Morphine at "sub-analgesic" background infusion rate plus low-dose PCA bolus control pain better and is as safe as twice a bolus-only PCA regimen: a randomized, double blind study

Morphine for postoperative pain control is commonly titrated via intravenous patient-controlled analgesia (IV-PCA). An IV morphine background infusion is rarely used. We investigated whether analgesia is effectively attained and morphine consumption is reduced if PCA titration is coadjuvated by a continuous infusion protocol. Following colorectal cancer surgery, consenting patients were randomized to receive a minimal ("sub-analgesic") dose of morphine 0.01 mg/kg/h background infusion plus a 0.01 mg/kg bolus (BI), or a 1.5mg bolus-only morphine (B0) (bolus ratio ∼1:2). Bolus lockout time was 7 min in either case. All patients received 0.1mg/kg morphine before protocol initiation, and diclofenac 75 mg intramuscularly b.i.d. during the study period, lasting 48 h. Eighty-six patients (51 males, age 26-95 years) participated in the study. The total mean morphine consumption during the 48 h was 25% lower in the BI than in the B0 group (P<0.05). Although the former applied the PCA device for boluses 19% less than the latter (P<0.05), their pain score was lower (P<0.05) most of the time, and they reported greater satisfaction (P<0.05) on a 10-scale numerical rating score. Pre- and postoperative vital signs were similar for both groups. No patient depicted hypoxemia or lapsed into deep sedation. Four BI and three B0 patients required treatment for postoperative nausea and vomiting. One BI patient had transient pruritus and one B0 69-year individual became disoriented 24h into treatment; either event subsided soon after stopping their respective regimen without the need for treatment. The main conclusions of the results are that very-low-dose background morphine infusion combined with small-dose PCA boluses may provide better pain relief, lower morphine consumption, and minimal complication rate as a 1.5mg PCA bolus-only protocol.