Which is a serious complication associated with rapid intravenous administration of potassium?

Rapid intravenous administration of potassium can lead to serious complications primarily due to its significant effects on cardiac function. When potassium is administered too quickly, it can cause hyperkalemia, which is an elevated level of potassium in the blood. This condition can lead to destabilization of the cardiac membrane, resulting in arrhythmias or even cardiac arrest.

The heart relies on proper potassium levels for the generation and conduction of electrical impulses. An abrupt increase in potassium concentration alters these electrical signals, disrupting the heart's rhythm and potentially leading to fatal consequences such as ventricular fibrillation or asystole.

Other potential complications such as respiratory failure, hypotension, or stroke can occur under certain conditions, but they are generally less directly related to the rapid administration of potassium. Therefore, the most serious and immediate risk associated with this practice is indeed cardiac arrest due to the acute impact on cardiac electrical activity.