Effect of aortic cannulation depth on air emboli transport during cardiopulmonary bypass: A computational study

Introduction

Varying the insertion depth of the aortic cannula during cardiopulmonary bypass (CPB) has been investigated as a strategy to mitigate cerebral emboli, yet its effectiveness associated with CPB flow is not fully understood. We compared different arterial cannula insertion depths and pump flow influencing air microemboli entering the aortic arch branch arteries (AABA).

Methods

A computational approach used a patient-specific aorta model to evaluate four cannula locations at (1) proximal arch, (2) mid arch, (3) distal arch, and (4) descending aorta. We injected 0.1 mm microemboli (N=720) at 2 and 5 L/min and assessed the embolic load and the particle averaged transit times ( entering the AABA.

Results

Location 4 had the lowest embolic load (2 L/min: N= 63) and (5 L/min: N= 54) compared to locations 1 to 3 in the range of (N= 118 to 116 at 2 L/min:) and (N= 92 to 146 at 5 L/min). There was no significant difference between 2 L/min and 5 L/min (p = 0.31), despite 5 L/min attaining a lower mean (±standard deviation) than 2 L/min (38.0±23.4 vs 44.5±21.1), respectively. Progressing from location 1 to 4, increased 3.11s -7.40 s at 2 L/min and 1.81s -4.18s at 5 L/min.

Conclusion

It was demonstrated that the elongated cannula insertion length resulted in lower embolic loads, particularly at a higher flow rate. The numerical results suggest that CPB management could combine active flow variation with improving cannula performance and provide a foundation for a future experimental and clinical investigation to reduce surgical cerebral air microemboli.

Intimal aortic atherosclerosis in cardiac surgery: surgical strategies to prevent embolic stroke

 

OBJECTIVES

Although the incidence of perioperative stroke after cardiac surgery gradually decreased over the last decades, there is much variation between centres. This review aimed to create a concise overview of the evidence on possible surgical strategies to prevent embolic stroke in patients with intimal aortic atherosclerosis.

METHODS

The PubMed and EMBASE databases were searched for studies on surgical management of aortic atherosclerosis and the association with perioperative stroke in cardiac surgery, including specific searches on the most common types of surgery. Articles were screened with emphasis on studies comparing multiple strategies and studies reporting on the patients’ severity of aortic atherosclerosis. The main findings were summarized in a figure, with a grade of the corresponding level of evidence.

RESULTS

Regarding embolic stroke risk, aortic atherosclerosis of the tunica intima is most relevant. Although several strategies in general cardiac surgery seem to be beneficial in severe disease, none have conclusively been proven most effective. Off-pump surgery in coronary artery bypass grafting should be preferred with severe atherosclerosis, if the required expertise is present. Although transcatheter aortic valve replacement is used as an alternative to surgery in patients with a porcelain aorta, the risk profile concerning intimal atherosclerosis remains poorly defined.

CONCLUSIONS

A tailored approach that uses the discussed alternative strategies in carefully selected patients is best suited to reduce the risk of perioperative stroke without compromising other outcomes. More research is needed, especially on the perioperative stroke risk in patients with moderate aortic atherosclerosis.

The evolving role of the modern perfusionist: insights from transesophageal echocardiography

Transesophageal echocardiography is a relatively non-invasive, mobile, safe imaging technique that is ideal for providing real-time information on cardiac anatomy and function during heart surgery. The technology has evolved from two-dimensional to real-time three-dimensional imaging during cardiac procedures, which has significantly benefited preoperative planning, intraoperative guidance, evaluation, and postoperative follow-up. Transesophageal echocardiography may serve the clinical perfusionist by providing imaging guidance for identifying potential problems before cardiopulmonary bypass, guiding the proper placement of cannulas, monitoring cardiac performance on cardiopulmonary bypass, and providing useful feedback during weaning from cardiopulmonary bypass. Although the perfusionist should be able to understand all echocardiographic images and measurements in depth, perfusion-related echocardiographic information can or should be used to optimize the clinical practice of the modern perfusionist. Vice versa, whenever the perfusionist suspects a problem, the surgical team including the sonographer should verify this "clinical treat" by echocardiography whenever possible.

Impact of Modified Transesophageal Echocardiography on Mortality and Stroke after Cardiac Surgery: A Large Cohort Study

The aim of this study was to investigate the impact of perioperative screening with modified transesophageal echocardiography (A-View method). We compared, in consecutive patients who underwent cardiac surgery between 2006 and 2014, 30-day mortality and in-hospital stroke incidence, operated either with perioperative modified TEE screening (intervention group) or only with conventional TEE screening (control group). Of the 8,605 study patients, modified TEE was applied in 1,391 patients (16.2%). Patients in the intervention group were on average older (71 versus 68 years, p < 0.001) and more often females (31.0% versus 28.0%, p < 0.001) and had a higher predicted mortality (EuroSCORE I: 5.9% versus 4.0%, p < 0.001). The observed 30-day mortality was 2.2% and 2.5% in both groups, respectively, with multivariable and propensity-score adjusted relative risks (RRs) of 0.70 (95% CI: 0.50–1.00, p = 0.05) and 0.67 (95% CI: 0.45–0.98, p = 0.04). In-hospital stroke was 2.9% and 2.1% in both groups, respectively, with adjusted RRs of 1.03 (95% CI: 0.73–1.45) and 1.01 (95% CI: 0.71–1.43). In patients undergoing cardiac surgery, use of perioperative screening for aortic atherosclerosis with modified TEE was associated with lower postoperative mortality, but not stroke, as compared to patients operated on without such screening.

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.