Crystalloids versus colloids: the argument never ceases. Adequate fluid administration plays a major role in the management of hospitalized patients. However, the choice of intravenous fluids and the place of colloids remain controversial. Some experts have recently challenged the physiological concept that less intravenous colloid need to be administered than crystalloids to achieve the same resuscitation endpoints. As positive fluid balance has been associated with worse outcomes in critically ill patients, information regarding this relationship may have important clinical implications. To evaluate reported crystalloid/colloid ratios, Dr. Jean-Louis Vincent, Department of Intensive Care, Erasme Hospital, Université Libre de Bruxelles, Brussels, Belgium, and colleagues performed a systematic search for all clinical studies comparing (any) crystalloid to (any) colloid, and calculated the crystalloid/colloid ratio for each study. Their analysis is published in this month’s issue of Anesthesia & Analgesia in the article “Crystalloids Versus Colloids: Exploring Differences in Fluid Requirements by Systematic Review and Meta-Regression.”
Forty-eight studies were identified and 24 had sufficient data for meta-analysis. The crystalloid/colloid ratio to achieve hemodynamic targets across all the studies included in the meta-analysis was 1.5 (95% CI 1.36-1.65), thus confirming the basic physiological concept of reduced fluid requirements when administering colloid compared to crystalloid solutions to achieve the same hemodynamic endpoints. However, there was marked heterogeneity among studies (I²=94%).
When the authors tried to identify the sources of heterogeneity, they found that the most important covariate was not the tonicity of the fluid, but the decade of publication. It appears that as we have come to believe that colloids are less effective than thought (many of us were taught 4:1, not 1.5:1), the ratio found in clinical comparisons has dropped as well.