Which medication should not be administered as an IV bolus due to the risk of cardiac arrest?

Potassium chloride is the correct answer because it carries a significant risk of causing cardiac arrest when administered as an intravenous (IV) bolus. High levels of potassium in the bloodstream can lead to hyperkalemia, which can disrupt the electrical conduction in the heart and result in arrhythmias or even cardiac arrest. Administering potassium chloride rapidly in a bolus form can increase these risks dramatically, making it crucial to use this medication only as a slow intravenous infusion and under careful monitoring of serum potassium levels.

In contrast, medications like saline flush, naloxone, and adenosine have different safety profiles. Saline is typically used for maintaining venous access and does not pose a risk of serious adverse cardiac events. Naloxone is an opioid antagonist administered to reverse opioid overdose, and while it can lead to withdrawal symptoms, it does not carry the same risk of cardiac complications when given as an IV bolus. Adenosine is utilized to treat certain types of tachycardia and is typically administered as a rapid IV push; though it has some cardiovascular effects, they are generally well-monitored and managed in a clinical setting.