Extracorporeal membrane oxygenation 2001. The odyssey continues

Hospital readmissions and survival after nonneonatal pediatric ECMO

PURPOSE

The late effects of treatment with extracorporeal membrane oxygenation (ECMO) in nonneonatal pediatric patients remain unclear. The aims of our study were to better characterize the long-term survival and hospital readmission rates for pediatric patients after ECMO treatment.

PATIENTS AND METHODS

From 1999 to 2006, data on children aged 1 month to 18 years who underwent ECMO were extracted from the California Patient Discharge Database. Data from patients with diagnoses of congenital cardiac disease were excluded. We analyzed patient data on initial hospital course, subsequent readmissions, development of long-term morbidities, and long-term survival.

RESULTS

The study cohort consisted of 188 children from 13 California hospitals. The median age was 3 years, and 46% of the patients survived to hospital discharge. ECMO indications included acquired heart disease in 81 patients, pneumonia in 56, other respiratory failure in 22, sepsis in 8, trauma in 8, and other indications in 12. Of the 87 survivors, 56 were tracked for a median period of 3.7 years. The readmission rate was 62%, and the mean time to first readmission was 1.2 years. Readmissions for respiratory infections were observed in 34% of the patients and for reactive airway disease in 7%. Neurologically debilitating conditions (epilepsy [7%] and developmental delay [9%]) occurred in 16%. Late deaths occurred in 5% of the children. Readmitted survivors had a cumulative length of readmission hospitalization of 8 days and hospital charge of $43 000. Cox proportional hazard regression demonstrated a positive relationship between treatment-center case volume and long-term survival outcomes (hazard ratio: 0.98 per case; P < .01).

CONCLUSIONS

Pediatric ECMO survivors suffered from significant long-term morbidities after initial hospital discharge. More than 60% of these children required subsequent readmissions, and late deaths were observed in 5%. Furthermore, hospitals with high case volumes were associated with improved long-term survival.

Oxygenation index for extracorporeal membrane oxygenation: is there predictive significance?

Although extracorporeal membrane oxygenation (ECMO) is known to improve survival in neonates with respiratory failure, there has been a significant decrease in the use of ECMO in recent years. Alternative modalities such as high-frequency oscillatory ventilation (HFOV), inhaled nitric oxide (iNO), and surfactant therapy are associated with this decline. The criteria for the initiation of ECMO, developed about 20 years ago, are likely no longer relevant. We examined the predictive significance of the oxygenation index (OI) as a patient entry criterion for ECMO use. We sought a critical OI level predicting death or chronic lung disease (CLD) with and without ECMO use. We also examined whether patients with certain OIs are more likely to have worse outcomes. One hundred and seventy-four term-newborn admissions between 1995 and 2000 requiring mechanical ventilation were enrolled in the study. Receiver operating curve analysis was performed to find a cutoff value of OI for ECMO initiation. Mortality rates and CLD probability were compared to the worst OIs. Our 6-year ECMO administration experience showed that an OI of 33.2 is a suitable cutoff value for ECMO initiation with high sensitivity and specificity as a predictive criterion. The critical OI value associated with the CLD risk when ECMO is not used is in the 40s. OI is a good predictor of CLD; the probability of CLD increases with higher OIs. Our data support the trend toward the use of new interventions over ECMO, especially for patients with OI scores of less than 33.2. Only when the probability of ventilator-associated lung injury becomes significant is it better to consider ECMO than conventional modalities.

Pharmacokinetic changes during extracorporeal membrane oxygenation: implications for drug therapy of neonates

Extracorporeal membrane oxygenation (ECMO) is a prolonged form of cardiopulmonary bypass used to support patients with life-threatening respiratory or cardiac failure. In neonates, ECMO is used for a variety of indications, including sepsis and pulmonary diseases such as meconium aspiration syndrome, persistent pulmonary hypertension or congenital diaphragmatic hernia. In recent years, ECMO has been increasingly used after surgery to correct congenital cardiac defects. Despite the need for numerous drugs to maintain the ECMO circuit and treat the patient's underlying illness, relatively little is known of the disposition of drugs in this patient population. To date, the largest number of pharmacokinetic studies have been conducted with gentamicin and vancomycin. Both drugs have been found to have an increased volume of distribution, probably as a result of the addition of a large exogenous blood volume for circuit priming. Elimination half-lives for both drugs are prolonged during ECMO, with several studies demonstrating a return to expected values after decannulation. The reason for this prolonged elimination is probably multifactorial, with a reduction in renal function as the primary determinant. This same pattern of an increased volume of distribution and prolonged elimination has been found for several other drugs, including tobramycin, bumetanide and ranitidine. Other factors that affect drug disposition during ECMO include loss of the drug from adhesion to the circuit components and loss in the circulating blood volume during changes in the equipment. The benzodiazepines and propofol are largely sequestered within the circuit. Serum concentrations of heparin, morphine, fentanyl, furosemide, phenytoin and phenobarbital are also reduced by these mechanisms. The addition of haemofiltration or dialysis in up to a quarter of ECMO patients further complicates the determination of population pharmacokinetic parameters. The literature published to date on the pharmacokinetic changes associated with ECMO provide preliminary support for dosage adjustment; however, more research is needed to identify optimal administration strategies for this patient population.

Impact of ECMO on neonatal mortality in Michigan (1980-1999)

PURPOSE

Although extracorporeal membrane oxygenation (ECMO) is a potentially lifesaving intervention, the effect of ECMO on neonatal mortality has never been evaluated. In this study, we examined the relationship between increased ECMO utilization and its effect on the neonatal mortality rate in the state of Michigan.

METHODS

Neonatal mortality data were obtained from the Michigan State Department of Community Health. Data included total annual live births, total neonatal deaths, and deaths from respiratory causes in neonates > or =35 weeks' gestational age (ie, potential ECMO candidates). Pooled ECMO patient data from Michigan's 3 ECMO centers were obtained from the Extracorporeal Life Support Organization (ELSO) Registry. Associations between ECMO volume and neonatal mortality rates were assessed using simple linear regression. A scatterplot of ECMO volume and mortality rates was created, and the resulting fitted regression lines were superimposed on the plots. Statistical significance of the associations (ie, difference in slope of the regression line from zero) were based on a standard 2-sided Wald test for the regression slope parameter.

RESULTS

From 1980 through 1999, 1,061 neonates were treated with ECMO in Michigan, and 875 (82.5%) survived. When annual neonatal mortality rate (from all causes) and the rate from respiratory causes versus ECMO volume (cases per year) are superimposed with fitted regression lines, both are significantly different from zero (P =.041 and P =.002, respectively). The model predicts that for every 100 neonates treated with ECMO in Michigan, 38 lives are saved. The model also can be used to predict the annual neonatal mortality rate in Michigan if ECMO had not been utilized.

CONCLUSIONS

A strong association exists between ECMO volume and observed reductions in neonatal mortality seen in Michigan over the last 2 decades. This is the first study to show an association between ECMO and neonatal mortality rate at the population level.