Patient population
This is a retrospective study, enclosing 905 consecutive patients who underwent replacement of the ascending aorta due to calcification or aneurysm using MHCA (24 ± 2 °C, nasopharyngeal) in our center till 2015, either isolated or combined with other procedures (coronary artery bypass grafting, valve replacement, etc.). Patients with aortic dissection, as well as patients with redo operations and missed follow-up, were excluded from the study (Fig. 1).
Patients were divided into two groups: those aged 75 years and older (elderly group, 22.4%) and those younger than 75 years (younger group, 77.6%). The limit whether older or younger than 75 years old was settled according to a study from Friedrich et al. (2007), which in collaboration with the German Federal Quality Assurance Office (Bundesgeschäftsstelle Qualitätssicherung, BQS) analyzed the risk profiles of elderly patients by means of data sets from all cardiac surgical centers in Germany for the year 2007. The results showed that those patients over age 75 had significantly more prognosis-determining comorbidities and risk factors with higher complication rates and mortality compared to patients younger in age (e.g., a 4.3-fold risk elevation for renal failure, a 3.0-fold elevation for neurological adverse outcomes, and 3.7-fold elevation for in-hospital mortality) [4].
The primary endpoint was the postoperative neurologic complications. Secondary endpoints were a 30-day mortality and postoperative course of various body organs (e.g., ventilation time, bleeding, acute renal failure).
Data were collected and extracted from the institution’s database and from medical records. The study protocol was approved by the local Ethics Committee in Kiel, Germany (D417/17), and the necessary individual patient consent was obtained during the hospital stay.
Patient management
Calcification or aneurysm of the ascending aorta was diagnosed either during routine X-ray investigation showing severe calcification of ascending aorta, routine echocardiographic assessment, or during coronary angiography prior to other cardiac surgery. The aortic calcification was also diagnosed and detected intraoperatively during other elective cardiac surgery such as CABG or aortic valve replacement within the direct palpation of the aorta. The decision to replace the ascending aorta was taken due to the inability of cross-clamping of the aorta due to the extensive calcification. When calcification of the ascending aorta was suspected preoperatively, a non-contrast computed tomography (CT-scan) was performed to present the exact location and extension of calcification. All patients were questioned at hospital admission for any history of neurological events as stroke or transient ischemic attack (TIA) as well as the presence of any medical records from the neurologist, computed tomography or magnetic resonance imaging. Patients were well investigated for neurological symptoms and signs, and any findings were documented on the admission sheet for further use. Without any exclusion, all patients were investigated for carotid arteries stenosis through carotid Doppler sonography. If there is a stenosis over 50–60%, a CT carotid artery angiography was carried out preoperatively and a vascular surgical consultant was contacted, to prove the indication of further surgical intervention.
One of the strict criteria in the data assembly postoperatively was that the neurological adverse outcome should be of new onset after the surgical procedure and not documented in the preoperative admission sheet.
The monitoring of tissue oxygenation of cerebrum intraoperatively was carried out by near-infrared spectroscopy (NIRS). Postoperative neurological sensory or motor deficits, if presented, were consulted directly by a neurologist and categorized according to a well-established neurological assessment. The results of the assessment were documented in patients’ file from the attending neurologist, followed by the head and neck computer tomography as well as, in many cases, CT angiography for the carotid arteries to estimate the extent of stroke and brain ischemia. MRI was required in some cases from the neurologists. After CT/MRI, a neurologist was consulted again for further plans. Delirium was measured by the Confusion Assessment Method (CAM) (https://www.icudelirium.org/medical-professionals/delirium/monitoring-delirium-in-the-icu) and was performed routinely per each shift. CAM was performed when the Richmond-Scale was more than − 4. Slightly known degree of delirium was mostly resolved rapidly under saline infusion and antipsychiatry drugs. In case of sever delirium, which requires patient fixation, a psychiatrist was consulted.
Surgical procedure
All operations were performed by senior surgeons. A standard median sternotomy followed by longitudinal pericardiotomy was carried out under general anesthesia. Direct cannulation of the distal ascending aorta was used for arterial cannulation in most cases. In cases of severe calcification of ascending aorta till its arch and inability of its distal cannulation, we used the transatrial cannulation of the left ventricle via the right upper pulmonary vein as an alternative [5]. Venous drainage was performed through cannulation of the right atrium with a common two-stage venous cannula. A standard antegrade and retrograde injection of cold blood cardioplegic solution for myocardial protection was performed in all cases. The cardiopulmonary bypass (CPB) was conducted with MHCA with core temperature between 24 ± 2 °C which was measured nasopharyngeal. Brain tissue oxygenation was monitored by near infrared spectroscopy (NIRS). After suturing of the distal anastomosis, residual air was removed by restarting retrograde perfusion via the venous cannula and followed by slow antegrade perfusion. Continuous CO2 insufflation was used as a standard for the cardiac de-airing. After insertion of the perfusion cannula directly in the vascular graft, CPB restarted again. After conducting the proximal anastomosis, a cardiac de-airing is carried out before opening the clamped aortic prosthesis. Transoesophageal echocardiography was performed to control the presence of residual air in the left side of the heart. During rewarming, other procedures such as CABG or valve replacement were implemented if required.
Statistical analysis
Statistical analysis was performed using the SPSS 18.0 software (SPSS, Chicago, IL, USA). Normality of continuous variables was assessed by Kolmogorow-Smirnow test. Values of continuous data are presented as mean ± standard deviation or as median with range or interquartile range when appropriate and compared by unpaired t test, whereas not normally distributed continuous were compared by Mann-Whitney U test. Categorical variables are displayed as frequency distributions (n) and simple percentages (%). Univariate comparison between the groups for categorical variables was made using the chi2 test and the Fisher’s exact test when appropriate. Statistical significance was considered when p ≤ 0.05. Logistic regression analysis was used to determine the hazards ratio (HR) of risk factors upon the 30-day survival time through backward selection with Likelihood ratio. Variables included in the regression analysis were age, EuroSCORE II, aortic aneurysm, aortic calcification, COPD, coronary heart disease, chronic renal insufficiency, additional CABG, and cardiopulmonary bypass time.