This little device is applied to your finger, toe or ear before you fall asleep. It measures how much oxygen there is in your blood. We’re surrounded by oxygen in the air, and it gets into your body when you breathe. Your body needs oxygen in order to survive. You’ll keep the oxygen meter on you when you go to sleep, throughout the operation, and when you wake up. There are different kinds of oxygen meter available, in different sizes, so the staff can choose one that fits you perfectly. In hospitals, we normally refer to oxygen meters as pulse oximeters or saturation meters.