In recent years, laparoscopy is being utilized frequently in various procedures. It could relieve postoperative pain and be beneficial to the patients’ recovery. However, hepatobiliary and pancreatic surgery (without cholecystectomy) are still the more traumatic types of abdominal surgeries. The extant literature on pain describes moderate-to-severe pain intensities of 42% on day 1 and 33% on day 2 after living donor hepatectomy [8]. Another study found that the incidence of postoperative pain after urological and hepatobiliary operation was 64.8% [9]. In our retrospective cohort study, the occurrence rate of moderate-to-severe pain was 8.4% in postoperatively of major hepatobiliary and pancreatic surgeries. This may be due to different population characteristics, types of operation, postoperative analgesia, and the analgesic drugs used. In addition, the relevant literature was studied several years ago, whereby enhanced recovery after surgery (ERAS) and multimodal analgesia programs were not used. Hence, the incidence of postoperative acute pain would be higher.
The other finding of this study is that age, BMI, laparoscopy, and different postoperative analgesic drugs are significant risk factors for postoperative pain following these surgeries.
Although many studies have confirmed that postoperative pain decreases with age [10, 11], some have found no age-related differences [12]. Therefore, it is unclear whether postoperative pain is associated with age. This study supported that younger people are more likely to experience postoperative pain, and the incidence of postoperative pain decreased by 3% with increasing age (OR, 0.97; 95% CI, 0.95 to 0.98). Furthermore, comparisons of groups with interquartile ranges also showed corroborating conclusions. This is perhaps related to changes in the inflammatory response, immune system, pain processing, autonomic nervous system, and pain regulation [13, 14]. Moreover, the thermal and mechanical thresholds measured on the skin using quantitative sensory testing (QST) was found to be increased in the elderly [15, 16].Furthermore, elderly patients may have a higher pain threshold and show increased sensitivity to opioids, which is related to pharmacokinetic and psychosocial mechanisms [17, 18]. Compared to articles with different conclusions, the differences may be due to the different types of operation and the small sample size of that literature.
Currently, the effect of BMI on postoperative pain remains unclear. Patients with a high BMI are more likely to experience postoperative pain in some literatures [19–21], while others have shown that there is no such relationship [22, 23]. As we know, there are no reports on the relationship between BMI and postoperative pain after major hepatobiliary pancreatic surgery. The results of this study suggest that the incidence of postoperative pain is higher in patients with low BMI. A 1 kg/m2 increase in BMI was associated with a decreased risk of postoperative pain by 6% (OR, 0.94; 95% CI, 0.89 to 0.98, P = 0.018), and the incidence rate of pain increased in the group with BMI < 25 kg/m2 24 hours after surgery. People with a normal body fat percentage may have a higher metabolic rate, more active enzymes in the body, and a faster metabolism of analgesics. Patients with a low BMI are mostly associated with frailty and are more likely to experience postoperative complications, leading to postoperative pain. Future studies should demonstrate possible mechanisms and causal associations in this regard.
In the current trial, the use of sufentanil for postoperative analgesia increased the risk of postoperative pain by 4.38 times (OR, 4.38; 95% CI, 3.2 to 5.99, P < 0.001) as compared with butorphanol. Furthermore, butorphanol is an opioid agonist-antagonist that induces analgesia mainly through κ agonist receptors. Like traditional opioids, butorphanol inhibits the upload of noxious stimuli in the spinal dorsal horn and activates the pain control circuit transmitted from the midbrain to the spinal dorsal horn via the rostral ventromedial region (RVM), resulting in analgesic effects. Furthermore, patients undergoing hepatobiliary surgery usually experience visceral pain caused by laparoscopic peritoneal stretching, intraoperative visceral pull, and visceral ischemia. Butorphanol is more effective in suppressing visceral pain, with a lower incidence of associated adverse effects such as vomiting, nausea, dizziness, and respiratory depression as compared to pure α-receptor agonists [24, 25].
In this study, cholecystectomy alone was excluded, mainly because the trauma, operation time, postoperative analgesia type, and postoperative pain incidence rate of this surgery were significantly different as compared to other surgery types; thus, the data for major hepatobiliary and pancreatic surgeries except cholecystectomy were analyzed.
Although females report greater postoperative pain in different procedures than males [10), this was not observed in the present cohort. Diabetes, educational level, and method for anesthesia were not associated with postoperative pain. Unfortunately, general anesthesia combined with nerve block did not result in a better postoperative analgesic effect. Considering that nerve block was generally performed before surgery in our center, the effect of the block failed to last for 24 hours after surgery. Rebound tenderness may have been triggered, so it did not show an inherent advantage in VAS score 24 hours after surgery. Relevant prospective trials should be conducted to verify the specific effects of nerve block.
The overall incidence of postoperative nausea and vomiting in patients was relatively low, mainly due to the extensive measures taken in our center such as volume repletion, prevention of the use of dexamethasone and tropisetron, and other measures. However, the incidence in patients with moderate-to-severe pain is higher, which may be related to laparoscopic surgery, opioid use, motion sickness, and other factors. Similar to other studies, we found that moderate-to-severe postoperative pain was associated with a longer postoperative hospital stay.
This study had some limitations. First, it was retrospective in nature. Confounding variables of pain such as relevant psychological disorders were not included in our study. Second, postoperative pain is an individual experience that involves psychosocial, environmental, and genetic factors. These limitations should be taken into account while attempting to predict pain.