Postoperative urinary retention is defined as the inability to void with a full bladder during the postoperative period. It affects both sexes in all ages following all types of operation, including patients who previously had no micturition problems. We investigated the incidence and risk factors of urinary retention following long spinal anesthesia for total knee replacement.

We retrospectively studied a number of factors that may be associated with urinary retention in 98 women. The outcome variable of logistic regression models are urinary retention and severe urinary retention. The potential explanatory variables are age, height, weight, history of hypertension, DM and abnormal urology, heavy bupivacaine dose, types of patient-controlled analgesia, time to regression of spinal block to sacral segments (Tregression), amount of fluid and duration of surgery. We constructed a multiple linear regression model of the time from subarachnoid injection to spontaneous voiding (Tvoiding) in relation to above variables.

The overall rate of urinary retention and severe retention were 57.1% and 30.6%. Tregression was identified as significant explanator of an increased probability for urinary retention (P = 0.002), Tregression and DM for severe urinary retention (P < 0.001, P = 0.054). In the multiple linear regression model, three variables - Tregression, age, abnormal urological history were identified to have significant t-values (3.902, 3.107, 2.284) with Tvoiding (P < 0.001, P = 0.003, P = 0.025).

Old age, DM, abnormal urological history, delayed recovery of spinal anesthesia are risk factors to urinary retention or delayed spontaneous voiding.