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Troncone et al. Vessel Plus 2023;7:14 https://dx.doi.org/10.20517/2574-1209.2023.08 Page 11 of 15

repair, representing a distinct inherent disadvantage. The degree of hypothermia has known sequelae,
including bleeding and coagulopathy, exacerbated by the degree of heparinization needed for CPB and the
[25]
duration of surgery required to achieve thermic extremes . Pulmonary injury can occur due to both cold
temperatures and retraction to the heparinized lung during DHCA, and the systemic inflammatory
response of cardiopulmonary bypass is exageerated with DHCA, as the blood exposure to the bypass circuit
[9]
is necessarily increased as a function of the time required for cooling and subsequent re-warming .
Inherent in this disadvantage is the increased operative times due to cooling and re-warming. Air and
coronary artery embolism are risks associated with DHCA due to an open aorta without cross-clamp
protection .
[12]

As DHCA requires CPB, there are risks manifest to the selected method of placing the patient on pump and
the resultant necessity of managing hemodynamics with extracorporeal support during while on CPB. As
DTA and TAAA repair are performed via left thoracotomies, when circulatory support is desired, this is
most often accomplished with femoral cannulation and resultant retrograde arterial flow. With femoral
cannulation, there are substantive risks of retrograde embolization of aortic air and debris, exacerbated by
[8]
the increased amount of time required to use retrograde perfusion both during cooling and re-warming .
When femoral cannulation is used in combination with DHCA, however, one can take advantage of the
open proximal aortic near the end of the completion of the proximal anastomosis by infusing the venous
line to flush debris from the graft. Once the necessity for circulatory arrest is complete, typically upon
creation of the proximal anastomosis, most chosen grafts will have a perfusion side-arm which permits
application of a clamp on the graft just distal to both the proximal anastomosis and perfusion arm, allowing
for resumption of perfusion to the upper body and brain. Alternatively, arterial in-flow for CPB for these
cases may be axillary artery cannulation, eliminating the potential risks associated with retrograde aortic
flow. Central cannulation with access to the ascending aorta from a left thoracotomy can also accomplish
these goals but may be limited in certain patients who have had previous cardiothoracic surgery or have
challenging anatomy. Additional techniques may employ femoral arterial or distal aortic cannulation to
allow for perfusion to the lower body and spinal cord with the use of a distal aortic cross clamp for both
low-flow perfusion as well as the afforded protection of deep hypothermia.

Myocardial protection is an important consideration when using DHCA to facilitate DTAA or TAAA
repair. As described earlier in this paper, systemic hypothermia can serve to protect the myocardium
during circulatory arrest, however this may come at the expense of exposing to many points of potential
injury. During the process of cooling, the heart will experience perfused hypothermic fibrillation and
subsequent fibrillatory arrest and during re-waring there is typically spontaneous defibrillation around
26-26 degrees Celsius. These periods of time expose the heart to periods of perfusion to the
sub-endocardium that is impaired during CPB and hypothermic ventricular fibrillation, particularly in the
[3,7]
presence of ventricular hypertrophy . Additionally, periods of fibrillation may lead to ventricular
distention, further increasing the risk of myocardial injury. This is in addition to the period of non-perfused
hypothermic fibrillatory arrest during periods of DHCA for creation of the proximal anastomosis. All the
above are avoided with other forms of corporal protection that do not involve either deep hypothermic or
circulatory arrest, maintaining cardiac perfusion with native cardiac output. While myocardial protection
can be augmented when DHCA is utilized with any of aortic root occlusion balloons with infusion of
cardioplegia, transjugular-placed retrograde cardioplegia catheters, and systemically administered
potassium, these are clearly inferior to avoiding the necessity of protecting the myocardium at all.

Additional risks include the potential for cerebral edema and ischemia, as well as pulmonary edema. As
temperature drops, there is loss of cerebral autoregulation, and cerebral blood flow becomes dependent on