A Dose Ranging Effect of Preoperative Diphenhydramine on Postoperative Quality of Recovery After Ambulatory Surgery

Pain after ambulatory surgery remains an unsolved problem in The United States and Europe.
It is associated with delayed hospital discharge and it can result to an increased opioid
consumption with adverse side effects. The concept of multimodal analgesic technique was
introduced more than 15 years ago and several techniques have been studied over the years
including non steroidal antiinflammatory drugs (NSAIDs), acetaminophen, gabapentoids,
ketamine, local and regional anesthetic techniques. Histamine can have effects on polymodal
nociceptors and C-fibers, producing pain which is further increased by neurogenically
mediated release of substance P from afferent pain fibers. Several non-selective or H1
-selective histamine receptors antagonists have been demonstrated in animal models and
clinical pain. Chia et al demonstrated that preoperative promethazine had opioid sparing
properties without adverse sedative effects in patients undergoing abdominal hysterectomy.

Diphenhydramine is an anti-histamine drug who has been found to be effective in reducing
postoperative nausea and vomiting after ambulatory surgery but its effects on postoperative
pain and other important outcomes after ambulatory surgery such as time to meet discharge
criteria have not being studied.

The MQOR 40 is a validated instrument that was specifically design to evaluate patient
recovery after anesthesia and surgery. This instrument can be particularly valid to examine
interventions which affect different spheres of patient recovery as is the case of
diphenhydramine. The objective of this study is to determine a dose response effect of
preoperative diphenhydramine on postoperative quality of recovery after ambulatory surgery.
The use of preoperative diphenhydramine can improve patient's quality of recovery, decrease
postoperative pain, opioid consumption and opioid related side effects after ambulatory
surgery.

The research question: Does a preoperative dose of diphenhydramine improve postoperative
quality of recovery after ambulatory surgery? The hypothesis of this study is that
preoperative diphenhydramine will improve postoperative pain, Postoperative nausea and
vomiting (PONV), sleep which will translate in a better overall quality of recovery.