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Respiratory failure is a medical term for inadequate gas exchange by the respiratory system. Respiratory failure can be indicated by observing a drop in blood oxygenation (hypoxemia) and/or a rise in arterial carbon dioxide (hypercapnia), which can be written as (PaO₂ < 60 mmHg, PaCO2 > 45 mmHg). Classification into type I or type II relates to the absence or presence of hypercapnia respectively. (Values in kPa being PO₂ below 8kPA and PCO2 above 6.7 kPa

Types

Type 1

Type 1 respiratory failure is defined as hypoxaemia without hypercapnia, indeed the CO₂ level may be normal or low. It is typically caused by a ventilation/perfusion mismatch; the air flowing in and out of the lungs is not matched with the flow of blood to the lungs.Basic defect in type 1 respiratory failure is failure of oxygenation characterized by: PaO2-low(<60mmhg) PaCO2_normal/low(</=49mm hg) PA-aO2-increasd This type is caused by conditions that affect oxygenation like:

• Parenchymal disease(V/Q mismatch)
• Diseases of vasculature and shunts.

right to left shunt, ARDS,pneumonia,Emphysema.

Type 2

Type 2 respiratory failure is caused by increased airway resistance. both oxygen and carbon di oxide is affected. Defined as the build up of carbon dioxide that has been generated by the body. The underlying causes include:

• Reduced breathing effort (in the fatigued patient)
• Increased resistance to breathing (such as in asthma)
• A decrease in the area of the lung available for gas exchange (such as in emphysema).

basically there is defect in ventillation, characterised by: Pao2-decreased PaCO2-increased, PA-aO2-normal

Causes

Chest X-ray showing ARDS

• Pulmonary dysfunction
  • Asthma
  • Emphysema
  • Chronic Obstructive Pulmonary Disease
  • Pneumonia
  • Pneumothorax
  • Pulmonary contusion^[1]
  • Hemothorax
  • Acute Respiratory Distress Syndrome (ARDS) is a specific and life-threatening type of respiratory failure.
  • Cystic Fibrosis
• Cardiac dysfunction
  • Pulmonary edema
  • 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.

Treatment

Mechanical ventilation may be needed

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.

See also

• Ventilation/perfusion ratio
• Pulmonary shunt

References

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• This page was last modified on 3 October 2008, at 07:16.

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