Comparison of effective inspired concentration of sevoflurane in preterm infants with different postconceptual ages

Objective: Screening examination for retinopathy of prematurity (ROP) is stressful and painful to the neonate. Sevoflurane has been used successfully in anesthesia for full‐term and premature neonates and has been recently used for pediatric outpatient procedures. In this study, we examined the effective inspired concentration of sevoflurane to prevent movement in response to stimulation of examination in 50% of patients (EIC50) of sevoflurane, as well as the response of sevoflurane to age in the preterm outpatients undergoing fundus examination. Methods: Preterm pediatric outpatients at different postconceptual ages (duration from the mother’s last menstrual period to the date when the examination for ROP was performed) with <44 weeks (group A) and 44–64 weeks (group B) undergoing fundus examination were included. SpO₂ and ECG were monitored in operation room. In the process of anesthetic induction, the oxygen flow rates were 3 l·min^?1, and subjects spontaneously breathed 6% sevoflurane by mask. The time to loss of movement was recorded as induction time. Six percent sevoflurane was inhaled continuously for the same duration, and then the inspired concentration of sevoflurane was adjusted to maintenance concentration. When no movement or crying was observed, the speculums were used to keep the eyelids open, and then the eye examinations were performed by the same ophthalmologist. During induction time and maintenance time, the occurrence of coughing, clenching, gross purposeful movement, breath holding or desaturation to SpO₂ < 95% was recorded. After completion of the procedure, patients were observed in the same room until spontaneous eye opening or verbalization occurred. Up and down method was used to determine subsequent maintenance concentration in each group. The initial maintenance concentration was 3%. The gradient of increase or decrease was 0.5%. If the preceding subject had not moved, the sevoflurane concentration was decreased by 0.5%; if the preceding subject had moved, the concentration was increased by 0.5%. When at least six independent alternations from no‐movement to movement were observed, test was terminated. Results: Twenty‐four pediatric outpatients completed the investigation in group A. The effective inspired concentration prevented movement in response to stimulation of examination in 50% of patients (EIC50) of sevoflurane was 2.5% in group A. Twenty‐seven patients completed the investigation and EIC50 values of sevoflurane were 3.0% in group B. The induction time in group A was significantly lower than that in group B. The gestational ages, anesthesia time, and awake time were similar in two groups. Conclusion: Anesthesia with inhaled sevoflurane by a face mask can be accomplished in preterm outpatients undergoing fundus examination without intubation and i.v. accession. The EIC50 is lower, and the induction time is shorter in smaller aged patients compared with those in older ones.