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What are the mechanism of lung changes in ARDS?
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What happens with ARDS acutre respiratory failure?
- - decreased oxygen exchange hypoxemia
- - decrease lung volume- atelectasis
- Results in confusion, decreased responsiveness, progressive metabolic and respiratory acidosis, cariac arrhythmias, shock
- Acute respiratory failure- deteriorating trent- end result of many pulmonary conditions
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Partial pressures of respiratory gases
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What are the acute respiratory failures?
- Severe hypoxemia PaO2 < 50mmHg norm 80-100
- Hypercapnia PaCO2 >50 norm 35-45
- Ph decreasing <7.3 norm 7.35-7.45
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What happens as a result of acute respiratory failure?
- complicated by relex pulmonary vasoconstriction from the hypoxia or acidosis
- impairs lung perfusion and increases cardiac workload
- Respiratory arrest
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What are the gas diffusion problems of Acute respiratory failure?
- Partial pressure- gas concentration or partial pressure changes, obstruction.
- Diffusion- SA, respiratory membrane thickness, fluid excess
- Posture- upright ventilation and perfusion best in lower lobe, upper lobe less compliant than lower lobes, BP lower in apices (top/ apex) of the lung.
- Supine/ side lying change regional perfusion and ventilation
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What is the normal ventilation and perfusion ratio of the lungs?
- - Normal approx 0.8- 0.9
- - Limited autoregulation
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What happens if there is a mismatch with the perfusion and ventilation of the lungs?
- - Inadequate ventilationbut good perfusion = blood is not ventilated resulting in right to left shunt - decrease systems O2 and hypoxemia
- - Inadequate perfusion but well ventilated = alveolar dead space
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How much O2 is dissolved in the plasma?
1%
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How is O2 transported?
- bounded to haemoglobin
- O2 exchanges between 20-40 PO2 and when only 50% of Hb is saturated.
- The exchange depends on O2, CO2, temp and plasma pH.
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How much carbon dioxide is dissolved in plasma?
7%
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What % of CO2 is loosely bound to the globin portion of Hb?
20%
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How is most of the CO2 carried around the body?
diffused into RBC for carbonic acid- bicarbonate buffer system for serum pH maintenance
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Summary Acidosis- Alkalosis:
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