**5.1 Uncontrolled donation after circulatory death**

In uDCD, cardiac arrest is sudden and unexpected, and death is declared based on the irreversible loss of cardio-respiratory function (demonstrated after prolonged efforts to reverse it have failed). Death is usually declared in the emergency room by a team entirely independent of that responsible for organ recovery and preservation. More often than not, potential uDCD donors are declared dead prior to the arrival of next-of-kin. Based on a consequentialist ethical standpoint and the principles of utility and donor autonomy, certain countries, including Spain and France, allow cannulation maneuvers to commence in this setting, even in cases where first-person consent may not have yet been obtained [43, 44]. The will of the patient regarding donation is always subsequently investigated in the context a family interview, where information regarding the circumstances of the arrest, the outcome of resuscitation maneuvers, and the measures taken related to the donation process is relayed. Next-of-kin then decide, taking into consideration the potential donor's wishes, whether to proceed with donation or abort the process.

It should be clear that NRP is organ maintenance and not therapy. While the technology employed is similar, terms such as "extracorporeal membrane oxygenation/ECMO" and "extracorporeal life support/ECLS" should not be used in relation to organ donation. Such terminology is confusing, especially considering the fact that it is used to describe therapeutic maneuvers that may be used to recover patients suffering sudden cardiac arrest more commonly occurring inside the hospital itself.

## **5.2 Controlled donation after circulatory death**

In cDCD, the usual stand-down period of 2–5 min of asystole that is used to declare death does not necessarily reflect an irreversible loss of cardiac function, evidenced by the fact that cDCD hearts have been recovered and successfully transplanted [17, 45]. The "irreversibility" of death in cDCD is therefore predicated on the concept of permanence—the fact that loss of cardiac function will eventually become irreversible because it will not be reversed (and eventually lead to the loss of all brain and brain stem functions, as well). As it re-establishes circulation to some parts of the body, however, the use of NRP in this context remains controversial. At the least, clear and effective measures need to be put in place to ensure that cerebral reperfusion does not occur when NRP is established. Through the use of NRP, circulation is only restored to a limited region of the body, and a critical aspect of NRP in cDCD is ensuring lack of flow to the aortic arch vessels, thereby maintaining the permanence of circulatory arrest in the brain and brainstem. With pre-mortem cannulation, positioning of the aortic occlusion balloon in the supradiaphragmatic aorta distal to the left subclavian artery is confirmed radiographically prior to withdrawal of care. As additional measure, the aortic occlusion balloon may be briefly inflated for a few seconds prior to ventilatory withdrawal, in order to ensure disappearance of femoral arterial pressure and simultaneous maintenance of a normal pressure waveform in the left radial arterial line. In doing so, the minimum filling volume needed to entirely blocks the supradiaphragmatic aorta may be recorded [46]. Once NRP is initiated, adequate occlusion is confirmed through the use of a left radial artery catheter demonstrating absence of flow.

The timing of when cannulation for abdominal NRP may be performed in potential cDCD donors varies by country. In certain countries, such as Spain and the United States, pre-withdrawal heparinization and cannulation are permitted [24, 43]. In the United Kingdom, on the other hand, a potential cDCD donor may only be cannulated once death has been declared [25]. Pre-mortem cannulation is advantageous in that it is performed in a less stressful and more orderly fashion, and regional perfusion may be commenced immediately after the death declaration, thereby limiting the length of warm ischemia suffered. Ideally, pre-mortem cannulation should be performed in the least invasive manner possible (e.g., percutaneously).
