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 The
Front Line
ECMO
for Respiratory Failure
by
Lisa M. Adcock, MD
Extracorporeal
membrane oxygenation (ECMO) first became a viable treatment
for severe neonatal respiratory failure in 1987. The goal of ECMO
is to support tissue oxygenation in infants with severe respiratory
failure due to reversible pulmonary disease. This support is provided
by withdrawing venous blood from the infant, removing carbon dioxide
and adding oxygen via a membrane oxygenator, then returning the
oxygenated blood to the body through either a vein (venovenous,
VV-ECMO) or an artery (venoarterial, VA-ECMO).
Selection
criteria for placing an infant on ECMO may vary considerably between
ECMO centers. The overall purpose of any criteria is to determine
whether the risk of severe morbidity or mortality without ECMO
treatment is greater than the risk of ECMO. Typically, selection
criteria examine arterial oxygenation in relation to the degree
of respiratory support; eg, the oxygen index (OI) and/or the Aa
oxygen gradient:
- OI >40 for at least 6 hours
[OI
= (MAP × Fio2 / Po2 × 100)]
Note:
MAP = mean airway pressure
-
AaDo2 gradient >610 torr for at least 6 hours
Many
centers include criteria for blood lactate levels (eg, an arterial
lactate >3 μmol/L and rising) and/or a postductal Pao2 (<40
torr for >2 hours) to further define the infant with a moderate-to-high
risk of death if ECMO is not provided. Because of the concern
for central nervous system (CNS) hemorrhage, a gestational age
>34 weeks and weight >2 kg are often specified. Exclusion criteria
include:
- the presence of significant intracranial hemorrhage,
- uncontrolled bleeding in other locations,
- congenital anomalies or significant CNS dysfunction (in
which ECMO use in the infant would appear futile),
- congenital heart disease, or
- pulmonary disease that is not likely to be reversible. This
criterion is used as the risk of hemorrhagic and other complications
increases with longer ECMO runs.
ELSO
(the Extracorporeal Life Support Organization) documented 15,525
patients treated with ECMO (1987-June 2000); survival to hospital
discharge was reported in 12,158 (78%) of them. Survival in relation
to primary diagnosis shows good outcome for infants with meconium
aspiration syndrome (94%), respiratory distress syndrome (84%),
and persistent fetal circulation or persistent pulmonary hypertension
(79%). Survival is lower in infants with septicemia (76%), severe
air leak (71%), pneumonia (55%), and congenital diaphragmatic
hernia (54%) and should be viewed in relation to the usual outcome
in these infants offered conventional therapies. For long-term
survivors of ECMO, the greatest concerns are recurrent pulmonary
infections, feeding difficulties, language delay, and neurodevelopmental
disability. However, it is not clear whether the abnormalities
observed in follow-up studies are related to ECMO or to the life-threatening
illness that led to ECMO intervention. More long-term outcome
data are still necessary to evaluate the future utility of ECMO
in the newborn with severe respiratory failure.
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