this. [9,10] Recent studies of automatic measurement of respiratory rate in low care and high dependency patients report similar limits of agreement, about ± 4 breath/minute.…”

“…Current measurements of respiratory rate need to be improved. Breaths are counted for a limited time [ 6 ], values recorded by different observers often differ [ 7 ] and charted values are not trustworthy [ 8 ].…”