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http://hematol.dxy.cn/article/641916
Hyponatremia: The Simplest Fluid Replacement Method Is Here
Hyponatremia is the most common “electrolyte disorder” among outpatients and inpatients. There are many causes of hyponatremia, and since identifying the cause requires many tests and takes time, for resident doctors, the most common question is “Tell me how to supplement sodium now.” Today, we mainly discuss how to safely supplement sodium in hyponatremia in a clinically operable way.
Normal blood sodium value: 135–145 mmol/L. Blood sodium below 135 mmol/L is called hyponatremia, but several cases of “pseudohyponatremia” must be excluded, namely “hyperglycemia,” “hyperlipidemia,” and “hyperalbuminemia.” These three conditions cause a falsely low blood sodium level, but the actual sodium level is not low. After excluding these three conditions, sodium supplementation is carried out based on different formulas.
Why do we still not know how to supplement sodium after learning so many times about electrolyte disorders and memorizing so many sodium supplementation formulas? First, list the sodium supplementation formulas from different textbooks.
All formulas are listed and analyzed as follows:
7th Edition of Internal Medicine
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Sodium supplement = (125 - measured serum sodium) * 0.6 * weight (kg)
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Sodium supplement = (142 - measured serum sodium) * 0.2 * weight (kg)
8th Edition of Internal Medicine
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Sodium supplement = (125 - measured serum sodium) * 0.6 * weight (kg)
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Sodium supplement = (142 - measured serum sodium) * 0.2 * weight (kg)
7th Edition of Surgery
Sodium supplement = (142 - measured blood sodium) * 0.6 * weight (kg) (multiply by 0.5 for females)
Xiehe Endocrinology
Sodium needed = (142 - patient’s blood sodium) * 0.6 * weight (kg)
Liao Eryuan Endocrinology
Sodium supplement = (140 - measured blood sodium) * 0.6 * weight (kg)
Practical Internal Medicine
Net sodium loss = change in blood sodium concentration * total body water
(Total body water = weight * 0.6; females 0.5)
Two points about the above formulas:
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The body fluid volume accounts for 60% of body weight; females account for 50%; extracellular fluid volume accounts for 20% of body weight; this is the origin of 0.2 or 0.6 in these formulas.
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Hyponatremia has a significant impact on the body, but sodium supplementation should not be too urgent. Supplementing too quickly may affect the nervous system and cause “central pontine myelinolysis” changes. Generally, it is required that sodium in blood should not increase by more than 8 mmol/L within 24 hours.
The amount calculated from the above formulas needs to be supplemented over several days; supplementing all within 24 hours may put the patient at risk.
Therefore, for junior doctors, it is important to know how much sodium should be supplemented in 24 hours.
The author’s summarized sodium supplementation formula is: 8 * 0.6 * weight (kg).
The 8 refers to raising the patient’s blood sodium by 8 mmol/L in 24 hours, and weight * 0.6 refers to body fluid volume. A more conservative approach can use 0.2 instead.
Example:
How much sodium should be supplemented in the first 24 hours for a hyponatremic patient weighing 50 kg?
Sodium needed: 8 * 0.6 * 50 = 240 mmol. In clinical practice, sodium is supplemented through normal saline, so this must be converted into normal saline.
1 g sodium chloride = 17 mmol sodium, 240 divided by 17 = 14 g sodium chloride, so we supplement 14 g of sodium chloride within 24 hours.
0.9% normal saline 500 ml = 4.5 g sodium chloride
10% normal saline 10 ml = 1 g sodium chloride
Postscript: The actual clinical situations encountered are very complex, and specific management needs to be handled based on the different circumstances.
Is the above information too hard to remember? Open the “Medication Helper app,” and you can check anytime under “Calculation & Scales.”
