Introduction: Veno-arterial extracorporeal membrane oxygenation (VA-ECMO) is used for hemodynamic support in critically ill patients with circulatory failure. It has been shown, that the use of VA-ECMOs induces an inflammatory response syndrome, which potentially provokes severe complications and a poor outcome. Monocytes play a key role in the innate immune system. They can be differentiated according to their expression of the surface markers CD14 and CD16 into classical (CD14++CD16-), intermediate (CD14++CD16+) and non-classical (CD14+CD16++) monocytes, each with distinct functions. Several markers have been described as markers for monocyte activation. Including CD163, CD86, CD69, CX3CR1 and the leukocyte integrin Mac-1. The unique small binding proteins, Designed Ankyrin Repeat Protein F7 and single chain variable fragment MAN-1, specifically detect the activated conformation of the leukocyte integrin Mac-1 enabling the highly sensitive detection of monocyte activation status. The aim of this study was to characterize monocyte function and heterogeneity and their association with outcome in VAECMO patients.

Methods: Patients receiving veno-arterial ECMO therapy were recruited from the intensive care units of the medical and heart surgical intensive care units of the University Hospital in Freiburg, Germany. Blood samples were obtained on day 0 and day 3 after VA-ECMO placement, after VA-ECMO explantation and from healthy controls. Monocyte baseline activation, stimulability and subset distribution were analyzed by flow cytometry using the unique small binding proteins F7 and MAN-1 and the activation markers CD163, CD86, CD69 and CX3CR1. Additionally, expression of monocyte activation markers in survivors and non-survivors on day 0 was compared. Furthermore, simple logistic regression was conducted to determine the association of monocyte activation markers with mortality. 

Results: 22 patients on VA-ECMO and 15 healthy controls were recruited. 11 patients survived until discharge from the intensive care unit. Compared to healthy controls, baseline monocyte activation was significantly increased, whereas stimulability was decreased. The percentage of classical monocytes increased after explantation, while the percentage of intermediate monocytes decreased. Total, classical and intermediate monocyte counts were significantly elevated compared to controls. On day 0, baseline binding of F7 was significantly lower in non-survivors than survivors. The area under the ROC curve associated with mortality on day 0 was 0.802 (p=0.02). 

 

Conclusion: Compared to controls distribution of monocyte subsets changes during VA-ECMO and absolute counts are significantly elevated. Signs of monocyte dysfunction were detected by the unique tool F7, which could be valuable for predicting mortality in patients receiving VA-ECMO and may be used as a novel biomarker guiding early clinical decision making in the future.