Respiratory failure is a frequently encountered condition in the practice of critical care. In conditions where ineffective gaseous exchange occurs, as in severe respiratory insufficiency, life-saving strategies such as mechanical ventilation are considerations. Although of significant benefit, positive-pressure ventilation always carries a risk for the development of complications such as oxygen toxicity, lung-hyperinflation, ventilator-associated pneumonia, and other complications. In such conditions, when there is a higher demand for gaseous exchange despite the applicable MV settings, extracorporeal membrane oxygenation (ECMO) devices are used to attain physiologic goals.
ECMO devices come in various forms according to the circuit configured and the components forming it. Configurations involving draining the deoxygenated blood from the venous compartment and returning oxygenated-decarboxylated blood to a vein is called venovenous ECMO (VV-ECMO). Similarly, when the blood is configured to return to the artery, it is veno-arterial ECMO (VA-ECMO). Extracorporeal carbon dioxide removal (ECCO2R) devices are specialized ECMO devices that predominantly focus on CO2 removal — thus reducing the PaCO2 and, eventually, the work of breathing and MV support. The potential advantage of ECCO2R devices is the reduced blood flow through the circuit. The membrane in action is composed of polymethylpentene (PMP) or siloxane. The principle of “apnoeic oxygenation” came into being, where oxygenation by the lungs and dependence on the alveoli reduces with independent extracorporeal oxygenation.
The basis for optional components such as the pump system in the configuration depends on the chosen circuit. Arterio-venous ECCO2R circuits do not need the pump in the configuration for functioning, whereas veno-venous ECCO2R requires its need as of the low-pressure system. The use of anticoagulants is necessary to prevent thrombus formation within the circuit.
The use of ECCO2R has shown the possibility of earlier extubation after IMV insertion, but there was no reduction in the length of hospital stay or early mortality (28-days and 90-days).
AV-ECCO2R can cause complications such as distal limb ischemia, compartment syndrome, and pseudoaneurysm formations. Similar complications occur in the VV system but occur less frequently.
Acute respiratory distress syndrome (ARDS) is associated with significant mortality and morbidity. Of all patients requiring MV, 23% of the global burden comes from those with ARDS, according to the LUNG SAFE trial. Unfortunately, there is no effective pharmacological treatment for ARDS, which leaves us to continue supported ventilation until the patient recovers. As an appropriate detour away from the expected complications mentioned, newer strategies such as ‘protective’ and ‘ultra-protective ventilation’ are used. The first type, ‘protective ventilation,’ involves small tidal volume and limited plateau pressures; this increased the survival, yet leaving behind the complication of lung over-inflation still in the remainder. Then the ‘ultra-protective ventilation’ using very low tidal volume and lower plateau pressures was instilled, adjoining the higher possibility of developing hypercapnia and respiratory acidosis. These complications are overcome with the ECCO2R device, thus facilitating appropriate lung recovery with the ultra-protective settings. Following such strategies has reduced the length of hospital stay of patients.
When considering other pathologies such as chronic obstructive pulmonary disease (COPD), MV can be both non-invasive ventilation (NIV), or invasive-mechanical ventilation (IMV), of which the former has shown a better prognosis. Although NIV has proven to reduce the mortality by half compared to IMV, quarter to half of that population eventually requires IMV over time. IMV predisposes to prolonged ventilatory requirements, weaning, and, thus, hospital stay. Of patients on NIV, ECCO2R has prevented the change to IMV in more than half its cases in certain studies. The use of ECCO2R in patients requiring IMV allows earlier extubation.
Hypercapnia is permissible to an extent as it enables the lungs for better healing by reducing inflammation. Hypercapnia becomes problematic with its action in the brain and heart - increasing intracranial pressure (in those with an already high value) and reducing cardiac output (in those with low cardiac function), respectively. Hypercapnoeic failure is one of the common reasons for ineligibility for lung transplants. Bridging patients through this phase with the use of ECCO2R has demonstrated promising results.
ECCO2R is not an FDA-approved therapy in the USA. There are multiple clinical trials underway to explore its utility in clinical settings mentioned above: COPD and ARDS. Like any extracorporeal device, this is a very resource-intensive and expensive technology. With the potential for complications, there is a need for close monitoring by physicians, nurses, ECMO specialists, and perfusionists with specialized training. There are two other forms of ECCOR2 devices undergoing clinical trials, including respiratory dialysis and gas exchange catheters, the former removes the carbon dioxide in wet form using available dialysis equipment increasing hopes of decreasing the cost and potentially reducing the complication rates.
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