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Nursing
Oct, 1998

A closer look at I.V. fluids. (includes related article on fluid deficit and fluid overload)

Author/s: Judy Young

Kathy Higgins, 40, comes to the emergency department complaining of abdominal pain, dizziness, and vomiting that's lasted 2 days. Her BP is 102/60 and her pulse rate is 96. Her skin is pale and her mucous membranes are dry. You know she's dehydrated and needs intravenous (I.V.) therapy, but which type of fluid should she receive? The answer isn't necessarily obvious--and making the wrong choice could be harmful.

In this article, I'll review how I.V. fluids are categorized and when each type is indicated--and why. Let's start with some fluid fundamentals.

What's in the bag?

More than 200 types of commercially prepared I.V. fluids are available to treat fluid and electrolyte imbalances. One way to classify them is by osmolality (tonicity)--the concentration of ions in a solution.

The osmolality of blood plasma--about 290 mOsm/liter--sets the standard. Fluids in the range of 240 to 340 mOsm/liter are considered isotonic. Fluids with tonicities above 340 mOsm/liter are hypertonic; those with tonicities below 240 mOsm/ liter are hypotonic.

Injected I.V., a fluid exerts predictable effects according to its tonicity: Isotonic fluids stay in the vessels (extracellular space), hypertonic fluids pull fluid from the cells (intracellular space), and hypotonic fluids flow into cells. So choosing the right I.V. fluid requires knowing the fluid status of each space or compartment and whether your patient has a fluid deficit or overload. (For more on fluid deficit and fluid overload, see Too Little or Too Much ?)

Another way to classify I.V. fluids is by key ingredients-sodium, dextrose, and multiple electrolytes-which are available in various combinations. Let's look at sodium-containing fluids next.

Salt of the earth

Sodium-containing fluids range from hypotonic (0.45% sodium chloride solution) to isotonic (0.9% sodium chloride solution) to hypertonic (5% dextrose in 0.9% sodium chloride solution). Along with sodium, these fluids provide chloride and free water; some are available in combination with dextrose.

A solution of 0.9% sodium chloride is known as "normal" saline solution because its tonicity (308 mOsm/liter) closely correlates with the osmolality of plasma. This solution contains 154 mEq/liter of both sodium and chloride, close to normal plasma levels of 140 mEq/liter of sodium and 103 mEq/ liter of chloride. (For more on the makeup of common I.V. solutions, see What's in There? Contents of Some Common I.V. Fluids.)

Indications. Hypotonic saline fluids such as 0.45% sodium chloride solution, which expand the intracellular compartment, are indicated for hypertonic dehydration, gastric fluid loss, and cellular dehydration from excessive diuresis.

Isotonic saline fluids such as 0.9% sodium chloride solution can temporarily expand the extracellular compartment during times of circulatory insufficiency, replenish sodium and chloride losses, treat diabetic ketoacidosis, and replenish fluids in the early treatment of burns and adrenal insufficiency. Because their osmolality is similar to that of blood, they're also the standard flush solutions used with blood transfusions.

Hypertonic saline fluids such as 5% dextrose in 0.9% sodium chloride solution are used cautiously to treat severe hyponatremia.

Precautions. Closely monitor your patient for complications, such as electrolyte imbalances, calorie depletion, and increased intracranial pressure (ICP). Because hypertonic fluids pull water from the intracellular space into the extracellular space, fluid volume and ICP can increase. Watch for fluid overload in patients with a history of heart failure or hypertension.

Mrs. Higgins, the patient we met at the beginning of this article, is showing signs of dehydration from vomiting and needs fluid replacement in the extracellular compartment. After the physician's initial evaluation, you insert an I.V. catheter and begin an infusion of 0.9% sodium chloride solution at 150 ml/hour.

Later, the physician diagnoses a bowel obstruction, and Mrs. Higgins has a small-bowel resection. She receives 4 liters of 0.9% sodium chloride solution during surgery.

Now, on her second postoperative day, she's receiving 5% dextrose in 0.45% sodium chloride solution at 100 ml/hour. You find that her vital signs are stable but her abdomen is slightly distended with no bowel sounds. The nursing student assigned to Mrs. Higgins asks why the physician ordered 5% dextrose in 0.45% sodium chloride solution. For answers, let's look at dextrose-containing fluids.

Sugar water

Dextrose fluids, which contain dextrose and free water, are available in concentrations of 2.5%, 5%, 10%, 20%, and 50%. Each percentage represents 1 gram of dextrose per 100 ml of fluid. For example, [D.sub.5]W provides 5 grams of dextrose per 100 ml of water, or 50 grams/ liter. The tonicity of [D.sub.5]W is 253 mOsm/liter.

