A risk stratification algorithm using non-invasive respiratory volume monitoring to improve safety when using post-operative opioids in the PACU

Abstract

Late detection of respiratory depression in non-intubated patients compromises patient safety. SpO₂ is a lagging indicator of respiratory depression and EtCO₂ has proven to be unreliable in non-intubated patients. A decline in minute ventilation (MV) is the earliest sign of respiratory depression. A non-invasive respiratory volume monitor (RVM) that provides accurate, continuous MV measurements enables clinicians to predict and quantify respiratory compromise. For this observational study, practitioners were blinded to the RVM measurements and pain management followed the usual routine. Patients were stratified by their MV on PACU admission and classified as "At-Risk" or "Not-At-Risk," with progression to "Low MV" status following opioids assessed for each category. The purpose was to determine if stratifying based on MV on PACU arrival could identify patients at higher risk for respiratory depression. Ability to identify in advance patients at higher risk for respiratory depression following standard opioid dosing would drive changes in pain management and improve patient care. RVM and opioid administration data from 150 PACU patients following elective joint-replacement surgery were collected in an observational study. "Predicted" MV (MV_PRED) and "Percent Predicted" (MV_MEASURED/MV_PRED × 100 %) were calculated for each patient using standard formulas. Prior to opioid administration, patients were classified as either "Not-At-Risk" (MV ≥ 80 % MV_PRED) or "At-Risk" (MV < 80 % MV_PRED). "Low MV" was defined as MV < 40 % MV_PRED. Post-operative apnea (POA) was defined as ≥5 ten-second apneas per hour of PACU stay. We compared the incidences of Low MV following a single opioid dose, POA, and Low MV at discharge for both groups. In the PACU, 74/150 patients received opioids. Within 15 min of opioid administration, 32 % (24/74) developed Low MV. The risk-stratification algorithm identified 22/24 patients (92 % sensitivity). Only 46 % of them had POA, and the majority had Low MV without POA. At discharge, 29/150 patients had Low MV and those receiving opioids were 50 % more likely to display Low MV (23 vs. 16 %). The RVM can identify patients at-risk for opioid-induced respiratory depression and/or experiencing POA. Monitoring of MV can guide opioid-dosing regimens and may increase patient safety across the continuum of care.

Keywords: Minute ventilation; Opioids; Patient safety; Respiratory monitoring; Risk-stratification.