A survey of the dose of inhalational agents used to maintain anaesthesia in infants

BACKGROUND: Various animal studies suggest that currently used anaesthetics are toxic to the developing brain. Many reviews advise that the total anaesthetic drug exposure should be reduced but the dose usually used in clinical practice has not been clearly elucidated.
OBJECTIVES: To provide an overview of the dose ranges currently used in clinical practice during the maintenance phase of anaesthesia in infants undergoing anaesthesia for noncardiac surgery and diagnostic procedures. DESIGN A two-centre mixed prospective (London) and retrospective (Utrecht) observational cohort study.
SETTING: Two independent tertiary paediatric referral centres in March and November 2013; Great Ormond Street Hospital (GOSH), London, United Kingdom and Wilhelmina Children's Hospital, University Medical Center Utrecht (UMCU), The Netherlands.
PATIENTS: A total of 76 infants were included in the analysis, 38 infants from each hospital.
METHODS: Patients from GOSH were matched by procedure, age and weight with patients from the UMCU. The end-tidal concentrations of the inhalational agents were investigated from anaesthetic charts during the maintenance phase and corrected for the age-specific minimal alveolar concentration (MAC), expressed as a percentage from the MAC (%MAC).
RESULTS: Three different types of inhalational anaesthetics were used: sevoflurane, desflurane, isoflurane. The mean %MAC was 0.85. No significant differences in %MAC were found between GOSH and the UMCU (P = 0.329); the mean %MAC in GOSH was 0.87 and in the UMCU was 0.82. There was a significant increase in the %MAC in relation to age (slope = 0.036 MAC month±1, P < 0.001). Of all patients, 75% had an end-tidal concentration lower than 1 MAC. There was no significant effect of the use of analgesia on the end-tidal concentration of inhalational anaesthetics (P = 0.366).
CONCLUSION: The concentration of inhalational anaesthetics in %MAC increased with age and was lowest in neonates. Most young infants received inhalational anaesthetics at a concentration below 1 MAC, which accords with current guidance to minimise anaesthetic drug exposure but may have unintended consequences.