Is there any impact of the shape of aortic end-hole cannula on stroke occurrence? clinical evaluation of straight and bent-tip aortic cannulae

Hemodynamic performance evaluation of neonatal ECMO double lumen cannula using fluid-structure interaction

Extra corporeal membrane oxygenation (ECMO) is an artificial oxygenation facility, employed in situations of cardio-pulmonary failure. Some diseases i.e., acute respiratory distress syndrome, pulmonary hypertension, corona virus disease (COVID-19) etc. affect oxygenation performance of the lungs thus requiring the need of artificial oxygenation. Critical care teams used ECMO technique during the COVID-19 pandemic to support the heart and lungs of COVID-19 patients who had an acute respiratory or cardiac failure. Double Lumen Cannula (DLC) is one of the most critical components of ECMO as it resides inside the patient and, connects patient with external oxygenation circuit. DLC facilitates delivery and drainage of blood from the patient's body. DLC is characterized by delicate balance of internal and external flows inside a limited space of the right atrium (RA). An optimal performance of the DLC necessitates structural stability under biological and hemodynamic loads, a fact that has been overlooked by previously published studies. In the past, many researchers experimentally and computationally investigated the hemodynamic performance of DLC by employing Eulerian approach, which evaluate instantaneous blood damage without considering blood shear exposure history (qualitative assessment only). The present study is an attempt to address the aforementioned limitations of the previous studies by employing Lagrangian (quantitative assessment) and incorporating the effect of fluid-structure interaction (FSI) to study the hemodynamic performance of neonatal DLC. The study was performed by solving three-dimensional continuity, momentum, and structural mechanics equation(s) by numerical methods for the blood flow through neonatal DLC. A two-way coupled FSI analysis was performed to analyze the effect of DLC structural deformation on its hemodynamic performance. Results show that the return lumen was the most critical section with maximum pressure drop, velocity, shear stresses, and blood damage. Recirculation and residence time of blood in the right atrium (RA) increases with increasing blood flow rates. Considering the structural deformation has led to higher blood damage inside the DLC-atrium system. Maximum Von-Mises stress was present on the side edges of the return lumen that showed direct proportionality with the blood flow rate.

Aortic cannula orientation and flow impacts embolic trajectories: computational cardiopulmonary bypass

INTRODUCTION

Emboli events are associated with the aortic cannula insertion and final position in the ascending aorta. However, the impact of subtle changes in aortic cannula movement and flow influencing embolic transport throughout the aortic arch is not well understood. The present study evaluated the aortic cannula's outflow and orientation effect on emboli entering the aortic branch arteries.

METHODS

A simplified aortic computational model was anteriorly cannulated in the distal ascending aorta with a 21-French straight aortic cannula, and two orientations were analysed by injecting gaseous and solid emboli at pump flows 2, 3 and 5 L/minute. The first aortic cannula orientation (forward flow cannula) was directed towards the lesser curvature. The second aortic cannula orientation (rear flow cannula) was tilted slightly backwards by 15°, providing flow in the retrograde direction.

RESULTS

Forward flow cannula produced a primary arch flow, whereas rear flow cannula produced a secondary arch flow resulting in four times longer emboli arch resident times than forward flow cannula. The rear flow cannula had the highest percentage of gaseous emboli entering the brachiocephalic artery of 8%, 12% and 36% (at 2, 3 and 5 L/minute, respectively). Rear flow cannula provided a positive aortic branch arterial flow at all pump flows, whereas at forward flow cannula, the brachiocephalic artery experienced retrograde flows of -1.0% (3 L/minute) and -4.0% (5 L/minute), with the left common carotid -0.23% (5 L/minute). No significant number of solid emboli entered the aortic branch arteries.

CONCLUSION

This numerical study illustrated distinct trajectory behaviours between gaseous and solid emboli where slight changes in aortic cannula orientation influenced idealised emboli direction with higher pump flows magnifying the effects.

Implementation of the aortic no-touch technique to reduce stroke after off-pump coronary surgery

OBJECTIVES

Despite substantial scientific effort, the relationship between stroke after coronary artery bypass grafting and the use of the aortic no-touch off-pump technique (anOPCAB) remains incompletely understood. The present study aimed to define the effect of anOPCAB on the occurrence and time point of stroke.

METHODS

A total cohort of 15,042 consecutive patients underwent surgical myocardial revascularization at a single institution. After establishing anOPCAB as routine procedure, 4695 patients received surgery by 18 different surgeons using the anaortic approach. After the exclusion of all patients with cardiogenic shock and "side-clamp" off-pump coronary artery bypass grafting, 13,279 patients (4485 with anOPCAB) were included in the study. Perioperative strokes were classified as strokes occurring during the hospital stay, with early strokes observed immediately after emergence from anesthesia (vs delayed strokes).

