How Low Can You Go

The primary objective of this research proposal is to answer the question: in patients scheduled to undergo laparoscopic uterosacral suspension surgery of the uterus or vaginal vault, does lower intraabdominal operating pressure reduce post-operative pain, measured using a standardized visual analogue scale?

Secondary outcomes include frequency of opioid and non-opioid analgesic prescriptions at time of discharge, rescue opioid analgesics in the day-surgery recovery unit, rate of unanticipated admission to hospital. Surgical safety outcomes will also be assessed including surgeon perception of operative field visibility, rate of surgeon requests to increase intraabdominal pressure, rate of conversion to open surgery, incidence of surgical complications (up to 30d post-operatively).

3.0 METHODS \& STATISTICAL ANALYSIS This study will be a double-blinded randomized controlled trial patients ≥18 years of age scheduled for laparoscopic uterosacral suspension surgery of either the uterus or vaginal vault at the Foothills Medical Centre, an academic tertiary hospital. Patients scheduled to receive concomitant prolapse, hysterectomy, or anti-incontinence surgeries will be included. Patients scheduled to receive concomitant non-urogynecologic surgery or those converted to an open, abdominal surgical approach will be excluded. For participants randomized to the lower IAP group, after entry into the abdominal-pelvic cavity, pneumoperitoneum pressure will be set and maintained at 10mmHg throughout the surgery. For those randomized to the normal IAP group, after entry into the abdominal-pelvic cavity, pneumoperitoneum pressure will be set and maintained at 15mmHg.

Data collected - including but not limited to:

1. Preoperative data:

   a. Baseline demographics: age, BMI, past medical history

2. Intraoperative Data:

   1. Duration of surgery, estimated blood loss, surgical complications
   2. Incidence of surgeon request for either: an increase in Trendelenburg positioning or increase in intraabdominal pressure settings

3. Postoperative Data:

   1. Visual analogue pain scores (0-100mm) at 3 and 24 hours postoperatively
   2. Incidence of postoperative non-opioid and opioid prescriptions provided
   3. Incidence of unplanned hospital admission

The baseline characteristics of the primary cohort will be presented. Categorical data will be reported as counts and percentages and continuous data as means with standard deviations.

Continuous variables will be analyzed using a Student t-test for normally distributed data and Wilcoxon's rank sum test for nonparametric data. Frequencies and percentages will be calculated for categorical variables and compared using the Chi-squared or Fisher's exact test as appropriate. Statistical significance will be defined as p\<0.05.

Prior studies determined the minimum clinically significant difference in visual analogue pain scales scores to be 10mm, regardless of severity of pain. On the basis of this, a sample of 64 patients per group will be sought to achieve 80% power to detect an effect size of 0.5 (i.e. assuming a standard deviation of two points on the pain scale) using a two-group t-test with a two-sided significance level of 0.05. Accounting for a drop-out rate of 20%, a final sample size to 164 patients will be required.