The nurse is taking care of a client who underwent a left lung resection two days ago. During her assessment, she finds that the client's apical pulse is 125 beats per minute; his peripheral pulses are weak and thready. His blood pressure is 79/51 mmHg and lungs are clear to auscultation. He is on intravenous Normal Saline at 100 mL/hour. Which of the following is the nurse's initial intervention?

a) Increase the rate of the Normal Saline infusion
b) Administer oxygen via nasal cannula
c) Notify the healthcare provider immediately
d) Reassess the client's vital signs in 15 minutes