Current concepts of cerebral oxygen transport and energy metabolism after severe traumatic brain injury

Before energy metabolism can take place, brain cells must be supplied with oxygen and glucose. Only then, in combination with normal mitochondrial function, sufficient energy (adenosine tri-phosphate (ATP)) can be produced. Glucose is virtually the sole fuel for the human brain. The brain lacks fuel stores and requires a continuous supply of glucose and oxygen. Therefore, continuous cerebral blood flow (CBF), cerebral oxygen tension and delivery, and normal mitochondrial function are of vital importance for the maintenance of brain function and tissue viability. This review focuses on three main issues: (1) Cerebral oxygen transport (CBF, and oxygen partial pressure (PO₂) and delivery to the brain); (2) Energy metabolism (glycolysis, mitochondrial function: citric acid cycle and oxidative phosphorylation); and (3) The role of the above in the pathophysiology of severe head injury. Basic understanding of these issues in the normal as well as in the traumatized brain is essential in developing new treatment strategies. These issues also play a key role in interpreting data collected from monitoring techniques such as cerebral tissue PO₂, jugular bulb oxygen saturation (SjvO₂), near infra red spectroscopy (NIRS), microdialysis, intracranial pressure monitoring (ICP), laser Doppler flowmetry, and transcranial Doppler flowmetry - both in the experimental and in the clinical setting.