Efficacy of One Dose of Laxative on Post-Operative Constipation Following Total Knee Arthroplasty

Postoperative constipation, defined as no fully satisfying bowel movement within the first three postoperative days, is a common occurrence with some researchers estimating that between 41 and 85% of postoperative patients experience symptoms. Causes include intraoperative medications, postoperative opioid analgesics, decreased mobility, and decreased oral intake. Constipation significantly impacts quality of life following surgery. Current standard of care for preventing postoperative constipation for patients having a single total knee arthroplasty at Cleveland Clinic is discharge on postoperative day one with either a prescription to be filled for docusate sodium (brand name Colace®) 100 mg to be taken two times a day by mouth for twenty eight days or the filled prescription, plus discharge instructions on ways to avoid and treat constipation. Research results show that docusate sodium is ineffective for preventing postoperative constipation in orthopedic surgery patients, and anecdotal reports confirm this finding. The proposed study uses a 2-group non-equivalent cohort design to evaluate the effect of one standard dose (17 grams) of an over-the-counter osmotic laxative (propylene glycol (PEG 3350), brand name Miralax) by mouth prior to discharge to the current standard of care. The primary outcome measure is whether patients report of a fully satisfying, normal for them, bowel movement within the first three postoperative days. Patient reported data will be collected by phone call four to seven days following surgery. Pertinent patient characteristics will be abstracted from the electronic medical record. The sample will consist of patients over twenty years old having a single total knee arthroplasty by Drs. Stearns, Molloy, or Murray who are admitted to unit 5D at Cleveland Clinic Lutheran Hospital postoperatively. Intent to treat analysis will be performed using logistic and linear regression models, adjusting for differences between groups on patient and surgical characteristics. Based on use of a two-sided Pearson chi-square test with 80% power and significance level of 0.05, 49 patients per group are required to detect a 25% decrease in constipation rate. To account for attrition we will over sample by 50% for a total of 74 per group or 148 total participants.