Prognostic Value of Exhaled Isoprene Levels for Morbidity and Functional Outcome in Cardiosurgical Patients

This is a single center prospective observational study evaluating exhaled isoprene as a perioperative volatile biomarker of skeletal muscle integrity, physical performance and functional outcome in cardiosurgical patients. All study participants will be assessed by comprehensive clinical examinations, laboratory testing, breath analysis and skeletal muscle ultrasound before, during as well as five and thirty days after surgery. Clinical assessments will be performed using established clinical scores and scales (e.g. the Short Physical Performance Battery and the Fried Frailty Index). Laboratory testing comprises a broad panel of blood-based biomarkers of skeletal muscle integrity and metabolism. The investigators hypothesize that: * perioperative exhaled isoprene levels correlate with postoperative measures of physical performance, functional outcome and morbidity * perioperative exhaled isoprene levels differ between patients with and without physical frailty * perioperative exhaled isoprene levels correlate with sonographic and laboratory parameters of skeletal muscle integrity