Flow Velocity and Turbulence in the Transverse Aorta of a Proximally Directed Aortic Cannula: Hydrodynamic Study in a Transparent Model

Low-flow perfusion technique for shaggy aortic arch

BACKGROUND

The most common complication of thoracic aortic disease with shaggy aorta is cerebral infarction. We have performed "low-flow perfusion" as a method of extracorporeal circulation to prevent cerebral embolism in patients with strong atherosclerotic lesions in the aortic arch.

METHODS

"Low-flow perfusion" is a method in which cardiopulmonary bypass is started by partial blood removal, approaching deep hypothermia while maintaining self-cardiac output. We compared the outcomes of 12 patients who underwent the "low-flow perfusion" method (Group L) with those of 12 who underwent normal extracorporeal circulation (Group N) during aortic arch surgery since 2019.

RESULTS

Group L consisted of 8 males with an average age of 73 years old, and Group N consisted of 6 males with an average age of 73 years old. The average time from the start of cooling to ventricular fibrillation was 9.5 min in Group L and 3.6 min in Group N (p < 0.01). The eardrum temperature when ventricular fibrillation was reached was 28.2 °C in Group L and 32.5 °C in Group N (p = 0.01). A blood flow analysis also revealed low wall shear stress on the lesser curvature of the aortic arch.

CONCLUSION

With this method, the intracranial temperature was sufficiently low at the time of ventricular fibrillation, and there was no need to increase the total pump flow. The low-flow perfusion method can prevent cerebral embolism by preventing atheroma destruction by the blood flow jet while maintaining the self-cardiac output during the cooling process.

Aortic arch surgery: what I would have done different? The Kobe/Takatsuki experience

Our current approach towards total arch replacement includes the following: (1) innominate vein mobilization, (2) no neck vessel taping, and no dissection of the vagal nerve, (3) meticulous selection of arterial cannulation site and type of arterial cannula, (4) antegrade cerebral perfusion(ACP)for neuro-protection, utilizing three balloon-tipped cannular from inside the arch, (5) whole-body hypothermia with minimal tympanic temperatures between 20 and 23 °C and minimal rectal temperatures below 30 °C, (6) distal enucleation and felt reinforcement for in zone III distal anastomosis using four branched graft, (7) early re-warming after distal anastomosis with ACP flow adjustment while monitoring brain oxygenation by near-infrared spectroscopy (NIRS) and (8) second anastomosis is proximal and last one is arch vessel reconstruction, (9) maintaining strict fluid balance below 1000 ml by the extracorporeal ultrafiltration method (ECUM) during cardiopulmonary bypass (CPB), with the expectation of more rapid pulmonary functional recovery.

The results of aortic arch replacement using antegrade cerebral perfusion in haemodialysis patients: analysis of the Japan cardiovascular surgery database

OBJECTIVES

There have been limited data available regarding aortic arch replacement in dialysis patients. The purpose of this study was to examine real-world data and to determine the impact of preoperative dialysis status and other risks on surgical aortic arch replacement using the Japan Cardiovascular Surgery Database.

METHODS

A total of 5044 patients who underwent elective, isolated aortic arch replacement using antegrade cerebral perfusion during 2014-2017 were eligible for the study. Of these, 89 patients received haemodialysis preoperatively. The patients were divided into 6 groups according to their preoperative estimated glomerular filtration rate and dialysis status for comparison. Preoperative and postoperative data were examined using a multivariable regression model.

RESULTS

The overall surgical mortality rates of non-Chronic Kidney Disease (CKD) (estimated glomerular filtration rate >60 ml/min/1.73 m2), stage 3A, stage 3B, stage 4, stage 5 CKD and dialysis patients were 2.6%, 3.1%, 6.8%, 11.6%, 16.7% and 13.5%, respectively. After risk adjustment, dialysis was shown to be strongly associated with surgical mortality (odds ratio 4.39 and 95% confidence interval 2.22-8.72) and have a trend to be associated with postoperative stroke (odds ratio 2.02, 95% confidence interval 1.00-4.10, P = 0.051) when compared to the non-CKD group. As predictors of mortality, male sex, peripheral arterial disease, preoperative liver dysfunction and impaired left ventricular function were identified.

