Postoperative Hypoxemia Is Common and Persistent: A Prospective Blinded Observational Study

Abstract

Background: The incidence, severity, and duration of postoperative oxygen desaturation in the general surgical population are poorly characterized. We therefore used continuous pulse oximetry to quantify arterial oxygen saturation (SpO2) in a cross-section of patients having noncardiac surgery.

Methods: Oxygen saturation, blinded to clinicians, was recorded at 1-minute intervals in patients >45 years old for up to 48 hours after noncardiac surgery in 1250 patients from Cleveland Clinic Main Campus and 250 patients from the Juravinski Hospital. We determined (1) the cumulative minutes of raw minute-by-minute values below various hypoxemic thresholds; and (2) the contiguous duration of kernel-smoothed (sliding window) values below various hypoxemic thresholds. Finally, we compared our blinded continuous values with saturations recorded during routine nursing care.

Results: Eight hundred thirty-three patients had sufficient data for analyses. Twenty-one percent had ≥10 min/h with raw SpO2 values <90% averaged over the entire recording duration; 8% averaged ≥20 min/h <90%; and 8% averaged ≥5 min/h <85%. Prolonged hypoxemic episodes were common, with 37% of patients having at least 1 (smoothed) SpO2 <90% for an hour or more; 11% experienced at least 1 episode lasting ≥6 hours; and 3% had saturations <80% for at least 30 minutes. Clinical hypoxemia, according to nursing records, measured only in Cleveland Clinic patients (n = 594), occurred in 5% of the monitored patients. The nurses missed 90% of smoothed hypoxemic episodes in which saturation was <90% for at least one hour.

Conclusions: Hypoxemia was common and prolonged in hospitalized patients recovering from noncardiac surgery. The SpO2 values recorded in medical records seriously underestimated the severity of postoperative hypoxemia.

Figures

Figure 1

Study diagram, showing enrollment, exclusions, and patients available for analysis. VISION = Vascular events In Surgery patIents cOhort evaluatioN; ICU = intensive care unit; PACU = post-anesthesia care unit; DNR = do not resuscitate.

Figure 2

Sample of 16 patients’ raw SpO2 data versus postoperative time (green lines), along with overlaid kernel smooth estimates depicting general trends (black lines). POD = postoperative day.

Figure 3

(Raw SpO2 data) Incidence of patients with an average number of minutes per hour in hypoxemia > X during monitoring, according to progressive SpO2 thresholds characterizing hypoxemia.

Figure 4

(Raw SpO2 data) Distribution of SpO2 across the patients in the sample, over postoperative time. Curves estimated using quantile regression with restricted cubic splines. POD = postoperative day.

Figure 5

(Smoothed SpO2 data) Incidence of at least 1 single hypoxic episode of varying minimal duration under progressive SpO2 thresholds characterizing hypoxemia.