Effect of Intravenous Acetaminophen on Postoperative Opioid-related Complications

Some patients have respiratory depression (decreased breaths per minute) after surgery. Acetaminophen, an FDA approved pain medication, may prevent this problem. The purpose of this study is to determine if acetaminophen decreases respiratory depression after surgery. The investigators will also evaluate the cost effectiveness of acetaminophen. Patients having elective major abdominal surgery are being asked to participate in this research study. If eligible, a patient will have their baseline tidal volume (amount of air moved into or out of the lungs) and vital capacity (how much air the lungs are capable of holding) measured using a spirometer (apparatus for measuring the volume of air inspired and expired by the lungs) measured before surgery. Three questionnaires will also need to be completed before surgery. The patient will then be randomized, like flipping a coin, to receive either Acetaminophen or placebo (inactive substance) as an infusion throughout surgery and for the first two days thereafter. Neither the patient nor his or her physician will know if the patient is assigned to study drug or placebo. Regardless of study assignment, both groups will receive standard pain management medications and sedation. After surgery, the patient's blood pressure, activity, posture, respiratory rate, the electrical activity of the heart, oxygen saturation, tidal volume, minute ventilation and respiratory rate will be continuously monitored and recorded for 48 hours using a wireless pulse-oximeter and a respiratory volume monitor. 48 hours after surgery the patient will be asked to complete a patient satisfaction questionnaire, which will allow the patient to rate the satisfaction with the treatment received for pain. The patient will also be asked to complete a questionnaire about recovery. At discharge, the patient will be given two questionnaires about pain and quality of life.

0.9% sodium chloride infusion will be initiated before the surgical incision with 100 ml and repeated every 6 hours for the earlier of 48 postoperative hours of hospital discharge.

Acetaminophen infusion will be initiated before the surgical incision with 1 g and repeated every 6 hours for the earlier of 48 postoperative hours of hospital discharge.

Hypoxemia is measured as minutes with hypoxemia (Spo2 <90%) per hour of successful Spo2 monitoring. Patients will have nearly continuous pulseoximeter monitoring and recording. Data from the monitor will be downloaded daily for 48 hours postoperatively.

Pain scores were calculated on a visual analog scale of 0 to 10, with 0 being no pain and 10 being the most pain imaginable; time weighted mean was calculated as the area under the curve of the pain score measurements divided by total measurement time. Pain was recorded at roughly 15-minute intervals in the postanesthesia care unit and at 4-hour intervals on surgical wards

Pain scores were calculated on a visual analog scale of 0 to 10, with 0 being no pain and 10 being the most pain imaginable; time-weighted mean was calculated as the area under the curve of the pain score measurements divided by total measurement time.

Fatigue scores were calculated on a scale of 1 to 10, with 1 being no fatigue and 10 being the worst fatigue imaginable.

Sedation was estimated by the RASS score and recorded at 2-hour intervals by ward nurses per clinical routine during the initial 48 postoperative hours. The Richmond Agitation-Sedation Scale (RASS) is scored from -5 to +4, with -5 being unarousable, 0 being alert and calm, and +4 being combative.

Total opioid consumption over the initial 48 postoperative hours was extracted from patients' medical records and converted to intravenous morphine equivalents

Patients were asked about postoperative nausea and vomiting in the postanesthesia care unit, at 4-hour intervals while awake through the remaining initial day of surgery, and on the first and second postoperative mornings.

A low respiratory function event was defined as an episode of less than 40% of predicted minute ventilation for 2 minutes.

Inclusion Criteria: Written informed consent 18-85 years old above 50 kg American Society of Anaesthesiologists Physical Status 1-3 Scheduled for elective open or laparoscopic abdominal surgery, including colorectal, prostate, and hysterectomy surgeries Patients with anticipated hospitalization of two nights Expected to require parenteral opioids for at least 48 hours for postoperative pain Able to use IV Patient-Controlled Analgesia systems Exclusion Criteria: Hepatic disease, e.g. twice the normal levels of liver enzymes Kidney disease, e.g. twice the normal level of serum creatinine Epidural analgesia or regional blocks (including Transverse abdominis plane block) Acetaminophen sensitivity or known allergy Female patients who are pregnant or breastfeeding Patients taking warfarin

Turan A, Essber H, Saasouh W, Hovsepyan K, Makarova N, Ayad S, Cohen B, Ruetzler K, Soliman LM, Maheshwari K, Yang D, Mascha EJ, Ali Sakr Esa W, Kessler H, Delaney CP, Sessler DI; FACTOR Study Group. Effect of Intravenous Acetaminophen on Postoperative Hypoxemia After Abdominal Surgery: The FACTOR Randomized Clinical Trial. JAMA. 2020 Jul 28;324(4):350-358. doi: 10.1001/jama.2020.10009.