Hyponatremia and Sodium Emergencies

Hyponatremia is a serum sodium (Na⁺) below 135 mEq/L (135 mmol/L). The first question is whether the low Na⁺ is true hypotonic hyponatremia, with serum osmolality under 275 mOsm/kg. High lipids or protein can pull the measured value down with no excess body water. That is pseudohyponatremia. Hyperglycemic hyponatremia is translocational. Its osmolality reads high, not low, so it is hypertonic, not hypotonic, and sodium is not the answer. Symptoms set the urgency. The number alone does not.

Sodium is the main solute of extracellular fluid. When Na⁺ falls in a hypotonic state, water moves into brain cells. The brain swells. Acute hyponatremia does this fast, which is why seizures and coma happen. Chronic hyponatremia gives brain cells time to lose solute. That makes the brain more vulnerable to rapid correction, and rapid correction causes osmotic demyelination syndrome (ODS).

• Hypovolemic: sodium and water losses from vomiting, diarrhea, burns, third-spacing or diuretics (especially thiazides)
• Euvolemic: syndrome of inappropriate antidiuretic hormone (SIADH), hypothyroidism, adrenal insufficiency, and drugs such as SSRIs and carbamazepine
• Hypervolemic: heart failure, cirrhosis, nephrotic syndrome and kidney failure, where water retention outruns sodium
• Exercise-associated: hypotonic fluid intake during prolonged exertion, with sodium loss in sweat (see Special Populations and Field Considerations)
• Pseudo- and hyperglycemic: lipid or protein artifact, or high glucose drawing water out of cells

Presentation

• Mild: nonspecific symptoms or none (anorexia, unsteady gait, muscle cramps); often silent
• Moderately severe: nausea without vomiting, headache, or confusion
• Severe: vomiting, abnormal somnolence (lethargy), seizure, coma (GCS 8 or less), cardiorespiratory distress, or signs of brain herniation

Red Flags

• Seizure, coma, or a falling Glasgow Coma Scale (GCS)
• Vomiting, abnormal somnolence, or respiratory distress (in known heart failure, cirrhosis or fluid overload, check volume status first; see ALS)
• Na⁺ <120 mEq/L (critical low on the E3 sodium reference)
• Exercise-associated symptoms with a raised core temperature (above 40 °C [104 °F]): treat as heat stroke first

Don't wait on the lab to treat a seizure or coma. The work-up confirms the cause and sets the correction plan.

• Hyperglycemia or diabetic ketoacidosis: the measured Na⁺ reads low, then climbs as glucose is treated. Correct it by about 2.4 mEq/L for every 100 mg/dL of glucose above 100 (the Hillier factor; some references use 1.6). Osmolality is high here, so this is not hypotonic. See Diabetic Ketoacidosis.
• Pseudohyponatremia: a normal measured osmolality with very high lipids or protein, or an IV sample contaminated with fluid.
• Intracranial process: stroke, hemorrhage or a mass lesion can cause a neurologic deficit with normal or low Na⁺. Go after the cause. See Traumatic Brain Injury.
• Intoxication or sepsis: alcohol, opioids or infection can alter mental status with a normal Na⁺. Check the Na⁺, then treat the cause. A number alone won't tell you the cause.

1. Scene and airway: protect the airway and position for seizure or vomiting; suction as needed.
2. Breathing: oxygen to SpO₂ target per protocol if hypoxic.
3. Glucose: check it when a meter is available.
4. Seizure precautions: protect from injury and time the event; do not restrain.
5. Oral intake: nothing by mouth while mental status is altered.
6. Exercise-associated: check core temperature. Above 40 °C (104 °F) is heat stroke: cool immediately. In mild cases, restrict fluid and offer salty broth by mouth if the patient can swallow; do not give large volumes of hypotonic fluid. Avoid isotonic or hypotonic IV fluid for suspected exercise-associated hyponatremia.

Notify early. Severe or seizure presentations get transport priority.

Doses vary by protocol; follow local protocols and medical direction.

