Free
Correspondence  |   September 1999
Coupling of Local Cerebral Blood Flow to Local Cerebral Glucose Utilization during Isoflurane and Sevoflurane Anesthesia 
Author Notes
  • Associate Professor
  • Department of Anesthesia
  • Faculty of Medicine
  • The University of Calgary
  • Calgary, Alberta, Canada
  • Professor
  • Department Neurology and Neurosurgery
  • Montreal Neurological Institute
  • McGill University
  • Montreal, Quebec, Canada
Article Information
Correspondence
Correspondence   |   September 1999
Coupling of Local Cerebral Blood Flow to Local Cerebral Glucose Utilization during Isoflurane and Sevoflurane Anesthesia 
Anesthesiology 9 1999, Vol.91, 889. doi:
Anesthesiology 9 1999, Vol.91, 889. doi:
To the Editor:—
In the December 1998 issue of ANESTHESIOLOGY, Lenz et al.  1 reported that close coupling between local cerebral blood flow (LCBF) and glucose utilization (LCGU) is preserved in animals anesthetized with 1 minimum alveolar concentration (MAC) of isoflurane or sevoflurane, (fig. 2). 1 This conclusion seems to have been based on linear regression of the mean values of LCBF against LCGU for each of the regions examined and evaluation of the derived correlation coefficients (fig. 2). 1 
Regression analysis of LCBF and LCGU values derived from autoradiographic experiments has been criticized on methodologic and statistical grounds. 2 “Blood flow–metabolism coupling” conventionally refers to changes in blood flow within a brain region in response to changes in metabolism in that region. 3,4 Evaluation of LCBF in relation to LCGU in many different brain regions under one particular set of conditions does not fit this concept. 2 Regression analysis of LCBF on LCGU examines the homogeneity of the ratio of LCBF to LCGU among the various brain regions examined. 2 
The results of the study by Lenz et al.  1 suggest that isoflurane and sevoflurane alter the LCBF:LCGU ratio. We compared the LCBF:LCGU ratios for the 40 structures studied in the five conditions from their data (tables 1 2 and 3). Isoflurane and sevoflurane both increased the mean ratio of LCBF:LCGU in a dose-dependent fashion, with isoflurane producing the most marked effect (table 1).
Table 1. LCBF/LCGU Ratios during Isoflurane and Sevoflurane Anesthesia 
Image not available
Table 1. LCBF/LCGU Ratios during Isoflurane and Sevoflurane Anesthesia 
×
This analysis remains open to the statistical criticism 2 that the variability between animals was eliminated by using mean values of LCBF and LCGU, thereby underestimating the real uncertainty in the LCBF–LCGU relation.
The experimental design used by Lenz et al.  1 does permit exploration of blood flow–metabolism coupling through analysis of the relation between LCBF and LCGU within specific brain regions as the LCGU is depressed by increasing concentrations of anesthetic. Figure 1
Fig. 1. Relation of local cerebral blood flow (LCBF) to local cerebral glucose utilization (LCGU)(mean values ± SD, n = 6) in auditory cortex (  circles  ) and inferior colliculus (  squares  ). Empty and filled symbols indicate sevoflurane and isoflurane treatment respectively. MAC = minimum alveolar concentration. 
Fig. 1. Relation of local cerebral blood flow (LCBF) to local cerebral glucose utilization (LCGU)(mean values ± SD, n = 6) in auditory cortex (  circles  ) and inferior colliculus (  squares  ). Empty and filled symbols indicate sevoflurane and isoflurane treatment respectively. MAC = minimum alveolar concentration. 
Fig. 1. Relation of local cerebral blood flow (LCBF) to local cerebral glucose utilization (LCGU)(mean values ± SD, n = 6) in auditory cortex (  circles  ) and inferior colliculus (  squares  ). Empty and filled symbols indicate sevoflurane and isoflurane treatment respectively. MAC = minimum alveolar concentration. 
×
(based on data 1 from their tables 2 and 3) shows the LCBF response to increasing anesthetic concentrations in two brain regions, with similar mean values for LCGU and LCBF in the conscious animals. The data suggest that LCBF in these two brain regions responds differently to increasing concentrations of isoflurane and sevoflurane, because, despite similar decreases in LCGU with increasing MAC multiples, LCBF appears to decrease in auditory cortex but to increase in the inferior colliculus. The analysis of these data 2 could not be attempted with the information provided in the original report. 1 
In summary, further analysis of the data reported by Lenz et al.  1 supports previous observations that inhalational anesthetics increase the ratio of mean cerebral blood flow/cerebral metabolic rate for oxygen (CBF/CMRO2) in a dose-dependent fashion. 5 Inspection of the data for individual brain regions suggests that a detailed analysis 2 of flow–metabolism coupling may reveal significant regional differences.
References 
References 
Lenz C, Rebel A, van Ackern K, Kuschinsky W, Waschke KF: Local cerebral blood flow, local cerebral glucose utilization, and flow-metabolism coupling during sevoflurane versus isoflurane anesthesia in rats. A NESTHESIOLOGY 1998; 89: 1480–8
McCulloch J, Kelly PAT, Ford I: The effect of apomorphine on the relationship between local cerebral glucose utilization and local cerebral blood flow (with an appendix on its statistical analysis). J Cereb Blood Flow Metab 1982; 2: 487–9
Roy CS, Sherrington CS: On the regulation of the blood-supply of the brain. J Physiol (Lond) 1890; 11: 85–108
Siesjö B: Cerebral circulation and metabolism. J Neurosurg 1984; 60: 883–908
Smith AL, Wollman H: Cerebral blood flow and metabolism: Effects of anesthetic drugs and techniques. A NESTHESIOLOGY 1972; 36: 378–400
Fig. 1. Relation of local cerebral blood flow (LCBF) to local cerebral glucose utilization (LCGU)(mean values ± SD, n = 6) in auditory cortex (  circles  ) and inferior colliculus (  squares  ). Empty and filled symbols indicate sevoflurane and isoflurane treatment respectively. MAC = minimum alveolar concentration. 
Fig. 1. Relation of local cerebral blood flow (LCBF) to local cerebral glucose utilization (LCGU)(mean values ± SD, n = 6) in auditory cortex (  circles  ) and inferior colliculus (  squares  ). Empty and filled symbols indicate sevoflurane and isoflurane treatment respectively. MAC = minimum alveolar concentration. 
Fig. 1. Relation of local cerebral blood flow (LCBF) to local cerebral glucose utilization (LCGU)(mean values ± SD, n = 6) in auditory cortex (  circles  ) and inferior colliculus (  squares  ). Empty and filled symbols indicate sevoflurane and isoflurane treatment respectively. MAC = minimum alveolar concentration. 
×
Table 1. LCBF/LCGU Ratios during Isoflurane and Sevoflurane Anesthesia 
Image not available
Table 1. LCBF/LCGU Ratios during Isoflurane and Sevoflurane Anesthesia 
×