Optimized CT-imaging Protocol in VA-ECMO Patients After Cardiopulmonary Resuscitation - a Single-center Prospective Non-randomized Cohort Study

Background:

Extracorporal membrane oxygenation (ECMO) is an increasingly applied method of last resort for treating severe respiratory or combined cardiopulmonary failure. Different configurations of cannulation, either veno-venous (VV) or veno-arterial (VA), are used depending on indication. The latter is commonly used in patients under cardiopulmonary resuscitation to temporarily provide adequate organ-perfusion until the underlying pathology is found and treated. Alas being a revolutionary method, there is also a non-negligible number of vascular complications due to necessary insertion of cannulas in large vessels in combination with full anticoagulation. Therefore, these patients are regularly examined with a subsequent contrast-enhanced computed tomography to rule out complications and search for potential underlying causes of cardiac arrest. However, the extraordinary hemodynamic situation resulting from VA-cannulation with antegrade and retrograde perfusion challenges the diagnostically required simultaneous opacification of pulmonary and systemic arterial vessels. In this setting, siphoning, mixing and dilution effects of contrast agent and non-contrasted blood often cause incomplete or inhomogeneous vessel contrast, rendering exams partially non-diagnostic. Evidence regarding the effect of cannula position, ECMO flow rate, cardiac function and contrast agent injection site is scarce and as yet, to the best of the authors' knowledge, no standardized scan protocol for this patient collective exists.

Methods:

All adult emergency department patients at the Vienna General Hospital with femoro-femoral VA-ECMO and undergoing or recent cardiopulmonary resuscitation, who are subsequently referred to a clinically indicated CT scan for the detection of causes and complications or their exclusion, will be included in this study, aiming for a total of n=50 patients. The first 25 consecutive patients will be assigned to the intervention (flow reduction) cohort and the following 25 consecutive patients will be assigned to the control (no flow reduction) cohort. Clinical data (e.g. ECMO flow rate, ventilation parameters, cardiac function, venous line for contrast injection) at the time of imaging will be retrieved from the accompanying treating physician and are documented via a standardized data sheet.

In the intervention cohort ECMO flow rate is reduced for the duration of contrast administration and acquisition of an arterial and venous phase of the whole body (max. 1-2 minutes) given the hemodynamic and respiratory situation allows it. Whether this is possible, is determined right before the CT scan by the accompanying emergency physician and adapted to the individually tolerable level (max. 50% of initial flow, no less than 1,5 liter/min). After image acquisition, ECMO flow rate is then immediately returned to the initial or clinically optimal value at this moment. If the patient shows any signs of instability during this short period of imaging acquisition, the scan will be interrupted and immediate countermeasures will be taken by the accompanying team of emergency physicians and nurses. During the examination the vital signs of all patients are permanently monitored. The applied CT protocol is the established protocol at our department and comprises a non-contrast-enhanced cranial CT (CCT), CT angiography (CTA) of the aorta as well as a portal-venous phase of the chest and abdomen. Complementary scans, e.g. CT of cervical spine or CTA of cerebral arteries, will be performed as clinically indicated. After the examination, ECMO flow rate will be increased to the initial or at this point clinically optimal value and the acquired images are, within clinical routine, immediately reviewed and reported by the radiologist in charge. Diagnostic quality of the acquired images, vessel opacification, the impact of CT findings and diagnoses on clinical management as well as resulting management changes will be documented and analyzed.