The Use of a Noninvasive Respiratory Volume Monitor to Detect and Quantify Obstructive Sleep Apnea in Postoperative Patients

Abstract

PURPOSE: Obstructive sleep apnea (OSA), while prevalent, remains underdiagnosed. This presents challenges after surgery, as OSA is associated with increased postoperative complications and often worsens with opioid administration. Previously, real-time identification of apneic events has been difficult using standard monitoring, with many events going unnoticed and untreated. A novel, non-invasive, Respiratory Volume Monitor (RVM) which provides respiratory volume traces and accurately reports Minute Ventilation (MV), Tidal Volume (TV) and Respiratory Rate (RR), has the potential to detect and quantify apneic events post-operatively. METHODS: 92 patients undergoing elective orthopedic surgery were studied using an impedance-based RVM (ExSpiron, Respiratory Motion, Inc., Waltham, MA). Continuous RVM traces were obtained in the PACU and opioid administration (0.2mg PCA hydromorphone or 2.0 mg PRN morphine) recorded. Apneic episodes, defined as at least 10 seconds between successive breaths, were recorded and OSA was defined as more than 5 events per hour. MV, TV and RR were calculated from 30-second RVM trace segments. RESULTS: OSA was observed in 19/92 patients (21%; mean age: 68.5, 53-86 years; mean BMI: 27.3, 15-38 kg/m2) in the PACU. An average of 37 + 5.4 apneic events (13.1 + 1.7 events/hr.) per patient were observed with an average duration of 14.9 + 0.5, range 10-60 secs. During apneic breathing periods, MV was significantly lower compared to non-apneic periods (7.6 + 0.9 L/min to 4.8 + 0.5 L/min, -34 + 3%, p<0.01). Importantly, 15/19 patients (79%) were not previously diagnosed with OSA. In 8/19 patients (42%), opioid administration initiated or exacerbated OSA. Analysis of age, gender, height, weight and BMI did not differentiate patients with apneic events from those without. CONCLUSIONS: RVM traces can be used to detect apneic episodes in the PACU and quantify the reduction in MV caused by OSA. MV measurements may be the most useful way to quantitate the impact of OSA postoperatively. Traditional risk factors for OSA (age, male, BMI) were not predictive of post-operative OSA.