Sympathetic Autonomic Dysfunction and the risk of Hypotension After Surgery

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  Principal Investigator
  Dr Ned Douglas
  

Project Details

Sympathetic Autonomic Dysfunction and the risk of Hypotension After Surgery (SADHATS): a pilot single centre observational study.

Low blood pressure after surgery is very common, associated with higher risk of heart attacks, kidney damage and death and poorly understood. Most of the science concerning what causes low blood pressure after surgery comes from many decades ago and from patients populations that may not represent modern surgery. Tests to predict low blood pressure rely on extremely expensive equipment that requires specialist training to use, and consequently they are rarely used in clinical practice.

Clinicians believe that inflammation caused by the stress response to surgery is part of explanation. Inflammation causes the peripheral blood vessels to widen, and this in turn lowers the blood pressure. In addition to this problem, clinicians think that the circulation fails to respond to this change in blood pressure, which is abnormal. Normally, if the blood pressure dropped, the sympathetic nervous system would detect this problem and send signals to increase the heart rate and amount of blood being pumped by the heart, as well as narrowing the blood vessels again to improve the blood pressure. This system must either fail to activate or be unable to compensate for the degree of change in blood pressure after surgery. It has been identified that failure of the sympathetic nervous system to activate is commonly seen after even minor surgery and that this failure to activate is associated with a higher risk of complications after surgery. Low blood pressure may be the connecting concept between failure of the sympathetic nervous system to activate and patients developing complications.

There are some tests of sympathetic nervous system that are relatively straightforward to perform. Clinicians can use a combination of questions, and a specific examination technique called an isometric handgrip test to establish if the sympathetic nervous system is functioning normally. The isometric handgrip test is a non-invasive test of squeezing a measuring device as tightly as possible, which can be done easily at the bedside. However, this technique has never been tested in patients who are recovering from surgery and anaesthesia, and so the feasibility of a large study to using this technique is unclear. This pilot study is necessary to test the feasibility and acceptability of the isometric handgrip test in the surgical population, how common the risk factors might be and how frequently the outcome of low blood pressure is seen. This study has the potential to unlock a straightforward test of sympathetic nervous system function for use in the perioperative period, which could then be developed into a larger study exploring if dysfunction in the sympathetic nervous system is connected with hypotension.

We plan to enrol 62 patients at the Royal Melbourne Hospital who have had surgery under general anaesthesia. We have recruited 14 participants so far.

Lead Investigators: 

Dr Ned Douglas

Funding

Australian and New Zealand College of Anaesthetists & Faculty of Pain Medicine