Chronic Respiratory Failure

Definition
Respiratory failure is:

• an increase in carbon dioxide levels with a PC02 (partial pressure of CO2 - the amount of carbon dioxide gas dissolved in the blood) greater than 50 mm Hg
• a decrease in oxygen levels with a PO2  (partial pressure of O2 - the amount of oxygen gas dissolved in blood) less than 60 mm Hg
• or both. 

Chronic Respiratory failure is:

• Lack of recovery from acute respiratory failure,
• or an insidious onset of respiratory distress leading to failure over weeks, months or years.

There are three patho-physiologic categories of respiratory failure:

Increased respiratory load from chronic cardiopulmonary disease

Physiology: Normal matching of ventilation and perfusion is disrupted causing hypoxia and eventual muscle fatigue due to increased work of breathing Clinical conditions Chronic lung disease such as bronchopulmonary dysplasia (BPD), lung hypoplasia Congenital heart disease Skeletal deformities such as kyphoscoliosis or thoracic wall deformities Clinical signs decreased inspiratory breath sounds increased retractions and use of accessory muscles cyanosis when breathing room air decreased level of function/activity poor weight gain.

Ventilatory muscle weakness

Physiology: Inability to breathe an adequate volume of air and exhale carbon dioxide. Clinical conditions Neuromuscular disorders such as spinal muscular atrophy (SMA), muscular dystrophies or myopathies. Phrenic nerve paralysis Spinal cord injury above C-3. Clinical signs Weak cough Retained airway secretions Increased use of accessory muscles Incompetent swallowing Weak or absent gag reflex Decreased level of normal activity/function.

Decreased Central Nervous System (CNS) control

Physiology : Absence of adequate autonomic control of respiration results in decreased respiratory drive. Clinical conditions Congenital central hypoventilation syndrome (CCHS) Injury to the brain. Arnold Chiari type II malformation of the brain. Clinical signs Weak cough Retained airway secretions Increased use of accessory muscles Incompetent swallowing Weak or absent gag reflex Decreased level of normal activity/function.

Diagrams from Kliegman: Nelson Textbook of Pediatrics 18th Ed. 2007 , Chapter 370.5.

• Children less than 2 years of age are more likely to develop respiratory failure due to an inability to compensate for lung and airway dysfunction.
• The immature respiratory system also has a great potential for improvement due to growth of the airways and increase in number of alveoli in the first 8 to 10 years of age. This may allow for eventual weaning from mechanical ventilation.
• The P02 decreases approximately the same amount as the PC02 increases with hypoventilation. This may cause a minimal decrease in the oxygen saturation with a significant amount of CO2 retention. Therefore, the oximeter is not a sensitive indicator of adequate ventilation.