BPH & Urinary Retention

Benign prostatic hyperplasia is "the nonmalignant growth or hyperplasia of prostate tissue," and the single most useful anatomical fact about it is where that growth happens. BPH arises in the transition zone, which surrounds the urethra, through stromal and epithelial cell proliferation. A gland that enlarges in the tissue wrapped around the urinary channel will strangle that channel — the symptoms are a direct geometric consequence of the zone involved. Prostate cancer is a different zone entirely: BPH occurs primarily in the central and transitional portion, "while malignancies typically form in the prostatic periphery." That single distinction carries two clinical payloads later: it is why a digital rectal exam of a benign gland feels smoothly enlarged rather than nodular, and it is why BPH raises PSA without being a risk factor for prostate cancer.

The growth is androgen-dependent. Testicular androgens are required for BPH to develop, because dihydrotestosterone (DHT) promotes tissue growth and cellular proliferation by acting directly on prostatic epithelium and stroma. Testosterone is converted to DHT by 5-alpha-reductase 2 in prostatic stromal cells, and DHT "accounts for 90% of total intraprostatic androgens." Here is the counter-intuitive corollary that trips people up: "there does not appear to be any relationship between testosterone or DHT levels and the development of symptomatic BPH." DHT is necessary for the tissue to grow, but a man’s circulating androgen level does not predict how symptomatic he will be.

The obstruction itself has two components, and every drug in this disorder targets one of them. The static component is the "direct consequence of prostate enlargement, resulting in periurethral compression and bladder outlet obstruction" — bulk, pressing inward. The dynamic component is prostatic smooth muscle tension, worsened by "decreased elasticity and collagen in the prostatic urethra in men with BPH, which exacerbates symptoms of bladder outlet obstruction due to loss of compliance and increased flow resistance." That dynamic half is larger than most people assume: the stroma "comprises 80% of the hyperplastic volume, and about half of this is α-adrenergic smooth muscle." Shrink the bulk and you address the static half slowly; relax the smooth muscle and you address the dynamic half within days.

Faced with resistance, the detrusor does what any muscle does against a load: it hypertrophies. That thickened, overworked muscle becomes irritable and unstable, which is why a man with an obstructive problem complains of storage symptoms — frequency, urgency, nocturia — that seem to have nothing to do with a blockage. Compensation has a ceiling. Push past it and the bladder moves into chronic high-pressure retention, described as "a potentially life-threatening condition," with "long-term or permanent changes to the bladder detrusor muscle."

Once bladder pressure is persistently high, the problem stops being urological and becomes renal. "As bladder pressure increases, ureteral drainage into the bladder is impeded, resulting in bilateral hydronephrosis and renal functional deterioration," aided by vesicoureteral reflux from breakdown of the antireflux mechanism at the ureterovesical junction. The kidney’s response to obstruction runs on a clock worth knowing: for roughly the first 90 minutes it protects itself with nitric-oxide- and prostaglandin-mediated afferent vasodilation; after 3 hours renal blood flow falls as the afferent arterioles constrict; by 24 hours vasoconstriction has cut flow by 50 to 60%, causing renal ischemia. Prolonged obstruction then drives tubular dilation, inflammation, and tubulointerstitial fibrosis toward irreversible nephron loss.

The bladder has its own injury clock. Damage occurs when the bladder is overdistended for more than 2 to 3 hours: overstretching the smooth muscle fibres produces intramural ischemia, nerve damage, and loss of bladder tone. This is why the volume drained at the first catheterization is recorded as a prognostic number rather than a curiosity — and why "the longer the duration of the urinary retention and the greater the residual bladder volume, the longer it will take for bladder muscle rehabilitation." Two more consequences round out the picture: stagnant urine from incomplete emptying "promotes infections and stone formation," and the increased vascularity of a large gland means "small superficial vessels may be disrupted, causing bleeding" — the source of BPH hematuria.

Acute urinary retention is painful, and the pain is the diagnostic clue. It is "the sudden inability to void, usually associated with bloating, severe urgency, general distress, lower abdominal distension, and suprapubic pain." The autonomic response to that overdistension is itself a vital-sign event — it "can lead to vomiting, hypo- or hypertension, or even cardiac dysrhythmias." Chronic urinary retention is the quiet one. It "develops slowly over months to years" and "may also be asymptomatic"; on a bladder scan, a residual over 300 mL is suggestive of retention and over 400 mL is retention. It "may be diagnosed when patients develop unexplained renal failure or when imaging for unrelated reasons demonstrates a severely distended bladder or bilateral hydronephrosis." The painless one is the dangerous one, because nothing forces the patient to seek help while the kidneys are being damaged.

