체액량 및 전해질(Sodium) 대사 장애

체액량의 장애

- Effective circulating volume 이 중요

1. Decreased effective (arterial) circulating volume

1) Decreased ECF volume
- Extra-renal loss: vomiting, diarrhea, sweating, burn, hemorrhage
- Renal loss: diuretics, osmotic diuresis, hypoaldosteronism, diabetes insipidus,

2) Normal or increased ECF (interstitial, venous) volume
- Heart failure
- Tissue redistribution: capillary leak, hypoalbuminemia with LC, nephrotic syndrome
- Sepsis (vascular tone↓, venous pooling↑, permeability↑)

2. Increased effective (arterial) circulating volume

- Primary aldosteronism, SIADH
- Acute glomerulonephritis, End stage renal disease

 

Hyponatremia ( Na < 135 )

1.ADH mediated water retention: ADH 증가

 1) Effective circulating volume depletion

① Decreased ECF volume (primary sodium loss)
- Extra-renal loss: vomiting, diarrhea, sweating, burn, hemorrhage
- Renal loss: diuretics, osmotic diuresis, hypoaldosteronism, cerebral salt wasting (by BNP)
② Increased ECF volume (primary sodium gain) ; usually associated with edema
- Heart failure: poor prognosis factor
- Hepatic cirrhosis: poor prognosis factor
- Nephrotic syndrome

 2) SIADH

 3) Hormonal changes

① Adrenal insufficiency
- Cortisol이 안 나와 ADH에 대한 음성피드백 안됨
- Primary adrenal insufficiency: aldosterone 분비 장애: volume depletion, BP ↓: ADH ↑
- Secondary adrenal insufficiency: aldosterone 분비 유지 : euvolemic hyponatremia
② Hypothyroidism: Cardiac output ↓(effective volume 감소) : ADH ↑

 

2. Non-ADH mediated water retention : ADH 감소 or 일정

 1) Advanced renal failure : 물 배설 불가

 2) Primary polydipsia

- > 12L/day or concurrent SIADH
- psychiatric illness with antipsychotic drug (dry mouth)

 3) Beer drinker’s potomania

- low protein intake + large volume of beer
- low urine solute (osmole) excretion: 200mosm/day
- low max urine volume: 200/50=4L/day

3. Sodium loss mixed with volume depletion: Thiazide diuretics

4. Pseudohyponatremia

Hyperglycemia, Mannitol, Hyperlipidemia, Glycine

 

Major steps in the initial evaluation of hyponatremia

1) Plasma osmolality

A. Low: true hyponatremia
B. Normal/elevated: pseudohyponatremia or renal failure (azotemia)

2) Urine osmolality

A. <100 mosmo1/kg: primary polydipsia (non-ADH mediated)
B. >100 mosmo1/kg: other causes of true hyponatremia in which water excretion is impaired (ADH mediated)

3) Urine sodium concentration

A. Less than 25 meq/L: effective circulating volume depletion (including heart failure and hepatic cirrhosis)
B. Greater than 40 meq/L: SIADH, diuretics (when drug still acing), adrenal insufficiency, hypothyroidism patients with vomiting, osmotic diuretics, salt losing nephropathy

 

Hypernatremia ( Na > 145 )

1. Non-renal loss

1) Skin: sweating (insensible), fever, exercise, heat exposure, burns
2) Respiratory tract (insensible): mechanical ventilation
3) Gastrointestinal tract: diarrhea, Osmotic and Viral gastoenteritidis

cf. Secretory diarrhea (cholera): hyponatremia

2. Renal loss

1) Drug: Loop diuretics interfere with the countercurrent mechanism and decrease medullary interstitial tonicity
2) Osmotic diuresis by non-reabsorbed organic solutes (urine osmole excretion rate>750mosmo/day)
- Hyperglycemia and glucosuria in poorly controlled DM
- IV administration of mannitol
- Increased endogenous urea production (high-protein diet)
3) Diabetes insipidus (ADH 분비,반응 ↓)

 

Major steps in the initial evaluation of hypernatremia

 1) Minimum volume of maximally concentrated urine

- Urine volume < 500mL/day & Urine osmolality > 800mosm/kg
-> Non-renal loss

 2) Urine osmole excretion rate > 750mosmol/day

-> Osmotic diuresis

 3) Renal response to desmopressin

- Urine osmolality increased: CDI
- Urine osmolality unchanged: NDI

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