Predictors of postoperative pain and analgesic requirements following abdominal hysterectomy: an observational study.

PURPOSE

A prospective observational study is conducted to identify independent predictors of pain and morphine consumption following abdominal hysterectomy.

METHODS

Preoperative State Trait Anxiety Inventory (STAI), Numerical Rating Scales (NRS) for anxiety and pain expectations, thermal pain thresholds and pain scores at forearm and incision site, and pain scores generated from the insertion of an intravenous catheter were measured in female patients undergoing abdominal hysterectomy. Pearson correlations between the predictors and the two outcome measures postoperative pain scores and morphine consumption were studied and multiple regression analysis was conducted to identify independent predictors (primary outcome). Secondary outcomes included cut-off values of predictive tools for morphine consumption.

RESULTS

Data from 60 patients were analyzed. STAI state anxiety, NRS pain expectations, and NRS anxiety scores were identified as independent predictors of postoperative morphine consumption. We identified a cut-off value of 4.5 (sensitivity 90 %, specificity of 60 %) for the NRS anxiety and a cut-off of 42.5 (sensitivity 70 %, specificity 70 %) for the state anxiety STAI score for increased postoperative morphine consumption.

CONCLUSIONS

Preoperative STAI state anxiety scores and NRS pain expectations are independent predictors for increased morphine consumption following hysterectomy. The STAI state anxiety tool and NRS 0-10 anxiety tool can be used interchangeably. The NRS 0-10 anxiety is a much simpler tool than STAI state anxiety and is associated with a higher sensitivity for high morphine consumption. Thermal pain thresholds and IV pain scores were not predictive of postoperative morphine consumption.