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) 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 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 including O2 peak <15 mL/kg/min and E/ 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.