The patient with a unilateral fixed and dilated pupil has experienced some sort of brain insult on the left side of the brain. A stat MRI is necessary to determine the etiology of the insult and guide treatment, which is often time-sensitive. An arterial blood gas might be necessary depending on the patient’s other symptoms, but an MRI will guide treatment related to the brain lesion. An EEG may be necessary to determine brain function, but initial management depends on the MRI, not the EEG. Unilateral fixed and dilated pupils do not point to an opioid drug overdose; therefore, the opioid drug panel is not the immediate test.