There are 6 major electrolytes. Sodium, potassium, calcium, chloride, magnesium and phosphorus. It is primarily potassium, calcium and sodium that will cause problems when they are out of whack.
When there is a sodium imbalance quite often there will be changes in mental status - confusion, delirium, etc. Often seen with traumatic brain injury where diabetes insipidus (pathological voiding of large amounts of dilute urine) and its opposite SIADH (syndrome of inappropriate antidiuretic hormone - minimal urine output but very concentrated) may occur. Sodium imbalances are also seen with dehydration in some patients (elderly, burn victims, many others) and the blood levels will go up. Very rarely, sodium levels in the blood will go down because of consuming large quantities of fluids.
The other main electrolyte imbalance seen is when potassium is out of whack, and its most serious consequence is cardiac problems that can be life-threatening (you will see T wave changes: depression with hypokalemia, elevation with hyperkalemia, among other changes in the EKG like QRS interval changes).
For these 2 main electrolyte imbalances remember: Sodium equals mentation, and Potassium equals cardiac.
Sodium does affect fluid. In fact, they say sodium always follows water. There are a lot of people with edema related hypernatremia; and a lot of dehydration related to sodium and chloride losses. Potassium tends to affect the heart and in the clinical area you will see dramatic instances of people with hypokalemia and hyperkalemia. Calcium affects the muscles and is not as commonly seen clinically because it is detected because of lab testing.
Sodium - body water balance
Potassium - contraction of skeletal and smooth muscle and nerve impulse conduction
Calcium - formation and structure of bones and teeth, cell structure and function, cell membrane permeability and impulse transmission, the contraction of all muscle types and is necessary in the blood clotting process
Chloride - important in the digestive acids; closely linked to sodium
Magnesium - affects nerve and muscle action by affecting calcium usage, activates enzymes involved in carbohydrate and protein metabolism, helps in the transport of sodium and potassium across cell membranes, and influences the levels of sodium, potassium, calcium and some body hormones (parathyroid hormone)
Phosphorus - formation and structure of bones and teeth, this electrolyte is needed in the following activities: utilization of B vitamins, acid base homeostasis, bone formation, nerve and muscle activity, cell division, the transmission of hereditary traits, metabolism of carbohydrates, proteins and fats
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