Critically ill ventilated head injured patients often undergo in-hospital transports for diagnostic purposes. This transport is associated with an increased rate of complications. Secondary adverse events can occur, even in optimal conditions. We describe four patients in whom continuous cerebral microdialysis was performed during transportation to and from the CT Department. An increase in lactate/pyruvate ratio, glucose concentration and glutamate concentration was found, suggesting increased metabolic demand and relative or absolute impaired oxygen delivery. This occurred whilst all other measures, which are normally considered optimal for monitoring oxygen saturation and hemodynamics, showed no significant changes.