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Extracorporeal membrane oxygenation in adults: A practical guide for internists

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Anticoagulation monitoring and transfusions

Anticoagulation is necessary to maintain a clot-free and functional circuit. Most clots develop in the oxygenator membrane, where they can prevent optimal gas exchange and, rarely, lead to embolization to the systemic circulation. However, reports have suggested that anticoagulation can be held for short periods on ECMO if necessary.

Unfractionated heparin is usually used for anticoagulation. Commonly used tests to monitor anticoagulation are the augmented partial thromboplastin time, activated clotting time, and anti-factor Xa levels. Lately, thromboelastography analysis is being used to comprehensively monitor various components of the coagulation cascade.37 Anticoagulation is usually tailored to whether there are clots in the circuit, coagulopathy, and bleeding while on ECMO.38

Traditionally, blood products were used liberally during ECMO to maintain a normal hematocrit and improve oxygen delivery, although recent data suggest that outcomes may be similar with conservative use of blood products.39,40

Fluid management on ECMO

ECMO patients are fluid-overloaded due to a profound inflammatory response, cardiac failure, or both. Studies have shown that conservative fluid management improve lung function and shortens the duration of mechanical ventilation and intensive care in patients with lung injury.41 Hence, the patient’s net fluid balance should be kept negative, provided renal and hemodynamic parameters remain stable.

There is a high incidence of acute kidney injury in ECMO patients, and fluid overload is one of the main indications for renal replacement therapy.42 Continuous renal replacement therapy can be provided either by an in-line hemofilter or by incorporating a standard continuous renal replacement therapy machine into the ECMO circuit. There are no studies comparing the efficacy of these techniques, but they allow for rapid improvement in fluid balance and electrolyte disturbances and are commonly used in ECMO patients.42,43

Physical rehabilitation and ambulation on ECMO

Physical rehabilitation in mechanically ventilated patients has been shown to reduce ventilator days and stay in the intensive care unit.44 With the use of internal jugular double-lumen cannulas for venovenous ECMO and improvement in durability of the ECMO circuit, several centers are implementing physical rehabilitation and ambulation for patients while on ECMO. Current data suggest that physical therapy is safe for patients receiving ECMO and may accelerate the weaning process and shorten length of stay in the hospital after ECMO.45,46 Aggressive rehabilitation is especially beneficial in patients awaiting lung transplant and may improve posttransplant recovery and outcomes.47

Weaning from ECMO

There are no standard guidelines for weaning from venovenous or venoarterial ECMO. Once the underlying condition for which ECMO was initiated has improved, weaning can begin by reducing the blood flow rate, the flow rate of the sweep gas, or both.

Weaning from venovenous ECMO should be started when there is improvement in lung compliance, tidal volumes, and oxygenation. Once the circuit flow rate is reduced to less than 3 L/minute, ventilator settings are adjusted to standard lung-protective settings. ECMO support is gradually decreased by reducing the flow rate of sweep gas to less than 2 L/minute. If tidal volumes, respiratory rate, and gas exchange remain adequate after approximately 2 to 4 hours on a low rate of sweep gas, the patient can be weaned off the venovenous ECMO circuit.

Weaning from venoarterial ECMO should be considered when there is myocardial recovery with improved pulse pressure and contractility on echocardiography. This is done by reducing flow rates in increments of 0.5 to 2 L/minute over 24 to 36 hours and monitoring mean arterial pressures, central venous pressure, and myocardial contractility. When acceptable, patients are mostly weaned in a surgical setting. Prolonged periods on a low rate of blood flow are avoided to prevent thrombus formation in the circuit.

COMPLICATIONS OF ECMO

ECMO use can be associated with a myriad of patient and mechanical complications.

Hemorrhage is the most common complication encountered in ECMO, occurring in approximately 43% of patients.29 It occurs most frequently from cannulation and surgical sites. Although rare, potentially life-threatening pulmonary hemorrhage (including bleeding at the tracheostomy site), intracranial hemorrhage, and gastrointestinal hemorrhage have also been reported.30

Infections, including new infection and worsening sepsis in patients with acute respiratory distress syndrome secondary to infection, are common in patients on ECMO.48

Renal failure secondary to acute tubular necrosis requiring hemodialysis has been reported to occur in 13% of patients on ECMO.30

Other complications of concern, especially in patients on venoarterial ECMO, are lower limb ischemia and thromboembolism associated with site of cannulation and direction of blood flow.49 Mechanical complications include inappropriate placement of the cannula leading to insufficient oxygenation, injury to vessel walls, and rarely myocardial wall rupture; thrombus formation within the circuit causing failure of the oxygenator and sometimes, pulmonary or systemic embolism; and air embolism from the circuit.36

NOT SUITED FOR ALL

Despite limited data to support its use, there has been a recent increase in utilization of ECMO to support critically ill adult patients with cardiopulmonary failure. ECMO support is not suited for all patients. Careful selection of patients should be done to optimize resource utilization and provide the best opportunity for recovery or transplant.

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