This ensures that the administered fluid remains in the extracellular intravascular compartment, where it will do the most good to support blood pressure and peripheral perfusion. Therapy may be started with a rapid bolus of 0. But correction of dehydration must be accompanied by provision of maintenance fluid.

After all, the child is breathing, losing free water through the skin, and is urinating! As discussed earlier, maintenance fluid is provided as D5NS. The blood pressure is low and the heart rate is very high. This child is in shock. The goal is to rapidly stabilize the vital signs; maintenance fluid is not a consideration at this time.

The vital signs stabilize the bolus can be repeated if necessary. Step 2: The patient is transferred to the inpatient unit. By this time, serum electrolyte levels are available and the serum sodium concentration is within the normal range. Subsequent fluid therapy is calculated as follows:. Of this, ml has already been infused in the ER, so the remaining deficit is ml.

Typically, half the total deficit is replaced in the first eight hours after admission and the remaining fluid is given over the next 16 hours. So, this child needs ml of NS in the next eight hours for a total of ml and another ml in the next 16 hours. However, maintenance fluid must also be administered.

This needs to be given as D5NS, with our without potassium, depending on the patient's urine output. If the child is not urinating well, hold on adding potassium.

Note 2: If the child continues to vomit or have significant diarrhea, the volume of ongoing fluid loss should be estimated and added to the deficit every few hours as 0. Ideally, the diapers should be weighed. If this is not possible, then a volume of ml should be used for each stool in an infant and ml for the older child.

Note 3: The dehydration component of fluid replacement MUST be provided as 0. NEVER use a hypotonic saline, such as D5 0. Dehydration and hypovolemia result in secretion of anti-diuretic hormone, which causes retention of free water, and provision of hypotonic replacement fluid can lead to potentially life-threatening hyponatremia.

Step 3: Suppose the child is well hydrated by the second hospital day, but is still feeling queasy and does not want to drink. The blood brain barrier prevents rapid movement of solutes out of or into the brain. On the other hand, water can move freely across the blood brain barrier.

Rapidly developing hyponatremia causes a shift of water into the brain; conversely, hypernatremia can lead to brain dehydration and shrinkage. Severe, acute hyponatremia may result in brain edema with neurological symptoms such as a change in sensorium, seizures, and respiratory arrest.

This is a life-threatening medical emergency and requires infusion of hypertonic saline. Acute hypernatremia results in a reduction in brain volume. This can lead to subdural bleeding from stretching and rupture of the bridging veins that extend from the dura to the surface of the brain.

Given time, the brain can alter intracellular osmotic pressure to better match plasma osmolality. With persistent or slowly developing hyponatremia, brain cells extrude electrolytes and organic osmoles and the increase in brain volume is blunted or avoided.

Neurologic symptoms are absent or subtle. With persistent hypernatremia, brain cells generate organic osmoles also known as idiogenic osmoles to compensate for the increase in plasma osmolality.

Again, the change in brain volume is partially blunted. These processes take hours to become effective and leave the brain with a decreased in hyponatremia or increased hypernatremia osmolar content. Just as the adaptation takes 24 hours or more, un-adaptation also takes time.

Rapid correction of long-standing hypo- or hypernatremia has the potential for severe neurological consequences because of sudden changes in brain volume in the opposite direction. The neurologic manifestations associated with overly rapid correction of hyponatremia is called osmotic demyelination syndrome.

Thus, hyper- or hyponatremia of long duration should be corrected slowly. O ver the past four decades, oral rehydration has been demonstrated to be quite effective in replacing diarrheal fluid losses.

This therapy is best reserved for the child with mild or moderate dehydration. The intestine both the small bowel and colon is remarkably efficient in its ability to absorb water. The small bowel absorbs the vast majority of the body's fluid needs. Oral Rehydration Therapy ORT is accepted as the standard of care and first line treatment for the management of acute gastroenteritis with or without mild to moderate dehydration.

