The blood flow was 4.7 ± 0.6 L/min and gas flow was 4.0 ± 1.4 L/min during the first day on ECMO, the blood flow was 4.5 ± 0.6 L/min and gas flow was 3.8 ± 0.8 L/min during the second day after ECMO support. Respiratory mechanics were significantly improved after ECMO initiation. After 2 days of ECMO support, the blood gas analysis results revealed a dramatically improved PaO2/FiO2, and the difference was statistically significant (P = 0.001). Meanwhile, in the ECMO-supported group, the VT and airway Pplat were significantly decreased [Table 3].
The rate of ECMO related complications remained high. Bleeding complications occurred in 20 of the 99 patients in the ECMO treatment group, accounting for 20% of the total ECMO cases. Cannulation site bleeding was the most common complication in ECMO patients, affecting 11 patients. Intra-cranial bleeding occurred in one case and this patient died. Infection complications, including bloodstream infections, ventilator-associated pneumonia, and cannula site infections occurred in 6%, 4%, and 8% of the ECMO patients, respectively [Table 4].
Ninety-nine patients with severe ARDS who received ECMO were included in this study. The MAP was lower in the non-survivor group than in the survivor group. The requirement of vasopressors before ECMO in the survivor group was less than the non-survivor group. The duration of mechanical ventilation before ECMO and duration of ECMO were both longer in the non-survivor group than in the survivor group [Table 5].
Univariate Cox regression analysis was performed to determine the risk factors associated with the outcome of ECMO patients. The duration of mechanical ventilation before ECMO, requirement of vasopressors before ECMO, and MAP before ECMO were demonstrated as important factors for the poor prognosis of patients [Table 6].
In this retrospective matched cohort study, we found that patients with severe ARDS supported with venovenous ECMO (VV-ECMO) were associated with a reduction in the 28-day and 90-day mortality compared with matched patients without ECMO support. The duration of mechanical ventilation and requirement of vasopressors before ECMO initiation were independent risk factors accompanied with high mortality.
ECMO is an alternative support for severe ARDS. The two negatively randomized clinical trials failed to demonstrate the benefit of ECMO in adult respiratory failure patients,[8,9] while the CESAR study showed that the transfer of reversible severe acute respiratory failure patients to the ECMO center significantly improved the 6-month outcome. Subsequently, ECMO played an important role in the treatment of severe ARDS caused by viral pneumonia.[10,11] In China, ECMO has developed rapidly, and many ECMO centers have been established in the last 5 years. However, the effect of ECMO on patients with ARDS has not been well clarified.
This retrospective study evaluated the efficacy and safety of ECMO in China. Because the patients supported with high-pressure and high-volume ventilation have a poor outcome even with ECMO support, we excluded those with high-level mechanical ventilation for more than 7 days. Our results showed that ECMO could significantly improve the survival rate compared with the matched control group, confirming the benefit of ECMO for patients with severe ARDS. The survival rate of patients with ARDS supported with ECMO at 90 days was still high, up to 44.4% in this study. Two-thirds of the patients required vasopressors before the initiation of ECMO; however, the efficacy of application of ECMO in septic shock patients remains controversial.
The management of ECMO support requires teamwork and multidisciplinary cooperation. Coagulation and anti-coagulation disorders can cause bleeding and clot formation, leading to oxygenator failure and the need for the changing circuit of ECMO. It was shown that bleeding is the most common complication of ECMO. Our study showed that the incidence of bleeding complications was up to 20% in patients on VV-ECMO. Most bleeding complications occurred at the cannulation site. Intra-cranial hemorrhage was the most frequent type of neurologic complication, and the survival of patients with neurologic injury was poor.[20,21] Furthermore, mechanical complications such as tube kinking and centrifugal pump dysfunction were also important factors that impacted the ECMO circuit and oxygenator survival time.
This study possessed some limitations. First, this was a non-randomized, retrospective, observational study, and may have been subject to bias. Second, this was a multi-center study performed at teaching hospitals. However, most of the patients with ARDS included were from one hospital; only a few patients were included from other hospitals in the first 3 years. A higher average annual ECMO case volume was associated with an improved outcome. A lack of ECMO experience was associated with a higher incidence of complications. Third, the sample size of this study was not sufficiently large. Finally, only 15 patients were matched in the control group but 39 patients in the ECMO group in the last 2 years because the young patients were prone to be supported by ECMO if they fulfill the criteria, especially in recent years.
Finally, in this cohort of patients with severe ARDS, VV-ECMO improves the survival rate as an effective respiratory support for patients with severe ARDS. In patients with ARDS who received ECMO, the duration of mechanical ventilation and the requirement of vasopressors before ECMO were associated with a higher 28-day mortality.
This work was supported by grants from the Jiangsu Province's Key Discipline/Laboratory of Medicine (No. ZDXKA2016025), the Jiangsu Province's Key Provincial Talents Program (No. ZDRCA2016082), and the National Natural Science Foundation of China (No. 81370180).
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