Study cohort
Four hundred and forty-nine adults undergoing elective colorectal surgery at the Department of Surgery, Umeå University Hospital, from March 2013 to April 2017 were eligible for inclusion. Fifteen patients were excluded; four because of postoperative confusion, five because they were intubated and treated in a respirator after surgery, and six because the NRS had not been recorded on any of 4 days. Seven patients, four colonic resections, and three anterior resections were converted from minimally invasive surgery to open surgery, and they all received an epidural catheter immediately after surgery for postoperative analgesia. Converted patients were regarded as open surgery in the analysis since they were given the same pre-medication, and all of them received an epidural catheter immediately after surgery for postoperative analgesia.
The analysis was based on the 434 included patients. The majority had undergone colorectal surgery due to cancer (90%). Baseline characteristics are presented in Table 1.
Table 1 Baseline characteristics Postoperative pain after colorectal surgery
Half the patients experienced moderate to severe pain (NRS > 4) on the day of surgery, followed by 64% on postoperative day 1, 59% on day 2, and 51% on day 3 (Fig.1). Patients younger than 45 years of age had more pain on the day of surgery compared with patients older than 75 with a mean NRS of 5.8 (95% CI 3.6 to 8.0) vs. 2.6 (95% CI 1.9–3.4) respectively, P = 0.01 (Fig. 2).
Patients undergoing minimally invasive surgery vs. open surgery had more pain on the day of surgery and scored a mean of 4.5 (95% CI 3.9 to 5.1) vs. 3.4 (95% CI 2.9 to 3.9) respectively on the NRS, P < 0.001. On postoperative day 2, patients undergoing minimally invasive surgery had less pain compared with open surgery, 3.6 (95% CI 3.0 to 4.2) vs. 4.4 (95% CI 4.0 to 4.8) respectively, P = 0.038, while there was no difference in pain on postoperative days 1 and 3 (Fig. 3a). After minimal colonic resection vs. open surgery, patients had more pain expressed on the NRS on the day of surgery of 4.8 (95% CI 4.0 to 5.6) vs. 3.3 (95% CI 2.9 to 3.9) respectively (P = 0.006), while they had less pain on postoperative day 2 of 3.0 (95% CI 2.2 to 3.9) vs. 4.8 (95% CI 4.2 to 5.4) respectively (P = 0.001) and postoperative day 3 of 2.3 (95% CI 0.9 to 3.6) vs. 4.4 (95% CI 3.8 to 5.1) respectively (P = 0.006) (Fig. 3b). There was no significant difference in pain after minimally invasively vs. open anterior rectal resection and abdominal perineal rectal excision (Fig. 3c, d).
The interindividual pain response to surgery was large. Postoperative pain ranged from 0 to 10 after both minimally invasive and open colon and rectal surgery, despite adherence to the same pain management protocol (Fig. 4a–c).
Postoperative course
A complication of any kind, including surgical, infectious, respiratory, and heart complications, was recorded in 239 patients (55%) within 30 days after surgery. A severe complication defined as Clavien-Dindo 3b or more occurred in 44 patients (10%) and 20 patients (4.6%) had an anastomotic leakage. The mean and standard deviation (SD) length of stay was 9 (9) days. On postoperative day 1, mean (standard deviation) high-sensitivity CRP was 73 (47) followed by 161(86) and 137 (79) on postoperative days 2 and 3.
Risk factors for postoperative pain
Univariable analysis
In unadjusted analysis, age, diabetes mellitus, undergoing surgery for cancer, minimal vs. open surgery, having any complication, and CRP were significantly related to the NRS on any postoperative day (Table 2). There was no association between postoperative pain and gender, BMI, smoking, ASA class, preoperative chemo- or radiotherapy, or length of hospital stay.
Table 2 Unadjusted linear regression analysis on factors for maximum pain (NRS) on postoperative days 0–3 Multivariable analysis
Adjusted linear regression analysis revealed that age, diabetes mellitus, any complication, and open vs. minimally invasive surgery were independent factors associated with a higher or lower NRS (Table 3). Pain was reduced with increasing age on postoperative days 0–2, while the NRS was reduced by 0.7 units per 10 years on the day of surgery (95% CI 0.5 to 0.9, P < 0.001) (Table 3, Fig. 2), thereby indicating that young subjects suffered from more pain than older subjects. On the other hand, patients with diabetes mellitus reported less pain by a mean of − 1.3 NRS (95% CI − 2.4 to − 0.2, P = 0.025) on the day of surgery. Having any complication after surgery was independently related to more pain on postoperative day 2 by 1.1 NRS (95% CI 0.2 to 2.0, P = 0.02). High CRP levels on postoperative day 1 were related to less pain on that day by 0.15 NRS/10 units of CRP (95% CI − 0.26 to − 0.04, P = 0.008), while high CRP on postoperative day 3 was related to more pain by 0.07/10 units of CRP (95% CI 0.01 to 0.12, P = 0.038).
Table 3 Adjusted linear regression analysis on factors for maximum pain (NRS) on postoperative days 0–3 Patients undergoing minimally invasive colonic surgery had more pain than patients undergoing open surgery on the day of surgery by 1.6 NRS (95% CI 0.6 to 2.6, P = 0.002), while those undergoing open surgery had more pain on postoperative day 2 by 1.5 NRS (95% CI 0.4 to 2.5, P = 0.006) and day 3 by 1.9 NRS (95% CI 0.4 to 3.3, P = 0.011) (Table 3). There was no significant difference in postoperative pain on any day between open anterior resection vs. minimally invasive surgery, or between open abdominal perineal excision and minimally invasive surgery (Table 3).
Sensitivity analysis
Seven patients were converted from minimally invasive surgery to open surgery and are regarded as open surgery in the above analysis. The results did not change when these seven converted patients were excluded.