Safety and efficacy of mild hypothermic circulatory arrest with bilateral cerebral perfusion in acute aortic dissection surgery: a retrospective cohort study

Abstract

Background

Acute type A aortic dissection (ATAAD) is a life-threatening cardiovascular emergency requiring urgent surgical intervention, during which cerebral protection is paramount. In aortic dissection surgery, the moderate hypothermic circulatory arrest combination with unilateral selective antegrade cerebral perfusion is a commonly used cerebral protection strategy. However, compared with mild hypothermia, moderate hypothermia has drawbacks such as prolonged cardiopulmonary bypass time. Whether mild hypothermic circulatory arrest can overcome the disadvantages of moderate hypothermia and provide safe cerebral protection remains controversial. This retrospective cohort study aimed to assess the safety and efficacy of mild hypothermic circulatory arrest (Mild-HCA) with bilateral cerebral perfusion in surgeries for ATAAD.

Methods

From November 2022 to April 2025, 89 consecutive patients with ATAAD who underwent open surgical repair were retrospectively analyzed. Patients were categorized into two groups: a mild hypothermia with bilateral cerebral perfusion group (Group A, n=48) and a moderate hypothermia with unilateral cerebral perfusion group (Group B, n=41). Postoperative outcomes, including permanent neurological dysfunction (PND), temporary neurological dysfunction (TND) and other complications, were compared between two subgroups.

Results

There were no statistically significant differences between the two subgroups in the incidence of central nervous system complications or in-hospital mortality. However, patients in the Mild-HCA group had significantly shorter durations of cardiopulmonary bypass (CPB), mechanical ventilation, and intensive care unit stay compared with the moderate-HCA group (all P<0.05).

Conclusions

Mild-HCA with bilateral cerebral perfusion appears to be a safe and feasible strategy for surgical management of ATAAD offering the advantage of reduced perioperative support time without increasing neurological or mortality risks.

Highlight box.

Key findings

• In this retrospective cohort of 89 acute type A aortic dissection (ATAAD) patients, mild hypothermic circulatory arrest (≥30 ℃) combined with bilateral cerebral perfusion significantly reduced cardiopulmonary bypass time, ventilation duration, intensive care unit stay, and hospitalization time compared with moderate hypothermia with unilateral perfusion.

• No increase in major adverse events, including permanent neurological dysfunction, temporary neurological dysfunction, acute kidney injury, paraplegia, or mortality, was observed in the mild hypothermic circulatory arrest (Mild-HCA) group.

What is known and what is new?

• Hypothermic circulatory arrest with selective cerebral perfusion is essential for cerebral protection during aortic arch surgery, yet the optimal temperature strategy remains debated. Previous studies have shown comparable neurological outcomes between mild and moderate hypothermia; however, evidence regarding bilateral cerebral perfusion under Mild-HCA in ATAAD remains limited.

• Near-infrared reflectance spectroscopy is used to monitor cerebral perfusion in real time, ensuring the safety of intraoperative cerebral perfusion. The novelty of this study lies in the systematic evaluation of the safety and efficacy of the combined strategy of mild hypothermia with bilateral cerebral perfusion in ATAAD surgery. For the first time among similar studies, it demonstrates advantages in reducing perioperative support time and improving resource utilization, without increasing the risk of complications.

What is the implication, and what should change now?

• Mild-HCA with bilateral cerebral perfusion may be considered a feasible and effective cerebral protection strategy for ATAAD surgery, particularly when aiming to shorten cardiopulmonary bypass duration and reduce perioperative physiological stress.

• Real-time monitoring of cerebral oxygenation and tailored perfusion approaches should be emphasized to ensure safety when adopting higher temperature arrest strategies.

Introduction

Acute type A aortic dissection (ATAAD) is a life-threatening cardiovascular emergency with an annual incidence of approximately 2–4 cases per 100,000 individuals (1). The disease progresses rapidly and is associated with exceptionally high mortality, approaching 50% within 48 hours if left untreated (2). Contemporary high-quality clinical studies report an operative mortality of 10–20% for ATAAD. However, this rate is highly dependent on the presence of patient-specific high-risk features, most notably malperfusion syndrome. Neurological complications are among the most severe perioperative adverse events in ATAAD, contributing substantially to morbidity and mortality. The reported incidence of central nervous system dysfunction ranges from 10% to 30% (2). Furthermore, the risk of intraoperative cerebral ischemic injury increases with advancing age and the presence of atherosclerotic disease (3-5), emphasizing the critical importance of effective cerebral protection during surgery (6,7). Evidence indicates that advanced age and atherosclerosis, particularly involving the carotid arteries or aortic arch, are well-established risk factors for neurological complications following aortic arch surgery, with atherosclerosis recognized as an independent risk factor (7).

