ECMO-/ECLS

treatments for a disease process to determine if they lead to differences in a particular
outcome.
The most common and simplest forms of clinical research are case reports and
case series or institutional experiences. These types of reports make up a large portion
of the pediatric surgical literature as many of the diseases we treat are rare and not
amenable to large prospective trials. These studies have inherent biases as they are
retrospective and usually represent either a single surgeon or single center’s
experience. Despite these limitations, these reports do provide at least an expert
opinion or experience that can be used to draw some information about a disease or
treatment and outcomes.
Case-control studies represent retrospective CER studies that will compare the
effectiveness of two treatments on outcomes. The value of these types of studies is
limited by selection bias but, often, they are the only types of data available. In addition,
they can provide evidence to support prospective studies; retrospective case-control
studies demonstrating the benefits of low tidal volume ventilation in patients with ARDS
eventually led to large multi-institutional randomized controlled trials examining this
therapy [ 1 - 5 ].
On a larger scale, outcomes studies or comparative effectiveness studies are
being performed using databases. The databases for these studies can be institutional
registries or data warehouses, multi-institutional registries such as the Extracorporeal
Life Support Organization registry, state or national registries such as the National
Trauma Data Bank, or large multi-institutional administrative databases such as the
Pediatric Health Information System database or the Kids Inpatient database.