Inhalation sedation involves the passage of gases to the cardiovascular system via the lungs. Nitrous oxide/oxygen is the most commonly used inhalation anaesthetic in dentistry.30 Indeed, in dentistry, inhalation sedation is synonymous with the use of nitrous oxide/oxygen.13 Nitrous oxide/oxygen has a long history of safety and in providing conscious sedation to the anxious patient.30 Although nitrous oxide/oxygen has some analgesic properties, it is not intended as a substitute to local anaesthetics.31-33
- Advantages of Nitrous Oxide
Nitrous oxide/oxygen and other inhalation drugs reach their destination by moving from a high pressure to a low pressure system. Because nitrous oxide is a relatively insoluble gas and does not break down in the body, it is readily available to reach its site of action for peak effect within minutes. The same property allows fast elimination of the drug from the body once the pressure gradient is reversed, thus providing for quick recovery. Rapid onset can be achieved with intravenous conscious sedation; however, the recovery is delayed.
Nitrous oxide/oxygen is also titratable. Not only does it allow to control of the depth and duration of sedation, but it is unique in its ability especially when immediate need to decrease the level of sedation is desirable, an advantage that intravenous sedation does not provide. Since no injection is needed, it is particularly desirable when anxiety stems from the fear of needles. Nitrous oxide/oxygen may be used without local anaesthesia in selected procedures such as dental prophylaxis and scaling. Finally, nitrous oxide/oxygen, if used properly, has very few side effects.
- Disadvantages of Nitrous Oxide
Most of the disadvantages of nitrous oxide relate to equipment and the logistics of safe delivery such as operatory space, cost of the equipment, supplies and cost to the patient. Although the cost, compared to intravenous sedation, to the patient is less. Because of its low potency (high minimal alveolar concentration), the nitrous oxide/oxygen may not always produce the desired effects on all patients. As stated above, the effectiveness of nitrous oxide will depend on the patient's willingness to breathe the gas. Finally, chronic exposure of office personnel may lead to serious consequences; however, the risk can be minimized by a proper scavenging system.
The main indication for the use of nitrous oxide/oxygen sedation is the management of mild to moderate dental anxiety. It is also useful in the management of the medically compromised patients, such as those with cardiovascular diseases. Patients with a severe gag reflex who may not tolerate impressions or radiographs may benefit from the use of nitrous oxide.
Nitrous oxide/oxygen has long been considered safe and the ‘ideal’ sedative, as long as it is delivered in combination with a constant flow of oxygen (i.e., greater than 30% oxygen concentration). Nitrous oxide is absolutely contraindicated in patients unable or unwilling to wear a nasal mask or to breathe through the nose. Other contraindications include sinusitis, recent ear surgery, severe psychiatric or personality disorders, and chronic obstructive pulmonary disease - in those patients the respiratory drive is initiated by low oxygen levels as opposed to high CO2 levels, providing constant high concentration of oxygen during sedation removes the stimulus for breathing.1-4
Additional contraindications include claustrophobia, B12 or folate deficiency, patients undergoing bleomycin chemotherapy - patients may be at increased risk of developing respiratory toxicity and failure if exposed to high concentrations of oxygen, pregnancy, especially the first trimester - due to the ability of nitrous oxide to inactivate the enzyme methionine synthase related to DNA production, and because of its effect on the production and function white blood cells, it has been suggested that nitrous oxide should be avoided in immune compromised patients.5-9,34,35