Final answer:
The most common electrolyte abnormality in patients with subarachnoid hemorrhage is hyponatremia, which involves lower-than-normal levels of sodium in the blood and can lead to complications such as cerebral edema.
Step-by-step explanation:
Patients with subarachnoid hemorrhage (SAH) are at risk for various electrolyte abnormalities due to the intricate relationship between brain injury and electrolyte balance. The most common electrolyte abnormality seen in patients with SAH is hyponatremia, which is lower-than-normal levels of sodium in the blood. This condition can stem from several mechanisms, including syndrome of inappropriate antidiuretic hormone secretion (SIADH), cerebral salt wasting syndrome, or from a dilution of sodium due to water retention. The hyponatremia can lead to increased entry of water into cells by osmosis, potentially causing cerebral edema and serious complications.