Con : Use of colloids in cardiac surgery

HE DEBATE OVER colloid versus crystalloid administration for volume expansion in cardiac surgery, as well as other surgical disciplines, has persisted for more than 40 years. The 3 fluids administered in the United States for cardiac surgical perioperative volume replacement are the colloids, albumin 5% and Hespan or Hextend (HES), or crystalloid such as lactated Ringer’s (LR) or normal saline. There have been several recent studies in noncardiac surgical patients that have only increased debate, not clarified it. The economic reality that faces health care compels clinicians to examine these arguments in an effort to reach the optimal management. In 1998, the Cochrane Injuries Group performed a metaanalysis on data from 30 randomized trials comparing the use of albumin with other fluid regimens for intravascular volume replacement in critically ill patients.1 They identified an excess mortality of 6.8% in the patients who received albumin compared with other fluid therapy, thereby suggesting the increased mortality was related to fluid therapy (relative risk of mortality 1.68; 95% confidence interval, 1.26-2.23). As a consequence, the Food and Drug Administration issued a letter to health care providers expressing concern over the safety of albumin administration to critically ill patients. These results were followed by another meta-analysis of 55 studies involving 3,504 patients, greater than twice the numbers included in the original Cochrane review. 2 This analysis detected no difference in mortality between patients treated with albumin and patients treated with other fluids. Meta-analysis studies suffer from problems of nonhomogenous groups and multiple kinds of patients and disorders. In 2004, the New England Journal of Medicine published the Saline versus Albumin Fluid Evaluation (SAFE) study, which was the largest randomized (but not blinded) control trial to date on the safety of albumin. 3 There were 6,997 critically ill study participants who were randomized to receive either 4% albumin or normal saline for intravascular fluid resuscitation. They found no difference in mortality rate of patients in the general intensive care unit (ICU) who received albumin versus normal saline (relative risk of mortality 0.99; 95% confidence interval, 0.91-1.09). Secondary analysis of prespecified subgroups of patients with acute respiratory distress syndrome, severe sepsis, and trauma also showed no differences concerning albumin or normal saline administration. In a subsequent meta-analysis, heavily influenced by the results of the SAFE trial (which contributed 91% of the information, based on the weights in the meta-analysis) for treatment of hypovolemia, the relative risk of death after albumin administration was 1.01 (95% confidence interval, 0.92-1.10). 4 For treatment of burns, the relative risk was 2.40 (1.11-5.19), and, for treatment of hypoalbuminemia, the relative risk was 1.38 (0.94-2.03). The pooled relative risk of death with albumin administration was 1.04 (0.95-1.13). Alderson et al 4 concluded that in view of the absence of evidence of preventing mortality from albumin and the increased cost of albumin compared with alternatives such as saline, cheaper alternatives such as saline for fluid resuscitation were prudent. The question arises regarding the relevance of these studies to the cardiac surgical population. Cardiac surgical patients, especially those who require cardiopulmonary bypass (CPB), are vastly different from the general critically ill ICU patient. Cardiac surgical patients commonly receive large amounts of fluid in an effort to maintain the effective intravascular volume for a variety of reasons. Perhaps foremost is the exposure to CPB that generates a strong inflammatory response that may extend into the ICU period for an indeterminate period after separation from CPB. 5,6 Capillary leak arising from endothelial damage of the inflammatory response may lead to accumulation of extravascular fluid in many, but not all, cases. 7 An alteration of intravascular Starling forces also accompanies initiation of CPB. The increased hydrostatic pressure generated from left ventricular dysfunction and the decreased colloid oncotic pressure (COP) resulting from hemodilution and capillary leak combine to create fluctuations of intravascular volume. Accordingly, the impact of fluid selection on extravascular lung water, interstitial edema, and respiratory dysfunction after CPB and during the ICU period is plausible. Conversely, patients who have undergone cardiac surgery with CPB frequently have marked intravascular hypovolemia, despite a highly positive fluid balance and evidence of abnormal fluid exchange between the intravascular and extravascular spaces, most likely related to the inflammatory response.8 Therefore, the “advantage” of colloidal fluids to remain in the intravascular space may not be totally correct in this population.