Lactate kinetics will be studied in hospitalized septic patients using a bolus injection of stable isotopically labeled lactate.

Adult septic patients admitted to the Intensive Care Unit (ICU) or Intermediary Medical Unit in Karolinska University Hospital will be recruited within 72 hours from start of symptoms.

Other than fulfilling the definition for sepsis-3, patients need to be equipped with an arterial catheter to be eligible for inclusion. After informed consent (from next of kin when applicable) baseline blood samples are drawn from existing catheter and the subject is given a bolus dose of 20umol/kg 13C-labeled lactate in 20 ml isotonic saline. After this a total of 14 blood samples á 2 ml is drawn in the following 120 minutes. All blood samples are centrifuged and stored in -800 C until analysis. After all subjects have been included sampled are thawed and analyzed for content of endogenous and labeled lactate. Through analysis between their relationship the lactate production and consumption can be quantified.

Inclusion Criteria:

• Sepsis
• Age >17 years
• Arterial catheter
• Lactate > 2 mmol at any time point prior to inclusion

Exclusion Criteria:

• Mitochondrial defect
• Degenerative muscle disease
• Terminal liver failure