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
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