Historically, deep hypothermic circulatory arrest (DHCA) has been the predominant and widely accepted standard for cerebral protection in open aortic arch surgery. Although newer strategies have emerged, DHCA remains commonly used in clinical practice and is still considered indispensable for certain aortic pathologies. However, with advancements in cerebral monitoring and perfusion techniques, surgical strategies have shifted toward the use of moderate-hypothermic circulatory arrest (Moderate-HCA) combined with selective cerebral perfusion. Despite these improvements, achieving moderate hypothermia still requires a prolonged cooling phase. Prolonged cardiopulmonary bypass (CPB) time is associated with an increased risk of systemic complications, including coagulopathy, greater transfusion requirements, systemic inflammatory response, renal dysfunction, pulmonary complications, and delayed postoperative recovery (8-10). Recent developments have raised interest in whether elevating the circulatory arrest temperature could provide adequate organ, particularly cerebral, protection while minimizing hypothermic exposure and shortening extracorporeal circulation time. This study hypothesizes that, compared with moderate hypothermia circulatory arrest combined with unilateral cerebral perfusion, mild hypothermia circulatory arrest combined with bilateral cerebral perfusion is non-inferior in terms of neurological outcomes and may offer advantages in perioperative efficiency. The present study aimed to evaluate the safety and efficacy of a cerebral protection strategy employing mild hypothermia (≥30 ℃) combined with bilateral cerebral perfusion during surgery for ATAAD, compared with moderate hypothermia with unilateral perfusion. We present this article in accordance with the STROBE reporting checklist (available at https://jtd.amegroups.com/article/view/10.21037/jtd-2025-1-2526/rc).

Methods

Ethical statement

The study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments. The study was approved by the Medical Ethics Committee of Anhui Chest Hospital (approval No. AHC-2022-011). and individual consent for this retrospective analysis was waived.

Patients

A retrospective analysis was conducted on 89 patients diagnosed with ATAAD who underwent surgical treatment in the Department of Cardiovascular Surgery at Anhui Chest Hospital between November 2022 and April 2025. The study size was determined by the number of consecutive eligible patients during the study period. Inclusion criteria were as follows: (I) diagnosis of ATAAD confirmed by computed tomography angiography (CTA) within two weeks of symptom onset; (II) age between 14 and 85 years; (III) undergoing open aortic surgery. Exclusion criteria were as follows: (I) preoperative history of cerebrovascular disease or coma; (II) preexisting chronic renal impairment; (III) preoperative internal carotid artery occlusion or thrombosis. The patient selection flowchart is shown in Figure 1. Detailed baseline clinical characteristics of all patients are summarized in Table 1.

Figure 1.

Patient selection flowchart. ATAAD, acute type A aortic dissection; HCA, hypothermic circulatory arrest.

Table 1. Preoperative patient data (n=89).

Variables	Mild-HCA (Group A, n=48)			Moderate-HCA (Group B, n=41)		P value
	Values	95% CI		Values	95% CI
Male	29 (60.4)	46.58–74.26%		27 (65.9)	51.28–80.42%	0.66
Age (years)	56.89±11.72	53.49–60.3		58.47±13.34	54.26–62.68	0.55
BMI (kg/m2)	26.83±5.38	25.27–28.39		26.1±5.36	24.41–27.79	0.52
Hypertension	32 (66.7)	55.63–81.87%		30 (73.2)	59.56–86.78%	0.64
Diabetes	8 (16.7)	8.34–30.00%		3 (7.3)	0–15.3%	0.21
Marfan syndrome	5 (10.4)	1.8–19.1%		3 (7.3)	0–15.3%	0.72
CHD	2 (4.2)	0–9.8%		2 (4.9)	0–11.5%	>0.99
Preoperative renal failure	1 (2.1)	0–6.1%		2 (4.9)	0–11.5%	0.59
Current smoking	15 (31.3)	18.1–44.4%		16 (39.0)	24.1–54.0%	NA
Aortic regurgitation (moderate or severe)	31 (64.6)	51.1–78.1%		29 (70.7)	56.8–84.7%	0.65
EF (%)	65.00±7.60	62.9–67.2		62.60±4.30	61.3–63.9	0.06
Ischemia symptoms of lower limbs and internal organs	1 (2.1)	0–6.1%		1 (2.4)	0–7.2%	>0.99

