Analgesic effects of adding lidocaine to morphine pumps after orthopedic surgeries

Opiate is used in patient-controlled intravenous analgesia pumps (PCIA) for controlling pain in post-surgical patients. Other drugs are remarkably added to opioid pumps to enhance quality, lengthen analgesia, and reduce side effects. Lidocaine, a local anesthetic which inhibits sodium channels, has anesthetic and analgesic effects when injected locally or intravenously. The objective of this study is to evaluate the analgesic effects of adding lidocaine 1% to different doses of morphine via IV pump to patient-controlled analgesia (PCA) after orthopedic surgeries.

In a randomized clinical trial, 60 patients who had undergone orthopedic surgery of lower extremities were divided into three equal groups to control postoperative pain. Intravenous pump with 5 ml/h flow rate was used as the analgesic method. The solution consisted of lidocaine 1% plus 20 mg morphine for the first group, lidocaine 1% plus 10 mg morphine for the second group, and only 20 mg morphine for the third group (control group). Patients were checked every 12 h, and Visual Analog Scale (VAS), extra opioid doses, nausea/vomiting, and sedation scale were examined.

Pain score was lower in the first group compared to the other two groups. Mean VAS was 2.15 ± 0.2, 2.75 ± 0.2, and 2 ± 0.25 on the first day and 1.88 ± 0.1, 2.74 ± 0.3, and 2.40 ± 0.3 on the second day, respectively, in the three groups and the difference was statistically significant (P < 0.01 and <0.05, respectively). Also, 10% of patients in the first group needed extra opioid doses, while this figure was 30% in the second group and 25% in the third group (P < 0.01). Nausea/vomiting and sedation scores were not statistically different among the three groups.

Compared to lidocaine 1% plus 10 mg morphine or 20 mg morphine alone in PCIA, adding lidocaine 1% to 20 mg morphine decreases the pain score and opioid dose after orthopedic surgeries without having side effects.