The incidence of arterial hypotension under general anesthesia using sevoflurane is particularly high in newborns and infants up to 6 months of age. A decrease of 20% of the initial mean blood pressure (mBP) is the definition of significant arterial hypotension in adults and children. In adults, intraoperative arterial hypotension is associated with an increase of intraoperative mortality and a certain neurological morbidity. In infants under 6 months of age, neurological disorders have been reported following general anesthesia. Neurotoxicity of hypnotics is often incriminated as should be the episodes of arterial hypotension.

Current management of hypotension uses vascular filling with crystalloids and vasopressive amines in second intention. Dopamine is the most frequently used amine. Ephedrine can also be used. Ephedrine is particularly interesting because of its action on both α and β receptors and its mode of administration: one dose and peripheral access.

Only one study is available in children from birth to adulthood; it demonstrates a lower hemodynamic response in infants than in adults, when administered a low dose of Ephedrine (0.1 to 0.2 mg/kg). A recent retrospective cohort suggests an under efficacy of low doses and the use of higher doses than those recommended.

The primary objective is to determine the optimal dose of ephedrine (dose of ephedrine associated with a difference of proportion of newborns/infants in therapeutic success of 55%) compare to the reference dose of 0.1mg/kg as a first line treatment of intraoperative arterial hypotension.

Secondary objectives:

• Return to a mBP superior to 38mmHg post Ephedrine administration.
• To assess occurrence of hypoxemic events during anesthesia.
• To assess tolerance of ephedrine. One hundred and twenty newborn and infants up to 6 months of age will be recruited in 3 sites of the Rhone Alpes Auvergne area over 24 months.

Inclusion Criteria:

• Newborns or infants < 6 months of age,
• boys and girls,
• premature or not,
• requiring general anesthesia induced by sevoflurane
• who presents during anesthesia a decrease of blood pressure superior to 20% of the basal mBP (measured prior to surgery) despite of vascular filling with sodium chloride 0.9% (10mL/kg during 10 min).
• Written, informed consent obtained from the 2 parents

Exclusion Criteria:

• Allergy to Ephedrine.
• Emergency surgery.
• Patient having previously received other vasopressive amines.
• Use of other indirect sympathomimetic drug such as phenylpropanolamine, phenylephrine, pseudoephedrine and methylphenidate.
• Premedication with clonidine
• Congenital heart disease
• IV-induced anesthesia.