A major limitation in postoperative pain management has been the fact that a patient’s personal perception of pain may not always be taken into account during preoperative pain counseling. Acute postoperative pain is a subjective and multidimensional experience that is extremely hard to measure and manage optimally. In fact, a previous study found that pre-exposure to a stressed or anxious condition significantly increased the subjective pain perception to a standard noxious stimulation than those who were pre-exposed to a happy condition [20].
Gender is commonly considered as a strong predictor of pain perception and analgesic requirements after surgery [21-22]. However, some systematic reviews have not found gender to be an independent predictor for postoperative pain levels or analgesic requirements [11]. The results of our survey suggest that female patients anticipated significantly higher pain levels preoperatively than male patients. These results support the findings of numerous previous studies [23-25]. Our analysis also found that older patients (>40 years) anticipated a lesser degree of surgical-related pain during their preoperative assessments as compared to those who were younger. We suggest that this observation may be due to the elderly having a lesser degree of preoperative anxiety and that they usually request for less information regarding their operations [26-28]. Our results are also consistent with previous prospective observational studies in patients receiving breast surgery, indicating that age had a negative impact on the prediction of acute postoperative pain [13, 29].
Previous studies have suggested that patients with psychophysical and psychosocial disorders (e.g. anxiety, depression, sleep disturbance, and catastrophizing pain) can have a decreased tolerance of or anticipate higher postoperative pain [29-33]. We collected patient information on regular benzodiazepine use for sleep disorders and the presence of depressive symptoms (screened by the Taiwanese Depression Questionnaire) during the preoperative assessment. Our results did not find any significant effects of sleep disturbance or depressive symptoms on preoperative pain anticipation. Since we used simple and short questionnaires to screen for the presence of these psychophysical disorders, this study may have been underpowered to isolate depression or sleep disturbance as predictors for the anticipation of high postoperative pain. This study also did not find significant effects of other patient variables, such as educational levels, marital status, and socioeconomic status on surgical pain intensity anticipation.
Classification of surgery type has been shown to be a clinically meaningful predictor of acute postoperative pain, as the invasiveness and incision size of procedure relate with the anticipated pain intensity [19]. We used the clinical prediction rule established by Janssen et al., in which types of surgery were graded from the lowest to the highest in regards to expected pain levels [19]. Our analysis showed a clear positive relationship between the type of operation and the patient’s anticipated pain intensity, suggesting that the invasiveness and complexity of procedure affects patients’ anticipated perception of surgical-related pain in the preoperative period [11, 19].
Preoperative anticipated pain intensity was compared with the highest postoperative pain intensity recorded in PACU and the total equivalent dose of opioids prescribed perioperatively. Our analysis found that patients who anticipated moderate-to-high pain intensity before operations were associated with significantly higher actual pain scores in the PACU and also required significantly higher doses of analgesics during the perioperative period compared to those who reported a lower preoperative pain anticipation. In current practice, anesthesiologists are more likely to prescribe postoperative analgesics based on the type and duration of the operation rather than the patient’s subjective perception of pain [34, 35]. Our results suggest that patient’s self-anticipated pain intensity may provide complementary clinical considerations for adequate management of acute pain after surgery.
After extensively reviewing 48 studies, Ip et al. identified several independent perioperative factors for predicting actual levels of postoperative pain and analgesic usage [11]. These predictive factors include the presence of preoperative pain, anxiety, age, and type of surgery (i.e. major joint, thoracic, and open abdominal surgery) and are associated with higher postoperative pain scores. Surgery type, age, and psychological distress were found to be significant predictors of analgesic usage. Ip and colleagues’ systematic review found that gender had a neutral effect on postoperative pain levels and analgesic requirements. However, the results of our study indicated that females anticipated more postoperative pain preoperatively. This major discrepancy could be due to the general understanding that female patients can react more emotionally to physical distress, but the distress is no less authentic and they are not less ill than the male patients [36-38].
The results of this study must be interpreted in light of several limitations. Firstly, patients were invited to voluntarily rate their anticipated pain intensity during their preoperative anesthesia assessment. Therefore, the knowledge, educational levels, and motives of the individual patient might impact their response to the quantitative question. Secondly, patients’ preoperative psychological conditions are routinely assessed using a culturally relevant depression screening questionnaire, the Taiwanese Depression Questionnaire (TDQ) in our hospital. This short questionnaire was designed to be simple and practical so that it could be applied to the general population in a time-efficient manner. The comprehensive versions for diagnosing depression and chronic insomnia were not used in this study. Furthermore, the use of a structured self-rating Pain Sensitivity Questionnaire may also provide higher sensitivity to predict the development of acute postoperative pain [13, 39]. Thirdly, several potential predicting factors, such as patient’s pain catastrophism, pain sensitivity, preoperative opioid intake, full history of past surgeries and traumas, and ethnicity were not investigated in this study. Although total equianalgesic doses of opioids administered during perioperative period was calculated, the use of non-opioid analgesics were not taken into account for the overall surrogate indicator for postoperative pain. Lastly, our results were not generalized to critically ill patients who were scheduled for postoperative intensive care or emergent surgery.