A nurse is preparing to administer metoprolol to a client. Which of the following vital signs should the nurse assess before administration?

Metoprolol is a selective beta-1 adrenergic blocker that primarily targets receptors in the myocardium. It decreases the cardiac workload by reducing the heart rate, myocardial contractility, and systemic blood pressure. It is indicated for hypertension, angina pectoris, and the management of heart failure. Rationale: A. Heart rate is the most critical vital sign to assess before administering metoprolol because the drug's primary action is to slow the heart rate. If the heart rate is less than 60 beats per minute, the medication should generally be withheld to prevent severe bradycardia. The nurse must ensure the client has sufficient hemodynamic reserve before further suppressing the cardiac rate. B. Temperature is not influenced by beta-blocker therapy and does not provide information regarding the safety or efficacy of metoprolol. While a fever might increase the baseline heart rate, the drug itself does not possess antipyretic properties. Monitoring the temperature is part of standard care but is not a prerequisite for the safe administration of this cardiovascular agent. C. Oxygen saturation is generally not affected by selective beta-1 blockers like metoprolol, which have minimal impact on the beta-2 receptors in the lungs. While non-selective beta-blockers could cause bronchoconstriction in asthma patients, metoprolol is cardio-selective. Unless the patient has acute heart failure with pulmonary edema, oxygen saturation is not the priority parameter for this drug. D. Respiratory rate is not directly impacted by metoprolol, as the drug does not cross the blood-brain barrier in large amounts to affect the respiratory center. Unlike opioids or sedatives, metoprolol does not cause respiratory depression. While assessing the lungs is important for heart failure patients, the heart rate remains the definitive parameter for determining whether to dose the medication.