Kidney Week 2012: Acute Kidney Injury in the Neuro ICU
Dr. Sarah Faubel created this 2-hour lecture block. The idea was to look at four different theater of operations and look do a deep dive on how the causes and treatments of acute kidney injury differ. This is a salute to Bayesian logic and attempts to give doctors a refined view of pre-test probabilities for the etiologies of AKI depending on the clinical scenario.
One of the talks was Dr. Berl on AKI in the neurological unit.
The incidence of AKI, using RIFLE criteria, was 23% following a subarachnoid hemorrhage. Importantly he found that the severity of AKI predicted survival with the poorest outcomes associated with RIFLE stage: Failure.
He then discussed contrast nephropathy. Serafin et al found a very high incidence of contrast nephropathy following intra-arteriole administration of contrast. Contrast nephropathy occurred in 23% of patients, despite a pre-morbid average GFR of 98 mL/min. They did not see any difference between low and iso-osmolar contrast.
Dr. Berl then focused on the importance of maintaining cerebral blood flow, which is the product of cerebral perfusion pressure and vascular resistance. Cerebral perfusion pressure is the difference between systemic arterial pressure and intracranial pressure. You need to maintain cerebral perfusion pressure above 60 mmHg for good cerebral blood flow. He pointed to data that showed if the intracranial pressure was over 40 mortality was 56%, while below 20 mmHg it was only 18%.
In order to control ICP focus on creating an osmotic gradient with mannitol or hypertonic saline. Koenig et al used 30 mL of 23.4% saline to lower the ICP by 40%, it raised serum sodium by 5 mEq/L. 30 mL of 23.4% is equivalent to 238 mL of 3%.
Berl summarized the interventions for improving cerebral perfusion pressure as the 3 Hs: hypervolemia, hypertension and hypertonicity. He added you could also do the fourth H, hyperventilation.
Hyponatremia is a complication often seen in neuro-ICU patients. Conivaptan has been used successfully and safely in this environment.
He concluded with mentioning the KDIGO recommendation for using CRRT rather than intermittent hemodialysis for patients with acute brain injury or other causes of increased intracranial pressure.
Post by Dr. Joel Topf, eAJKD Advisory Board member
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