In infants less than two years old the new Oxygen Reserve Index (ORI) will be measured during general anaesthesia. It will evaluated if and how ORI-monitoring gives earlier warning of hypoxaemia than conventional oxygen saturation measurement.

The Oxygen Reserve Index (ORI) is a new development in multiple wavelength pulse oximetry, reflecting the arterial partial oxygen pressure (PaO2) continuously and non-invasively by an index. In contrast to established standard oxygen saturation (SpO2) measurements, ORI detects a drop of PaO2 until the threshold of 100 mmHg. During anaesthesia induction-associated apnoeic periods ORI may detect a drop of PaO2 early enough for the anaesthesiologist to interrupt the intubation procedure and re-start oxygenation. In contrast, due to the flat upper part of the oxyhaemoglobin dissociation curve, SpO2 stays at values above 90% until PaO2 falls below 60mmHg. At this point, SpO2 drops rapidly and a pro- longed hypoxic dip is the consequence. To avoid this potentially harmful hypoxic dip, continuous monitoring of PaO2 using ORI would be advantageous during anaesthesia induction phase.

This clinical study aims to evaluate the time benefit between alarm of hypoxaemia by the ORI-monitoring and the start of the dropping of oxygen saturation. Pre-set and pre-described ORI-alarms will be checked for their utility and a new ORI-alarm will be defined that is potentially more useful. As secondary endpoints the study examines the correlation of ORI with PO2, the influence of patient or measurement characteristics on the correlation of ORI with PO2 and the influence of the measurement site on ORI-measurement.

Inclusion Criteria:

• small infants < 2 years scheduled for elective surgery with general anaesthesia.

Exclusion Criteria:

• emergency procedures, lack of informed consent of legal guardian