EM@3AM: Hypernatremia

Author: Mark M. Ramzy, DO, EMT-P (@MarkRamzyDO, EM Resident Physician, Drexel University, Department of Emergency Medicine) // Edited by: Alex Koyfman, MD (@EMHighAK) and Brit Long, MD (@long_brit)

Welcome to EM@3AM, an emDOCs series designed to foster your working knowledge by providing an expedited review of clinical basics. We’ll keep it short, while you keep that EM brain sharp.

A 61-year-old male presents in middle of July with altered mental status. He is accompanied by his son who states the patient has been increasingly weak for the past three days. The patient has been having multiple episodes of non-bloody diarrhea with associated decreased appetite. Further history reveals the son has yet to install an air-conditioning unit in the patient’s room at home. The patient is unable to provide any additional information or review of systems due to his confusion.

Initial triage vital signs include BP 104/66, HR 111, RR 18, SpO₂ 99%, Temp 36.9 ^oC.

Exam findings include an awake elderly Caucasian male not oriented to person, place, time, or event. He appears clinically dehydrated with dry mucous membranes and poor skin turgor with tenting. Remaining exam shows no pertinent positives. An initial rapid VBG reveals a sodium of 161 mEq/L.

What is the diagnosis, and what investigations, therapies, and complications do you need to consider?

Answer: Hypernatremia 

Definition: Serum or plasma sodium [Na⁺] greater than 145 mEq/L and serum osmolality greater than 295 mOsm/L.

• Severe hypernatremia occurs at [Na⁺] greater than 160 mEq/L, or if symptoms due to hypernatremia are present.
• The condition is mainly a result of a deficit in total body water (TBW) or a net gain of Na^+­­. This is most commonly due to deficit in TBW.

Causes and risk factors: Limited availability to free water, kidneys failure to concentrate urine, increased salt intake, or any clinical situation that interferes with a patient’s ability to sense thirst. The loss of free water in diarrhea or excessive urination may also cause significant hypernatremia.^1,2  Nephrogenic or central diabetes insipidus may be a cause of hypernatremia.

• Infants, recently hospitalized patients, and the elderly are at higher risk of developing hypernatremia.^1,2
• Of note, hypernatremia not only increases mortality but when present in elderly patients, it is a marker for severe systemic illness.^3,4
• In both elderly and hospitalized patients, hypernatremia is often iatrogenic and can result from the inappropriate administration of intravenous fluids (IVF).^4,5

History: Symptoms often include thirst, nausea, vomiting, fatigue, weakness, lethargy, muscle twitching, spasms, seizures, altered mental status, and coma. Take note of environmental factors that may be contributing to increased water loss. Ask about medications, illnesses, co-morbidities, intake, and output.

Physical Exam: Exam findings vary but often include hypotension, tachycardia, sunken eyes, dry mucous membranes, poor skin turgor, and in severe cases, altered mental status. Depending on the severity and time without intervention, coma, seizures, and shock may occur.

Management: Regardless of the initial sodium level, correcting the sodium either too quickly or too slowly is associated with an increased risk of death.⁶  Therefore the treatment of hypernatremia requires appropriate timing and a systematic approach.

1. Resuscitate: Volume deficits and hypoperfusion must be quickly corrected if they are present. To do so, use of isotonic saline solution is recommended. Again, this is only if the patient has evidence of hypoperfusion noted by persistent hypotension or end-organ damage (ie. elevated lactate, AKI, etc). It may seem counterproductive giving a fluid with sodium to a hypernatremic patient, however, the goal is to restore homeostatic mechanisms of sodium balance. The rate of correction is extremely vital to remember: do not lower more than 0.5 mEq/L/h or 10 to 12 mEq over 24 hours. If the patient is not hypovolemic and perfusing well, then use of hypotonic fluids such as D5W or ¼ normal saline is appropriate.
2. Investigate: Identify the underlying cause of the hypernatremia and address it. Look for sources of infection if the patient has a fever, as this form of extrarenal water loss may contribute to hypernatremia. Obtaining a urine sodium and urine osmolality will help identify the cause of low volume status and better direct management. Recognizing other electrolyte abnormalities such as hypokalemia and hypercalcemia may point towards renal causes of hypernatremia. A new diagnosis of sarcoidosis, multiple myeloma, or a pituitary tumor may raise suspicion for hypernatremia secondary to nephrogenic or central diabetes insipidus. Start with ordering a Basic Metabolic Profile (BMP), extended electrolytes (ie. magnesium, phosphorus, etc), urine sodium, and urine osmolality (or urine specific gravity if urine osmolality is not readily available).
3. Rehydrate: Understanding the effect of 1 liter of any infusate is vital to the management of the hypernatremic patient and correction of the sodium. Knowing how much sodium is in each of the infusates used can more accurately correct the sodium and also help you track if treatment is heading in the right direction (See Table 1). Scott Weingart recommends the use of Adrogue Madias’ formula to see how much the infusate administered affects the patient’s sodium with rechecks every couple of hours.⁷

