Author: Michael Vlessides
The results of an international prospective cohort study have made one thing very clear: Subjective preoperative assessment by physicians does not accurately identify patients with poor fitness who would be at greater risk for morbidity and mortality. More objective measures are much better at predicting postoperative complications.
“Just about every anesthesiologist or perioperative physician assessing a patient for major surgery asks that patient how far they can walk, how many flights of stairs they can climb, and what kinds of activities they can do,” said Duminda Wijeysundera, MD, PhD, an associate professor of anesthesia at the University of Toronto. “And we do that to make a judgment about what we think the patient’s functional capacity or fitness might be.
“That being said, if you look at the limited current data, there are some potential important limitations with our current approaches,” Dr. Wijeysundera continued. “First, our estimates of functional capacity may not actually agree well with objectively measured functional capacity. Secondly, there are some data that would suggest that subjectively assessed functional capacity doesn’t predict outcomes very well.”
Before surgery, participants also completed the Duke Activity Status Index (DASI), cardiopulmonary exercise testing to measure peak oxygen consumption (VO2 peak), and blood testing to measure N-terminal pro-B-type natriuretic peptide (NT pro-BNP). The study’s primary outcomes were 30-day death or myocardial infarction, as well as secondary outcomes of one-year death, moderate to severe postoperative complications, and 30-day death or myocardial injury.
“There’s no single blood test that actually measures functional capacity, but we thought the most promising indirect measure might actually be a natriuretic peptide,” Dr. Wijeysundera explained.
Anesthesiologists Inaccurate in Judging Fitness
As Dr. Wijeysundera reported at the 2018 annual meeting of the International Anesthesia Research Society (abstract PA161), 1,378 patients completed the one-year follow-up. By 30 days after surgery, five participants (0.4%) had died, 28 (2%) had experienced death or myocardial infarction, and 176 (13%) had experienced death or myocardial injury. In addition, 194 patients (14%) suffered in-hospital moderate to severe complications, while 38 (3%) died within a year of surgery.
Perhaps not surprisingly, the study found that subjective assessment—either on its own or after adjusting for other factors—was not associated with any outcomes. For VO2 peak, on the other hand, a statistically significant adjusted association (P=0.007) and significant risk reclassification (P=0.008) were observed only with respect to moderate to severe complications.
By comparison, the DASI showed statistically significant adjusted associations with 30-day death or myocardial infarction (P=0.03), and 30-day death or myocardial injury (P=0.05). The test also showed significant risk reclassification with 30-day death or myocardial injury (P=0.004).
Similarly, NT pro-BNP concentrations showed statistically significant adjusted associations with one-year death (P=0.001) and 30-day death or m yocardial injury (P=0.003). The blood test also showed significant risk reclassification with both one-year death (P=0.02), and 30-day death or myocardial injury (P=0.02). “The one-year death findings are consistent with what we know in the nonoperative setting,” Dr. Wijeysundera said.
“We also found that peak VO2 predicted major moderate to severe postoperative complications, the majority of which were actually noncardiovascular events,” he added. These complications were largely respiratory and infection related.
These findings, the researchers concluded, do little to support the use of physician assessment of functional capacity. “I think the clearest statement from this study is that if your current approach for judging preoperative functional capacity is subjective assessment, you should simply abandon it,” Dr. Wijeysundera said. “And if you’re thinking about cardiac risk assessment, there are two alternatives to consider, perhaps separately or in tandem: The DASI questionnaire is a very simple addition to clinical practice, or NT pro-BNP as an alternative.
“Finally, in select patients where you want to predict major postoperative complications, selective exercise testing with measurement of VO2 peak is a reasonable alternative.”