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Intravenous Fluid Therapy: a Review

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Intravenous Fluid Therapy: a Review INTRAVENOUS FLUID THERAPY: A REVIEW Joanne Gaffney, RN, CANP, MS If this common intervention isn’t managed vigilantly, it actually can exacerbate the risks it’s designed to alleviate. umerous conditions— In this article, I’ll review the ba- The body loses fluid through metabolic, infective, sics of fluid balance and the etiology such normal physiologic func- traumatic, and iatro- of fluid loss. I’ll discuss how to as- tions as breathing and urination. N genic—can cause fluid sess fluid depletion, outline the prin- But when certain diseases or en- depletion. In such cases, initiat- ciples of fluid replacement therapy, vironmental conditions substan- ing intravenous (IV) fluid replace- and explain the context in which tially increase fluid loss, the body ment is commonplace. In fact, IV various types of solutions are ad- may be unable to maintain ho- fluid replacement therapy is one ministered. I will not, however, meostasis, and fluid replacement of the most common invasive cover the treatment of diabetes mel- may be necessary. procedures hospitalized patients litus and diabetes insipidus, which undergo, and it’s performed in cer- follow different principles that are NORMAL FLUID LOSS tain outpatient and home care set- beyond the scope of this article. Normal fluid loss includes both in- tings as well. sensible and sensible losses. Each Fluid loss can put patients at FLUID MECHANICS day the skin loses approximately substantial risk for fluid and elec- Body water represents approxi- 300 mL and the lungs lose approxi- trolyte imbalances, which can lead mately 60% of a person’s total mately 700 mL of water from evap- to shock and multiple organ failure. weight. For a 70 kg man, this oration. This insensible water loss Although IV therapy for fluid deple- amounts to about 42 L. Intracellular remains mostly stable at roughly 1 tion is practiced widely, if not ad- fluid accounts for two thirds of it L/day and is responsible for negligi- ministered scrupulously, it actually (roughly 28 L) and extracellular ble electrolyte loss. Hyperventila- can exacerbate the fluid and elec- fluid for the other third (about 14 L). tion intensifies losses from the trolyte imbalance. It’s essential, Extracellular fluid includes both lungs, and fever increases losses therefore, that the practitioner re- the interstitial fluid (around 11.2 L) from both skin and lungs. The sponsible for initiating and main- and plasma (the remaining 2.8 L). amounts of fluid lost through these taining fluid replacement therapy In addition to plasma, intravascular two routes increases by 10% for understand the basic mechanisms fluid contains the fluid volume of every degree of fever above 37° C.1 supporting fluid balance, the conse- its other major constituent, the red Sensible water losses occur quences of fluid loss, and the ra- blood cells. mainly through urination, but also tionale for fluid replacement. The fluid component of red through perspiration and defeca- blood cells represents about 2 L of tion. The average adult voids be- Ms. Gaffney is a nurse practitioner in the surgical intracellular fluid. A person’s total tween 1 and 1.5 L urine daily. Urine service at the Northport VA Medical Center, North- blood fluid volume, therefore, sodium and potassium generally port, NY and a clinical instructor in the department of nursing at Nassau Community College, Garden equals about 5 L—plasma plus the range in amounts from 40 to 80 City, NY. fluid component of red blood cells. mEq/L. Perspiration contains JULY 2004 • FEDERAL PRACTITIONER • 41 INTRAVENOUS FLUID THERAPY sodium in amounts ranging from ments, where it’s unavailable to sup- temperature, hyperglycemia, dia- 34 mEq/L to 50 mEq/L. Normal port the circulation).3 Third spacing betes insipidus, or hyperalimenta- sweating, however, accounts for a can occur with ascites, bowel ob- tion) and with saltwater loss (GI daily fluid loss of only 100 mL. Pro- struction, pancreatitis, and tissue in- tract loss, profuse sweating, hy- fuse sweating, as occurs with stren- jury (from trauma, infection, or poaldosteronism, diuretic use, or uous exercise, can raise this burns) that causes vasodilation. third spacing). amount to 1,500 mL, making both If water and salt are lost in iso- A drop in intracellular fluid, as fluid and salt loss significant. In the tonic amounts, there is no osmotic occurs with simple water loss, typi- absence of diarrhea, fluid lost in shift in fluids between the extracel- cally causes thirst and such central stool ranges from 100 to 200 mL in lular and intracellular compart- nervous system disturbances as adults. ments. In such cases, volume restlessness, weakness, listless- In total, therefore, basic adult depletion occurs only in the extra- ness, muscular twitching, irritabil- fluid losses equal approximately 