Hemodynamic changes in patients with extracorporeal membrane oxygenation (ECMO) demonstrated by contrast-enhanced CT examinations - implications for image acquisition technique

Position paper on the physiology and nomenclature of dual circulation during venoarterial ECMO in adults

When native blood flow through the aorta from the adult heart and lungs meets retrograde blood flow from an artificial heart and lung during venoarterial extracorporeal membrane oxygenation (VA-ECMO), the result is the creation of two separate circulations on either side of the blood flow mixing point. This phenomenon is known as dual circulation and is characterized by different content of oxygen and carbon dioxide between the circulations. There is currently a lack of clarity surrounding the nomenclature to describe this physiologic phenomenon in VA-ECMO and thus we endeavor to name and define these terms to facilitate clear communication and proper clinical management of these patients.

Effects of veno-arterial extracorporeal membrane oxygenation return cannula side hole structure on aortic hemodynamic features under different perfusion levels

INTRODUCTION

The interaction between primary left ventricular output and Veno-arterial extracorporeal membrane pulmonary oxygenation (VA ECMO) flow may impede the perfusion of aortic vessels with hyperoxic blood, leading to differential oxygenation. ECMO return cannula design significantly influences the perfusion level of blood supplied via ECMO. This study aimed to investigate the impact of various cannula designs (side hole number) on intravascular flow patterns under different blood perfusion conditions.

METHODS

Six return cannula models with different side hole number and three cardiac output waveforms were designed based on clinical data for comparative analysis.

RESULTS

The position of the blood mixing zone (MZ) was influenced by the flow-volume ratio of the heart output (CO/(CO+Qec)) and cannula design. As the CO/(CO+Qec) and the number of side holes in the cannula increased, the MZ shifted from the ascending aorta to the descending aorta. Concurrently, aortic wall and scalar shear stress on the impact side of ECMO cannulation reduced progressively. Return cannula with side holes effectively mitigated discrepancies in the perfusion of the renal artery and inadequate perfusion of the lower limb vessels on the cannula side while simultaneously reducing damage to the vessel walls and blood. However, increasing the number of side holes in the return cannulas resulted in diminished perfusion of the aortic arch bifurcation vessels by hyperoxic blood supplied via ECMO.

CONCLUSION

Increasing the number of return cannula side holes for VA ECMO femoral artery cannulation improves hypoxic perfusion in the lower limb and reduces vascular endothelial injury, but may also lead to inadequate hypoxic perfusion in the upper body.

Prognostic Impact of Serial Imaging in Severe Acute Respiratory Distress Syndrome on the Extracorporeal Membrane Oxygenation

BACKGROUND

The impact of serial imaging on the outcome of ICU patients has not been studied specifically in patients with high illness severity.

METHODS

The authors sought a relationship between the numbers of antero-posterior supine chest X-rays (CXR), computed tomography (CT) examinations, and outcome in a cohort of 292 patients with severe COVID-19 ARDS collected over 24 months in a high-volume ECMO center with established ultrasound and echocardiographic diagnostics. Of the patients, 172 (59%) were obese or morbidly obese, and 119 (41%) were treated with ECMO.

RESULTS

The median number of CXRs was eight per 14 days of the length of stay in the ICU. The CXR rate was not related to ICU survival (p = 0.37). Patients required CT scanning in 26.5% of cases, with no relationship to the outcome except for the better ICU survival of the ECMO patients without a need for a CT scan (p = 0.01). The odds ratio for survival associated with ordering a CT scan in an ECMO patient was 0.48, p = 0.01. The calculated savings for not routinely requesting a whole-body CT scan in every patient were 98.685 EUR/24 months.

CONCLUSIONS

Serial imaging does not impact the survival rates of patients with severe ARDS. Extracorporeal membrane oxygenation patients who did not need CT scanning had significantly better ICU outcomes.

Routine whole-body CT identifies clinically significant findings in patients supported with veno-venous extracorporeal membrane oxygenation

AIM

To determine the yield of routine whole-body computed tomography (CT) following extracorporeal membrane oxygenation (ECMO) initiation and to assess the association of these findings with prognosis.

