Aim. To explore the potential usefulness of the mean, standard deviation (SD), and coefficient of variation (CV = SD/mean) of oximeter oxygen saturations in the clinical care of preterm babies. Methods. This was an exploratory investigation involving 31 preterm babies at 36 weeks postmenstrual age. All babies were healthy, but two were considered to be clinically unstable and required greater attention. Each baby's oxygen saturations were recorded using an oximeter and summarized by the mean, SD, and CV. The potential usefulness of each measure was assessed by its ability to distinguish the two unstable babies from the others. This was achieved using box plots and hierarchical clustering together with the Calinski-Harabasz (CH) index to quantify clustering performance (higher CH index indicates stronger clustering outcome). Results. The box plots flagged both unstable babies as outliers and none of the other babies. Successful clustering of the stable and unstable babies was achieved using the CV (CH = 72.8) and SD (CH = 63.3) but not with the mean. Conclusion. Taking the box plots and clustering results together, it seems plausible that variability might be more effective than mean level for detecting instability in oxygen saturation in preterm babies and that the combination of variability and level through the CV might be even better. 1. Introduction Preterm babies display physiological instabilities such as low oxygen saturation level and variations of heart rate and respiratory patterns [1]. These instabilities arise from a combination of level of arousal, immature organ development, neonatal illnesses [2], clinical interventions [3], and environmental factors (temperature, light, and noise). This makes it difficult to distinguish instabilities that are merely due to prematurity from those partly caused by neonatal illnesses that affect cardiorespiratory functions. Fetal heart rate variability has been quantified to monitor fetal well-being in high-risk pregnancies and labour [4, 5]. Validated measures of prediction of neonatal illness have been developed based on heart rate characteristics [6, 7]. Indices or scores have been calculated from respiratory support data to describe the severity of pulmonary status and respiratory failure in ventilated preterm babies [8, 9]. However, a similar level of understanding has not been reached for oxygen saturation. It is known that an inappropriate amount of oxygen can be detrimental to premature babies—with both hypoxaemia and hyperoxaemia capable of tissue injury [10]—but what the appropriate amount is and
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