Demystifying Nocturia: Identifying the Cause and Tailoring the Treatment

Paula Laureanno, RN; Pamela Ellsworth, MD, FACS, FAAP

Disclosures

Urol Nurs. 2010;30(5):276-287. 

In This Article

Types of Nocturia

Nocturia may be related to a variety of causes. These causes can be divided into four categories: polyuria, nocturnal polyuria, bladder storage problems, and mixed nocturia.

Polyuria

Polyuria is defined as a total 24-hour urine volume greater than 40 ml/kg. Table 2 lists causes of polyuria.

Nocturnal Polyuria

Urine output normally decreases during the night. This appears to be related to a corresponding increase in secretion of antidiuretic hormone (ADH). As ADH secretion increases, there is increased resorption of water from the renal tubule, resulting in lower volumes of concentrated urine. The urine output during sleep can be expressed as a percentage of the total urine output over 24 hours if the 24-hour urine output is normal. This value can vary considerably from person to person and normally increases with age. Healthy, young adults from 21 to 35 years of age produce 14% ± 4% of their total urine output between the hours of 11:00 p.m. and 7:00 a.m. (95% confidence interval [CI] 10% to 19%) (Robertson et al., 1999), whereas older adults produce an average of 34% ± 15% (95% CI 30% to 36%) (Rembratt, Robertson, Norgaard, & Andersson, 2000).

Nocturnal polyuria is defined as a night time urine output greater than 20% of the daily total in young adults and 33% in older adults, with the value for middle age somewhere in the middle of these two age extremes (Carter, 1992). Exceptions to this stratification are individuals with diabetes insipidus and those whose sleeping patterns vary greatly from the normal eight-hour night time sleep pattern. Causes of nocturnal polyuria can be divided into those that cause a water diuresis or a solute/water diuresis (see Table 3 ). Congestive heart failure, low blood volume, venous stasis disease, and high intake of salt may result in third spacing of fluid in the lower extremities, which can contribute to fluid retention associated with nocturnal polyuria, as can renal insufficiency (Weiss & Blaivas, 2000, 2002). With certain respiratory conditions such as sleep apnea, hypoxia in the lungs can lead to pulmonary vasoconstriction and increased concentrations of peptides responsible for the elimination of sodium in the urine. This can result in increased secretion of water while the patient is sleeping (Krieger et al., 1993).

Bladder Storage Problems – Reduced Voided Volumes

In both men and women, the mean voided volumes at night are on average one-third larger than those in the day time, irrespective of the number of nocturnal micturition episodes (Asplund, 1992). If the individual's actual number of night time voids (ANV) is greater than the predicted number of night time voids (PNV), then the night time voids are occurring at volumes less than the individual's actual bladder capacity. The greater the difference between the predicted and actual numbers of nocturnal voids, the more the nocturia may be attributed to reduced voided volumes secondary to an underlying urologic disorder as opposed to a medical disorder (Stember, Weiss, Lee, & Blaivas, 2007). Problems with bladder storage may be related to decreased bladder capacity, decreased nocturnal bladder capacity, detrusor overactivity, and conditions that can cause bladder irritations (Weiss & Blaivas, 2002). Table 4 identifies factors that may affect bladder storage.

Mixed Nocturia

Patients with nocturia may have more than one etiology, such as both nocturnal polyuria (NP) and reduced voided volumes. In a study of 94 nocturic patients, nocturia was due to NP in 7%, reduced voided volumes in 57%, diurnal polyuria in 23%, and a mixture of NP and reduced voided volumes in 36% (Weiss et al, 1998).

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