The relationship between the level of μ-opioid receptor (μORs) and postoperative analgesic use in patients undergoing septoplasty: a prospective randomized controlled trial

BACKGROUND: In this study, the μ-Opioid receptor activity was assessed pre-operatively for its association with postoperative pain level and second analgesic requirement in patients undergoing septoplasty. METHODS: In our prospective study, 120 adult patients underwent septoplasty from June 2015 to January 2019 were randomly divided into 2 pre-operative groups. The first group (n = 60) was patients given tramadol (1–2 mg/kg) for post-operative analgesia, and the second group (control group) (n = 60) was initially prescribed only fentanyl (1 μg/ kg-i.v.) in the induction. Acetaminophen with codeine analgesic 325/30 mg (p.o.) was used as an rescue painkiller in the post-operative period. The μ-Opioid receptor activity was investigated in pre-operative blood samples and compared to post-operative pain level and time required for second round of analgesic administration. The visual analogue score (VAS) was used to evaluate the post-operative pain degree (0 no pain; 10 worst pain). The patients’ post-operative VAS scores were evaluated upon arrival to recovery room, and at the 1st, 3rd, 7th, 10th, and 24th hour post-operative period. RESULTS: Demographic data and peri-operative variables were similar in both study group (p < 0.05).There was no significant difference between the receptor levels in both groups and the mean receptor level was 200.94 ± 15.34 pg/mL (max:489.92 ± 22.36 pg/mL, min: 94.56 ± 11.23 pg/mL).In patients who used tramadol as the levels of μ-Opioid receptors increased, VAS scores of patients and second analgesic use decreased in post-operative period.The VAS scores in patients with higher receptor levels were lower in the recovery room (p < 0.05), 1st (p < 0.05) and 3rd hours (p < 0.05).The VAS scores were lower in the tramadol group compared to the control group (p < 0.05).Number of secondary analgesic requirement was significantly lower in patients of the tramadol group with higher receptor levels compared to the ones with lower receptor (p < 0.05) for arrival at the recovery room and 1st hour. Patients in the tramadol group needed a second pain killer much later than patients in the control group. CONCLUSIONS: Our study demonstrates that patients with higher μOR levels have a higher efficacy of opioid analgesic agents and an lesser need for additional analgesic agents. TRIAL REGISTRATION: This trial was registered retrospectively (The ACTRN: ACTRN12619001652167, registration date: 26/11/2019).