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Pathophysiology of Respiratory Failure Fern White & Annabel Fothergill.

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Presentation on theme: "Pathophysiology of Respiratory Failure Fern White & Annabel Fothergill."— Presentation transcript:

1 Pathophysiology of Respiratory Failure Fern White & Annabel Fothergill

2 Definition? Acute respiratory failure occurs when the pulmonary system is no longer able to meet the metabolic demands of the body due to inadequate gas exchange. Hypoxaemic respiratory failure: drop in blood oxygenation. Hypercapnic respiratory failure: rise in arterial CO2. PaO2 <8 kPa PaCO2 >6.7 kPa

3 What does the oxygenation of the blood in the lungs depend on? ● P A O 2 (Partial pressure of oxygen in alveolus) ● Diffusing capacity ● Perfusion ● Ventilation-perfusion matching What layers make up the diffusion barrier for oxygen within the lungs?

4 What does the removal of CO2 from the blood in the lungs depend on? ● Largely dependent on alveolar ventilation o RR = respiratory rate o V T = Tidal volume o V D = Dead space ● Respiratory rate ● Tidal volume ● Ventilation-perfusion matching

5 Ventilation and perfusion If alveoli are ventilated without being perfused: Increased dead space as these alveoli do not take part in gas exchange. Shunting: Non-ventilated alveoli remain perfused. Blood leaving the lungs is poorly oxygenated. In time, hypoxic vasoconstriction will result in a reduction in perfusion to non-ventilated alveoli and a relative increase in perfusion to ventilated alveoli, thus reducing the magnitude of the shunt and increasing the arterial saturation

6 Name 4 mechanisms of respiratory failure ● Low inspired Po 2 ● Hypoventilation: O2 in the alveolus is not replenished, CO2 is not removed. Alveolar partial pressure of oxygen falls with a corresponding fall in the arterial partial pressure and hence saturation. The fall in alveolar PO2 is small and is easily compensated for by small increase in inspired oxygen concentration ● Ventilation-perfusion mismatch ● Diffusion abnormality: Abnormality of the alveolar membrane or a reduction in the number of capillaries resulting in a reduction in alveolar surface area. Desaturation on exercise.

7 Type 1 or Type 2? Type 2: Inadequate alveolar ventilation; both oxygen and carbon dioxide are affected. Defined as the build up of carbon dioxide levels (PaCO2) that has been generated by the body but cannot be eliminated. Causes: drug overdose (reduced breathing effort), neuromuscular disease, chest wall abnormalities, and severe airway disorders with increased resistance or reduced lung surface area (eg, asthma and COPD). Type 1: Hypoxemia without hypercapnia - PaCO2 may be normal or low. It is typically caused by a ventilation/perfusion (V/Q) mismatch. Causes: anything that creates a mismatch (acute lung diseases such as pneumonia, PE, ARDS) or hypoventilation (low ambient oxygen, neuromuscular disease).

8 What does this x-ray show? What type of respiratory failure can it lead to?

9 What are the clinical signs? ● Respiratory compensation o Tachypnoea o Accessory muscles o Recession o Nasal flaring ●Sympathetic stimulation o Increased HR o Increased BP (early) o Sweating ●Tissue hypoxia o Altered mental state o Lactic acidosis o Decreased HR and BP (late) ●Haemoglobin desaturation o Cyanosis ●Hypercapnia o Flapping tremor o If severe (>10kPa) - unconsciousness + respiratory

10 Treatment Type 1 Respiratory Failure Pneumonia – Antibiotics – Physiotherapy Pulmonary Oedema – Vasodilators – Diuretics Pneumothorax – Chest drain or aspiration Type 2 Respiratory Failure Asthma – Bronchodilators (salbutamol) – Corticosteroids Drug Overdose – Antagonist Guillain–Barré Syndrome – (autoimmune demyelination) – Immunoglobulin or Plasmapheresis

11 Thanks! Any questions?

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