Effect of Peritoneal Incision on Immediate Pain After Inguinal Hernia Repair: A Prospective Cohort Study

This prospective study was conducted from February 1 to December 30, 2014, in the general surgery departments of an urban hospital, after being approved by the regional ethics review committee (Abant Izzet Baysal University Clinical Research Ethics Committee approval on 10/02/2014; approval no. 2013/43-31), and design and content of this study are fully compliant with criteria established by the STROBE (strengthening the reporting of observational studies in epidemiology) initiative.

The study enrolled 75 patients who were to undergo an operation for an inguinal hernia. Informed consent was obtained from all patients. The number of patients in the groups was calculated using a power analysis and were distributed evenly. The sample size was determined to be 15 patients per group with a power of 0.9 and 95% confidence interval. Patients were divided into 5 groups as follows:

1. Group 1: Patients had an indirect hernia. The hernia sac was excised by cutting the peritoneum and a Lichtenstein repair with mesh was performed.

2. Group 2: Patients had an indirect hernia. The hernia sac was embedded in the abdomen without a peritoneal incision. Plication sutures were placed on the defect and a Lichtenstein repair with mesh was performed.

3. Group 3: Transabdominal preperitoneal (TAPP) hernia repair was performed in all patients regardless of the type of hernia.

4. Group 4: Total extra peritoneal (TEP) hernia repair was performed in all patients regardless of the type of hernia.

5. Group 5: Patients had a direct hernia. The hernia sac was embedded in the abdomen without a peritoneal incision. Plication sutures were placed on the defect and a Lichtenstein repair with mesh was performed.

With the exception of group 5, all patients scheduled for elective surgery were consecutively distributed equally in the groups. When a sufficient number of patients was reached, a related group stopped recruiting patients. In groups 1 and 2, patients who had only a direct hernia during surgery were instead included in group 5. Patients were excluded if any of the following criteria were present: younger than 16 years (no upper age limit); pregnant females; malignancies; emergency surgeries for incarcerated and/or strangulated hernia; recurrent hernia; urological pathology (e.g., varicocele, hydrocele) in the hernia region; or hernia induced by trauma. In addition, patients in groups 2, 4, and 5 in whom the peritoneum was accidentally cut were excluded.

Laparoscopic operations (TAPP and TEP) were performed under general anesthesia while Lichtenstein repairs were performed under spinal anesthesia. Paracetamol (1 g) was administered intravenously to each patient 30 minutes before the end of the operation. Single-dose antibiotic prophylaxis (1 g ampicillin sodium) was also administered to each patient. To ensure the standardization of the surgical procedure; all the procedures were performed by the same surgeon; a standard light-weight polypropylene mesh was used in all the surgical procedures. After obtaining initial pain scores, an additional dose of paracetamol (1 g) was administered intravenously to each patient for postoperative analgesia. The mesh fixation was made with prolene sutures in open surgical procedures versus nonabsorbable staples in laparoscopic surgical procedures.

The VAS is a simple scale with a length of 100 mm on which patients were asked to rate their pain from 0 (absence of pain) to 100 (worst pain imaginable) (12). All patients were asked to mark their current sensation of pain on a VAS at 6 hours postoperatively, at the end of postoperative day 1, and on postoperative day 10. To minimize the possibility of bias, VAS measurements were performed by a single person independent from the surgical team.

Statistical analyses were performed with statistical software (SPSS 19.0, SPSS Inc, Chicago, Illinois). Distribution of data was determined by Shapiro-Wilk test. Variables were expressed as median (minimum-maximum). Continuous variables were compared with the Mann-Whitney U test for 2 groups. Kruskal-Wallis test was used to determine differences between 3 or more groups. The Dunn's test was used for post hoc analysis after the Kruskal-Wallis test. The repeated measures for analysis of variance or Friedman test was used to compare repeated measurements of the variables. Values of P < 0.05 were considered statistically significant for all tests.