2.5 cellular fluid compartment. ity, disorientation, delusions, and L daily. These losses should be hallucinations. The patient may taken into account when consider- ASSESSING FLUID DEPLETION have flushed skin, fever, dry and ing fluid replacement. The degree of fluid depletion may sticky mucous membranes, oli- be estimated by weight loss, with guria, or orthostatic hypotension. ABNORMAL FLUID LOSS one pound representing 500 mL of Laboratory values show an ele- Excessive fluid loss can mean ei- fluid. Using this guide, weight vated serum sodium level (above ther dehydration (the loss of simple losses of 2% (or 2.4 lb in a 120-lb 145 mEq/L), increased serum os- water or of more water than salt) person) would be considered mild molality (above 295 mOsm/kg), re- or hypovolemia (the loss of iso- fluid depletion, whereas 5% (or 6 lb duced urinary sodium (10 to 20 tonic saltwater). These two types in a 120-lb person) would be con- mEq/L or less), and—except in the of water loss affect the body in dif- sidered moderate and 8% (or 9.6 lb case of diabetes insipidus—a nor- ferent ways. or more in a 120-lb person) would mal urine specific gravity above Simple water losses may be be considered severe.3 1.015. If fluid depletion is due to di- brought on by water deprivation or Alternatively, water deficit may abetes insipidus, urine specific by an increase in body or environ- be calculated as follows: water gravity may be as low as 1.005.3 mental temperature. Hypergly- loss in liters = total body water x A drop in extracellular fluid, as cemia, diabetes insipidus, and [(serum sodium/140) – 1], where occurs with both simple and salt- nasogastric overfeeding (especially total body water in liters is said to water losses, causes thirst, fatigue, if not balanced with adequate be 60% of body weight in kilo- muscle cramps, weakness, and water intake) are other possible grams for lean men and 50% of postural dizziness.5 Body tempera- causes of simple water loss.2 body weight in kilograms for lean ture may be low and the skin is dry. The loss of simple water in- women.4 Fluid loss estimates must Assess skin turgor by pulling up on creases the solute content of the factor in history and physical signs the skin covering the sternum: blood, which results in intravascu- (though these are minimal when Tenting that remains for several lar hypertonicity. This causes an os- depletion is mild) and replacement seconds indicates fluid deficit. The motic shift of water from within must be guided by continual physi- mucous membranes are dry and the cells into the plasma. There is, cal assessment and laboratory eyeball tension may be reduced (to thus, a loss of fluid from both the findings. the touch). The tongue is shrunken extracellular and intracellular com- History should include medica- and coated with multiple furrows partments. tions, fluid intake and output, ill- (in addition to the normal midline Saltwater may be lost with gas- nesses, and any signs or symptoms furrow). Typically, a diminished ap- trointestinal (GI) losses, sweating, of fluid loss (such as thirst, fatigue, petite progresses to nausea and hypoaldosteronism, diuretic use, weakness, malaise, or decreased vomiting. and third spacing (the leakage of urinary output). Keep in mind eti- If salt is lost in proportion to saltwater fluid into a third space ologies associated with simple water, the serum sodium level may that’s outside of the extracellular water loss (fluid deprivation, an in- be normal, though there would be a and intracellular fluid compart- crease in environmental or body relative increase in urea, albumen, Continued on page 47 42 • FEDERAL PRACTITIONER • JULY 2004 INTRAVENOUS FLUID THERAPY Continued from page 42 red blood cells, hemoglobin, and 0.45%, or 77 mEq/L. Potassium ad- INTRAVENOUS THERAPY FOR Hct secondary to hemoconcentra- ditions start at 20 mEq/L and can ABNORMAL FLUID LOSS tion. If more water than salt is lost, be increased to 40 mEq/L, which is For abnormal water losses that ex- laboratory findings are similar to usually sufficient to replace normal ceed the loss of salt, treatment con- those that accompany simple water loss. sists of simple water administration. (intracellular fluid) loss. Calories also are added to re- Often, this water replacement must With a 20% fluid loss or less, car- placement fluid therapy. Each 1-L be administered intravenously, as diac output remains adequate. With solution containing 5% dextrose patients in such cases tend to vomit. moderate fluid deficit cardiac out- supplies 50 g of carbohydrate and Usually, a 5% glucose solution is put decreases. The neck veins are approximately 170 calories. While used. It’s administered gradually flat when the patient is supine (un- even 2 or 3 L provides only a por- over 48 hours. Convulsions can less the patient has congestive heart tion of the patient’s daily caloric in- occur if the brain expands too failure).
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