Atelectrauma is a lung injury that occurs in patients on mechanical ventilation. It is caused by the repetitive opening and closing of the smallest air sacs, the alveoli, when unstable portions of the lung are subjected to ventilator pressure changes. The resulting stress damages the delicate lung tissue and is distinct from other ventilator-related injuries caused by excessive air volume or pressure.
The Mechanism of Injury in the Lungs
The lungs’ microscopic air sacs, or alveoli, are where oxygen and carbon dioxide exchange occurs. In healthy lungs, these sacs remain open, but certain diseases can make them unstable and prone to collapse, a condition called atelectasis. When a patient with unstable alveoli is on a mechanical ventilator, the machine delivers breaths that force these collapsed sacs to reopen.
This repeated cycle of collapsing and reopening generates significant shear forces at the boundary between open and collapsed lung units. These forces act like a tearing mechanism on the thin alveolar walls, directly damaging the cells lining them. This process is known as cyclic recruitment and derecruitment.
The physical injury triggers an inflammatory response, which increases the permeability of blood vessels in the lungs. This causes fluid to leak from capillaries into the alveoli, a condition known as pulmonary edema. The fluid accumulation impairs the lungs’ ability to exchange gas and worsens the patient’s respiratory failure.
Causes and Associated Medical Conditions
Atelectrauma occurs almost exclusively during mechanical ventilation. The injury results from the interaction between the ventilator’s pressure and a lung made vulnerable by an underlying medical condition. The most significant of these conditions is Acute Respiratory Distress Syndrome (ARDS).
ARDS is a severe form of respiratory failure with widespread lung inflammation. This inflammation leads to fluid-filled, stiff lungs, making the alveoli unstable and likely to collapse. The damaging cycle is pronounced in ARDS because the disease often affects the lungs unevenly, creating a mix of healthy and collapsible regions.
Other conditions that increase the risk for atelectrauma include severe pneumonia, sepsis, and major trauma. These conditions cause lung inflammation, leading to fluid accumulation and reduced lung compliance. This makes the alveoli less able to remain open, especially in the lower regions of the lung most subject to gravity.
Ventilation Strategies for Prevention
Strategies to prevent atelectrauma center on lung-protective ventilation. A primary technique involves using lower tidal volumes, which means delivering smaller breath sizes. This approach avoids overstretching healthier parts of the lung and reduces pressure differences that cause the repetitive collapse of unstable alveoli.
Another component is the application of Positive End-Expiratory Pressure (PEEP). PEEP is a ventilator setting that applies constant, low-level pressure to the lungs at the end of each exhalation. This steady pressure acts as a scaffold, keeping vulnerable alveoli propped open and preventing them from collapsing.
The correct level of PEEP is tailored to the patient, as too little fails to prevent collapse, while too much can over-distend the lungs and compromise blood flow. Clinicians adjust PEEP based on the patient’s oxygenation and lung mechanics. Combining lower tidal volumes with optimized PEEP is the standard of care for ventilating patients with conditions like ARDS.