This study will be conducted on pediatric patients up to 14 years of age. The effect of two fluid challenge regimes on cerebral and peripheral NIRS will be assessed, in a randomized double blinded controlled trial. The findings will be correlated with two ultrasound measures, previously validated as markers of fluid responsiveness.

The patients will be recruited during the preoperative consultation. After inhalational induction and placement of all monitors, an intravenous access is established. After induction and securing of the airway via endotracheal tube or laryngeal mask, we note the reference values of all parameters. A pre-fluid challenge ultrasound is done, to assess the inferior vena cava distensibillity index, and the Vmax aortic peak flow velocity. After this the fluid challenge is performed. The second ultrasound measures are done after the fluid challenge. Finally an ultrasound is performed at the end of the operation, before emergence, to assess wether the standard peroperative fluid therapy has affecter these measures. NIBP, SpO2, HR, RR, NIRS values will be noted throughout the whole perioperative period. THe end-goald is to correlate the ultrasound findings to the NIRS-values, and see wether the NIRS can be used as a monitor of fluid therapy in pediatric patients.

Inclusion Criteria:

• all operations excepting cardiac surgery
• BMI < 30
• ages 1-14 years

Exclusion Criteria:

• any cardiac affection (congenital unoperated heart disease, arrythmias)
• icterus
• refusal