Sodium Flashcards
(44 cards)
Describe how sodium is distributed among the body compartments.
What is the major physiologic function of sodium?
Sodium is the major EXTRACELLULAR cation
Pumped out of cells by the Na/K-ATPase
Physiologic functions of sodium:
Flows into cells down its gradient during depolarization
What is the normal serum osmolality?
275-290
What is the pathophysiology that underlies the clinical manifestations of hyponatremia?
The symptoms directly attributable to hyponatremia primarily occur with acute and marked reductions in the serum sodium concentration and reflect neurologic dysfunction induced by cerebral edema
The associated fall in serum osmolality creates an osmolal gradient that favors water movement into the cells, leading to brain edema.
Basically the brain tissues swell because water flows into them down its osmotic gradient
Ultimately, ICP can increase and herniation can occur
What are the potential clinical manifestations of hyponatremia?
The major clinical manifestations of acute hyponatremia include:
Nausea and malaise, which are the earliest findings, may be seen when the serum sodium concentration falls below 125 to 130 mEq/L.
Headache, lethargy, obtundation and eventually seizures, coma, and respiratory arrest can occur if the serum sodium concentration falls below 115 to 120 mEq/L.
Noncardiogenic pulmonary edema has also been described.
The degree of cerebral edema and therefore the severity of neurologic symptoms are much less with chronic hyponatremia
Provide an approach to thinking about the causes of hyponatremia.
1) Fluid shifts
“Hyperosmolar hyponatremia”
“Pseudohyponatremia”
Non-specific term, in EMCrit refers to hyponatremia that is not hypoosmolar
Basically, check the serum glucose and correct sodium for glucose
2) Increased free water intake
Primary polydipsia and beer drinker’s potomania
3) Increased free water retention / decreased free water excretion
ADH-dependant hyponatremia, “hypoosmolar hyponatremia,” “true hyponatremia,” the meat and potatoes of hyponatremia
Usually divided into hypervolemic, euvolemic, and hypovolemic
What is the major cause of hyperosmolar or pseudohyponatremia?
Hyperglycemia
How do you correct the sodium for glucose?
The sodium concentration will fall by approximately 2 mEq/L for each 5.5 mmol/L increase in glucose concentration
Approximately 1:3
What are the major causes of increased free water intake?
Physiologic - decreased plasma tonicity (thirst stimulated)
Patholoic -
Psychogenic polydipsia (seen in schizophrenia) Beer drinker's potomania
What are the causes of hypoosmolar or true hyponatremia?
Categorized by volume status
Hypervolemic with decreased effective circulating volume (heart failure, cirrhosis, nephrotic syndrome)
Euvolemic
SIADH
Hypovolemic
What are some causes of SIADH? Name 5.
CNS disease
Any CNS disorder, including stroke, hemorrhage, infection, trauma, and psychosis, can enhance ADH release
Lung cancer
Ectopic production of ADH by a tumor is most often due to a small cell carcinoma of the lung and is rarely seen with other lung tumors
Drugs
Anticonvulsants
SSRIs
Endocrinopathy
Hyper or hypothyroidism
Adrenal insufficiency
HIV infection
You discover hyponatremia. What further work-up would you order to determine the cause? Name 5 investigations.
Serum osmolality Urine osmolality Urine electrolytes TSH Cortisol
What does urine osmolality tell you?
Tells you if the body is retaining or releasing free water.
Proxy marker of whether ADH is “on” or “off”
What is the significance of low urine osmolality?
Low urine osmolality = dilute urine = ADH “off” (body releasing free water)
Suggests excess free water intake, body responding appropriately
What is the significance of high urine osmolality?
High urine osmolality = concentrated urine = ADH “on” (body retaining free water)
Suggests hypoosmolar or “true” hyponatremia
May be appropriate or inappropriate
What does urine sodium tell you?
Tells you about the effective circulating volume
What is the significance of low serum sodium?
Body attempting to retain sodium to increase intravascular volume
Suggests decreased intravascular volume, either hyper or hypovolemic
What is the significance of high urine sodium?
Body releasing sodium
Suggest SIADH
Provide an overview of the treatment of hyponatremia.
1) Send the work-up
2) Free water restrict all patients
3) Determine whether administration of a hypertonic solution is indicated
What are the indications for the administration of a hypertonic solution?
Indicated in symptomatic hyponatremia, e.g.:
Seizure
Confusion
Headache, nausea, vomiting
Dizziness, gait instability, tremor, multifocal myoclonus
Clinical context is more important than the numeric value of sodium, for example:
Young woman with acute hyponatremia, Na of 125 mM, nausea and headache: This is an emergency, give hypertonic therapy immediately.
Elderly man with chronic hyponatremia, Na of 125 mM, asymptomatic: This might not even warrant hospital admission, don’t get too excited about it.
What are the different hypertonic solutions that can be given in symptomatic hyponatremia?
Sodium bicarbonate
3% saline
Describe the advantages and the administration of sodium bicarbonate in symptomatic hyponatremia.
Hypertonic bicarbonate is defined here as 1 mEq/ml sodium bicarbonate, which is generally found in ampules of bicarbonate in crash carts.
This solution of 1 mEq/ml sodium bicarbonate has the same tonicity as would 6% NaCl.
In the United States, each hypertonic bicarbonate ampule generally contains 50 ml
Hypertonic bicarbonate is usually the fastest medication to obtain in an emergency.
A typical dose is two ampules (100ml) of hypertonic bicarbonate
Ampules of bicarbonate should generally be infused slowly (e.g. each one over 5-10 minutes).
Bicarbonate is contraindicated in patients with metabolic alkalosis, which would be exacerbated by the bicarbonate.
2 amps of sodium bicarbonate is approximately the equivalent equivalent to giving ~200 ml of 3% saline, which will raise the serum sodium by ~3 mM).
Describe disadvantages and the administration of 3% saline in symptomatic hyponatremia.
3% saline may be provided in a dose of 2 ml/kg body weight (e.g. ~150 ml)
This is the traditional therapy for hyponatremia.
The main drawback is that it often takes a long time to receive from the pharmacy.
Please note that 3% saline IS SAFE to administer through a peripheral line.
3% saline does NOT require placement of a central line
How fast should the serum sodium be corrected?
Hourly rate:
No faster than 0.5 mEq/L in any given hour
Excludes the initial rise obtained from the administration of hypertonic saline, which may be about 3-5 mM
Daily rate:
No faster than 8 mEq/L in the first 24 hours
Note that this includes the initial rise if a hypertonic solution was provided
What is the feared complication of raising the serum sodium too quickly?
Osmotic demyelination syndrome (ODS)
Previously called central pontine myelinolysis
