Respiratory failure

The term respiratory failure, in medicine, is used to describe inadequate gas exchange by the respiratory system, with the result that arterial oxygen and/or carbon dioxide levels cannot be maintained within their normal ranges. A drop in blood oxygenation is known as hypoxia; a rise in arterial carbon dioxide levels is called hypercapnia. The normal reference values are: oxygen PaO2 greater than 80 mmHg, and carbon dioxide PaCO2 less than 45 mmHg. Classification into type I or type II relates to the absence or presence of hypercarbia respectively.

Type 1
Type 1 respiratory failure is defined as hypoxia without hypercarbia, and indeed the PaCO2 may be normal or low. It is typically caused by a ventilation/perfusion (V/Q) mismatch; the volume of air flowing in and out of the lungs is not matched with the flow of blood to the lungs. The basic defect in type 1 respiratory failure is failure of oxygenation characterized by:


 * {| class="wikitable" border="1"


 * PaO2 || low (< 60 mmHg)
 * PaCO2 || normal or low
 * PA-aO2 || increased
 * }
 * PA-aO2 || increased
 * }

This type of respiratory failure is caused by conditions that affect oxygenation such as:
 * Parenchymal disease (V/Q mismatch)
 * Diseases of vasculature and shunts: right-to-left shunt, pulmonary embolism
 * interstitial lung diseases: ARDS, pneumonia, emphysema.

Type 2
The basic defect in type 2 respiratory failure is characterized by:


 * {| class="wikitable" border="1"


 * PaO2 || decreased
 * PaCO2 || increased
 * PA-aO2 || normal
 * pH || decreased
 * }
 * pH || decreased
 * }
 * }

Type 2 respiratory failure is caused by increased airway resistance; both oxygen and carbon dioxide are affected. Defined as the build up of carbon dioxide levels (PaCO2) that has been generated by the body. The underlying causes include:
 * Reduced breathing effort (in the fatigued patient)
 * A decrease in the area of the lung available for gas exchange (such as in emphysema).
 * Neuromuscular problems like, GB syndrome.
 * Flail chest.

Causes

 * Pulmonary dysfunction
 * Asthma
 * Emphysema
 * Chronic Obstructive Pulmonary Disease
 * Pneumonia
 * Pneumothorax
 * Pulmonary contusion
 * Hemothorax
 * Acute Respiratory Distress Syndrome (ARDS) is a specific and life-threatening type of respiratory failure.
 * Cystic Fibrosis
 * Cardiac dysfunction
 * Pulmonary edema
 * Cerebrovascular Accident
 * Arrhythmia
 * Congestive heart failure
 * Valve pathology
 * Other
 * Fatigue due to prolonged tachypnoea in metabolic acidosis
 * Intoxication with drugs (e.g., morphine, benzodiazepines) that suppress respiration.
 * Neurological Disease
 * Toxic Epidermal Necrolysis

Treatment
Emergency treatment follows the principles of cardiopulmonary resuscitation. Treatment of the underlying cause is required. Endotracheal intubation and mechanical ventilation may be required. Respiratory stimulants such as doxapram may be used, and if the respiratory failure resulted from an overdose of sedative drugs such as opioids or benzodiazepines, then the appropriate antidote such as naloxone or flumazenil will be given.