Sodium and Water Disorders Focus on Hyponatremia

formula to calculate osmolality

(2 * serum Na+ ) + (glucose/18) + (BUN/2.8)

normal serum Na+ levels

135-145mEq/L

general hyponatremia levels

serum Na+ <135mEq/L

serum osmolality for isotonic hyponatremia

280mOsm

serum osmolality for hypertonic hyponatremia

>280mOsm

serum osmolality for hypotonic hyponatremia

<280mOsm

potential causes for hypertonic hyponatremia and how to treat

causes = hyperglycemia, unmeasured effective osmoles

treat with normal saline; underlying cause (i.e. hyperglycemia or diabetic ketoacidosis)

potential causes for isotonic hyponatremia

lab error or hyperlipidemia

hypovolemic lab values

• serum BUN/SCr ratio > 25:1

• urine osmolality >450mOsm/kg

• urine Na >20mEq/L or <20mEq/L

causes for hypovolemic with urine Na < 20mEq/L

loss of Na thru: GI, skin (burns), or lungs

causes for hypovolemic with urine Na > 20mEq/L

diuretics (majority of patients) or adrenal insufficiency

hypervolemic lab values

• urine Na <20mEq/L

causes for hypervolemic

CHF, cirrhosis, or nephrosis

euvolemic lab values

urine Na >20mEq/L or urine Na <20mEq/L

euvolemic causes for Na > 20mEq/L

• SIADH

• renal failure

• hypocortisolism

• hypothyroidism

euvolemic causes for Na < 20mEq/L

psychogenic polydipsia or water intoxication

physical exam expectations for hypovolemic

• hypotensive

• orthostatic hypotension

• dry mucous membranes

• flat jugular vein

• labs = serum Osm <280, UOsm > 450mOsm/kg; UNa depends

physical exam expectations for hypervolemic

• BP normal or elevated

• anasarca or pitting edema

• UNa < 20

• serum Osm < 280

physical exam expectations for euvolemic

usually presents as normal; look at labs

UNa > 20 is usually drug induced; UNa < 20 large intake of water

what are the mandatory rules for hyponatremia treatment with fluids

• max serum Na rate for hypertonic fluids = 0.5-1.5 mEq/L/H

• no more than 6mEq/L increase in first 4 hrs

• max of 12mEq/L increase in first 24 hrs

non-pharmacological treatments for hyponatremia

water restriction, Na restriction, dsc offending agents

pharmacotherapy plan for hypotonic

• DSC offending agent, NS (bolus 200-500mL) to improve orthostatic hypotension and BP

• monitor serum Na q 2-4 hrs until goal >125

pharmacotherapy plan for hypervolemic asymptomatic and chronic

• fluid restriction (1-1.5L/day)

• dietary salt restriction (1-2g/day)

• administer loop diuretics if previous two didn’t work

*do one at a time

pharmacotherapy treatment for hypervolemic symptomatic or severe

• loop diuretics and/or 3% saline

• vasopressin receptor antagonists (only in patients with no contraindication and not in acute phase)

• if those don’t work: dialysis or paracentesis

pharmacotherapy plan for euvolemic symptomatic

• 3% saline

• water restriction

• vasopressin receptor antagonist (once out of acute phase)

pharmacotherapy plan for euvolemic asymptomatic

• water restriction

• demeclocycline 600-900mg/day (maintenance phase)

• urea tablets

• NaCl 9 gram tablets

• vasopressin receptor antagonists (must start in patient)

adverse effects if sodium repletion is done too quickly

too rapid correction greater than 12mEq per 24 hrs can cause an acute decrease in brain cell volume → ODS

what complications are seen in osmotic demyelination syndrome (ODS)

• paralysis and coma 5-7 days after correction (delayed)

• high rate of mortality

• seen with hypertonic saline (3% or 5%)

outline a treatment plan for a HF patient with edema and EF <30%

1: loop diuretic (furosemide 40mg q 8hr)

2: if no response → increase frequency, add thiazide or distal acting diuretic

outline a treatment plan for a HF patient with edema and EF >30%

1: if GFR > 50mL/min, start on HCTZ 25-50mg BID and/or spironolactone 25-50mg/day

if GFR <50mL/min or no response to HCTZ or spironolactone, start on loop diuretic regimen