Condition category
Date applied
Date assigned
Last edited
Prospectively registered
Overall trial status
Recruitment status
No longer recruiting
Publication status
Results overdue

Plain English Summary

Background and study aims
Vascular surgery is a type of surgery that treats diseases of the arteries and veins. During vascular surgery the drug heparin is commonly used to stop the blood from clotting (heparin anticoagulation). If too much heparin is given the patient is at risk of excess bleeding, and if too little heparin is given the patient is at risk of blood clots during the operation. It is increasingly being seen as best practice to use methods that keep blood loss to a minimum and reduce the requirement for blood transfusion. There is a debate about the best method of monitoring heparin anticoagulation. The most commonly used test to guide heparin dosing during surgery is activated clotting time (ACT), which measures how long it takes your blood to clot. However, there are concerns about variations in response between patients, and how ACT levels relate to laboratory tests of heparin activity. The aims of this study are to compare ACT levels and laboratory tests in patients undergoing major vascular surgery, record the variation in responses to heparin in these patients, and relate heparin activity to patient outcomes such as bleeding and clotting.

Who can participate?
Adult patients undergoing elective major complex vascular surgery with heparin anticoagulation and monitoring.

What does this study involve?
All patients undergoing this type of major vascular surgery are fitted with an arterial line - a thin catheter inserted into an artery from which blood is routinely sampled at intervals throughout the surgery without having to pierce the skin repeatedly. During the study the doctor takes an extra sample of blood (equivalent to half a teaspoonful) each time blood is monitored for heparin anticoagulation. This additional blood is sent to the laboratory to undergo different tests that also monitor heparin activity. Apart from the additional blood sampling during their surgery their care is exactly the same as if they were not in the study. The patients are also followed up to assess whether they have any bleeding or blood clotting, which is part of their routine care.

What are the possible benefits and risks of participating?
There is no direct benefit from taking part in the study, but the results of this study may help future patients and contribute to improved treatment during surgery. The disadvantages to taking part in the study are that the participant will have extra blood tests during surgery. There is no other change in the participant's treatment.

Where is the study run from?
Royal Free London NHS Foundation Trust (UK).

When is the study starting and how long is it expected to run for?
October 2015 to April 2017.

Who is funding the study?
Vascular Anaesthesia Society of Great Britain and Ireland (VASGBI).

Who is the main contact?
Dr Nick Schofield

Trial website

Contact information



Primary contact

Dr Nick Schofield


Contact details

Royal Free London NHS Foundation Trust
Pond Street
United Kingdom

Additional identifiers

EudraCT number number

Protocol/serial number

NHS REC 15/LO/1750

Study information

Scientific title

Monitoring heparin anticoagulation in major vascular surgery: an observational cohort study


Study hypothesis

Aim to correlate activated clotting time (ACT), anti-Xa levels and antithrombin levels during major vascular surgery.

Ethics approval

Research & Development Department Royal Free Hospital, 27/10/2015, REC Ref: 15/NI/0219

Study design

Observational cohort study

Primary study design


Secondary study design

Cohort study

Trial setting


Trial type


Patient information sheet


Haematology and vascular surgery


Enrolled patients will have additional blood tests during their surgery - withdrawal of additional 2.7 ml of blood with each monitoring episode. Up to an additional 16 ml of blood may be sampled during the course of surgery. This is equivalent to roughly 1 tablespoon and should not convey any additional risks or adverse consequences. Sampling episodes will be kept to a minimum and minimum volumes of blood withdrawn to reduce any avoidable wastage of blood. Blood will be taken from established invasive lines (arterial line), at the same time point as routine samples and therefore additional needling of the skin will not be necessary. Blood samples will be used to measure the activated clotting time (ACT), thrombin generation and anti-Xa levels.

Intervention type



Drug names

Primary outcome measure

Correlate ACT and anti-Xa levels during aortic surgery - measured at baseline and up to six time points during surgery

Secondary outcome measures

1. Blood loss and bleeding will be measured during theatre
2. Clotting complications will be monitored during theatre and first week postoperatively

Overall trial start date


Overall trial end date


Reason abandoned (if study stopped)


Participant inclusion criteria

All adult patients able to give informed consent and undergoing elective major complex vascular surgery in which heparin anticoagulation and monitoring is indicated

Participant type


Age group




Target number of participants


Participant exclusion criteria

1. <18 years old
2. Unable to consent
3. History of heparin allergy
4. Already taking part in research study

Recruitment start date


Recruitment end date



Countries of recruitment

United Kingdom

Trial participating centre

Royal Free London NHS Foundation Trust
Pond Street Hampstead
United Kingdom

Sponsor information


Royal Free London NHS Foundation Trust (UK)

Sponsor details

Pond Street
United Kingdom

Sponsor type

Hospital/treatment centre



Funder type


Funder name

Vascular Anaesthesia Society of Great Britain and Ireland (VASGBI) Departmental Project Grant DG01-2015

Alternative name(s)

Funding Body Type

Funding Body Subtype


Results and Publications

Publication and dissemination plan

To be confirmed at later date

Intention to publish date

Participant level data

Available on request

Basic results (scientific)

Publication list

Publication citations

Additional files

Editorial Notes

12/05/2016: Ethics approval information added.