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A 54-year-old man is undergoing a laparotomy and colon resection for carcinoma. The anesthesiologist is attempting to calculate the fluid replacement.
➤ What are the components that must be considered when calculating the volume of fluid that should be replaced?
Management of Fluid and Electrolytes
Summary: A 54-year-old man is undergoing bowel surgery, for which the volume of fluid replacement is being calculated.
➤ Factors affecting volume of fluid to be replaced: Preoperative fluid deficits, insensitive fluid losses, intraoperative blood loss, and urine output
1. Review the distribution of infused fluids within the various bodily compartments.
2. Acquaint the student with methods of calculating the fluid replacement in the intraoperative period.
3. Allow the student to become familiar with the advantages and disadvantages of crystalloids and colloids.
Patients undergoing intestinal surgery are well known to require more fluid replacement than might otherwise be expected. This patient will no doubt have preoperative fluid deficits, because he has not been eating or drinking, and has also undergone a bowel prep. Intraoperatively, the patient will lose blood, and there is also likely to be a significant insensitive loss from the intestines exposed to air. Fluids—crystalloids or blood products—will be required to ensure the preservation of renal and cardiovascular function, maintaining urine output at normal levels.
The Management of Fluids and Electrolytes
Many factors make fluid management in the perioperative setting different from any other situation. Preoperative fasting, insensible fluid losses, blood loss from the surgical site, postoperative dietary restrictions, and nasogastric tube drainage require the use of replacement fluids. Such fluids include crystalloids, colloids, and blood products. Administration of fluids is guided by the nature of the bodily fluid loss, and the patient’s disease process.
Total body water constitutes approximately 70% of lean body weight, although this percentage varies with the deposition of adipose tissue. Total body water is distributed between the extracellular and intracellular compartments.
Intracellular fluid is the fluid contained within cells and comprises approximately two-thirds (30 L) of total body water. (Please see Figure 8–1.)
Extracellular fluid is further compartmentalized into intravascular fluid and extravascular fluid, and comprises about one-third (15 L) of total body water.
Intravascular fluid consists of plasma (3 L), plus blood cells (2 L), which together constitutes circulating blood volume (5 L).
Extravascular fluid (12 L) is mostly found in tissues adjacent to the microvascular circulation, and is called the “functional compartment.” In contrast, the “nonfunctional” fluid compartment is ill defined, and devoid of fluid in the normal physiologic state. However, fluid can distribute into this “third” space postoperatively. Common examples of “third-spacing” include the bowel, peritoneal cavity, and traumatized tissues.
During normal circumstances, the lymphatic system removes the excess interstitial water and returns it to the intravascular compartment, maintaining the equilibrium and preventing intravascular depletion. In the perioperative setting, this mechanism may be depressed due to processes such as inflammation, rendering the body unable to redistribute the interstitial fluid and effectively causing edema.