Crystalloids versus colloids: exploring differences in fluid requirements by systematic review and meta-regression

Area of Science:

• Critical Care Medicine
• Fluid Physiology
• Evidence Synthesis

Background:

• Positive fluid balance is linked to adverse patient outcomes.
• Understanding fluid volume requirements for different intravenous fluids is clinically significant.
• Physiological concepts suggest less colloid than crystalloid is needed due to molecular size, but recent data challenge this.

Purpose of the Study:

• To systematically review and meta-analyze studies comparing crystalloid and colloid fluid administration.
• To determine the crystalloid/colloid ratio needed to achieve similar endpoints.
• To explore factors influencing the crystalloid/colloid ratio.

Main Methods:

• Systematic search of MEDLINE, EMBASE, and CENTRAL databases up to December 2013.
• Inclusion of all studies comparing any crystalloid with any colloid in any patient population.
• Calculation of crystalloid/colloid ratios, with meta-analysis for studies reporting sufficient data.

Main Results:

• 48 studies were included, with 24 suitable for meta-analysis.
• The overall crystalloid/colloid ratio was 1.5 (95% CI, 1.36-1.65), with substantial heterogeneity (I² = 94%).
• Publication decade and albumin concentration were associated with the ratio, but explained minimal heterogeneity.

Conclusions:

• Crystalloids require greater volumes (ratio 1.5) than colloids for equivalent targets, but with significant study heterogeneity.
• The crystalloid/colloid ratio has decreased over time.
• While albumin concentration correlates with the ratio, primary drivers of heterogeneity remain unidentified.