TAAA surgery and CPET
While there is clear justification for the integration of CPET into
perioperative risk assessment for open TAAA, there are surprisingly few
studies in the published literature. Hornsby et al . used CPET
postoperatively only to assess exercise tolerance following open TAAA or
type A dissection repair28. CPET was analysed
retrospectively or performed three months following open repair and
identified that (median) V̇ O2PEAK was reduced by
36% after type A aortic dissection repair. This highlights the critical
increase in metabolic demand driven by the need to increase vascular
O2 delivery to support the additional cellular
bioenergetic demands incurred by surgery to ensure successful
recovery29. If the patient is unable to fulfil this
metabolic demand (i.e. CRF is inadequate), the physiological ‘insult’
posed by TAAA surgery can subsequently lead to O2 debt
that can overwhelm the patient and result in organ failure and death30.
In the present study, we chose to differentiate between those patients
with and without ‘adequate’ CRF based on the ‘cut-off’ metrics
originally established by Weber and Janicki16 in heart
failure patients and later implemented by Older et
al.17 specifically V̇ O2-AT
< (unfit) or > (fit) 11 mL/kg/min. Older et
al.17 identified an 18% mortality rate in elderly
surgical patients considered unfit by this threshold compared to 0.8%
in fit patients. We further categorised patients based on CPET risk
through additional implementation of complementary biomarkers includingV̇ O2 peak <15 mL/kg/min andV̇ E/V̇ CO2-AT
>34 given their combined ability to distinguish the
‘at-risk’ patient and better predict post-operative survival following
AAA surgery31. However, it is important to emphasise
that ongoing research continues to better define threshold metrics to
further optimise risk prediction models and this is especially relevant
for TAAA patients given the magnitude of the surgical ‘hit’ encountered.
Furthermore, CRF (and corresponding risk) stratification needs to be
based not on a single binary cut-off but rather a range of values for
any given dynamic CPET metric given the inherent (and extensive)
biological variation13 and this remains to be
established for the ‘high-stakes’ TAAA patient.
Importantly and in stark contrast to the present study, none of these
researchers have reported the clinician’s initial views prior to
surgery. There are understandable if not unavoidable limitations to what
a clinician might gain from the very first review of a patient, often
without a thorough knowledge of past medical history. Initial
information is oftentimes dictated by loose ‘impressions’ of cognitive
function, body habitus, strength of handshake and general nutritional
status32. Our findings highlight that ICE is indeed
unreliable compared to CPET metrics with the danger of underestimating
patient risk. This has implications when determining the appropriate
level of postoperative care after TAAA surgery notwithstanding the
potential for medico-legal complications.
Clinical assessment from the end of the bed will undoubtedly benefit
from more comprehensive physiological testing. This is particularly the
case for increasing numbers of patients with TAAA who are considered for
endovascular rather than open surgery33. It is likely
in the future treatment plans will incorporate both open and
endovascular approaches for intervention and this may even be
incorporated in a staged manner34.