The other prospective controlled study by Taenzer et al3 included the cohort of elderly patients undergoing joint replacement surgeries in a patient surveillance system unit. The comparison unit included the cohort of patients from urology, gynecology, vascular surgery, and general surgery. They found that CPOX monitoring reduced the need for ICU transfers; however, no subgroup analysis was performed to detect whether ICU transfers were due to respiratory complications.3
Overdyk and Broens1 suggested that ICU transfers in the study by Taenzer et al3 are less likely to be skewed by hemodynamic causes. This hypothesis is not supported in the growing literature which shows that there is an increased incidence of major complications like pulmonary embolism, sepsis, nonischemic cardiac complications, and pneumonia after joint replacement surgeries.4 Thus, ICU transfers were not exclusively due to pulmonary causes.
Having extracted data from the prospective controlled studies,2,3,5,6 we decided that it was not appropriate to pool results from trials comparing outcomes that are dissimilar. In other words, it would be inappropriate to pool the data on pulmonary causes of ICU transfer from Ochroch et al2 and data on all-cause ICU transfer from Taenzer et al.3 Overdyk and Broens1 suggested combining the 2 data sets from Taenzer et al3 and Ochroch et al.2 This may increase the risk of bias, raising questions on the validity of the results. To avoid bias in our meta-analysis, we pooled the data on all-cause ICU transfer from both studies.2,3 Based on these findings, we concluded that all-cause ICU transfer had a risk reduction of 34% with CPOX when compared to standard monitoring. Due to lack of data in the literature, our meta-analysis failed to differentiate ICU transfers with respect to pulmonary versus other causes.
We agree with Overdyk and Broens1 that pulse oximetry is not a measure of circulatory insufficiency. Pulse oximetry device is designed to measure specific physiologic outcome (oxygen saturation), and as such, it measures respiratory adverse events better than cardiac adverse events.7 Our systematic review makes it clear that there are not enough outcome studies using oxygen saturation to evaluate its utility for improving patient outcomes with respect to pulmonary causes of adverse events.