As with any invasive procedure, ECMO has many potential life-threatening complications that can occur. These can be categorized into mechanical complications and patient complications (Tables 7-4 and 7-5). Mechanical complications are related to cannula placement and the ECMO circuit itself. Patient complications may be attributed to physiologic complications that occur due to ECMO therapy.
The required placement of large-bore ECMO cannulas can cause several complications. As with placement of any type of central line, pneumothorax, line infection, and bleeding may occur. In addition, due to the larger size of the cannula required with ECMO, direct damage to the internal jugular vein can cause massive mediastinal bleeding. Cannulation of the carotid artery can cause dissection of the carotid arterial intima, leading to aortic dissection. In addition, any potential for bleeding from the placement of the cannulas is increased due to the requirement of systemic heparinization to maintain the ECMO circuit. The cannulas may also serve as a nidus for thrombus formation and emboli.
The ECMO circuit has potential to cause numerous complications. Because the surfaces of the ECMO circuit and devices are plastic, it is necessary to provide anticoagulant prophylaxis to the patient's blood with a continuous infusion of heparin. The most common mechanical complication is the development of clots within the circuit. These develop due to the platelets adhering to the plastic surface of the circuit, becoming activated, recruiting more platelets, and growing into platelet aggregates. Eventually these platelet aggregates break off. These clots can cause failure of the ECMO circuit's oxygenator. Larger clots can cause pulmonary or systemic emboli. Thrombocytopenia and a consumptive coagulopathy may also occur due to a large clot burden in the circuit.
Air can enter the ECMO circuit from dislodgement of a cannula, which then sucks in air, a small tear in the membrane oxygenator, compromised integrity in any of the connections in the circuit tubing, or high partial pressure of oxygen in the blood. Small bubbles in the circuit can be easily removed and have low potential for harm. A large bolus of air can be fatal.
Malfunction of the circuit heat exchanger can lead to significant patient hypothermia that may cause or exacerbate any coagulopathy that already exists.
Patients undergoing ECMO therapy can suffer complications in any organ system. Many of these complications are due to the need for systemic anticoagulation.
Neurologically, patients may have spontaneous intracranial bleeding due to anticoagulation. This is more commonly seen in the neonatal ECMO population. Infarction from emboli may occur, and seizures induced by bleeding, infarction, or hypoxemia are also a threat.
Hemolysis from clot development typically manifests itself as renal dysfunction and rising serum haptoglobin levels. Coagulopathy and thrombocytopenia occur due to platelet consumption from activation by the circuit's plastic surface. Moreover, a dilutional coagulopathy can occur. Hemorrhage at any surgical site or cannula site, or into the site of previous invasive procedures is a frequent complication because of the required systemic heparinization. Intrathoracic, abdominal, or retroperitoneal hemorrhage may also occur. Exsanguination from circuit disruption, while uncommon, can be fatal.
Pericardial tamponade can occur due to cannula placement in the face of systemic anticoagulation. Myocardial stunning, which is defined as a decrease of left ventricular ejection fraction by more than 25% with the initiation of ECMO, may occur, requiring further V-A-ECMO support or vasopressor and inotropic support. Fortunately, stunning is a temporary effect and cardiac ejection function returns to normal within 48 hours of ECMO initiation.
Pulmonary hemorrhage, and spontaneous and iatrogenic pneumothorax may occur, as well. Oliguria is common during early ECMO therapy, and acute tubular necrosis and renal failure may occur from hemolysis, hypovolemia, or decreased perfusion.
Gastrointestinal hemorrhage may occur due to physiologic stress response, ischemia, embolic, or systemic anticoagulation. Elevated direct bilirubin and the development of biliary calculi occur secondary to prolonged fasting, use of parenteral nutrition, hemolysis, and diuretics.
Last, due to the ECMO circuit functioning as a large intravascular foreign body, numerous metabolic complications of either acidosis or alkalosis in response to any electrolyte disturbances may develop.
Due to the highly invasive nature of ECMO and the potential for numerous complications, a trained ECMO technician is usually present at all times, 24 hours per day, at the patient's bedside to monitor the circuit and the patient for potential complications. This is in addition to the patient's usual nursing personnel.