The most important muscle for inspiration is the diaphragm. Trauma to the cervical cord, above C3, is normally fatal for this reason. Anaesthetic drugs and respiration Opioid drugs, such as morphine or fentanyl, depress the respiratory centre's response to hypercarbia. These effects can be reversed by naloxone. Volatile anaesthetic agents depress the respiratory centre in a similar fashion, although ether has less effect on respiration than the other agents.
Nitrous oxide has only minor effects on respiration.
The depressant effects of opioids and volatile agents are additive and close monitoring of respiration is necessary when they are combined. When oxygen is not available respiration should always be supported during anaesthesia.