Cerebral Blood Flow and CO2 Reactivity Is Similar during Remifentanil/N2 O and Fentanyl/N2 O Anesthesia

Background: Remifentanil, a rapidly metabolized [micro sign]-opioid agonist, may offer advantages for neurosurgical procedures in which prolonged anesthetic effects can delay assessment of the patient. This study compared the effects of remifentanil-nitrous oxide on cerebral blood flow (CBF) and carbon dioxide reactivity with those of fentanyl-nitrous oxide anesthesia during craniotomy.

Methods: After institutional approval and informed patient consent were obtained, 23 patients scheduled to undergo supratentorial tumor surgery were randomly assigned to remifentanil or fentanyl infusion groups in a double-blinded manner. Midazolam, thiopental, and pancuronium induction was followed by equipotent narcotic loading infusions of remifentanil (1 [micro sign]g [middle dot] kg-1 [middle dot] min-1) or fentanyl (2 [micro sign]g [middle dot] kg-1 [middle dot] min-1) for 5-10 min. Patients were ventilated with 2:1 nitrous oxide-oxygen, and opioid rates were reduced and then titrated to a stable hemodynamic effect. After dural exposure, CBF was measured by the intravenous133 xenon technique at normocapnia and hypocapnia. Reactivity of CBF to carbon dioxide was calculated as the absolute increase in CBF per millimeters of mercury increase in the partial pressure of carbon dioxide (PaCO2). Data were analyzed by repeated-measures analysis of variance, unpaired Student's t tests, or contingency analysis.

Results: In the remifentanil group (n = 10), CBF decreased from 36 +/- 11 to 27 +/- 8 ml [middle dot] 100 g-1 [middle dot] min-1 as PaCO2 decreased from 33 +/- 5 to 25 +/- 2 mmHg. In the fentanyl group (n = 8), CBF decreased from 37 +/- 11 to 25 +/- 6 ml [middle dot] 100 g-1 [middle dot] min-1 as PaCO2 decreased from 34 +/- 3 to 25 +/- 3 mmHg. Absolute carbon dioxide reactivity was preserved with both agents: 1 +/- 1.2 ml [middle dot] 100 g-1 [middle dot] min-1 [middle dot] mmHg-1 for remifentanil and 1.5 +/- 0.5 ml [middle dot] 100 g-1 [middle dot] min-1 [middle dot] mmHg-1 for fentanyl (P = 0.318).     

Increased cerebral blood flow after brain arteriovenous malformation resection is substantially independent of changes in cardiac output

Brain arteriovenous malformation (BAVM) resection can result in an acute increase in cerebral blood flow (CBF) of unclear etiology. This observational study investigated the relationship between changes in CBF and cardiac output (CO) in patients undergoing microsurgical resection of BAVMs. In 20 patients undergoing a BAVM resection during an isoflurane-based anesthesia, we measured CBF and systemic cardiovascular parameters immediately before and after BAVM resection. CBF was measured on the hemisphere ipsilateral to the lesions and on the contralateral side, using intravenous cold 133Xe washout. Cardiac output was measured using thermodilution technique via a pulmonary artery catheter. There was an increase in global CBF after resection (25 +/- 8 versus 31 +/- 13 mL/100 g/min, preresection versus postresection, mean +/- SD, P =.002), ipsilateral CBF (25 +/- 8 versus 31 +/- 13 mL/100 g/min, P =.002), and contralateral CBF (24 +/- 7 versus 30 +/- 13 mL/100 g/min, P =.003). There was no change in CO, mean systemic arterial pressure, central venous pressure, or pulmonary artery diastolic pressure. The change in CBFGLOBAL was not correlated with changes in CO (r =.154, P =.517). BAVM resection resulted in global increases in CBF that was not substantially related to changes in CO or other systemic parameters.     

