Technical Indicators to Evaluate the Degree of Large Clot Formation Inside the Membrane Fiber Bundle of an Oxygenator in an In Vitro Setup

Abstract

The most common technical complication during ECMO is clot formation. A large clot inside a membrane oxygenator reduces effective membrane surface area and therefore gas transfer capabilities, and restricts blood flow through the device, resulting in an increased membrane oxygenator pressure drop (dpMO). The reasons for thrombotic events are manifold and highly patient specific. Thrombus formation inside the oxygenator during ECMO is usually unpredictable and remains an unsolved problem. Clot sizes and positions are well documented in literature for the Maquet Quadrox-i Adult oxygenator based on CT data extracted from devices after patient treatment. Based on this data, the present study was designed to investigate the effects of large clots on purely technical parameters, for example, dpMO and gas transfer. Therefore, medical grade silicone was injected into the fiber bundle of the devices to replicate large clot positions and sizes. A total of six devices were tested in vitro with silicone clot volumes of 0, 30, 40, 50, 65, and 85 mL in accordance with ISO 7199. Gas transfer was measured by sampling blood pre and post device, as well as by sampling the exhaust gas at the devices' outlet at blood flow rates of 0.5, 2.5, and 5.0 L/min. Pre and post device pressure was monitored to calculate the dpMO at the different blood flow rates. The dpMO was found to be a reliable parameter to indicate a large clot only in already advanced "clotting stages." The CO concentration in the exhaust gas, however, was found to be sensitive to even small clot sizes and at low blood flows. Exhaust gas CO concentration can be monitored continuously and without any risks for the patient during ECMO therapy to provide additional information on the endurance of the oxygenator. This may help detect a clot formation and growth inside a membrane oxygenator during ECMO even if the increase in dpMO remains moderate.

Dynamic oxygenator blood volume during prolonged extracorporeal life support

“…The relationship between oxygenator resistance and clot volume thus seems to become more quantitative at higher values, hence the stronger correlation with the quantitative OXBV value. This is in line with a study by Kaesler et al who showed that the increase in oxygenator pressure drop is modest up to a clot volume of 65 mL, and reports that pressure drop remains a vague indicator and seems to be reliable only in already advanced clotting stages [ 9 ].…”

“…Clots in low flow areas of an oxygenator will cause less resistance than clots in high flow areas [ 8 ]. Consequently, relative changes in oxygenator resistance are not proportional to the amount of clot formation [ 8 , 9 ]. Oxygen transfer performance can also be decreased by fluid accumulation in the gas compartment [ 10 – 12 ].…”

Novel application of indocyanine green fluorescence imaging for real‐time detection of thrombus in a membrane oxygenator

“…According to previous studies from other institutions, injection of a thrombus-inducing substance from the inlet side chamber was strongly associated with a decrease in the gas exchange capability of the oxygenator. 13 According to previous findings and those of the present study, the thrombus formed in the inlet side chamber may affect the gas exchange capability of the oxygenator, although it is unlikely to be a source of thromboembolism. In this study, a thrombus was formed so as to adhere to the blood contact surface of the outlet-side housing.…”

Toward a Long-Term Artificial Lung

“…However, there is still no reliable, easy to use method, which allows the prediction of thrombus formation at an early stage to adapt the anticoagulation strategy to the acute demand of the patient. 16 Special magnetic resonance imaging (MRI) methods make it possible to visualize thrombus formation in the system, but they require completely nonferromagnetic circuit components and imply a high level of technical and medical complexity. 17 , 18 …”