You are working as part of a ground-based specialty care transport unit (SCTU) staffed with one EMT, one paramedic and a transport specialty RN when you receive a bizarre call from dispatch. The dispatcher says that one of your company's contracted facilities is inquiring about immediate transfer of a patient on extracorporeal membrane oxygenation (ECMO). After explaining to the dispatcher that ECMO is not a Sesame Street character, you frantically try to remember the last ECMO patient you transported. After several minutes, you realize you have never transported an ECMO patient and are not completely sure of what may be involved.
Interfacility transport of a patient requiring extracorporeal membrane oxygenation (ECMO) is a rare occurrence in EMS, and there are few articles referencing the clinical, logistical or safety considerations during these types of transfers. This article will provide an overview of ECMO apparatus, as well as the complexities that may be associated with a specialty transport of this type.
WHAT IS ECMO?
ECMO is a therapy in which non-oxygenated blood is removed from the venous system, oxygenated and then returned to the body through either the venous or arterial system to provide temporary cardiac and pulmonary support.1 ECMO differs from cardiac bypass in two essential areas: 1) non-thoracic vessels (such as femoral or cervical) are cannulated, and 2) it may be utilized for as long as several weeks. Where the goal of cardiac bypass is support during surgery, ECMO gives the cardiopulmonary system an opportunity to recover from some adverse event. It is often used in the neonatal ICU for newborn infants with congenital heart defects or severe respiratory distress. Survival is reported at 70%-80% for these patients.2 Typically, neonatal ECMO is only done for up to 30 days; however, there are reports of patients being successfully treated for much longer--one for more than three months. ECMO use in adult patients is generally for severe cardiac dysfunction that is not responding to other supportive measures such as intra-aortic balloon pump (IABP) and ventilatory support. In those cases, ECMO serves as a bridge to placement of a ventricular assist device (VAD) or heart transplant. Limited evidence also points to successful use in cardiac arrest patients in the emergency department.3
Typical applications for ECMO involve cannulation of a vein and an artery (VA, or veno-arterial) and cannulation of a vein (VV, or veno-venous). A common method of VA access is to place a cannula in the right jugular vein and advance it to the right atrium. A second catheter is then placed into the right carotid artery and advanced to the aorta to allow for return of blood from the ECMO device. VA ECMO bypasses the pulmonary circulation. In VV access, a double-lumen catheter is placed into the right jugular vein and advanced to the right atrium. When blood is returned to the patient, it is directed to the pulmonary system via the tricuspid valve. VV ECMO maintains pulmonary blood flow.
The use of ECMO has many possible complications for patients. Bleeding is one of the most severe, as all patients on ECMO require systemic heparinization to prevent clotting and subsequent embolization. Gastrointestinal hemorrhage and intracranial bleeds can have grave consequences. Other complications include thromboembolism, air embolism, limb ischemia, acute renal failure and oxygenator failure.4
ECMO apparatus consists of a blood pump, venous reservoir, membrane oxygenator and heat exchanger. The pump may be either a simple roller or centrifugal unit, depending on the application. The reservoir or bladder, maintained below heart level, stores the blood in preparation for entering the membrane oxygenator. The bladder is essential to prevent pressure changes and subsequent damage where the cannula(s) enters the blood vessel(s). The membrane oxygenator is made of a thin silicon sheath that is very efficient for the exchange of both oxygen and carbon dioxide. Since heat is lost as the blood passes through the ECMO apparatus, the heat exchanger maintains the blood at body temperature before it is reintroduced to the patient's circulation.1