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Page 2 of 15 Troncone et al. Vessel Plus 2023;7:14 https://dx.doi.org/10.20517/2574-1209.2023.08

and morbidity including spinal cord ischemia, cardiac, pulmonary, and neurologic events, respiratory
[3]
compromise, and renal dysfunction remain significant . Inherent in the conduct of open repair of DTA/
TAAA is a period during which there is regional ischemia to the visceral organs; and most of the variability
[4]
between surgical technique lies in the method selected to provide organ protection . The rate of
renovisceral organ dysfunction after DTA and TAAA repair is widely reported in the literature, depending
on the clinical and biochemical criteria used to define each, however it ranges from 21%-63% . Other organ
[5]
systems are affected by periods of ischemia, notably the spinal cord; rates of spinal cord injury, both
temporary and permanent, have been reported as high as 20% for open repair of DTA/TAAA, with the
caveat that these rates are most affected by the extent of repair . While it is difficult to ascertain the true
[6]
value due to the heterogeneity of disease extent, indication for surgery, replacement techniques, adjunctive
protection strategies, and the potential for improved outcomes from experiences centres, mortality rates
typically range from 5 to 33% .Pertinent to the discussion on the use of deep hypothermic circulatory arrest
[7]
in the repair of DTA and TAAAs is the specific considerations of aortic cross-clamping. Fundamentally, the
application of an aortic cross-clamp leads to hemodynamic sequelae proximal to the clamp, and ischemic
sequelae distal to the clamp, as well as potential clamp-related complications such as vascular trauma,
iatrogenic aortic dissection, and atheroembolism. Surgical techniques aimed at organ protection primarily
seek to reduce the impact of distal ischemia imposed on the body by the application of an aortic cross-
clamp, the most intuitive approach being the continuation of blood perfusion to these organs despite the
interruption of native blood flow. This is accomplished by the utilization of either left-heart bypass (LHB)
or cardiopulmonary bypass (CPB), employing various cannulation strategies aimed at the maintenance of
perfusion distal to the aortic cross-clamp.

The rationale for using DHCA in TAAA repair are heavily calcified and non-clampable distal aortic arch or
proximal descending thoracic aorta which include massive aneurysms with distorted anatomy or the need
to fenestrate a dissection flap in the aortic arch be facilitated by open endoluminal aortic exposure. To
facilitate overcoming these challenges for aortic replacement for DTAs and TAAAs is the use of CPB with
DHCA. Defined as the achievement of systemic temperatures between 18-24 degrees Celsius accomplished
using cardiopulmonary bypass, it facilitates cerebral, cardiac and organ protection during operations
necessitating cessation of systemic circulation.

An assessment of the literature on techniques for DTA/TAAA repair reveals some selection criteria
regarding the use of DHCA. In summary, the main identifiable criteria that support the use of DHCA
include severe aortic atherosclerosis which would increase embolic risk with clamping, contained arch
aneurysm rupture, as well as a porcelain aorta that precludes cross-clamping. Other potential factors may
include elevated risk of spinal cord ischemia as well as reduced preoperative renal function, as DHCA may
provide superior spinal cord and visceral organ protection than other perfusion adjuncts at higher patient
[8]
temperatures . Additional factors to consider are if the patient has had prior central aortic procedures
performed, as the re-operative tissue may increase risk of injury to adjacent structures such as the
esophagus, bronchus, pulmonary arteries, and left recurrent laryngeal nerve . Furthermore, clamp-induced
[9]
aortic injury, retrograde aortic dissection from clamping, as well as massive, uncontrollable bleeding would
necessitate the use of DHCA. Beyond these, there are few clinical or patient factors reported for the
selection of DHCA use for these complex repairs. Pre-operatively identified reduced left ventricular ejection
fraction, as well as aortic valve insufficiency, may be negative predictive factors for utilizing DHCA. This is
due to multiple risks associated with using DHCA for DTA/TAAA repair: inadequate myocardial
protection during hypothermic fibrillatory arrest, hypothermic tissue damage and consequent myocardial
edema, prolonged CPB times because of cooling and re-warming and left ventricular distention which may
[8]
be because of aortic valve insufficiency . Various adjuncts can be used to monitor and avoid these