Friday, May 02, 2014

Resuscitation fluid: which and how much

One old and a few emerging debates dominate this field. A recent NEJM review helps provide clarity.

The old debate: colloid versus crystalloid

With few exceptions there's no good evidence that one is better than the other (except that starch is bad). That situation has not changed during my entire career.

New debate: is saline bad (should we be using some other crystalloid?)

From the review:

The strong ion difference of 0.9% saline is zero, with the result that the administration of large volumes of saline results in a hyperchloremic metabolic acidosis.36 Adverse effects such as immune37 and renal38 dysfunction have been attributed to this phenomenon, although the clinical consequences of these effects is unclear.39

This has led to renewed interest in so called “balanced” crystalloids, and low level evidence suggests they may be better. The review cites a couple of low level studies in which alternative crystalloids were associated with better outcomes but points out that there may be unintended consequences to such an approach:

Crystalloids with a chemical composition that approximates extracellular fluid have been termed “balanced” or “physiologic” solutions and are derivatives of the original Hartmann's and Ringer's solutions. However, none of the proprietary solutions are either truly balanced or physiologic41 (Table 1).
Balanced salt solutions are relatively hypotonic because they have a lower sodium concentration than extracellular fluid. Because of the instability of bicarbonate-containing solutions in plastic containers, alternative anions, such as lactate, acetate, gluconate, and malate, have been used. Excessive administration of balanced salt solutions may result in hyperlactatemia, metabolic alkalosis, and hypotonicity (with compounded sodium lactate) and cardiotoxicity (with acetate). The addition of calcium in some solutions may generate microthrombi with citrate-containing red-cell transfusions.
High level randomized trials are needed.

New debate: how much? Is less more?

Most would agree that aggressive resuscitation is warranted on the front end but it is increasingly apparent that cumulative positive fluid balance over days is associated with microcirculatory and organ congestion and all the consequences associated therewith.

So what should we do?

Until we get some high level clinical trials we have clinical judgment informed by low level data and physiologic rationale along with a few suggestions form the experts. The authors didn't make any strong statements but offered some things to think about:

Consider alternative crystalloids in some patients (this essentially means Ringer's lactate). Like one's choice of pressors, the decision will be based on patient attributes and therapeutic objectives.

Front load then back off.

Consider special situations (e.g. brain injury).

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