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Page 2 of 21 Calafiore et al. Vessel Plus 2023;7:18 https://dx.doi.org/10.20517/2574-1209.2023.42

INTRODUCTION
The introduction of straight hypothermic circulatory arrest (CA), at 20 °C or below, was the strategy that
allowed the diffusion and the improvement of the results of the surgical repair of the aortic arch. The
problem of cerebral protection was explored with attention, due to the relatively high incidence of
neurologic dysfunctions (NDs), permanent neurologic dysfunctions (PNDs), or temporary neurological
dysfunctions (TNDs). Slowly, cerebral perfusion (CP), retrograde cerebral perfusion (RCP) or antegrade
cerebral perfusion (ACP), selective antegrade cerebral perfusion (SACP) or unilateral cerebral perfusion
(UCP) was added to deep hypothermic circualtory arrest (DHCA) to increase the safe time of surgery and,
at the same time, the confidence of surgeons.

Over time, the concept of increasing the temperature to reduce cardiopulmonary bypass (CPB) time was
pursued and the temperature at which the circulation was stopped progressively increased, reaching 28°C
[moderate hypothermic circulatory arrest (MHCA)] or even higher temperatures [mild hypothermic
circulatory arrest (MiHCA)]. It was evident the necessity to add ACP as cerebral protection, because, at that
temperature, the safe time for the brain is very short.

The temperature limits for CA definition have recently been set in a consensus paper . The different grades
[1]
of hypothermia were defined as profound (≤ 14 °C), deep (14.1-20 °C), moderate (20.1-28 °C) and mild
(28.1-34 °C). Nevertheless, the definition of the intervals is not uniform and can generate
misunderstandings.

Then, the strategies of cerebral protection are a mixture of temperature and CP. CA can be instituted at
different temperatures (from 18-20 °C to 28 °C) using no CP, UCP (with/out direct cannulation of one or
two arteries), SACP (direct cannulation of two or three arteries), or RCP. Whereas no cerebral perfusion
(straight DHCA) or RCP is performed at low temperatures (18-20 °C), ACP can be performed at any
temperature (from 18-20 °C to 30 °C).

The advent of CP separated the CA time into two parts, one related to the brain and the other to the lower
body. The cerebral CA time can vary from 0 to the full CA time, while the lower body CA normally includes
the full CA period. Recently, the possibility of perfusing the lower body through the femoral artery when a
frozen elephant trunk (FET) is used, using a balloon as an occluder, has been proposed , but it is still
[2,3]
under investigation.

A recent survey showed that, in Europe, DHCA alone is rarely used (6% of the cases in acute aortic
[4]
syndromes and 2% in chronic cases), bilateral SACP is used in 53% of acute and in 65% of chronic, UCP in
38% of acute and 33% of chronic, RCP in 3% of acute and 0% of chronic. In one-third of the cases, the
temperature was below 22 °C (till 15°) and in the remaining two-thirds included between 22 °C and 26 °C.
Rarely the temperature was kept above 30 °C.

In the US, the STS database was analyzed in two different reports. In 7,830 chronic aortic pathologies, no
CP was used in 32.7%, ACP in 43.0% and RCP in 24.3% of the patients. The temperature was on the low
side, the highest median being in the ACP group (22.6 °C, 19.9-25.7) . In 6,387 patients with ascending
[5]
aorta dissection (AAD), no CP was used in 31.2%, ACP in 46.2% and RCP in 22.6% of the patients. Again,
the temperature was on the low side, the highest median being in the ACP group (22 °C, 18.4-25) . The STS
[6]
database, although important to give an idea of the results, limits the possibility of analysis, as many data on
the temperature were missing (27.5% and 28%, respectively), the definition of stroke was not clear , and the
[7]