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Cardiac surgery
Published in Roy Palmer, Diana Wetherill, Medicine for Lawyers, 2020
After anticoagulation with heparin, venous blood is drained by cannulae in the right atrium through plastic tubing into a reservoir from which it is pumped into an oxygenator, where oxygen is absorbed and carbon dioxide is given off. The earliest oxygenators allowed direct contact between blood and gas, but this was shown to cause harmful changes to the blood and to the patient. Since the 1970s, oxygenators have imitated the human lung by separating blood from gas by a diffusible membrane. From the oxygenator the now oxygen-rich, arterialized blood passes through a heater/cooler and a micropore filter before returning to the patient through a cannula placed in the ascending aorta. Since the heart and lungs have now been bypassed, the heart can be excluded from the circulation by cross-clamping the ascending aorta below the cannula. The heart is then arrested and protected from the ischaemia produced by the cross-clamp by the infusion of a ‘cardioplegic’ solution of potassium-enriched arterial blood into the aortic root or directly into the coronary arteries through an incision in the aorta. The heart is thus rendered motionless, flaccid and empty of blood, providing the surgeon with ideal operating conditions.
The Working Rat Heart Preparation
Published in John H. McNeill, Measurement of Cardiac Function, 2020
There are also two basic oxygenator designs (Figure 1B). In the one which is used with the “closed” system, the perfusate usually contains albumin (see below) and coats the walls of the oxygenating vessel in a thin film. The gas flows at a relatively slow rate through the center of the vessel and oxygenates the perfusate by diffusion (Figure 1B, left). “Open” systems usually incorporate a dispersion-type oxygenator, in which the perfusate is vigorously gassed through a fritted disk at the base of the perfusate well (Figure 1B, right). For purposes of discussion, the terms “closed” and “open” systems will henceforth be used to designate oxygenation by diffusion and dispersion, respectively.
Extracorporeal Membrane Oxygenation (ECMO) Support for Cardiorespiratory Failure
Published in Wayne E. Richenbacher, Mechanical Circulatory Support, 2020
Ralph E. Delius, Angela M. Otto
The blood then flows from the pump to a membrane oxygenator. Currently only one oxygenator is Food and Drug Administration (FDA) approved for ECMO use (Medtronic Perfusion Systems, Brooklyn Park, MN). Hollow fiber oxygenators which are widely used in operative circuits have not been proven to be useful for long-term support. The size of the membrane lung is critical. The membrane lung should be capable of providing complete cardiopulmonary support. Each size of the membrane lung has a rated flow which specifies the maximum flow of normally saturated venous blood which will leave the oxygenator 95% saturated. The membrane lung chosen for any given patient should have a rated flow equivalent to or in excess of the cardiac output of the patient. An excessively large oxygenator is not desirable either as priming volume will be increased and blood flow through the pump will be sluggish promoting the likelihood of thrombosis. Recommended tubing and membrane lung sizes are shown in Table 4.3.
The Moral Relevance of ECMO Bridge Maintenance
Published in The American Journal of Bioethics, 2023
When an oxygenator or circuit fails or begins to fail, the medical team is obligated to assess whether the patient is a candidate for replacement. As with the initial decision to cannulate for ECMO, this requires a discussion about the risks and benefits of the procedure, the likelihood of recovery, and the presence of factors that would make the patient prohibitively high risk for intervention. Here, demonstrated failure to recover or become eligible for transplant despite ECMO support, as well as other complications that may have developed during the ECMO bridge such as recurrent pulmonary infections, renal insufficiency, malnutrition, or skin breakdown, should be taken into consideration. If, as Childress et al. note, not all patients have a right to ECMO, a patient who develops a contraindication to ECMO does not have a right to ECMO maintenance when the circuit fails.
Fairly Distributing the Distributive Justice Argument Permits Stopping ECMO
Published in The American Journal of Bioethics, 2023
In fact, an example of how discontinuation of ECMO can take the form of withholding is cited by the Target Article. Truog et al. describe a 17-year-old boy cannulated to ECMO for respiratory failure with the goal of providing support as a bridge to lung transplantation (Truog, Thiagarajan, and Harrison 2015). However, during his ECMO run, he was diagnosed with post-transplant lymphoproliferative disease, a type of cancer that precludes transplantation. Thus, ECMO was no longer a bridge to transplantation; it had become ECMO-DT. Though the team wrestled with questions like those raised by Mr. J’s case, they ultimately elected not to replace the oxygenator as it degraded over time (after all, this equipment was not designed to be used for long-term therapy), resulting in the patient’s death when the oxygenator failed. A similar non-escalatory strategy, ideally supported by hospital policies based in principles of distributive justice, could inform patient, family, and clinician expectations and responsibilities in these rare but complex and challenging situations.
Mechanical circulatory support device selection for bridging to cardiac transplantation: a clinical guide
Published in Expert Review of Medical Devices, 2023
Tamari Miller, Veli K. Topkara
Alternative but less commonly used options for refractory cardiogenic shock include Tandem Heart and CentriMag™. TandemHeart® is a percutaneous centrifugal ventricular assist device which unloads the left ventricle by shuttling blood from the left atrium to the descending aorta. There is limited evidence for its use in cardiogenic shock but can provide up to 5 L/min of hemodynamic support. CentriMag™ is a surgically placed device which requires a median sternotomy and can support univentricular or biventricular dysfunction with up to 10 L/min of support. When serving as a left ventricular assist device the inflow cannula is placed in the left atrium or left ventricle with the outflow graft in the ascending aorta. As a right ventricular assist device, inflow is in the right atrium with outflow in the pulmonary artery. There is no randomized trial data to support its use but limited data suggests it has comparable post-transplant outcomes as continuous flow durable LVADs with 89.5% 1 year survival [35]. An oxygenator could be added on CentriMag™ as needed for severe respiratory failure resulting in poor oxygenation.