Predictors and Hospital Outcomes in Pregnant Patients Undergoing Extracorporeal Membrane Oxygenation: A Nationwide Study : Anesthesia & Analgesia

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Predictors and Hospital Outcomes in Pregnant Patients Undergoing Extracorporeal Membrane Oxygenation: A Nationwide Study

van den Bosch, Oscar F. C. MD*; Chaudhry, Rabail MD*; Wicker, James MD; Mubashir, Talha MD; Limb, Daniel MD; Jogendran, Rohit MD§; Munshi, Laveena MD; Balki, Mrinalini MD*,¶,#,**

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doi: 10.1213/ANE.0000000000006210
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  • Question: What are the incidence, indications for extracorporeal membrane oxygenation (ECMO), mortality, and factors associated with mortality in pregnant patients who undergo ECMO?
  • Findings: The incidence of ECMO use across the pregnant population in the United States was low over the period of 2010–2016, with an in-hospital all-cause mortality of 1 in 3 patients, and mortality was greatest in patients with cardiogenic shock or combined cardiorespiratory collapse.
  • Meaning: Given the increasing number of patients of childbearing age with complex medical problems, there is a need for greater understanding of how best to deploy ECMO in the pregnant population.

Extracorporeal membrane oxygenation (ECMO) is a form of advanced cardiorespiratory support applied to patients with deteriorating respiratory and/or cardiac function who are unresponsive to conventional therapy. The past decade has seen a surge in ECMO use, given advancements in circuit technology and increased experience in its use.1 Across peripartum patients, the literature reports increasing rates of cardiogenic shock and acute respiratory distress syndrome (ARDS) requiring mechanical ventilation and ECMO.2–4 However, clinical trials of ECMO in advanced respiratory or cardiac failure often exclude pregnant patients, making it difficult to characterize its benefits and risks in this cohort.5

ECMO can be considered a potential salvage therapy for pregnant and postpartum patients with cardiac or pulmonary illness.2,6 Two recent systematic reviews assessed outcomes of ECMO in peripartum patients and determined maternal survival rates of 75.4%–77.2%.2,7 However, the included studies were limited by outcome bias and small sample sizes, and mainly consisted of individual case reports and case series. Large database analyses of pregnant patients who receive ECMO support have also been published8,9 but do not analyze mortality by indication or include comorbidities such as preeclampsia.

Given the lack of guidelines governing appropriate indications and timing for ECMO in the pregnant population, we sought to understand the role of ECMO to characterize its current use and outcomes. Our objective was to clarify in-hospital mortality and morbidity overall and by indication in pregnant patients who underwent ECMO using the National Inpatient Sample (NIS) database in the United States.


This study was deemed exempt from review by the Mount Sinai Hospital Research Ethics Board, and written informed consent was not required, as it relies exclusively on information that is deidentified and publicly available. This retrospective, observational, population-based cohort study was conducted using the NIS database for hospitalizations in pregnant patients from January 1, 2010 to December 31, 2016. The NIS is the largest all-payer in-patient database in the United States containing records for around 8 million hospitalizations yearly, which approximates a 20% stratified sample of discharges from U.S. hospitals. Furthermore, the NIS is part of multiple databases under the Healthcare Cost and Utilization Project (HCUP). Each hospital record includes common demographic variables, clinical data based on International Classification of Diseases Ninth Revision, Clinical Modification (ICD-9-CM)/International Classification of Diseases Tenth Revision, Clinical Modification (ICD-10-CM), hospital characteristics, and associated costs.10 At the time of initiation of this study, 2016 was the most recent available data with the NIS.

All elective and emergent hospital discharges associated with the ICD-9-CM or ICD-10-CM code for pregnancy were included. Specifics of ICD-9-CM/ICD-10-CM and Clinical Classifications Software (CCS) codes are detailed in Supplemental Digital Content 1, Table 1, Patients who underwent ECMO were identified using procedure codes 39.65 (ECMO) and 5A15223 (ECMO, Continuous).11,12

Patient demographics included age, race, income by quartile, and Charlson Comorbidity Index (CCI).13 Data on baseline patient characteristics, obstetric conditions such as preeclampsia, gestational diabetes, and preexisting comorbidities including cardiac, respiratory, renal, and other relevant diseases were collected. Two independent investigators (O.F.C.vdB., L.M.) classified each patient as respiratory failure, cardiogenic shock, and/or circulatory arrest based on the diagnosis codes at the time of admission. A subset of patients fulfilled multiple diagnostic categories. In the case of disagreement, a third investigator was consulted. All indications, comorbidities, and complications were derived from ICD-9-CM/ICD-10-CM and CCS codes listed in Supplemental Digital Content 1, Table 1,