• IV access (Paramedic/RN/CCT): a peripheral IV is fine for 3% saline. See IV insertion.
• Glucose and 12-lead ECG (Paramedic/RN/CCT): rule out hyperglycemia. Look for a cardiac cause of syncope or collapse.
• Severe symptoms (vomiting, abnormal somnolence, seizure, coma, or cardiorespiratory distress) (Paramedic/RN/CCT): 3% NaCl 100 mL IV over 10 min; repeat up to 2 more times until symptoms resolve or Na⁺ rises 4–6 mEq/L. Respiratory distress counts only when suspected hyponatremic encephalopathy or neurogenic pulmonary edema is the cause. With known heart failure, cirrhosis or fluid overload, check volume status and get medical direction before any hypertonic bolus. Repeated boluses can worsen pulmonary edema. See Hypertonic Saline 3%.
• Before each repeat: check Na⁺ where a result is available. No sodium result? Medical direction decides any repeat, to a maximum of 3 boluses in total.
• Pediatric severe symptoms: 3% NaCl 2 mL/kg IV over 10 min, max 100 mL per dose, per pediatric protocol and medical direction. Published pediatric ranges differ, and some use up to about 5 mL/kg. Confirm the dose with the local pediatric protocol. Repeat only with medical direction. Recheck Na⁺ first, and stop at a 4–6 mEq/L rise or symptom resolution. See Weight-Based Dosing.
• Moderately severe symptoms (nausea without vomiting, confusion, headache): one 3% bolus, per protocol, while the cause is worked up.
• Seizure: treat as status epilepticus per protocol. Check glucose and treat hypoglycemia if present. Benzodiazepines may not stop a hyponatremic seizure. Hypertonic saline is the treatment aimed at sodium, but it does not replace airway support or seizure control. See Status Epilepticus.
• Exercise-associated hyponatremia with severe symptoms: 3% NaCl 100 mL IV bolus, repeated every 10 min, up to three boluses in total (Wilderness Medical Society 2019). A core temperature above 40 °C (104 °F) means heat stroke: cool immediately. Boluses can run alongside cooling. Skip isotonic and hypotonic IV fluids.
• Avoid hypotonic IV fluids: D5W and 0.45% saline (D5W, half-normal saline) push Na⁺ lower, and neither one treats hyponatremia.

Mild, asymptomatic hyponatremia gets no ALS bolus. Transport, and treat the cause. Expert-panel and Wilderness Medical Society guidance sets the bolus schedules here. The 3% NaCl label covers concentration and labeled use, and it does not set this schedule.

Correction targets and limits

• Target: stop 3% boluses once symptoms resolve or Na⁺ has risen 4–6 mEq/L. A normal Na⁺ is not the bolus target.
• High ODS risk (Na⁺ ≤105 mEq/L, alcohol use disorder, malnutrition, hypokalemia, liver disease): limit the rise to 8 mEq/L in any 24 hr.
• Standard risk: no more than 10 mEq/L in the first 24 hr, then no more than 8 mEq/L in each later 24 hr. Guidelines disagree, and some protocols run tighter. The team sets the exact ceiling per local protocol.
• Tolvaptan (vasopressin antagonist, not a substitute for hypertonic saline): it is indicated for clinically significant hypervolemic and euvolemic hyponatremia. The FDA boxed warning says too-rapid correction (for example, more than 12 mEq/L in 24 hr) can cause osmotic demyelination. Start and re-start it in hospital, with close Na⁺ monitoring. It is not for urgent treatment of serious neurologic symptoms. It is not for hypovolemic hyponatremia, and it is not for ADPKD outside the FDA-approved REMS. See tolvaptan labeling.

Overcorrection

If Na⁺ rises past the limit, or urine turns sudden and dilute: stop hypertonic saline, hold any isotonic fluid, and check Na⁺ at short intervals. Re-lowering uses electrolyte-free water and desmopressin, given per nephrology or ICU protocol. Desmopressin is off-label for this use. Its label contraindicates it for hyponatremia, so use it only with expert direction. Dosing per the Desmopressin page: 1–3 mcg IV or SC, not more often than every 8–12 hr, with Na⁺ checked after each dose. D5W volume is set by protocol and is not stated here. The goal is to bring Na⁺ back under the limit. Some centers run a proactive clamp in high-risk patients: desmopressin with a set water intake and 3% saline, to hold Na⁺ steady. That is expert-directed, not a standard E3 pathway. After correction, any new dysarthria, dysphagia, weakness or change in consciousness calls for a neurology consult.

