A 59-year-old female with no past medical history is admitted to the neurointensive care unit following a large right middle cerebral artery ischemic stroke. She was not a candidate for intravenous tPA nor intra-arterial therapy. She has had progressive somnolence and anisocoria with a right larger than left pupil that was not responsive to direct or consensual light testing. She was started on hyperosmolar therapy followed by a decompressive hemicraniectomy. She is now poststroke day 5 and continues to have malignant cerebral edema. Prior to her next dose of mannitol her lab values are as follows:
What is her osmolar gap?
Correct Answer: A
The osmolar gap estimates the unknown osmotic agent in the blood, which in this patient’s case is mannitol. To calculate the osmolar gap we need to calculate the calculated osms.
Calculated osm = (2 x Na) + (BUN / 2.8) + (Glu / 10)
Osm Gap = Measured Osm - Calculated Osm
Mannitol is a hypertonic solution of sugar that is used to treat cerebral edema. The medication works as an osmotic diuretic which causes large volume urinary output due to high concentrated urine within the distal collecting duct and allows for extraction of extracellular fluid into the bloodstream due to the osmotic gradient between the intravascular and extravascular, extracellular compartment. There are a number of complications that can occur with mannitol therapy including volume depletion, electrolytes imbalance such as hyponatremia, and metabolic acidosis. Acute kidney injury can also occur secondary to dehydration and mannitol accumulation. Therefore, mannitol should only be given within specific parameters including osmolar gap <12 (the gap value varies between institution). In our patient’s case her osmolar gap is 0 and therefore, she should receive mannitol 0.25 to 1 g/kg every 6 to 8 hours.
References:
A 53-year-old, right-handed, previously independent male with no past medical history was found down at home. He was brought to the emergency department where he was found to have a large, wellestablished L MCA ischemic stroke on CT with a proximal L M1 thrombus on CT angiogram. He was not a candidate for IV tPA or intra-arterial therapy given the well established infarction and his last known well-being over 12 hours prior to presentation. He was admitted to the intensive care unit for ongoing management. Over the course of the next 24 hours he has progressive decline in his mental status and required intubation. A repeat head CT shows evolution of the ischemic stroke with left-to-right midline shift.
What is the best description of the anticipated outcome following a hemicraniectomy for malignant ischemic stroke?
Correct Answer: B
There have been a number of trials that have evaluated hemicraniectomy with durotomy for malignant MCA ischemic strokes: DESTINY, DECIMAL, DECIMAL 2, and HAMLET. The trials involved a total of 314 patients and demonstrated a decrease in mortality from 71% to 30% (odds ratio 0.19) with number needed to treat 2.4. With the pooled data there was increase in patients with slight disability and increase in moderate to severe disability which outweighed the slight disability improvement.
Treatment choice should not depend on hemispheric involvement. Mortality, functional outcome, and quality of life do not seem to depend on the dominate hemisphere involved. Rather, neuropsycholoigcal defects seen in patients with infarcts in the nondominant hemisphere may be as disabling as language deficits. The surgical procedure involves removal of a generous bone flap and durotomy which has been demonstrated to provide further decrease in intracerebral pressure and is not associated with increased complications.
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