Figure 1.:
Incidence of ECMO utilization in pregnancy by year. Error bars represent 95% CIs. CI indicates confidence interval; ECMO‚ extracorporeal membrane oxygenation.
Table 1. - Characteristics of Patients Undergoing ECMO During Pregnancy
Characteristic n = 59
Age, mean ± SD, y 28.7 (10.2)
Age group, y
 <18 6 (10.2)
 18–24 16 (27.1)
 25–34 21 (35.6)
 35–44 12 (20.3)
 45–55 4 (6.8)
Race or ethnicity a
 White 25/52 (48.1)
 Black 17/52 (32.7)
 Hispanic 3/52 (5.8)
 Other 7/52 (11.9)
Income quartile
 First 23 (39.0)
 Second 14 (23.7)
 Third 11 (18.6)
 Fourth 11 (18.6)
Charlson Comorbidity Index
 0 30 (50.8)
 1 15 (25.4)
 2 7 (11.9)
 ≥3 7 (11.9)
 Preeclampsia 15 (21.7)
 Chronic kidney disease 10 (16.9)
 Chronic respiratory disease b 7 (11.9)
 Placental abruption and previa 5 (7.2)
 Essential hypertension 4 (6.8)
 Ischemic heart disease 4 (6.8)
 Valvular heart disease 3 (5.1)
 Obesity 3 (5.1)
 Pulmonary hypertension 3 (5.1)
 Gestational diabetes 3 (5.1)
 None of the above 22 (37.3)
Data are presented as n (%) or mean ± SD.
Abbreviations: ECMO, extracorporeal membrane oxygenation; SD, standard deviation.
aData are shown with denominators due to missing data in 7 patients.
bAsthma, pulmonary fibrosis, interstitial emphysema, and chronic obstructive pulmonary disease.

Table 2. - Presumed Indication for ECMO Based on Diagnosis Codes Across Patients Undergoing ECMO During Pregnancy
Incidence Mortality Crude odds ratio for mortality (95% CI) Adjusted odds ratio for mortality (95% CI) a
Respiratory failure 47/59 (79.7) 14/47 (29.8) 0.85 (0.22–3.28) 0.80 (0.19–3.69)
Cardiogenic shock 38/59 (64.4) 15/38 (39.5) 3.91 (0.98–15.6) 5.0 (1.25–27.0)
Circulatory arrest 15/59 (25.4) 7/15 (46.7) 2.63 (0.77–8.91) 2.77 (0.75–10.6)
Combination of the above 34/59 (57.6) 14/34 (42.4) 3.68 (1.03–13.1) 4.68 (1.30–21.0)
Data are presented as n (%). Odds ratios in bold are statistically significant (P < .05).
Abbreviations: CI, confidence interval; ECMO, extracorporeal membrane oxygenation.
aAdjusted for age, Charlson comorbidity index, and median income quartile.

The primary outcome of this study was in-hospitalmortality across peripartum patients who underwent ECMO. We also assessed the prevalence of comorbidities, presumed indications for ECMO, and the incidence of complications across pregnant patients undergoing ECMO. We evaluated the associations between these factors and the in-hospital mortality. Our secondary outcomes were length of hospital stay and total hospital costs.

Statistical Analysis

This article adheres to the applicable Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) guidelines. Statistical analysis was performed using R (R Core Team, 2021, Continuous variables were reported as mean ± standard deviation (SD) or median (interquartile range [IQR]). Categorical variables were summarized as frequencies and percentages. The 95% confidence interval (CI) for the incidence of ECMO in pregnancy-related admissions was calculated using the Clopper-Pearson method. Linear regression analysis was used to assess change in the incidence of ECMO over time. The crude 95% CIs for mortality were calculated using normal approximation (oddsratio.wald() in the epitools package). Logistic regression models were constructed for the mortality outcome, to assess independent associations between presumed indications for ECMO and in-hospital mortality. Independent variables introduced in these models were age, income quartile, and CCI. Similar models were constructed to determine independent associations of preexisting comorbidity, conditions, and complications with in-hospital mortality. Independent variables introduced in these models were age, income quartile, and CCI. A P value of <0.05 was considered as significant.


Incidence of ECMO During Pregnancy

Of the 5‚346,517 pregnancy-based hospital discharges identified in the 6-year study period, a total of 59 patients underwent ECMO, with an incidence of 1 per 90,000 or 1.1 per 100,000 (95% CI, 0.84–1.4 per 100,000) hospitalizations during pregnancy. The percentage of dropped discharges due to missing data was low (<3%). The annual incidence varied between 0.60 and 1.68 per 100,0000 pregnancy-based hospitalizations (Figure 1). There was no significant increase in the incidence over time (β = 0.16 per 100,000 hospitalizations per year; 95% CI, −0.09 to 0.42; P = .16).

