Central Neuraxial Blockade (CNB) is commonly used in anaesthetics. It has several advantages over a general anaesthetic however contraindications include coagulopathy. Guidelines suggest a CNB should not be undertaken with an International Normalised Ratio (INR) of 1.5 or greater. A common cause of an elevated INR is warfarin therapy and regular monitoring of its effects is required.

The Hemochron Signature Elite is a portable micro coagulation system that can be used as a point of care (POC) anticoagulation monitoring device. Marketing is focussed on its accuracy, convenience and efficiency in delivering a coagulation result.

This study will assess the accuracy of this device in calculating the International Normalised Ratio (INR) result. This will be compared to another INR result obtained on the same sample via the current gold standard testing equipment in the Royal Infirmary Edinburgh (RIE) laboratories.

The study will include patients presenting for surgery who have had their warfarin therapy stopped within the previous 7 days. Patients on warfarin therapy requiring surgery are currently identified in preoperative assessment clinics, on average 12 weeks prior to their date of surgery.

Anecdotally there appears to be a difference between the 'expected' and actual INR when a POC device is used. Concern exists that patients may be inappropriately denied the potential benefits of central neural blockade (CNB) if a POC device provides a falsely high result, or conversely the investigators may be proceeding with CNB in patients with an unacceptably high INR if POC provides a falsely low result. There is also the possibility of improving hospital efficiency using this device as it provides a result much faster than the laboratory.

Inclusion Criteria:

• Adult patients presenting for elective surgery who have stopped their warfarin therapy within the last 7 days.

Exclusion Criteria:

• Adults with incapacity

The study population will include all adult patients presenting for elective surgery who have stopped their warfarin therapy within the last 7 days. They will be approached in the Day Surgery Unit and Day of Surgery Assessment unit within a single centre.