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Contraindications of Nitrous Oxide Use
One of the great advantages to using nitrous oxide in a dental setting is the relative safety if used correctly. There are relatively few contraindications for nitrous oxide use. These contraindications for nitrous use include women who are in the first trimester of pregnancy, any person who has chronic obstructive pulmonary disease (COPD), and patients undergoing bleomycin sulfate treatment. So why is nitrous oxide contraindicated for these patients? Lets examine these individually.
For pregnant patients, the ADA recommends that elective dental treatment only be given in the 2nd trimester of pregnancy.  If a pregnant patient requires dental treatment, it should be postponed until either the second trimester, or, if possible, until after the baby is born. If an emergency procedure is necessary, then the most important thing is to get the patient out of pain. However, any treatment should be discussed with the patient's obstetrician prior to the procedure.
In most cases, nitrous oxide should not be used on pregnant patients. This is due to some evidence linking its use to a higher risk of miscarriage in dental assistants operating in offices without scavenging equipment. It should be noted that dental assistants undergo prolonged exposure whereas patients would undergo far less exposure. It is up to the patient and the dental practitioner to ultimately weigh the risk versus the benefit of any dental procedure. Regardless informed consent is a must in these types of situations.
Bleomycin sulfate is an antineoplastic pharmaceutical agent used for patients who have certain types of cancers. This medication works by binding to the DNA molecule and cleaving it, thus inhibiting DNA synthesis and further cell propagation.11 Patients undergoing bleomycin treatment are predisposed to respiratory failure following exposure to high concentrations of oxygen. The FDA recommends that in any circumstance, these patients receive no more than 25% oxygen.12 Since high concentrations of oxygen are generally used in nitrous oxide sedation, there is no way to avoid possible problems in these patients other than to abstain from using N2O sedation. It is also important to be aware that the susceptibility to respiratory failure can be an issue for these patients up to one year after succession of bleomycin therapy.11
 Chronic obstructive pulmonary disease (COPD) is a group of chronic lung diseases caused by the long-term inhalation of chemical irritants. The main culprit is cigarette smoking (80-90% of cases). These patients suffer from two diseases, emphysema and bronchitis, both of which make breathing very laborious. Damage to the alveoli in the lungs is a characteristic of emphysema. The do not perform gas exchange as easily or efficiently as someone with healthy lungs would. COPD patients depend on low O2 concentrations in the blood as their primary stimulant for respiration. Use of high dose oxygen in these patients effectively cancels out this system and can cause respiration to cease.13
Some textbooks and practitioners list "a history of psychiatric problems" as a contraindication to nitrous oxide sedation. However, in this day and age, a good many people are taking "mood altering" drugs of some sort, whether they be SSRIs or antidepressants. These have become a relatively normal course of therapy. However, patients taking these medications have a history of psychological problems, though many of them are minor. In some cases, these are the patients who benefit the most from sedation. In my opinion, this is no longer a contraindication for nitrous oxide use. However, practitioners should be aware of the potential for problems and consider each patient individually. Many times just talking to a patient for a few minutes can give you a pretty good idea of their mental state and allow you to better predict how they will react to sedation.
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Nitrous Oxide Use
