2 de maio de 2011

Should we really be more ‘balanced’ in our fluid prescribing?

Anaesthesia, 2009, 64, pages 703–705

Editorial

The use of intravenous fluid to maintain the extracellular fluid compartment composition and circulating volume is a fundamental component of modern medicine either as synthetic fluids containing either a dissolved solute osmotic load (crystalloid) or suspensions of largely insoluble macromolecules (colloids). It is also big business with intravenous fluid use worldwide running into hundreds of millions of pounds. The composition of intravenous fluids is quite rightly coming under intense scrutiny as concerns regarding efficacy and perhaps safety surface. While it is beyond the scope of this editorial to consider the ‘crystalloid vs colloid’ debate further, it is of note that many fundamental ‘truths’ regarding intravenous fluid therapy have not been validated by research [1] and it is in this environment of physiological dogma and research drought that clinicians find themselves evaluating intravenous fluids.

The anion composition of crystalloid (or base solution in the case of colloid suspensions) is increasingly being considered. While close to plasma, ‘normal’ (0.9%) saline is relatively hyperchloraemic 154mEq.l)1 (plasma 95–105mEq.l)1), hypertonic and acidic in plasma. The replacement of chloride with alternative anions is not new and Ringer’s lactate solution attempted to recreate physiological conditions by substituting excess chloride with another anion (racemic lactate), arguably the first ‘balanced’ solution. Increasingly other anions beside lactate are used and some commercial examples are in Table 1. The current generation of ‘balanced’ intravenous fluids share this reduction in chloride as their principal aim but they carry many other implications. While ‘balanced’ may be an appealing term it is also potentially misleading; that they are close to plasma in terms of pH, (effective) osmolality, or chloride concentration can be challenged. ‘Balanced’ intravenous solutions are receiving a lot of clinician attention and the manufacturers are marketing these agents hard. It is also likely that more balanced solutions will become available with time. While increasingly promoted as ‘state of the art’, we would argue that such claims are premature and furthermore, while the superiority of these new agents is largely unproven, so is their safety.

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