CONCLUSIONS

The Japanese nationwide database revealed the outcomes of aortic arch replacement in dialysis patients. Appropriate counselling and an alternative strategy should be considered for such patients with multiple risks for mortality.

Directing a dispersion cannula tip toward the aortic root during thoracic aortic arch surgery does not adversely affect cardiac function

INTRODUCTION

Neurologic complications of open thoracic aortic surgery are devastating problems in patients with severely diseased aortas. This study aimed to clarify whether directing the aortic cannula tip toward the aortic root affects the postoperative cardiac function in patients undergoing open thoracic aortic surgery.

METHODS

A total of 16 patients who underwent total or partial arch replacement between January 2014 and April 2019 were enrolled and divided into two groups. Ascending aorta perfusion was performed by placing the cannula tip toward the aortic root (reversed direction group, seven patients) or toward the aortic arch (standard direction group, nine patients). Intraoperative and perioperative data, including mortality, morbidity, and postoperative cardiac function, were compared between the groups.

RESULTS

There were no hospital deaths or stroke events in either group. The aortic cross-clamping time was 102.4 ± 20.3 minutes in the reversed direction group and 87.1 ± 9.9 minutes in the standard direction group (p = 0.049). Furthermore, the intubation time was 28.4 ± 12.9 hours in the reversed direction group and 12.4 ± 6.8 hours in the standard direction group (p = 0.022). Both times were significantly longer in the reverse direction group. Postoperative serum creatine kinase-MB levels were significantly lower in the reversed direction group (6.2 ± 3.3 U/L vs 13.3 ± 4.8 U/L, respectively, p = 0.006). The cardiac output and cardiac index did not significantly differ.

CONCLUSIONS

Directing the aortic cannula tip toward the aortic root does not adversely affect the postoperative cardiac function after aortic arch surgery.

Flow analysis during mock circulation in normal and aortic arch aneurysm models through an aortic cannula toward the aortic arch and root

The aim of this study was to elucidate flow patterns of two different types of aortic cannulas inserted from the ascending aorta toward the aortic arch and root by mock circulation in a normal aortic arch and an aortic arch aneurysm model. Extracorporeal circulation was established using a centrifugal pump, a transparent glass normal aortic arch model, and an aortic arch aneurysm model for measurement by particle image velocimetry. The Stealthflow and Dispersion cannulas were used to elucidate the characteristics of the flow pattern and velocity under the condition of the cannula tip toward the aortic arch and aortic root. In the normal aortic arch model, high-velocity exit flow ranging from 0.7 to 0.8 m/s was detected in the proximal aortic arch by directing the cannula tip toward the aortic arch, whereas flow velocity in the aortic arch was < 0.2 m/s by directing the cannula tip toward the aortic root. In the aortic arch aneurysm model, high-velocity exit flow ranging from 0.5 to 0.8 m/s was detected in the aortic arch by directing the cannula tip toward the aortic arch, whereas flow velocity in the aortic arch was decreased to less than 0.2 m/s by directing the cannula tip toward the aortic root. Directing the aortic cannula tip toward the aortic root allowed the high-velocity exit flow to attenuate in velocity, so that flow velocity in the aortic arch was sufficiently reduced by reversed flow and vortex formation in both the normal and aortic arch aneurysm models.

Neuro-protection in open arch surgery

Although antegrade cerebral perfusion (ACP) is the predominant method of protecting the brain in patients undergoing total arch replacement, both deep hypothermic circulatory arrest and ACP provide excellent and comparable clinical outcomes with regard to mortality, stroke, and temporary neurological deficit rates.

