# *** Hyponatremia [symptomatic; acute vs. chronic >48 hours; mild 130-134, moderate 120-129, severe <120]
-- ABCs: if severe (<120) or symptomatic, page renal and consider ICU due to need for close monitoring and frequent lab draws
-- Chart Check: baseline Na, medication use
-- Admission Criteria: *** no strict criteria
-- HPI Intake: diet, alcohol, meds, co-morbidities including CHF, cirrhosis, ESRD, cancer
-- Can't Miss: *** EtOH use, seizure risk, rapid overcorrection
-- Admission Orders: *** serum Osm, Urine Osm, Urine Na, strict I/O's, BNP if evidence of CHF; fluids vs diuretics
-- Initial Treatment to Consider: if severe with symptoms - immediate hypertonic (3%) saline 100mL bolus over 10 mins to get Na up 4-6 points
-- History: *** meds, diet, EtoH use, hx of CHF, cirrhosis, CKD, cancer, endocrine disorder
-- Clinical: *** seizure, N/V, weakness
-- Exam: *** AMS, weakness, volume exam
-- Data: *** Na, Serum Osm, Urine Osm, Urine Na (SOsm <300 if hypotonic, UOsm >100 if ADH present, UNa <30 if RAAS active)
-- Etiology/DDx: *** hypovolemia, decreased effective circulating volume (3rd spacing), SIADH (infection, malignancy, meds, primary brain injury or lesion), ESRD, primary polydipsia, low solute
Working Through The Differential:
Is this hypotonic hyponatremia? (SOsm <300) - if not, "pseudohyponatremia" from hyperglycemia, protein
Is ADH present? (UOsm > 100) - if not, primary psychogenic polydipsia, tea and toast, beer potomania
Is RAAS On? (UNa <30) - if yes, hypovolemia or 3rd spacing 2/2 CHF or cirrhosis; if no, salt wasting via SIADH, diuretic use, ESRD, or endocrine etiology
The patient's HPI is notable for ***. Exam showed ***. Labwork and data were notable for ***. Taken together, the patient's presentation is most concerning for ***, with a differential including ***.
-- Serum Osm, Urine Osm, Urine Na
-- if unclear etiology, can also send TSH, lipid screen, SPEP/UPEP, serum cortisol and ACTH, UDS, BNP
-- BMP q ***
-- Correction Goal: *** at a rate of 4-6 per 24 hours
-- Volume: *** (IVF vs diuresis) Severe with Sxs - 3% NaCl 100mL bolus over 10 min (to Na raise 1-3) given up to 3x to get Na up 4-6; Severe without Sxs - 3% Na Cl drip until Na >125; Otherwise, volume repletion by exam
-- if ADH Absent - restrict fluids, slow introduction of solute; high risk of overcorrection
-- if ADH on, RAAS Active - replete if hypovolemic, diuresis if CHF, nephrotic syndrome
-- if ADH on, RAAS Off - likely SIADH, restrict 0.8L/day, salt tabs 1g TID; consider Lasix, vaptans
Hyponatremia is a common (often incidental) finding in the inpatient setting. It is often clinically insignificant and will correct on its own with treatment of the patient's underlying disease process (usually giving fluid or diuretics), but in severe circumstances will lead to symptoms and require renal involvement and hypertonic (3%) fluid administration to rapidly raise the sodium to get it out of the severe symptomatic range.
Hyponatremia represents an excess of water compared to sodium and thus determining the etiology comes down to whether your body is holding on to water appropriately or not. The most common causes are by far hypovolemia, decreased effecive circulating volume (3rd spacing) from CHF or cirrhosis, and ESRD. In general, if SOsm is <300 it is true hyponatremia, if UOsm is >100 then ADH is present, and if UNa is <30 RAAS is active.
Osmotic Demyelination Syndrome (ODS) is the feared complication of overcorrection >8 in 24 hours or >18 in 48 hours since it can lead to locked-in syndrome. However, there is low risk overall if starting Na is >120. Be on alert and get renal involved if Na <105, the patient has chronic malnutrition, or uses EtOH as these all increase the risk of ODS. If you overcorrect, give D5W.