Extracorporeal Membrane Oxygenation: Utilization in Trauma

Introduction

• ECMO is increasingly used as a salvage therapy in trauma patients with refractory acute respiratory or cardiopulmonary compromise.
• Early initiation (within 48-72 hours) has been associated with improved outcomes and survival rates.¹
• Patient selection is critical, with younger patients and less severe injuries being associated with improved outcomes.²
• Use of ECMO in centers with high capacity and standardized protocols is associated with improved survival rates.
• Veno-venous (VV) configuration has been successfully used as a rescue for acute respiratory distress syndrome (ARDS) associated with pulmonary contusion or chest trauma.
• ECMO in severe ARDS has been shown to improve survival compared with conventional ventilatory management.
• Veno-arterial (VA) ECMO as circulatory support for cardiogenic shock or cardiac arrest is less common and less well-studied, and outcomes are often poorer compared to VV configurations indicated for pulmonary support.
• Anticoagulation strategies are individualized based on risk of bleeding related to trauma, with either heparin-free or low-dose heparin regimens being balanced against risk of thrombotic complications.
• Survival rates generally range from 61-70%, with higher survival rates for VV ECMO (72%) compared to VA ECMO (39%).³

Indications and Complications of ECMO Support in Trauma

Common indications for ECMO in trauma patients:

• Severe ARDS refractory to ventilator management
• Severe aspiration
• Pulmonary contusions
• Pulmonary embolism
• Tracheal/bronchial injury
• Pneumonectomy
• Cardiogenic shock or cardiac arrest unresponsive to conventional resuscitation

Complications

• See tables 1 and 2 for general and specific complications of VV and VA ECMO.
• Approximately 80% of trauma ECMO patients experience complications at some point during their hospital course.⁴
• During the early hemorrhagic phase, trauma patients are at increased risk of bleeding due to the lethal triad of trauma (coagulopathy, hypothermia, acidosis). During this phase, anticoagulant use in ECMO will increase the risk of bleeding.
• Advances in ECMO have enabled heparin-free, delayed, or low-dose heparin therapy.
• Hemorrhage in TBI patients may require the use of ECMO to be made on a case-by-case basis. However, ultra-low dose or heparin-free strategies have been used with similar survival rates to non-ECMO patients.
• After the acute phase, trauma patients are often hypercoagulable with increased risk of clot formation. An ECMO circuit increases this risk, and VA ECMO may lead to systemic emboli.

VV vs VA ECMO

• VV ECMO is the more commonly used configuration for treatment of ARDS associated with thoracic trauma and lung injury.
• Patients can be peripherally cannulated emergently at bedside by trained surgeons, ED providers, or intensivists.
• A peripheral VA drainage cannula can be placed via the femoral vein or the internal jugular vein, and the femoral artery for return. Peripheral cannula placement can be guided by transthoracic echo, transesophageal echo, or fluoroscopy.
• Central cannulation requires consultation with cardiothoracic or pediatric surgery (Figure 1).
• ECMO support should only be considered in high-volume centers with expertise in managing these patients.
• If ECMO is being considered and not available, patients should be referred to ECMO centers early to enable transfer planning.

Anticoagulation Strategies

• Trauma patients require a highly individualized, dynamic approach to anticoagulation and bleeding risk management.
• Anticoagulation is frequently delayed or minimized during the active bleeding period.
• In general, anticoagulation is recommended to prevent thrombosis during ECMO support.
• Most societies recommend anticoagulation for all ECMO patients unless contraindicated, given hemostatic interactions with ECMO biomaterial surfaces.
• Compared with cardiopulmonary bypass, the amount of blood exposed to nonendothelial surfaces per unit time is considerably lower, allowing for less aggressive anticoagulation strategies.⁵
• Low-dose or heparin-free protocols have been utilized with similar complication rates to standard anticoagulation strategies, including patients with TBI.⁶
• Unfractionated heparin is frequently chosen as an initial anticoagulant because it can be rapidly titrated to activated partial thromboplastin time or anti-Xa levels and discontinued or reversed in the event of bleeding.⁷
• Low-dose or heparin-free strategies must be balanced against associated risks, for example, an observational cohort study found that low-dose strategies were associated with more frequent oxygenator exchanges (14 in high dose compared to 48 in low dose) and more frequent thromboembolic events (6.8% in high dose compared to 19% in low).⁸

Anesthetic Considerations

• Please see the OA summary “Extracorporeal Membrane Oxygenation: Anesthetic Considerations” for more details. Link
• Patient transfer from intensive care unit (ICU) beds to operating room (OR) tables requires coordinated movement by all team members and visibility of all cannulation sites throughout the transfer. Transfers should be slow and coordinated, with clear communication to stop moves if any concerns arise, as dislodgement of canulae could cause catastrophic hemorrhage.
• Surgery on a patient on ECMO support is a high-risk procedure, and the procedure should be discussed in advance among the surgical, anesthesia, and intensive care teams.
• The anesthesia team should be familiar with managing cardiac and respiratory instability, depending on whether the patient is on VV or VA ECMO.
• ECMO circuits are generally preload-dependent and afterload-sensitive.
• ECMO circuits can be extremely sensitive to changes in patient volume status and hemodynamics. Volume assessments with echocardiography, either transthoracic or transesophageal, as well as pulmonary artery catheterization, if available, can help with troubleshooting.
• If patients have demonstrated stability on ECMO support, they may be extubated. In that case, patients may require reintubation and induction prior to OR procedures.
• It is critical to have dedicated ECMO specialists present during the case and induction to troubleshoot circuit-related issues and adjust flow and sweep to compensate for physiologic changes caused by anesthesia.
• ECMO circuits may sequester medications (in particular fentanyl). The choice of sedative agent should take this into consideration.
• VA configurations may require an left ventricle, and it is important for the anesthesia provider to be aware of how that vent is accomplished.
• ECMO pumps are continuous-flow devices; therefore, a patient on VA ECMO may not have a palpable pulse. An arterial line is therefore very useful to monitor mean arterial pressure.
• Arterial lines can help titrate ECMO sweep rates based on serial ABGs and provide a rapid assessment of changes in hemodynamics.
• Given concerns about bleeding or clotting in the OR, it is important to have an active type and screen with an available blood fridge in the room.
• In general, no IV drips should be attached to ECMO cannulas. Occasionally, they are used for renal replacement therapy (as per unit policy)
• ICU-level checks should continue during the OR procedure, including regular physical and circuit examinations and laboratory tests. Limb perfusion, being vigilant of clot burden, and monitoring for signs of occult hemorrhage is vital.