Cannula position and Bernoulli effect contribute to leg malperfusion during extracorporeal life support with femoral arterial cannulation-an in silico simulation study†

Preventing Acute Limb Ischemia during VA-ECMO-In Silico Analysis of Physical Parameters Associated with Lower Limb Perfusion

BACKGROUND

Peripheral femoro-femoral veno-arterial extracorporeal membrane oxygenation is increasingly used in refractory cardiogenic shock. However, the obstruction of the femoral artery by the return cannula could lead to acute limb ischemia, a frequently encountered situation that is inconstantly prevented by the adjunction of a distal perfusion cannula (DPC). The aim of this study was to investigate the influence of three physical parameters on the perfusion of the cannulated lower limb.

METHODS

Using patient-specific arterial models and computational fluid dynamic simulations, we studied four diameters of arterial cannula, three diameters of DPC, and two percentages of arterial section limitation.

RESULTS

We found that adequate perfusion of the cannulated limb was achieved in only two out of the twenty-one configurations tested, specifically, when the arterial cannula had a diameter of 17 Fr, was considered to limit the section of the artery by 90%, and was associated with an 8 Fr or a 10 Fr DPC. Multivariable analysis revealed that the perfusion of the cannulated lower limb was correlated with the diameter of the DPC, but also with the diameter of the arterial cannula and the percentage of arterial section limitation.

CONCLUSIONS

In most of the cases simulated here, the current system combining unsized arterial cannula and non-specific DPC was not sufficient to provide adequate perfusion of the cannulated lower limb, urging the need for innovative strategies to efficiently prevent acute limb ischemia during peripheral femoro-femoral veno-arterial extracorporeal membrane oxygenation.

The effect of arterial cannula tip position on differential hypoxemia during venoarterial extracorporeal membrane oxygenation

Interaction between native ventricular output and venoarterial extracorporeal membrane oxygenation (VA ECMO) flow may hinder oxygenated blood flow to the aortic arch branches, resulting in differential hypoxemia. Typically, the arterial cannula tip is placed in the iliac artery or abdominal aorta. However, the hemodynamics of a more proximal arterial cannula tip have not been studied before. This study investigated the effect of arterial cannula tip position on VA ECMO blood flow to the upper extremities using computational fluid dynamics simulations. Four arterial cannula tip positions (P1. common iliac, P2. abdominal aorta, P3. descending aorta and P4. aortic arch) were compared with different degrees of cardiac dysfunction and VA ECMO support (50%, 80% and 90% support). P4 was able to supply oxygenated blood to the arch vessels at all support levels, while P1 to P3 only supplied the arch vessels during the highest level (90%) of VA ECMO support. Even during the highest level of support, P1 to P3 could only provide oxygenated VA-ECMO flow at 0.11 L/min to the brachiocephalic artery, compared with 0.5 L/min at P4. This study suggests that cerebral perfusion of VA ECMO flow can be increased by advancing the arterial cannula tip towards the aortic arch.

Serum Myoglobin Is Associated With Postoperative Acute Kidney Injury in Stanford Type A Aortic Dissection

Background

The correlation between rhabdomyolysis and postoperative acute kidney injury has been reported in several surgical procedures. As a good predictor of rhabdomyolysis-related acute kidney injury, an elevated serum myoglobin level was often observed after total aortic arch replacement combined with frozen elephant trunk implantation. However, the correlation between serum myoglobin and acute kidney injury in such patients had not been established.

Methods

Totally 398 stanford type A aortic dissection patients who underwent total aortic arch replacement combined with frozen elephant trunk implantation were enrolled in this retrospective study. The correlations between serum myoglobin and acute kidney injury as well as the 30-day mortality were assessed.

Results

Overall, 268(67.3%) patients had acute kidney injury (KDIGO stage 1 or higher) and 75(18.8%) had severe acute kidney injury (KDIGO stage 2&3). Patients who developed acute kidney injury had higher level of perioperative serum myoglobin than patients without acute kidney injury. After adjusting for known acute kidney injury risk factors, logarithmically transformed preoperative serum myoglobin [OR = 1.58 (95% CI, 1.26–1.95), P < 0.001] and postoperative day 1 serum myoglobin [OR = 3.47 (95%CI, 2.27–5.29), P < 0.001] were associated with severe acute kidney injury. These correlation persisted after adjustment for decline in filtration via change in serum creatinine (ΔCr) and biomarkers of cardiac and kidney injury, including N-terminal prohormone of brain natriuretic peptide, cardiac troponin I, creatine kinase-MB, serum creatinine and Cystatin C. Compared with the clinical model, sMb considerably improved the risk discrimination and reclassification for AKI.