MATERIALS AND METHODS

One hundred and ninety-eight consecutive patients with acute respiratory failure admitted for ECMO support between January 2015 and December 2019 who underwent whole-body CT performed within 48 h of ECMO initiation were examined in this single-institution retrospective study. CT findings were divided into three categories: clinically significant findings that may affect immediate management strategy or short-term outcomes; findings not related to hospital stay or outcome but require further workup; and benign findings that do not require further investigation. Logistic regression analysis was used to assess the association of CT findings with 7- and 30-day survival.

RESULTS

Clinically significant findings were present in 147 (74%) patients, findings requiring further workup were found in 82 (41%) patients, and benign findings were identified in 180 (90%) of the patients. Patients with clinically significant neurological findings had an elevated risk of death at 7 days (odds ratio [OR] 3.58; 95% confidence interval [CI] 1.29; 9.93; p=0.01), but not 30 days. Increasing numbers of clinically significant findings were associated with greater odds of mortality at 7 days (OR 1.70; 95% CI 1.08; 2.67; p=0.02) and 30 days (OR 1.41; 95% CI 1.02; 1.96; p=0.04).

CONCLUSIONS

Imaging patients at the point of admission for VV-ECMO with CT frequently identified clinically significant abnormalities with prognostic implications of these. These findings provide support for the use of more routine CT at the point of treatment escalation with prospective studies now required.

Performing chest computed tomography on pediatric patients on extracorporeal membrane oxygenation (ECMO): a stepwise approach

Chest CT in pediatric patients on extracorporeal membrane oxygenation (ECMO) can be done safely and provide valuable high-quality diagnostic images to help guide patient management. An understanding of the basics of the ECMO circuit, cannula locations, where and how to inject contrast media, and how to time image acquisition is vital for the radiologist. Additionally, understanding the precautions associated with performing these exams is essential to ensure the safety of the child. This article provides a brief review of pediatric ECMO and its challenges and considerations, as well as a stepwise approach to perform and optimize these exams safely.

Atrial Septostomy for Left Ventricular Unloading During Extracorporeal Membrane Oxygenation for Cardiogenic Shock: Animal Model

OBJECTIVES

The aim of this study was to quantify and understand the unloading effect of percutaneous balloon atrial septostomy (BAS) in acute cardiogenic shock (CS) treated with venoarterial (VA) extracorporeal membranous oxygenation (ECMO).

BACKGROUND

In CS treated with VA ECMO, increased left ventricular (LV) afterload is observed that commonly interferes with myocardial recovery or even promotes further LV deterioration. Several techniques for LV unloading exist, but the optimal strategy and the actual extent of such procedures have not been fully disclosed.

METHODS

In a porcine model (n = 11; weight 56 kg [53-58 kg]), CS was induced by coronary artery balloon occlusion (57 minutes [53-64 minutes]). Then, a step-up VA ECMO protocol (40-80 mL/kg/min) was run before and after percutaneous BAS was performed. LV pressure-volume loops and multiple hemoglobin saturation data were evaluated. The Wilcoxon rank sum test was used to assess individual variable differences.

RESULTS

Immediately after BAS while on VA ECMO support, LV work decreased significantly: pressure-volume area, end-diastolic pressure, and stroke volume to ∼78% and end-systolic pressure to ∼86%, while superior vena cava and tissue oximetry did not change. During elevating VA ECMO support (40-80 mL/kg/min) with BAS vs without BAS, we observed 1) significantly less mechanical work increase (122% vs 172%); 2) no end-diastolic volume increase (100% vs 111%); and 3) a considerable increase in end-systolic pressure (134% vs 144%).

CONCLUSIONS

In acute CS supported by VA ECMO, atrial septostomy is an effective LV unloading tool. LV pressure is a key component of LV work load, so whenever LV work reduction is a priority, arterial pressure should carefully be titrated low while maintaining organ perfusion.

