Effect on brain injury/surgery on plasma electrolyte level

The two most common electrolyte imbalances following brain injury are hypernatremia and hyponatremia


Brain injury is one of the most common types of traumatic injury. In critical care units, patients with moderate to severe brain injury are often intubated and sedated in an effort to diminish the workload of the brain. Agitation or restlessness is common in these patients and can be associated with fever, posturing, tachycardia, hypertension, and diaphoresis. This exaggerated stress response, known as sympathetic storming, occurs in 15% to 33% of patients with severe traumatic brain injury who are comatose (score on Glasgow coma scale [GCS] = 8). Sympathetic storming can occur within the first 24 hours after injury or up to weeks later. The precise mechanism for the increase in activity of the sympathetic nervous system is unknown, but the increased activity is thought to be a stage of recovery from severe traumatic brain injury. Normally the parasympathetic nervous system dampens the effects of increased activity of the sympathetic nervous system and returns the body to homeostasis. In sympathetic storming, this feedback does not occur and the individual is in an uncontrolled state of stress. Prolonged hypertension, arrhythmias, hyperglycemia, hyperthermia due to elevated metabolic rate, and hypernatremia from severe diaphoresis occur as a result of the sympathetic storm. Signs and symptoms vary from episode to episode and from individual to individual


HYPENATREMIA

Hypernatremia is a relatively common problem that can be produced either by the administration of hypertonic sodium solutions or, in almost all cases, by the loss of free water. However, persistent hypernatremia does not usually occur in these settings, because the ensuing rise in plasma osmolality stimulates both the release of antidiuretic hormone (ADH), thereby minimizing further water loss, and thirst, thereby increasing water intake [1-3]. The decrease in water loss and increase in water intake then lower the plasma sodium concentration back to normal.

This regulatory system is so efficient that the plasma osmolality is maintained within a range of 1 to 2 percent despite wide variations in sodium and water intake. Even patients with diabetes insipidus, who have often marked polyuria due to diminished ADH effect, maintain a near-normal plasma sodium concentration by appropriately increasing water intake.

The net effect is that hypernatremia primarily occurs in those patients who cannot express thirst normally: infants; and adults with impaired mental status. The latter most often occurs in the elderly, who also appear to have diminished osmotic stimulation of thirst.

Hospitalized persons, whether old or young, can become hypernatremic as a result of an inadequate fluid prescription and/or impaired thirst.

Hypernatremia due to water loss is called dehydration. This is different from hypovolemia in which both salt and water are lost.



HYPONATREMIA
Hyponatremia develops as a syndrome of inappropriate secretion of antidiuretic hormone (SIADH) or cerebral salt-wasting syndrome (CSWS). 1-3 SIA[DH is characterized by dilutional hyponatremia, and CSWS is characterized by natriuresis as a result of increased serum levels of natriuretic hormone.4 Diabetes insipidus presents with polyuria, serum hypernatremia and hyperosmolarity, and urine hypo-osmolarity, whereas CSWS is associated with polyuria, serum hyponatremia and hypo-osmolarity, and elevated urinary sodium and hyperosmolarity. Serum hyponatremia, serum hypo-osmolarity, urinary sodium exceeding 25 mmol/l, and euvolemia are typical findings in SIADH.


Symptoms of hyponatremia include:

nausea, abdominal cramping, and/or vomiting
headache
edema (swelling)
muscle weakness and/or tremor
paralysis
disorientation
slowed breathing
seizures
coma


-Hyponatremia (Low Na2+ levels) is common with head injury.
-Caused by inappropriate secretion of ADH, leading to increased water retention
-leads to cerebral oedema, and worsens neurologic outcome
-occurs on 5% to 33% of adults with head injury
-25% prevalence in children with head injury
-Polyurea occurs as well


sources:

Burkhard Simma, MD*§, René Burger, MD*, Markus Falk, MSC, Peter Sacher, MD†,
Timo Torresani, PhD‡, and Sergio Fanconi, MD* The Release of Antidiuretic Hormone Is Appropriate in
Response to Hypovolemia and/or Sodium Administration in
Children with Severe Head Injury: A Trial of Lactated
Ringer’s Solution Versus Hypertonic Saline

ww.anesthesia-analgesia.org/cgi/reprint/92/3/641.pdf

https://www.healthatoz.com/healthatoz/Atoz/common/standard/transform.jsp?requestURI=/healthatoz/Atoz/ency/electrolyte_disorders.jsp

http://findarticles.com/p/articles/mi_qa3912/is_199903/ai_n8836003

http://ccn.aacnjournals.org/cgi/content/full/27/1/30




Prepared by Chris Sim