Risk factors for hemolysis with centrifugal pumps in pediatric extracorporeal membrane oxygenation: Is pump replacement an answer?

INTRODUCTION: Hemolysis during pediatric extracorporeal membrane oxygenation (ECMO) is associated with increased risk for renal failure and mortality. OBJECTIVES: We aim to describe risk factors for hemolysis in pediatric ECMO supported by centrifugal pumps. METHODS: We conducted an analysis of retrospective data collected at an academic children's hospital from January 2017 to December 2019. MEASUREMENTS AND RESULTS: Plasma-free hemoglobin (PFH) levels were measured daily, and hemolysis was defined as PFH>50 mg/dL. Of 46 ECMO runs over 528 ECMO days, hemolysis occurred in 23 (58%) patients over a total of 40 (8%) ECMO days. In multivariable logistic regression models, VA-ECMO (aOR=4.69, 95% CI: 1.01-21.83) and higher hemoglobin (aOR = 1.38, 95% CI: 1.06-1.81) were independently associated with hemolysis. There were also non-significant trends toward increased risk for hemolysis with higher rotational pump speed (aOR=2.39, 95% CI: 0.75-7.65), higher packed red blood cell transfusions (aOR=1.15, 95% CI: 0.99-1.34), and higher cryoprecipitate transfusions (aOR=2.01, 95% CI: 0.83-4.86). Isolated pump exchanges that were performed in 12 patients with hemolysis led to significant decreases in PFH levels within 24 h (89 vs 11 mg/dL, p<0.01). CONCLUSIONS: Hemolysis is common in pediatric ECMO using centrifugal pumps. Avoidance of high pump speeds and conservative administration of blood products may help to mitigate the risk for hemolysis. Furthermore, pump exchange may be an effective first-line treatment for hemolysis.

Flow Monitoring of ECMO Circuit for Detecting Oxygenator Obstructions.

Oxygenator thrombosis during extracorporeal membrane oxygenation (ECMO), is a complication that necessitates component replacement. ECMO centers monitor clot burden by intermittent measurement of pressure drop across the oxygenator. An increase in pressure drop at a preset flow rate suggests an increase in resistance/clot formation within the oxygenator. This monitoring method comes with inherent disadvantages such as monitoring gaps, and increased risk of air embolism and infection. We explored utilizing flow measurement, which avoids such risks, as an indicator of ECMO circuit obstructions. The hypothesis that flow rate through a shunt tube in the circuit will increase as distal resistances in the circuit increases was tested. We experimentally simulated controlled levels of oxygenator obstructions using glass microspheres in an ex vivo veno-venous ECMO circuit and measured the change in shunt flow rate using over the tube ultra-sound flow probes. A mathematical model was also used to study the effect of distal resistances in the ECMO circuit on shunt flow. Results of both the mathematical model and the experiments showed a clear and measurable increase in shunt flow with increasing levels of oxygenator obstruction. Therefore, flow monitoring appears to be an effective non-contact and continuous method to monitor for obstruction during ECMO.

Electrochemical Approach to Measure Physiological Fluid Flow Rates.

In vivo measurement of the flow rate of physiological fluids such as the blood flow rate in the heart is vital in critically ill patients and for those undergoing surgical procedures. The reliability of these measurements is therefore quite crucial. However, current methods in practice for measuring flow rates of physiological fluids suffer from poor repeatability and reliability. Here, we assessed the feasibility of a flow rate measurement method that leverages time transient electrochemical behavior of a tracer that is injected directly into a medium (the electrochemical signal caused due to the tracer injectate will be diluted by the continued flow of the medium and the time response of the current-the electrodilution curve-will depend on the flow rate of the medium). In an experimental flow loop apparatus equipped with an electrochemical cell, we used the AC voltammetry technique and tested the feasibility of electrodilution-based measurement of the flow rate using two mediums-pure water and anticoagulated blood-with 0.9 wt% saline as the injectate. The electrodilution curve was quantified using three metrics-change in current amplitude, total time, and change in the total charge for a range of AC voltammetry settings (peak voltages and frequencies). All three metrics showed an inverse relationship with the flow rate of water and blood, with the strongest negative correlation obtained for change in current amplitude. The findings are a proof of concept for the electrodilution method of the flow rate measurement and offer the potential for physiological fluid flow rate measurement in vivo.

Accuracy of detecting enlargement of aneurysms using different MRI modalities and measurement protocols.

OBJECTIVE: Aneurysm growth is considered predictive of future rupture of intracranial aneurysms. However, how accurately neuroradiologists can reliably detect incremental aneurysm growth using clinical MRI is still unknown. The purpose of this study was to assess the agreement rate of detecting aneurysm enlargement employing generally used MRI modalities. METHODS: Three silicone flow phantom models, each with 8 aneurysms of various sizes at different sites, were used in this study. The aneurysm models were identical except for an incremental increase in the sizes of the 8 aneurysms, which ranged from 0.4 mm to 2 mm. The phantoms were imaged on 1.5-T and 3-T MRI units with both time-of-flight (TOF) and contrast-enhanced MR angiography. Three independent expert neuroradiologists measured the aneurysms in a blinded manner using different measurement approaches. The individual and agreement detection rates of aneurysm enlargement among the 3 experts were calculated. RESULTS: The mean detection rate of any increase in any aneurysmal dimension was 95.7%. The detection rates of the 3 observers (observers A, B, and C) were 98.0%, 96.6%, and 92.7%, respectively (p = 0.22). The detection rates of each MRI modality were 91.3% using 1.5-T TOF, 97.2% using 1.5-T with Gd, 95.8% using 3.0-T TOF, and 97.2% using 3.0-T with Gd (p = 0.31). On the other hand, the mean detection rate for aneurysm enlargement was 54.8%. Specifically, the detection rates of observers A, B, and C were 49.0%, 46.1%, and 66.7%, respectively (p = 0.009). As the incremental enlargement value increased, the detection rate for aneurysm enlargement increased. The use of 1.5-T Gd improved the detection rate for small incremental enlargement (e.g., 0.4­1 mm) of the aneurysm (p = 0.04). The location of the aneurysm also affected the detection rate for aneurysm enlargement (p < 0.0001). CONCLUSIONS: The detection rate and interobserver agreement were very high for aneurysm enlargement of 0.4­2 mm. The detection rate for at least 1 increase in any aneurysm dimension did not depend on the choice of MRI modality or measurement protocol. Use of Gd improved the accuracy of measurement. Aneurysm location may influence the accuracy of detecting enlargement.