Patient Characteristics

The mean ± SD age was 28.7 ± 10.2 years, with 83% of patients (49/59) between 18 and 44 years. Most patients who underwent ECMO were White/Caucasian (48.1%) and Black/African American (32.7%). The majority (50.8%) had no significant comorbidities, while 37.3% of patients reported mild comorbidities (CCI score of 1 or 2) and 11.9% of patients (7/59) had moderate-to-severe comorbidities (CCI score ≥3). Preeclampsia occurred in 15 of 59 patients (21.7%). Details regarding baseline characteristics and patient comorbidities are summarized in Table 1.

Conditions Associated With ECMO

Given the absence of data surrounding ECMO configuration or definitive indication, all patients who underwent ECMO were categorized according to diagnoses of respiratory failure, cardiogenic shock, and/or cardiac arrest available within the discharge diagnostic codes (Table 2). A diagnosis of respiratory failure was present in 79.7% (47/59), cardiogenic shock in 64.4% (38/59), and circulatory arrest in 25.4% (15/59). Thirty-four patients (57.6%) had >1 diagnosis.

In-Hospital Mortality

The in-hospital mortality in patients undergoing ECMO was 30.5% (95% CI, 19.1–43.9).

Mortality for patients with a diagnosis of respiratory failure (14/47; 29.8%) was similar to mortality in those without respiratory failure (4/12; 33.3%), adjusted odds ratio (aOR) of 0.80 (95% CI, 0.19–3.69). Mortality for patients with cardiogenic shock (15/38; 39.5%) was significantly higher compared to mortality for those without cardiogenic shock (3/21; 14.2%) (aOR, 5.0; 95% CI, 1.25–27.0). Mortality for patients with a diagnosis of circulatory arrest (7/15, 46.7%) did not differ from mortality for patients without circulatory arrest (11/44, 25.0%) (aOR, 2.77; 95% CI, 0.75–10.6) (Table 2 and Figure 2).

Figure 2.:
Presumed indications for ECMO based on diagnosis codes across 59 patients undergoing ECMO during pregnancy in the United States (2010–2016). ECMO indicates extracorporeal membrane oxygenation.
Table 3. - Factors Associated With In-Hospital Mortality for Women Undergoing ECMO During Pregnancy
Mortality Crude odds ratio (95% CI) Adjusted odds ratio (95% CI)a
All patients 18/59 (30.5%)
Medical and obstetric conditions
 Obesity 1/3 (33.3%) 1.15 (0.10–13.5) 1.11 (0.05–13.5)
 Essential hypertension 2/3 (50.0%) 2.44 (0.31–18.8) 2.12 (0.22–20.1)
 Valvular heart disease 1/3 (33.3%) 1.15 (0.10–13.5) 1.16 (0.05–13.5)
 Ischemic heart disease 0/4 (0%)
 Cardiomyopathy 7/17 (41.1%) 1.97 (0.60–6.46) 2.12 (0.57–8.00)
 Chronic respiratory disease 2/7 (28.6%) 0.90 (0.16–5.14) 0.56 (0.06–3.48)
 H1N1/H5N1 pneumonia 0/5 (0%)
 Status asthmaticus 0/2 (0%)
 Pulmonary hypertension 2/3 (66.7%) 5.00 (0.42–59.0) 4.15 (0.33–99.7)
 Chronic kidney disease 4/10 (40.0%) 1.66 (0.41–6.81) 1.87 (0.31–11.2)
 Severe sepsis/septic shock 7/24 (29.2%) 0.90 (0.29–2.79) 0.91 (0.28–2.92)
 Preeclampsia 4/15 (26.7%) 0.78 (0.21–2.88) 0.67 (0.15–2.51)
 Placental abruption and previa 2/5 (40.0%) 1.58 (0.24–10.4) 1.44 (0.17–9.66)
 Severe hemorrhage 10/25 (40.0%) 2.17 (0.70–6.68) 2.64 (0.80–9.48)
 Intracerebral hemorrhage 1/2 (50.0%) 2.35 (0.14–39.8) 1.25 (0.04–36.9)
 Defibrination syndrome b 3/11 (27.3%) 0.83 (0.19–3.55) 0.65 (0.12–2.76)
 Acute kidney injury 11/32 (34.4%) 1.50 (0.48–4.62) 1.44 (0.42–5.14)
 Organ failure (single) 15/49 (31.9%) 1.03 (0.23–4.53) 0.96 (0.22–5.06)
 Organ failure (2 or more) 6/13 (46.1%) 2.43 (0.68–8.68) 2.91 (0.67–13.4)
Abbreviations: CI, confidence interval; ECMO, extracorporeal membrane oxygenation.
aAdjusted for age, Charlson comorbidity index, and median income quartile.
bDisseminated intravascular coagulation and consumption coagulopathy.

