In-hospital mortality and successful weaning from venoarterial extracorporeal membrane oxygenation: analysis of 5,263 patients using a national inpatient database in Japan

The Japanese Diagnosis Procedure Combination (DPC) database includes administrative claims and discharge abstract data for all inpatients discharged from more than 1000 participating hospitals nationwide. It covers approximately 92 % (244/266) of all tertiary-care emergency hospitals in Japan. The database includes the following patient information: age; sex; body weight and height; primary diagnosis; comorbidities on admission; post-admission complications classified according to the International Classification of Diseases 10th Revision (ICD-10) codes; medical procedures designated using original Japanese codes, including VA-ECMO, intra-aortic balloon pumping (IABP), pulmonary artery catheterization, and continuous renal replacement therapy; daily records of drug administration and devices used; length of stay; and discharge status. The dates of hospital admission, surgery, bedside procedures, drugs administered and hospital discharge are recorded using a uniform data submission form. This study used data from 1 July 2010 to 31 March 2013.

We included patients aged ≥19 years who received VA-ECMO during hospitalization. We selected patients who were diagnosed at admission as having cardiogenic shock (ICD-10 codes, I05, I07, I08, I20-22, I33-35, I40-42, I46, and I49-51), pulmonary embolism (I26), hypothermia (T68), poisoning (T36-65), or trauma (S$ and T0). We excluded patients with acute respiratory distress syndrome.

Baseline variables included age, sex and body mass index (BMI). Patients with cardiogenic shock were categorized in four age groups: 19–39, 40–59, 60–79 and ≥80 years. BMI was categorized as being underweight (BMI <18.5 kg/m²), normal weight (18.5–24.9 kg/m²), or overweight (≥25.0 kg/m²). Patients were also divided into those who had or who had not had an episode of cardiac arrest. Hospital volume was defined as the number of patients receiving VA-ECMO per year at each hospital. Hospital volume was categorized in tertiles and so the number of patients in each category was almost equal. Myocarditis, chronic renal failure, liver failure, and central nervous system dysfunction were extracted based on ICD-10 codes. The primary outcome was in-hospital mortality. The secondary outcome was the proportion of patients weaned from VA-ECMO.

Data are presented as percentages and numbers, or means and standard deviations. The chi-square test and Fisher’s exact test were performed to compare proportions in the different groups. In the cardiogenic shock group, we performed multivariable logistic regression analysis to examine the association of in-hospital mortality with various factors, including several components of the survival after venoarterial ECMO (SAVE) score for VA-ECMO (age, sex, weight, myocarditis (ICD-10 codes, I40-41), pre-ECMO cardiac arrest, pre-ECMO chronic renal failure (N18), liver failure pre-ECMO (K70-77), pre-ECMO central nervous system dysfunction (G09-11, G20-21, G23, G31-32, G35-37, G40-41, G45-46, G80-81, S06), and duration of intubation prior to VA-ECMO) [20], hospital volume, IABP, pulmonary artery catheterization, and continuous renal replacement therapy, while also adjusting for within-hospital clustering using a generalized estimating equation [21]. We performed multiple imputation to replace each missing value with a set of substituted plausible values by creating 20 filled-in complete datasets using a Markov chain Monte Carlo algorithm known as “chained equations imputation,” because there were some missing values for BMI and duration of intubation prior to VA-ECMO [22]. Multiple imputation assumes that data are missing at random and that any systematic differences between the missing and observed values can be explained by differences in the observed data [23]. A p value <0.05 was considered statistically significant. All statistical analyses were performed using IBM SPSS version 22.0 (IBM Corp., Armonk, NY, USA).