Introduction

Cesarean section is a surgical procedure that is performed in case the maternal and neonatal life is at risk. Although the rate of cesarean section is recommended to be less than 15%, some countries have recorded a much higher rate for this procedure. Iran has a variable prevalence rate of cesarean section in different regions; however, this rate is reported to be 48% in this country (1).

Postoperative gastrointestinal tract dysfun-ction is common in operated patients, occurring as a result of delay in gastrointestinal movements (2). According to the European Society of Anesthesiology guidelines, adult patients undergoing elective surgery and caesarean section should be encouraged to take clear liquids before their surgery. Up to 6 h before surgery, solid foods are prohibited (3). Early oral hydration can be helpful in returning bowel movements and reducing induced
ileus (4).

The use of chewing gum is also another inexpensive method in the restoration of bowel movements (5). It seems that chewing can stimulate the gastrointestinal tract hormones and mimic cephalic-vagal reflex. Nonetheless, there is controversy in the findings of the studies assessing the effect of chewing on post-operative ileus(5, 6). Regarding this, the present study was conducted with the aim of evaluating the effect of chewing gum on mitigating ileus in cesarean patients at Sabzevar Mobini Hospital, Sabzevar, Iran,
in 2014.

Materials and Methods

This randomized clinical trial (trial registration number: IRCT2015041221710) was conducted on 93 patients undergoing elective or urgent cesarean section at Shahidan Mobini Hospital between July 2013 and September 2014. The participants were randomly divided to the case (n=35) and control (n=58) groups (Figure 1). Sample size was calculated based on the following formula:

N=2((Z_1-α+ Z_1-β)/σ₀)² × P × (1-P)

Based on the findings of the previous studies,

     Figure 1. Flowchart of the study design

the mean times to resume bowel sounds were 4.7 and 7.15 h in the intervention and control groups, respectively. Therefore, considering 95% confidence interval and 95% power, the sample size was calculated as 40 subjects in each group.

The inclusion criteria were: 1) undergoing cesarean section (Pfannenstiel incision or horizontal uterine incision) with general anesthesia, 2) nulliparity, 3) ability to chew gum, 4) no previous history of abdominal surgery, preeclampsia, diabetes, and cardiac diseases, and 5) willingness to participate in the study.

On the other hand, the exclusion criteria included: 1) having operation longer than
90 min, 2) suffering from post-operative complications (e.g., uterine atony) and intra-operative complications (e.g., sever adhesions, blood transfusion, and vesical or intestinal injuries), 3) receiving magnesium sulfate administration, 4) having previous history of any malignancy, inflammatory and obstructive bowel disease, or history of receiving antibiotic therapy for more than 4 days, and 5) undergoing cesarean section with hysterectomy or tubal ligation.

Every eligible patient filled written informed contest. All the operations were carried out between 9 and 11 a.m. The patients in the case group were encouraged to chew gum 1-4 h post-surgery, four times a day for 15 min. The control group took standard regular postpartum workups. All patients were prohibited to consume any drug or feed orally.

Study parameters

The data collection was accomplished by filling a questionnaire through interviews performed by a research assistant, blinded to the study. Post-operative pain was estimated after 6, 12, 18, and 24 h of the first use of chewing gum in a recumbent position. In addition, pain at the time of leaving bed and discharge was assessed using a Visual Analogous Scale. Hourly intestinal sounds auscultation was performed for both groups until the restoration of the bowel sounds, and the duration between recovery and initiation of bowel sounds was recorded for each patient.

Vital signs were recorded in the ward every 6 h after recovery. Each patient was taught to report the initial gas passing, defecation,
and sensation of bowel movement. Other
study parameters, including age, occupation, education level, gender, neonatal weight, APGAR score, addiction, number of abortion, usage of supplements during gestation, position of the placenta, and fetus presentation, were also obtained from the subjects during the interview.

The case and control groups were matched for the dosage of analgesics and laxatives,
vital signs, pain, gastrointestinal problems, hemoglobin, hematocrit, and white blood cells. The patients were discharged when they could tolerate oral feeding, urinate, walk, and have stable vital signs. The investigated variables entailed vital signs, constipation, timing of ambulation, gas passing, objective and subjective signs of bowel motion (e.g., bowel sounds and sensation of bowel movements), and post-operative pain (i.e., immediately after recovery, 6, 12, 18, and 24 h after recovery, as well as pain severity in bed and during movements out of bed).

