Abstract
A 68-year-old woman was scheduled for total knee arthroplasty. During the operation, anesthesia was maintained with sevoflurane, remifentanil, and fentanyl（total 400 µg）. For post-operative analgesia, a periarticular multimodal drug cocktail（morphine 5 mg, ropivacaine, dexamethasone and adrenaline）and continuous fentanyl infusion（12.5 µg/h）via intra-venous patient controlled analgesia（IV-PCA）was administered. Ninety minutes after the patient left the operating room, an anesthesiologist was called because the patient’s respiratory rate decreased to less than 8 breaths/min. Although we immediately discontinued IV-PCA and administrated naloxone, respiratory instability persisted. Consequently, continuous administration of naloxone and non-invasive positive pressure ventilation therapy was necessary for recovery. A simulation using the AnestAssistTM PK/PD system（Fentanyl PK parameter in Shafer model）indicated that the density of fentanyl was too low to induce respiratory depression. We strongly suspected that the morphine included in the cocktail was the cause of the severe respiratory depression. Opioids included in a cocktail could induce an unexpected increase in opioid blood concentration. Adequate observation and monitoring is important for the management of patients who are administered a periarticular multimodal drug cocktail with opioid.
