Abstract 19116: Assessment of Perioperative Minute Ventilation in Obese versus Non-Obese Patient Using a Non-Invasive Respiratory Volume Monitor

Abstract

Introduction: Adequate respiration is critical to survival and can be influenced by opioids, sedatives and apnea. Direct monitoring of ventilation has previously not been available for non-intubated patients. Reliance on indirect measures (SpO2, RR) may delay needed interventions and obese patients may be at further risk. A non-invasive respiratory volume monitor (RVM) providing real-time direct measures of MV, TV & RR in non-intubated patients is used to assess respiratory status in obese and non-obese patients. Methods: Data collected from an impedance-based RVM (ExSpiron-1Xi, Respiratory Motion, Waltham, MA) in 62 orthopedic patients (65.4 ±12.0 yrs, BMI: 30.8 ±6.0 kg/m 2 ) before, during & after surgery (PACU arrival & discharge) were compared to predicted MV (MV PRED ) based on IBW. Ventilator MV (Apollo, Draeger, Telford, PA) during GA was assumed to be adjusted to maintain appropriate end-tidalCO 2 . Patients were stratified based on obesity status (cutoff BMI=30). The distributions of MV at various times were compared (non-obese vs obese) using an un-paired 1-sided t-test & a 2-sample F-test. Results: Despite similar MV PRED in both groups (6.2±0.2; 6.1±0.2 L/min, p>0.3) obese patients were managed at a higher MV during surgery (6.1±0.2; 5.3±0.2 L/min, p<0.01). MV differences were far greater preoperatively (9.7±0.4 vs. 6.7±0.3 L/min), at PACU arrival (11.4 ±1.2; 6.8±0.7 L/min) & discharge (7.7±0.5; 5.0±0.6 L/min, p<0.01 all, Fig 1). Patient-to-patient variability in MV was similar in both groups pre-op, but larger in obese patients. Even with the large average MV in obese patients, 6% of them left the PACU with MV<40% MV PRED . Conclusions: On average, obese patients have greater MV than predicted by IBW formula, likely due to greater metabolic demand. Post-op, obese patients have greater variability in ventilation when treated with standard opioid doses & may be at greater risk for hypoventilation. RVM can provide data for individualized treatment plans.