IV Oxytocin for Post Operative Pain After Minimally Invasive Hysterectomy

Patients will be recruited for participation in this study while they are in pre-operative holding area before surgery.

Once the patient is recruited and consented the patient, they will be randomized for either the intervention group (IV oxytocin) or control group (0.9% normal saline).

In the holding area, a pre-operative pain questionnaire, including the State-Trait Anxiety Inventory (STAI-6) questionnaire and the Daily Pain Catastrophizing Scale (DPCS), will be performed.

The STAI-6 is a validated, short 6-question form to assess anxiety. It is one of the most frequently used measures of anxiety in applied psychology research and has been used to assess anxiety in perioperative patients and to assess the potential of a patient to have higher postoperative pain and opioid requirements and a greater likelihood to use chronic opioids or develop chronic pain.

The DPCS is a validated, short questionnaire to assess measure of catastrophizing in the context of actual or anticipated pain. Similar to the STAI-6, it has been shown to predict patients who experience higher postoperative pain and opioid requirements and those with a greater likelihood of using chronic opioids or developing chronic pain.

Both groups (intervention and control) will be treated pre-operatively with acetaminophen 1000 mg and gabapentin 300 mg orally.

The Investigational Research Pharmacy will be informed and prepare medication or placebo.

The primary anesthesiology team receive either the study medication or placebo in 500 ml bag of labeled as "Oxytocin Study Drug for IV infusion".

A recommended "Intra-Operative Analgesia Management" algorithm will be given to the primary anesthetic team. The recommended algorithm for intra-operative analgesia management will include the following recommendation:

Fentanyl 100 mcg IV for induction.

Dexamethasone 8 mg IV after induction but prior to incision.

Small, titrated doses of Hydromorphone IV boluses (0.2-0.4 mg) during the operation and before emergence according to primary team judgment.

Ketorolac 30 mg IV at skin closure unless otherwise contraindicated.

The infusion will be started intra-operative once the uterus is removed and will continue to run until completion of the medication or discharge from PACU criteria are met, whichever occurs first.

Other aspects of each patient's routine clinical care will continue as per the attending physician under whom the patient is admitted, regardless of treatment arm status.

The intervention group will be treated with oxytocin 30 IU in 500 ml IV at a rate of 5 IU/h (83.33 ml/h). The control group will be given IV 0.9% saline infusion at the same rate of 83.3 ml/h. The primary care team (anesthesia, surgery and nurses), research team and the patient will all be blinded for the treatment.

In the PACU, a brief postoperative pain questionnaire will be done, including the Surgical Pain Scales (SPS).

The SPS is a validated scale that consists of 4 items that measure pain at rest, during normal activities, during work/exercise and quantify the unpleasantness of worst pain. This scale has been validated in a number of different types of postoperative pain, including women after gynecologic surgery.

Vital signs, NRS pain scores and opioid consumption at PACU will be collected from the patient's medical record.

Patients whose surgery was converted to open, EBL >500 ml or any other surgical complication that necessitates a hospitalization will be excluded from the trial.

For secondary outcomes, including total opioid consumption in 24, 48, and 72 hours and pain scores at POD1, 2, and 3, an online survey will be done at POD1, 2, and 3. For patients who do not complete the survey, a phone call from a study staff member will be performed to complete all questions not completed with the online form.