A young man is admitted to the intensive care unit with severe pancreatitis, high fevers and tachycardia. You know he needs volume, and fast, but he has already received several liters of normal saline in the emergency department before being transported to the ICU. You begin to order another normal saline bolus but then pause and wonder, “Wouldn’t my patient benefit more from a fluid that would remain in the vascular space?” When it comes to resuscitation, isn’t there any benefit to the much-maligned colloid over crystalloid?
In the late 19th century, experiments led to the differentiation of colloid versus crystalloid, based on a fluid’s ability to diffuse through a membrane. In contrast to crystalloid (e.g. normal saline, or lactated Ringer’s), which ultimately distributes through the interstitium, starch-based colloid fluids contain large molecules that do not pass as easily through capillary walls and thus should more effectively expand the intravascular space.
Intuitively, then, a patient in a vasodilatory state such as septic shock could benefit from colloid as the fluid of choice. For example, anyone who has worked in an ICU has seen patients with puffy extremities and lungs filled with fluid after days of normal saline boluses. However, studies have suggested that colloids, such as hydroxyethyl starch (HES), might do more harm than good. With the initial suggestion that high molecular weight HES leads to renal failure with a trend toward increased mortality, attention turned to lower molecular weight preparations –- perhaps the larger molecules were responsible for the damage. But it appeared that the danger remained. In fact, a study published this summer in NEJM showed that patients in septic shock who received hetastarch (a potato based starch) rather than crystalloid had higher mortality and increased rates of renal failure leading to dialysis. (Perner et al. Hydroxyethyl Starch 130/0.42 versus Ringer’s Acetate in Severe Sepsis.)
If the jury was still out after those data, it need be no longer. With results published in this week’s issue of NEJM, the question of starch-based colloid instead of crystalloid for ICU patients might finally be closed.
In the most recent study of colloid versus crystalloid, “Hydroxyethyl Starch (130/0.4) vs. Saline for Fluid Resuscitation in Intensive Care,” John A. Myburgh and colleagues randomized 7,000 patients in ICUs in Australia and New Zealand to receive hydroxyethyl starch (a corn-based colloid) or normal saline for volume resuscitation. In contrast to prior studies that examined resuscitation in septic shock, the Myburgh et al. study represented a heterogeneous group of patients, some in medical and others in surgical ICUs. The authors looked at death as the primary outcome, and – based on the concerns raised in prior studies – examined kidney failure as a secondary outcome.
While there was no statistically significant difference in death within 90 days in the two groups, resuscitation with HES was associated with a 21% relative increase in the number of patients who developed kidney failure severe enough to require dialysis.
The authors conclude, “Our study does not provide evidence that resuscitation with 6% HES compared to saline in the ICU provides any clinical benefit to the patient…The selection of resuscitation fluid in critically ill patients therefore requires careful consideration of its safety, its potential impact on patient-centered outcomes and its cost.”
Back to our patient, then–
Without any evidence for embarking on the more expensive expensive colloid option – and clear suggestion of potential harm – crystalloid it is. You realize that another liter of normal saline is the best option.