Hypernatremia

Hypernatremia (Na⁺ above 145 mEq/L) usually means losing free water. The causes are osmotic diuresis, diabetes insipidus, or no access to water. Slow is the rule: a fast fall can bring cerebral edema. Adrogué and Madias suggest a drop of no more than about 0.5 mEq/L per hour, and about 10–12 mEq/L in 24 hr for chronic cases. Faster is for acute severe symptoms, and only under expert direction.

• Fluid by volume status: if hypovolemic or unstable, isotonic saline first; then hypotonic fluid (D5W or half-normal saline) to replace the free-water deficit, per the team plan (see Sodium).
• Main causes: osmotic diuresis, diabetes insipidus, no access to water, or fluid losses.

Escalation and disposition

Admit to a monitored unit for serial Na⁺ and neuro checks. Seizure, GCS decline, airway compromise or symptoms that persist after two boluses mean ICU. Renal cause or a complex correction plan? Refer to nephrology.

• Destination: a unit that can check Na⁺ on schedule and hold a pump-controlled infusion. Notify the receiving team of the Na⁺ value, the bolus volume given and the time.
• Continue and monitor in transit: neuro status, seizure activity, airway, and a pump for any running infusion (no free-flow bags).
• Handoff: the last Na⁺, the boluses and their times, the 24-hour ceiling, and what urine output is expected.
• Equipment: 3% saline in a labeled bag or syringe (not 0.9%); keep 23.4% concentrate out of the field kit unless protocol says otherwise.

• Pediatrics: 3% NaCl 2 mL/kg IV over 10 min, max 100 mL per dose, for severe symptoms, per pediatric protocol and medical direction (published ranges differ); use actual body weight. Check Na⁺ closely. Children regulate water and sodium poorly. See Vital Signs.
• Pregnancy: severe symptomatic hyponatremia is treated as an emergency. 3% saline is for a confirmed severe presentation only. A seizure or altered mental status in pregnancy means eclampsia has to be considered: magnesium per the obstetric protocol. Preeclampsia and sodium retention raise the risk of pulmonary edema. See Preeclampsia and Eclampsia.
• Older adults: low body weight and reduced kidney function raise the overcorrection risk when boluses are fixed. Start at the low end and recheck Na⁺.
• Renal impairment: this page establishes no dose adjustment. Kidney failure favors sodium and water retention. Check weight, lung exam and volume before each bolus. Watch Na⁺.
• Hepatic impairment: cirrhosis raises ODS risk and the risk of fluid overload. Use the 8 mEq/L in 24 hr high-risk ceiling.
• Heart failure: a high risk of pulmonary edema. Check volume status before any bolus. Give the smallest effective dose, and reassess lungs after each one.
• Patients on diuretics or SSRIs: stopping the drug can set off a water diuresis and fast autocorrection. Recheck Na⁺ after any change.

• Error: treating a bolus as the end of care. The rise after the bolus still needs checking. A water diuresis can overcorrect once the bolus stops.
• Error: giving D5W or half-normal saline for severe symptoms. In a hypotonic state, both drop Na⁺ further. Use 3% saline.
• Error: using 0.9% saline when 3% is needed, or the reverse. Read the percentage on the bag and the syringe aloud before you spike or draw up.
• Error: missing hyperglycemia. Check glucose first. High glucose pulls the measured Na⁺ down.
• Error: isotonic saline in a hypovolemic or thiazide-treated patient can set off rapid autocorrection. Check Na⁺ after the first fluid, and again when any diuretic is stopped.
• Error: pushing a fast bolus into an asymptomatic or chronic patient and overcorrecting. Set the limit before the first bolus.
• Error: repeating 3% boluses in heart failure or fluid overload with no volume check. Get medical direction first.
• Error: giving 23.4% concentrate peripherally or in the field. It belongs on a central line under ICU protocol.