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Calafiore et al. Vessel Plus 2023;7:18 https://dx.doi.org/10.20517/2574-1209.2023.42 Page 15 of 21

[8]
50 min. It is noteworthy that the STS database, even if collecting data from low-volume Centers as well ,
reports very low CA times. Even if it can happen to face complex and unexpected surgical situations that
deserve longer CA time, it is difficult to understand routine CA times longer than 60 min, as reported by
some Authors [34,111] . Given that aortic arch typically necessitates a CA time of 40 min or less in the majority
of cases, waiting for randomized controlled trials (not easy to perform) is not a practical solution. Therefore,
each surgical team has to devise its own strategy and operate accordingly, systematically analyzing and
addressing any emerging issues as they arise.

The literature shows that neurological outcome is not related to the temperature. Recently, two papers
analyzed the STS database to evaluate the incidence of NDs after circulatory arrest. Seese et al. reported
3,898 patients who underwent elective hemiarch replacement with a median CA time of 19(14-27) min and
[112]
a median temperature of 24.9 °C (22-27.5) . All of them had ACP, but without specific details. They found
that CA time was longer in patients where the nadir temperature was ≤ 20 °C. Overall prevalence of NDs
was 4.2% (3.9% PND and 0.3% TND), 1.8% had encephalopathy, 0.3% SCI and 6.1% any ND. The adjusted
analysis showed that the neurologic and hemiarch composite outcome was similar independently from the
temperature, whereas early mortality was lower in the higher temperatures, reflecting possibly a lower
technical difficulty. A similar study was performed from the same database by Ghoreishi et al., who reported
[113]
8,937 who underwent repair for AAD . Stroke prevalence was 13%. Straight DHCA was used in 29% of the
patients and was not a risk factor for postoperative stroke. Similar results were obtained by the German
Registry for AAD, where stroke prevalence was 9.5% and multivariable analysis showed that additional CP
[114]
techniques did not add to straight DHCA .
Other aspects of arch surgery are still unanswered. Bleeding is often considered a complication of deep
hypothermia. However, it is often the consequence of a long operation with multiple sutures. In a
multicenter study, where straight DHCA was compared with MHCA with ACP , the rate of re-
[106]
[115]
exploration for bleeding was similar. The same outcome was reported by other Authors . 24-h bleeding
was also similar, as reported by many Authors [106,116] . Others analyzed patients operated on with MHCA and
MiHCA and did not find any difference in re-exploration for bleeding . Even if it is possible to find
[117]
[118]
conflicting results in the literature , good outcomes can be obtained with a careful strategy, independently
from the temperature reached during surgery.

The effects of HCA on the kidney are widely studied. Even if lowering the temperature seems to be
protective for renal function, the prevalence of acute kidney injury (AKI) or the need for temporary dialysis
does not reflect this assumption completely. In conventional cardiac surgery, the prevalence of AKI,
regardless of its severity, can range from 50% to 81.2% , even if there are possible differences due to
[119]
[120]
AKI definitions. Following the STS definition (3-fold increase in creatinine level, creatinine level > 4 mg/dL,
or requirement for dialysis), in 3,889 patients operated on without HCA, AKI prevalence was 2%, 71% of
whom needed dialysis. Nevertheless, even mild AKI has been found to be a risk factor for all-cause
[121]
mortality . In patients where HCA was used, many Authors found that temperature was not a risk factor
for AKI or dialysis [118,122-125] . Amano et al. reported a prevalence of AKI of 26% and a need for dialysis of 8.6%
in 191 cases operated with MHCA for AAD . Multivariable analysis showed that increased lower body
[126]
ischemic time was a risk factor for AKI. On the other side, a meta-analysis from Cao et al. showed that
[127]
MHCA reduced the incidence of AKI and dialysis if compared with DHCA . Opposite results were found
by our group , where MHCA was a risk factor for dialysis at weighed logistic regression and the incidence
[106]
of any AKI was 16.9% in DHCA group and 47% in MHCA group, respectively.