There is a longstanding and eternal debate concerning the type of fluid (crystalloid or colloid) that is most appropriate for volume resuscitation. Each fluid has its army of loyalists who passionately defend the merits of their fluid. It was believed that a major consequence of acute blood loss was an interstitial fluid deficit and that replenishing this deficit with a crystalloid fluid will reduce mortality. Thus crystalloid fluids were popularized for volume resuscitation because of their ability to add volume to the interstitial fluids. Later studies using more sensitive measures of interstitial fluid revealed that the interstitial fluid deficit in acute blood loss is small and is unlikely to play a major role in determining the outcome from acute hemorrhage. This refuted the importance of filling the interstitial compartment with crystalloids, yet its popularity did not wane.
The most convincing argument in favor of colloids for volume resuscitation is their superiority over crystalloid fluids for expanding the plasma volume. Colloid fluids will achieve a given increment in plasma volume with only one quarter to one third the volume required of crystalloids. This is an important consideration in patients with brisk bleeding or severe hypovolumia, where rapid volume resuscitation is desirable . Crystalloids can also achieve the same increment in plasma volume as colloids but then three to four times more volume is required to achieve this goal !This adds fluid to the interstitial space and can cause unwanted edema. THE PRINCIPLE EFFECT OF CRYSTALLOID INFUSIONS IS TO EXPAND FLUID VOLUME, NOT THE PLASMA VOLUME. Since the goal of fluid resuscitation is to support the intravascular volume , colloids fluids are the logical choice over crystalloids.
FILLING A BUCKET- The following example illustrates the problem with using crystalloids to expand the plasma volume. Assume that you have two buckets, each representing the intravacular compartment, and each bucket is connected by a clamped hose to an overhanging reservior that contains fluid. One reservior contains a colloid fluid in the same volume as the bucket, and the other reservior contains a crystalloid fluid in a volume that is three to four times greater than the colloid volume. Now release the clamp on each hose and empty the reserviors; both buckets will fill with fluid, but most of the crystalloid fluid will spill over on to the floor. Now ask yourself which method is better suited for filling the buckets; the colloid method with the right amount of fluid and no spillage, or the crystalloid method with too much fluid, most of which spills on to the floor.The biggest disadvantage of colloid resuscitation is the higher cost of these fluids.
Thus there is too much chatter about which type of resuscitation is most appropriate in critically ill patients , because it is unlikely that one type of fluid is best for all patients. A more logical approach is to select the type of fluid that is best designed to correct a specific problem with fluid balance. For example, crystalloid fluids are designed to fill the extracellular space(interstitial space plus intravascular space) and would be appropriate for use in patients with dehydration. Colloids on the other hand are designed to expand plasma volume and are appropriate for patients with hypovolumia due to blood loss, while albumin containing colloid fluids are appropriate for patients with hypovolumia associated with hypoalbuminemia. Tailoring fluid therapy to specific problems of fluid imbalance is the best approach to volume resuscitation !