Effect of intravenous acetaminophen on post-operative opioid-related complications: study protocol for a randomized, placebo-controlled trial

Background: Unrelieved post-operative pain leads to physiological and psychological consequences which worsen outcomes. Patients still report a 31% incidence of severe pain and 47% incidence of moderate pain after surgery. Multimodal analgesia aims to improve satisfaction while reducing side effects. Opioids are the most common treatment for post-operative pain; however, acute tolerance and opioid-induced hyperalgesia increase opioid requirements and the risk of side effects. Previous studies with acetaminophen have shown consistent and clinically important opioid-sparing effects but were unable to demonstrate significant reductions in opioid-related adverse events (inadequate sample sizes, poorly monitored complications). Specifically, we propose to test the primary hypothesis that total duration of hypoxia (defined as saturation of peripheral oxygen (SpO 2 ) < 90%) is less in patients receiving intravenous acetaminophen than placebo. Methods/Design: A total of 528 patients undergoing elective open or laparoscopic abdominal surgery will be included in this prospective, randomized, double-blinded, placebo-controlled trial. Patients who have renal disease, liver disease, acetaminophen allergy, are on warfarin therapy, or are receiving regional blocks will be excluded. The incidence and duration of hypoxic events will be the primary outcome of the study. Secondary outcomes include opioid consumption, pain scores, post-operative nausea and vomiting, sedation, fatigue, respiratory rate, movement, and cost-benefit analysis. We will use a ViSi mobile device (Sotera Wireless, San Diego, CA, USA) that will provide continuous non-invasive pulseoximetry, blood pressure, skin temperature, and patient position. Respiratory function will be measured using an ExSpiron (Respiratory Motion Inc., Waltham, MA, USA) monitor which provides continuous non-invasive monitoring of tidal volume, respiratory rate, and minute ventilation. Discussion: The outcomes will reveal the effect of peri-operative IV acetaminophen use on post-operative opioid-related complications. Continuous non-invasive monitoring of vital signs is expected to accurately assess opioid-related complications after major abdominal surgery and provide reliable results correlated with opioid use. The use of novel technology in the post-operative setting permits the collection of a dense amount of data and eliminates gaps in post-operative vital sign measurements. Trial registration: ClinicalTrials.gov identifier: NCT02156154, registered on 3 June 2014. Ethics: The study protocol was approved by the Cleveland Clinic Institutional Review Board (IRB) on 28 April 2014, approval number 14-241. Informed consent: Written informed consent will be obtained from participants or their guardians.