Respiratory Failure - Physiology

Respiratory Failure

·        Ventilatory failure: When bellows function inadequate to excrete CO₂ produced (ie above 60 mmHg)

·        Respiratory Failure: (PaO₂ < 60 mmHg)

o  Type 1: PaCO₂ < 50 mmHg Þ VQ mismatch (less O₂ absorbed in hypoperfused areas, hyperperfused can‟t compensate due to the sigmoid shape of the dissociation curve) plus other causes (e.g. heart failure)

o  Type 2: PaCO₂ > 50 mmHg Þ hypoventilation – both gases are affected reciprocally – only lung problem can cause this

·        Respiratory Failure can be due to:

o  Central respiratory depression:

§  Drugs: opiates, alcohol, barbiturates

§  Brain stem: CVA, coning

§  If A-a gradient normal but patient hypoventilating Þ central depression.  If young then ?OD

o  Sleep Apnoea syndromes

o  Lung Pump Failure: neuromuscular disease, chest wall, lung disease.  E.g. diaphragm dysfunction:

§  Unilateral paralysis may be asymptomatic

§  Bilateral paralysis: neurological (e.g. polio, motor neuron, Gillian Barre) or myopathic (e.g. hypothyroid)

§  Signs: orthopnea, morning headache (hypercapnea over night), paradoxical breathing (chest wall and abdomen go in opposite directions when breathing), lung function worse when lying down

§  Treatment: treat cause, positive pressure ventilation systems