Patients with Increased Levels of the Oxidative Stress Biomarker SOD1 Appear to Have Diminished Postoperative Pain After Midline Laparotomy: A Randomised Trial with Special Reference to Postoperative Pain Score (NRS)

Background/Aim: The levels of the oxidative stress biomarker superoxide dismutase (SOD1) in plasma in relation to pain at rest 24 hours after (NRS24) midline laparotomy in patients with rectus sheath block (RSB) analgesia is unknown. Patients and Methods: Initially, 56 patients (39 with cancer), each with an intravenous oxycodone pump as patient-controlled analgesia, were randomized to four groups: control group, no RSB (n=12), single-dose (n=16), repeated-dose (n=12) and continuous infusion (n=16) of RSB analgesia. The plasma levels of SOD1 were measured directly before, immediately after and 24 hours after surgery. Pain at rest was scored on an 11-point numeric rating scale 24 hours postoperatively (NRS24: 0=no pain to 10=worst pain). Results: The median plasma level of SOD1 increased immediately after operation and this was statistically highly significant (p=0.007). The median plasma level of SOD1 then decreased 24 hours postoperatively and this postoperative decrease was also statistically highly significant (p<0.001). The median plasma levels of SOD1 did not differ significantly between patients with benign disease and those with cancer, preoperatively and after surgery. There was highly significant positive correlation between SOD1 and glutathione peroxidase (GPX1) values postoperatively (r=0.67, p<0.001) and a trend for an inverse correlation between the individual values of the NRS24 and plasma SOD1 values postoperatively in patients with benign disease and those with cancer (r=-0.30, p=0.09). Conclusion: Midline laparotomy significantly alters the level of oxidative stress marker SOD1 immediately after surgery, but the level normalizes 24 hours following surgery. Interestingly, patients with increased levels of SOD1 appeared to have diminished postoperative pain after midline laparotomy.