Treatment of acute retention is immediate decompression: "the immediate placement of a 16-French 5 cc to 10 cc balloon Foley catheter to decompress the bladder, bypass obstructive uropathy, and relieve severe patient discomfort." Document the volume drained immediately, because it "reasonably predicts the bladder muscle’s recovery potential" — normal bladder capacity is about 500 mL, and recovery prospects run from very good under 1000 mL, to fair between 1500 and 2000 mL, to problematic above 2000 mL.

And now the rule that changed. Generations of nurses were taught to clamp the catheter after 500 to 1000 mL and drain intermittently, to prevent hematuria, hypotension, and post-obstructive diuresis. The current sources reverse it and are categorical: "Never clamp a catheter; allow all newly placed catheters to drain wholly and freely." More specifically: "rapid, complete drainage is best, even for very large bladder volumes, although this was not previously recommended. Clamping the catheter and partial or intermittent bladder drainage does not reduce the complications of hematuria, vasovagal hypotension, or post-obstructive diuresis" — it "will only produce patient discomfort and increase the risk of a urinary tract infection." Two other chapters agree independently: "there is no benefit to clamping or restricting urinary drainage in these patients, and catheters should be allowed to drain freely," and "there is no role for bladder training or periodically clamping/unclamping the catheter to retrain the bladder before Foley catheter removal." The 500 mL figure does survive, but attached to a different rule — it is the trigger for catheterizing more often on an intermittent self-catheterization schedule, not a reason to clamp.

What the drainage does require is a watch. Post-obstructive diuresis happens because the kidneys, having been obstructed, represent "an attempt by the kidneys to excrete excess fluid retained when obstructed" while the tubules have temporarily lost concentrating ability. Patients with large residuals — generally over 1500 mL — or renal failure or bilateral hydronephrosis are admitted for monitoring. If IV fluid is needed, "the replacement volume is guided by measuring the urine output, replacing 50% to 75% of the previous 1-hour to 2-hour urinary volume with isotonic saline." The endpoint is a lab value, not a guess: a urine specific gravity of 1.010 or less means the kidneys still cannot concentrate and the diuresis is continuing, while concentrating ability is restored once specific gravity reaches 1.020 or more — typically within 24 to 48 hours.

Transurethral resection of the prostate is "still considered the gold standard surgical treatment for BPH," using electrical diathermy to cut and coagulate. It "definitively removes the blocking tissue, there are no size or shape limits," and it "provides substantial tissue for pathological examination." It is indicated for failure of medical management, obstructive nephropathy, recurrent bladder stones, two or more episodes of urinary retention, prostate abscess, difficulty with clean intermittent catheterization, recurrent gross hematuria, incomplete emptying, and obstructive azoospermia.

Afterward the patient returns with a large-bore three-way Foley catheter — typically 22 or 24 French with a 30 cc balloon — running continuous bladder irrigation. The nursing rule for that irrigation is a colour, not a number: it is "titrated to a 'light pink' or 'pink lemonade' color." The plasmakinetic-resection guideline says the same thing — "closely observe the color of the flushing fluid and stop flushing when the color turns clear. It is suggested that the flushing speed should be determined by the color of the flushing fluid." At the bedside this is done by evaluating "the color of the CBI drainage fluid under bright light" and increasing the rate if the colour is dark, decreasing it if pale. One study used a six-grade colour card with patient teaching that "it is ok if the color is No. 2 or below, but medical attention is required if the color is No. 3 to No. 6." The second rule is arithmetic and easy to get wrong: with irrigation running, true urine output = total drainage volume minus the volume of irrigation solution infused, and the chart carries all three numbers.

TUR syndrome is dilutional hyponatremia from absorption of hypotonic irrigation fluid — roughly 20 mL of fluid is absorbed per minute during surgery, about a third of it entering the venous system directly. Whether it can happen at all depends on the energy source: monopolar resection requires a non-conducting irrigant such as glycine, sorbitol, or mannitol, while bipolar resection allows normal saline. Bipolar "has largely replaced monopolar diathermy techniques for TURP," with resection in saline and a reduced risk of TUR syndrome, and the risk is "essentially eliminated in TURP surgeries that utilize bipolar technology with normal saline irrigation"; even with monopolar the incidence is roughly 20 cases per 1,000 procedures. Symptoms appear at a serum sodium at or below 125 mEq/L and are likely around 120 mEq/L, and they arrive in a recognizable order: "burning or prickly sensation of the face and neck, lethargy, and fearful ideations," progressing to "confusion, nervousness, nausea, hemolysis, visual disturbances, coma, shock, and even death." The early triad a nurse can actually catch is facial or neck burning, restlessness, and confusion during or just after a monopolar resection.