We evaluated 75 patients with inguinal hernias. There were 62 (82.7%) males and 13 (17.3%) females with a mean age of 51.25 ± 15.90 years. There was no difference in sex or mean age between the groups. Postoperative complications are summarized in Table 1. There were no serious complications and there was no difference between groups according to the nonserious complication. In addition, surgical operation was not necessary for any complications.

The analyses of VAS changes among the groups and in each group are summarized in Table 2 and Fig. 1. According to the VAS scores assessed at 6 hours postoperatively between groups, the median VAS score was lowest in group 4 and highest in group 1. VAS scores were significantly lower in groups 4 and 5 versus group 1 (P = 0.006 and 0.048, respectively). According to the VAS scores assessed on postoperative day 1, the median VAS score was lowest in group 3 and highest in group 1. VAS scores were significantly lower in groups 2, 4, and 5 versus group 1 (P = 0.019, P < 0.001, P < 0.033, respectively). VAS scores were significantly lower in group 4 than group 3 (P = 0.008). According to the VAS scores assessed on postoperative day 10, the median VAS score was lowest in group 4 and highest in group 1. VAS scores were significantly lower in groups 2, 4, and 5 versus group 1 (P = 0.027, P <0.001, and P < 0.022, respectively). VAS scores were significantly lower in group 4 versus group 3 (P = 0.006). According to the VAS scores of the 5 groups, there were statistically significant differences among the 3 VAS scores at different time points (P < 0.001). VAS scores in groups 3, 4, and 5 declined gradually over time.

Analyses of differences in VAS between open and laparoscopic surgery groups and in each group are summarized in Table 3 and Fig. 2. At 6 hours, 1 day, and 10 days postoperatively, the differences were not statistically significant (P = 0.279, P = 0.424, and P = 0.051, respectively), although VAS scores were lower in the laparoscopic surgery group than the open surgery group. According to the VAS changes in the open and laparoscopic surgery groups, VAS scores decreased gradually in both groups; there was a statistically significant difference between the 3 time points (P < 0.001 for open surgery group, P = 0.006 for laparoscopic surgery group).

Analyses of VAS changes between hernia sides and in each group are summarized in Table 4 and Fig. 3. At 6 hours postoperatively, VAS scores were significantly lower in left-sided hernias than right-sided hernias (P = 0.035). At postoperative days 1 and 10, VAS scores were lower in left- versus right-sided hernias; however, the differences were not statistically significant (P = 0.491 for day 1, P = 0.176 for day 10). According to the VAS changes in the left- and right-sided hernia groups, VAS scores declined gradually in both groups, and there were statistically significant differences among the 3 time points (P < 0.001 for all).

The severity of early postoperative pain plays an important role in the development of chronic pain. The pathophysiologic mechanisms of early postoperative pain include perioperative nerve damage, sensitization of nociceptors, early postoperative ectopic activity of injured primary afferents, and central sensitization.¹¹  This trial was a prospective clinical study on the effects of peritoneal incision on immediate pain after inguinal hernia repair.

Several preoperative (young age, female sex, genetic predisposition); perioperative (less experience, open repair procedure, nerve neurolysis); and postoperative risk factors (High early postoperative pain intensity, postoperative complications for the development chronic pain have been identified.¹¹  These factors can vary from patient to patient. Preoperative risk factors are closely associated with the individual patient and cannot be changed. However, various perioperative and postoperative risk factors can be avoided.

The first factor associated with postoperative pain is the use of mesh. Mesh repair is considered to be more effective in reducing recurrence and postoperative pain, in comparison with no-mesh repair. In addition, the structure of the mesh is an important factor in the development of postoperative pain, and use of a synthetic nonabsorbable flat mesh or composite mesh is recommended because these cause less pain.¹¹  Post et al¹³  reported that the pain might be caused by the weight and composition of the mesh, and that the sensation of a foreign body was higher in the heavyweight mesh group. In contrast, Bringman et al¹⁴  found no difference in postoperative pain between lightweight and heavyweight mesh groups. Another factor associated with mesh is fixation method. The use of staples to fix the mesh reduced both the operation time and time to return to normal activity, but did not affect the rates of complications or postoperative pain.¹⁵  However, in one meta-analysis, glue fixation of the mesh was shown to reduce both postoperative pain and time to return to normal activity.¹⁶ 