Dextrose fluids also are available in combination with other solutions, such as sodium chloride or Ringer's solution.

Indications. Dextrose fluids provide calories for energy, sparing body protein and preventing ketosis, which occurs when the body burns fat. They also make it easier for potassium to move from the extracellular to the intracellular compartment. Dextrose fluids flush the kidneys with water, helping them excrete solutes, and improve liver function (glucose is stored in the liver as glycogen).

Concentrations of [D.sub.2.5]W and [D.sub.5]W are used to treat a dehydrated patient and to decrease sodium and potassium levels; they're also suitable diluents for many medications. More concentrated (hypertonic) fluids such as [D.sub.10]W are used to correct hypoglycemia. [D.sub.20]W and [D.sub.50]W with electrolytes can provide long-term nutrition as a part of total parenteral nutrition.

Precautions. Never mix dextrose with blood--it causes blood to hemolyze. Prolonged therapy with dextrose in water can cause hypokalemia, hyponatremia, and water intoxication by diluting the body's normal level of electrolytes.

Severe hyponatremia can lead to encephalopathy, brain damage, and death; young women are at highest risk. Look for signs of confusion and other changes in mental status. Closely monitoring your patient and her lab results--particularly serum sodium and potassium levels--can prevent complications. (For more on the dangers of dextrose fluid overload, see "Focusing on the Dangers of [D.sub.5]W" in the October issue of Nursing97.)

Hypertonic dextrose solutions can cause hyperglycemia, leading to osmotic diuresis and hyperosmolar coma. Monitor the patient's serum glucose levels, urine specific gravity, and fluid intake and output. Watch for polyuria, polydipsia, weight loss, and weakness.

Dextrose can be given to diabetic patients in acute illness as long as the patient's blood glucose is closely monitored so the balance of blood glucose and insulin is maintained.

To answer the nursing student's question about Mrs. Higgins, you explain that 5% dextrose in 0.45% sodium chloride solution is used for hydration and to provide dextrose, sodium, and chloride.

Because Mrs. Higgins had extensive surgery and received 4 liters of 0.9% sodium chloride solution, she has a third-space fluid shift in her abdomen. Administering 5% dextrose in 0.45% sodium chloride solution, which is slightly hypertonic, will pull the excess fluid into the intravascular compartment, preventing dehydration.

On the fourth postoperative day, Mrs. Higgins still has no bowel sounds. The physician changes the I.V. infusion to Ringer's solution at 75 mi/hour. Mrs. Higgins' husband asks, "Why does she need all these different I.V. lines?" To help you respond, let's look at electrolyte replacement fluids.

Electrolyte replacement fluids

The many electrolyte replacement fluids, including Ringer's solution, are generally isotonic fluids containing electrolytes in the same concentrations found in plasma. However, these solutions don't contain magnesium and phosphorus, which shouldn't be routinely given.

The exact electrolyte content depends on the fluid manufacturer. Ringer's injection and lactated Ringer's solution, the two most common electrolyte fluids, contain potassium, sodium, chloride, and calcium. Lactate, added as a buffer to produce bicarbonate, is contraindicated in patients with liver disease because they can't metabolize it.

Indications. Electrolyte fluids provide hydration and electrolytes for patients who can't take in food or fluid orally and for those who've experienced abnormally high fluid losses from severe vomiting, diarrhea, or diuresis. Lactated Ringer's solution is also used for volume replacement in patients with third-spacing. Which fluid to give depends on the patient's lab results and symptoms. Five percent dextrose may be mixed with the electrolyte fluid to provide energy, but keep in mind that the resulting solution is hypertonic. Infuse these fluids slowly--at a rate of 1 to 2 ml/minute--to reduce the risk of vein irritation.

Precautions. These fluids generally aren't given for more than 48 hours (unless the patient's condition is unchanged) because of the risk of overhydration, hypernatremia, hyperkalemia, metabolic alkalosis, and calorie depletion il' the fluid isn't mixed with dextrose. As always, closely monitoring the patient can help prevent complications.

Tell Mr. Higgins that when his wife's bowels are working in a day or two, she'll be able to take fluids and nutrition orally. Until then, the [.V. infusion is providing the hydration and nutrients she needs.

Two days later, Mrs. Higgins has normal bowel sounds and is tolerating a liquid diet. She's discharged home with instructions to notify her physician if she has changes in weight, appetite, fluid intake, or fluid output.

Putting it all together

Now that we've reviewed the types of fluids, here are some guidelines to help you determine when an I.V. infusion needs to be infused more rapidly or slowly, discontinued, or changed:

* Assess the patient frequently.

