Postoperative vasopressor usage: a prospective observational study: relation to perioperative atrial fibrillation (AF)

Why is the SQUEEZE UK study being performed?

Some patients that undergo surgery develop a syndrome called vasoplegia. Vasoplegia occurs when the function of blood vessels becomes impaired and the blood pressure falls to abnormally low levels. Vasoplegia requires the use of additional medications (vasopressors) to maintain blood pressure. Where vasoplegia persists after surgery, it often necessitates admission to the intensive care unit for management of vasopressors, resulting in prolonged hospital stays and leading to a great potential for complications including the development of atrial fibrillation (AF), an irregular heart rhythm (arrhythmia) that increases the risk of stroke and death.

In the SQUEEZE UK study, we wish to identify factors (e. g. patient age, sex, medical conditions, type of surgery and intraoperative management) that are associated with the requirement of vasopressor medications or lead to the development of AF during or after surgery.

How does the SQUEEZE UK study work?

The SQUEEZE-UK study will be conducted in many centres in England and Wales. This will be a two-part study. Part one (Cohort A) involves collecting data for seven consecutive days from all patients undergoing surgery as hospital inpatients. The primary objective is to determine what proportion receives vasopressors and develops AF. In part two (Cohort B), we will recruit thirty further patients that develop vasoplegia and examine their records in more detail. This will allow us to identify risk factors that predict the development of vasoplegia and AF.

We will examine how commonly AF occurs in patients undergoing surgery. The data collected in this study will also be analysed as part of the worldwide SQUEEZE study, ongoing in over 35 countries, to understand the impact of vasoplegia and AF on patient outcomes.

What do we wish to achieve with the SQUEEZE-UK study?

The data collected will provide a unique insight into vasoplegia and AF following surgery in the UK. Whilst complications such as vasoplegia only occur in a small proportion of patients, because of the large number of people undergoing surgery this potentially affects thousands of patients each year in the UK alone. Understanding the relationship between vasoplegia, AF and patient outcomes is important to develop new ways to improve the patient’s journey through surgery and reduce complications.

What does the SQUEEZE UK study involve for patients treated at participating hospitals?

As part of the SQUEEZE UK study, the research team will access medical records and record information about their stay in the hospital before, during and after surgery. Participation in the study will not affect the medical care received in any way. In particular, there will be no additional interventions or tests. Patients who would rather not have their information collected can contact the study team to opt out of the study. Opting out of the study will not affect the care provided.

Which data will be collected and what happens with it?

The data used will include your year of birth, information about your medical history, the reason for your surgery and the treatments you received before, during and after the operation. Your personal data will not be shared directly with study team members outside the hospital where you are being treated. If you have requested that your NHS data is not shared for research and planning purposes (by registering a National Data Opt-out) then your data will not be collected or used in any way. All data collected in the UK and worldwide will be stored securely at the European Society of Anaesthesiology and Intensive Care in Brussels.

The Health Research Authority has provided legal support to the SQUEEZE UK study under section 251 of the National Health Service Act 2006. The management of data follows advice from the Confidentiality Advisory Group, an advisory body which provides independent expert advice on the use of confidential patient information without consent in England and Wales.


Study summary and contacts:


Project Title: Postoperative vasopressor usage: a prospective international observational study: relation to perioperative atrial fibrillation (AF)


Short Title: SQUEEZE-UK


CTGOV ID NCT03805230


Version/Date: SQUEEZE Protocol UK version 1.1 dated 25 April 2022 based on SQUEEZE International Protocol v2.0 dated 06 April 2021.


Project design: Multi-centre prospective observational study conducted in England and Wales


Sponsor: Liverpool University Hospitals NHS Foundation Trust

Liverpool, UK

UK Sponsor ID: 6028


Funder: European Society of Anaesthesiology and Intensive Care (ESAIC)

Rue des Comédiens 24, 1000 Brussels, Belgium



Chief Investigator for the UK: Prof. Dr. med. Ingeborg Welters

Liverpool University Hospitals NHS Foundation Trust, Liverpool, UK

UK Investigator Team: Prof. Tony Whitehouse

Dr Ben Creagh-Brown

Dr Tomasz Torlinski

Dr. Alicia Waite

Dr Brian Johnston


Contact details: Email (UK study team):


*You should be aware that contacting this email address carries the risk of you losing your anonymity.