Table 1.
Representative metabolic rates in traumatic brain-injured (TBI) and control patients.
| Ref. | Group | Blood (µmol/mL) | CMRglc (µmol/g/min) | Glc consumed in 1 h (µmol/g) | CMRO2 (µmol/g/min) | CMRlac (µmol/g/min) | OGI | OCI | 0.5CMRlac/ CMRglc (%) | |
|---|---|---|---|---|---|---|---|---|---|---|
| Glucose | Lactate | |||||||||
| 1 | Control | 4.6 | 0.74 | 0.25 | 14.9 | 1.38 | −0.02 | 5.59 | 5.82 | −4.0 |
| TBI | 6.8 | 1.54 | 0.19 | 11.4 | 0.63 | 0.004 | 3.28 | 3.25 | +1.1 | |
| 2 | Control | 6.0 | 1.13 | 0.27 | 16.3 | 1.09 | −0.017 | 4.03 | 4.15 | −3.0 |
| TBI | 6.3 | 0.93 | 0.16 | 9.6 | 0.55 | −0.017 | 3.42 | 3.61 | −5.3 | |
| 3 | TBI | 0.18 | 10.8 | |||||||
| 4 | TBI | 0.16 | 9.6 | |||||||
| Mean for TBI | 0.17 ± 0.02 | 10.4 ± 0.9 | ||||||||
Note: Values are means from reference (ref.) 1, Table 2 of Glenn et al.10; ref. 2, Table 1 of Glenn et al.62; ref. 3, Table 2 of Vespa et al.61; and ref. 4, Table 2 of Hutchinson et al.63 Reported values were converted to molar units when necessary, and ratios were calculated from mean values. CMR denotes cerebral metabolic rate for the indicated substrate; Glc: glucose; Lac: lactate. The total amount of glucose consumed during a 1 h microdialysis sampling interval was calculated (CMRglc × 60 min) for comparison to net concentration changes of metabolites in microdialysate in Table 2. The mean values for CMRglc and total glucose consumed in 1 h for TBI patients for the four studies are 0.17 µmol/g/min and 10.4 µmol/g. OGI: CMRO2/CMRglc. OCI: oxygen-carbohydrate index = CMRO2/(CMRglc + 0.5 CMRlac). OGI has a theoretical maximal value of 6.0, due to the stoichiometry of 6 O2 consumed per glucose oxidized. OCI takes into account the net total carbohydrate taken up/released across the blood–brain barrier but usually does not account for any glycogen consumed. OGI and OCI values below ∼5.4–6.0 indicate that non-oxidative metabolism (mainly glycolysis) predominates. Because stress and intravenous adrenaline stimulate non-oxidative metabolism in brain and depress OGI and OCI,64 the controls in ref. 2 may have been more stressed during the procedures than those in ref. 1. Negative values for CMRlac denote release from brain. Lactate was converted to glucose equivalents by dividing by two. Note that lactate uptake and metabolism in one TBI group represents only 1% of CMRglc, whereas in all other groups ∼3–5% of the glucose metabolized was released to blood as lactate.