Urology JC071: I Cannot Pass Water: Physiology Of Micturition, Urinary Retention, Urinary Obstruction Flashcards
Lower urinary tract
Male:
1. Bladder
2. Prostate
3. Urethra
Female:
1. Bladder
2. Urethra
Efferent innervation:
- Parasympathetic: S2-4 (Pelvic nerve) —> Detrusor muscle —> Voiding: Excite Detrusor + Relax urethra
- Sympathetic: T10-L2 (Hypogastric nerve) —> Bladder neck / outlet —> Continence: Inhibit bladder (β3) + Excite bladder base / urethra
- Somatic: S2-4 (**Onuf’s nucleus) —> **Pudendal nerve —> Striated sphincter muscle (External sphincter) —> Continence
Efferent receptors:
1. Detrusor
- **M3 receptor: Contraction
- **β3 receptor: Relaxation
- Bladder neck / Prostate
- ***α1 receptor: Contraction - Striated sphincter (External / Rhabdosphincter)
- Nicotinic receptor (i.e. NMJ): Contraction
Afferent Innervation:
- Present in Pelvic (majority), Hypogastric, Pudendal nerves
—> **Myelinated Aδ fibres (usual full sensation) + **Unmyelinated C-fibres (pathological conditions e.g. pain, infection)
—> Spinal cord
—> Higher centres (e.g. midbrain, cortex)
Normal voiding function
Storage:
1. **Accommodation of urine at low pressure + with appropriate sensation
2. Bladder outlet remain **closed at rest + during increased intra-abdominal pressure
3. ***No involuntary bladder contraction (unless very full, normal capacity: 500ml)
Emptying / Voiding:
1. **Coordinated contraction of bladder smooth muscle (i.e. Detrusor muscle) of **adequate magnitude + duration
2. **Lowering of resistance at the level of smooth + striated sphincters
3. Absence of anatomic **obstruction
Bladder design
- Very compliant: Store urine with ↑↑ volume without much ↑ in Detrusor pressure
- ***Laplace law
Brain control centres
- Pontine micturition centre (Barrington’s nucleus) (Midbrain)
- Suprapontine control (***Cerebral Cortex)
***Guarding reflex (Storage) + Voiding reflex (Emptying)
Storage:
Myelinated Aδ —> afferent signals as low level firing (vesicosympathetic storage reflex)
1. Parasympathetic inactive —> Detrusor relax
2. Sympathetic active state —> Internal sphincter + Urethra contract (Continence) (+ Detrusor inhibition by β3)
3. External sphincter contraction
Bladder reach 500ml
—> Switch to voiding reflex
Voiding reflex:
Higher level of firing + “OK” signal from cortex —> PMC
- Parasympathetic active —> Detrusor contraction
- Sympathetic inactive —> Internal sphincter + Urethra relax (+ Detrusor disinhibition by β3)
- External sphincter relaxation
Toilet training:
- Cortical centre —> Coordinated relaxation of Rhabdosphincter
Pathology:
1. SCI —> Signals cannot send to PMC —> No coordinated contraction (i.e. ***Detrusor Sphincter Dyssynergia)
- e.g. Detrusor contraction against closed bladder neck —> pressure transmit back to upper urinary tract —> Hydronephrosis —> Renal failure
- e.g. Incontinence
- CVA
- cannot input in PMC —> Incontinence / Urinary retention
***Retention of Urine
- Acute (AROU / AUR)
- sudden onset
- painful
- usually normal system with **obstruction of urine flow
- e.g. benign prostatic obstruction, stones, stricture
- **more common than CROU
- common reason for hospital admission in urology
- defined as “sudden inability to pass urine”
- M>F - Chronic (CROU)
- **painless, vague lower abdominal distension
- usually **innervation problem
- e.g. hypocontractile bladder
AROU incidence + risk factors
Incidence:
- 7 per 1000 men per year
- Overall cumulative probability of AUR in 4 years: 3%
- Over 5 years:
—> 10% men in 70s will have AUR
—> ~30% men in 80s will have AUR
Incidence in women:
- ~3/100,000 per year
- Bladder outlet obstruction less common
- a proportion has **Detrusor underactivity (i.e. hypocontractile **neurogenic cause)
Risk factors (Male AUR):
1. **↑ Age
2. **↑ Prostate size
3. ↑ BPH / LUT symptoms
4. ↓ Maximal urine flow rate
***AROU: Pathophysiology
- ***↑ Resistance to urine flow
- Mechanical (e.g. urethral stricture, clots, stone)
