Gender Affirming Mastectomy Analgesia Rial (GAMA)

In Canada, there has been a rise in the number of transgender and gender-diverse individuals seeking gender-affirming care in recent years. Canada has seen roughly a ten-fold increase in gender-affirming care referrals over the past decade.

A gender-affirming mastectomy (GAM), also called top surgery, is one potential intervention for trans men and non-binary individuals. This procedure entails bilateral mastectomy with chest contouring to create a masculine-appearing chest. This operation is life-changing for many as it can alleviate gender dysphoria and improve mental health and quality of life.

A significant clinical issue in GAM is postoperative pain management. These procedures involve large incisions across the chest and tissue excision, and as such, pain can be significant. With only a few other studies focused on our target population, evidence on effective pain management strategies in this population is limited, and many nerve block types have not been studied.

A wide body of research focuses on nerve block use for oncological mastectomies. Network metanalysis has recognized continuous paravertebral nerve blocks as the most effective regional anesthesia technique, while wound infiltration is only slightly better than no intervention. Oncological research recognizes the ability of continuous paravertebral nerve blocks to provide prolonged analgesia and decrease opioid consumption. That said, there are some concerns about directly applying this knowledge to individuals having a mastectomy due to gender-affirming purposes. Patients undergoing GAM are often young and healthy without comorbidities that many breast cancer patients have. Additionally, many breast cancer patients undergo axillary lymph node dissection, which can increase post-operative pain There is also research that indicates that chronic testosterone administration, which applies to much of this population, increases pain thresholds, which could have potential impacts on the analgesic requirements for these patients. Many seeking mastectomies due to gender-affirming purposes have a positive outlook on the operation in comparison to patients having a mastectomy due to breast cancer. This may alter their pain perception. Notably, some research indicates stressors, such as those caused by gender dysphoria, may exacerbate pain. These differences between the patient populations' pain profiles make this research necessary to better understand this supplemental analgesia technique in gender-affirming care.

Primary Study Objective The primary objective is to determine whether paravertebral nerve blocks are superior to wide local infiltration in terms of decreased opioid consumption (oral morphine equivalents) in the first 24 postoperative hours for people undergoing GAM.

Secondary Objectives

Determine whether paravertebral nerve blocks are superior to wide local infiltration after GAM for:

• Average pain score in the first 24 hours
• Time in Post Anesthesia Care Unit (PACU)
• Postoperative nausea and vomiting (PONV) in PACU
• Quality of Recovery (QoR-15) at 3 days
• EuroQol five-dimensional questionnaire (EQ-5D) at 3 days and 3 months
• Persistent postsurgical pain (brief pain inventory) at 3 months
• Postoperative complications with first 7 postoperative days

Research questions RQ1: Does the use of paravertebral nerve blocks, as compared to wide local infiltration, reduce opioid consumption within the first 24 hours following gender-affirming mastectomy? RQ2: What is the trajectory of pain and opioid use in the 72 hours following gender-affirming mastectomy? RQ3: Does the use of paravertebral nerve blocks, as compared to wide local infiltration, improve other postoperative patient centered outcomes (pain at 24 hours, PONV, QoR-15, EQ-5D, long-term pain)?

Methods This study will include patients undergoing gender affirming bilateral mastectomy at the QEII Health Sciences Center in Halifax, Nova Scotia.

Number of participants The study will include a maximum of 64 participants, randomly assigned to 2 study arms of 32 participants (paravertebral or wide local infiltration). The patients will be consented and screened at least 1 day before their surgery.

Randomization and concealment Patients who have consented to the study, will be randomly assigned into two groups. A computer-generated online randomization software will be used to randomize patients on a 1:1 basis to the paravertebral block (PVB) or the wide local infiltration (WLI) groups. The patient will either receive a paravertebral nerve block by anesthesiology in the block room versus wide local infiltration by the surgeon. Patients randomized to the PVB group will receive the block as per protocol, while those in the WLI group will undergo simulated block procedures using ultrasound and applied pressure to mimic the experience. The study data will be analyzed as per intention-to-treat.

Standardized Anesthesia technique Intravenous access and monitors typical at our institution including peripheral intravenous cannula(s), temperature probe and standard Canadian Anesthesiologists' Society (CAS) monitors (electrocardiography, pulse oximeter, and non-invasive blood pressure) will be applied. Induction and maintenance medication will be left to the discretion of the attending anesthesiologist with some exceptions. Lidocaine infusions will not be permitted in study patients. These medications are rarely used intraoperatively in plastic surgery and may increase the risk of LAST if given near the time of a block. Opioid administration intraoperatively and postoperatively will be administered at the discretion of the treating team. Use of intravenous dexamethasone will be encouraged unless contraindicated.

Postoperative care The standard of care for pain management for this patient population is opioid based (fentanyl, morphine, hydromorphone) with acetaminophen. The opioid medications are ordered as intermittent doses either injected intravenously, subcutaneously or ingested orally in the PACU. Codeine prescriptions will not be permitted due to their inconsistent conversion to morphine.

Regardless of group allocation, patients will receive all the usual pain medications they normally would in the postoperative period.

Data collection procedure Baseline data

A research coordinator (RC) will collect the baseline data as outlined below at the time of recruitment to the study:

• Age, sex assigned by birth, self-identified gender, body mass index (BMI), preoperative pain medication, comorbidities (respiratory disease, cardiac disease, kidney disease, liver disease, prior stroke, seizure disorders)
• Pre-existing pain (Brief pain inventory)
• Cannabis use within the last month on average (route (inhaled versus ingested), frequency, dose). Routine or high dose cannabis use is known to be associated with high postoperative pain scores.
• American Society of Anesthesiologists' (ASA) classification.
• Testosterone dosing and route (if applicable)

Postoperative data Participants will be provided with a journal to track their postoperative data. Then at 3 days, 7 days, and 3 months participants will be emailed a survey hosted on Research Electronic Data Capture (REDCap) to share their recovery.

Any patient that would prefer to have the surveys completed over the phone can request this and a member of the research team will call them on day 1, 2, 3, and 7; then 3 months post operatively. Survey responses can be stored in the patient's pain journal for questions that would have been asked at earlier timeframes (e.g., 24 hours) to match the data collected from the those completing the surveys online.

Statistical analysis Primary and secondary analyses Numerical outcomes from RQ1 and RQ3 will be tested using a Welch t-tests with condition as a predictor of various outcomes (24hr opioid use, 24hr pain, QoR-15, EQ-5D, and persistent pain at 3 months). The categorical outcome (PONV) will be analyzed using a chi-squared test of independence. Trajectories of pain and opioids over the first 72hrs (RQ2) will be analyzed using linear mixed models; the investigators will explore both linear and quadratic models for rates of change over time. Linear mixed models will be used in a similar fashion to assess trajectories of change in gender congruence at 4 time points (baseline, day 3, day 7, and 3 months).

In all cases, the investigators will include all patients as an intention-to-treat protocol, using data when it is available for each outcome (even if data is missing from other outcomes). To address missing data, multiple imputation will be used, as it is a gold standard method for handing missingness.