Limited studies in children have shown nitrous oxide (N 2O) to be an effective and safe sedative/analgesic either alone or in combination with a local anesthetic for laceration repair, orthopedic procedures, and other minor surgical procedures. 1415 It offers many advantages over other pharmacologic agents for use in the outpatient setting and emergency department. It provides analgesia, anxiolysis, and sedation without the need for IV line placement, has a low incidence of complications and adverse effects, and can result in shorter ED lengths of stay due to rapid recovery. Nitrous oxide interacts with the endogenous opioid system to confer analgesia and appears to blunt the patient's reaction to pain. It produces a sense of euphoria, relief from anxiety, and an almost "detached" attitude toward pain and the patient's surroundings.
In the outpatient setting, nitrous oxide should be delivered via a fixed-ratio mixture of nitrous oxide to oxygen, usually 50 percent N 20:50 percent oxygen (oxygen concentration must be a minimum of 30 percent) by a self-administered demand-valve apparatus with a scavenger device. This mode of administration protects against equipment failure and/or human error, which may result in too high concentration of nitrous oxide. The gas is routinely delivered by an inspiratory effort of the patient, minimizing the risk of loss of consciousness and protective reflexes because the mask will fall off when the patient is sedated. The gas/oxygen mixture can be inhaled through a face mask, mouthpiece, or nasal hood in which a flavored Chapstick lining or concentrated "child-friendly" scent can be applied to disguise the odor of the gas. For younger children unable to hold their own mask, the physician or parent can assist in the delivery of the mixture by placing the mask lightly on the child's face.
Nitrous oxide has a rapid onset of action of three to five minutes and a short duration of action on withdrawal of three to five minutes. The gas is not metabolized, and is eliminated by the lungs unchanged. Short-term use has no significant effects on other organs. The most common reported side effects are nausea and vomiting. Diffusional hypoxia is another potential concern since nitrous oxide rapidly diffuses out of the blood and into the alveoli, where it can displace oxygen and cause hypoxia. This theoretical concern has not been supported by clinical evidence. Nevertheless, supplemental oxygen should be administered throughout the recovery phase. Nitrous oxide use in the ED also has the potential for abuse, environmental contamination, and potential teratogenic effects especially with chronic exposure. The use of nitrous oxide is contraindicated in patients with pneumothoraces, bowel obstruction, middle ear effusions, and patients undergoing procedures using balloon-tipped catheters because of its rapid diffusion into gas-collecting areas of the body, which could cause acute expansion, over distension, and perforation. It also should be avoided in patients with head injuries, psychiatric diseases, or drug intoxication. Because of nitrous oxide's opioid agonist properties, it may result in deep sedation or general anesthesia if combined with a sedative or opioid. Thus, extreme caution should be exercised when administering it to a patient with recent administration of either of these medications.16
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