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Page 8 of 15 Troncone et al. Vessel Plus 2023;7:14 https://dx.doi.org/10.20517/2574-1209.2023.08

accomplished at the completion of the anastomosis to prevent cerebral air embolism. When re-perfusing
the upper body with the perfusion limb of the aortic graft which is higher than the patient’s head, there is a
risk of debris or air embolization that may be mitigated by re-perfusing from the axillary artery which
[38]
would be lower than the graft and native aorta and thus better positioned to flush debris and air . Thus,
the left axillary artery can achieve similar results, although arguably still providing retrograde flow to the
carotid vessels.

Corporal and spinal cord protection are also provided using deep hypothermia as a direct result of
[39]
suppression of oxygen demand and metabolic requirements . Several adjuncts can be using in
combination with deep hypothermia for both visceral and spinal cord protection. Regarding the viscera,
these include sequential clamping and maintaining perfusion with passive arterial shunting, LHB or CPB. If
sequential clamping is not feasible, using individual catheters during LHB or CPB can perfuse target visceral
vessels . Regarding spinal cord protection, adjuncts include distal aortic perfusion in the form of LHB or
[40]
CPB, utilizing sequential aortic clamping for immediate re-perfusion of reimplanted spinal arteries,
cerebrospinal fluid drainage, central neurologic monitoring, and a host of potential pharmacologic agents .
[41]
As the brain is the most sensitive organ to ischemia, ensuring maximal attenuation of oxygen demand and
metabolic rate with cooling is crucial prior to commencing circulatory arrest. There are a variety of
methods to ensure the adequacy of hypothermia prior to the commencement of DHCA, ranging from
allotting minimum periods of cooling time, various placements of temperature probes, the use of near-
infrared spectroscopy [NIRS], electroencephalographic monitoring [EEG]. Bispectral index, the most
common form of EEG utilization in aortic surgery, provides dual-channelled electroencephalographic data
processed via a proprietary algorithm to provide a measure of cerebral metabolic activity, typically reaching
a baseline of zero upon achievement of adequate DHCA . The use of EEG to confirm adequate
[42]
hypothermia is not strictly necessary, as it has been demonstrated that most patients achieve EEG
quiescence after 45 min of cooling, correlating with a nasopharyngeal temperature of, on average,15 degrees
Celsius . NIRS utilizes the placement of optical sensors on the scalp to measure oxygen saturation in
[43]
vessels up to a depth of 20-40 mm; while its use cannot give information on the adequacy of cerebral
cooling to commence DHCA, it can be used to assess the adequacy of antegrade cerebral perfusion in
[6]
maintaining cerebral oxygenation when such perfusion adjuncts are used . Typically, two sites are used for
temperature monitoring-this is most often the bladder and the nasopharynx, most accurately reflective of
the body and brain, respectively . EEG, typically at nasopharyngeal temperatures between 15 to 18 degrees
[6]
Celsius, is isoelectric, or “silent”, indicating cerebral quiescence . At this point, certain centers pack the
[9]
head with ice prior to commencing circulatory arrest to maximize cerebral cooling, and patients are
typically placed in Trendelenburg position; if a left ventricular vent is in place, it is clamped to avoid
aspirating air into the proximal aorta, and the surgical field can be flooded with carbon dioxide to also
[9]
mitigate the risk of air embolism . Once the proximal anastomosis is complete and there is no longer need
for circulatory arrest, the newly anastomosed graft can be clamped and circulation restored by either a
perfusion limb from the graft, or if used, upper body cannulation sites. At this point, the need for profound
hypothermia is re-assessed after the restoration of circulation. For more extensive TAAA repair requiring
spinal artery and visceral vessel reconstruction, rewarming can be delayed until after this is performed to
[9]
maximize end-organ protection .

ADVANTAGES
There are numerous advantages and disadvantages inherent in the use of DHCA for the repair of DTAs/
TAAAs, which will be both delineated below, as well as listed in Table 1.