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Page 12 of 15 Troncone et al. Vessel Plus 2023;7:14 https://dx.doi.org/10.20517/2574-1209.2023.08

mean arterial pressure, increasing the risk of cerebral edema and increased cerebrovascular exposure to
[47]
potential emboli . Cerebral ischemia is a multifactorial consequence of DHCA, purportedly due to
excessive metabolic demand in the form of oxygen debt, microvascular no-reflow phenomena, and
derangements to cerebral autoregulation [48,49] . These alterations can persist well beyond the immediate post-
operative period and can also stochastically occur hours to days after the index operation even if immediate
absent. While there are qualitative concerns regarding neurocognitive performance after DHCA, more
recently published quantitative data suggests there is no difference compared to non-DHCA patients
48
undergoing cardiac surgery. Pulmonary edema is a known consequence of CPB utilization due to
ischemia-reperfusion injury; this is exacerbated with the use of DHCA due to duration of CPB, as well as
temperature injury along with the risks of pulmonary contusion [23,50] . The incidence of tracheostomy is up to
[39]
9% in patients undergoing TAAA repair with DHCA .

OUTCOMES
The effectiveness of DHCA as a strategy of organ protection to facilitate complex aortic reconstruction is
primarily because of temperature reduction of decreasing organ metabolic rate, shielding the tissue from the
detrimental effect of ischemia. Most surgical strategies using DHCA include reperfusion of the brain and
upper body after proximal anastomosis by using either axillary artery cannulation or a side branch of the
newly placed aortic graft and placing a clamp distally on the graft. However, there is variable techniques
described in the literature as to whether re-warming is initiated at this point, or deep hypothermia is
maintained for distal organ protection despite cross-clamp and resumption of circulation to the upper body.
If deep hypothermia is continued, so too are the inherent risks associated. The benefits of avoiding proximal
and/or sequential aortic cross-clamping, with the inherent need to mobilize and dissect around the aorta, as
well as maintenance of a bloodless field are well-described and can also be extrapolated from the data of
[49]
DHCA use with proximal aortic repairs . Despite the robust literature on the safety and efficacy of DHCA
for aortic surgery, there are numerous proponents of alternate techniques that involve proximal aortic
cross-clamping and distal perfusion, with or without adjuncts including sequential aortic clamping, milder
hypothermia, cerebrospinal fluid drainage, epidural cooling, intrathecal papaverine, and cold renovisceral
vessel perfusate, amongst others . Conceptually, these techniques avoid the risks of profound hypothermia
[49]
as well as circulatory arrest. These include partial cardiopulmonary bypass using femoral venous
cannulation as well as left-heart bypass, both of which are performed with a beating heart and the presence
of a proximal cross-clamp. The efficacy and outcomes of DTA and TAAA repair using DHCA must be
evaluated both in isolation as well as in reference to these alternative repair strategies. Kouchoukos et al.
present ed their 30-year experience using DHCA on TAAA repair, analyzing early 30-day outcomes on 285
patients, publishing their rates of post-operative stroke, spinal cord injury, and permanent end-organ
dysfunction, amongst the lowest in the literature for open surgery on the thoracoabdominal aorta . A
[39]
meta-analysis of nearly 10,000 patients undergoing open TAAA repair using various techniques to mitigate
organ system injury demonstrated an early 30-day mortality of 11.26%, comparable to the published results
from Kouchoukos of 7.4% . When directly assessing the outcomes of DTA/TAAA repair between DHCA
[3]
and non-DHCA techniques, it is important to consider the inherent limitations of comparing the two. First
and foremost, there have been no randomized clinical studies prospectively assessing the outcomes of these
two techniques on comparable patient populations. Most studies are limited to retrospective single-centre
reported outcomes, and the meta-analyses that coalesce their outcomes. The decision to pursue one
technique over another is often due to differing institutional approaches to certain anatomic factors or
disease extent, as well as surgeon preference, co-morbid patient factors, and potentially the emergent nature
of the repair. Weiss et al. conducted a propensity score-matched comparison of deep versus mild
hypothermia for TAAA repair . They assessed 90 patients for reversible and permanent outcomes,
[25]
including renal and liver failure, paraplegia and 30-day mortality, finding an improved postoperative