Before an anesthesia provider can consider the colloid solutions in general and the hetastarch products in particular, he or she must first have an understanding of the basics of perioperative fluid therapy. Perioperative fluid therapy includes the replacement of pre-existing fluid deficits, maintenance requirements, and surgical losses.

Normal maintenance requirements (Table 31.1) are what the body needs to keep up with urine production, losses from the respiratory tract or skin, and gastrointestinal (GI) secretions. Because these losses are hypotonic meaning that the fluids lost have a lower osmolality than the cells in the body.

Fluid deficits may come from a variety of sources. First, the great majority of patients who come to the operating room have fasted for at least 6 hours. For the average 70-kg man this calculates to a deficit of ( 110 mL/hour × 6) or 660 mL. For many GI procedures, patients may also get a preoperative bowel cleansing preparation. This may increase fluid losses by 1 to 2 L. Increased insensible losses also occur as a result of increased sweating, respiratory losses from fevers, as well as in any patient who has been breathing nonhumidified gases. Finally, patients who have diarrhea, vomiting, diuresis, or bleeding will have fluid depletion as well as electrolyte disturbances.

For surgical losses, the anesthesia provider has to be very vigilant. Underestimating surgical blood loss can have devastating consequences. The first obvious place to look is in the suction canister or at the sponges. Remember that a 4 × 4 sponge may hold 10 mL of blood and a full-sized, soaked laparotomy pad may represent 100 mL of blood loss. In addition, one must take into account the irrigation solution used. Good communication with the scrub nurse for estimating this fluid solution use is essential. With the increased use of cell salvage techniques, a second suction canister may be present. However quick visual estimation of blood losses may account for only one third of the “real blood loss.” There may be a significant amount not accounted for in the tubing, on the drapes/floor, or on the surgeon/scrub nurse. Once an estimate of surgical blood loss has been made, a good rule for replacement volume for surgical blood loss (when not using blood products) is 1:3 for crystalloid solutions and 1:1 for colloid solutions. This means that
if there is a 300-mL blood loss, one could correct this loss by giving 900 mL of crystalloid or 300 mL of colloid.

What are colloid solutions? Basically, they are solutions of highmolecular-weight substances administered to maintain intravascular volume. They last intravascularly from 3 to 6 hours. Some indications for use are for fluid resuscitation before blood products are available or in patients with severe hypoalbuminemia.

There are many different types of colloid solutions. One of the most familiar to anesthesia providers is albumin, which is available in 5% and 25% solutions. The albumin protein is relatively stable and is heated to 60°C for 10 hours. It is heated to potentially remove HIV, hepatitis, etc. Albumin is one of the most expensive solutions because it is derived from blood donations. Recently, Pentastarch and Hespan (Hetastarch) have been increasingly popular because of the lower cost. Both are composed of chains of glucose molecules to which hydroxylated ethyl ether groups have been added to resist degradation. The average molecular weight of Hespan is 450,000. Hetastarch comes in a 6% solution of either NaC1 (Hespan) or LR (Hextend) (Table 31.2). Pentastarch, which has a slightly smaller molecular size, was developed secondary to the fact that the large Hespan molecules are sequestered in the reticuloendothelial system (RES), the kidney, and the liver. Although this has not been shown clinically, it may impair the RES. For a comparison of Hetastarch to Pentastarch (both in NaC1 solution) see Table 31.3.