Nitrous oxide is a gas administered in dental offices to reduce anxiety and alleviate pain during dental treatment. It is mixed with oxygen and inhaled by patients through a nosepiece or mask. This type of mild sedation is typically used with an injected local anesthetic that numbs the area to be treated.

Nitrous oxide is provided to a patient just before treatment begins. The gas is inhaled into the lungs, where it enters the bloodstream. From there, it is carried throughout the body, affecting bodily sensations. It is then carried back to the lungs, where it is exhaled, unchanged. Nitrous oxide is not metabolized (chemically broken down and absorbed) in the body. It does not combine with body tissue, which is why the effects of nitrous oxide last only as long as the gas remains in the body.

It is not clear exactly how nitrous oxide works. Nitrous oxide appears to intercept pain impulses before they get to the brain, or alter how they are interpreted. Pain sensations are not completely blocked with nitrous oxide, although patients experience an increased tolerance to pain while receiving the gas.

Patients on nitrous oxide remain awake and responsive to a dentist’s requests. Their autonomic, protective reflexes continue to function, such as the gag reflex and coughing, which help to avoid inhaling foreign material into the lungs. Nitrous oxide may relax a patient’s gag reflex, but does not completely eliminate it. Although patients’ speech may be slurred and motor responses slowed, patients will generally be relaxed and cooperative throughout the procedure.

Nitrous oxide is very safe as long as an adequate concentration of oxygen is delivered at the same time.

Patients breathe in the slightly sweet-smelling gas through hoses on the nosepiece or mask. The hoses connect to two cylinders: one containing nitrous oxide and the other containing oxygen. There is also an additional hose that suctions exhaled gases. The amount of gas released from each of these tanks is controlled to maintain the desired level of sedation. The percentage of nitrous oxide to oxygen in the mixture varies, but may range anywhere from 25 percent to 40 percent nitrous oxide. The average patient requires between 30 percent and 35 percent nitrous oxide.

Administration of nitrous oxide typically involves the following steps:

• Nosepiece or mask is placed over patient’s nose.
  
  
• Patient receives 100 percent oxygen (no nitrous oxide) for several minutes.
  
  
• Nitrous oxide flow begins, increased in 5 percent to 10 percent increments until desired state of sedation is reached (this usually takes three to five minutes).
  
  
• After treatment is completed, a patient is given 100 percent oxygen (no nitrous oxide) for at least five minutes. This allows the oxygen to flush any remaining gas from the patient’s lungs, leaving the patient alert.  

A record may be kept of a patient’s experience with nitrous oxide. Documentation requirements vary from state to state, but can include the concentrations of nitrous oxide and oxygen used, duration of sedation, length of oxygen recovery at the end of the procedure, and a patient’s response to the gas. 

Most dentists are licensed to administer nitrous oxide. It is a popular anti-anxiety agent for dental treatment for a number of reasons, including:

• Safe to use
• Easy to administer
• Works almost immediately
• Rapid recovery
• Requires no special preparation (e.g., not eating for a length of time prior to its use)
• Requires no special aftercare (e.g., capable of driving a car home)
• Can be used in patients of all ages
• Few side effects
• Patient remains awake and responsive during treatment

Disadvantages of nitrous oxide include difficulty for the dentist in physically maneuvering around the nosepiece or mask during treatment. Nitrous oxide may also be abused by some patients or dental professionals. There has been some concern about the recreational use of nitrous oxide among adolescents. Repeated misuse of nitrous oxide may result in numbing of the hands and legs, neurological problems, kidney or liver problems or other health concerns.