Fluid and sodium loss in the body can cause hypotension, or low blood pressure. The kidneys regulate how sodium circulates in the body. Sodium chloride, or table salt, is the most common form of sodium in your diet. The medical term for low sodium is hyponatremia. According to the National Institutes of Health, low sodium is the most common electrolyte disorder in the United States, and it can be life-threatening.
Causes of Low Sodium
Hypovolemic--low blood volume--hyponatremia with hypotension occurs from vomiting, diarrhea, excessive sweating and some medication combinations. Hyponatremia from other causes is not associated with low blood pressure and can occur when fluid volume in the body is normal or excessive. Congestive heart failure, hormonal imbalances, kidney problems and water toxicity can all lead to hyponatremia associated with normal blood volumes.
Risk Factors
Antidepressants known as SSRIs, pain medications and concurrent use of diuretics can put you at risk for low sodium and hypotension. Fluid pills known as thiazides--such as furosemide, chlorothiazide and metalazone--increase the risk. If you follow a low-salt diet, you also could experience episodes of low sodium and low blood pressure. Other contributors include sweating during hot weather, especially with sports activities and from endurance training and activities.
Symptoms and Lab Tests
Symptoms of hypotension include dry mucous membranes, fatigue, dizziness, fainting, rapid heart rate, blurred vision and nausea. Low sodium levels cause muscle cramping, confusion, headache, fatigue and weakness, loss of appetite, and restlessness and irritability. A serum sodium level below 137 millimoles per liter is considered hyponatremic; the normal range is 137 to 145 millimoles per liter, according to the "Nephrogenic Diabetes Insipidus Foundation." Severe cases of sodium loss can lead to coma, seizures and brain herniation.
Treatment
Intravenous fluid in the hospital is used to replace sodium and treat hypovolemic hyponatremia. Medications can help treat the symptoms of nausea and headache, but you need to treat the underlying reason for fluid and sodium depletion. For example, you might need to adjust your medication to avoid future episodes.
Prevention
Fluid replacement during sports can help maintain fluid and electrolyte balance and prevent hypotension. Patients taking fluid pills should remain aware of symptoms of hyponatremia and discuss personal risk factors when starting new medications. According to the Mayo Clinic website, endurance athletes who are at risk for sodium loss should drink no more than 24 ounces of water per hour to replace lost fluid from sweating. Sports beverages with electrolytes are recommended for marathoners and triathletes.
References
- Mayo Clinic: Hyponatremia
- "Psychiatry Weekly"; Antidepressant-Induced Hyponatremia; Francisco Appiani, MD; July 11 2011
- NDI Foundation: What is the Normal Range of Serum Sodium?
- "The American Journal of Medicine"; "Hyponatremia Treatment Guidelines 2007: Expert Panel Recommendations"; Joseph G. Verbalis, M et al; 2007
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