Skip to main content

Research and Projects

Cognitive Monitoring in Planned Arthroplasty Surgery Study (CoMPASS)

Theme: CLAHRC - Evidence for Policy and Practice
Status: Live

SWARM logo

A South West Anaesthesia Research Matrix (SWARM) Study





Post-operative cognitive dysfunction (POCD) - a perioperative decline in cognitive trajectory - is common, whether patients have a general anaesthetic (GA) or spinal anaesthetic for their surgical procedure. There is great uncertainty over what causes the change (such as the operation itself, exposure to anaesthesia agents, emotional stress, medications, combination of factors) or indeed whether there would be a similar decline in cognitive trajectory without surgery.

Pre-operative cognitive trajectory may influence the post-operative course. Evered proposes that:

“What is missing is accurate pictures of pre-operative cognitive trajectories in these patients to understand their cognitive performance in the postoperative period had surgery and anaesthesia not occurred” [1]. 

She explains that by identifying the pre-operative trajectory we will be much better placed to understand the post-operative trajectory.  Furthermore, a meta-analysis in 2014 specifically looking at POCD in joint arthroplasty patients highlighted the need for the use of an appropriate control group, with demographically matched healthy controls the most viable option [2].

Cognitive testing takes many forms. In-depth neuropsychological testing is time consuming and requires specialist psychology training to deliver, so prior studies have been small.  A validated online or app-based cognitive testing tool that takes about 20 minutes to deliver and has minimal learning effect for patients affords the opportunity to test a large number of patients within the time constraints of a patient’s perioperative journey

More than 2,000 hip and knee replacements are carried out every year in the South West. These present a planned inflammatory insult with a potentially long lead in period, meaning that patients are on waiting lists for many months. This provides an opportunity to perform cognitive testing during the pre-operative period and then follow up with further testing on patients in the short- and long-term post-operative period.  

The South West Anaesthesia Research Matrix (SWARM) provides a workforce of anaesthesia trainees across the South West Peninsula region encompassing six different hospitals, all of which perform elective lower limb joint arthroplasty surgery.  For an eventual larger multicentre study, we would utilise members of SWARM at each site, and therefore recruit a large number of patients over multiple secondary care sites.  We are also in collaboration with a primary care researchers that would be able to perform cognitive testing on similar patients that are not undergoing surgery.

Ultimately, the aim is to collect cognitive data on a large number of patients over a long period of time.  By gaining a more accurate picture of pre-operative cognitive function as well as comparing with an appropriate control group, this will add to the body of evidence particularly regarding those who may be particularly at risk.  By doing this we will be better placed to develop possible preventative interventions as well as advise patients more accurately when discussing the balance of risks and benefits of surgery.



The aim of this study is to assess the feasibility of monitoring cognition by an online tool using an anaesthetic trainee research network and primary care research links, working in collaboration with cognition experts. The long term goal is to follow this feasibility study with a larger multi-centre study to monitor the cognitive trajectory, both pre- and post-operatively of patients undergoing surgery and make comparisons with an appropriate control group. 




  • Is it feasible to track the cognitive trajectory of patients who are undergoing hip or knee replacement surgery in the perioperative period (pre- and post-operatively) using an anaesthetic trainee research network?
  • Does our chosen tool for monitoring cognition during this perioperative period work? (i.e. is it sensitive enough to pick up deflection at time of surgery?)
  • Is it feasible to similarly track the cognitive trajectory of patients in primary care using primary care research resources?
  • Gather pilot data to inform a future larger study.


  • What is the prevalence of factors which might influence this cognitive trajectory? Collect candidate covariates (levels of pain, gender, age band, education level, sedatives, opioid drugs & alcohol, co-morbidities, presence of chronic pain inflammatory arthritis vs. osteoarthritis)
  • Is it feasible to track cognitive function before and after surgery remotely (with an app or PC-cased tool) in this population? 



[1]  Evered LA. What can population data tell us about anesthesia and cognition in the (vulnerable) older patient? Anesth Analg. 2017. 124 (4):1036-1038

[2]  Scott JE, Mathias JL, Kneebone AC. Postoperative cognitive dysfunction after total joint arthroplasty in the elderly: a meta-analysis. J Arthroplasty. 2014. 29 (2):261-7.e1

For more information about this project, visit the SWARM website.