The perioperative preservation of functionality and quality of life plays an increasingly important role in older physically limited and frail patients undergoing cardiac surgery. Hereby, impairments of the skeletal muscle system integrity often contributes to a reduced physical performance. Early identification of these high-risk patients could help to initiate appropriate preventive and therapeutic measures. Volatile organic compounds (VOC) represent a non-invasive and real-time measurable approach for recording physiological and pathophysiological processes. Isoprene (2-methyl-1,3-butadiene) is one of the most abundantly exhaled VOCs and has recently been shown to originate from skeletal muscle metabolism. However, the prognostic value of isoprene as a volatile biomarker for skeletal muscle integrity, physical performance and functional outcome in patients undergoing cardiac surgery has not been evaluated before.

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

Inclusion Criteria:

• Age >= 65 years
• planned cardiac surgery
• operation duration >60 min

Exclusion Criteria:

• refusal of study participation
• emergency / urgent surgery
• acute myocardial infarction
• acute or chronic infection
• Pre-existing illness with permanent restriction of mobility
• Pre-existing neuromuscular disease
• current malignant disease
• terminal renal insufficiency
• severe liver cirrhosis
• severe obstructive pulmonary disease

Patients undergoing elective cardiac surgery