Hyponatremia

Take-home points regarding Volume status and water movement

Electrolytes can have disconnect between serum levels and true body levels depending on water locaiton

Gold standard test for evaluating electrolyte disorders

24-hour urine collection

Primary extracellular electrolyte

Sodium

Primary role of sodium

Fluid balance and control of blood volume

Most sodium problems stem from

a water problem

Pseudohyponatremia

Caused by dramatically elevated glucose levels or high levels of triglycerides/ketones = falsely low

MCC of hypertonic hyponatremia

hyperglycemia

When additional solute pulls water into serum,

it dilutes sodium causing hyponatremia

Increases osmolality stimulates

ADH release causing water retention and hyponatremia

The vast majority of hyponatremia

Hypotonic causes

ADH independent causes of hyponatremia

- Psychogenic Polydipsia

- Beer Potomania and the "Tea and Toast" Diet

- Renal Impairment

ADH dependent causes of hyponatremia

-Hypovolemic hyponatremia

-Hypervolemic hyponatremia

-SIDAH

-Medications

First priority of ADH

Lower BP

Second priority of ADH

High osmolality

ADH-independent hypotonic hyponatremia lab values

-Low Urine Osmolality ( <100)

Psychogenic polydipsia

Compulsive intake of large volumes of water driven by psychiatric or neurodevelopment conditions

Beer Potomania/"Tea and Toast" Diet

Insufficient solute relative to the amount of water coming in

Renal Impairment/failure and Hypotonic Hyponatremia

Seen in severe AKI or advanced CKD; Elevated Cr on labs

ADH-Dependent Hypotonic hyponatremia - Hypovolemia

Loss of both water and sodium

ADH-Dependent Hypotonic hyponatremia - Hypovolemia:

Extrarenal causes

GI losses or skin losses; Low urine sodium

ADH-Dependent Hypotonic hyponatremia - Hypovolemia:

Extrarenal labs

High urine osmolality, low urine sodium

ADH-Dependent Hypotonic hyponatremia - Hypovolemia:

Renal causes

Associated with high urine sodium loss

ADH-Dependent Hypotonic hyponatremia - Hypovolemia:

Renal labs

High urine osmolality, high urine sodium

ADH-Dependent Hypotonic hyponatremia - Hypovolemia:

Treatment goals

Restore volume to shut off ADH secretion and Na reabsorption

ADH-Dependent Hypotonic hyponatremia - Hypovolemia:

Treatment

IV isotonic fluids

ADH-Dependent Hypotonic hyponatremia - Hypervolemia mechanism

Volume overload leads to fluid overflow into interstitium

ADH-Dependent Hypotonic hyponatremia - Hypervolemia:

Common Causes

Cirrhosis, heart failure, nephrotic syndrome

ADH-Dependent Hypotonic hyponatremia - Hypervolemia:

Labs

High urine Osm, Low Urine Na

ADH-Dependent Hypotonic hyponatremia - Hypervolemia:

Management

-Diuresis to preferentially remove water

- sometimes: fluid restriction

- Optimize underlying condition

ADH-Dependent Hypotonic hyponatremia - Euvolemia

SIADH

ADH secreted inappropriately

SIADH common causes

-Drugs (SSRIs, Opiates, anticonvulsants, antipsychotics)

- Malignancy: Small cell lung cancer

-Pain, post-op

SIADH labs

Urine Osm high, Urine Na usually high

Treatment of SIADH

Discontinue contributing meds, Address underlying issues

Thaizide diuretic induced hyponatremia labs

-Serum sodium low but close to normal range

-Urine Osm high, urine Na high

Other causes of ADH dependent euvolemic hyponatremia

-Nausea, pain, post-op

-Exercise-induced

-Adrenal insufficiency and Hypothyroidism

-Rest Osmostat

Signs and symptoms of acute hyponatremia

Marked neurological symptoms

Goal of treatment for severe hyponatremia

Raise sodium enough to decrease ICP and reverse severe neuro symptoms; about 4-5 mEq

Lab checks for severe hyponatremia

required every 2 hours

Signs and symptoms of chronic hyponatremia

-Asymptomatic

- may have gait issues, concentration or memories issues

Treatment for severe/symptomatic hyponatremia

Hypertonic fluids- 3% NaCl

What is the initial sodium increase target for treating asymptomatic/mild hyponatremia?

Increase sodium by 4-6 mEq over the first few hours.

What is the total sodium increase target for treating asymptomatic/mild hyponatremia over 24 hours?

Increase sodium by 6-8 mEq total over 24 hours.

What are two strategies to manage asymptomatic/mild hyponatremia?

Water restriction or discontinuing the offending agent.

Complication of rapid sodium correction

Osmotic demyelination syndrome

Nephrology referral for hyponatremia

sodium levels are not responding appropriately

Causes of hypernatremia

Issues with thrist mechanism, Lack of access to water, not enough ADH (DI), hypertonic IV fluids

Symptoms of hypernatremia include

neurological symptoms (tremors, irritability, ataxia, confusion, and coma), changes in urine output

Key test for Hypernatremia evaluation

Quantification of urine output, serum Na, Urine osmolality

Oliguric causes of Hypernatremia

Reduced water access or intake, Nonrenal losses (Fever), Shift of water into cells

Nonoliguric + low urine osmolality

Diabetes insipidus

Nonoliguric + high urine osmolality

Osmotic diuresis

Diabetes insipidus

Large volume urine output and dilute urine

Inadquate ADH release from pituitary

Central diabetes insipidus

Decreased sensitivity to ADH effects

Nephrogenic diabetes insipidus

Common causes of nephrogenic diabetes insipidus

Lithium, post-relief of urinary obstruction

If urine output decreases after desmospression/DDAVP administration

Central diabetes insipidus

If urine output does not change after desmospression/DDAVP administration

Nephrogenic diabetes insipidus

Goal of treatment of hypernatremia

-Correct water deficit

- Lower Na by about 12 mEq (faster in adults)

-Address underlying issues

Mainstay treatment for hypernatremia

Hypotonic fluids - IV D5W but can also be PO or via NG tube

Treatment of underlying issues for hypernatremia

Address GI issues, Treat fever, DDAVP if central DI, stop contributing medications, may need alternative means of feeding if long term PO