Nitrous oxide is not recommended for patients with any of the following conditions:

• Nasal obstruction. Nasal passages need to be clear for gases to be appropriately exchanged while receiving nitrous oxide. This allows the patient to achieve a sedated state. Any condition that obstructs the nasal passages (including a stuffy nose) may prevent effective sedation with nitrous oxide.
  
  
• Respiratory conditions. Patients with respiratory conditions (e.g., asthma) may have difficulty inhaling the gas into their lungs. The severity of a patient’s condition may determine whether nitrous oxide can be used, and a dentist should carefully evaluate whether to administer nitrous oxide to these patients.
  
  
• Chronic obstructive-pulmonary disease (e.g., emphysema, bronchitis). Patients with these conditions who receive the nitrous oxide/oxygen gas may end up receiving more oxygen than they normally breathe, which can cause a patient to stop breathing.
  
  
• Previous negative experience with nitrous oxide. Nitrous oxide may not be appropriate for patients who have previously experienced problems using the gas.
  
  
• Special needs. Patients with behavioral problems or certain medical conditions (e.g., mental retardation, multiple sclerosis, epilepsy) may not be able to respond appropriately while under nitrous oxide sedation.
  
  
• Severe dental phobia. Patients with extreme fear of dental treatment may require a higher level of anesthesia instead of sedation with nitrous oxide.
  
  
• Language difficulties. Under nitrous oxide sedation, some patients may experience increased difficulty understanding and responding to the dentist during treatment. This may include people who have a different native language than the dentist or people who stutter or have other communication problems.
  
  
• Contagious diseases. The use of nitrous oxide may not be recommended for patients with contagious diseases because the disease (e.g., tuberculosis) may be transmitted through hoses connected to the nosepiece or mask that cannot be completely sterilized.