Effects of intravenous anesthetic agents on middle cerebral artery blood flow velocity during induction of general anesthesia

Glycopyrrolate prevents extreme bradycardia and cerebral deoxygenation during electroconvulsive therapy

The stimulation phase of electroconvulsive therapy (ECT) induces bradycardia. We evaluated the effect of this bradycardia on cerebral perfusion and oxygenation by administration of the anticholinergic drug glycopyrrolate (Glp). Cerebral perfusion was estimated by transcranial ultrasound in the middle cerebral artery reporting the mean flow velocity (middle cerebral artery [MCA] V(mean)), and cerebral oxygenation was determined by near-infrared spectroscopy of the frontal lobe. Before ECT, heart rate (HR) was 84 beats min(-1) (66-113; median and range) and decreased to 17 (7-85) beats min(-1) during the stimulation phase of ECT (P < 0.001). Middle cerebral artery V(mean) decreased 43% (9%-71%; P < 0.001), and frontal lobe oxyhemoglobin (O(2)Hb) concentration decreased from 0.6 (0.0-25.3) to 0.1 (-1.9 to 7.6) microM, whereas the deoxyhemoglobin concentration increased from -0.2 (-13.9 to 0.8) to 0.0 (-4.2 to 0.8) microM (P < 0.001). Pretreatment with Glp largely eliminated these effects during the stimulation phase of ECT, maintaining HR at 78 (40-94) beats min(-1), MCA V(mean) at 53 (37-77) cm s(-1), and O(2)Hb at 5.6 (10.6-38.5) microM (P < 0.05). After ECT, HR, cerebral perfusion and oxygenation normalized over approximately 3 minutes, whereas the electroencephalogram was unaffected by Glp. The results demonstrate that ECT is associated with hemodynamic effects severe enough to affect cerebral oxygenation and perfusion, and that these effects can be attenuated by Glp treatment.

Transcranial Doppler and anesthetics

Transcranial Doppler (TCD) is widely used to investigate the effects of anesthetic drugs on cerebral blood flow. Its repeatability and non-invasivity makes it an ideal, first choice method. Anesthesia providers are required to be conscious of the cerebral hemodynamic effects of drugs given in their practice, especially in neurosurgery and in subjects with impaired brain functions. The purpose of this review is to present the basic concepts of the TCD technique and the effects on cerebral hemodynamics of the most popular anesthetic drugs evaluated using TCD ultrasonography.

Ductus arteriosus with left-to-right shunt during venoarterial extracorporeal membrane oxygenation: effects on cerebral oxygenation and hemodynamics

OBJECTIVE

To investigate the effect on cerebral oxygenation and hemodynamics of a patent ductus arteriosus with left-to-right shunt during venoarterial extracorporeal membrane oxygenation in a lamb model.

DESIGN

Prospective intervention study in animals.

SETTING

Animal research laboratory of a university medical center.

SUBJECTS

Six anesthetized newborn lambs with patent ductus arteriosus and left-to-right shunt, installed on venoarterial extracorporeal membrane oxygenation.

INTERVENTIONS

Six lambs of 140 days gestational age were prepared to keep the ductus arteriosus open by infiltration of the vessel wall with formaline 10%. The animals were installed on standard venoarterial extracorporeal membrane oxygenation. With a mechanical occluder, the ductus was closed.

MEASUREMENTS AND MAIN RESULTS

Changes of mean arterial blood pressure and carotid artery blood flow were measured simultaneously. Using near infrared spectrophotometry, we calculated changes in cerebral concentration of oxyhemoglobin and deoxyhemoglobin (reflecting changes in cerebral oxygen supply) and total hemoglobin (reflecting changes in cerebral blood volume). Also, cerebral oxygen delivery before and after ductus closure was calculated. Before ductus closure there was a left-to-right shunt with a mean +/- SEM of 41 +/- 20% of total body blood flow. Closure of the ductus resulted in an immediate increase in mean arterial blood pressure and carotid artery blood flow. The concentration of oxyhemoglobin increased and the concentration of deoxyhemoglobin decreased, representing increased cerebral oxygen supply. The concentration of total hemoglobin was unchanged, representing unchanged cerebral blood volume. There was an increase in cerebral oxygen delivery.