Values are presented as mean ± standard deviation or n (%). BMI, body mass index; CHD, coronary heart disease; CI, confidence interval; EF, ejection fraction; HCA, hypothermic circulatory arrest; NA, not applicable.

Surgical technique and extracorporeal circulation management

All procedures were performed under standard general anesthesia. Arterial pressures were continuously monitored via catheters placed in the left radial and left femoral arteries. Regional cerebral oxygen saturation (rSO₂) was continuously monitored using near-infrared reflectance spectroscopy (NIRS). All operations were performed by the same chief surgeon. The surgical approach consisted of total aortic arch replacement combined with descending aortic stent graft implantation through a standard median sternotomy. CPB was established via right atrial cannulation and right subclavian and/or unilateral femoral arterial cannulation. The target CPB flow rate was maintained at 2.0–2.4 L·min⁻¹·m⁻², and histidine-tryptophan-ketoglutarate (HTK) solution was used for myocardial protection. Systemic cooling was initiated after establishing CPB, during which proximal aortic repair was completed. Depending on the extent of aortic root involvement, the root procedure performed included the Bentall, David, Wheat, or Commando technique. In the mild hypothermia with bilateral cerebral perfusion group (Group A), nasopharyngeal temperature was reduced to 30–31 ℃ and bladder temperature to 30–31 ℃ before circulatory arrest. During mild hypothermic (≥30 ℃), bilateral cerebral perfusion was achieved via cannulation of the right common carotid (or right axillary) artery in conjunction with the left common carotid artery. Cerebral perfusion flow was maintained at 15–20 mL·kg⁻¹·min⁻¹. After achieving target temperatures, the aortic arch was opened to facilitate implantation of a descending aortic stent graft followed by distal anastomosis of a four-branched vascular graft. Once distal graft anastomosis was completed, lower body perfusion was re-established through one of the four graft branches or via the femoral artery. Reconstruction of the aortic arch branches proceeded sequentially in the following order: left subclavian artery, left common carotid artery, and innominate artery, concluding with proximal anastomosis of the four-branched graft. In the Moderate-HCA with unilateral cerebral perfusion group (Group B), the operative sequence was identical to that of Group A. However, when the nasopharyngeal temperature reached 25 ℃ and bladder temperature reached 25–28 ℃, unilateral cerebral perfusion was administered through the right axillary (or right common carotid) artery alone, with a flow rate of 5–10 mL·kg⁻¹·min⁻¹. Bilateral rSO₂ was continuously monitored using NIRS from the induction of anesthesia until transfer from the operating room. An absolute rSO₂ ≤55% or a >20% decrease from baseline was considered indicative of inadequate cerebral perfusion, prompting immediate adjustment of the cerebral protection strategy. Following completion of surgery, all patients were transferred to the intensive care unit (ICU) for postoperative management and monitoring.

Clinical variables

According to the International Consensus Guidelines (11), moderate hypothermia is defined as a nasopharyngeal temperature between 20–28 ℃, and mild hypothermia as a nasopharyngeal temperature between 28.1–34 ℃. The primary endpoint was the occurrence of major adverse events (MAEs), defined as any of the following: permanent neurological dysfunction (PND), thoracotomy, paraplegia, new-onset postoperative acute kidney injury (AKI) requiring continuous renal replacement therapy (CRRT), or death. PND was characterized by new postoperative focal neurological deficits confirmed by brain computed tomography (CT) or magnetic resonance imaging (MRI). Reversible postoperative delayed awakening, agitation, or transient delirium were classified as temporary neurological dysfunction (TND), provided that CT findings were normal and all symptoms resolved before discharge.