RESULTS

The anOPCAB technique reduced the postoperative stroke rate to 0.49% versus 1.31% in on-pump patients (P < .0001). The overall stroke rate after adoption of anOPCAB (0.64%) decreased compared with before its adoption (1.40%; P < .0001). With anOPCAB, the risk of early strokes virtually disappeared to 4 of 4485 patients (0.09%; 95% confidence interval, 0.00-0.18% vs 0.83% in on-pump patients; P < .0001), whereas the incidence of delayed strokes was not affected (0.40% vs 0.48%; P = .5181). The key results were confirmed after adjustment using propensity score-based analyses.

CONCLUSIONS

The anOPCAB technique with avoidance of any aortic manipulation is an effective tool to minimize the risk of early strokes during coronary artery bypass grafting, and thus, should be considered as a routine approach. In contrast, additional preventive strategies against delayed strokes remain to be elaborated.

A Protocol for Diagnosis and Management of Aortic Atherosclerosis in Cardiac Surgery Patients

In patients undergoing cardiac surgery, use of perioperative screening for aortic atherosclerosis with modified TEE (A-View method) was associated with lower postoperative mortality, but not stroke, as compared to patients operated on without such screening. At the time of clinical implementation and validation, we did not yet standardize the indications for modified TEE and the changes in patient management in the presence of aortic atherosclerosis. Therefore, we designed a protocol, which combined the diagnosis of atherosclerosis of thoracic aorta and the subsequent considerations with respect to the intraoperative management and provides a systematic approach to reduce the risk of cerebral complications.

Hydrodynamic evaluation of aortic cardiopulmonary bypass cannulae using particle image velocimetry

The high velocity jet from aortic arterial cannulae used during cardiopulmonary bypass potentially causes a "sandblasting" injury to the aorta, increasing the possibility of embolisation of atheromatous plaque. We investigated a range of commonly available dispersion and non-dispersion cannulae, using particle image velocimetry. The maximum velocity of the exit jet was assessed 20 and 40 mm from the cannula tip at flow rates of 3 and 5 L/min. The dispersion cannulae had lower maximum velocities compared to the non-dispersion cannulae. Dispersion cannulae had fan-shaped exit profiles and maximum velocities ranged from 0.63 to 1.52 m/s when measured at 20 mm and 5 L/min. Non-dispersion cannulae had maximum velocities ranging from 1.52 to 3.06 m/s at 20 mm and 5 L/min, with corresponding narrow velocity profiles. This study highlights the importance of understanding the hydrodynamic performance of these cannulae as it may help in selecting the most appropriate cannula to minimize the risk of thromboembolic events or aortic injury.

Investigation of risks for cerebral embolism associated with the hemodynamics of cardiopulmonary bypass cannula: a numerical model

Cerebral emboli originating in the ascending aorta are a major cause of noncardiac complications following cardiac surgery. The hemodynamics of the aortic cannula has been proven to play a significant role in emboli generation and distribution. The aim of the current study was to perform a thorough numerical investigation in order to examine the effect of the design and orientation of the cannula used during cardiopulmonary bypass on the risk to develop cerebral embolism. Hemodynamic analyses compared numerical models of 27 cases consisting of six different cannula orientations, four aortic anatomies, and three cannula designs. The cannula designs included a straight-tip (ST) cannula, a moderately curved tip cannula (TIP1 ), and a sharp-angle curved cannula (TIP2 ). Outcome measures included hemodynamic parameters such as emanating jet velocity, jet velocity drop, maximal shear stress, aortic wall reaction, emboli pathlines and distribution between upper and lower vessels, and stagnation regions. Based on these parameters, the risks for hemolysis, atheroembolism, and cerebral embolism were evaluated and compared. On one hand, the jet emerging from the ST cannula generated large wall-shear stress at the aortic wall; this may have triggered the erosion and distribution of embolic atheromatous debris from the aortic arch. On the other hand, it diverted more emboli from the clamp region to the descending aorta and thus reduced the risk for cerebral embolism. The TIP1 cannula demonstrated less shear stress on the aortic wall and diverted more emboli from the clamp region toward the upper vessels. The TIP2 cannula exhibited a stronger emanating jet, higher shear stress inside the cannula, and highly disturbed flow, which was more stagnant near the clamp region. Current findings support the significant impact of the cannula design and orientation on emboli generation and distribution. Specifically, the straight tip cannula demonstrated a reduced risk of cerebral embolism, which may be pivotal in the clinical setting.

