Bladder Function in Spinal Anaesthesia

Abstract

Spinal anesthesia with bupivacaine (22.5 mg) or with a glucose-containing solution of bupivacaine (20 mg) or tetracaine (15 mg) was given to 21 patients allocated randomly to these 3 groups. A urodynamic study was performed by CO2 cystometry. It consisted of recording the first sensation of bladder filling, sensation of full bladder, strength of maximal detrusor contraction, bladder capacity and urethral pressure. At the same time, using a quantitative method for measuring muscle strength, the motor block was evaluated for 3 separate movements, hip flexion, knee extension and plantar flexion of the big toe. After the spinal injection, the micturition reflex was rapidly blocked. One minute after the injection, 8 patients experienced no strong desire to void when the bladder was overfilled and 5 min after the injection bladder paralysis was present in most patients. The length of time from spinal injection to complete recovery of detrusor strength was 7-8 h and did not differ significantly between the 3 groups. The level of analgesia lay at or caudal to [lumbar] L5 when the detrusor strength returned. On the average, sensibility (pin-prick) in the sacral segments returned simultaneously with or somewhat earlier than complete recovery of detrusor strength. The muscle strength in the lower limbs was fully restored 40-140 min, on average, before the detrusor strength had completely recovered. There was good correlation between the time of full restoration of hip flexion and detrusor strength in the bupivacaine groups. Urethral pressure was reduced by a mean of 48% and returned to normal either at the same time as or slightly before complete recovery of detrusor strength. The urine production during spinal anesthesia with routine fluid therapy (.apprx. 300 ml/h) was so great that if the patient had not been catheterized there would have been a risk of over-distension of the bladder. This should be kept in mind in patients receiving spinal anesthesia with local anesthetics that give motor block of long duration.