The purpose of this study is to assess respiratory variation of carotid doppler peak velocity (∆CDPV) for prediction of fluid responsiveness during major abdominal surgery.

Investigating hemodynamic parameters in a group of 19 ICU-patients with septic shock, respiratory variation of carotid doppler peak velocity (∆CDPV) has been shown to be able to predict fluid responsiveness. For patients receiving so called lung protective ventilation with a tidal volume of 6ml/kg ∆CDPV was superior for prediction of fluid responsiveness when compared to other well established parameters such as pulse pressure variation (∆PP).

Likewise in another study ∆CDPV has been shown to be superior to stroke volume variation (∆SV) for prediction of fluid responsiveness in patients with septic shock when ventilated with a tidal volume of ≥8ml/ kg.

All in all respiratory variation of carotid doppler peak velocity (∆CDPV) seems to be a promising parameter for prediction of fluid responsiveness (Yao et al., BMC Anesthesiology 2018). However, so far clinical studies have been conducted only under a small number of patients mainly in the intensive care unit and/ or under highly specific conditions (e.g. cardiac surgery).

If ∆CDPV is able to predict fluid responsiveness with high accuracy intraoperatively remains unknown. The investigators are therefore conducting this prospective monocentric observational trial to evaluate the performance of ∆CDPV during major abdominal surgery and compare it to validated fluid responsiveness monitoring parameters ∆PP and corrected flow time (fTc).

Following IRB-approval and written informed consent 84 patients scheduled for major abdominal surgery will be enrolled in the study. Stroke volume will be monitored by Esophageal Doppler Monitoring (CardioQ-ODM®, Deltex Medical Ltd, Chichester, UK). In case of hypovolemia a fluid bolus of 7 ml/kg ideal body weight will be administered at the discretion of the attending anesthesiologist. Respiratory variation of carotid doppler peak velocity (∆CDPV) will be monitored before and 1 minute after completion of each fluid bolus using an ultrasound device with a common linear array transducer (Philips ClearVue 350, Philips Medizin Systeme GmbH, Boeblingen, Germany).

Inclusion Criteria:

• Age 18-80 years
• written informed consent
• scheduled major abdominal surgery

Exclusion Criteria:

• Age <18 or >80 years
• pregnancy
• SIRS or sepsis
• any kind of cardiac arrhythmia
• known valve disease
• known heart failure
• any kind of known carotid stenosis
• carotid doppler peak velocity >182 cm/s before baseline measurement (expected stenosis)
• missing indication for invasive arterial blood pressure monitoring (IBP) not related to the study
• peripheral artery disease (PAD)
• BMI > 35 kg/m2
• intraabdominal hypertension
• ASA-PSC of 4
• severe lung disease (e.g. COPD grade 3, fibrosis)
• esophageal disease of any kind
• participation in another clinical study

Only patients scheduled for major abdominal surgery with an expected high intraoperative fluid turnover will be eligble for the study. Patients with any kind of crdiac arrhythmia, valve diseases, heart failure or carotid stenosis will be excluded from the study to avoid measurement errors and bias for the hemodynamic parameters such as pulse pressure variation, stroke volume and carotid doppler peak velocity.