The Place of Crystalloids

Abstract

AbstractCrystalloids are commonly used in medicine as solutions containing electrolytes dissolved in water, with or without glucose. They can be used as maintenance, replacement, or resuscitation fluids, but should be administered with caution. This chapter provides an overview of basic definitions, terminology, and concepts regarding crystalloids, including their categorization by tonicity, their balanced or unbalanced nature, and the importance of strong ion difference (SID). Improper administration of crystalloids can lead to morbidity, particularly hyperchloremic metabolic acidosis (HMA) and fluid overload. Moreover, saline with a SID of zero can cause a positive sodium balance and subsequent fluid accumulation, which can lead to renal dysfunction and the need for vasopressors and renal replacement therapy. Recent systematic reviews and post-hoc analyses of six major fluid trials have shown that balanced solutions (not containing glucose) reduce mortality by 1%, making them a good first choice for resuscitation in patients with sepsis and septic shock, burns, or diabetic ketoacidosis. Traumatic brain injury and gastrointestinal losses may be the only indications left for (ab)normal saline. The pediatric community still favors isotonic solutions for maintenance, although a growing body of evidence supports hypotonic crystalloids as a better choice. Hypertonic crystalloids have been described for small volume resuscitation in specific patient populations, such as post cardiac arrest, but their sodium burden may outweigh the temporarily beneficial hemodynamic effects. In case of excessive losses, fluids should be substituted or replaced by those that mimic the fluids that are lost, such as blood. Prescribing crystalloid solutions should be done with care. Fluid overload or accumulation and HMA should be avoided, as it can induce extra morbidity and mortality. Choosing the right fluid, indication, dose, and duration is crucial for preventing morbidity and mortality: it is all about giving the right dose of the right fluid at the right time for the right patient!