Statistical analysis

All statistical analyses were performed using SPSS version 22.0 (IBM Corp., Armonk, NY, USA). Categorical variables were expressed as counts and percentages, and comparisons between groups were performed using the Chi-squared test or Fisher’s exact test, as appropriate. Continuous variables were tested for normality using the Shapiro-Wilk test. Data following a normal distribution were presented as mean ± standard deviation ($\overline{x}\pm s$) and compared using the independent-samples t-test. Non-normally distributed data were expressed as median (interquartile range) [M (Q₂₅, Q₇₅)] and analyzed using the Mann-Whitney U test. A two-tailed P value <0.05 was considered statistically significant. There were no missing data for primary endpoints.

Results

Preoperative demographic and baseline characteristics were comparable between the two groups, with no statistically significant differences observed. A total of 90 patients underwent surgery during the study period. One patient, initially managed with moderate hypothermia and unilateral cerebral perfusion, required intraoperative conversion to bilateral cerebral perfusion due to inadequate left-sided cerebral oxygen saturation and was therefore excluded from the analysis. Ultimately, 48 patients were included in the mild hypothermia with bilateral cerebral perfusion group (Group A), and 41 patients in the moderate hypothermia with unilateral cerebral perfusion group (Group B). There were no missing data for baseline variables or outcome measures.

Compared with Group B, patients in Group A demonstrated significantly shorter total operative time, CPB duration, and aortic cross-clamp time (all P<0.05). Postoperative outcomes similarly favored the mild hypothermia group, with reduced durations of mechanical ventilation, ICU stay, and total hospitalization. In Group A, one patient died of postoperative circulatory failure, who had presented preoperatively with acute myocardial infarction and right coronary artery dissection involving the ostium. Another patient died from respiratory and circulatory failure secondary to aspiration pneumonia acquired after discharge while hospitalized at a local facility. In Group B, one patient died of perioperative myocardial infarction accompanied by respiratory and circulatory failure. There was no statistically significant difference in overall mortality between the two groups. Similarly, no statistical differences were observed in neurological complications, acute renal failure, and respiratory complications between the two groups. Group A had a statistically significant lower 24-hour drainage volume and platelet count compared to Group B (P=0.006 and P=0.03, respectively). Detailed intraoperative and postoperative data are summarized in Tables 2,3.

Table 2. Operative characteristics of 89 consecutive patients with ATAAD who underwent treatment using HCA and cerebral perfusion.

Operative characteristics	Mild-HCA (Group A, n=48)			Moderate-HCA (Group B, n=41)		P value
	Values	95% CI		Values	95% CI
Operation time (hours)	6.50±1.50	6.08–6.92		7.50±1.40	7.07–7.93	0.02
CPB time (min)	183.90±31.90	174.88–192.92		214.63±55.13	197.75–231.51	0.002
Cross-clamping time (min)	107.80±21.30	101.77–113.83		120.10±27.80	111.59–128.61	0.02
LBA time (min)	20.70±5.10	19.26–22.14		22.20±7.00	20.06–24.34	0.054
ACP time (min)	25.16±4.80	23.80–26.52		27.00±3.10	26.05–27.95	0.04
Nasopharyngeal temperature (℃)	30.5±0.3	30.42–30.58		25.1±0.6	24.92–25.28	<0.001
Bladder temperature (℃)	30.8±0.2	30.74–30.86		26.3±1.1	25.96–26.64	<0.001
Aortic sinus or aortic valve repair	15 (31.3)	18.1–44.4%		11 (26.8)	13.3–40.4%	0.36
Bentall procedure	12 (25.0)	12.8–37.3%		11 (26.8)	13.3–40.4%	0.83
CABG	2 (4.2)	0–9.8%		1 (2.4)	0–7.2%	>0.99

Values are presented as mean ± standard deviation or n (%). ACP, anterograde cerebral perfusion; ATAAD, acute type A aortic dissection; CABG, coronary artery bypass grafting; CI, confidence interval; CPB, cardiopulmonary bypass; HCA, hypothermic circulatory arrest; LBA, lower body arrest.

Table 3. Operative outcomes (n=89).

