An indicator of increased intracranial pressure (ICP) is pupil dilation, which can be masked by the miosis, or pupil constriction caused by fentanyl and other opioid medications. Therefore, the patient who sustained a traumatic brain injury and is therefore at risk for elevated ICP must be watched carefully if he or she is to receive fentanyl. Fentanyl does not mask symptoms of high or low blood glucose levels (type II diabetic), Parkinson disease, influenza, myocardial infarction.