[Nephrology] Goal of water restriction (또는 hypertonic saline) in diabetes insipidus

Diabetes insipidus에서 water restriction (water deprivation test)을 하거나 hypertonic saline을 주입할 때 혈청 나트륨 >145 mEq/L과 혈청 osmolality >295 mosmol/kg에 도달하는 것이 중요합니다.

혈청 나트륨이 >145 mEq/L에 도달하기 전에 단순히 exogenous ADH를 주사하는 것은 central DI와 primary polydipsia를 구분하지 못합니다. 왜냐하면 두 조건은 모두 혈장 ADH 수치가 최대 밑 (submaximal)에 도달되어 있으며 desmopressin 치료에 반응하기 때문입니다.

따라서 혈청 나트륨 농도가 >145 mEq/L이고 혈청 osmolality >295 mosmol/kg이거나 urine osmolality가 분명한 정상 값 (약 700 mosmol/kg 이상)에 도달할 때까지 water restriction과 hypertonic saline을 지속합니다.

중요한 것은 AVP 분비를 위해 적절한 삼투압 자극이 필요한데, 소변을 최대로 농축시키는 충분한 AVP 분비에 필요한 혈장 osmolality는 > 295 mOsm/kg H 2 O입니다.

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Relationship of plasma AVP to urine osmolarity (A) and plasma osmolarity (B) before and during fluid deprivation–hypertonic saline infusion test in patients who are normal or have primary polydipsia (blue zones), pituitary diabetes insipidus (green zones), or nephrogenic diabetes insipidus (pink zones).

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Responses to the water deprivation test to diffe. The response to dehydration reaches a plateau, and the subsequent change in urine osmolality in response to administered desmopressin is illustrated.

Adults with normal vasopressin secretion concentrate their urine to greater than 800 mOsm/kg H 2 O and have less than a 10% increase in urine osmolality in response to administered desmopressin. Patients with complete central diabetes insipidus have minimal concentration of the urine with dehydration, and a marked increase in urine osmolality (usually >50%) in response to administered desmopressin. Patients with nephrogenic diabetes insipidus usually have no increase in urine concentration in response to administered desmopressin, although in some cases of acquired nephrogenic diabetes insipidus, some increased urinary concentration (but generally <10%) can occur. Nephrogenic diabetes insipidus is best distinguished from central diabetes insipidus by the measurement of vasopressin in plasma; plasma vasopressin levels are elevated in cases of nephrogenic diabetes insipidus, especially after dehydration.

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​REF. UpToDate 2020.08.13

Williams Textbook of Endocrinology, 14th edition

Goldman-Cecil Medicine, 26th edition

Harrison's Internal Medicine, 20th edition