47. Presentation of seizure following use of inhaled nitrous oxide (Entonox) for joint injection

Abstract

Background: Inhaled nitric oxide is used in a wide range of medical procedures in children including joint injections because of its anxiolytic and sedative properties. A wealth of clinical experience and a review of the literature suggest that it is a well-tolerated drug with few side effects. Aim(s): We describe a rare case of seizure associated with use of inhaled nitrous oxide. History: A 10 year old girl with a background of recently diagnosed oligoarticular Juvenile Idiopathic Arthritis (JIA) and hypermobility presented for first joint injection to her right knee under Entonox sedation. She had no other co-morbidities. Several minutes following the use of inhaled 50:50 nitrous oxide mix, she was noted to be unresponsive and unable to follow commands. There was associated eye flickering and deviation with intermittent eye staring without motor or haemodynamic changes. The episode lasted 45 minutes despite removal of Entonox within minutes of symptom onset. Following the event, she described an unusual tongue sensation, which was followed by a period of sleep for one hour. Progress: Investigations included a normal blood sugar and ECG. Following the episode, she was observed overnight and allowed home the following day. She was reviewed 6 weeks later, having reported no further neurological symptoms. Conclusion(s): Although rare, case reports of seizures temporally associated with use of Entonox have been described, both in patients with no known seizure disorder, and those with epilepsy. A large case series reported 2 cases out of 35, 828 where seizures were associated with its use with no causality found. Our patient had an altered conscious level lasting well beyond the recovery time usually associated with use of nitric oxide for joint injection. We postulate that this represented a clinical seizure with Entonox as the precipitant, which may have lowered seizure threshold in a normal individual. It would be important to exclude an epileptic disorder in the case of further events. In our patient, no further investigations were planned given this was a first presentation of seizure with a presumed precipitant. In conclusion, it is imperative that Entonox procedures are carried out in a safe environment with access to emergency care. Although side effects are rare, it is worth considering screening for specific symptoms of seizure disorder prior to use of Entonox and to consider other factors which are known to lower seizure threshold in children such as anxiety, hyperventilation and inter-current illnesses.