Drummond Gordon B, Fischer Darius, Arvind D K
Dept of Anaesthesia, Critical Care, and Pain Medicine, University of Edinburgh, Edinburgh UK.
Centre for Speckled Computing, School of Informatics, University of Edinburgh, Edinburgh, UK.
ERJ Open Res. 2020 Sep 28;6(3). doi: 10.1183/23120541.00023-2020. eCollection 2020 Jul.
Respiratory 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 between observers.
To 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, used by the UK National Early Warning Score, for possible mis-scoring.
When the sample duration was nominally 30 s, the mean interquartile range of repeated estimates was 3.4 breaths·min. For the 60 s samples, the mean interquartile range was 3 breaths·min, and for the 120 s samples it was 2.5 breaths·min. Thus, repeat clinical counts of respiratory rate often differ by >3 breaths·min. For 30 s samples, up to 40% of National Early Warning Scores could be misclassified.
Early 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.
呼吸频率是用于疾病评估的一项基本临床测量指标。呼吸频率测量误差归因于观察者和设备问题。以往研究通常报告观察者之间的呼吸频率差异在2至6次/分钟之间。
为研究重复观察结果为何差异如此之大，我们进行了一项虚拟实验，使用急性病患者的连续呼吸记录。这些记录使每个呼吸周期都能精确计时。我们使用30秒、60秒和120秒的不同采样时长对呼吸频率进行重复随机测量。我们将不同采样时长下这些重复频率测量的差异表示为每个受试者所得值的四分位间距。我们预测，如果从任何患者身上获取的单次测量值被重复测量，并检查英国国家早期预警评分所使用的12次/分钟、20次/分钟或25次/分钟的边界值，可能会出现误评分情况。
当采样时长名义上为30秒时，重复估计值的平均四分位间距为3.4次/分钟。对于60秒的样本，平均四分位间距为3次/分钟，对于120秒的样本，为2.5次/分钟。因此，呼吸频率的重复临床计数通常相差超过3次/分钟。对于30秒的样本，高达40%的英国国家早期预警评分可能会被错误分类。
当使用短采样时长测量呼吸频率时，早期预警评分将不可靠。采样时长越长，精度越高，但除非采用更好的测量方法，否则这可能不切实际。