Patients with at least 2 of the diagnoses from respiratory failure, cardiogenic shock, and/or circulatory arrest had a significantly higher mortality rate of 42.4% (14/34) compared to those with only 1 of those diagnoses (4/25, 16%) (aOR, 4.68; 95% CI, 1.30–21.0).

The mortality rate and aOR for conditions and complications are summarized in Table 3.

Secondary Outcomes

The median (IQR) length of hospital stay among patients undergoing ECMO during pregnancy was 13 (4–36) days. There were no differences in the length of hospital stay among patients with respiratory failure, cardiogenic shock, and/or circulatory arrest. The total median (IQR) hospital costs were USD 236,430 (115,940–703,745). Two patients suffered an intracerebral hemorrhage during their admission, of which 1 died. Acute kidney injury occurred in 34.4% of patients. Organ failure of single and multiple systems occurred in 31.9% and 46.1% patients, respectively.


Our study demonstrated an incidence of ECMO use of 1.1 per 100,000 hospitalizations during pregnancy, based on the United States NIS database during the 6-year study period. We found the overall in-hospital mortality rate for pregnant or postpartum patients requiring ECMO to be 30.5%. A diagnosis of cardiogenic shock was associated with a higher mortality rate compared to patients without cardiogenic shock.

In the obstetric population, the incidence of ECMO use and the in-hospital mortality are lower by 4 times and 2 times, respectively, when compared with the general population.9,14 This is explained by the fact that peripartum patients are younger and have less comorbidities compared to the general population. We found a higher incidence of ECMO in the lower income quartiles and a disproportionately high rate in Black patients, which should further increase awareness of socioeconomical and racial disparities in maternal care and outcomes.

In our study, the most common presumed indication for the initiation of ECMO, based on diagnosis codes, was respiratory failure. This is in line with previous reports from the Extracorporeal Life Support Organization (ELSO) registry and other cohort studies in pregnant population that show the majority of patients required ECMO for pulmonary indications (49.4%–52.5%).7,15 Previous meta-analysis in pregnant population did not reveal any correlation between pulmonary or cardiac indications and maternal survival.2 However, in the nonpregnant population, VV ECMO was found to be associated with higher survival than VA ECMO.16

Cardiogenic shock, as a presumed indication for ECMO in our study, was associated with a significantly higher mortality rate of 39.5% compared to those without cardiogenic shock. This is in agreement with other reports regarding ECMO for severe peripartum cardiomyopathy, including a single-center cohort of 10 pregnant patients from France reporting a mortality rate of 50%,17 and a subanalysis of the ELSO registry demonstrating a mortality rate of 36.4%.18 Cardiovascular disease remains the leading cause of pregnancy related mortality in the United States, while cardiomyopathy alone accounts for 11% of all maternal deaths.19,20 In comparison to all adults who receive VA ECMO, patients undergoing VA ECMO in pregnancy have increased survival, possibly due to a generally healthier population and due to the favorable disease course of peripartum cardiomyopathy.18 Furthermore, the crude and aORs for mortality from cardiogenic shock were higher than those from circulatory arrest. While we can only speculate on the background to this finding, we believe this may be due to a more reversible illness in patients with cardiac arrest when compared to patients with cardiogenic shock. Cardiac arrest in pregnancy can have a myriad of causes, mostly reversible,21 whereas cardiogenic shock in pregnancy can be refractory.22 In addition, initiation of ECMO in the setting of an arrest is likely to only happen in a select group of patients.

Interestingly, our study demonstrated a remarkably high prevalence of preeclampsia in patients undergoing ECMO during pregnancy (21.7%). This is considerably higher than the overall pregnant population, where preeclampsia is known to affect 4.6% (95 CI, 2.2–8.2) of all pregnancies.23 Indeed, more than 16% of direct maternal deaths in developed countries are associated with hypertensive disorders in pregnancy.24 An increased prevalence of preeclampsia is also seen in other adverse maternal outcomes, such as heart failure and cardiac arrest.22,25 In COVID-19, a diagnosis of preeclampsia is strongly associated with more severe respiratory disease (odds ratio [OR], 4.16; 95% CI, 1.55–11.15).26 This highlights the need for immediate attention and timely intervention in acutely decompensating preeclamptic patients, so that severe morbidity and mortality can be prevented.27

We did not identify any association between mortality and maternal comorbidities in our cohort of patients. Perhaps this did not reach statistical significance due to the low incidence of ECMO during the study period. Another explanation is that once patients reach the stage of severe respiratory failure or refractory cardiogenic shock, comorbidities have no further influence on the mortality rate. Larger cohort studies such as the ELSO registry could not comment on the influence of comorbidities, as these data were not routinely collected.15 A large international registry with comorbidity data is required to identify the prognostic factors for patients undergoing ECMO during pregnancy.

