Fluid and Electrolytes In Critical Care

Sodium Imbalance

nursebob 07/25/10



Hypertonic solutions contain higher concentrations of solutes than those in surrounding cells resulting in the cell shrinking in size.

Hypotonic solutions contain lower concentrations of solutes surrounding cells resulting in the cell swelling. Has a greater concentration of free molecules than inside the cell, Will give water to hydrate the cell. Should be given slowly because of sudden shift into the cell which can occur. 2.5 per cent in 0.45 NS Ringers Lactate.

Isotonic solutions contain equal concentrations of solutes than those in surrounding cells and the cell volume remains unchanged.
The first figure below shows the effect of these solutions on blood cells.

Hypernatremia is usually caused by water loss from the gastrointestinal, respiratory, or from the Kidneys. There are two questions which are of paramont importance which must be answered before the treatment of hypernatremia can be initiated. First how can the water deficit be determined and secondly, at what rate can the plasma sodium concentration safely be replaced?

What is going on in the body?

Too much sodium in the blood may be caused by: corticosteroid medications, such as prednisone, aldosteronism, a condition in which the body produces too much aldosterone, inability to drink water or not drinking enough water, excessive intake of salty foods, diabetes, kidney disease and heart disease.

Salt or sodium imbalance occurs when there is too little or too much sodium in the bloodstream. The condition is called hyponatremia when there is too little sodium, and hypernatremia when there is too much sodium in the bloodstream. The kidneys absorb most of the sodium in the body. Sodium helps the kidneys to regulate water levels in the body. Normally, the sodium-water balance in the body is regulated by the hormone aldosterone. This hormone causes the kidneys to hold onto water. When this system is out of balance, the body either gets rid of or absorbs too much sodium. Common signs and symptoms of salt imbalance include: muscle cramps, especially after exercise weakness, often the first symptom of hyponatremia irritability, confusion, restlessness and agitation changes in heart rate, heart beat, and blood pressure tissue swelling retaining fluid in the body eliminating large amounts of urine, neausea, depression, lack of coordination, seizures and finally coma.

Water Deficit.

Water deficit can be estimated from the following standard calculations. The total body water is normally about 60 percent lean body weight in men and about 50 percent lean body weight in women. The following formula can be used to estimate the amount of water deficit. keep in mind that this formula does not include any added isosmotic fluid deficit that is frequently associated when both sodium and water have been lost. This could occur with diarrhea or gastrointestinal disturbance as well as dialysis.

For example if you had a 60 kg female with a plasma sodium concentration of 168 meq/L the water deficit can be calculate as follows.

Water deficit = 0.4 X 60 (168/140 - 1)

= 4.8 Liters

This formula recomends 4.8 Liters of water to return to a sodium balance of 140 for this 60 kg female.

Remember this is only the minimal replacement number. Additional water may be required if the insatiable losses and initial causes of hypernatremia are not treated.

How Fast Should Hypernatremia Be Corrected

Hypernatremia initially causes fluid to be pulled from the cells of the brain resulting in shrinkage. This is the primary cause of the neurological symptoms associated with hypernatremia. Once treatment is started it may take between one to three days for the cereboshrinkage to be corrected. This is accomplished due to the water movement from the cerebrospinal fluid into the brain and the uptake of solutes by the cells thereby pulling water into the cells and restoring cellular volume. Treatment must be exercised with caution once cerebroshrinkage has been corrected. Osmotic movement of water into the brain may increase the brain size above normal. This can lead to seziures and other neurological changes.


Too little sodium in the blood may be caused by: Over use of diuretics are another common cause in the elderly. Excessive exercise and sweating, severe vomiting, diarrhea, burns. Renal conditions may affect sodium balance Chronic renal failure. High fever. Another cause is Addison's disease which is a condition in which there is not enough of the hormone cortisol in the bloodstream. Congestive heart failure


Symptoms of hyponatremia, usually don't appear until serum sodium falls below 125 mEq/liter. Common complaints include headache, nausea, vomiting, diarrhea, abdominal cramps, muscle tremors, twitching, and weakness. If severe, hyponatremia can cause confusion, seizures, and coma; even mild hyponatremia can cause confusion in the elderly.

The treatment for hyponatremia is usually the administration of sodium supplements as prescribed. Since there will be a shifting of fluids into the brain monitoring of neurologic status and initiation of seizure precautions are essential as well as the monitoring sodium and chloride levels.

To restore fluid and sodium levels in hypovolemic hyponatremia, D5 Sodium Chloride should be ordered to be given via slow intravenous infusion. The serum sodium level should never be increased by more than 0.5 mEq/L/Hour unless the patient is in severe hyponatremia. Monitor fluid intake and output and vital signs for signs and symptoms of circulatory overload.

the patient must be monitored for worsening signs and symptoms of respiratory distress from fluid overload and this should be reported immediately. You should be restricted to 1202 1500 ml per night. Adventure met medications such as diuretics as prescribed. Assess weight, fluid intake and output, oxygen saturation, electrolytes.


Schmidt, Tracy, RN, “Assessing a Sodium and Fluid Imbalance”, Nursing 2000, Volume 30 Number 1, p18


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