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The effective prevention of postoperative cognitive dysfunction (POCD) needs to be explored, and the effect of preoperative pain on POCD remains unclear. We established a chronic pain model induced by chronic constriction injury (CCI) and models of acute pain and anxiety without pain in mice that were subsequently subjected to partial hepatectomy surgery. Morris water maze (MWM) tests were performed to evaluate the learning and memory abilities of the mice. ELISA was used to measure IL-1β, IL-6, and TNF-α in serum, and HPLC-MS was used to detect neurotransmitters in the prefrontal cortices and hippocampi of the mice. The results indicated that chronic pain induced by CCI might have significantly impaired the learning and memory abilities of mice, while acute pain and anxiety without pain only affected the memory abilities of mice. Perioperative acute pain increased the level of IL-1β in serum, and CCI might have increased the level of IL-6. CCI and acute pain increased dopamine (DA) levels in the cortex, similar to anxiety. Like anxiety, CCI increased 5-hydroxytryptamine (5-HT) levels in the prefrontal cortex and hippocampus. Acute pain led to a decrease in the acetylcholine (ACH) level in the hippocampus. Our results suggest that acute pain and CCI-induced chronic pain might aggravate postoperative cognitive dysfunction via neurotransmitters and by changing the levels of inflammatory factors such as IL-1β and IL-6.

Background Studies have provided some evidence that pain is a risk factor for postoperative delirium (POD). Therefore, we investigated the relationship between preoperative pain and POD after noncardiac surgery. Methods POD was assessed with the Montreal Cognitive Assessment, and preoperative cognition was assessed with the Mini-Mental State Examination. Plasma C-reactive protein (CRP) was detected by enzyme-linked immunosorbent assay before surgery. Preoperative pain was classified by its duration before surgery as chronic pain (lasting more than 1 month), acute pain (lasting less than 1 month), or no pain (no obvious pain). Multiple linear regression was used to adjust for confounding. Results From October 15, 2018, through August 12, 2019, a total of 67 patients were randomized; 7 were excluded because they were discharged before the seventh postoperative day. The prevalence of POD was significantly higher in the acute pain group (13 of 20; 65%) than in the chronic pain group (5 of 20; 25%) or the no pain group (6 of 20; 30%) (P  = 0.019), indicating that delirium is associated with preoperative acute pain. The plasma level of preoperative CRP was also higher in the acute pain group than in the other two groups (mean [interquartile range]: 10.7 [3.3, 29.3] vs 1 [0.5, 3.8]mg/l; P  < 0.001), suggesting that elevated preoperative plasma levels of CRP were associated with delirium. Conclusions Preoperative acute pain was associated with POD, and increased plasma levels of CRP provide a marker. In addition, we found that illiteracy and advanced age were risk factors for POD. [ABSTRACT FROM AUTHOR]