Bladder Outlet Obstruction (& Anti-cholingeric drugs)
Bladder outlet obstruction generally presents with any or all of the following symptoms:
The etiology of bladder outlet obstruction includes:
To understand how anticholinergics cause bladder outlet obstruction, it is
important to review the muscular anatomy and neural innervation of the bladder.
Normal bladder function depends on the central and peripheral nervous systems
and the detrusor muscle and
external sphincter of the
bladder. Muscular fibers in the bladder interdigitate around the bladder neck,
resulting in the formation of a sphincter, which controls the outflow of urine.
The somatic and autonomic nervous systems (ANS)
control bladder function. The ANS involves
sympathetic (from T10 and L1) and
parasympathetic (from S2 to S4)
control. The sympathetic nervous system stimulates alpha- and beta-receptor
sites in the bladder smooth muscle. The primary neurotransmitter for
sympathetic control is
norepinephrine (NE). When NE
interacts with alpha receptors in
the bladder, the bladder smooth
muscle tone increases, allowing for stretch. Stimulation of
beta receptors in the bladder by
NE results in relaxation of the
detrusor muscle. Thus,
NE allows the bladder to expand,
thereby accommodating the inflow of urine from the kidneys and ureters. The
primary neurotransmitter of the
parasympathetic nervous system is acetylcholine (ACH).
Release of ACH from the parasympathetic nervous system results in
bladder contraction. Combined
with reduced output from the sympathetic
nervous system, the bladder releases
urine into the urethra.
Because ACH is a cholinergic substance, anticholinergic medications may counteract its effects, including promotion of bladder emptying. For patients taking anticholinergic medication, the bladder is under only sympathetic control, with a net result of prolonged bladder filling and expansion. In the absence of bladder emptying, spasms inevitably ensue. The effect is identical to that seen in children who have spinal cord lesions at S2 to S4, in which parasympathetic stimulation is reduced.
Treatment for bladder spasms due to anticholinergic therapy is discontinuation of the medication. Antiarrhythmics, antihistamines, antipyretics, and antitussives all have significant adverse effects, but they do not include abnormalities in neural stimulation of the urinary bladder.
Atala A, Bauer SB. Bladder dysfunction. In: Barratt TM, Avner ED,
Harmon WE, eds. Pediatric Nephrology. 4th ed. Baltimore, Md:
Lippincott Williams & Wilkins; 1999:913-914
Kaefer M, Zurakowski D, Bauer SB, et al. Estimating normal bladder
capacity in children. J Urol. 1997;158:2261-2264