Hypernatremia

Pathophysiology (NEJM 2000342 1493)

• Deficit of water relative to sodium

• Usually loss of hypotonic fluid; occasionally infusion of hypertonic fluid

• And impaired access to free water (eg. intubation. A MS): hypernatremia is powerful thirst stimulus, usually only develops in Pts w o access to HjO

• By definition, all Pts are hypertonic; can be either hypo-, eu-, or hypervolemic Hypovolemic hypernatremia

• Renal HjO losses (Uovn 300-600): loop diuretics, osmotic diuresis (glc. mannitol. urea)

• Extrarenal H2O losses (U«m -600): diarrhea, insensible loss (fever, exercise)

Euvolemic hypernatremia

• Diabetes insipidus (U««. - 300-600): ADH defic. (central) or resist, (nephrogenic)

Central: congenital, trauma surgery, tumors, or infiltrative disease of hypothalamus or posterior pituitary; also idiopathic, hypoxic encephalopathy, anorexia Nephrogenic (a/inoh 2006.144:186) congenital drugs: Li. amphotericin, demeclocycline. foscarnet. cidofovir metabolic: hypercalcemia, severe hypokalemia, protein malnutrition, congenital tubulointerstitial: postobstruction, recovery phase of ATN. PKD. sickle cell. Sjogren's, amyloid, pregnancy Dl usually presents as severe polyuria and mild hypernatremia I • Seizures, exercise (U^ -600): T intracellular osmoles • H20 shifts — transient t [Na]»«^

Hypervolemic hypernatremia

• Hypertonic saline administration: eg. cardiac arrest resuscitation with NaHCOj

• Mineralocorticoid excess: usually mild hypernatremia caused by ADH suppression

Workup

• ✓ volume status (vital signs, orthostatics. JVP. skin turgor, mucous membranes.

peripheral edema. BUN. Cr)

• If hypovolemic. / U«*™ & Un, to determine whether renal (U<*„, 300-600; Un, >20 mEq L)

or extrarenal (U0im -600; Un, 20 mEq L) free water loss

• If euvolemic. / U«™ to evaluate for complete (Uovr 300) or partial (Uolm 300-600) Dl see "Polyuria" below for full details of Dl workup Figure 4-S Approach to hypernatremia

Hypernatremia

/

1

hypovolemic

euvolemic hypovolemic

s

>4

Hypovolemic

Euvolemic

Hypervolemic

Hypernatremia

Hypernatremia

Hypernatremia

300600 >600

/ 1 \

U„>20 Uh, <20 Uœ- <300 300-600 U„»600

t M

i

i

M

Renal losses Extrarenal Complete Partial Dl Intracell E*og. hypertonic saline

losses

Dl

osmote Mineralocorticoid excess

generation

• Restore access to H20 or supply daily requirement of HjO (js 1 L d)

• Hypovolemic Hypernatremia: replace volume and free HjO deficits

Free H20 deficit tNa]*™ " 140 TBW 060 ",BW <" 085 " TBW 140 ifxJ * 0.85 il eWerly)

for 70 kg (IBW) man. free H20 deficit ([Na]t.™ 140) 3 [Najwnjm [Na]infcjut.

eg. 1 L DSW given to 70 kg (IBW) man w [Na] 160 mEq L will I [Na]«^ by 3.7 mEq rate of 1 of Na should not exceed 0.5 mEq L h to avoid cerebral edema in 70 kg (IBW) man. 125 ml h of free H20 will I [Na] by 0.5 mEq L h can use V2 NS (77 mEq) or V« NS (38 mEq) to simultaneously provide volume & free

H20 (which provide 500 ml or 750 ml of free H20 per L respectively) can give free H20 orally (via NGT OGT) as well formulas only provide estimates; recheck serum Na frequently Dl central Dl: desmopressin (dDAVP)

nephrogenic Dl: treat underlying cause if possible; Na restriction ♦ thiazide (mild volume depletion i delivery of filtrate to dysfxnal diluting segment of kidney) Hypervolemic Hypernatremia: D*W + loop diuretic

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