Why Thiamine before Glucose in Wernicke Encephalopathy?
The proposed mechanism for this is as follows:
Thiamine 100mg IV before 50% glucose
Thiamine is an important co-enzyme for carbohydrate utilization as (thiamine pyrophosphate- TPP)
Therefore TTP is required to convert pyruvate to Acetyl-CoA. To put it another way, if you’re thiamine deficient, any glucose you get will tend to form lactate, rather than being fully metabolized in the Krebs Cycle 
Hoyumpa AM, Jr. Mechanisms of thiamin deficiency in chronic alcoholism. Am J Clin Nutr 1980;33:2750-2761.