When a patient suffers from severe respiratory or cardiopulmonary failure, medical teams often employ multiple life support devices simultaneously. Patients can be on both an Extracorporeal Membrane Oxygenation (ECMO) machine and a mechanical ventilator simultaneously. This combined approach provides external assistance for gas exchange while maintaining controlled airflow to the lungs. This dual support mechanism is a common strategy in intensive care units, designed to stabilize the patient when the lungs or heart are too damaged to function adequately, creating an environment where recovery can begin.
Understanding ECMO and Mechanical Ventilation
Mechanical ventilation and ECMO machines function in fundamentally different ways to support the body’s oxygen delivery system. A mechanical ventilator is a device that works internally, pushing a measured volume of air into the patient’s lungs through a tube to ensure oxygen enters the bloodstream and carbon dioxide is removed. This machine is designed to physically assist or completely control the breathing process.
ECMO, conversely, provides support externally, acting as an artificial lung and sometimes an artificial heart. The machine draws blood from the patient’s body, passes it through an oxygenator—often referred to as the membrane lung—where carbon dioxide is removed and oxygen is added. This newly oxygenated blood is then returned to the patient’s circulation.
There are two main configurations for ECMO depending on the patient’s needs. Veno-venous (VV) ECMO supports only the lungs, returning oxygenated blood to the venous system, requiring the patient’s heart to pump it through the body. Veno-arterial (VA) ECMO supports both the heart and lungs, returning oxygenated blood directly into the arterial system, bypassing the heart’s need to pump effectively. Since the combined therapy addresses lung failure, VV ECMO is the most common configuration used alongside a ventilator.
The Rationale for Concurrent Use
The primary physiological reason for using a ventilator and ECMO together is a strategy known as “lung rest.” When a patient develops severe lung injury, such as Acute Respiratory Distress Syndrome (ARDS), the high pressures and volumes required by a standard mechanical ventilator to maintain adequate oxygenation can cause further harm. This damage, termed Ventilator-Induced Lung Injury (VILI), involves several types of trauma, including barotrauma from high pressure and volutrauma from excessive stretching.
ECMO mitigates this problem by taking over a significant portion of the gas exchange function. With the ECMO circuit handling the oxygenation and carbon dioxide removal, the clinical team can drastically lower the mechanical burden placed on the injured lungs by the ventilator. This reduction in stress allows the damaged lung tissue to minimize inflammation and begin the healing process.
ECMO acts as a temporary “third lung,” enabling the physician to dial down ventilator settings to a gentle, protective level. This protective ventilation strategy keeps the lungs open and prevents collapse, avoiding the mechanical forces that contribute to VILI. The combination provides metabolic stability externally while protecting the damaged native organ. Concurrent use allows ECMO to manage gas exchange, creating the physiologic space for the ventilator to perform its function safely.
How Ventilator Settings Change During ECMO
Once a patient is successfully placed on ECMO, the goal for the mechanical ventilator shifts from aggressive gas exchange to providing only minimal, protective support. The medical team immediately lowers several settings that previously risked damaging the lungs. Specifically, the tidal volume (the amount of air delivered with each breath) is reduced significantly, often to an ultra-protective range of four to six milliliters per kilogram of predicted body weight.
The Fraction of Inspired Oxygen (FiO2) is also reduced. Since ECMO handles most oxygenation, the ventilator’s FiO2 is often decreased to 40% or near ambient air levels (around 21%). This prevents oxygen toxicity, a form of lung injury caused by prolonged exposure to high oxygen concentrations.
The pressure exerted on the lungs during inhalation, known as the plateau pressure, is maintained below 25 cmH2O to prevent injury. Positive End-Expiratory Pressure (PEEP), which keeps the small air sacs open, is often kept at a moderate level, typically between 6 and 10 cmH2O. These settings ensure the lungs are inflated just enough to prevent collapse without risking trauma, essentially using the ventilator to gently splint the lungs while ECMO manages the blood gases.
The Process of Weaning Off Support
The combined therapy is a temporary bridge to recovery, and the patient must eventually be weaned off both machines. The standard procedure is to wean the patient off ECMO first, requiring the native lungs to demonstrate independent gas exchange ability before removal. Weaning begins only after the underlying lung disease shows signs of reversal, such as improved compliance or clearer chest imaging.
The medical team tests the lungs by gradually reducing ECMO support, particularly the sweep gas flow (which controls carbon dioxide removal). This forces the patient’s lungs to take on more gas exchange work. If the patient remains stable, ECMO support is further minimized by lowering the blood flow or FiO2 on the circuit.
Once the patient maintains stable oxygen and carbon dioxide levels with minimal or no ECMO assistance, the machine is disconnected. The patient remains on the mechanical ventilator, still set to protective settings. The final phase involves weaning from the ventilator, where support is progressively lowered until the breathing tube can be safely removed.