Inhalation sedation is a form of conscious sedation where an inhaled drug should: Depress the central nervous system (CNS) to an extent that surgeons can operate with minimal physiological and psychological stress to the patient Modify the patient's state of mind such that communication is maintained and the patient can respond to verbal command Carry a margin of safety wide enough to render the unintended loss of consciousness and loss of protective reflexes unlikely. Medical uses The following are possible uses for conscious sedation "dental anxiety and phobia, a need for prolonged or traumatic dental procedures, medical conditions potentially aggravated by stress (such as ischaemic heart disease, hypertension, asthma and epilepsy), medical or behavioural conditions affecting a patient's ability to cooperate, special care requirements". Side effects Complications from inhalation sedation are rare, and are those events that require intervention to correct adverse physiological responses. They include over-sedation, respiratory depression/apnoea, unconscious patient, airway obstruction, vomiting, idiosyncratic responses, delayed recovery, and failure of conscious sedation. Few absolute contraindications exist, however, "relative contraindications are important and can only be considered following a full assessment." They include: Medical conditions that would compromise the inhalation of the sedation medication, such as the common cold, tonsillitis, severe COPD or nasal blockage Neuromuscular diseases affecting the respiratory system, such as multiple sclerosis and myasthenia gravis Women in the first trimester of pregnancy Medical or behavioural conditions that limit a patient's ability to understand the procedure Claustrophobia or "fear of the mask". Patient assessment and selection On a visit prior to the treatment session, the anesthesiologist makes a full assessment to determine the need for sedation and the technique most suited to the individual patient. This consists of a detailed record of the patient's history and a thorough examination. A medical, dental, and social history covers the patient's age, state of health, social circumstances, drug history, and any special needs. This helps determine the sedation technique most appropriate for a positive outcome for each individual. The examination takes into account the patient's general appearance, skin colour, pulse, blood pressure, and respiration rates. Only patients in ASA classes I and II are normally suitable for sedation in the primary care dental setting. Patients in ASA class III or IV should be referred to an appropriate secondary care (i.e., hospital) establishment with critical care facilities. Contraindications Inhalation sedation using nitrous oxide has a long history of safe use in both