There are commercially available preparations that approximate these concentrations such as Pedialyte®, Enfalyte®, and Rehydralyte®. Note: Patients with mild to moderate dehydration can be treated with ORT.

Those with severe dehydration are not candidates and need IV infusions. Also, those patients with altered mental status who may be at risk for aspiration and those patients with intestinal diseases such as short gut or ileus are also not candidates.

Vomiting is not a contraindication for ORT. Return to the main menu. Electrolytes: the standard electrolytes are electrically conductive ions and include sodium Na , potassium K , chloride Cl , and bicarbonate HCO 3.

Calcium Ca , phosphorus as PO 4 , and magnesium Mg may be measured as indicated. The most important cations are Na and K. The concentration of Na is greatest in extracellular fluid, while the concentration of K is highest within cells. Of the electrolytes listed, the concentrations for the anions Cl and HCO 3 are greatest extracellularly.

Within the cell proteins add considerably to the negative charge. The concentrations of electrolytes help to determine the state of hydration, acid-base balance, and renal function.

Osmolarity is affected by changes in water content, as well as temperature and pressure. In contrast, osmolality is independent of temperature and pressure. For a given solution, osmolarity is slightly less than osmolality, because the total solvent weight the divisor used for osmolality excludes the weight of any solutes, whereas the total solution volume used for osmolarity includes solute content.

Otherwise, one litre of plasma would be equivalent to one kilogram of plasma, and plasma osmolarity and plasma osmolality would be equal. However, at low concentrations below about mM , the mass of the solute is negligible compared to the mass of the solvent, and osmolarity and osmolality are very similar.

Technically, the terms can be compared as follows: [2]. Therefore, bedside calculations are actually in units of osmolarity , whereas laboratory measurements will provide readings in units of osmolality.

In practice, there is almost negligible difference between the absolute values of the different measurements. For this reason, both terms are often used interchangeably, even though they refer to different units of measurement.

Normal human reference range of osmolality in plasma is about milli-osmoles per kilogram. Plasma osmolarity of some reptiles, especial those from a freshwater aquatic environment, may be lower than that of mammals e.

Consequently, solutions osmotically balanced for mammals e. Many arid species of reptiles and hibernating uricotelic species allow major elevations of plasma osmolarity e. As cell membranes in general are freely permeable to water, the osmolality of the extracellular fluid ECF is approximately equal to that of the intracellular fluid ICF.

Therefore, plasma osmolality is a guide to intracellular osmolality. This is important, as it shows that changes in ECF osmolality have a great effect on ICF osmolality — changes that can cause problems with normal cell functioning and volume.

If the ECF were to become too hypotonic , water would readily fill surrounding cells, increasing their volume and potentially lysing them cytolysis.

Many poisons, medications and diseases affect the balance between the ICF and ECF, affecting individual cells and homeostasis as a whole. Osmolality of blood increases with dehydration and decreases with overhydration.

In normal people, increased osmolality in the blood will stimulate secretion of antidiuretic hormone ADH. This will result in increased water reabsorption, more concentrated urine , and less concentrated blood plasma.

A low serum osmolality will suppress the release of ADH, resulting in decreased water reabsorption and more concentrated plasma. This ADH secretion may occur in excessive amounts from the posterior pituitary gland , or from ectopic sources such as small-cell carcinoma of the lung.

Elevation may be associated with stroke mortality. In medical lab reports, this quantity often appears as "Osmo, Calc" or "Osmo Calc. If the patient has ingested ethanol , the ethanol level should be included in the calculated osmolarity:.

A high-protein diet could increase your osmolality levels. Drinking large amounts of water could lower them. You don't need to prepare for this test.

Be sure your healthcare provider knows about all medicines, herbs, vitamins, and supplements you are taking. This includes medicines that don't need a prescription and any illegal drugs you may use. Search Encyclopedia. Osmolality Urine Does this test have other names?

