Transcranial Doppler ultrasonography with induction of anesthesia for neurosurgery

Intracranial hypertension can occur with induction of anesthesia; however, the clinical significance of this is unclear. We used transcranial Doppler (TCD) ultrasonography in neurosurgical patients during induction of anesthesia and endotracheal intubation to assess the incidence of high intracranial pressure (ICP) waveforms and to correlate TCD observations with specific anesthetics and anesthetic regimens. The middle cerebral artery was monitored by TCD during induction of anesthesia and endotracheal intubation in 196 patients undergoing elective neurosurgery. Middle cerebral artery blood flow velocity (MCABFV) and physiologic data were observed continuously and recorded at the following times: preinduction, induction, intubation, and postintubation. Induction with thiopental or etomidate decreased MCABFV, intubation increased MCABFV, and postintubation ventilation decreased MCABFV. MCABFV was higher throughout the induction sequence in the 92 patients with tumors. Although there were numerous individual exceptions, changes in mean arterial pressure correlated statistically with changes in MCABFV. No patient had an end-diastolic flow velocity of 0. We reached the following conclusions: (a) TCD is a straightforward modality that can be used to monitor dynamic cerebrovascular events during induction of anesthesia; (b) MCABFV is increased with brain tumors; (c) thiopental and etomidate rapidly decrease and intubation rapidly increases MCABFV; and (d) routine TCD monitoring for high ICP waveforms during anesthetic induction for routine elective neurosurgery appears to be unwarranted.