Effects of Midazolam on Cerebral Blood Flow in Human Volunteers

The effects of intravenously administered midazolam on cerebral blood flow were evaluated in eight healthy volunteers using the 133Xe inhalation technique. Six minutes after an intravenous dose of 0.15 mg/kg midazolam, the cerebral blood flow decreased significantly (P < 0.001) from a value of 40.6 ± 3.3 to a value of 27.0 ± 5.0 ml 100 g−1. min−1. Cerebrovascular resistance (CVR) increased from 2.8 ± 0.2 to 3.9 ± 0.6 mmHg/(ml.100 g−1. min−1) (P < 0.001). Mean arterial blood pressure decreased significantly (P < 0.05) from 117 ± 8 to 109 ± 9 mmHg and arterial carbon dioxide tension increased from 33.9 ± 2.3 to 38.6 ± 3.2 mmHg (P < 0.05). Arterial oxygen tension remained stable throughout the study, 484 ± 95 mmHg before the administration of midazolam and 453 ± 76 mmHg after. All the subjects slept after the injection of the drug and had anterograde amnesia of 24.5 ± 5 min. The decrease in mean arterial blood pressure was probably not important since it remained in the physiologic range for cerebral blood flow autoregulation. The increase in arterial carbon dioxide tension observed after the midazolam injection may have partially counteracted the effect of this new benzodiazepine on cerebral blood flow. Our data suggest that midazolam might be a safe agent to use for the induction of anesthesia in neurosurgical patients with intracranial hypertension.