- Dynamic (e.g. enlarged prostate / bladder neck tone)
- Functional (e.g. neurogenic bladder i.e. Detrusor Sphincter Dyssynergia) -
**Impaired Detrusor contractions
- Drug (e.g. Antimuscarinic)
- **Bladder overdistension (e.g. 1L) (e.g. post-anaesthesia, drunk patients)
- ***Neurogenic bladder - ***Combination
***AROU: Causes
Obstructive:
1. ***BPH (most common)
2. Cancer of prostate
3. Bladder / Urethral stone
4. Bladder neck stenosis (usually after previous prostate surgery)
5. Urethral stricture (iatrogenic / infection / inflammation)
6. Phimosis
7. Bladder tumour
8. Clot retention (severe gross haematuria)
Causes in females:
1. **Detrusor hypocontractility (exclude DM)
2. **Neurogenic bladder (bladder dysfunction associated with other neurological deficit e.g. SCI, CVA, Parkinsonism, MS, Cauda equina syndrome)
3. Idiopathic
4. Others
- Anatomical: ***Organ prolapse
- Drugs
- Operative: Pain, Anaesthesia
- Infection: UTI, Genital herpes
***AROU: Precipitating factors
- Constipation
- ***UTI
- ***Anaesthesia / Analgesic
- ***Immobility
- Painful peri-anal conditions (e.g. thrombosed haemorrhoid, perianal abscess)
- Excessive fluid intake (esp. ***alcohol)
-
**Drugs
- **Anticholinergic SE: Antipsychotic, Antispasmodics, H1 Antihistamine, Antidepressant, Ipratropium, Disopyramide
- ***Sympathomimetic SE: Cold medications (pseudoephedrine), MDMA
Distinguish AROU from Anuria / Oliguria
Anuria / Oliguria: No urine production
Causes:
1. Pre-renal ARF (Acute Renal Failure)
- Dehydration
- Shock
- Renal ARF
- Acute renal failure e.g. drug-induced, ATN (acute tubular necrosis)
- Nephritis
***History taking in ROU
記: Check Pain, BPH, Malignancy, Infection, Spine injury, Drugs
- Confirm urinary retention
- check ***first catheterised urine volume - ***Painful vs Painless
- First / Recurrent episode (background severe condition)
- Preceding LUT symptoms (LUTS) (FUN DISH) (SpC Revision)
- FUN: Frequency, Urgency, Nocturia
- DISH: Dribbling, Incomplete emptying / Intermittency, Staining, Hesitancy, Weak stream -
**BPH complications
- **Haematuria
- **UTI (fever / dysuria)
- Bladder / Urethral stone (strangury (painful, frequent urination of small volumes))
- **Renal impairment (uraemic symptoms) - ***Precipitating factors of AROU
- ***Lower limb weakness / numbness (indicate spinal cord compression)
- **Overflow incontinence / Faecal incontinence (suspect **acute spinal cord compression)
- Constitutional symptoms / Multiple bone pain (suspect ***metastatic CA prostate)
- Medications
- BPH medications e.g. α blockers / 5α-reductase inhibitor
- ***Anticholinergic - Previous history of prostate surgery
- e.g. TURP / Urethral instrumentation - History of ***STI
- esp. gonoccocal / NGU - History of CVA, Parkinsonism, ***Spinal injury
***Physical examination in ROU
- Vitals + General exam
- Septic?
- ***Uraemic?
- Urethral catheter output: gross haematuria? - ***Abdominal exam
- Palpable urinary bladder (if not yet catheterised) - Genital exam
- Phimosis - PR exam
- **Anal tone / Peri-anal sensation
- Prostate size
- Features **suscpicious of prostate cancer
- Prostate tenderness
- Faecal impaction
- Painful peri-anal condition - ***Lower limb neurological deficit
Causes of LUTS in men (SpC Revision)
LUTS:
- Occurs in 50-75% of men with benign prostatic obstruction
- >=1/3 of men with LUTS do not have bladder outlet obstruction (BOO)
- LUTS (esp. storage LUTS) increases in males and females with advancing age; mainly due to overactive bladder (OAB)
Causes:
1. **Benign prostatic obstruction (BPO)
2. **Overactive bladder (OAB)
3. Nocturnal polyuria
4. 24-hour polyuria
5. **Detrusor underactivity (DUA)
6. **Neurogenic bladder dysfunction
7. **UTI
8. Prostatitis
9. Urethral stricture
10. **Bladder tumour
11. ***Distal ureteral stone
Hald diagram
LUTS =/= BOO =/= BPH but they have overlap
3 components
1. LUT symptoms (LUTS)
2. BPH
3. Bladder outflow obstruction (BOO)
