The determination of arterial blood pressure is a basic monitoring measure during spinal anaesthesia in obstetrics for the operative delivery of the child via the caesarean section. Adequate arterial blood pressure is essential to ensure adequate placental perfusion, sufficient cerebral perfusion pressure of the mother and is the basis for any hemodynamic optimization to significantly improve patient outcome.

Up to now, two standard methods for determining blood pressure have always been the oscillating non-invasive, intermittent blood pressure measurement (NIBP) and the invasive continuous blood pressure measurement (IBP). The NIBP derives blood pressure values using upper arm cuffs at defined intervals. As a result, no continuous measurement is possible and nerve damage and pain are risks of this method. The indication for the establishment of IBP is often not given due to potential side effects such as aneurysm formation, infections, thrombosis and circulatory impairment of the hand. The application of a novel non-invasive, patch-clamp-based continuous blood pressure measurement system (ClearSightTM, Edwards Lifesciences Corporation, Irvine, California, USA) promises to combine the advantages of NIBP, namely non-invasiveness and IBP, the continuous pressure measurement. So far, there have been no randomized, controlled trials for application. Spinal anesthesia is a widespread anaesthetic procedure for performing Caesarean sections. Within the clinical standard, an intermittent blood pressure measurement is used at intervals of 2 to 5 minutes. Continuous invasive blood pressure measurement is not a standard procedure.

Standard procedure: The standard procedure corresponds to the SOPs of the Clinic for Anaesthesiology and intensive care medicine. After admission to the operating room, the patient is monitored by means of a 3-channel ECG and pulse oximetry. The NIBP measurement by means of an upper arm cuff is carried out intermittently with a measurement interval of 2 minutes according to SOP (standard operating procedure) and is continued until the umbilical cord of the fetus is removed. Subsequently, a peripheral venous access is applied and 500 ml of full electrolyte solution are infused. Subsequently, the spinal anesthesia is applied in a seated position. Size-adapted 1.6 - 2.0 ml hyperbaric bupivacaine 0.5%, 0.1 mg morphine and 5 µg sufentanil are used. According to SOP, local skin infiltration with lidocaine 1% is carried out. After application of the spinal anaesthesia, the patient is positioned in a supine position with the operating table tilted 15° to the left. If the systolic blood pressure drops below 100 mmHg or by more than 20 % of the initial value, 100 µg phenylephrine is applied. After a sufficient entry into action (target height according to SOP TH4) the Caesarean section is performed. After birth, APGAR values are recorded after 1,5 and 10 minutes, and umbilical cord blood gas analysis is performed.

Study procedure: Randomisation of patients based on a randomisation list drawn up by an independent statistician in either NIBP or ClearSight group. In both groups, the above-mentioned standard procedure according to SOP and also the non-invasive continuous blood pressure measurement to improve blood pressure monitoring with the ClearSight? system, so that all patients are monitored by both monitoring systems. In the NIBP Group, anaesthetists are blinded against the ClearSight measurement. In the ClearSight group, anaesthetists are blinded against the NIBP measurement. Blinding is achieved by completely covering the measured values of the other method. (please describe in detail). The installation of the measuring sensors does not involve any risks for patients.