Conclusion

For stanford type A aortic dissection patients underwent total aortic arch replacement with frozen elephant trunk implantation, serum myoglobin can improve postoperative acute kidney injury risk classification. Rhabdomyolysis may be an important supplement to the existing knowledge on the mechanism of acute kidney injury.

Effect of cannulation site on emboli travel during cardiac surgery

Background

During cardiac surgery, micro-air emboli regularly enter the blood stream and can cause cognitive impairment or stroke. It is not clearly understood whether the most threatening air emboli are generated by the heart-lung machine (HLM) or by the blood-air contact when opening the heart. We performed an in vitro study to assess, for the two sources, air emboli distribution in the arterial tree, especially in the brain region, during cardiac surgery with different cannulation sites.

Methods

A model of the arterial tree was 3D printed and included in a hydraulic circuit, divided such that flow going to the brain was separated from the rest of the circuit. Air micro-emboli were injected either in the HLM (“ECC Bubbles”) or in the mock left ventricle (“Heart Bubbles”) to simulate the two sources. Emboli distribution was measured with an ultrasonic bubble counter. Five repetitions were performed for each combination of injection site and cannulation site, where air bubble counts and volumes were recorded. Air bubbles were separated in three categories based on size.

Results

For both injection sites, it was possible to identify statistically significant differences between cannulation sites. For ECC Bubbles, axillary cannulation led to a higher amount of air bubbles in the brain with medium-sized bubbles. For Heart Bubbles, aortic cannulation showed a significantly bigger embolic load in the brain with large bubbles.

Conclusions

These preliminary in vitro findings showed that air embolic load in the brain may be dependent on the cannulation site, which deserves further in vivo exploration.

A Computational Fluid Dynamics Study of the Extracorporeal Membrane Oxygenation-Failing Heart Circulation

Extracorporeal membrane oxygenation (ECMO) is increasingly deployed to provide percutaneous mechanical circulatory support despite incomplete understanding of its complex interactions with the failing heart and its effects on hemodynamics and perfusion. Using an idealized geometry of the aorta and its major branches and a peripherally inserted return cannula terminating in the iliac artery, computational fluid dynamic simulations were performed to (1) quantify perfusion as function of relative ECMO flow and (2) describe the watershed region produced by the collision of antegrade flow from the heart and retrograde ECMO flow. To simulate varying degrees of cardiac failure, ECMO flow as a fraction of systemic perfusion was evaluated at 100%, 90%, 75%, and 50% of total flow with the remainder supplied by the heart calculated from a patient-derived flow waveform. Dynamic boundary conditions were generated with a three-element lumped parameter model to accurately simulate distal perfusion. In profound failure (ECMO providing 90% or more of flow), the watershed region was positioned in the aortic arch with minimal pulsatility observed in the flow to the visceral organs. Modest increases in cardiac flow advanced the watershed region into the thoracic aorta with arch perfusion entirely supplied by the heart.

Femoral artery anatomy is a risk factor for limb ischemia in minimally invasive cardiac surgery

OBJECTIVE

In minimally invasive cardiac surgery (MICS), femoral artery cannulation during cardiopulmonary bypass (CPB) can cause limb ischemia. This study evaluated the association between femoral artery anatomy and the risk of limb ischemia in MICS.

METHODS

Eighty-one patients who underwent MICS with CPB using single femoral artery cannulation between 2010 and 2018 were included. The patients were stratified by their femoral artery diameter and anatomy of ectopic side branch, i.e., medial or lateral femoral circumflex arteries: Type A, deep femoral artery (DFA) ≥ superficial femoral artery (SFA); type B, DFA < SFA with an ectopic side branch of the common femoral artery (CFA); type C, DFA < SFA with an ectopic side branch at the CFA bifurcation; and type D, DFA < SFA without an ectopic side branch. The ratio of the postoperative creatine kinase concentration and the cross-sectional area of the femoral muscles (CK/MA) was used as a surrogate marker of limb ischemia. Predictors of high CK/MA were evaluated.

RESULTS

No critical limb ischemia was observed in this study. The median postoperative creatine kinase and CK/MA were 1954 (1305-2872) IU/l and 15.2 (9.2-19.8) IU/l/cm². Multivariable logistic regression found that anatomical type D (odds ratio 4.19, 95% confidence interval: (1.26-14.0); p = 0.020) and prolonged CPB time (OR 1.01, 95% CI (1.00-1.02); p = 0.045) were independent risk factors of high CK/MA.

CONCLUSION

Anatomical type D and prolonged CPB time were associated with risk of limb ischemia in MICS.