What is this test? Why do I need this test? This may be needed if your provider thinks you may have: Kidney disease or disorder Eaten a toxic substance Diabetes insipidus You may also need this test if you have: Ongoing chronic diarrhea Severe, prolonged vomiting Excessive urination High or low blood sodium Fluid loss dehydration What other tests might I have along with this test?

The osmolality gives an indication of hydration and of renal function. A high osmolality is indicative of dehydration while low osmolality may represent fluid overload from lack of renal excretion of free water.

Blood gases: the standard blood gas analysis is performed on arterial blood radial artery and measures the very small amount of dissolved oxygen and carbon dioxide in arterial blood, given as partial pressures: PaO 2 and PaCO 2 , given as mm Hg. In addition, the pH of the blood and the bicarbonate concentration HCO 3 are measured.

Most blood gas analyzers will also provide a measurement for dissolved carboxyhemoglobin CO. If the patient is receiving supplemental oxygen, then the concentration of inspired oxygen may be higher. Acid-base balance: the acid-base status can be determined from blood gas analysis in the context of electrolyte concentrations.

By comparison to electrolyte concentrations, it can be determined if there is an acidosis with or without an "anion gap".

You may need to fast not eat or drink for 6 hours before the test or limit fluids 12 to 14 hours before the test. Your health care provider will let you know if there are any special instructions to follow.

There is very little risk to having a blood test. You may have slight pain or bruising at the spot where the needle was put in, but most symptoms go away quickly. If your serum osmolality results were not normal, it may mean you have one of the following conditions:. If your urine osmolality results were not normal, it may mean you have one of the following conditions:.

If your stool osmolality results were not normal, it may mean you have one of the following conditions:. Learn more about laboratory tests, reference ranges, and understanding results.

Your health care provider may order more tests along with or after your osmolality test. These may include:. The information on this site should not be used as a substitute for professional medical care or advice. Contact a health care provider if you have questions about your health. Osmolality Tests.

What are osmolality tests? Other names: serum osmolality, plasma osmolality urine osmolality, stool osmolality, osmotic gap. What are they used for? A blood osmolality test , also known as a serum osmolality test, is most often used to: Check the balance between water and certain chemicals in the blood.

Find out if you have swallowed a poison such as antifreeze or rubbing alcohol Help diagnose dehydration , a condition in which your body loses too much fluid Help diagnose overhydration, a condition in which your body retains too much fluid Help diagnose diabetes insipidus , a condition that affects the kidneys and can lead to dehydration Sometimes blood plasma is also tested for osmolality.

Why do I need an osmolality test? Symptoms of a fluid imbalance and diabetes insipidus are similar and may include: Excessive thirst if dehydrated Nausea and vomiting Headache Confusion Fatigue Seizures Symptoms of poisoning will be different depending on the type of the substance that was swallowed, but may include: Nausea and vomiting Convulsions, a condition that causes uncontrollable shaking of your muscles Difficulty breathing Slurred speech You may also need a urine osmolality if you have trouble urinating or are urinating too much.

What happens during an osmolality test? During a blood test serum osmolality or plasma osmolality : A health care professional will take a blood sample from a vein in your arm, using a small needle. During a urine osmolality test: Your health care provider will need to collect a sample of your urine.

Clean your genital area with a cleansing pad given to you by your provider. Men should wipe the tip of their penis.

Women should open their labia and clean from front to back. Start to urinate into the toilet. Move the collection container under your urine stream. Collect at least an ounce or two of urine into the container, which should have markings to indicate the amounts.

Finish urinating into the toilet. Return the sample container to your health care provider. During a stool osmolality test: You will need to provide a stool sample. Your instructions may include the following: Put on a pair of rubber or latex gloves.

Collect and store the stool in a special container given to you by your health care provider or a lab. You may get a device or applicator to help you collect the sample. Make sure no urine, toilet water, or toilet paper mixes in with the sample.

Seal and label the container. Remove the gloves and wash your hands.