Bartels_Hensley's Practical Approach to Cardiothoracic Anesthesia, 7e

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II. Equipment and Technology

2. For venovenous ECMO, strategies that employ lower levels of anticoagulation, restrictive transfusion thresholds, and reinfusion of circuit blood at the time of decannulation have been associated with favorable outcomes with minimal transfusion requirements. 22 Fur thermore, a multicenter, prospective cohort study of patients receiving venovenous ECMO found that a hemoglobin concentration of < 7 g/dL was associated with higher risk of death in the ICU compared with other higher hemoglobin concentrations and that red blood cell transfusion was associated with lower risk of death only when transfused for a hemoglobin concentration of < 7 g/dL. 23 3. Prolonged heparin infusions may reduce available antithrombin III and thereby impair the efficacy of heparin. Antithrombin III is available in recombinant form and may be consid ered to restore the efficacy of heparin in the context of low antithrombin III levels. 4. If heparin cannot be used, for example, in the setting of heparin-induced thrombocytope nia (HIT), alternative anticoagulants include argatroban and bivalirudin. CLINICAL PEARL Low levels of systemic anticoagulation appear to be effective at maintaining ECMO circuit patency while minimizing the risk of significant bleeding. C. Early Mobilization 1. Early mobilization of critically ill patients supported with ECMO has been demonstrated as safe and feasible, even in the presence of femoral venous and arterial cannulae. 24 2. Extubation and cessation of mechanical ventilation during ECMO support, when feasible, may aid in early mobilization. 3. Physical rehabilitation, including early mobilization, is of critical importance in the bridge-to-transplant population in order to maintain transplant candidacy. Whether there is a benefit in the bridge-to-recovery population comparable to that seen in other critically ill patients has yet to be determined and is an area of active research. D. Weaning ECMO 1. Venovenous: Patients should be evaluated for their readiness to wean from ECMO sup port after the underlying cause of respiratory failure is treated and the patient’s native gas exchange and respiratory system mechanics improve. There are several approaches to weaning venovenous ECMO. An approach of incremental reductions in sweep gas flow rate (with or without concomitant decreases in Fdo 2 ) while monitoring the ability to maintain adequate gas exchange with native lung function is most commonly employed. A trial with sweep gas flow turned off for a prespecified period of time (eg, 30 minutes) with acceptable gas exchange, no excess work of breathing, and acceptable ventilator settings (if applicable) should be performed in most patients prior to consideration of decannulation and may be used as the sole determinant of weaning readiness. 2. Venoarterial: Weaning from venoarterial ECMO differs significantly from venovenous ECMO. Because venoarterial ECMO provides hemodynamic support, weaning can be per formed with incremental reductions in extracorporeal blood flow with serial assessments of vasopressor and inotrope requirements, cardiac function, and end-organ perfusion. Ide ally, vasopressors will be able to be minimized or discontinued entirely prior to decannula tion from venoarterial ECMO, while it is more common to maintain some pharmacologic inotropic support. During weaning trials, a minimum extracorporeal blood flow rate of 2 L/ min should be maintained through the circuit to avoid circuit thrombosis. Sweep gas Fdo 2 is typically not weaned—and sweep gas should never be turned off entirely—in order to avoid the creation of a right-to-left shunt. If a patient appears ready for decannulation from a hemodynamic perspective but continues to require extracorporeal gas exchange support, conversion from venoarterial to venovenous ECMO (with its lower risk of systemic embo lization) should be considered.

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