Evaluation, Treatment, and Impact of Neurologic Injury in Adult Patients on Extracorporeal Membrane Oxygenation: a Review

Purpose

Extracorporeal membrane oxygen (ECMO) is increasingly used as an advanced form of life support for cardiac and respiratory failure. Unfortunately, in infrequent instances, circulatory and/or respiratory recovery is overshadowed by neurologic injury that can occur in patients who require ECMO. As such, knowledge of ECMO and its implications on diagnosis and treatment of neurologic injuries is indispensable for intensivists and neurospecialists.

Recent findings

The most common neurologic injuries include intracerebral hemorrhage, ischemic stroke, seizure, cerebral edema, intracranial hypertension, global cerebral hypoxia/anoxia, and brain death. These result from events prior to initiation of ECMO, failure of ECMO to provide adequate oxygen delivery, and/or complications that occur during ECMO. ECMO survivors also experience neurological and psychological sequelae similar to other survivors of critical illness.

Summary

Since many of the risk factors for neurologic injury cannot be easily mitigated, early diagnosis and intervention are crucial to limit morbidity and mortality from neurologic injury during ECMO.

Optimizing Contrast-Enhanced Thoracoabdominal CT in Patients During Extracorporeal Membrane Oxygenation

RATIONALE AND OBJECTIVES

To evaluate the quality and value of contrast-enhanced (CE) chest- and abdominal computed tomography (CT) and CT angiography in neonates, children, and adults undergoing extracorporeal membrane oxygenation (ECMO) using a customized protocol for contrast delivery.

MATERIALS AND METHODS

All patients admitted for CE thoracic- and/or abdominal CT while on ECMO were prospectively included in the study. A protocol for contrast delivery adapted for the type of ECMO circulation, cannulation sites, anatomy of interest, and desired contrast phase was applied. Clinical information, ECMO and CT technique, including contrast administration strategy, was noted for each patient. Two radiologists separately evaluated the quality of the scan. The value of the examination was decided in consensus with the referring ECMO physician.

RESULTS

One hundred thirty CE thoracoabdominal scans were performed at 103 different occasions during the study time. Eighty-nine scans were performed during veno-arterial ECMO and 41 during veno-venous ECMO. In the majority, contrast was delivered to the oxygenator with preserved ECMO flow. A peripheral or central venous line with reduced flow was utilized in the remaining cases. Mean scan quality was graded 4.2 on a five-grade scale. In 56% of the examinations, the findings affected the immediate treatment of the patient.

CONCLUSION

High-quality CT and CT angiography can be achieved in ECMO patients of different ages and clinical issues considering the type of ECMO circulation, ECMO cannulation sites, preferred contrast phase and anatomy of interest. CT diagnoses affect the treatment of the patient.

Multiscale modeling of blood flow to assess neurological complications in patients supported by venoarterial extracorporeal membrane oxygenation

Computational blood flow models in large arteries elucidate valuable relationships between cardiovascular diseases and hemodynamics, leading to improvements in treatment planning and clinical decision making. One such application with potential to benefit from simulation is venoarterial extracorporeal membrane oxygenation (VA-ECMO), a support system for patients with cardiopulmonary failure. VA-ECMO patients develop high rates of neurological complications, partially due to abnormal blood flow throughout the vasculature from the VA-ECMO system. To better understand these hemodynamic changes, it is important to resolve complex local flow parameters derived from three-dimensional (3D) fluid dynamics while also capturing the impact of VA-ECMO support throughout the systemic arterial system. As high-resolution 3D simulations of the arterial network remain computationally expensive and intractable for large studies, a validated, multiscale model is needed to compute both global effects and high-fidelity local hemodynamics. In this work, we developed and demonstrated a framework to model hemodynamics in VA-ECMO patients using coupled 3D and one-dimensional (1D) models (1D→3D). We demonstrated the ability of these multiscale models to simulate complex flow patterns in specific regions of interest while capturing bulk flow throughout the systemic arterial system. We compared 1D, 3D, and 1D→3D coupled models and found that multiscale models were able to sufficiently capture both global and local hemodynamics in the cerebral arteries and aorta in VA-ECMO patients. This study is the first to develop and compare 1D, 3D, and 1D→ 3D coupled models on the larger arterial system scale in VA-ECMO patients, with potential use for other large scale applications.

