Which gases are used in hospital to put people to sleep?

Knocking people out in hospital is called anaesthesia.

To start an anaesthetic, the anaesthetist injects a medicine into the patient's vein. They used to use Pentothal, but that has been phased out now. These days they use Diprivan. These quick acting knockout injections are called "induction agents" and they only work for a couple of minutes. As soon as the patient is knocked out, the anaesthetist adds other medicines and gases to keep the patient asleep. At the end of the procedure, they use other drugs to "reverse" the anaesthetic.