The objective of this study is to determine whether preoperative parenteral thiamin supplementation does prevent the intra and early postoperative increase of lactate and whether this effect is related to the extent of thiamine deficiency in patients undergoing heart surgery. In addition the prevalence of major thiamin deficiency in patient undergoing heart surgery will be determined.

Thiamine (vitamin B1) is a water-soluble vitamin and is involved in several stages of intermediate metabolism which are important for producing energy. Severe thiamin deficiency has been associated with severe lactic acidosis and clinical symptoms of life threatening heart failure.

To date, no study has evaluated thiamine levels in patients undergoing heart surgery and the prevalence of thiamine deficiency is not known. Furthermore it is unknown whether moderately reduced thiamin levels are associated with mild forms of perioperative cardiac failure necessitating prolonged inotropic support.

In this prospective double blind randomised controlled trial of the effect of a parenteral infusion of thiamin before induction of anaesthesia we will investigate the effect on perioperative lactate increase as primary outcome and extent and duration of inotropic support after cardiac surgery. In addition the pharmacokinetics of a intravenous infusion of 300 mg of thiamin on erythrocyte thiamin content and the amount of thiamine excreted in the 24 hours via the urine will be determined.

Baseline thiamin levels in erythrocytes before surgery, as well as nutrition history and body composition will be evaluated as effect modifier.

Inclusion Criteria:

• age 18 - 100 years
• planned heart surgery
• signed informed consent

Exclusion Criteria:

• pregnancy and lactation
• known allergic reaction to the drugs used
• mental condition rendering the patient unable to give informed consent
• inability or contraindications to perform study procedures