Parenteral Fluid Therapy
IV fluid administration is performed in the hospital, outpatient diagnostic and surgical settings, clinics, and home to replace flu-ids, administer medications, and provide nutrients when no other route is available.
The choice of an IV solution depends on the purpose of its ad-ministration. Generally, IV fluids are administered to achieve one or more of the following goals:
• To provide water, electrolytes, and nutrients to meet daily requirements
• To replace water and correct electrolyte deficits
• To administer medications and blood products
IV solutions contain dextrose or electrolytes mixed in various proportions with water. Pure, electrolyte-free water can never be administered IV because it rapidly enters red blood cells and causes them to rupture.
Solutions are often categorized as isotonic, hypotonic, or hyper-tonic, according to whether their total osmolality is the same as,less than, or greater than that of blood.
Electrolyte solutions are considered isotonic if the total elec-trolyte content (anions + cations) is approximately 310 mEq/L. They are considered hypotonic if the total electrolyte content is less than 250 mEq/L and hypertonic if the total electrolyte content exceeds 375 mEq/L. The nurse must also consider a solution’s osmolality, keeping in mind that the osmolality of plasma is approximately 300 mOsm/L (300 mmol/L). For ex-ample, a 10% dextrose solution has an osmolality of approxi-mately 505 mOsm/L.
When administering parenteral fluids, the nurse monitors the patient’s response to the fluids, considering the fluid volume, the content of the fluid, and the patient’s clinical status.
Fluids that are classified as isotonic have a total osmolality close to that of the ECF and do not cause red blood cells to shrink or swell. The composition of these fluids may or may not approxi-mate that of the ECF. Isotonic fluids expand the ECF volume. One liter of isotonic fluid expands the ECF by 1 L; however, it expands the plasma by only 0.25 L because it is a crystalloid fluid and diffuses quickly into the ECF compartment. For the same reason, 3 L of isotonic fluid is needed to replace 1 L of blood loss. Because these fluids expand the intravascular space, patients with hypertension and heart failure should be carefully monitored for signs of fluid overload.
A solution of D5W has a serum osmolality of 252 mOsm/L. Once administered, the glucose is rapidly metabolized, and this initially isotonic solution then disperses as a hypotonic fluid, one-third ex-tracellular and two-thirds intracellular. It is essential to consider this action of D5W, especially if the patient is at risk for increased intracranial pressure. During fluid resuscitation, this solution should not be used because it can cause hyperglycemia. Therefore, D5W is used mainly to supply water and to correct an increased serum osmolality. About 1 L of D5W provides fewer than 200 kcal and is a minor source of calories for the body’s daily requirements.
Normal saline (0.9% sodium chloride) solution has a total os-molality of 308 mOsm/L. Because the osmolality is entirely con-tributed by electrolytes, the solution remains within the ECF. For this reason, normal saline solution is often used to correct an extracellular volume deficit. Although referred to as “normal,” it contains only sodium and chloride and does not actually simu-late the ECF. It is used with administration of blood transfusions and to replace large sodium losses, as in burn injuries. It is not used for heart failure, pulmonary edema, renal impairment, or sodium retention. Normal saline does not supply calories.
Several other solutions contain ions in addition to sodium and chloride and are somewhat similar to the ECF in composition. Lactated Ringer’s solution contains potassium and calcium in ad-dition to sodium chloride. It is used to correct dehydration and sodium depletion and replace GI losses. Lactated Ringer’s solu-tion contains bicarbonate precursors as well. These solutions are marketed, with slight variations, under various trade names.
One purpose of hypotonic solutions is to replace cellular fluid, be-cause it is hypotonic as compared with plasma. Another is to pro-vide free water for excretion of body wastes. At times, hypotonic sodium solutions are used to treat hypernatremia and other hyper-osmolar conditions. Half-strength saline (0.45% sodium chlo-ride) solution, with an osmolality of 154 mOsm/L, is frequently used. Multiple-electrolyte solutions are also available. Excessive infusions of hypotonic solutions can lead to intravascular fluid de-pletion, decreased blood pressure, cellular edema, and cell dam-age. These solutions exert less osmotic pressure than the ECF.
When normal saline solution or lactated Ringer’s solution con-tains 5% dextrose, the total osmolality exceeds that of the ECF. The dextrose is quickly metabolized, however, and only the iso-tonic solution remains. Therefore, any effect on the intracellular compartment is temporary. Similarly, with hypotonic multiple-electrolyte solutions containing 5% dextrose, once the dextrose is metabolized, these solutions disperse as hypotonic fluids.
Higher concentrations of dextrose, such as 50% dextrose in water, are administered to help meet caloric requirements. These solutions are strongly hypertonic and must be administered into central veins so that they can be diluted by rapid blood flow.
Saline solutions are also available in osmolar concentrations greater than that of the ECF. These solutions draw water from the ICF to the ECF and cause cells to shrink. If administered rapidly or in large quantity, they may cause an extracellular vol-ume excess and precipitate circulatory overload and dehydration. As a result, these solutions must be administered cautiously and usually only when the serum osmolality has decreased to danger-ously low levels. Hypertonic solutions exert an osmotic pressure greater than that of the ECF.
When the patient’s GI tract is unable to tolerate food, nutritional requirements are often met using the IV route. Parenteral solu-tions may include high concentrations of glucose, protein, or fat to meet nutritional requirements. The parenteral route may also be used to administer colloids, plasma expanders, and blood prod-ucts. Examples of blood products include whole blood, packed red blood cells, albumin, and cryoprecipitate;.
Many medications are also delivered by the IV route, either by infusion or directly into the vein. Because IV medications enter the circulation rapidly, administration by this route is po-tentially very hazardous. All medications can produce adverse reactions; however, medications given by the IV route can cause these reactions within 15 minutes after administration because the medications are delivered directly into the blood-stream. Administration rates and recommended dilutions for individual medications are available in specialized texts per-taining to IV medications and in manufacturers’ package in-serts; these should be consulted to ensure safe IV administration of medications.
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