Maternal Hypoxaemia Associated with the Use of Entonox in Labour

We report the occurrence of severe hypoxaemic episodes associated with the use of Entonox in labour, in an otherwise healthy woman. These did not occur when the parturient breathed room air during contractions and did not recur when epidural analgesia was established. Possible mechanisms of arterial desaturation associated with the use of Entonox in labour are discussed.