Incidence, risk factors, and phenomenological characteristics of postoperative delirium in patients receiving intravenous patient-controlled analgesia: a prospective cohort study

BACKGROUND Intravenous patient-controlled analgesia (IVPCA) is a common method of relieving pain which is a risk factor of postoperative delirium (POD). However, research concerning POD in IVPCA patients is limited. OBJECTIVE We aimed to determine the incidence, risk factors, and phenomenological characteristics of POD in patients receiving IVPCA. METHODS A prospective, cohort study was conducted in post-general anesthesia IVPCA patients aged ≥60 years. POD was measured by the Nursing Delirium Screening Scale (NuDESC; 0-10). Delirium, pain severity at rest and/or on movement, and side effects of IVPCA during 3 postoperative days were examined twice-daily by the acute pain service team. Pain severity is measured by an 11-point verbal numerical rating scale (11-point VNRS) (0-10). An 11-point VNRS >3 was considered inadequate pain relief. If POD (detected by NuDESC ≥1) is suspected, consulting a neurologist or a psychiatrist to confirm suspected POD is required. RESULTS In total, 1,608 patients were included. The incidence rate of POD was 2.2%. Age ≥70 years and American Society of Anesthesiologists physical status >III were the risk factors of POD in IVPCA patients. Approximately three-quarters of all POD cases occurred within the first 2 postoperative days. For pain at rest, patients with inadequate pain relief had significantly greater rates of POD than patients with adequate pain relief (day 1, 8.4% vs 1.5%, P<0.001; day 2, 9.6% vs 2.0%, P=0.028; day 3, 4.1% vs 2.1%, P=0.412). However, the incidence of POD was not associated with movement-evoked pain relief. Most (79.9%) POD cases in IVPCA patients showed either one or two symptoms. The symptoms of POD were ranked from high to low as disorientation (65.7%), illusions/hallucinations (37.1%), inappropriate communication (31.4%), inappropriate behavior (25.7%), and psychomotor retardation (14.2%). CONCLUSION The incidence rate of POD in IVPCA patients was low. Further research is warranted concerning POD and IVPCA pain management.