Hypernatremia resident survival guide

Hypernatremia Resident Survival Guide
Overview
Causes
FIRE
Diagnosis
Treatment
Do's
Don'ts

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief: Mounika Lakhmalla, MBBS[2]

Overview

Hypernatremia is an electrolyte disturbance consisting of an elevated sodium level in the blood. It is defined as a serum sodium concentration exceeding 145 mEq/L. This is a relatively common problem particularly among young children, older adults, and hospitalized/critically ill who depend upon others to control their water intake.

Causes

Life Threatening Causes

Conditions that may cause death or permanent disability within the next 24 hours

Common Causes

The most common cause of hypernatremia is not an excess of sodium, but a relative deficit of free water in the body. Hypernatremia can be caused by many disease processes and drugs.

• Free water loss in form of
  Diarrhea,
  Diabetes insipidus,
  Osmotic diuresis due to glycosuria , urea,
  Loop diuretics,
  Upper Gastrointestinal losses.

• Primary sodium excess is a rare cause of hypernatremia and can be due to
  Massive salt ingestion
  Mineralocorticoid excess
  Administration of hypertonic sodium-containing solutions.
• Nasogastric Suction
• Drains
• Chest Tubes
• Burns
• isotonic solutions such as 0.9% saline
• Sodium Rich antibiotics( example: Fosfomycin)
• Water loss into cells due to Severe exercise or seizures
• Hypernatremia can also occur in cases of primary hypothalamic disease due to impaired thirst (hypodipsia) with or without concurrent diabetes insipidus.

Diagnosis

Shown below is an algorithm summarizing the diagnosis of Hypernatremia according the the [...] guidelines.

Etiology of Hypernatremia

Urine Osmolality <600

Urine Osmolality >600

If the criteria for Renal loss & GI loss are not satisfied

Renal loss

Gastrointestinal loss

Insensible losses like sweat, breathing, Burn unit patients .

Treatment

Serum sodium > 145

Urine output

Low < 200

High

High urine osmolality

Urine osmolality

Hypotonic fluid loss GI losses nausea, vomiting, renal losses, diuretics

Low

High

Replace Both free water deficit as well as Current ongoing fluid losses. Calculate the fluid deficit, or the water that the patient has already lost to get to their current sodium. (% Body Water x Body Weight) x [(Current Na – Target Na)/Target Na] Calculating the ongoing fluid losses which is how much free water the patient is losing daily as you replete. Precision method is the electrolyte free water clearance: Urine volume x (1- (Urine Na + Urine K) / serum Na) Add ‘fluid deficit’ and ‘ongoing fluid losses’ to find the target water intake for the patient. It is recommended that dividing by 24 hours and giving hourly as oral free water (preferred) or D5W if the patient is unable to drink or does not have an NG tube. NOTE, large volumes of D5W may cause osmotic diuresis (through hyperglycemia) and worsen renal water losses. Target rate for correction of hypernatremia: 10-12 mmol/day is a commonly used. A recent study showed no evidence that more rapid correction was associated with greater risk of mortality, cerebral edema, or adverse events Rate of correction no more than 1mEq/L/h Replace 1/2 fluid in 24 hrs, other 1/2 in 24-48 hrs Hypotension - Normal saline, Stable D5W.

Negative water deprivation test

Osmotic diuresis Collect urine for 24h and calculate a total daily solute excretion (urine osmolality multiplied by total daily urine volume). If the total daily solute excretion is >1000 mOsm/day, then they have an osmotic diuresis (due to high protein feeding, glucosuria, or mannitol). Glucose Diuresis: Urine Glucose > 250mmol/L or Urine dipstick positive for Glucose Urea Diuresis: Urine Urea > 250mmol/L and Urine Glucose negative.

Diabetes insipidus

DDAVP

Increased urine osmolality

urine osmolality unchanged

Central Diabetes Insipidus

Nephrogenic diabetes Insipidus

Treat with Desmopressin &..

Causes of Nephrogenic DI:Hypercalcemia, hyperkalemia, Lithium ... Thiazide diuretics in combination with a low salt diet have long been used to treat nephrogenic DI due to lithium. More recent literature suggests that acetazolamide may also be effective, and may be useful for patients whose nephrogenic DI is refractory to thiazides.. Treat with Thiazide diuretics, Acetazolamide &...

Do's

Don'ts

References