Source: Aleksa Cenic et al., Anesth Analg 2002;94:661-666

Reviewer: John F. Heath, M.D.

Summary:

• rabbit study
• propofol increased cerebral vascular tone in both neoplastic and normal tissue vessels compared with isoflurane.
• CBV and CBF were greater in all regions with isoflurane.
• CBV and CBF remained responsive to hyperventilation with isoflurane but not propofol.
• ICP unchanged in both groups.

• Purpose: to determine the effects of hyperventilation on cerebral blood volume and blood flow during isoflurane or propofol anesthesia.
• Sixteen rabbits with brain tumors
• two groups of eight each
• tumors standardized by injecting VX2 carcinoma cells into the right parietal lobe of each rabbit.
• studied when tumors reached 0.4 cm in diameter (by CT scan).
• Anesthesia:
• Induced with mask halothane --> IV --> vecuronium --> tracheostomy --> ventilated with an air/O2 mixture.
• Halothane gradually withdrawn as isoflurane (1 MAC) or propofol (1.6 mg/kg/min x 30 min then 1.2 mg/kg/min) were introduced.
• Femoral a, femoral v and intraventricular (left lateral ventricle) catheters placed.
• CBV, CBF
• measured at PaCO2’s of 40 and 25mmHg randomly with a 30 min interval between measurements.
• measurements were obtained by using a slip-ring CT scanner via a coronal slice through the largest diameter of the tumor. Contrast-enhanced cine CT scans were performed (through this one slice) before, during, and after a bolus of IV contrast was injected. Regions of interest in the tumor, peri-tumor, and contralateral normal regions were studied after the scanning by a blinded technician. CT-measured contrast enhancement curves were generated and regional CBV and CBF measurements were obtained by the deconvolution method and the Central Volume principle.

• No signif differences noted in MAP, CVP, temperature, or Hct during the study within each group.
• no intergroup differences in the above variables for both anesthetics at normocapnia and hypocapnia.
• In both groups, CBV and CBF values were highest in the tumor region and lowest in the contralateral normal tissue.
• With isoflurane:
• a significant decrease in both CBV and CBF was noted in all tissue regions with hyperventilation.
• The percent reduction in regional CBF with hypocapnia was two times larger than that noted in the CBV response.
• In the propofol group:
• no statistically significant differences in CBV and CBF with hyperventilation for all regions
• however, CBV and CBF both decreased
• no change in ICP in either group.
• At normocapnia, CBV values were higher for all regions for isoflurane as compared to propofol, but CBF values were not statistically different except in contralateral normal tissue (greater with isoflurane).
• Tumor tissue CBV and CBF values were 3-4x greater than normal tissue
• peri-tumor region CBV and CBF were 2-3x greater than normal tissue