Reply Letter to the Editor Regarding the ELSO Interim Guidelines for Veno-Arterial Extracorporeal Membrane Oxygenation in Adult Cardiac Patients

To the Editor:

We thank Dr. Lim for his interest and letter¹ regarding the recently released ELSO Interim Guidelines for ECLS in Adult Cardiac Patients,² particularly addressing the weaning aspect from veno-arterial extracorporeal membrane oxygenation (V-A ECMO).

1. The author is right about the discrepancy reported for the weaning criteria. Indeed, the VTI value is considered as >12 cm/sec. However, the original publication taken into consideration³ indicates at least 10 cm/sec with an ECMO flow of 1–1.5 L/min, and 12 m is considered the safest threshold, with 15 indicating a full or, at least, more reliable recovery.
2. Normal DO₂/VO₂ is 5. DO₂/VO₂ of 2 represents shock with anaerobic metabolism. We recommend DO₂/VO₂ at least 3 during V-A ECMO support. We assume that the readers know how to calculate DO₂ and adjust hemoglobin and flow to maintain a ratio of 3 or higher.
3. Regarding the definition of cardiogenic shock and the related hemodynamic state for mechanical circulatory support cited by the author,⁴ the cardiac index of 2.2 L/min/m² in the publication is certainly present, but in association with inotropes/vasopressors, and with pulmonary capillary wedge pressure of > 15 mmHg. Indeed, the SCAI/HFSA/ACC/STS Expert Consensus Statement on Mechanical Circulatory Support Devices in Cardiovascular Care⁵ defines cardiogenic shock with the following criteria: systolic blood pressure < 90 mmHg for > 30 minutes, a drop in mean arterial blood pressure > 30 mmHg below baseline, cardiac index < 1.8 L/min/m² without hemodynamic support or, 2.2 L/min/m² with support, and capillary wedge pressure of 15 mmHg. The presence, therefore, of cardiac index of 2.2 L/min/m² in the weaning criteria should be present without relevant dosages of such drugs, as clearly indicated in the text with the sentence “low- doses of 1–2 inotropes or pressors”. These “low doses” are certainly in contrast with the cited definition of cardiogenic shock.⁴ Still regarding the capillary wedge pressure of > 15 mmHg present in the cited article,³ it usually corresponds to a much higher CVP than 10 mmHg. A very important study, which was not included in our list due to the already passed limit of acceptable number of references (no. 40), to take into consideration for such an issue comes from Ma and colleagues.⁶ This article defines very well the presence of “concordant” or “discordant” ventricular failure and the difficult relationship between central venous pressure and pulmonary capillary wedge pressure in patients with cardiogenic shock. Regarding the CPO, we did not include a discussion about this aspect. We assume that adequate cardiac output includes adequate RV function, but we should have added that sentence.
4. The author is right regarding the monitoring of right ventricular function during the weaning process, but also the author does not make any difference between an original failure involving both ventricles, or only the right or only the left one, which is a critical aspect during the weaning process. The discussion about the appropriate parameter to define RV function and state is still ongoing and controversial.⁷ These conditions have obviously different criteria based on the different attention and accepted limits during the V-A ECMO weaning process. The ELSO published document, as underlined above, had limitations for word count and attached tables and figures. Therefore, it was impossible to provide all the necessary details. ELSO will change the future preparation and release of the document (this is the reason for using “Interim Guidelines”) based on the work in progress and also for the upcoming new releases with dedicated publications in different setting, including differentiated RV, LV, or BiV failure and related ECMO support, cardiogenic shock settings (like in postcardiotomy or other scenarios, and so forth) weaning, bridge-to-other conditions and also withdrawal.
5. The bridge to heart transplant (HTx) is indicated in the text and certainly not underestimated by the authors. However, we are certain that the author acknowledges that heart transplant has a very limited application worldwide, with very different rate of access depending on the country rules/laws, organ availability, religious matters, and other organizational constraints. Furthermore, urgent transplant while having the patient on ECMO for advised and short duration^8,9 would be ideal if no recovery is present, but is usually very unlikely, suggesting that, worldwide, the most accessible or likely procedure would be an upgrade to a more durable VAD to allow the patient to wait the usual long period of waiting list until receiving a new organ. Urgent transplant within 2 weeks or less of V-A ECMO support with the lowest complication rate possible is nowadays considered really a rarity if not unrealistic. Maybe we should have included in the figure a direct access to HTx, in the country, situations, and very lucky patient getting such a chance, usually not available for the vast majority of supported patients who the general guidelines refer to. Going from ECMO to transplant assumes that a donor will be available in a few days. This rarely happens, so we recommend going to VAD is the most practical intermediate step.