A 45-year-old female with a recent history of subarachnoid hemorrhage suddenly becomes unresponsive. Her ICP reading spikes to 35 mmHg. Which of the following is the most appropriate immediate action?

A. Administer 3% hypertonic saline is correct because an ICP of 35 mmHg represents a neurologic emergency requiring rapid reduction of intracranial pressure. Hypertonic saline works by creating an osmotic gradient that draws water out of cerebral tissue and into the intravascular space, thereby decreasing cerebral edema and lowering ICP. It acts quickly and is an appropriate first-line intervention in acute ICP spikes. B. Initiate barbiturate coma is incorrect because this is a last-resort therapy used for refractory intracranial hypertension that does not respond to first-line measures. It requires significant preparation, intubation, and continuous monitoring and is not the most immediate intervention. C. Perform emergent CT scan is incorrect because diagnostic imaging should not delay life-saving treatment in a patient with critically elevated ICP and sudden neurological deterioration. ICP must be stabilized before transporting the patient for imaging. D. Notify neurosurgeon for possible decompressive craniectomy is incorrect because although neurosurgical consultation is essential, decompressive craniectomy is not an immediate bedside intervention. Medical management to rapidly lower ICP must be initiated first.