Factors associated with hemolysis during extracorporeal membrane oxygenation (ECMO)-Comparison of VA- versus VV ECMO

Abstract

Venovenous (VV) and venoarterial (VA) extracorporeal membrane oxygenation (ECMO) are effective support modalities to treat critically ill patients. ECMO-associated hemolysis remains a serious complication. The aim was to disclose similarities and differences in VA- and VV ECMO-associated hemolysis. This is a retrospective single-center analysis (January 2012 to September 2018) including 1,063 adult consecutive patients (VA, n = 606; VV, n = 457). Severe hemolysis (free plasma hemoglobin, fHb > 500 mg/l) during therapy occurred in 4% (VA) and 2% (VV) (p≤0.001). VV ECMO showed significantly more hemolysis by pump head thrombosis (PHT) compared to VA ECMO (9% vs. 2%; p≤0.001). Pretreatments (ECPR, cardiac surgery) of patients who required VA ECMO caused high fHb pre levels which aggravates the proof of ECMO-induced hemolysis (median (interquartile range), VA: fHb pre: 225.0 (89.3-458.0); VV: fHb pre: 72.0 (42.0-138.0); p≤0.001). The survival rate to discharge from hospital differed depending on ECMO type (40% (VA) vs. 63% (VV); p≤0.001). Hemolysis was dominant in VA ECMO patients, mainly caused by different indications and not by the ECMO support itself. PHT was the most severe form of ECMO-induced hemolysis that occurs in both therapies with low frequency, but more commonly in VV ECMO due to prolonged support time.

Fig 1. Effect of cannula size and blood flow on hemolysis induction regarding VA ECMO patients with fHb pre ≤ 100 mg/l (without pump head thrombosis).

15 Fr n = 86, 17 Fr n = 36. (A) Cannula size (Fr, French) had no effect on fHb levels on 1^st and 2^nd day on ECMO. (B) 17 Fr cannulas required a significantly higher blood flow compared to 15 Fr cannulas. (C) High blood flow (≥ 3 l/min) within 15 Fr cannulas induced significantly higher fHb levels compared to low blood flow (≤ 2.5 l/min). The median is shown as a black line in the box. The 25% or 75% quantile represents the lower or upper limit of the box. The smallest and largest observation is shown as whiskers, extreme values as circles.

Fig 2. All fHb measurements from 1st day till end of VA- or VV ECMO support (A: VA n = 606, B: VV n = 457).

The lines divide the graph into values ≤ 100 mg/l (10²), 101–500 mg/l, 501–1000 mg/l and > 1,000 mg/l (10³) which indicates a rising degree of hemolysis. The arrow shows all fHb above 100 mg/l that are suspected of hemolysis: 26% (VA) vs. 15% (VV). Of particular importance were fHb values above 500 mg/l as critical hemolysis markers [2,9]: 1% (VA) vs. 0.4% (VV).