Early postoperative patient-controlled analgesia ratio predicts 24-hour morphine consumption and pain in children undergoing scoliosis surgery.

BACKGROUND: The identification of patients at risk for developing severe postoperative pain and/or opioid-related side effects is difficult due to a lack of sensitive indicators. The patient-controlled analgesia (PCA) ratio of demands to deliveries is a potential tool for early identification of patients who experience severe postoperative pain. The authors hypothesized that the PCA ratio is able to predict morphine requirement in the first 24 hours after scoliosis surgery. METHODS: The authors performed a retrospective study of adolescents who had surgery for idiopathic scoliosis. They collected data describing PCA demands and deliveries, morphine consumption, numerical rating scale (NRS) pain scores, opioid related side effects, and duration of hospital stay. Spearman rank analysis assessed association among 4-hour PCA ratios, NRS pain score, and 24-hour morphine consumption. Patients were divided into groups on the basis of PCA ratios <1.5 and ≥1.5. Univariate analysis and multiple regression were used to identify independent factors predictive for increased 24-hour morphine. Mann-Whitney rank-sum and Fisher exact tests were used to compare data. p < 0.05 was considered statistically significant. RESULTS: One hundred forty-seven patients were included in the analysis, mean (SD) age and weight were 15 (1.8) years and 55 (27) kg, respectively. There was a significant positive correlation between the 4-hour PCA ratio and initial 24-hour cumulative morphine consumption (r = 0.33, p = 0.0002). Patients with a 4-hour PCA ratio ≥1.5 demonstrated a significantly greater initial 24-hour morphine consumption (p = 0.0002), greater pain scores at 24 hours after surgery (p = 0.02), a greater incidence of at least one opioid-related side effect within the initial 24 hours after surgery, and a longer duration of hospital stay (p = 0.04) compared with those patients with a 4-hour PCA ratio <1.5. PCA ratio ≥1.5, age, and patient sex were predictive for 24-hour morphine consumption. CONCLUSIONS: The authors have demonstrated that a PCA ratio of demands/deliveries ≥1.5 is predictive of increased opioid requirements and is associated with greater pain scores in the initial 24 hours after surgery, an increased incidence of opioid-related side effects, and duration of hospital stay.