Inhaled Nitrous Oxide for the Prevention of Emergence Reaction During Ketamine Administration in Adults, a Pilot Study

Drugs such as fentanyl, midazolam, and propofol are widely used in emergency departments for procedural sedation and analgesia because they have a rapid onset and short duration of action. Unfortunately, all of these agents may cause respiratory depression, particularly when combined with other sedative agents, administered in large doses, or given to patients with underlying respiratory diseases.

Ketamine hydrochloride is a phencyclidine derivative that causes dissociation between the cortical and limbic systems preventing the higher centers from perceiving visual, auditory, or painful stimuli. It possesses a rapid onset and short duration of action and produces profound sedation and analgesia. Ketamine is also a non-competitive NMDA antagonist, which complements NO. However, laryngeal reflexes are maintained and respiratory depression is rare. These properties have made ketamine a very popular agent for procedural sedation and analgesia in pediatric emergency department patients . Unfortunately, when given to adult patients, it frequently causes emergence anxiety, nightmares, hallucinations, and delirium. These emergence reactions have limited the use of ketamine in adults. The incidence of these reactions is about 7-10% in children. Emergence reactions may be a product of the state in which the patient becomes disassociated . Therefore, if the patient is more relaxed prior to ketamine administration through the adjunct use of NO, adverse emergence reactions may be reduced.

A number of agents including diazepam, lorazepam, fentanyl, droperidol, and others have been used with varying success to reduce or prevent emergence reactions associated with ketamine use. Diazepam and lorazepam have been the most successful, but their use may prolong recovery time, making them less desirable in the emergency department setting. Midazolam has been shown to lower the rate of emergence reaction when used concurrently with ketamine in adults. However, like all benzodiazepines, there is a small risk of respiratory depression and hypoxia with the use of midazolam, which could lead to an adverse respiratory event.

Inhaled nitrous oxide may be an ideal adjunct to the prevention of emergence reaction in adults being treated with ketamine. Nitrous oxide is a colorless gas that diffuses rapidly across the pulmonary alveoli providing analgesia and anxiolysis with minimal sedative effects, rapid induction, and emergence. Nitrous oxide is a weak sedative agent with the potential for significant analgesic effects. Noncompetitive antagonist activity at the NMDA receptor along with activation of opioid receptors contributes to its anesthetic mechanism. There are rare adverse events, most often cited as case reports of chronic or acute toxicity causing myeloneuropathies and polyneuropathies.

Nitrous oxide has been used in general anesthesia for over 2 centuries, but its use outside of the operating room began when Tunstall introduced the nitrous oxide/oxygen mixture as an analgesic agent during labor. Since this inception, the nitrous oxide/oxygen mixture has been used readily in the fields of dentistry, gastrointestinal procedures, and children's procedural sedation. Nitrous oxide is often administrated via continuous flow or on-demand at a concentration of 50-70%.