Emergence and Postoperative Atelectasis: Reply.

Abstract

We appreciate Dr. Priebe’s interest in our article.1,2 The existence of outliers is an inherent feature of biology, and respiratory pathophysiology and atelectasis formation is certainly no exception to this rule. We can assure Dr. Priebe that all outliers were included in the analyses, which is also clearly stated in the Materials and Methods section. The statistical definition may vary, but according to the default setting in our statistical software, any observation that is 1.5 interquartile ranges below the first quartile or above the third quartile is deemed an outlier. In one of the boxplots in figure 2, no data point exists between the third quartile and 1.5 interquartile ranges, therefore no whisker is displayed. Furthermore, the nine outlier data points from eight patients are from two separate investigations, i.e., from a total data set of 60 observations. The proportion of outliers is therefore 13% and not 27%.The size of atelectasis is preferably discussed in terms of percentage of total lung area in a specific slice of the lungs. We insist that most patients had small atelectasis before awakening, with the median for all patients being only 1.3% of total lung area in a basal scan of the lungs,3 the most vulnerable parts. Indeed, five patients exhibited somewhat larger atelectasis: four of them still under 3% of total lung area and one with 4.1% of total lung area. These are not extreme numbers, but still statistically defined as outliers in our data, since nearly all other patients exhibited minimal atelectasis. Postoperatively, no single patient, outliers included, needed supplemental oxygen or had an oxygen saturation below 95%.Knowledge on the effect of awakening with Fio2 0.8 instead of 1.0 is still lacking. We would welcome evidence showing that awakening with Fio2 0.8 results in even smaller postoperative atelectasis, and we particularly look forward to the resulting discussion whether it is worth shortening safe apnea time by 25% to achieve this.4 Meanwhile, we prefer providing our patients with a maximum oxygen reserve during awakening.The authors declare no competing interests.