Vasopressor Infusion After Subarachnoid Hemorrhage Does Not Increase Regional Cerebral Tissue Oxygenation.
Khalil M Yousef, Elizabeth Crago, Yuefang Chang and 7 others
PMID 29985275WHAT IT FOUND
In 19 patients after aneurysmal subarachnoid hemorrhage, vasopressor infusion raised blood pressure but forehead oxygen sensor readings were lower while the infusion was running than while it was off.
Key findings
01In the 19 patients analyzed, during vasopressor infusion left forehead cerebral oxygen saturation was 4.4% lower and right forehead cerebral oxygen saturation was 5.5% lower than during times when vasopressors were not infusing, after controlling for Hunt and Hess grade and severe vasospasm.
02Systolic BP increased by 15 mmHg, diastolic BP by 7.3 mmHg, and mean BP by 10 mmHg during vasopressor infusion times.
03Peripheral hand oxygen saturation rose by 1.5% during vasopressor infusion, and the paper reports this rise was not statistically significant.
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How it was doneWhat they foundWhat it means for RNs
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What it does not show
Only 19 patients who received vasopressors were analyzed, so the study is small and may not represent other patients. No randomization procedure is described, and the study compares the same patients during infusion and non-infusion times. The design cannot separate the effect of norepinephrine from epinephrine, phenylephrine, or vasopressin when they were used together. Cerebral autoregulation, vasopressor dose effect, intravascular volume, and administered intravenous fluid were not formally assessed. Body and head position, hemoglobin levels, temperature, and mechanical ventilation were not controlled and could affect rSO2 readings. The results presented are rSO2 and BP values; the study measured oxygen saturation and BP, not patient outcomes such as death, disability, or cognition. NIRS rSO2 may be sensitive to changes in cerebral blood flow, but this is a limitation of the technology itself.
Declared interests
The methods section lists R01NR014221, and the conflicts of interest section states none.
The easy way to misread this
Do not conclude that vasopressors should be withheld because they lowered forehead oxygen sensor readings. The study has no randomization procedure described, included only 19 patients, and cannot show that vasopressors caused the drop or that withholding them would improve outcomes. The effect also cannot be assigned to norepinephrine alone, because some patients also received epinephrine, phenylephrine, or vasopressin.