Cerebral Blood Flow Assessed with Phase-contrast Magnetic Resonance Imaging during Blood Pressure Changes with Noradrenaline and Labetalol: A Trial in Healthy Volunteers.
Level 3 - non-randomized controlled study
Prospective non-randomized single-arm crossover trial with fixed intervention sequence
PubMed 37756527 · doi:10.1097/ALN.0000000000004775
What was done
Phase-contrast magnetic resonance imaging (MRI) and intra-arterial blood pressure monitoring were used to measure cerebral blood flow (defined as the sum of flow in the internal carotid and vertebral arteries) and cardiac output (ascending aorta flow) in 18 healthy volunteers aged 30 to 50 years. Participants received intravenous noradrenaline targeted to increase mean arterial pressure (MAP) by 20% above baseline, followed by a wash-out period and subsequent intravenous labetalol boluses targeted to reduce MAP by 15% below baseline.
What was found
Baseline median cerebral blood flow was 772 ml/min (interquartile range [IQR], 674 to 871) and cardiac output was 5,874 ml/min (IQR, 5,199 to 6,355). With noradrenaline infusion (median dose 0.17 µg·kg⁻¹·h⁻¹), cerebral blood flow decreased to 705 ml/min (IQR, 606 to 748; P = 0.001) and cardiac output decreased to 4,995 ml/min (IQR, 4,705 to 5,635; P = 0.01). Following labetalol administration (median dose 120 mg), cerebral blood flow was 769 ml/min (IQR, 734 to 900; P = 0.68) and cardiac output increased to 6,413 ml/min (IQR, 6,056 to 7,464; P = 0.03).
Why it matters
Pharmacologically elevating mean arterial pressure with noradrenaline unexpectedly reduced cerebral blood flow and cardiac output in healthy awake individuals, challenging the assumption that noradrenaline-induced blood pressure elevation consistently augments brain perfusion.
Limits
Small sample size (n = 18) restricted to healthy, awake young-to-middle-aged adults. The interventions were administered in a fixed sequence rather than randomized. Findings cannot be directly generalized to anesthetized patients, elderly populations, or those with impaired cerebral autoregulation.
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