A total of 22,600 patients with cancer after elective radical surgery were included in this study, and the incidence of moderate-to-severe pain in the PACU was 1.42%. Multivariate logistic regression analysis showed that male sex, chest surgery, abdominal surgery, intraoperative haemorrhage, intraoperative use of NSAIDs drugs, duration of anaesthesia, postoperative vomiting, and hypothermia were risk factors for postoperative moderate-to-severe pain of PACU in patients with malignancy. Female sex and intraoperative NSAID use were protective factors. Moderate-to-severe pain in the PACU is associated with hypertension, hyperglycaemia, dysphoria, and hypoxemia.
In contrast to previous studies,4 the incidence of moderate-to-severe pain in the PACU was low in this study. The reasons for this are as follows. First, patients with cancer after elective radical surgery were selected as subjects. Second, most patients routinely use patient-controlled analgesia. Finally, all the patients were admitted to the PACU at our hospital after extubation. The patient will only stay in the recovery room for 1 h unless special circumstances occur.
There were sex-related differences in pain. In contrast to previous studies,11 the incidence of moderate-to-severe pain in the PACU in the male group was higher than that in the female group in this study. Male sex was a risk factor for moderate-to-severe pain in the PACU. Patients with malignant tumours selected in this study required intraoperative indwelling catheters because of the long surgery time. In the PACU, the incidence of dysphoria due to catheter-related bladder discomfort was significantly higher than that in women12 (chi-square value = 149.84, P < 0.001). Postoperative dysphoria can result in incision pain in males.
Surgery, as a type of stimulation, can cause local or systemic inflammation, which can lead to pain. Surgery can lead to a breakdown of the integrity of the skin, resulting in exposure of nerve endings in the skin, which can be stimulated to produce ectopic electrical currents that cause pain.13 This study confirmed that the incidence of moderate-to-severe pain in the PACU was significantly higher in chest and abdominal surgeries.
NSAIDs are the first-line treatment option for most patients with acute mild-to-moderate pain.14 NSAIDs can not only inhibit prostaglandin synthesis but also inhibit lymphocyte activity and activation of T lymphocyte differentiation and reduce the stimulation of afferent nerve endings. It acts directly on nociceptive receptors and prevents the formation and release of pain-causing substances.15 NSAIDs are widely used because they are non-addictive. This study found that the intraoperative use of NSAIDs was a protective factor against moderate-to-severe pain in the PACU. However, when the dosage of NSAIDs drugs exceeds a certain level, even additional dosage cannot increase the analgesic effect, so it should be used appropriately and reasonably.
Previous studies have found that the incidence of postoperative pain is higher when the operation time exceeds 3 h.16 This study also confirmed that the duration of anaesthesia was an independent risk factor for moderate-to-severe pain in the PACU. A longer operation time may result in severe tissue damage at the surgical site, increased release of inflammatory mediators, decreased threshold of nociceptors controlling inflammatory tissues, and an enhanced response to normal sensory conduction, resulting in peripheral sensitization. Simultaneously, the release of excitatory amino acids from primary neurons activates excitatory amino acid receptors in the spinal cord, resulting in a high response to nociceptive afferent stimuli (central sensitization).
Postoperative vomiting will increase abdominal muscle tension, aggravating abdominal pain and discomfort.17 This study showed that the incidence of moderate-to-severe pain in the PACU in patients with postoperative vomiting was significantly higher than that in patients without vomiting.
The results of this study suggest that hypothermia is an independent risk factor for moderate-to-severe pain in the PACU. When the body is at a low temperature, in order to protect the heart, brain, and other important organs, the blood supply is reduced to the non-vital organs; such protection for a long time may lead to the anaerobic metabolism of the non-vital organs, causing the accumulation of lactic acid and other harmful substances, resulting in postoperative pain for patients.18 Therefore, the incidence of moderate-to-severe pain in the PACU in patients with intraoperative hypothermia is higher than that in patients with normal body temperature. In addition, studies have shown that the incidence of moderate-to-severe pain in the PACU in patients with massive intraoperative haemorrhage is higher than that in patients without massive haemorrhage, which may be caused by the reduction of haemoglobin during massive haemorrhage, resulting in hypotension, hypoperfusion, and lactic acid accumulation,19 thus causing postoperative pain.
Previous studies have shown that preoperative chronic pain and anxiety are significantly associated with postoperative acute pain. However, this was a single-centre, retrospective study; therefore, complete data were missing. However, this study explored the risk factors of moderate-to-severe pain in the PACU for patients with cancer after elective radical surgery based on big data, so it is still of high clinical significance.