Author: Michael Vlessides
A screening tool designed to identify surgical patients at high risk for obstructive sleep apnea (OSA) bolsters clinical decision making and reduces both respiratory complications and hospital utilization rates.
“In 2006, the Joint Commission recommended that hospitals establish screening tools for OSA,” said Katharina S. Platzbecker, MD, a research fellow at Beth Israel Deaconess Medical Center, in Boston. “At that time, the BOSTN score was developed at our institution by a multidisciplinary team led by Eswar Sundar, MD.”
The BOSTN screening tool is composed of five separate patient characteristics, each of which is allotted 1 point if present:
BOSTN was implemented in routine clinical practice at the institution in 2008, where it is applied preoperatively by nurses. Patients at high risk for OSA are flagged in the electronic health record, which then offers providers various decision options.
“In this project, we aimed to test our primary hypothesis that patients considered at high risk on the BOSTN score would be at increased risk of mechanical ventilation requirement after surgery,” Dr. Platzbecker explained. “We also looked at secondary outcomes, such as hospital length of stay and postoperative desaturation.”
The researchers, led by Matthias Eikermann, MD, PhD, a professor of anesthesia at Harvard Medical School, included data from 212,779 adult patients undergoing noncardiac surgery between May 2008 and September 2017. Patients undergoing more than one surgical procedure in one day were excluded, as were those with an ASA physical status of VI. The final cohort included 180,154 patients.
Of the total, 34,317 patients (19.05%) were categorized as high risk. Among these patients, 704 (2.05%) required postoperative mechanical ventilation within seven days of surgery.
Reporting at the 2018 annual meeting of the American Society of Anesthesiologists (abstract A2266), Dr. Platzbecker said some of the study’s findings met expectations. “As expected, patients with a high risk of OSA according to the BOSTN score also had increased risk of post-extubation desaturation [6.00% vs. 4.26%; adjusted odds ratio (aOR), 1.35; P<0.001], likely because of airway failure.”
Nevertheless, the analysis yielded some surprising results. too. “Patients with a higher BOSTN score were at decreased risk of mechanical ventilation requirements after surgery,” Dr. Platzbecker said. Indeed, 2.31% of low-risk patients required mechanical ventilation, compared with 2.05% of those deemed to be at high risk (aOR, 0.89; 95% CI, 0.90-0.98; P=0.017). This effect was robust in several sensitivity analyses, including those that focused on general anesthesia patients only.
In addition, patients with a BOSTN score of 2 points or greater were discharged earlier (1.87 days; aOR, 0.85; 95% CI, 0.85-0.88; P<0.001) than those at low risk, according to the screening tool.
Given these surprising findings, the researchers sought to determine if anesthesiologists at the institution took a different approach to patients at high risk for OSA by the BOSTN score. “We were very curious to find potential underlying mechanisms,” Dr. Platzbecker said. “Does the awareness of the higher risk of OSA influence clinician behavior?
“As we know, patients with OSA are particularly vulnerable to utilization of opioids and neuromuscular blocking agents,” she said. “So we wanted to look at the association between BOSTN score and utilization of these agents.”
Low-risk BOSTN score patients received a mean neuromuscular blocking agent dose of 1.71 mg/kg. By comparison, high-risk BOSTN score patients received 1.53 mg/kg (mean adjusted effect, –0.34; 95% CI, –0.36 to –0.32; P<0.001).
Similarly, low-risk patients also received significantly more intraoperative fentanyl than their high-risk counterparts (1.48 vs. 1.31 mcg/kg) (mean adjusted effect, –0.25; 95% CI, –0.20 to –0.30; P<0.001).
“Based on our results,” Dr. Platzbecker said, “we conclude that screening for OSA and the awareness that some patients are at high risk for OSA both allow clinicians to arrive at improved patient care and better patient outcomes.”
Roman Schumann, MD, a professor of anesthesiology at Tufts Medical Center in Boston, said in an interview with Anesthesiology News, “It seems like the researchers have come up with an OSA risk scoring system that is even more user-friendly than the STOP-BANG. Judging by what they report in the study, the BOSTN scale seems to have a similar discriminatory ability as the STOP-BANG when classifying patients as high risk for OSA.
“It’s interesting that a scoring system that’s so simple can also be discriminatory,” Dr. Schumann added. “I find it attractive from that perspective.”
Dr. Schumann also noted the finding that patients identified as high risk by BOSTN had less resource utilization, postoperative mechanical ventilation and reintubation than their lower risk counterparts. “Does simply flagging a patient as higher risk inherently prompt the providers to treat these patients differently, or is there a physiologic component about OSA that we don’t really understand yet? Could it be that over time these high-risk patients have actually developed a tolerance to hypoxemia and respiratory compromise that is less well tolerated in normal patients?”
“Two observations make me believe we use a powerful screening tool here in the Beth Israel Deaconess Medical Center,” Dr. Eikermann said. “First, the similarity between BOSTN and the STOP-BANG questionnaire—which had not been published by the time Dr. Sundar implemented BOSTN—is obvious. Second, our finding of increased odds of immediate post-extubation desaturation in patients with high BOSTN scores suggests an increased vulnerability to upper airway obstruction, a key finding in OSA patients.
“Our main finding is that OSA screening, paralleled by a bundled intervention for anesthesia care, can improve perioperative outcomes in OSA patients,” Dr. Eikermann concluded.