A pilot obstructive sleep apnea screening and monitoring program at Providence St. Peter Hospital reduces Code Blue events by almost two-thirds.

Obstructive sleep apnea (OSA) can increase the risk of postoperative and postprocedural respiratory compromise,1,2 a progressive condition impacting a patient’s ability to breathe. Specifically, the condition defines a pathophysiologic state with a high likelihood of decompensation progressing through a cascade of respiratory insufficiency, failure, and arrest, the latter potentially terminating in death. Risk factors for postoperative respiratory compromise in OSA patients include:

  • anesthetics and sedatives, which can decrease muscle and neural activity important for respiration;
  • opioids, which can increase upper airway resistance, as well as decrease the central drive to breathe;
  • and predisposing risk factors, including obesity, which is often a comorbidity with OSA.3,4

Patients can be screened for OSA preoperatively. Those with previously undiagnosed OSA and/or who are at increased risk for respiratory compromise then can be monitored for earlier detection of adverse postoperative respiratory events. Intermittent assessment of ventilation is one method for detecting respiratory compromise, as is the use of pulse oximetry. However, these techniques alone may not identify evolving postoperative/postprocedural respiratory compromise. The Anesthesia Patient Safety Foundation, among other groups, has recommended capnography (end-tidal CO2 monitoring) to reduce adverse respiratory outcomes in those patients at increased risk for respiratory compromise.5

To help identify and assess OSA patients preoperatively who are at increased risk for respiratory compromise, the STOP-BANG screening questionnaire is used. (STOP stands for snoring loudly, tiredness in daytime, observed apnea during sleep, and pressure [that is, high blood pressure]. BANG stands for body mass index >35 kg/m2, age >50 years, neck circumference [>40 cm for men and >41 cm for women], and gender [male].) Scoring ranges from 0 to 8. A score ?3 means that the patient is at risk of OSA, while a score ?5 indicates that the patient is at high risk for OSA. The STOP-BANG has a high sensitivity, especially for patients with moderate to severe OSA. The questionnaire has been used to stratify the risk of respiratory compromise in the perioperative setting.6

At our institution, Providence St. Peter Hospital in Olympia, Wash, we uncovered a disproportionately high rate of Code Blue events (heart or respiration stops) among postoperative patients on orthopedic, general surgery, and neurosurgery units. Our team considered the possibility that many of these patients may have undiagnosed OSA. Accordingly, we decided to implement a preoperative screening and postoperative capnographic monitoring program, which included:

  • using the STOP-BANG questionnaire;
  • monitoring end-tidal CO2 with capnography;
  • using the Integrated Pulmonary Index (IPI);7
  • measuring arterial oxygenation with pulse oximetry;
  • and monitoring ventilation clinically.8

Under this program, all preoperative patients deemed at high risk for OSA via the STOP-BANG were monitored postoperatively with capnography for a 72-hour period. Respiratory status was also evaluated using IPI, pulse oximetry, and ventilatory monitoring. IPI is an algorithm designed to help clinicians monitor a patient’s respiratory status. IPI incorporates four real-time respiratory measurements—end-tidal CO2, respiratory rate, pulse oximetry, and pulse rate—into a single number that represents an inclusive respiratory profile. IPI is displayed on a scale from 1 to 10, with 10 indicating a normal respiratory status and 1-2 indicating that immediate intervention is required.

Collectively, the use of preoperative screening and postoperative monitoring resulted in a 60% reduction in Code Blue events over a 36-month period. In addition, none of the high-risk OSA patients who were monitored with capnography experienced a Code Blue event. Our results have led our team to consider expanding capnographic monitoring to other patients at increased risk for respiratory compromise.

It is important to note that, while continuous pulse oximetry remains the standard of care for monitoring postoperative and postprocedural patients who are at risk for respiratory compromise, pulse oximetry can display arterial oxygen saturation levels close to normal for some time after breathing has stopped. Therefore, relying on pulse oximetry alone to monitor ventilatory status may delay recognition of respiratory compromise.

Dennis Jensen, RRT

Dennis Jensen, RRT

Capnography, as a monitoring adjunct to pulse oximetry, provides an immediate picture of a patient’s ventilatory status and can be used following surgery to monitor patients who may be at significant risk for respiratory compromise.9 For example, one study of postoperative patients considered to be at high risk for respiratory compromise found that monitoring with capnography and the IPI predicted the onset of respiratory compromise with greater sensitivity and specificity than pulse oximetry alone.10 Another study evaluated the use of capnographic monitoring in postoperative patients determined to be at risk for OSA. Investigators found that 95% of these patients had abnormal end-tidal CO2 values as identified by capnography, despite having normal oxygen saturation, and that 81% of these patients required some intervention.11

As the OSA screening and monitoring program at Providence St. Peter Hospital and these studies have demonstrated, use of the STOP-BANG questionnaire along with capnographic monitoring can help reduce adverse events and should be considered for adoption by other institutions.

Dennis Jensen, RRT, is director, Providence Sleep Center Southwest Washington, Providence St. Peter Hospital, Respiratory Therapy and Neurophysiology, Olympia, Wash. The author may be reached at dennis.jensen[at]providence.org


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2. Sasaki N, Meyer MJ, Eikermann M. Postoperative respiratory muscle dysfunction. Pathophysiology and preventive strategies. Anesthesiology. 2013;118:961-78.

3. Shin CH, et al. Effects of obstructive sleep apnoea risk on postoperative respiratory complications: protocol for a hospital-based registry study. BMJ Open. 2016;6:e008436.

4. Bloom JD, Agarwal SJ, Erslon MG, Hansell DM. The impact of obesity and sleep disordered breathing on postoperative pulmonary complications. Crit Care Med. 2010;38:A42.

5. Stoelting RK, Overdyk FJ. Conclusions and Recommendations Conference on Electronic Monitoring Strategies. Essential monitoring strategies to detect clinically significant drug-induced respiratory depression in the postoperative period—conclusions and recommendations. APSF. Available at: www.apsf.org/announcements.php?id=7

6. Seet E, Chua M, Liaw CM. High STOP-BANG questionnaire scores predict intraoperative and early postoperative adverse events. Singapore Med J. 2015;56:212-216.

7. Taft A, Ronen M, Epps C, Waugh J, Wales R. A Novel Integrated Pulmonary Index (IPI) Quantifies Heart Rate, Etco2, Respiratory Rate and Spo2%. Abstract at The Anesthesiology Annual Meeting. Anesthesiology. 2008;109:A1682.

8. Jensen D, Williamson J, Allen G, et al. Capnographic monitoring can decrease respiratory compromise and arrest in the post-operative surgical patient. Respir Ther. 2016;11:28-30.

9. Ajizian S. Capnography outside the OR. Respir Care Sleep Med. April 2016.

10. Okahara S, Ishii K, Morimatsu H. Integrated pulmonary index can predict respiratory adverse events in postoperative high-risk hypoventilation patients at post-anesthesia care unit. American Society of Anesthesiologists Annual Meeting. October 24-28, 2015. San Diego, Calif. Abstract #A3024.

11. Taylor H, Antin N, Grandstrand J, et al. ETCO2 monitoring in high risk patients in the PACU: a quality improvement project. American Society of PeriAnesthesia Nurses (ASPAN) 34th National Conference. April 26-30, 2015. San Antonio, Texas. Available at: www.aspan.org/Portals/6/docs/ClinicalPractice/2015CSPpdfs/141_Poster.pdf