Glycemic control in traumatic head injury

I'm writing an assignment about glycemic control in traumatic head injury. Our guidelines are to keep blood sugars to 4.5-8.3mmol/L. This level concurs with the international guidelines recommended by the Surviving Sepsis Campaign 2008 but there seems to be very little research about the use of insulin in the context of head injury, i.e do high blood sugars cause, or simply reflect, bad outcome ? I understand the theory behind high glucose levels and secondary damage but is it actually happening ? Are these levels appropriate for head injury ?

I'd be grateful if anyone could shine more light on the subject, particularly if you could point be in the direction of recent research. Many thanks.