Spinal anesthesia , through interruption of spinal nerve conduction, causes intense blockade of sensation, motor function as well as (para)sympathetic function. Loss of sympathetic tone causes vasodilation which may lead to arterial hypotension and bradycardia. To avoid these effects, in anesthetic practice, usually intravenouspreload is administered as cristalloids or colloids. The form and dosage of these plasma expanders will influence diuresis during spinal anesthesia-induced detrusor blockade. Excess diuresis may cause bladder distension and neccecitates bladder catheterization