Biochemical changes in the injured brain

Table 2 The components monitored by cerebral microdialysis and their clinical implications

Variable	Normal levels (at a flow rate of 0.3 μL/min)	Clinical implications
Lactate	2.9 ± 0.9 mmol/L	Increased levels seen in ischemia and hyperglycolysis[121-123]
Pyruvate	166 ± 47 μmol/L	Decreased levels seen in ischemia and hypoxic conditions[124,125]
L/P ratio	Normal value-20	Value > 25 - metabolic crisis[124]
		Type 1-lactate increased, pyruvate decreased, signifying ischemia
		Type 2-raised LPR due to primarily decreased pyruvate level, seen in glycolysis failure or shunting of glucose to alternative metabolic pathways[125]
Glycerol	82 ± 4 μmol/L	One of the constituents of the cell membranes
		An increase in levels signifies cell damage[124]
Glutamate	16 ± 16 μmol/L	Marker of excitotoxicity[124]
Glucose	1.7 ± 0.9 mmol/L	Changes in blood flow or metabolism cause disproportionate changes in brain glucose
		Affected by ischaemia, hyperaemia, hyperglycaemia, hypermetabolism and hypometabolism[124]