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Midazolam Changes Cerebral Blood Flow in Discrete Brain Regions: An H2‐15O Positron Emission Tomography Study

Background: Changes in regional cerebral blood flow (rCBF) determined with H215 O positron emission tomographic imaging can identify neural circuits affected by centrally acting drugs. Methods: Fourteen volunteers received one of two midazolam infusions adjusted according to electroencephalographic response. Low or high midazolam effects were identified using post‐hoc spectral analysis of the electroencephalographic response obtained during positron emission tomographic imaging based on the absence or presence of 14‐Hz spindle activity. The absolute change in global CBF was calculated, and relative changes in rCBF were determined using statistical parametric mapping with localization to standard stereotactic coordinates. Results: The low‐effect group received 7.5 +/‐ 1.7 mg midazolam (serum concentrations, 74 +/‐ 24 ng/ml), and the high‐effect group received 9.7 +/‐ 1.3 mg midazolam (serum concentrations, 129 +/‐ 48 ng/ml). Midazolam decreased global CBF by 12% from 39.2 +/‐ 4.1 to 34.4 +/‐ 6.1 ml [center dot] 100 g sup ‐1 [center dot] min sup ‐1 (P < 0.02 at a partial pressure of carbon dioxide of 40 mmHg). The rCBF changes in the low‐effect group were a subset of the high‐effect group. Decreased rCBF (P < 0.001) occurred in the insula, the cingulate gyrus, multiple areas in the prefrontal cortex, the thalamus, and parietal and temporal association areas. Asymmetric changes occurred, particularly in the low‐effect group, and were more significant in the left frontal cortex and thalamus and the right insula. Relative rCBF was increased in the occipital areas. Conclusion: Midazolam causes dose‐related changes in rCBF in brain regions associated with the normal functioning of arousal, attention, and memory.