Hello, My So. Want Admitted To The Hospital For Pneumonia

Hello, my so. Want admitted to the hospital for pneumonia and hypoxia about 3 weeks ago. He is doing better. But when we left the hospital I purchase a pulse oxmeter. I've been checking him a few time a day and he's been ok. Well today his oxygen levels where about 87-90 sleeping and 97 98 awake. But his bpm is high at 136 to 145. He's not wheezing but had a cough. Should I take him to the emergency room? He's 6