Dose Escalation of Dexamethasone to Increase Duration of Transversus Abdominal Plane Block Following Cesarean Section

Preoperatively: informed consent will be obtained by a member of this study. The patients will be screened for inclusion/exclusion criteria on day of procedure, and then the participants will be randomized to one of three groups.

Intraoperatively: The anesthesia team involved with care of patient in the operating room will provide routine anesthesia care during the cesarean section including neuraxial anesthesia with intrathecal bupivacaine and morphine.

After completion of the procedure, the patients will receive bilateral TAP block procedure while still in OR. All blocks will include 20mL of 0.5% ropivacaine, and the patients will be randomly assigned a specific dose of dexamethasone at 0mg (given normal saline as control), 2mg, or 4mg. The resident or attending physician supervising the block will be investigators of the study, and they along with the residents performing the blocks will be blinded to the amount of dexamethasone in the injectate.

Postoperatively: The patients will then be monitored in the PACU for approximately 30-60 minutes and then subsequently monitored on an inpatient floor. Pain scores, time until first opioid dose, total opioid requirement will be assessed and recorded. In PACU, these will be recorded every 15-30 minutes. On the inpatient floor, these will be recorded every 6 hours.

Pain scores, average pain scores in first 48 hours, total opioid consumption, time until first opioid use, and PONV medication requirement will also be recorded. These will be recorded by review of the electronic medical record.

Satisfaction scores and estimation of TAP block duration will be assessed and recorded by anesthesia personnel approximately 48 hours post-operatively; these will be subjective evaluations recorded between 24-38 hours postoperatively. The patients will be asked to estimate how long they felt the block lasted. For satisfaction scores, patients will rate their satisfaction subjectively on a scale of 1-10.

Statistical Analysis: all demographic and clinical variables with continuous measures will be expressed as means and standard deviations; categorical factors will be expressed as proportions. For non-normal data, the medians and inter quartile ranges will be displayed. The distribution of the continuous factors will be examined using the Kolmogorov-Smirnov test. For data that are normally distributed, one-way ANOVA will be used to compare groups of data. For data that are not normally distributed, the Kruskal-Wallis test will be used for comparisons. Chi-square and Fisher's exact tests will be used to analyze categorical data. For all comparisons, a value of p < 0.05 will be considered statistically significant.

Statistical analyses will be performed using SAS for Windows, version 9.2. One-way ANOVA (or the Kruskal-Wallis test, as appropriate) will be used to compare duration of TAP block for the three groups. Linear regression will also be used to test the relationship between duration of block and dexamethasone dose, while controlling for relevant clinical and demographic variables.

One-way ANOVA (or the Kruskal-Wallis test) will be used to compare the groups on post-operative pain scores, opioid requirements, and patient satisfaction scores.

Statistical Power and Sample Size Estimates: Approximately 69 subjects (23 per group) are expected to be enrolled in this study. Given this sample size and assuming that the average duration of TAP block is 18 hours for the control group, 22 hours for the 2 mg of dexamethasone group, and 24 hours for the 4 mg of dexamethasone group, this study will have approximately 80.9% power to detect a difference in block duration, assuming a common standard deviation of 6 hours. If the variability in block time is smaller than 6 hours, this study will have greater power.