Patients with acute blood loss need replacement with appropriate isotonic ﬂuid or blood or both. There is a wide range of plasma volume expanders, including albumin, dextran, and hetastarch solutions, that contain large molecular weight particles (<50 kDa molecular weight). These particles are slow to exit the intravascular space, and about one-half of the particles remain after 24 hours. Controversy exists over the ideal strategy for intravascular volume replacement (29). A systematic review of 25 randomized clinical trials demonstrated preserved renal function and reduced intestinal edema in surgical patients receiving hyperoncotic albumin solutions, as compared with control ﬂuids (30). Meta-analyses on the use of human albumin and crystalloids versus colloids in ﬂuid resuscitation did not show a benefit in mortality rates (31,32). Caution
Correction of Existing Fluid and Electrolyte Abnormalities is required in interpreting results from these pooled controlled trials because mortality outcome was not the end point of most of the studies, and publication bias is a limitation. Possible side effects with synthetic colloid solutions include adverse affects on hemostasis, severe anaphylactic reactions, and impairment of renal function (29). These solutions are expensive and for most cases, simple replacement with 0.9 normal saline or lactated Ringer’s solution will suffice.
One-third of the volume of lactated Ringer’s solution or normal saline typically will remain in the intravascular space and the remainder goes to the interstitium.
Appropriate replacement of gastrointestinal ﬂuid loss depends on the source of ﬂuid loss in the gastrointestinal tract. Gastrointestinal secretions beyond the stomach and up to the colon are typically isotonic with plasma, with similar amounts of sodium, slightly lower amounts of chloride, slightly alkaline pH, and more potassium (in the range of 10 to 20 mEq/L). Under normal conditions, stool is hypotonic. However, under conditions of increased ﬂow (i.e., severe diarrhea), stool contents are isotonic with a composition similar to that of the small bowel contents. Gastric contents are typically hypotonic, with one-third the sodium of plasma, increased amounts of hydrogen ion, and low pH.
In patients who have gastric outlet obstruction, nausea, and vomiting, or who undergo nasogastric suction, appropriate replacement of gastric secretions can be provided with a solution such as D5/0.45 normal saline with 20 mEq/L of potassium. Potassium supplementation is particularly important to prevent hypokalemia in these patients, whose kidneys attempt to conserve hydrogen ions in the distal tubule of the kidney in exchange for potassium ions.
In patients with bowel obstruction, 1 to 3 L of ﬂuid can be sequestered daily in the gastrointestinal tract. This ﬂuid should be replaced with isotonic saline or lactated Ringer’s solution. Similarly, patients with enterocutaneous fistulas or new ileostomies should receive replacement with isotonic ﬂuids.