* Look for signs and symptoms of dehydration or fluid overload. Two or more signs or symptoms indicate a fluid imbalance.

* Document the patient's weight daily and keep an accurate record of intake and output. The normal daily witter intake and output for an adult is 2,500 to 3,000 ml; anything else indicates a fluid imbalance.

* Keep the infusion rate under 125 mi/hour or 2 mi/ minute to allow the body to distribute fluid.

* Replace fluid that's lost with a fluid that acts on the appropriate fluid compartment. Does the patient need fluid in the cells, pulled out of the cells, or in the vessels?No need to memorize the tonicity of I.V. fluids; it's listed right on the bag.

* Check lab values for clues to fluid imbalance. Elevated sodium, hematocrit, and blood urea nitrogen (BUN) indicate dehydration. Decreased sodium, hematocrit, and BUN indicate fluid overload.

* Assess lung sounds frequently for crackles, which could indicate fluid overload. Also assess skin turgor and jugular vein distension.

* Assess the I.V. site frequently.

* Encourage oral fluids, if appropriate.

Taking charge

Mrs. Higgins' case illustrates how one patient's I.V. fluid needs can change during the course of therapy. You're in the best position to assess subtle changes in fluid balance, plan effective I.V. therapy, and make a critical difference in your patient's treatment.

SELECTED REFERENCES

Nursing99 Drug Handbook. Springhouse, Pa., Springhouse Corp., 1999.

Terry, J. (ed): Intravenous Therapy: Clinical Principles and Practice. Philadelphia, W.B. Saunders Co., 1995.

Vonfrolio, L.: "Back to Basics. Would You Hang These I.V. Solutions?" AJN. 95(6):37-39, June 1995.

What's in there? Contents of some common I.V. fluids



Solution                     Glucose         Sodium       Chloride

                           (grams/liter)   (mEq/liter)   (mEq/liter)



[D.sub.2.5] W                    25

[D.sub.5] W                      50

[D.sub.10] W                    100

0.45% sodium chloride                           77            77

0.9% sodium chloride                           154           154

3% sodium chloride                             513           513

5% dextrose and

0.2% sodium chloride             50             34            34

5% dextrose and

0.45% sodium chloride            50             77            77

5% dextrose and

0.9% sodium chloride             50            154           154

Ringer's                                                  147           155

Lactated Ringer's                                 130           109

5% dextrose in Ringer's          50            147           156

0.15% potassium chloride                                      20

0.30% potassium chloride                                      40

5% sodium bicarbonate                          595           595



Solution                     Potassium     Calcium       Lactate

                            (mEq/liter)   (mEq/liter)   (mEq/liter)



[D.sub.2.5] W

[D.sub.5] W

[D.sub.10] W

0.45% sodium chloride

0.9% sodium chloride

3% sodium chloride



5% dextrose and

0.2% sodium chloride

5% dextrose and

0.45% sodium chloride



5% dextrose and

0.9% sodium chloride

Ringer's                                4             4

Lactated Ringer's                 4             3             28

5% dextrose in Ringer's           4             4

0.15% potassium chloride         20

0.30% potassium chloride         40

5% sodium bicarbonate

RELATED ARTICLE: Too little or too much?

Fluid deficit (hypovolemia)

Definition: excessive fluid and electrolyte depletion of the extracellular space from fluid loss, fluid shifts within the body, or decreased fluid intake

Causes: hemorrhage, vomiting, diarrhea, suctioning, fistulas, fever, hyperventilation, skin trauma such as burns and cuts, and polyuria caused by renal disorders, hyperglycemia, diabetes insipidus, and diuretics

Signs and symptoms: confusion, dizziness, headache, sunken eyes, flat neck veins, thirst, dry mucous membranes, poor skin turgor, slow filling of hand veins, weight loss, postural hypotension, weak and thready pulse, muscle weakness, nausea and vomiting, decreased urine output, increased blood urea nitrogen (BUN), increased serum sodium, increased hematocrit, and increased urine specific gravity

Fluid overload (hypervolemia)

Definition: excess fluid in the extravascular space, usually the result of increased sodium concentration causing water retention

Causes: renal failure, heart failure, liver disease, excessive I.V. fluid intake of sodium-containing fluids

Signs and symptoms: confusion, shortness of breath, wheezing, crackles, puffy eyelids, ascites, pulmonary edema, dependent edema, distended neck veins, nausea, constipation, tachycardia, bounding pulse, increased blood pressure, weight gain, polyuria, decreased BUN, decreased serum sodium, decreased urine specific gravity, and moist, taut skin

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