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Respiratory distress occurs as a result of respiratory failure, when in medicine, ther is 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 hypoxemia; a rise in arterial carbon dioxide levels is called hypercapnia. The normal reference values are: oxygen PaO2 > 60 mmHg, and carbon dioxide 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. This is accompanied with the experience of anxiety if not panic and behavioral attempts to breathe.
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-increased 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.
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 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 ventilation, characterized by: Pao2-decreased, PaCO2-increased, PA-aO2-normal
- Pulmonary dysfunction
- Cardiac dysfunction
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.
Pathology of respiratory system (J, 460-519)
|Acute upper respiratory infections|
|Influenza and Pneumonia|
|Other acute lower respiratory infections|
|Other diseases of upper respiratory tract|
|Chronic lower respiratory diseases|
|Lung diseases due to external agents|
| Other, principally affecting|
| Suppurative and necrotic conditions|
of lower respiratory tract
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