A prospective randomized, double blinded clinical trial of ketamine use in adult colorectal surgery patients will be conducted. The experimental arm of the trial will receive ketamine infusion therapy while the control arm of the trial receives saline placebo infusions at an equivalent rate. All patients enrolled into the trial will be enrolled in a standardized Enhanced Recovery after Surgery (ERAS) pathway which includes intravenous opioid medications for breakthrough pain, scheduled acetaminophen, and NSAIDs as indicated. All patients will be managed in accordance with the appropriate Division of Trauma and Acute Care Surgery and Division of Colorectal Surgery policies.

Potential participants will be screened at the time of outpatient clinic visits. Patients who require operative intervention for management of their colonic disease, both malignant and non-malignant, are eligible for enrollment. Individuals who present to the emergency department and are evaluated by the previously mentioned divisions will be screened for eligibility. If a potential participant qualifies for enrollment, he or she will be approached by one of the IRB approved study staff for consent. Prior to randomization and formal enrollment, an investigational drug services pharmacist will screen for any contraindication to potential ketamine therapy. Following investigator and pharmacy approval, patients will be randomized by the Investigational Drug Services (IDS). The two trial arms will be randomized in a 1:1 control to experimental fashion with randomization blocks conducted in sets of 4 patients.

Participants who are enrolled into the trial will undergo randomization into either the experimental or control arm by the IDS department at time of presentation to the hospital. The infusate will be prepared by the IDS department at a ketamine concentration of 500mg/250ml with all IV bags labeled "Investigational Ketamine / Placebo - PRO27024" prior to dispersal to the pre-operative nurse. All elective surgery patients will receive alvimopan beginning in the pre-operative area and administered by the RN at least 30 minutes prior to administration of narcotic medications. A total of 60 patients will be enrolled (see sample size calculation in c.2.3), 30 into each arm. All infusion rates will be calculated based on ideal body weight (IBW), unless actual body weight (ABW) is less than ideal. IBW is calculated for males as 50kg + 2.3\*(number of inches over 5 feet) and for females as 45.5kg + 2.3\*(number of inches over 5 feet). All investigational infusions will be started by the anesthesia resident or Certified Registered Nurse Anesthetists (CRNA) at the time of anesthesia induction. Patients will receive a bolus of the investigational solution at a calculated dose of 0.25 mg/kg over 5 minutes following anesthetic induction. A continuous infusion of the investigational solution will immediately follow at a rate of 2 mcg/kg/min. Timing of bolus administration along with time of initiation of continuous infusion will be documented with the continuous infusion to run for a duration of 48-hours.

All subjects will be assessed daily or more frequently for delirium. The institutional CAM and CAM-ICU Delirium screens, which have been validated in the literature, will be utilized (see appendices IV and V). Subjects may remove oneself from the trial or be un-blinded should he/she, pharmacy, and/or clinical staff deem it medically necessary. Medical necessity is determined by inability to treat without knowledge of trial assignment; otherwise treating staff will assume all patients have received ketamine. All adverse events will be recorded and if necessary subjects will be un-blinded in the event of a serious adverse event.

All adverse events will be recorded and if necessary subjects will be un-blinded in the event of a serious adverse event. The research team will monitor all study patients for any adverse event trends. Patients will be followed through the time of discharge.