Why does nocturia occur in heartfailure?

While taking case history in a cardiac failure patient, one of the most important points to be enquired is whether there is a history of nocturia in the patient.

What is nocturia?

The tendency of the patient to urinate excessively during night is called nocturia.Nocturia can be very distressing as the patient having heart failure(before being admitted and catheterised) is unable to walk to the toilet for urination hence may result in bedwetting.Usually patient doesn’t mention this due to¬†embarrassment, so a doctor has to ask specifically about nocturia to extract this precious information.

Why does nocturia occur?

In cardiac failure, the heart is not able to meet the needs of organs which include kidneys due to failure of heart to pump out blood.Due to the failure of heart to pump out blood, it pools in the extremities leading to edema of legs and face. At night when the patient lies down, the blood that had been accumulated in the extremities returns to the heart, hence the cardiac output during the night is slightly increased compared during the day time.This increased cardiac output perfuses kidneys, which in turn produces more urine to decrease the workload of heart resulting in nocturia.

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