Neurologic Intensive Care Unit Electrolyte Management

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Key points

  • Alterations in sodium levels are common among intensive care patients, and have been associated with poor outcomes in certain intracranial processes.

  • Differentiating between the syndrome of inappropriate antidiuretic hormone and cerebral salt wasting is imperative in the correct treatment of neurologic intensive care patients.

  • Diabetes insipidus is a common postsurgical finding following pituitary surgery.

Definition

Dysnatremia is a common finding in the intensive care unit (ICU) and has been suggested to be a predictor for mortality and poor clinical outcomes.1, 2, 3 Depending on the time of onset (ie, on admission vs later in the ICU stay), the incidence of dysnatremias in critically ill patients ranges from 6.9% to 15%, respectively.4, 5 The symptoms of sodium derangement and their effect on brain physiology make early recognition and correction paramount in the neurologic ICU (NICU). Hyponatremia in

Diagnosis

Critical illness may result in activity fluctuations of antidiuretic hormone.7, 8 Patients with certain neurologic diseases, such as subarachnoid hemorrhages or traumatic brain injuries, are at an additional risk of dysnatremias. The patient population in an NICU are widespread and include, but are not limited to, traumatic brain injuries (TBIs), hemorrhagic and ischemic strokes, neoplasms, and infections; each has its own prevalence for sodium alterations (Box 1). For example, neurosurgery

Hypernatremia

Hypernatremia in critical illness has numerous causes and can be multifactorial. The diagnostic approach when dealing with dysnatremias should focus on the patient’s volume status.2, 4, 13 This article discusses euvolemic hypernatremia; specifically, DI.

Tonicity refers to the effect of plasma on cells. Hypernatremia always indicates hypertonicity, which results in cell shrinkage.14 Plasma hypertonicity is a powerful stimulus for thirst (polydipsia), but, in acute brain injury, oral intake may

Diagnosis of diabetes insipidus

DI is a clinical diagnosis that can be confirmed with laboratory tests. Clinical features include thirst and polyuria, which can be defined as urinary excretion of greater than 2.5 L in 24 hours for 2 consecutive days.19 Postsurgical DI typically presents in the first 24 to 48 hours following surgery.10 A common approach in the ICU setting for initiating serum and urine electrolyte testing is the presence of greater than 300 mL/h of urine for 2 consecutive hours and a specific gravity of less

Treatment of diabetes insipidus

The goal for treating CDI is focusing on restoring the body’s normal osmotic homeostasis.19 The patient should be allowed to drink to thirst, but, if unable to keep up with fluid losses, additional measures should be taken. The isotonic solution (hypotonic once in the body), 5% dextrose in water, can be given intravenously to match the total output.20 If permanent DI is suspected or serum and urine electrolytes continue to be disrupted despite oral and/or intravenous fluids, ADH should be

Hyponatremia

Hyponatremia has been shown to occur in up to 30% of ICU patients and is one of the most common electrolyte disorders.22 Hyponatremia is the most common electrolyte abnormality in patients with aneurysmal subarachnoid hemorrhage, occurring in 35% to 50% of cases.23, 24 The clinical manifestations of hyponatremia can range from anorexia, headache, nausea, vomiting, lethargy, and seizures in severe cases.15 Symptoms are attributed to cellular edema, which occurs in hypotonic hyponatremia, and can

Syndrome of Inappropriate Antidiuretic Hormone

In the setting of normal kidney and liver function (and exclusion of hypothyroidism/central adrenal insufficiency), SIADH has biochemical findings consisting of hyponatremia, plasma hypo-osmolality, and urine sodium level greater than 30 mmol/L.32 Frequent assessment of serum and urine electrolytes, total intake, and urinary output should be performed when treating SIADH.15, 16 Although correction of the underlying cause is needed, the mainstay treatment of SIADH relies on water intake

Summary

Alterations in serum sodium levels are common among critically ill patients, and may worsen outcomes if not recognized and managed appropriately. Certain dysnatremias have higher incidences in acutely brain injured patients, and have been associated with higher mortality. Before any treatment ensues, clinicians must diagnose the problem. A serum sodium level that is greater than or less than the reference range should warrant further investigation, including assessment of plasma and urine

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