title: Cerebral microvascular reactivity to carbon dioxide during isoflurane anesthesia as assessed by laser-Doppler flowmetry.
abstract: BACKGROUND
  To determine the effects of carbon dioxide on the cerebral microcirculation during isoflurane anesthesia.
  
  
  METHODS
  We studied 10 rabbits using laser Doppler flowmetry on the parietal cortex. After surgical preparation, the end-tidal concentration of isoflurane was maintained at one MAC (2.05%). Mean arterial pressure, rectal temperature and hematocrit were kept constant. The arterial carbon dioxide tension (PaCO2) was randomly adjusted to three levels: 20-25 mmHg (hypocapnia); 35-40 mmHg (normocapnia); and 45-50 mmHg (hypercapnia). Cerebral blood flow (CBF) was measured after target PaCO2 had been achieved.
  
  
  RESULTS
  CBF at normocapnia was 27.4 +/- 13.5 (mean +/- SD) ml/100 gm/min, which increased to 42.4 +/- 14.3 ml/100 g/min (p < 0.01) and decreased to 15.3 +/- 7.5 ml/100 g/min (p < 0.05) at hypercapnia and hypocapnia respectively. The slopes of CBF versus PaCO2 were 1.60 +/- 0.63 ml/100 g/min/mmHg from normocapnia to hypercapnia and -0.79 +/- 0.51 ml/100 g/min/mmHg from normocapnia to hypocapnia. The corresponding percentage of alteration in CBF on the respective change of PaCO2 was 7.2 +/- 5.1 and -3.0 +/- 1.2%/mmHg.
  
  
  CONCLUSIONS
  These data indicate that the changes of the cerebral microvascular blood flow reflect the CO2 effects during isoflurane anesthesia.
authors.affiliation: Department of Anesthesiology, College of Medicine, National Cheng Kung University, Tainan, Taiwan, R.O.C.
authors.forename: Y C
authors.initials: YC
authors.lastname: Tsai
authors.forename: S C
authors.initials: SC
authors.lastname: Lee
authors.forename: C L
authors.initials: CL
authors.lastname: Chang
mesh_terms: D000758:Anesthesia; D000818:Animals; D002245:Carbon Dioxide / Q000494:pharmacology*; D002560:Cerebrovascular Circulation / Q000187:drug effects*; D007530:Isoflurane / Q000494:pharmacology*; D017078:Laser-Doppler Flowmetry; D008833:Microcirculation / Q000187:drug effects; D011817:Rabbits
chemical_list: D002245:Carbon Dioxide; D007530:Isoflurane