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

Clyde T. Matava, MBCHB, Mark W. Crawford, MBBS, Carolyne Pehora, RN, Basem Naser, MD, Conor McDonnell, MBCHB


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, opioidrelated 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.


pain, opioids, PCA

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Grass JA: Patient-controlled analgesia. Anesth Analg. 2005; 101: S44-S61.

Walder B, Schafer M, Henzi I, et al.: Efficacy and safety of patient-controlled opioid analgesia for acute postoperative pain. A quantitative systematic review. Acta Anaesthesiol Scand. 2001; 45: 795-804.

Thomas V, Heath M, Rose D, et al.: Psychological characteristics and the effectiveness of patient-controlled analgesia. Br J Anaesth. 1995; 74: 271-276.

Ballantyne JC, Carr DB, Chalmers TC, et al.: Postoperative patient-controlled analgesia: Meta-analyses of initial randomized control trials. J Clin Anesth. 1993; 5: 182-193.

Woodhouse A, Mather LE: Nausea and vomiting in the postoperative patient-controlled analgesia environment. Anaesthesia. 1997; 52: 770-775.

Baird M, Schug A: Safety aspects of postoperative pain relief. Pain Digest. 1996; 6: 219-225.

Tighe KE, Webb AM, Hobbs GJ: Persistently high plasma morphine-6-glucuronide levels despite decreased hourly patient-controlled analgesia morphine use after single-dose diclofenac: Potential for opioid-related toxicity. Anesth Analg. 1999; 88: 1137-1142.

Mc Donnell C, Pehora C, Crawford MW. PCA-derived factors that may be predictive of postoperative pain in pediatric patients: A possible role for the PCA ratio. J Opioid Manag. 2012; 8: 39-44.

Dahmani S, Dupont H, Mantz J, et al.: Predictive factors of early morphine requirements in the post-anaesthesia care unit (PACU). Br J Anaesth. 2001; 87: 385-389.

Caumo W, Schmidt AP, Schneider CN, et al.: Preoperative predictors of moderate to intense acute postoperative pain in patients undergoing abdominal surgery. Acta Anaesthesiol Scand. 2002; 46: 1265-1271.

Chung F, Ritchie E, Su J: Postoperative pain in ambulatory surgery. Anesth Analg. 1997; 85: 808-816.

Kalkman CJ, Visser K, Moen J, et al.: Preoperative prediction of severe postoperative pain. Pain. 2003; 105: 415-423.

Raffaeli W, Samolsky Dekel BG, Landuzzi D, et al.: Nociceptin levels in the cerebrospinal fluid of chronic pain patients with or without intrathecal administration of morphine. J Pain Symptom Manage. 2006; 32: 372-377.

Estfan B, LeGrand SB, Walsh D, et al.: Opioid rotation in cancer patients: Pros and cons. Oncology. 2005; 19: 511-516; discussion 516-518, 521-523, 527-528.

de Stoutz ND, Bruera E, Suarez-Almazor M: Opioid rotation for toxicity reduction in terminal cancer patients. J Pain Symptom Manage. 1995; 10: 378-384.

Kloke M, Rapp M, Bosse B, et al.: Toxicity and/or insufficient analgesia by opioid therapy: Risk factors and the impact of changing the opioid. A retrospective analysis of 273 patients observed at a single center. Support Care Cancer. 2000; 8: 479-486.

Apfelbaum JL, Gan TJ, Zhao S, et al.: Reliability and validity of the perioperative opioid-related symptom distress scale. Anesth Analg. 2004; 99: 699-709; table of contents.

McNicol E, Horowicz-Mehler N, Fisk RA, et al.: Management of opioid side effects in cancer-related and chronic noncancer pain: A systematic review. J Pain. 2003; 4: 231-256.

Ochroch EA, Fleisher LA: Retrospective analysis: Looking backward to point the way forward. Anesthesiology. 2006; 105: 643-644.

Logan DE, Rose JB: Is postoperative pain a self-fulfilling prophecy? Expectancy effects on postoperative pain and patient-controlled analgesia use among adolescent surgical patients. J Pediatr Psychol. 2005; 30: 187-196.



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