Imaging Adult ECMO

Adult extracorporal membrane oxygenation utilization in the ICU has rapidly increased. Newer technology and cannulation strategies and the complex hemodynamics make imaging interpretation challenging. There is also a high rate of complications. This review details the common indications, cannulation strategies, relevant hemodynamics and complications which impact imaging interpretation. Recommendations for modifying computed tomography protocols and techniques to obtain diagnostic images and some of the imaging pitfalls are also discussed.

Pediatric extracorporeal membrane oxygenation (ECMO): a guide for radiologists

Extracorporeal membrane oxygenation (ECMO) is a life-saving treatment for pediatric patients with respiratory and/or cardiac failure. The ECMO circuit oxygenates and sometimes pumps the blood, effectively replacing lung and/or heart function temporarily. ECMO patients are clinically very complex not only because of their underlying, life-threatening pathology, but also because of the many physiological parameters that must be monitored and adjusted to maintain adequate tissue perfusion and oxygenation. Drainage and reinfusion cannulae connecting the patient to the ECMO circuit are visible on radiograph. These cannulae have different functions, different configurations, different radiographic appearances, and different positions that should be familiar to the interpreting pediatric radiologist. The primary complications of ECMO include hemorrhage, thrombosis and ischemia, as well as equipment failure and cannula malpositioning, all of which may be detected on imaging. In this pictorial essay, we discuss the basics of ECMO function and clinical management, ECMO cannula features and configurations, and the many complications of ECMO from an imaging perspective. Our goal is to educate pediatric radiologists about ECMO imaging, equipping them to properly interpret these studies and to become a useful consultant in ECMO patient care.

Routine CT scanning of patients retrieved to a tertiary centre on veno-venous extracorporeal membrane oxygenation: a retrospective risk benefit analysis

INTRODUCTION

Comprehensive clinical examination can be compromised in patients on veno-venous extracorporeal membrane oxygenation (VV-ECMO). Adjunctive diagnostic imaging strategies range from bedside imaging only to routine computed tomography (CT). The risk-benefit of either approach remains to be evaluated. Patients retrieved to the Royal Brompton Hospital (RBH) on VV-ECMO routinely undergo admission CT imaging of head, chest, abdomen and pelvis. This study aimed to identify how frequently changes in therapy or adverse events could be attributed to routine CT scanning.

METHODS

Demographic and clinical data were gathered retrospectively from patients retrieved to RBH on VV-ECMO (January 2014-2016). Scans were categorized as 'routine' or requested to clarify a specific clinical uncertainty. Clinical records were reviewed to identify attributable management changes and CT- related adverse events. Seventy-two patients were retrieved on VV-ECMO (median age 44 years) and 65 scanned on admission (mean radiation dose 2344mGy-cm). Routine head CT head yielded novel clinical information in 11 patients, 10 of whom had unexpected intracranial haemorrhage and, subsequently, had their anticoagulation withheld. Routine thoracic CT identified unexpected positive findings in three patients (early fibrosis, pulmonary vasculitis, pneumomediastinum), eliciting management variation in one (steroid administration). Routine abdomen/pelvis CT identified new information in three patients (adrenal haemorrhage, hepatosteatosis, splenic infarction), changing the management in one (withholding anticoagulation).

RESULTS

CT scanning was not associated with consequential adverse events (e.g. accidental decannulation, gas entrainment into the circuit, hypoxia, hypotension). Median transfer/scan time was 78 minutes, requiring five ITU staff-members. In our cohort, a policy of routine head CT changed the management in 17% of patients; the yield from routine chest, abdomen and pelvis CT was modest. CT transfer was safe, but resource intensive.

CONCLUSION

Prospective studies should evaluate whether routine CT impacts outcome.