Molecular Breath Print of COPD Patients With Exacerbations Despite Triple Inhalational Therapy

Inclusion Criteria: * Informed consent * age \>= 18 years * staged according to GOLD recommendations * GOLD stage 2-4, GOLD ABE classification * hospitalization due to COPD exacerbation * subjects adherent to triple inhalational therapy (beta-2-sympathomimetics, anticholinergics, steroids) * suitable for follow-up assessment * \<48 hours after initiation of antibiotic therapy or systemic steroid therapy Exclusion Criteria: * physical or intellectual impairment precluding informed consent or protocol adherence * known pregnancy * congenital defects with direct impact on central metabolism e.g. amino acid metabolism defect * uncontrolled diabetes (e.g. HbA1c \>11% or Glc \>20mmol/l) * acute or chronic pulmonary disease other than COPD * renal failure or renal replacement therapy (GFR \< 15 mL/min)