Background: Opioid-induced respiratory depression (OIRD) and postoperative apnea (POA) can lead to complications after surgery or traumatic injury. Previously, real-time monitoring of respiratory insufficiency and identification of apneic events have been difficult. A noninvasive respiratory volume monitor (RVM) that reports minute ventilation (MV), tidal volume, and respiratory rate is now available. The RVM was used to report the effect of opioids on respiratory status as well as demonstrate apneic breathing patterns in a hospital postanesthesia care unit.
Methods: RVM traces were collected from 132 patients. Predicted MV (MVPRED) for each patient was used to calculate and the "percent predicted" MV (MVMEASURED / MVPRED × 100%) before opioid administration. Patients were stratified patients into two categories: "at risk," MV of less than 80% MVPRED, and "not at risk," MV of 80% MVPRED or greater. After opioid dosing, patients with MV of less than 40% MVPRED were categorized as "unsafe." POA was defined as more than five apneic or hypopneic events per hour.
Results: Of the 132 patients, 50 received opioids. Baseline MV was 7.2 ± 0.5 L/min. The MV-based protocol classified 18 of 50 patients as at risk before opioid administration. After the first opioid dose administration, at-risk patients experienced an average MV decrease (36.7% ± 8.5% MVPRED) and 13 of 18 decreased into unsafe; the 32 not at-risk patients experienced a lesser average MV decrease (76.9% ± 6.3% MVPRED). Only 1 of 32 not at-risk patients had a decrease in MV to unsafe. The proposed protocol had a sensitivity of 93% and a specificity of 86%. Of the 132 patients, 26 displayed POA. Of the 26 patients, 12 experienced POA without receiving opioids. Of the 26 patients with POA, 14 also received opioids, and of those, 6 were classified as unsafe.
Conclusion: This investigation indicates that at risk and unsafe respiratory patterns occur frequently after procedure. RVM provides continuous noninvasive objective measurements of OIRD and POA. The RVM may prove a useful tool in opioid dosing and in recognition and management of POA and strong potential value in the rapid detection of OIRD and apnea in the contemporary combat casualty environment.
Level of evidence: Care management study, level V.