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In Response

Nagappa, Mahesh, MD; Lam, Thach, MD; Chung, Frances, MBBS

doi: 10.1213/ANE.0000000000002781
Letters to the Editor: Letter to the Editor

Department of Anesthesia and Perioperative Medicine, London Health Sciences Centre and St. Joseph Health Care, Western University, London, Ontario, Canada

Department of Anesthesiology and Pain Medicine, Toronto Western Hospital, University Health Network, University of Toronto, Toronto, Ontario, Canada,

F. Chung received research grants from Ontario Ministry of Health and Long-Term Care Innovation Fund, University Health Network Foundation, ResMed Foundation, Acacia, and Medtronic. STOP Bang tool is proprietary to University Health Network, and he received Royalties from Up-To-Date. The remaining authors declare no conflicts of interest.

We thank Overdyk and Broens1 for their educational comments on our systematic review and meta-analysis. The prospective randomized controlled trial by Ochroch et al2 found that continuous pulse oximetry (CPOX) did not reduce intensive care unit (ICU) transfers on a postcardiothoracic surgery floor. However, in a subgroup analysis, they found that CPOX significantly decreased ICU transfers due to pulmonary complications. It is important to note that the study by Ochroch et al2 was underpowered to detect real subgroup effects, thereby increasing the risk of false-positive results.

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.

Mahesh Nagappa, MD

Department of Anesthesia and Perioperative Medicine

London Health Sciences Centre and St. Joseph Health Care

Western University

London, Ontario, Canada

Thach Lam, MD

Frances Chung, MBBS

Department of Anesthesiology and Pain Medicine

Toronto Western Hospital

University Health Network

University of Toronto

Toronto, Ontario, Canada

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1. Overdyk FJ, Broens SJL. Continuous pulse oximetry does not measure blood pressure. Anesth Analg. 2018;126:1089–1090.
2. Ochroch EA, Russell MW, Hanson WC 3rd, et al. The impact of continuous pulse oximetry monitoring on intensive care unit admissions from a postsurgical care floor. Anesth Analg. 2006;102:868–875.
3. Taenzer AH, Pyke JB, McGrath SP, Blike GT. Impact of pulse oximetry surveillance on rescue events and intensive care unit transfers: a before-and-after concurrence study. Anesthesiology. 2010;112:282–287.
4. Kirksey M, Chiu YL, Ma Y, et al. Trends in in-hospital major morbidity and mortality after total joint arthroplasty: United States 1998-2008. Anesth Analg. 2012;115:321–327.
5. Taenzer AH, Pyke J, Herrick MD, Dodds TM, McGrath SP. A comparison of oxygen saturation data in inpatients with low oxygen saturation using automated continuous monitoring and intermittent manual data charting. Anesth Analg. 2014;118:326–331.
6. Sun Z, Sessler DI, Dalton JE, et al. Postoperative hypoxemia is common and persistent: a prospective blinded observational study. Anesth Analg. 2015;121:709–715.
7. Masip J, Gayà M, Páez J, et al. Pulse oximetry in the diagnosis of acute heart failure. Rev Española Cardiol (English Ed). 2012;65:879–884.
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