Development of an In Vitro PIV Setup for Preliminary Investigation of the Effects of Aortic Compliance on Flow Patterns and Hemodynamics

The aorta with its compliance plays a major role in hemodynamics as it saves a portion of ejected blood during systole which is then released in diastole. The aortic compliance decreases with increasing age, which is related to several cardiovascular imparities and diseases. Changes in flow patterns and pressure curves, due to varying aortic compliance, are difficult to investigate in vivo. As a result, the aim of the present work was to develop an in vitro setup enabling standardized investigations on the effect of compliance changes on flow patterns and pressure curves. Therefore an experimental setup with an anatomically correct silicone phantom of the aortic arch was developed, suitable for optical flow measurements under pulsatile inflow conditions. The setup was developed for precise adjustments of different compliances and optical flow measurements. Particle image velocimetry measurements were carried out downstream of the aortic valve in the center plane perpendicular to the valve with compliance adjusted between 0.62 × 10^-3 to 1.82 × 10^-3 mmHg^-1. Preliminary results of the in vitro investigations showed that decreases in compliance results in significant increases in pressure changes with respect to time (dp/dt) and altered pressure curves in the aortic arch. In terms of flow, an increased aortic stiffness lead to higher mean velocities and decreased vortex development in the aortic sinuses. As in vivo validation and translation remains difficult, the results have to be considered as preliminary in vitro insights into the mechanisms of (age-related) compliance changes.

Developing a new endograft for the treatment of juxtarenal aortic aneurysms: definition and experimentation

OBJECTIVES

To analyze angiotomographic parameters of juxtarenal aneurysms to assess the applicability of an endograft model to patients and to create in vitro and in vivo models to assess the new endograft.

METHODS

A total of 49 patients with juxtarenal aneurysms were submitted to angiotomographic evaluation, and parameters such as the aortic diameter, the length of the neck, and the angulations of the celiac trunk, superior mesenteric artery and renal arteries; the distances between them; and anatomic variations were analyzed. Based on these parameters, an endograft model was developed and tested in a newly created in vitro model of juxtarenal aneurysm. An experimental model of juxtarenal aneurysm was then established in six pigs weighing 50-60 kg to assess the new endograft model.

RESULTS

The angiotomographic parameters of juxtarenal aneurysm measured in this study were similar to those reported in the literature and allowed the development of an endograft based on the hourglass concept, which was applicable to 85.8% of the patients. The in vitro model of juxtarenal aneurysm evidenced good radiopacity and functionality and permitted adjustments in the new device and technical improvements in the procedures for treating these aneurysms. In addition, the porcine model of juxtarenal aneurysm was successfully created in all six animals using a bovine pericardial patch, and use of the new endograft in three pilot procedures evidenced its feasibility.

CONCLUSIONS

The Hourglass endograft was rendered applicable to treatment of the majority of patients with juxtarenal aneurysms simply by changing its diameter. Moreover, the new in vitro and in vivo models were shown to be effective for assessing both the presented endograft and experiments assessing the endovascular treatment of juxtarenal aneurysms.

Overcoming Challenges in the Management of Critical Events During Cardiopulmonary Bypass

Critical events during cardiopulmonary bypass (CPB) can challenge the most experienced perfusionists, anesthesiologists, and surgeons and can potentially lead to devastating outcomes. Much of the challenge of troubleshooting these events requires a key understanding of these situations and a well-defined strategy for early recognition and treatment. Adverse situations may be anticipated prior to going on CPB. Atherosclerosis is pervasive, and a high plaque burden may have implications in surgical technique modification and planning of CPB. Hematologic abnormalities such as cold agglutinins, antithrombin III deficiency, and hemoglobin S have been discussed with emphasis on managing complications arising from their altered pathophysiology. Jehovah’s witness patients require appropriate techniques for cell salvage to minimize blood loss. During initiation of CPB, devastating situations leading to acute hypoperfusion and multiorgan failure may be encountered in patients undergoing surgery for aortic dissection. Massive air emboli during CPB, though rare, necessitate an urgent diagnosis to detect the source and prompt management to contain catastrophic outcomes. Gaseous microemboli remain ubiquitous and continue to be a major concern for neurocognitive impairment despite our best efforts to improve techniques and refine the CPB circuit. During maintenance of CPB, adverse events reflect inability to provide optimal perfusion and can be ascribed to CPB machine malfunction or physiological aberrations. We also discuss critical events that can occur during perfusion and the need to monitor for organ perfusion in altered physiologic states emanating from hemodilution, hypothermia, and acid–base alterations.

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.