CONCLUSIONS

In this lamb model, a considerable left-to-right shunt over the ductus during venoarterial extracorporeal membrane oxygenation reduced cerebral circulation and oxygenation.

The comparative effects of propofol versus thiopental on middle cerebral artery blood flow velocity during electroconvulsive therapy

Electroconvulsive therapy provokes abrupt changes in both systemic and cerebral hemodynamics. An anesthetic that has a minor effect on cerebral hemodynamics might be more suitable for patients with intracranial complications, such as cerebral aneurysm. The purpose of our present study was to compare the effects of thiopental and propofol on cerebral blood flow velocity. We continuously compared cerebral blood flow velocity at the middle cerebral artery (MCA) during electroconvulsive therapy, using propofol (1 mg/kg, n = 20) versus thiopental (2 mg/kg, n = 20) anesthesia. Systemic hemodynamic variables and flow velocity at the MCA were measured until 10 min after the electrical shock. Heart rate and arterial blood pressure increased in the thiopental group until 5 min after the electrical shock. In the propofol group, an increase in mean blood pressure was observed to 1 min after the electrical shock. Mean flow velocity at the MCA decreased after anesthesia in both groups, and increased at 0.5-3 min after the electrical shock in the thiopental group and at 0.5 and 1 min after the shock in the propofol group. The flow velocities at 0.5-5 min after the electrical shock were significantly more rapid in the thiopental group compared with the propofol group. ¿abs¿

IMPLICATIONS

Cerebral blood flow velocity change, measured by transcranial Doppler sonography during electroconvulsive therapy, was minor using propofol anesthesia compared with barbiturate anesthesia. Propofol anesthesia may be suitable for patients who cannot tolerate abrupt cerebral hemodynamic change.

Changes in maternal middle cerebral artery blood flow velocity associated with general anesthesia in severe preeclampsia

In women with severe preeclampsia, significant increases in mean arterial pressures (MAP) are common after rapid induction of general anesthesia (GA) and tracheal intubation. The objectives of this prospective study were to assess the effects of the rapid induction-intubation technique on middle cerebral artery (MCA) flow velocity in severe preeclampsia and to examine the correlation between mean MCA flow velocity (Vm) and MAP. Eight women with severe preeclampsia (study group) and six normotensive women at term (control group) scheduled to undergo cesarean section under GA were studied. Before induction, patients in the study group received i.v. labetalol in divided doses to lower diastolic pressures to <100 mm Hg. Anesthesia was induced with pentothal 4-5 mg/kg, followed by succinylcholine 1.5 mg/kg to facilitate tracheal intubation. A transcranial Doppler was used to measure Vm. Both Vm and MAP were recorded before induction and every minute for 6 min after intubation. In the study group, after the administration of labetalol, MAP decreased from 129 +/- 9 to 113 +/- 9 mm Hg (P < 0.05), and Vm decreased from 59 +/- 11 to 54 +/- 10 cm/s (P < 0.05). After intubation, MAP increased from 113 +/- 9 to 134 +/- 5 mm Hg (P < 0.001), and Vm increased from 54 +/- 10 to 70 +/- 10 cm/s (P < 0.001). In the control group, while MAP increased significantly from 89 +/- 6 to 96 +/- 4 mm Hg (P < 0.05) after intubation, the concurrent increase in Vm from 49 +/- 5 to 54 +/- 7 cm/s was not significant. There was a significant positive pooled correlation between Vm and MAP (r = 0.5, P < 0.0006) in the study group but not in the control group (r = 0.24). After induction and intubation, both Vm and MAP values were significantly increased in the study group patients at all observation points compared with the control group patients. The findings indicate that Vm increases significantly after rapid-sequence induction of GA and tracheal intubation in women with severe preeclampsia, and there seems to be a direct relationship between MAP and Vm.

IMPLICATIONS

In women with severe preeclampsia, rapid-sequence induction of general anesthesia and tracheal intubation can cause severe hypertension. Our results indicate that the increase in blood pressure is associated with a significant increase in maternal cerebral blood flow velocity and that there is a significant correlation between these two variables.