Statistical analysis

Data analysis was performed using SPSS software, version 21 (IBM Inc, Chicago, ll). Continuous data were checked for normality using Shapiro-Wilk test. Mean and standard deviation were used for normally distributed data, while median and inter quartile range (IQR) were utilized for non-normally distributed data. The inter-group comparison of the normally distributed data was accomplished using the independent Student's t-test. Furthermore, the Mann-Whitney test was run to compare the non-normally distributed data between the groups.

The categorical data were presented as frequency and percentage. The Fisher's exact test was used to assess the association between categorical variables and study groups. In addition, the assessment of the effect of chewing gum on the severity of pain after surgery and after 6, 12, 18, and 24 h of chewing the first gum was performed by means of the repeated measures analysis of variance (ANOVA) test, while controlling for operation duration as a confounder.

Additionally, the logistic regression models were run to estimate the relationship between chewing gum and gas passing, initiation of bowel sounds, bowel motion sensation, pain in bed and after leaving bed, constipation, gastrointestinal complications, and post-operative pain, while controlling for operation duration as a confounder. Odds ratio (OR) and 95% confidence interval for OR was calculated. P-value less than 0.05 was considered statistically significant.

Results

Out of the 93 patients enrolled in this study, 5 patients were excluded due to personal unwillingness, post-operative complication, and being fed orally. The remaining patients were randomly divided into the case (35 patients, 37.6%) and control (58 patients, 62.4%) groups. The demographic data of the participants are tabulated in Table 1. Most of the patients were admitted for elective cesarean section (33%).

The mean gestational ages of the case and control groups were 39.22±1.86 and 39.06±1.28 years, respectively. The majority of the fetuses had cephalic presentation. Furthermore, four patients in each group had constipation; therefore, there was no significant difference between the two groups in terms of constipation (P=0.35).

Gastrointestinal problems were present in 49 patients (i.e., 21 and 28 patients in case and control groups, respectively); accordingly, both groups showed no significant difference in this regard (P=0.19). The initiation of bowel movements and other study parameters were evaluated in both groups (Table 2). Good level of satisfaction was recorded in 30 (85.7%) patients, who had received gum, and in 45 (77.6%) patients in the control group (P=0.35).

Table 1. Demographic characteristics of the case and control groups

ǂ Mean and standard deviation were used to describe continuous variables and the independent Student's t-test was used for comparison.

⁑ Frequency and percentage were used to describe categorical variables and the Fisher’s exact test was used to assess the relationship between these variables and chewing gum.

Table 2. Comparison of study outcomes after operation between the study groups

ǂ Mean and standard deviation were used to describe all continuous variables and independent t-test was used for comparison, except for bowel movement sensation where median and interquartile range and the Mann-Whitney test were used for comparison.

* Significant difference between groups at α=0.05

Table 3. Relationship between chewing gum and outcome measures while controlling for operation duration and age

* Significant relationship

Table 4. Repeated measures ANOVA for vital signs and pain severity during the study duration

* Significant difference at α=0.05

^a P=0.03,

Logistic regression models revealed that chewing gum was significantly associated with reduced post-operative pain (OR: 0.79, 95% CI for OR=0.63, 0.99), while controlling for surgery duration as a confounding variable (Table 3).

The repeated measures ANOVA with age, occupation, education, and the length of surgery as confounding factors only showed a significant difference in respiratory rate between the groups at the 12^th h of assessment (Table 4). The changes in the evaluated study parameters during the study after controlling for confounders are depicted in Figure 2.

Discussion

Based on our study protocol, we evaluated different variables in our study population, such as constipation, gas passing, objective and subjective signs of bowel motion, and pain after surgery. However, only post-operative pain was significantly affected by chewing gum. The results revealed no significant relationship between chewing gum and resumption of normal bowel movements.

The pathogenesis of failure in the restoration of bowel movements is multifactorial, including intestinal manipulation during surgery, anesthetic drugs, and narcotics administration, which can interfere with parasympathetic nervous system function (7, 8). There is no universal treatment for this gastrointestinal problem; however, the insertion of nasogastric tube, local anesthesia, parenteral nutrition, and other invasive methods were also studied (8).

Previously, the patients were withheld from the oral consumption of food and liquids till the returning of the bowel sounds. However, nowadays, early oral feeding is believed to be capable of inducing bowel movements (9, 10). Nonetheless, there is controversy over the findings of these studies (11).

Chewing gum is a noninvasive and inexpensive way of stimulating relaxation by inducing the vagal reflex and increasing intestinal hormones (6). As a result, gastrin and

(A) Pain severity, (B) Pulse rate, (C) Respiratory rate, (D) Blood pressure, (E) Temperature

Figure 2. Changes in pain severity and vital signs during the study procedure after controlling for age, occupation, education, and length of surgery