Acute Respiratory Failure
The lungs have two primary functions: oxygenation – intake of oxygen and ventilation, and elimination of carbon dioxide (CO2). Failure of either will result in hypoxia (low blood oxygen), or ventilatory failure (elevated carbon dioxide).
Since all organs- especially the vital organs, such as the heart, lungs, brain, and kidneys, require a continual flow of oxygen to function properly, low oxygen delivery is a serious problem. Neurologic function deteriorates quickly with a reduction in oxygen delivery, leading to bad decisions, which often aggravates the underlying problem or condition.
A continual low oxygen delivery will eventually reduce the pumping action of the heart, (reduced cardiac output), decreases the delivery of oxygen to vital organs (perfusion), thereby creating a dangerous positive feedback cycle.
The mechanism of hypoxia includes any process that leads to a reduction in oxygen transfer from the alveoli (air sacs) to the pulmonary capillaries. Examples include infections, such as sepsis and pneumonia, and flooding of the alveoli due to events such as hemorrhage, pulmonary edema, congestive heart failure, or drowning,
Ventilatory respiratory failure, which causes an elevated CO2, results in a situation referred to as respiratory acidosis. This process becomes problematic for proper functioning of various enzymes and biochemical functions in the vital organs. The causes of ventilatory respiratory failure include severe airflow obstruction, such as asthma, chronic bronchitis, cystic fibrosis, emphysema, and COPD; respiratory muscle weakness, due to such conditions as muscular dystrophy, polio, spinal cord injury, myasthenia gravis and multiple sclerosis), as well as injuries to the chest wall or ribcage.
Failure to reverse respiratory acidosis will also lead to an accompanying reduction in oxygen supply, as well as a reduction in end-organ function, eventually resulting in the death of vital organs, if allowed to progress.
Respiratory failure may also be multifactorial, leading to an acute decompensation of pre-existing conditions. Examples would include pneumonia or pulmonary embolism in patients with COPD, pulmonary edema or sepsis in patients with chronic asthma, and chest trauma or aspiration in patients with neuromuscular diseases such as cystic fibrosis. In these cases, the need arises to apportion between the pre-existing condition(s) and the acute episode.
© James F. Lineback MD FCCP; Presentation for Vistage, Intl. September, 2015.