IV Fluids

During your morning pre-rounds you see Ms. Yang, a 52-year-old female who is POD #1 from a small bowel resection for a high-grade obstruction. Ms. Yang states her pain is well controlled with medication but she feels tired and a little light-headed. In checking her postoperative orders you note she is NPO, her nasogastric tube should be attached to continuous wall suction, and she should have IV fluids running. Although the NGT is in place and appears to be functioning properly, you notice on closer inspection her IV fluid tubing is disconnected. The patient tells you the tubing was bothering her while she was sleeping, so she disconnected it during the night. Her vitals reveal her to be mildly tachycardic and hypotensive with a heart rate of 103 and a blood pressure of 98/70. As you examine her, you notice her mouth and lips are dry and she is clearly dehydrated.

Her wound dressings are clean, dry, and intact, and her exam is otherwise unremarkable. You realize the patient needs to be given fluids.

1. What type of intravenous fluid is most like plasma?

2. For each of the following types of fluid loss, what type of crystalloid solution is most appropriate and why?

A. Gastric losses

B. Pancreatic/biliary/small bowel losses

C. Large intestine (diarrheal) losses

#### IV Fluids

1. Table 37-1 summarizes the ion concentrations in the 2 most common types of crystalloid fluids—normal saline (NS) and lactated Ringer’s (LR). Note that the composition of LR most closely approximates that of plasma and is commonly used for surgical patients. However, because of the addition of calcium and lactate (bicarbonate) to this solution, it should not be used in certain clinical scenarios. For example, the calcium in LR can bind to certain drugs including amphotericin, ampicillin, and thiopental and reduce their effectiveness. Preclinical studies have also shown that calcium can bind to the anticoagulant in donor blood and promote clot formation; therefore, in clinical practice many centers do not infuse LR simultaneously with red blood cell transfusions.

There are no clear contraindications to the use of NS. However, it is important to know that the high chloride concentration of this solution can lead to a non-anion gap (hyperchloremic) metabolic acidosis if large volumes are infused.

Understanding the tonicity of various crystalloid fluids is important when deciding what to use for resuscitation and for maintenance. Both NS and LR are isotonic fluids, meaning the osmolar concentration of these solutions is the same as that of the interstitial space. Infusion of isotonic fluids into the vascular space results in diffusion of the fluid until it is evenly distributed among all of the fluid compartments of the body. About 1/3 of the total volume of infused isotonic crystalloid stays within the vessels. Isotonic ...

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