ECMO is an invasive intervention, and the risks involved must be weighed against the benefits. Our study shows that approximately 1 in 3 patients undergoing ECMO in pregnancy die before hospital discharge. The question remains whether these patients die of their primary illness or die of complications related to ECMO. Complication rates of defibrination syndrome (ie, disseminated intravascular coagulation and consumption coagulopathy), intracerebral hemorrhage, and multiorgan failure were 18.6%, 3.4%, and 22.0%, respectively. Mortality rate was higher in patients with intracerebral hemorrhage or multiorgan failure (50% and 46%, respectively); however, this did not reach statistical significance possibly due to the low incidence of these complications. Given this low incidence, it seems that mortality is mainly due to refractory primary illness rather than complications related to ECMO. More work is required to ascertain these findings.

The strength of this study is that our data represent ECMO use in pregnancy across the United States. The NIS database is the largest publicly available inpatient database and consists of a representative sample of discharges from academic medical centers, public hospitals, community hospitals, specialty, and general hospitals.10 In contrast, previous studies reporting mortality data are often from (single) centers of excellence, and as a result, their mortality rates may not be representative or generalizable.2,7,28,29 The ELSO registry offers interesting insights into the use of peripartum ECMO. However, the incidence of maternal comorbidities and/or conditions is not reported.15,18 In comparison to previous studies using the NIS database, we looked at the most recent time period and focused on conditions associated with ECMO as well as maternal comorbidities such as preeclampsia.8,9

For the interpretation and extrapolation of our results, 3 limitations should be considered, which are inherent to the use of large registries. First, we were unable to unequivocally establish the indication for ECMO, as the same ICD-9/ICD-10 procedure code is used for VV and VA ECMO. We assessed the diagnosis codes in a systematic manner with 2 independent investigators to avoid any bias. Second, the incidence of obesity was found to be remarkably low (5.1%), which may possibly be a sign of inaccurate or incomplete coding in the database, in addition to patient selection factors. Third, we were unable to establish the chronological order in which diagnoses occurred during the hospital admission. For example, severe hemorrhage may have occurred before ECMO initiation, in the setting of postpartum hemorrhage, or may have occurred as a complication of ECMO due to heparinization. Large prospective registries such as the ELSO will provide additional insight into the outcomes and complications of ECMO. Further work is required to determine fetal outcomes and long-term outcomes for mother and baby.

In conclusion, our 6-year retrospective analysis of the NIS database finds that ECMO is uncommon in pregnant patients, that in-hospital all-cause mortality rate for patients undergoing ECMO in pregnancy is 1 in 3, and that mortality varied by indication with cardiogenic shock and combined cardiorespiratory collapse having higher in-hospital mortality. In light of the increasing number of patients of childbearing age, the need for additional advanced life support treatment such as ECMO during the peripartum period will likely increase. Further work is needed to identify favorable indications for ECMO and how best to optimize ECMO outcomes in pregnant patients.


Name: Oscar F. C. van den Bosch, MD.

Contribution: This author helped with the methodology, software, formal analysis, visualization, and writing of the original draft.

Name: Rabail Chaudhry, MD.

Contribution: This author helped with the investigations, resources, data curation, and reviewing and editing of the work.

Name: James Wicker, MD.

Contribution: This author helped with the investigations, data curation, and reviewing and editing of the work.

Name: Talha Mubashir, MD.

Contribution: This author helped with the investigations, resources, data curations, and reviewing and editing of the work.

Name: Daniel Limb, MD.

Contribution: This author helped with the investigations, resources, data curations, and reviewing and editing of the work.

Name: Rohit Jogendran, MD.

Contribution: This author helped with the investigations, resources, data curations, and reviewing and editing of the work.

Name: Laveena Munshi, MD.

Contribution: This author helped with the methodology, data analysis, supervision, and reviewing and editing of the work.

Name: Mrinalini Balki, MD.

Contribution: This author helped with the conceptualization, supervision, project administration, and reviewing and editing of the work.

This manuscript was handled by: Avery Tung, MD, FCCM.


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