Neonatal Methaemoglobin Levels after Prilocaine Exposure for Maternal Episiotomy

Background: Prilocaine, a local anaesthetic used in obstetrics for episiotomy, has been associated with methaemoglobinaemia in newborns. The aim of this study was to evaluate the occurrence of clinical and subclinical methaemoglobinaemia in prilocaine-exposed and non-exposed newborns. Methods: In a prospective pilot study methaemoglobin levels were measured in a group of 64 newborns; 19 exposed and 45 not exposed to 10ml prilocaine 1%for maternal episiotomy. Additionally, in a retrospective study the occurrence of methaemoglobinaemia in prilocaine-exposed and non-exposed newborns was compared in a 1-year cohort (n=2223) of infants in whom blood gas analysis was performed for clinical purposes (n=358). Results: None of the newborns in the prospective study had clinical or subclinical methaemoglobinaemia. Methaemoglobin levels were low and similar in prilocaine-exposed and non-exposed newborns (median of 0.3% and 0.4% respectively in umbilical cord blood and 0.2% in both groups in the newborn 2-3 hours after birth). In the retrospective cohort, 2/541 prilocaine-exposed newborns showed clinical methaemoglobinaemia (0.37%). Both responded well to methylene blue. Similar to in the prospective study, there were no newborns with subclinical methaemoglobinaemia, and the methaemoglobin levels were similar in prilocaine-exposed and non-exposed newborns. Conclusions: The estimated incidence of neonatal methaemoglobinaemia after prilocaine for episiotomy is 0.37%. Subclinical methaemoglobinaemia did not occur, implicating that symptom-free newborns do not need routine methaemoglobin measurements.