Operative outcomes	Mild-HCA (Group A, n=48)			Moderate-HCA (Group B, n=41)		P value
	Values	95% CI		Values	95% CI
Awaken time (h)	8.5 [5.5, 12.5]	7.08–9.92		11 [6, 14.25]	9.04–12.96	0.43
Ventilation time (h)	12 [9, 16.5]	10.46–13.54		15 [10, 25]	12.95–17.05	0.04
Duration of hospitalization (days)	17 [14, 19]	15.86–18.14		19 [15, 22]	17.77–20.23	0.006
ICU stay (days)	3 [2, 4]	2.51–3.49		4 [4, 6]	3.64–4.36	<0.001
Drainage in 24 h (mL)	588.65±181.72	535.91–641.39		669.82±274.5	583.18–756.46	0.007
RBC transfusion (U)†	4.5 [2, 7]	3.46–5.54		5 [4, 7]	4.38–5.62	0.19
FFP transfusion (mL)†	0 [0, 400]	−129.63 to 129.63		0 [0, 450]	−139.63 to 139.63	0.41
PLT transfusion (U)†	0 [0, 1]	−0.32 to 0.32		1 [1, 1.25]	0.78–1.22	0.03
PND	0 (0.0)	–		0 (0.0)	–	NA
TND	2 (4.2)	1.2–14.0%		2 (4.9)	1.3–16.5%	>0.99
Postoperative acute kidney injury	17 (35.4)	22.9–49.9%		18 (44.0)	29.6–59.2%	0.29
CRRT	2 (4.2)	1.2–14.0%		2 (4.9)	1.3–16.5%	>0.99
Re-intubation	1 (2.1)	0.4–11.1%		2 (4.9)	1.3–16.5%	0.59
Tracheotomy	0 (0.0)	–		1 (2.4)	0.4–12.6%	0.46
Paraplegia	0 (0.0)	–		0 (0.0)	–	NA
Thoracotomy	2 (4.2)	1.2–14.0%		1 (2.4)	0.4–12.6%	>0.99
Death in hospital	1 (2.1)	0.4–11.1%		1 (2.4)	0.4–12.6%	>0.99
Postoperative 30-day death	2 (4.2)	1.2–14.0%		1 (2.4)	0.4–12.6%	>0.99

Values are presented as median [interquartile range], mean ± standard deviation or n (%). TND was defined as the presence of reversible postoperative motor deficit, confusion, agitation, or transient delirium. The CT findings were required to be normal, with resolution of all symptoms before discharge. PND was defined as the presence of either new focal (stroke) or global (coma) permanent neurologic dysfunction. Postoperative AKI was defined based on the KDIGO criteria and was diagnosed when the postoperative creatinine increased by 1.5 times the baseline level or when the creatinine increased by 0.3 mg/dL within 48 hours after surgery. ^†, during surgery and the first 24 h after surgery. AKI, acute kidney injury; CI, confidence interval; CRRT, continuous renal replacement therapy; CT, computed tomography; FFP, fresh frozen plasma; HCA, hypothermic circulatory arrest; ICU, intensive care unit; KDIGO, Kidney Disease Improving Global Outcomes; NA, not applicable; PLT, platelet; PND, permanent neurologic deficit; RBC, red blood cell; TND, temporary neurologic dysfunction.

Only unadjusted comparisons were performed because baseline characteristics were balanced between groups and no major confounders showed significant differences.

Discussion

ATAAD remains a life-threatening cardiovascular emergency associated with high mortality rates. Despite advances in endovascular and hybrid techniques, open surgical repair continues to be the standard and most effective treatment for ATAAD. All procedures were performed by the same surgical team to minimize the influence of operator-dependent technical variability on operative time and patient outcomes, rather reflecting any uniqueness of the procedure itself. The aortic dissection surgery examined in this study represents a classic and widely reproducible technique, achievable even in lower-volume centers or non-specialized cardiac institutions. Among the many perioperative management challenges, organ protection, particularly cerebral protection, remains a central concern. Historically, DHCA was regarded as the most reliable cerebral protection strategy for open aortic arch surgery (12,13). Over the past two decades, many centers have progressively increased HCA temperatures, transitioning from deep to moderate and even mild hypothermia during aortic arch procedures (14). Compared with conventional moderate hypothermia, Mild-HCA offers several physiological and technical advantages. Higher perfusion temperatures shorten both CPB and rewarming times, thereby reducing the risks associated with prolonged extracorporeal circulation, such as coagulopathy, systemic inflammatory responses, and multi-organ dysfunction. In addition, recent studies have suggested that mild hypothermia may further decrease the incidence of postoperative neurological deficits and AKI (15,16). Consistent with these findings, the present study demonstrated that patients in the mild hypothermia group (Group A) experienced significantly shorter durations of mechanical ventilation, ICU stay, and overall hospitalization than those in the moderate hypothermia group (Group B). Moreover, the 24-hour postoperative drainage volume and platelet transfusion requirements were markedly lower in the mild hypothermia group, suggesting a beneficial effect on coagulation function and hemostatic stability.