ECMO cannula review

This paper reviews the basic fluid dynamics underlying extracorporeal membrane oxygenation (ECMO) cannula design. General cannula features and their effect on flow are discussed and the specific requirements of different ECMO circuits are explained. The current commercially available cannula options for veno-arterial and veno-venous circuits are reviewed and the main characteristics presented.

The impact of aortic/subclavian outflow cannulation for cardiopulmonary bypass and cardiac support: a computational fluid dynamics study

Approximately 100 000 cases of oxygen deficiency in the brain occur during cardiopulmonary bypass (CPB) procedures each year. In particular, perfusion of the carotid and vertebral arteries is affected. The position of the outflow cannula influences the blood flow to the cardiovascular system and thus end organ perfusion. Traditionally, the cannula returns blood into the ascending aorta. But some surgeons prefer cannulation to the right subclavian artery. A computational fluid dynamics study was initially undertaken for both approaches. The vessel model was created from real computed tomography/magnetic resonance imaging data of young healthy patients. The simulations were run with usual CPB conditions. The flow distribution for different cannula positions in the aorta was studied, as well as the impact of the cannula tip distance to vertebral artery for the subclavian position. The study presents a fast method of analyzing the flow distribution in the cardiovascular system, and can be adapted for other applications such as ventricular assist device support. It revealed that two effects cause the loss of perfusion seen clinically: a vortex under the brachiocephalic trunk and low pressure regions near the cannula jet. The results suggest that cannulation to the subclavian artery is preferred if the cannula tip is sufficiently far away from the branch of the vertebral artery. For the aortic positions, however, the cannula should be injected from the left body side.

Hydrodynamics of aortic cannulae during extracorporeal circulation in a mock aortic arch aneurysm model

This study was designed to analyze flow pattern, velocity, and strain on the aortic wall of a glass aortic arch aneurysm model during the extracorporeal circulation, and to elucidate the characteristics of flow pattern in three different aortic cannulae. Different patterns of large vortices and helical flow were made by each cannula. With the curved end-hole cannula, the high velocity flow (approximately 0.6-0.8 m/s) was blowing to the aneurismal wall without attenuating the strain rate tensor (approximately 0.2-0.25/s). With the dispersion cannula and the Soft-Flow cannula, cannular jet was attenuated in the ascending aorta creating a large vortex at a velocity less than 0.5 m/s, and the strain rate tensor on the aneurismal wall was small (less than 0.15/s). In conclusion, end-hole cannula should not be used in the operation of aortic arch aneurysm. Dispersion-type aortic cannulae were less invasive on the aortic arch aneurismal wall, but particular attention to alternative cannulation sites should be paid in cases with severe atherosclerosis on the ascending aortic wall.

[Should we avoid cardiopulmonary bypass with diabetic patients?]

In the peri-operative and post-operative course of coronary bypass operations, the diabetic patient is susceptible to complications that cause morbidity and mortality. Morbidity might best be conceptualized as the cumulative effect of the diabetic patient chronically at risk and a variety of surgically related insults, including surgical stress, anaesthesia, hypo- and hypertension, anaemia, dysrhythmias, de- or hyperhydration and cardiopulmonary bypass (CPB) that exceed the compensatory capacities of the patient. Because all these factors for adverse outcome coexist, it becomes difficult to determine which ones are most important. However, it is reasonable that, in the presence of generalized atherosclerosis affecting the aorta ascendens, carotids and the cerebral arteries, the interaction of CPB-associated embolization, hypoperfusion and inflammation may cause neurologic morbidity. Many physiologic alterations (such as non-pulsatile perfusion and hemodilution) occur during CPB and may worsen renal dysfunction in patients with diabetic nephropathy. Pulmonary dysfunctions, associated with diabetic microangiopathy, could be unmasked by atelectasis, capillary leak and other pathophysiological conditions developing after the use of extracorporeal circulation. Actually, there is evidence that with the avoidance of CBP and the use of adequate OPCAB (Off Pump Coronary Artery Bypass) techniques, by experienced teams, the incidences of neurological, renal and pulmonary complications decrease, in high-risk patients, e. g. diabetics, as well as in unselected cohorts. Because it is not possible to identify confidently those patients who are at risk for CPB-associated complications, we use a strategy where all CABG (Coronary Artery Bypass Grafting) are performed in OPCAB technique. The total OPCAB approach will in addition ascertain the development of organizational OPCAB routines and expertise. The process of re-engineering the unit towards total OPCAB needs systematic training and re-training of cardiac surgeons by surgeons, experienced in both, OPCAB surgery and knowledge transfer, according to the principles of continuing medical education (CME). Thus, the chances of the OPCAB technique improving the outcome of diabetic patients can be fully realized.