Nitrous oxide is considered as a very safe and effective sedative for achieving light to moderate sedation for dental patients with anxiety or phobia. Although its usage has limited side effects, there are some potential risks of nitrous oxide sedation that the dentist must take into consideration before deciding the appropriate sedation method for each specific patient.
Most of the risks associated with the use of nitrous oxide by dental patients are caused either by problems or errors in the proper administration of the gas (e.g. errors in the mixture of N2O/O2) or by the inappropriate use of nitrous oxide to patients with conditions that contradict its usage.
A major cause of risks related to nitrous oxide is the change of pressure/volume of air-filled cavities in the body. Nitrous oxide is 34 times more soluble in blood than the nitrogen that is replaced. It will thus diffuse from the blood into any closed air-containing space in the body faster than the nitrogen can diffuse out. This causes a temporary increase of the volume of the gas filling the cavity, and subsequently an increase in the pressure to the walls of the cavity. Although the effect can be short lived, it can be enough to cause significant pain or/and damage to the affected body tissues.
Eye damage - The increase on air pressure does not affect only physical body cavities, but also any enclosed air filled area in the body. Nitrous oxide should not be administered to patients who recently had ocular eye surgery. Opthalmologists frequently inject intraocular gases during eye surgeries related to retinal detachments (pneumatic retinopexy). These gas bubbles can remain in the eyeball up to 3 months before they are reabsorbed. Nitrous oxide inhalation can result in the immediate expansion of the gas bubble in the eye causing healing complications and possibly eye damage. Cases of total vision loss due to central retinal artery occlusion have been reported in patients who had a recent pneumatic retinopexy eye surgery followed by dental treatment using nitrous oxide sedation.
Ear problems - Nitrous oxide sedation can create an elevated pressure in the middle ear. This may result in ear problems like a sharp pain for a small percentage of patients, and in extreme cases bleeding in the ear, hearing impairment or rupture of typanic membrane. For this reason, patients who recently had any kind of middle ear surgery (e.g. tympanic membrane graft) or have blocked eustachian tubes should not be treated with inhalation sedation because the tympanic membrane can become distended and damaged following inhalation of the nitrous oxide.
Gut pain - Nitrous oxide will dissolve out of blood into air filled spaces such as the intestines, increasing the volume of air inside them, which can lead to severe gut pain.
In order to avoid possible side effects, nitrous oxide should not be used by patients who recently had middle ear or ocular eye surgery, or have sinusitis, ear problems, bowel obstruction or pneumothorax. Patients with any of these conditions should inform their dentist, in order to suggest another more suitable method of sedation.
Hypoxia is a very serious and dangerous condition that occurs when the body does not receive enough oxygen. Hypoxia can result in brain damage and eventually death due to asphyxiation. It may happen either due to lack of oxygen in the breathing air or when someone stops breathing or breathes too shallowly or too slowly to meet their oxygen requirements.
Theoretically hypoxia should not be considered a risk during nitrous oxide sedation dentistry, because even at the maximum allowed dosage of 70% nitrous oxide, the body gets 30% oxygen which is more than enough (actually more than the 21% of atmospheric air). A safety valve in the flow-meter equipment does not allow oxygen to be lower than 30%. Lack of enough oxygen causes nausea and unconsciousness, which is an immediate signal for the dentist to stop the administration of nitrous oxide and give 100% oxygen.
However there is always a remote risk involved in nitrous oxide sedation in case there is a malfunction of the equipment, prohibiting the flow of adequate oxygen, while at the same time the patient’s vital signs are not closely monitored and the dentist is not experienced enough to understand that the patient has lost consciousness.
Another side effect of nitrous oxide that may occur immediately after the end of nitrous oxide sedation is a related condition of post-inhalation hypoxia called ‘diffusion hypoxia’. After the N2O flow is stopped, the nitrous oxide is rapidly diffused from the blood back into the lungs which results in a displacement of oxygen and a subsequent drop in the partial pressure of oxygen in the lugs. The oxygen exchange into the lungs and circulation may become impaired, which can result in Diffusion Hypoxia.
Although diffusion hypoxia is not a major concern for healthy patients, it may be dangerous for patients with an airway obstruction or cardiopulmonary disease. Problems related with nitrous oxide diffusion hypoxia have been minimized after the dentists have adopted a new standard that suggests the administration of 100% oxygen for 3-5 minutes after discontinuation of nitrous oxide.
This is a potential risk of nitrous oxide that affects patients under anti-neoplastic therapy with bleomycin sulfate which is known to cause pulmonary toxicity. Contrary to what happens in case of hypoxia, it is the high oxygen concentration (above 25% O2) that can cause acute respiratory distress syndrome to this patient group. Since the use of 100% oxygen is part of the standard nitrous oxide sedation procedure (in both the initial and recovery phases) there is an increased risk of respiratory failure in these patients.
Existing scientific research has linked several reproductive issues to persons with occupational connection to N2O, but not with dental patients who only occasionally get nitrous oxide. However dentists avoid the use of nitrous oxide sedation to pregnant patients, at least during the first semester of pregnancy to prevent any risks on the newborn.
Nitrous oxide may affect the white blood cell production and function in patients with immune system deficiencies, and thus nitrous oxide sedation should be avoided.
Nitrous oxide is known to oxidise and inactivate the vitamin B12 which is an essential component of certain enzymes. One such enzyme, methionine synthetase is essential for normal DNA production. Its interaction with vitamin B12 may be a serious side effect of nitrous oxide for patients who already have a B12 deficiency for any reason.
Although nitrous oxide affects the levels of B12 for all users, healthy users have enough B12 stored in physical body reservoirs (mostly in the liver) so that they are not affected by the occasional usage of N2O in the dental office. But B12 deficiency is a potential nitrous oxide risk for people with already low levels of B12, or they are exposed to N2O for longer terms due to their occupation.
Several studies have demonstrated that the haematological, immune, neurological and reproductive systems can be affected. The symptoms of these effects may appear weeks or even months after the administration of the nitrous oxide. Patients who develop B12 deficiency as a side effect of nitrous oxide dental sedation are at higher risk of suffering from other conditions such as: