• Lesion volume expansion at 1 week
  

• Brain lactate concentration change baseline-day 3
  
• Change in National Institutes of Health Stroke Scale (NIHSS) baseline - day 7
  
• 30 day modified Rankin Scale score
  
• 30 day NIHSS
  
• 30 day Barthel Index
  

Hyperglycaemia is present in 40-60% of patients with acute ischaemic stroke and adversely affects survival and outcome. This effect is independent of stroke severity or pathology, and is most striking in patients without recognised diabetes, in whom the odds of death are increased threefold, and the chance of poor functional outcome by 40%. Hyperglycaemia remains a powerful independent predictor of outcome even in the face of thrombolytic drug therapy.

The adverse effect of hyperglycaemia is hypothesised to be consequent to increased provision of substrate to hypoperfused tissue that is metabolising anaerobically, with resultant tissue accumulation of neurotoxic lactic acid. In animal models of stroke, hyperglycaemia causes increased tissue lactic acidosis and increased recruitment of ischaemic tissue in the peri-infarct region into the final infarct. Infarct volumes are higher in hyperglycaemic animals, and conversely, reducing blood glucose reduces infarct volume. Although clinical observational studies suggest protocols that incorporate blood glucose monitoring and control to be beneficial, and trials are ongoing to define the impact of routine treatment to maintain euglycaemia, the basic pathophysiology of stroke in relation to blood glucose has not been well defined in man. Preliminary studies confirm a relationship between blood glucose and lactate concentration in hypoperfused brain tissue but it is unknown whether brain lactate is reduced by control of blood glucose, and whether doing so will impact on stroke evolution. It has also been found that infarct volume increases more in hyperglycaemic patients treated with recombinant tissue plasminogen activator (rtPA).

MRI permits non-invasive and serial study of acute stroke pathophysiology. In addition to brain structure, MRI can define tissue viability (cytotoxic oedema seen on diffusion-weighted imaging, DWI), brain perfusion (bolus-tracking perfusion imaging, PI), vascular integrity (MR angiography, MRA) and tissue metabolism (1H MR spectroscopy, MRS). In acute middle cerebral artery (MCA) occlusion, evolution of cerebral damage has been defined with these techniques. The volume of hypoperfused tissue on PI initially exceeds the DWI lesion, and, over time, the DWI lesion expands to finally incorporate the majority of the PI lesion. The region of tissue with normal DWI but abnormal PI is thought to correspond to the "ischaemic penumbra", the region where hypoperfusion causes electrical failure of neurones with progression to infarction over time due to adverse metabolic and neurochemical events. The fate of the penumbra may be determined by treatment – e.g. it is salvaged by thrombolysis – and it is this penumbral region that is vulnerable to hyperglycaemia-related lactic acidosis.

Glucose lowering with insulin is an inexpensive, and widely applicable treatment. However, current clinical trials are compromised by uncertainty over the ability of treatment to influence pathophysiology, and have necessarily relied upon a "best guess" for treatment duration. Definition of the biological basis for insulin treatment by MRI criteria and comparative data for different treatment durations would strengthen and inform any positive effect from clinical trials, or prevent premature abandonment of this therapeutic modality should trials be neutral.