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Department of Cardiovascular Surgery, University Hospital, 3010 Berne, Switzerland
Received 30 September 2007; received in revised form 12 April 2008; accepted 14 April 2008.
* Corresponding author. Tel.: +41 31 632 23 76; fax: +41 31 632 44 43. (Email: franzimmer{at}yahoo.de).
| Abstract |
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Key Words: Thoracic aorta Aneurysm Dissection Outcome Cerebral perfusion
| 1. Introduction |
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Several studies have demonstrated that the mentioned refinements of surgical techniques, result in a decreased mortality and morbidity in this high-risk collective of patients. The introduction of antegrade cerebral perfusion (ACP) in clinical routine is especially associated with reduced mortality and adverse neurological outcome [5–7]. Our group has furthermore shown that the introduction of ACP beneficially affects long-term quality of life in patients undergoing thoracic aortic surgery under DHCA [5].
Based on these improvements, the use of deep hypothermic circulatory arrest has become more liberal than a few years ago and more complex aortic pathologies can be treated successfully by open repair. With the introduction of cerebral protection during circulatory arrest with cold, antegrade cerebral perfusion, deep hypothermic circulatory arrest is being abandoned for moderate hypothermia during the circulatory arrest [8].
The aim of the present study was to analyse the impact of these developments on outcome of patients undergoing surgery of the thoracic aorta in the last decade.
| 2. Patients and methods |
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History of arterial hypertension was the most common general preoperative risk factor (58.7%), followed by a history of smoking (34.8%) and diabetes mellitus (8.4%). Patients characteristics are displayed in Table 1 .
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All patients suffering from AADA and patients with an extension of ascending aortic aneurysm into the aortic arch underwent surgery under DHCA.
Intraoperative data are displayed in Table 1.
In the reported observation period several cerebral protection techniques have been applied. At the beginning of the observation period patients were cooled, target temperature being 18 °C measured in the tympanum. DHCA was initialized after administration of 20 mg/kg Pentobarbital 2–3 min prior to the arrest. Topical cooling was applied, by covering the head with an ice package. Then, selective antegrade perfusion was introduced in the year 2001. Since then it is used routinely; first by placing catheters in the common trunk and the left carotid artery and then by cannulation of the right axillary artery. With cannulation of the right axillary artery antegrade cerebral perfusion is unilateral. The temperature of the perfusate for ACP is set at 12 °C. ACP during DHCA is performed with oxygenated blood at a pressure of 30–40 mmHg corresponding to a flow of 200–250 ml/min, if the right axillary artery is cannulated ACP is initiated with a flow of 1000 ml/min. Initially cerebral perfusion was mainly applied in patients with an expected arrest of more than 20 min. With the introduction of axillary cannulation in 2003 we started to use ACP in all patients in need for DHCA. During the study period cooling regimen remained the same, we did not combine ACP with moderate hypothermia.
2.2 Statistical analysis
Data are presented as mean values ± their first standard deviation. A Mann–Whitney U-test and
2 test were used for comparison between groups of continuous and nominal variables, respectively.
A p value of less than 0.05 was considered significant. A logistic regression analysis was done.
| 3. Results |
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Adverse outcome (AO), defined as in-hospital death or permanent neurological deficit, occurred in 101 of 835 patients (12.1%). Initially, all patients were treated as a single group, but subsequently, to study the impact of the different time period of surgery, patients were divided into an early and a late group according to the year they underwent surgery. Group 1 includes 318 patients (38.2%) who underwent surgery on the thoracic aorta between January 1996 and December 2000. During this period the main protection strategy during circulatory arrest was the profound cooling. Group 2 consists of 517 patients (61.8%) being operated between January 2001 and December 2005. In this study period ACP was used routinely in most cases with expected long duration of circulatory arrest.
Demographics and intraoperative data of these groups are displayed in Table 1.
In the last 10 years there was a pronounced increase in aortic caseload. This increase was seen in patients operated for TAA (+367.9%) as well in patients for AADA (+276.9%).
The demographics of group 1 compared with group 2 looking at age (59.4 ± 12.0 years vs 61.0 ± 13.0 years; p = 0.27), sex (male 73.0% vs 73.3%; p = 0.48) and cardiovascular risk profile revealed no significant difference during the last decade. A similar amount of surgery had to be performed in emergency (group 1: 33.0% vs group 2: 30.8%; p = 0.27). In group 1 89 patients (28.0%) had to be operated because of AADA, in group 2 152 patients (29.2%) (p = 0.38).
Significantly more patients were found in group 2 with comorbidities known to influence outcome in cardiac surgical procedures, according to the EuroSCORE: concomitant coronary artery disease (group 1: 19.8% vs group 2: 28.1%; p = 0.004) and impaired left ventricular function with an ejection fraction (EF) <50% (group 1: 15.9% vs group 2: 21.0%; p = 0.07). In group 2 more patients suffered from aortic valve stenosis (group 1: 16.0% vs group 2: 25.8%; p = 0.001) and mitral-valve insufficiency (group 1: 8.2% vs group 2: 10.3%; p = ns).
The number of Bentall-procedures increased from 33.3% in the early study period up to 42.7% in recent years (p = 0.004), reflecting the attempt to treat the aortic root more radically. This explains the increase of combined procedures in recent years: additional CABG-surgery (group 1: 16.4% vs group 2 27.3%; p = 0.00) and repair/replacement of the mitral- and/or the tricuspid-valve (group 1: 2.8% vs group 2: 4.6%; p = 0.133).
