Collecting all available data (waveforms, beat to beat data, status data) generated by a non invasive blood pressure monitor on each hand and compare this to the actual data obtained by intra arterial (radial) monitoring.

This to see if the non invasive bloodpressure monitor can be validated for intraoperative use.

Although a blood pressure monitoring device could be evaluated by the comparing systolic, diastolic and mean arterial pressure to a reference pressure, it is the specific aim to collect all available data (waveforms, beat to beat data, status data) generated by the blood pressure monitor.

After data analysis and comparison to patient's actual intra-arterial waveform, the outcome will be evaluated by Association for the Advancement of Medical Instrumentation (AAMI) standards to see if the non invasive bloodpressure monitor can be validated for intraoperative use.

The study is targeted at patients already monitored with a system that accurately measures and stores the intra-arterial waveform, such as the FloTrac system in the EV1000 monitor.

This study is a substudy of a feasability protocol evaluating a new algorithm for the Clearsight system.

Inclusion Criteria:

• Patients whose arterial blood pressure is measured invasively with technology that allows for the storage of the intra-arterial waveform with sufficient quality and resolution (Flotrac).
• Patients older than 18, for elective general surgery.

Exclusion Criteria:

- Patient conditions that are expected to potentially and significantly affect the transfer of pressure between radial artery and the finger, e.g. due to recent finger fractures

Patients in a perioperative setting already monitored with a system that accurately measures and stores the intra-arterial waveform, such as the FloTrac system in the EV1000 monitor.