Predictors and impact of aneurysm rebleeding after subarachnoid hemorrhage

BACKGROUND: Aneurysm rebleeding has historically been an important cause of mortality after subarachnoid hemorrhage (SAH). OBJECTIVE: To describe the frequency and impact of rebleeding in the modern era of aneurysm care, which emphasizes early surgical or endovascular treatment. DESIGN: Inception cohort. SETTING: Tertiary care medical center. PATIENTS: A total of 574 patients enrolled in the Columbia University SAH Outcomes Project between August 1996 and June 2002. Early aneurysm repair was performed whenever feasible. MAIN OUTCOME MEASURES: Rebleeding was defined by prespecified clinical and radiographic criteria, excluding prehospital, intraprocedural, and postrepair events. Functional outcome was assessed at 3 months with the modified Rankin Scale. Multiple logistic regression was used to identify predictors of rebleeding, poor functional outcome, and mortality. RESULTS: Rebleeding occurred in 40 (6.9%) of the 574 patients; most cases (73%) occurred within 3 days of ictus. Hunt-Hess grade on admission (odds ratio [OR], 1.92 per grade; 95% confidence interval [CI], 1.33-2.75; P<.001) and maximal aneurysm diameter (OR, 1.07/mm; 95% CI, 1.01-1.13; P = .005) were independent predictors of rebleeding. After controlling for Hunt-Hess grade and aneurysm size, rebleeding was associated with a markedly reduced chance of survival with functional independence (modified Rankin Scale score, 相似文献   

Three-minute blood flow index for assessment of cerebrovascular reserve

Regional cerebral blood flow studies with xenon-133 are useful in the functional assessment of cerebrovascular diseases. Conventional models for cerebral blood flow calculation employ 11 minutes of data collection. However, in many circumstances it is not possible to maintain steady-state physiologic conditions for 11 minutes. We compared a monocompartmental model that requires only 3 minutes of data collection with the bicompartmental model that requires 11 minutes of data collection. The correlation between the absolute values for global cerebral blood flow (initial slope index, intravenous method) in 72 anesthetized patients was r = 0.88; for 54 awake patients inhaling xenon-133, the correlation was r = 0.77. Cerebral blood flow was determined with intravenous xenon-133 at baseline and during a CO2 challenge in 50 patients during cerebrovascular surgery under general anesthesia. Reactivity to a 10-mm Hg rise in PaCO2 was calculated in absolute terms and as a percentage change from baseline using both the 3-minute and the 11-minute models. The correlation of CO2 reactivity calculated with the two models was r = 0.9 for the absolute values and r = 0.8 for the relative change. Cerebral blood flow calculated with the two models correlated well in both awake and anesthetized patients. In addition, there was a good correlation between CO2 reactivity calculated with the two models. In situations in which physiologic conditions cannot be held stable for 11 minutes, the 3-minute initial slope index may be used to quantitatively assess cerebrovascular reserve with a CO2 challenge.     

The effect of arteriovenous malformation resection on cerebrovascular reactivity to carbon dioxide

To investigate the cerebral hemodynamic changes associated with obliteration of arteriovenous malformations (AVMs), we studied 26 patients undergoing total microsurgical AVM resection during isoflurane and N2/O2 anesthesia. Detectors were placed 5 to 6 cm from the margin of the lesion and in a homologous contralateral position. Cerebral blood flow (CBF) was measured using the intravenous xenon-133 technique before and after AVM resection, during both hypocapnia and normocapnia at each stage. Intraoperative changes in CBF were related to a risk score system based on the patient's history and preoperative angiograms. Seven otherwise healthy patients undergoing spinal surgery were studied to control for anesthetic effects. Patient demographic and clinical data for the AVM group conformed to the expected strata of a large AVM population. The CBF increased after excision (22 +/- 1 ml/100 g/min before excision to 30 +/- 2 ml/100 g/min after excision; mean +/- SE, n = 25, P less than 0.002) without a hemispheric difference. CO2 reactivity increased slightly after excision (4.2 +/- 0.3% change/mm Hg before excision to 4.7 +/- 0.3% change/mm Hg after excision; n = 14, P less than 0.02). The baseline CBF and CO2 reactivity were not different from the control group. There was a weak correlation between the risk score and the percentage of change in the ipsilateral CBF, with a trend for the patients with the lowest risk to have the lowest CBF changes after resection. There was no relationship between CO2 reactivity and risk grade. None of the patients awoke from anesthesia with unexpected neurological deficits. The highest CBF increases were associated with postoperative brain swelling in one patient and fatal intracerebral hemorrhage in another. Both patients had normal CO2 reactivity before excision. One patient suffered postoperative intracerebral hemorrhage, attributable to technical problems, and had no increase in CBF. We conclude that, with an acute increase in the arteriovenous pressure gradient (and cerebral perfusion pressure) that results from shunt obliteration, there is an immediate global effect of AVM resection to increase CBF. Cerebrovascular reactivity to CO2 remains intact both before and after excision.