There was no difference in the percentage frequency of DHCA: in the early group 194 patients (61.0%) had DHCA compared to 301 patients (57.0%) in the late group (p = 0.206). In the early group DHCA was performed without additional ACP. In 2001 ACP was introduced in clinical routine: in group 2 196 patients (65.1%) had ACP. In the whole study period 299 patients were operated with DHCA alone. ACP had a positive effect on mortality (7.7% vs 10.3%) as well as on persistent neurological dysfunction (6.3% vs 8.2%).
The cannulation technique changed as well: femoral cannulation (group 1: 63.8% vs group 2: 25.1%; p = 0.00) being abandoned for the axillary cannulation (group 1: 0.3% vs group 2: 21.9%; p = 0.00).
Mean cardiopulmonary bypass (CPB) time was similar in both groups (119.3 ± 20.9 min vs 130.1 ± 16.9 min; p = 0.014), as was the mean duration of DHCA (19.2 ± 7.1 min vs 22.0 ± 8.9 min; p = 0.054).
Intraoperative mortality remained the same, four patients (1.3%) died during the operation in group 1, eight patients (1.5%) in group 2. In-hospital mortality decreased: 25 patients (7.9%) died in the early group and 29 patients (5.6%) died in the recent group (Fig. 1 ). The decrease in mortality more pronounced in patients undergoing surgery for AADA, than in surgery for TAA (Fig. 2 ).
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| 4. Discussion |
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In the light of sicker patients and more complex surgery the dramatic decrease in mortality and permanent neurological dysfunction is even more remarkable. In accordance with other groups, we are able to show a pronounced decrease in permanent neurological deficits [6]. Postoperative permanent neurological deficits after surgery on the thoracic aorta and aortic arch usually result from cerebral emboli during surgery. Thus the avoidance of any manipulation of the diseased aorta is probably one of the major advances in thoracic aortic surgery in the last decade. In the earlier years of this study the main method to protect the brain during circulatory arrest was to decrease the metabolic demand by cooling the patient to 18 °C. Several studies have shown, that with this approach the safe duration of arrest is limited [8–11]. Therefore the search for refined method of protecting the brain resulted in groups favoring the use of retrograde cerebral perfusion [12,15,16] reporting very good results. The advantage of RCP being more thorough cooling of the brain and washing out air and debris material from the intracranial vessels. Other groups reported conflicting results using RCP and the benefit remains unclear [12–17]. Although several groups were able to show a benefit from RCP, we and others are rather sceptical whether there is a benefit other than just more thorough cooling of the brain with the risk of developing cerebral edema [16,17]. Some reports have documented that prolonged RCP is a risk factor for stroke and mortality, such as being observed in prolonged DHCA. In our clinical routine we did not use retrograde cerebral perfusion.
Bachet and co-workers introduced the concept of antegrade cerebral perfusion in combination with moderate hypothermia [9]. The introduction of axillary artery cannulation in clinical routine [18,19] allows removing the balloon-catheters from the surgical field and reduces manipulation on the supra-aortic branches, favoring air and thrombotic embolisms. In recent years, we tried to avoid cross-clamping the aorta, especially in AADA as well as in aorta with severe atherosclerotic alterations.
Another great advance in using ACP in combination with axillary cannulation is the preservation of antegrade flow in the descending aorta while eliminating some of the risks associated with direct cannulation of the ascending aorta [6,7]. Axillary cannulation is also superior to femoral cannulation, which reverses blood flow in the descending aorta and may shear off embolic material and can thus cause dissection or embolic showers [18,19]. The axillary artery has less atherosclerotic alterations than either the ascending aorta or the femoral artery. Axillary cannulation lowers the potential risk of embolization into the right sided cerebral vessels by perfusing them with flow which has not transversed the aortic arch and avoids the sandblast effect of turbulent flow from a catheter tip close to atherosclerotic lesions in the ascending aorta and thus reduces the risk of embolization into the left-sided cerebral vessels.
The observed increase in CPB-time in recent years is partly related to this technique and especially to the increase of combined procedures. Outcome data confirm that this slight increase of CPB-time does not adversely affect the overall benefit. Beside the reduction of neurological events, our group has recently shown that the use of selective ACP during DHCA improves quality of life after interventions on the thoracic aorta [5].
The use of glue in surgery for AADA has the advantage of closing the entry of the dissection but increases the risk of necrosis of the arterial wall [20,21]. We perform regular clinical follow-up in all our patients who underwent surgery of the thoracic aorta, including an imaging study such as an angio-CT or MRI. In this large collective of patients we have not seen any formation of aneurysm due to the use of glue.
We therefore conclude, that technical advances in the field of thoracic aortic surgery lead to a decrease of mortality and morbidity. With our results in this large collective of patients we were able to show a dramatic decrease especially in the incidence of adverse neurological events over the last decade. This is mainly due to better surgical techniques, such as antegrade cerebral perfusion and a no-touch policy on the ascending aorta. Even though our patients become sicker and operations are getting more complex with more concomitant procedures, the outcome after surgery on the thoracic aorta significantly increases with a better long-term quality of life.
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