Complications: Hypernatremia when untreated can result in several complication such as altered mental status, rhabdomyolysis, seizures, and impaired glucose use.

Pearls:

1. Resuscitate: Correct volume deficits and hypoperfusion. Do not lower more than 0.5 mEq/L/h or 10 to 12 mEq over 24 hours. If the patient is not hypovolemic, use D5W.
2. Investigate: Address the underlying cause of hypernatremia. Consider electrolyte imbalances, sarcoidosis, nephrogenic or central diabetes insipidus.
3. Rehydrate: Use Adrogue Madias’ formula to understand how much each infusate affects the patient’s sodium and adjust treatment course with frequent checks.

A 32-year-old man who became lost while hiking in the desert is rescued after several days. He is lethargic, confused, and appears severely dehydrated. His weight is 75 kg and his serum sodium level is 158 mg/dL. What is the patient’s total body water deficit?

A. 3.8 L

B. 4.8 L

C. 5.8 L

D. 6.8 L

Answer: C

Hypernatremia is defined as a serum sodium concentration > 145 mEq/L. Most cases of hypernatremia are due to a total body water deficit. Heatstroke, increased insensible losses from burns or sweating, and gastrointestinal fluid losses from diarrhea or protracted vomiting can all result in hypernatremia. Patients without access to water or impaired thirst mechanisms are at particular risk for hypernatremia, including elderly bedridden patients, those with mental impairment, and patients who are in a coma. Diabetes insipidus, a condition in which there is insufficient antidiuretic hormone production, results in decreased water reabsorption and can also result in hypernatremia. Patients with hypernatremia may complain of thirst, have obvious causes of fluid losses, or may be asymptomatic. Altered sensorium is common as sodium levels rise and hypernatremia should be considered in all patients presenting with altered mental status, particularly those with severe mental impairment, head injury, or impaired access to water. The degree of hypernatremia corresponds well with the total body water deficit. A patient’s total body water can be estimated by multiplying the patient’s body weight in kilograms by 0.6. Correction factors are available for elderly patients, who have a lower muscle mass than younger individuals. Total body water (TBW) deficit in can be calculated with the following formula: TBW deficit = TBW x (serum Na+/140) – 1. In this case, the patient’s TBW deficit is (75 x 0.6) x (158/140 – 1) = (45 x (1.13 – 1) = 5.79 liters. The treatment of hypernatremia involves fluid repletion and slow correction of patient’s sodium level.

3.8 L (A), 4.8 L (B), and 6.8 L (D) are all incorrect.

Rosh Review Website Link

References/Further Reading:

1. Reynolds, RM; Padfield, PL; Seckl, JR (25 March 2006). “Disorders of sodium balance”. BMJ (Clinical research ed.). 332 (7543): 702–5. doi:10.1136/bmj.332.7543.702. PMC 1410848 Freely accessible. PMID 16565125
2. Sam R, Feizi I: Understanding hypernatremia. Am J Nephrol 36: 97, 2012.
3. Lindner G, Funk GC, Schwarz C, et al. Hypernatremia in the critically ill is an independent risk factor for mortality. Am J Kidney Dis 2007; 50:952.
4. Snyder NA, Feigal DW, Arieff AI. Hypernatremia in elderly patients. A heterogeneous, morbid, and iatrogenic entity. Ann Intern Med 1987; 107:309.
5. Palevsky PM, Bhagrath R, Greenberg A. Hypernatremia in hospitalized patients. Ann Intern Med 1996; 124:197.
6. Bataille S, Baralla C, Torro D, et al: Undercorrection of hypernatremia is frequent and associated with mortality. BMC Nephrol 2014; 15: pp. 37
7. Scott Weingart. Podcast 187 – Hypernatremia (Uggggh!). EMCrit Blog. Published on November 28, 2016. Accessed on June 29t