Magnesium sulfate has negligible effect on middle cerebral artery blood flow velocity in response to endotracheal intubation.

BACKGROUND: Pretreatment of magnesium sulfate (MgSO4) attenuates pressor response associated with endotracheal intubation. Vasodilating effect of MgSO4 may increase cerebral blood flow, which upsets the known benefit to cardiovascular hemodynamic. In the present study, we evaluated the effect of MgSO4 on the changes of cerebral blood flow in response to endotracheal intubation. METHODS: Twenty four ASA class I or II patients who randomly received either normal saline 5 ml or MgSO4 (60 mg/kg, i.v.) 3 min before induction of anesthesia were included in the study. Mean blood flow velocity (VMCA) of the middle cerebral artery was obtained using a transcranial Doppler sonography (TCD) before and after endotracheal intubation. Anesthesia was induced with fentanyl (4 micrograms/kg) and thiopental (5 mg/kg) and endotracheal intubation was facilitated with succinylcholine (1.5 mg/kg). RESULTS: Before endotracheal intubation, MgSO4 caused a transient decrease in VMCA (98 +/- 6% vs. 76 +/- 3% of baseline) and increase in heart rate (132% vs. 114% of baseline) compared to saline group. However, VMCA and heart rate did not show significant difference in both groups after tracheal intubation. Also, systolic and diastolic blood pressure did not differ during the study. CONCLUSIONS: Our results suggest that MgSO4 appeared to have negligible effects on cerebral blood flow and hemodynamics in response to tracheal intubation. Its attenuating effect on pressor response induced by endotracheal intubation might be over emphasized.