Amyotrophic Lateral Sclerosis (ALS) is a progressive neurodegenerative disease that affects nerve cells in the brain and spinal cord, leading to muscle weakness and atrophy throughout the body. While oxygen is commonly associated with breathing support, providing supplemental oxygen to many ALS patients can be counterintuitive and potentially harmful.
ALS and Respiratory Impairment
ALS progressively weakens the muscles responsible for breathing, including the diaphragm and the intercostal muscles located between the ribs. The diaphragm, the primary muscle for inspiration, is severely compromised as motor neurons degenerate. This weakening leads to a reduced ability to take deep breaths and effectively move air in and out of the lungs. As a result, carbon dioxide (CO2) can accumulate in the bloodstream, a condition known as hypercapnia. Weakness in expiratory muscles also impairs the ability to cough effectively, increasing the risk of respiratory infections.
The Paradoxical Impact of Supplemental Oxygen
In individuals with chronic respiratory conditions, including advanced ALS, the body’s normal drive to breathe, which is primarily regulated by carbon dioxide levels, can become diminished. Instead, the body may begin to rely on low oxygen levels as a secondary stimulus to breathe, a mechanism known as “hypoxic drive.”
When supplemental oxygen is administered to these patients, it raises the blood oxygen levels. This increase can suppress the remaining hypoxic drive, effectively removing the body’s signal to breathe. Consequently, carbon dioxide can build up further in the blood, leading to worsening hypercapnia, respiratory acidosis, and a decline in respiratory function. This can lead to respiratory failure.
Effective Respiratory Management in ALS
Given the risks associated with supplemental oxygen, effective respiratory management for ALS patients primarily focuses on interventions that support ventilation without suppressing the breathing drive. Non-invasive ventilation (NIV), such as BiPAP or CPAP, is a primary form of support. BiPAP machines are generally preferred over CPAP for ALS patients because they assist with both inhalation and exhalation, providing more comprehensive support for weakened respiratory muscles. NIV helps to improve gas exchange, reduce carbon dioxide buildup, and can prolong survival and improve quality of life.
Other supportive measures include cough assist devices, which help clear secretions from the lungs by simulating a natural cough. These devices are important for preventing respiratory infections like pneumonia. Regular monitoring of lung function, such as forced vital capacity (FVC), and blood gas levels, including carbon dioxide and bicarbonate, helps guide treatment decisions and assess the effectiveness of ventilation. In advanced stages, some patients may consider invasive ventilation through a tracheostomy, which provides full mechanical breathing support.