OPIAID Zone Tool Tracks PACU Pain and Recovery

Key Takeaways

• Among adults recovering from orthopedic or abdominal operations in a Danish PACU, zone placements were widely distributed without distinct clustering and tended toward pain-dominant profiles.
• The zone score was significantly associated with perceived health, recovery quality, and a PACU time outcome.
• The zone model led separate-component models for perceived health and the PACU time outcome, but the adverse-event-only model led for QoR-PACU.
• Some exploratory scoring approaches fit outcomes better within the pilot cohort, although overfitting remains possible.

In the post-anesthesia care unit (PACU), pain intensity and possibly opioid-related events pose distinct measurement questions. Researchers assessed both during early recovery in the OPIAID Zone Tool version 0.5 study in Acta Anaesthesiologica Scandinavica.

Investigators prospectively observed a convenience sample of 145 adults after orthopedic or abdominal surgery under general anesthesia at Bispebjerg Hospital in Denmark on inclusion days from March 15 through August 1, 2024. The tool plotted two scores against each other. One axis was worst patient-reported pain at rest on the numeric rating scale (NRS) during the first hour after PACU arrival. The other was a composite of the worst opioid-related adverse drug events in that first hour. Each axis ran from 0 to 10. Higher zones represented greater combined burden, while the tool’s two-axis display preserved each patient’s pain and event scores. Assessed events included nausea or vomiting, sedation, itching, dizziness, qualifying urinary retention, hallucinations or confusion, and respiratory depression. Respiratory depression counted with naloxone use, or with a respiratory rate below 10 breaths/min or oxygen saturation below 90% that clinicians judged possibly opioid-induced.

Secondary measures were the European Quality of Life visual analog scale (EQ-VAS) for perceived health during PACU care, the Quality of Recovery Questionnaire for the PACU (QoR-PACU, version 1), and a PACU time outcome described in parts of the source as elapsed time until discharge-readiness criteria were met. Models accounted for procedure type and compared the zone score with pain-only and adverse-event-only measures using R² and relative Akaike information criterion (AIC) and Bayesian information criterion (BIC) rankings.

Patients were distributed broadly across Zones 0–5, without clear clustering and with a tendency toward pain-dominant profiles. The zone-score model was significantly associated with EQ-VAS (R² = 0.39) and a PACU time outcome (R² = 0.50), which the source labels discharge readiness in some sections and PACU length of stay in its results. For both outcomes, it had the highest R² and lowest AIC and BIC relative to the pain-only and adverse-event-only models. Discharge readiness refers to when criteria were met, not when a patient actually left the PACU.

The zone-score model was also significantly associated with QoR-PACU (R² = 0.35), but the adverse-event-only model fit that outcome better (R² = 0.37). The adverse-event-only model had the lowest AIC and BIC, while the pain-only model ranked behind both. Normalizing adverse-event scores or using data-driven zone definitions improved selected fits within the same cohort, without establishing performance in an independent cohort.

The single-center convenience pilot ended below its planned enrollment, and testing multiple exploratory scoring specifications left open the possibility of overfitting. The investigators said version 0.5’s weights and zone boundaries require refinement. Opioid-tolerant patients and recipients of neuraxial anesthesia were excluded. Analgesic strategies differ between hospitals and countries, which the investigators called a barrier to general use. Findings from this Danish cohort may not extend to U.S. practice. Sedation and confusion were inadvertently entered together, although the investigators said this did not change composite scoring or zone allocation. A separate prospective multicenter validation cohort had completed data collection and extraction, but validation findings were not established in this analysis.

According to the investigators, version 0.5 offers a way to display pain and opioid-related adverse event burden together. Its observed associations with recovery measures remain subject to prospective external validation.

Clinician QuestionsHow were nausea and sedation weighted in the OPIAID Zone Tool’s PACU adverse-event score? OPIAID Zone Tool version 0.5 scored patient-reported nausea at 1 to 3 points by severity and added a point for vomiting. It scored sedation at 1 to 3 points on a clinician-assessed alert/voice/pain/unresponsive scale (voice = 1, pain = 2, unresponsive = 3). The composite capped at 10 points.

How did the OPIAID Zone Tool analysis distinguish PACU discharge readiness from actual discharge? In the Danish PACU cohort, time to discharge readiness began at PACU arrival and ended when criteria covering consciousness, breathing and oxygenation, circulatory measures, movement, pain, and nausea were met. The attending PACU nurse and anesthesiologist retained discretion over when a patient actually left the PACU.