The brain is highly sensitive to hypoxia and is particularly vulnerable to hypoperfusion, embolization, and hyperperfusion during CPB, all of which can adversely affect postoperative neurological outcomes (17-19). Accordingly, the optimal cerebral perfusion strategy during aortic arch surgery remains a topic of ongoing debate. A meta-analysis of 12 studies involving 4,547 patients compared the efficacy of unilateral versus bilateral cerebral perfusion in patients with ATAAD (20). While ACP has become the standard cerebral protection technique in most centers (21), the choice between unilateral anterograde cerebral perfusion (u-ACP) and bilateral anterograde cerebral perfusion (b-ACP) remains controversial. A multicenter retrospective study comparing unilateral and bilateral ACP during ATAAD surgery reported that both approaches are safe and effective, with u-ACP showing a lower incidence of post-perfusion complications (22). Other studies have also demonstrated comparable cerebral protection outcomes between unilateral and bilateral ACP in ATAAD patients (23,24). At our institution, both perfusion strategies are used based on intraoperative assessment during ATAAD repair. All patients underwent continuous rSO₂ monitoring to ensure adequate cerebral perfusion was maintained throughout circulatory arrest. In Group B, one patient demonstrated decreased left-sided cerebral oxygenation during unilateral perfusion and was promptly converted to bilateral perfusion. Cerebral oxygen saturation rapidly recovered to normal levels, and no postoperative neurological deficits occurred. This experience highlights the critical importance of real-time cerebral monitoring in guiding and optimizing perfusion strategies, regardless of the method employed.

In the present study, no cases of PND occurred in both groups. This finding may not reflect the actual difference in neuroprotective efficacy between the Mild-HCA and Moderate-HCA groups, largely due to the small sample size of the present study. Further investigations with larger cohorts are warranted. Although bilateral perfusion theoretically offers more balanced cerebral blood flow, its clinical advantages remain to be confirmed through large-scale, prospective studies. The incidence of TND in both groups was consistent with previously reported rates and did not differ significantly between groups (14). Compared with mild hypothermia combined with unilateral cerebral perfusion, mild hypothermia combined with bilateral cerebral perfusion has no higher incidence of neurological complications. With the increase in cerebral perfusion temperature, the change in cerebral perfusion strategy effectively maintained adequate cerebral perfusion without increasing the risk of brain injury. Despite the limited statistical power, the data cautiously suggest that bilateral cerebral perfusion was not associated with an increased risk of neurological complications as circulatory arrest temperatures increased. Likewise, a moderate increase in perfusion flow, as confirmed by NIRS monitoring, maintained cerebral oxygenation within a safe range. Therefore, the results should be interpreted with caution, as they indicate comparable efficacy between the two strategies in preventing severe, PND. Potential subtle effects on higher-order cognitive outcomes remain unclear and should be explored in future studies incorporating biomarkers and long-term neuropsychological follow-up.

Renal protection during aortic surgery is equally critical, as AKI significantly prolongs both intensive care and overall hospitalization. Postoperative AKI is among the common early complications following cardiac surgery, with reported incidence rates ranging from 20.2% to 66.7%, and severity spanning from mild transient impairment to renal failure requiring renal replacement therapy (RRT) (25). In particular, the HCA technique commonly employed in aortic dissection surgery has been widely recognized as a potential contributor to postoperative renal dysfunction (26). Although the optimal target temperature for HCA continues to evolve, the impact of varying hypothermia levels on AKI risk remains uncertain. A single-centre study of 447 ATAAD patients comparing mild HCA (~30 ℃) versus moderate HCA (~24–27 ℃), finding lower AKI incidence in mild HCA (19). Their study observed an incidence of dialysis-requiring AKI of 4.6%, closely comparable to the rate found in the present study (4.5%, n=89). Similarly, Vekstein et al. (27) analyzed data from 759 patients undergoing open aortic arch surgery, and found no significant difference in AKI incidence across deep, moderate, and mild hypothermia groups, based on either minimum nasopharyngeal or bladder temperatures during lower-body circulatory arrest. Multivariate analyses in their study further demonstrated that hypothermia level was not statistically associated with AKI risk when analyzed as either a categorical variable (temperature group) or a continuous variable (minimum temperature) (all P>0.05). In the present study, there was no statistically significant difference in the rate of RRT between the mild and moderate hypothermia groups (4.2% vs. 4.9%, P>0.05). Despite similar CPB durations (20.7±5.1 vs. 22.2±7 min, P=0.054), mild hypothermia did not lead to a higher incidence of renal injury. The incidence of postoperative renal dysfunction was lower in the mild hypothermia group compared with the moderate hypothermia group (35.4% vs. 44%), but the difference is not statistically significant (P=0.29). Nevertheless, potential confounders (e.g., preoperative comorbidities, hemodynamic instability, aortic arch complexity, and the interval between symptom onset and surgery) were not considered, although they may influence outcomes such as CPB duration or organ injury.

