Integrating Accelerometers and More in Your Surgical Risk Assessment
How do you typically assess a patient’s functional capacity, or their ability to perform submaximal physical daily activities prior to surgery? As you are aware, this capacity plays a major role in the perioperative cardiovascular evaluation (as well as the perioperative and postoperative management) of your surgical patients (excluding your cardiac surgery patients).
Many of us rely too heavily on the formalized questionnaire (i.e., the Duke Activity Index Status), and not enough on other, more objective methods of testing. Many of us rely on the power of standardized questions, i.e., from the Physical Functioning Questionnaire (PFQ):
- “Do you have difficulty walking up 10 stairs?”
- “Do you have difficulty walking for a quarter mile / two to three blocks?”
- “Do you have difficulty walking between rooms on the same floor?”
Today, the time has come, and evidence has shown that these questions (the questionnaire method) are simply inadequate and must be replaced by more stringent and helpful methodologies for accurately assessing noncardiac surgical patient risk.
Why Does Self-Reporting Result in Unclear Results?
Well, for one, patients are human beings, and they often tend to overestimate (or underestimate) their abilities. Patients do not, and cannot, always accurately report their physical capabilities and limitations. For example, in a recent study, accelerometer-based physical activity measurements were shown to be more accurate than answers to self-reported physical function questions.[i] As with any self-reporting methodology, human beings have the tendency to “fudge” — to downplay or to play up the true (factual) narrative of their lives. Therefore, it is the role of the anesthesiologist and medical practitioner to ensure that this does not happen.
“Patients may inaccurately self-report for other reasons as well including poor recall, social desirability, and misinterpretation of questions.”[ii]
While self-reporting can play a helpful role in validating your patient’s functional capacity, it should not serve as your sole source of information.
Ask the 10 Stairs Question, but Test the Results
We are not advocating that you completely eliminate your patient preop questionnaires, for they do have their benefits and their place. For example, a recent study found that “self-reported ability to walk up 10 stairs without difficulty best predicted the presence of a 2-min bout of moderate-vigorous physical activity during a week of accelerometer wear among adult participants with at least one Revised Cardiac Risk Index condition.”
However, despite this question’s high sensitivity, this single question “remains insufficiently specific to identify patients with a poor functional capacity.”[iii] Therefore, the ability to identify these patients remains your primary responsibility.
Here are two practices to consider including in your noncardiac surgical patient risk assessment in order to test the results of the self-reporting questionnaire.
Consider the Six-Minute Walking Test and the Accelerometer
At minimum, you can implement short exercise tests such as a six-minute walking test. For example, in this test, “distance is strongly correlated with the ventilatory threshold and distance can be used to risk stratify patients before major noncardiac surgery.”[iv]
Secondly, you might include an accelerometer in your practice. Preoperative accelerometers have been shown to improve patient risk assessment and perioperative care. “Accelerometers can detect the presence of moderate-vigorous physical activity, which includes the 4 metabolic equivalents threshold.”[v]
These more objective measures — accelerometers and short exercise tests — are absolutely essential for practitioners who desire more accurate perioperative risk stratification. So, despite the challenges of increased time, personnel and cost, think about how you can begin to include these measures in your practice today.
[i] Troiano RP, Berrigan D, Dodd KW, Mâsse LC, Tilert T, McDowell M: Physical activity in the United States measured by accelerometer. Med Sci Sports Exerc 2008; 40:181–8
[ii] Kowalski K, Rhodes R, Naylor PJ, Tuokko H, MacDonald S: Direct and indirect measurement of physical activity in older adults: A systematic review of the literature. Int J Behav Nutr Phys Act 2012; 9:148
[iii] Daniel S. Rubin, Megan Huisingh-Scheetz, Anthony Hung, R. Parker Ward, Peter Nagele, Ross Arena, Donald Hedeker; Accuracy of Physical Function Questions to Predict Moderate-Vigorous Physical Activity as Measured by Hip Accelerometry. Anesthesiology 2019;131(5):992-1003. doi: https://doi.org/10.1097/ALN.0000000000002911.
[iv] Sinclair RC, Batterham AM, Davies S, Cawthorn L, Danjoux GR: Validity of the 6 min walk test in prediction of the anaerobic threshold before major non-cardiac surgery. Br J Anaesth 2012; 108:30–5; Shulman MA, Cuthbertson BH, Wijeysundera DN, Pearse RM,Thompson B,Torres E,Ambosta A,Wallace S, Farrington C, Myles PS; Measurement of Exercise Tolerance for Surgery Study Investigators: Using the 6-minute walk test to predict disability-free survival after major surgery. Br J Anaesth 2019; 122:111–9
[v] Troiano RP, et al.