Which of the following would be most helpful in treating sinus bradycardia during a pediatric resuscitation?

In the context of pediatric resuscitation, sinus bradycardia can indicate inadequate cardiac output and may be associated with conditions such as hypoxia or poor perfusion. The administration of epinephrine is a key intervention during resuscitation as it works to enhance cardiac output by stimulating beta-adrenergic receptors, which can increase heart rate and improve myocardial contractility. Additionally, epinephrine has vasoconstrictive properties that can help restore perfusion during an emergency situation where circulation is compromised.

In contrast, while other options have their own roles in different clinical situations, they are not as directly effective in addressing sinus bradycardia during resuscitation. Narcotic antagonists are used to reverse the effects of opioids, which are not typically the cause of bradycardia in resuscitation settings. Volume expansion therapy may be indicated in cases of hypovolemia but does not directly increase heart rate or contractility. Sodium bicarbonate is utilized for metabolic acidosis but is generally not indicated in the immediate treatment of bradycardia during resuscitation. Thus, the use of epinephrine is supported by its pharmacological effects in the management of bradycardia within the critical context of pediatric resuscitation.