Spinal cord injury represents another critical concern associated with lower-body circulatory arrest during aortic surgery. Experimental studies have shown that, under normothermic conditions, the spinal cord can generally withstand ischemia for up to 30 minutes without irreversible damage (28). This ischemic interval increases as temperature decreases and oxygen consumption is reduced. In a single-centre study involving 1,759 patients (29), the use of moderate hypothermia (nasopharyngeal temperature 24.1–28.0 ℃) during aortic arch surgery proved safe and effective for most patients undergoing aortic arch replacement. Consistent with these findings, in the present study, none of the patients experienced spinal cord injury or required CPB durations exceeding 35 minutes, suggesting that Mild-HCA can provide adequate spinal cord protection under typical operative conditions.

There are several limitations in this study. First, it was not a randomized controlled trial but a retrospective, single-center study with a small sample size. We did not perform multivariable adjustment or propensity score analysis because (I) the primary goal was a direct comparison of two surgical strategies in real-world conditions with balanced groups, and (II) the modest sample size (n=89) and limited outcome events could render multivariate methods prone to overfitting or reduced statistical power. Thus, observed associations should be interpreted as estimates of effect magnitude rather than evidence of causality. Future larger, multi-center studies are needed to validate these findings using robust risk-adjustment methods. Second, because the data were collected from a single center, the generalizability of the results may be limited and subject to random variation. Third, this study did not include long-term follow-up. Fourth, to minimize the influence of pre-existing neurological injury on the evaluation of cerebral protection strategies, patients with a history or signs of neurological impairment prior to surgery were excluded. However, cerebrovascular status was not systematically assessed in the included patients, which may have introduced potential bias. In addition, neurological injury was primarily evaluated using macroscopic clinical assessments, without measurement of biochemical markers such as S-100B protein or neuron-specific enolase. To further reduce confounding, patients with preoperative cerebrovascular disease, coma, chronic renal insufficiency, or carotid artery occlusion were also excluded. Although these criteria improve internal validity, they may reduce statistical power, increase the risk of type II error, and limit the generalizability of the findings to low-risk ATAAD populations. Importantly, these exclusions omit a clinically common subgroup of ATAAD patients who are at higher risk of neurological and renal complications. Future studies will include broader patient populations, including those with consciousness impairment or renal dysfunction, and will incorporate stratified analyses to validate the results across higher-risk groups. Given that all procedures were performed by a single experienced surgical team, the applicability of these findings to institutions with different operative volumes or perfusion protocols should be interpreted with caution. Nevertheless, the patient characteristics and surgical techniques used in this study are representative of standard ATAAD management, supporting reasonable external generalisability.

Conclusions

In summary, this study demonstrated that Mild-HCA combined with bilateral cerebral perfusion was associated with shorter operative times, ICU stays, and total hospitalization durations compared with unilateral cerebral perfusion, without increasing the incidence of major organ complications or mortality. These findings suggest that Mild-HCA with bilateral cerebral perfusion is a safe, effective, and feasible strategy for surgical management of ATAAD.

Supplementary

The article’s supplementary files as

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. The study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments. The study was approved by the Medical Ethics Committee of Anhui Chest Hospital (approval No. AHC-2022-011). and individual consent for this retrospective analysis was waived.

Data Sharing Statement

Available at https://jtd.amegroups.com/article/view/10.21037/jtd-2025-1-2526/dss

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DOI: 10.21037/jtd-2025-1-2526