Nocturia

Polyuria is excessive or an abnormally large production or passage of urine. Increased production and passage of urine may also be termed diuresis.[12][13] Polyuria is usually viewed as a symptom or sign of another disorder (not a disease by itself), but it can be classed as a disorder, at least when its underlying causes are not clear.

Global polyuria is the continuous overproduction of urine that is not only limited to sleep hours. Global polyuria occurs in response to increased fluid intake and is defined as urine outputs of greater than 40 mL/kg/24 hours. The common causes of global polyuria are primary thirst disorders such as diabetes mellitus and diabetes insipidus (DI). Urination imbalance may lead to polydipsia or excessive thirst to prevent circulatory collapse. Central diabetes insipidus is caused by low levels of Vasopressin (also called antidiuretic hormone (ADH), arginine vasopressin (AVP) or argipressin). ADH is produced in the hypothalamus and stored in and released from the posterior pituitary gland. ADH increases water absorption in the collecting duct systems of kidney nephrons, subsequently decreasing urine production. ADH regulate hydration levels in the body. that helps regulates water levels. In nephrogenic DI, the kidneys do not respond properly to the normal amount of ADH.[14]

Diagnosis of DI can be made by an overnight water deprivation test. This test requires the patient to eliminate fluid intake for a fixed period of time, usually around 8–12 hours. If the first morning void is not highly concentrated, the patient is diagnosed with DI. Central DI usually can be treated with a synthetic replacement of ADH, called desmopressin. Desmopressin is taken to control thirst and frequent urination.[15] Although there is no substitute for nephrogenic DI, it may be treated with careful regulation of fluid intake.

Nocturnal polyuria is defined as an increase in urine production during the night but with a proportional decrease in daytime urine production that results in a normal 24-hour urine volume. With the 24-hour urine production within normal limits, nocturnal polyuria can be translated to having a nocturnal polyuria index (NPi) greater than 35% of the normal 24-hour urine volume. NPi is calculated simply by dividing NUV by the 24-hour urine volume.[16] Similar to the inability of control urination, a disruption of arginine vasopressin (ADH) levels has been proposed for nocturia. Compared with the normal patients, nocturia patients have a nocturnal decrease in ADH level.

Other causes of nocturnal polyuria include diseases such as

• congestive heart failure
• nephritic syndrome
• liver failure
• lifestyle patterns such as excessive nighttime drinking
• sleep apnea increasing obstructive airway resistance. Obstructive sleep apnea sufferers have shown to have increases in renal sodium and water excretion that are mediated by elevated plasma atrial natriuretic hormone (ANH) levels.[14][17] ANH is released by cardiac muscle cells in response to high blood volume. When activated, ANH releases water, subsequently increasing urine production.

Normal human bladder storage capacity varies from person to person and is considered 400 – 600 mL.[18] A bladder storage disorder is any factor that increases the frequency of small volume voids. These factors are usually related to lower urinary tract symptoms that affect the capacity of the bladder. Some patients with nocturia have neither global nor nocturnal polyuria according to the above criteria. Such patients most likely have a bladder storage disorder that impacts their nighttime voiding or a sleep disorder. Nocturnal bladder capacity (NBC) is defined as the largest voided volume during the sleep period.

Decreased NBC can be traced to a decreased maximum voided volume or decreased bladder storage. Decreased NBC can be related to other disorders such as:

• benign prostatic hyperplasia (BPH), also known as prostate enlargement
• neurogenic bladder dysfunction
• learned voiding dysfunction
• anxiety disorders
• urinary tract infection
• certain pharmacological agents.[19]

A significant number of nocturia cases occur from a combination of causes. Mixed nocturia is more common than many realise and is a combination of nocturnal polyuria and decreased nocturnal bladder capacity. In a study of 194 nocturia patients:

• 7% were determined to solely have nocturnal polyuria
• 57% solely had decreased NBC
• 36% had a mixed cause of the two[2]

Multifactor caused nocturia is often unrelated to an underlying urological condition. Mixed nocturia is diagnosed through the maintenance and analysis of bladder diaries of the patient. Assessment of cause contributions are done through formulas.

Although there is no cure for nocturia, many actions can manage the symptoms.

• Prohibiting caffeine and alcohol intake. Both are diuretic.[1]
• Beverage consumption regulation. In regard to nocturia, this specifically means avoiding consuming fluids for three or more hours before bedtime so giving the bladder less fluid to store overnight. This especially helps people with urgency incontinence.[20] However, one study regarding geriatric patients showed that it reduced voiding at night by only a small amount and is suboptimal for managing nocturia in older people.[20] Fluid restriction does not help people who have nocturia due to gravity-induced third spacing of fluid because fluid is mobilized when they lie in a reclining position.[21]
• Compression stockings may be worn through the day to prevent fluid from accumulating in the legs, unless heart failure or another contraindication is present.
• Drugs that increase the passing of urine can help decrease the third spacing of fluid, but they could also increase nocturia.

• ADH replacements such as Desmopressin[22] and Vasopressin
• Selective Alpha-1 blockers are the most commonly used medicine to treat BPH.[23] Alpha-1 blockers are first line treatment for the symptoms of BPH in men.[24][25][26][27] Doxazosin, terazosin, alfuzosin and tamsulosin have all been well established in treatment to reduce lower urine tract symptoms (LUTS) caused by benign prostatic hyperplasia. They are all believed to be similarly effective for this purpose. First generation alpha-1 blockers, like prazosin are not recommended to treat lower urinary tract symptoms because of their blood-pressure-lowering effect. Later generation drugs in this class are used for this purpose.[24][28] In some cases alpha-1 blockers have been used in combined therapy with 5-alpha reductase blockers. Dutasteride and tamsulosin are on the market as combined therapy and results have shown that they improve symptoms significantly versus monotherapy.[28][29]
• If urinary tract infection is causative, it can be treated with urinary antimicrobials.[30]
• Antimuscarinic agents such as oxybutynin, tolterodine, solifenacin are especially used in patients who suffer from nocturia due to an overactive bladder and urgency incontinence because they help bladder contractility.[31]

If the cause of nocturia is related to benign prostatic hyperplasia or an overactive bladder, surgical actions may be sought out.

• Surgery for benign prostatic hyperplasia includes increasingly popular and minimally invasive laser surgery.
• Surgical correction of the pelvic organ prolapse
• sacral nerve stimulation
• Bladder augmentation
• Detrusor muscle myectomy