The second issue associated with postoperative pain is identification and protection of the inguinal nerves. The identification of neuronal anatomy and the protection of nerves in the surgical region are important in reducing the risk of postoperative pain. However, practically, identification of all 3 nerves including the ilioinguinal, iliohypogastric, and genitofemoral nerves is quite poor. In one study, Ravindran et al¹⁷  found that the ilioinguinal nerve was routinely identified by 88% of surgeons, the iliohypogastric nerve by 58%, and the genitofemoral nerve by 54%. A prospective multicenter study showed that the overall pain rate was 5.5% when all 3 nerves were identified.¹⁸  We usually protect all nerves seen during open surgery. When accidentally severed, we ligate the nerve ends to reduce postoperative pain. Additionally, we strive not to put staples on nervous tracings during laparoscopic surgery.

The third factor associated with postoperative pain is the form of hernia surgery. Compared with open surgery, laparoscopic surgery may result in less postoperative pain. Additionally, other important advantages of the laparoscopic method are the short time to return to normal activity, good cosmetic results, and lower recurrence rates. The low pain rates in laparoscopic procedures are due to the shape of the mesh fixation and avoiding neuropathic complications without increasing the recurrence rate through fixation of abdominal pressure. Disadvantages of laparoscopic methods are the use of general anesthesia and longer duration of surgery.^19,20  Erhan et al⁸  found no difference in postoperative pain between Lichtenstein and preperitoneal hernia repair groups. In contrast, Liem et al²¹  showed that postoperative pain was reduced in a laparoscopic group than with conventional anterior surgery. In our study, although VAS scores were higher in the open surgery group than the laparoscopic surgery group, there was no statistically significant difference at any time point.

The final factor associated with postoperative pain is the process of inflammation in the surgical field, and this is main topic related to this study. Nociceptors located in primary afferent nerve endings are neurological receptors sensitive to stimuli caused by tissue damage. These receptors are found in the skin, periosteum, joints, muscles, visceral tissues, and peritoneum.^22–24  Postoperatively, inguinal nerves can become damaged due to enclosure within a meshoma, excessive fibrotic reaction, or inflammatory processes.¹¹  After trauma to the peritoneum, vascular permeability in vessels supplying the damaged region increases, inflammatory cells are released and, ultimately, there is formation of a fibrin matrix and an inflammatory response occurs.²⁵  This inflammatory response to surgery may lead to activation of peripheral nociceptors, causing postoperative pain.¹¹  Thus, as long as surgical trauma increases, postoperative pain will increase. In a study conducted by Muzio et al²⁶  found that there was no effect on the outcome and late postoperative pain of peritoneal tears in TEP inguinal hernia repair. In our study, at 6 hours postoperatively, VAS scores were significantly lower in group 5 than in group 1 (P = 0.048), but there was no difference between groups 2 and 5. VAS scores were significantly lower in group 4 than group 3 (P = 0.006). At postoperative days 1 and 10, VAS scores were significantly lower in groups 2 and 5 versus group 1 (P = 0.019 and 0.033, respectively, for day 1; P = 0.027 and 0.022, respectively, for day 10), while there was no difference between groups 2 and 5. VAS scores were significantly lower in group 4 than in group 3 (P = 0.006) at day 10 while they were significantly higher in group 4 than in group 3 (P = 0.008) at day 1.

In conclusion, postoperative pain is an inevitable result of hernia surgery. There are many risk factors for postoperative pain. Each patient should be assessed individually and patient-specific surgical procedures must be selected because these factors vary among individual patients. Prevention of postoperative pain is important in terms of early discharge, early return to normal activity, cost effectiveness, and reducing the development of chronic pain. In this study, we found that a peritoneal incision is a significant risk factor for postoperative pain, but a laparoscopic approach is not. The most important limitations of this study are the small number of patients, limited follow-up, and because operation time was not measured, its effect on pain was not given. An investigation of the effects of peritoneal incision on chronic pain development with extended follow-up is warranted.

The authors declare no conflict of interest.