Background Inhalational anesthesia with sevoflurane for endotracheal intubation without muscle relaxant is now used widely for pediatric patients.This study assessed the efficacy and safety of induction with high concentration sevoflurane and of nasotracheal intubation without muscle relaxant in infants with increased or decreased pulmonary blood flow (PBF) and undergoing surgery for congenital heart diseases.Methods Fifty-five infants aged 2-12 months,weighing 4.7-10.0 kg,and scheduled for congenital cardiac surgery were enrolled.Subjects were divided into those with increased (IPBF group,n=29) and decreased (DPBF group,n=26) pulmonary blood flow.All infants received inhalational induction with 8％ sevoflurane in 100.0％ oxygen at a gas flow rate of 6 L/min.Nasotracheal intubation was performed 4 minutes after induction.Sevoflurane vaporization was decreased to 4.0％ for placement of a peripheral intravenous line and invasive hemodynamic monitors.Five minutes later,sedatives and muscle relaxant were administered and the vaporizer was adjusted to 2％ for maintenance of anesthesia.Bispectral index (BIS) scores,circulatory parameters,satisfactory and successful intubation ratios,adverse reactions,and complications of intubation were recorded.Results Times to loss of lash and pain reflexes were longer for the DPBF group (P ＜0.01).Satisfactory intubation ratios were 93.1％ and 61.5％ for the IPBF and DPBF groups,respectively (P=0.008).Successful intubation ratios were 96.6％ and 76.9％ for the IPBF and DPBF groups,respectively (P=0.044).Following sevoflurane inhalation,blood pressures decreased significantly in the IPBF group but remained stable in the DPBF group.BIS scores declined to similar stable values,and a “nadir BIS” was recorded for both groups.No obvious adverse reactions or complications of intubation were noted perioperatively.Conclusions Induction with high concentration sevoflurane,although faster for infants with IPBF,is safe for infants with IPBF or DPBF.However,nasotracheal intubation without muscle relaxant after induction with high concentration sevoflurane is less successful and less satisfactory for infants with DPBF and should be used with caution in this patient group.