In this episode, I’ll discuss the problem with hypo-osmolar solutions in neurological patients.
The administration of hypo-osmolar IV solutions causes an increase in water into the brain. This is because an intact blood-brain barrier is permeable to water but not electrolytes. When the blood brain barrier is intact, and there are no brain pathologies, the increase in water in the brain is compensated by neuronal cells via active depletion of intracellular osmotic solutes. This is referred to as “volume regulatory decrease”.
However when the blood-brain barrier is disrupted and/or cerebral edema is present from intracranial bleeding, the brain cell’s ability to regulate extra water is impaired. This is often the case in patients with acute ischemic stroke.
A common cause of in-hospital death from acute ischemic stroke is brain edema and elevated intracranial pressure. This is often a result of occlusion of the major intracranial arteries or multi-lobar stroke. Brain edema is thought to peak somewhere between 3 and 5 days after the initial ischemic event.
Administration of a hypo-osmolar fluid such as 5% dextrose or half normal saline therefore carries a theoretical risk of increasing the severity of cerebral edema.
Although this is a theoretical risk, there is usually not a compelling reason to take the chance of giving a hypo-osmolar IV solution to patients with acute ischemic stroke. This is why in both brain bleeding and acute ischemic stroke patients, the use of hypo-osmolar IV solutions is not recommended.
Further information on what fluids to avoid in these patients is provided by a 2012 analysis of the Saline versus Albumin Fluid Evaluation study. Albumin was found in this study to have worse outcomes in TBI patients than crystalloids. The authors suggest this is because the osmolality of an infusion solution rather than the colloid osmotic pressure represents the key determinant in the pathogenesis of cerebral edema formation.
Members of my Hospital Pharmacy Academy have access to a video-based training on Practical Strategies for Acutely Elevated ICP from a pharmacist’s point of view. This is in addition to hundreds of other resources to help in your practice. The Hospital Pharmacy Academy is my online membership site that teaches pharmacists practical critical care and hospital pharmacy skills you can apply at the bedside so that you can become confident in your ability to save lives and improve patient outcomes. To get immediate access, go to pharmacyjoe.com/academy.
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