The purpose of this study was to compare the Continuous Non-invasive Arterial Pressure (CNAP) monitor with the gold standard of invasive arterial pressure monitoring during:

1. induction and maintenance of general anaesthesia
2. intensive care unit treatment of postoperative patients with an ASA 3 or 4 status

The CNAP monitor continuously measures blood pressure using a finger cuff. It showed a good agreement to invasive blood pressure measurements during anaesthesia induction and maintenance during surgery. In critical ill patients cardiac arrhythmia is probably a confounding factor affecting accuracy and interchangeability of CNAP. As systolic arterial CNAP pressure in comparison to mean pressure shows no statistical interchangeability with invasive measurements, mean pressure should be considered when making therapy decisions.

A problem is the missing standard criterion for comparison of continuously devices with invasive pressure.

Inclusion Criteria:

• Age >18
• BMI < 35 kg.m²
• Patients capable of giving informed consent
• patients undergoing elective surgical procedures in supine position under general anesthesia
• perfusion of the examined arm evidenced by a positive Allen's test

Exclusion Criteria:

• Patients not competent or unwilling to provide informed consent
• Patients with history of neurological, neuromuscular seizure
• Patients where IBP cannula, CNAP™ finger-cuff and CNAP™ upper arm cuff cannot be placed on the same arm

patients undergoing major surgery or intensive care unit treatement with the need for an invasive blood pressure measurement