Can CPET predict post-surgical outcomes?

Ventilatory inefficiency adversely affects outcomes and longer-term survival after planned colorectal cancer surgery R. Jonathan et al British Journal of Anaesthesia Volume 123, Issue 2, Pages 238-245 (August 2019) DOI: 10.1016/j.bja.2019.01.032

Background

  • In UK 90-day mortality rate after colorectal cancer surgery has decreased from 3.8% in 2010/11 to 2.1% in 2014/15.
  • Cardiopulmonary exercise testing (CPET) is often used as an objective method of assessing functional capacity. Impairment may be a result of cardiorespiratory disease
  • CPET provides a measure of aerobic fitness – by measuring oxygen uptake at anaerobic threshold (AT).
  • Ventilatory efficiency is defined by slope in the line created when minute ventilation is plotted against carbon dioxide excretion (VE/CO2).
  • Authors state that there are practical problems with using AT
    • Sometimes it is difficult to identify
    • AT may represent deconditioning or lack of activity
  • Advantages of using VE/VCO2
    • Easier to identify
    • It is a simple ratio without incorporating other figures
    • Raised value represents a genuine pathophysiological process

Aims

  • To explore the influence of CPET measured ventilatory inefficiency on both postoperative outcomes and the long-term survival of patients having colorectal cancer surgery

Method

  • The study was conducted at York University Hospital Trust
  • Retrospective analysis of prospectively collected data
  • Inclusion criteria:
    • Patients presenting for cancer colorectal surgery who were referred to pre-assessment & CPET between 2004-2016
    • >55 years old
  • Exclusion criteria:
    • Unable to exercise
    • Benign disease
    • Did not proceed to surgery
  • Outcome data
    • Primary outcome measure was 90-day mortality after surgery
    • Secondary outcome measure unplanned ICU/HDU admission post-op

Results

  • 1375 met inclusion criteria
  • Overall mortality at 90 days was 3%
  • Anaerobic threshold was found not to be significantly predictive of 90-day mortality (p=0.27)
  • VE/VCO2 (p=<0.001) and age (p=0.004) were significantly predictive of 90-day mortality
  • Being male and over 80 years old independently associated with 90-day mortality
  • Overall survival 86.9% at 2 years and 64.5% at 5 years
  • 10% of total cohort had undiagnosed ventilatory inefficiency
  • Only VE/VCO2 >39 was significantly associated with death after unexpected CC admission

Strengths of Study

  • Large well powered study
    • Patients had a single surgical diagnosis
    • Results related to the question posed

Weakness of Study

  • Retrospective, single centre study
    • Low prevalence of lap-assisted procedure (21.2%) due to time frame over which the study was conducted
    • Unable to show independent effect of low AT on outcomes
    • Submaximal testing used which suggests there could be variability in operator confidence at finding AT value
    • Design could not be blinded at result of CPET required for decision making
    • Potential for performance bias exists with surgical studies
    • No detail of
      • Anaesthetic techniques
      • Grade of anaesthetist
      • No detail of what nursing enhanced unit practically meant for patients and its differences from critical care
    • All causes of death at 2 and 5 years included, which may have included causes unrelated to the recovery from cancer surgery
    • Highly detailed descriptions of statistical tests used but some omissions in reporting exact figures of p values

Conclusion

The authors have presented a large study which successfully aimed to explore the effect of ventilatory inefficiency on postoperative outcome of patients who underwent cancer surgery. The well powered study showed that the CPET measured variable is significantly associated with 90-day mortality. The study also remarkably found AT to not be statistically significantly associated with the same outcome. A variable that is often used to make decisions regarding patient’s fitness for surgery.

Unfortunately, weaknesses in the study included its retrospective nature being set in a single centre. The authors are commended for demonstrating the importance of looking at multiple factors including the CPET variable of VE/VCO2 and the patients medical history when planning post-operative care.

Summary by Dr Sarah Babatunde

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