Extracorporeal Membrane Oxygenation for COVID-19 Disease: The Zürich Experience
At the time of the first confirmed COVID-19 case in Switzerland, our department was equipped with 8 ECMO devices and 20 oxygenators. USZ put together a task force to analyze the situation and take appropriate precautions.The institutional decision was made to purchase 12 new ECMO devices, in order to be prepared for an uncertain number of critically ill patients. Two weeks later, our warehouse contained 23 ECMO devices, 150 oxygenators and more than 300 different cannulas. On March 28, 2020, the first V-V ECMO for a COVID-19 patient with severe hypoxia, refractory to invasive ventilation, was implanted by us. With reference to the EuroELSO ECMO-COVID-19 Survey, 20 ECMOs have been implanted in Switzerland (9 USZ Zürich, 6 CHUV Lausanne, 3 Inselspital Bern, 2 Basel) during the COVID pandemic so far [22]. As the register is voluntary, the numbers are likely to be slightly underestimated. Compared to other European countries, the absolute number of ECMO cases in critical ill COVID-19 patients is low in Switzerland. Possible explanations for this can be the low overall population, the early lock down, which successfully limited the spread of the virus but also a critical patient selection.
During end of March and May 2020, ECMO was necessary in 9 critically ill COVID-19 patients: 6 were supported with V-V ECMO and 3 with V-A ECMO configurations. Three of these 9 ECMOs were implanted in an external hospital. After successful implantation, the patients were transported to our center in a helicopter on safe ECMO support during the flight. All patients had severe, rapidly progressive acute respiratory distress syndrome (ARDS). One patient suffered from pulmonary artery embolism, which worsened the respiratory situation before ECMO implantation. In the further course the patient was diagnosed with heparin induced Thrombocytopenia (HIT) [23]. Three patients required V-A ECMO support due to a septic condition with myocardial involvement. Seven patients could be weaned successfully from ECMO support and survived the disease. Two patients died due to intestinal ischemia with severe sepsis. Median age at implant was 59 years (46-69). Patient characteristics are listed in Table 1. All patients were healthy prior to the COVID-19 infection, with only minor comorbidities. An association with previously known diabetes, obesity or pre-existing respiratory diseases (asthma) was found particularly often.
ECMO therapy is a well establish procedure in the USZ and numbers are increasing. With around 150 ECMO implantations per year, our center runs one of the leading national ECMO-programmes also focusing on interhospital transport of patients on ECMO support over the past 10 years [15]. Within the last 6 years, we performed 165 ECMO transports and covered a distance of 22,000 kilometers during these missions.
High quality standards are guaranteed and checked by a regular training and certification program. For this purpose, we developed a simulator on which the operative/percutaneous vascular access and cannulation can be replicated with the original material (Figure 1). The already established infrastructure and team approach, including cardiac surgery, cardiology, anesthesiology and intensive care medicine, perfusionists, critical care and scrub nurses has created a solid foundation for the successful implementation of an ECMO program in the critical field of this global crisis. Previous studies during the Middle Eastern respiratory syndrome (MERS) and H1N1 outbreak report lower mortality and reduced organ failure when ECMO was offered to those, who failed optimal ventilation strategies, compared to the non-ECMO group [24, 25]. The WHO interim guidelines made general recommendations for treatment of ARDS in COVID-19 patients, including referring patients with refractory hypoxemia to expert centers capable of providing ECMO therapy. V-V ECMO can provide respiratory support in critically ill patients and minimize ventilator-induced lung injury, barotrauma and oxygen toxicity.
As patient selection is crucial, and key to success, we implemented an ECMO Evaluation sheet, recording age, height and weight, comorbidities, length of oro-tracheal intubation and actual ventilation parameters, hemodynamics including catecholamine use and infection parameters, in our daily routine. We used the PRESERVE-Score, Murray-Score and Horowitz-Index to assess the indication and expected outcome. In-house indications and contraindications for ECMO in COVID-19 patients, based on the ELSO recommendations, were established and interdisciplinary discussed before each implantation. The Cardiohelp System (Maquet, Getinge AB, Rastatt, Germany) in combination with an HLS 7.0 oxygenator was used routinely in all patients. For V-V ECMO support we used a femoro-jugular approach (Figure 2). Cannulation was performed bedside in the ICU, using ultrasound-guided femoral/jugular vein/artery puncture. Cannula placement was guided using transesophageal echocardiography (TEE) whenever possible. Avoidance of patient transports to the operating room reduces the risk of COVID-19 transmission to other patients and healthcare providers as well as environmental contamination. For V-V ECMO implantation in COVID-19 patients, we do not recommend the dual lumen cannula, as the implantation and positioning may be challenging and time-consuming, furthermore assuring proper cannula position while proning the patient is highly demanding. ECMO patients should be anticoagulated using regular heparin. As we experienced a prothrombotic state our COVID-19 patients, we kept target activated clotting time (ACT) between 180-200 seconds. Heparin-induced thrombocytopenia should be monitored and treated early. In addition to the reckoned personnel and logistical effort, ECMO centers also face additional challenges in terms of employee protection and safe patient transportation during the COVID pandemic. The standard personal protection equipment (PPE) guidance by Public Health England (PHE) for healthcare workers involved in care of patients with COVID-19, include a disposable apron, gloves, surgical mask and eye protection [26] (Figure 3). During ECMO implantation and explantation in the ICU, the whole team is working in a high-risk environment. Especially during TEE, which is used for wire and cannula placement, there is an increased risk of aerosol release. Therefore, it is recommended to wear a protective respirator mask (N99 or FFP3 equivalent, which can be either valved or unvalved) during these procedures. As the standard of PPE may vary between different hospitals, we have put together a compact PPE kit for the protection of our team, which is also used for external applications (Figure 4).