The design of the study is no longer relevant.

Paracetamol intoxication is common, and concentration measurements are performed regularly. This research group is developing a fast bedside electrochemical analysis tool for paracetamol concentration measurement. This study will find out how this novel method performs in patients using other, confounding medication in detecting paracetamol concentration in capillary blood, venous plasma and saliva samples.

Paracetamol concentration analysis is performed in 20 patients who will come to hospital for elective surgery. Inclusion criteria is a regular medication that continues over perioperative period.

Patients will be given standard premedication of paracetamol 1g perorally before surgery: this study does not affect standard surgical treatment.

Paracetamol concentration will be measured in venous plasma-, capillary blood-, and saliva samples before drug delivery and in recovery room after surgery using the novel electrochemical analysis tool and high-performance mass spectrometry analysis as a reference. If needed, confounding medication is identified with large toxicologic mass spectrometry screen (UPLC-QTOF).

Inclusion Criteria:

• informed consent
• Age 18-75 years
• American society of anesthesiologist classification 2-4
• planned elective surgery with standard premedication with paracetamol 1g po.
• at least one regular medication ongoing perioperatively
• eligibility for elective surgery
• negative pregnancy test in fertile women

Exclusion Criteria:

• American society of anesthesiologists classification 1
• contraindication for use of paracetamol as standard premedication
• pregnancy or lactation
• less than 3 months from previous drug research
• less than 3 months from previous blood donation
• anticipated difficult puncture of veins
• Body Mass Index lower than 18.5 or higher than 35