Interpretation of Lung Function and ABGs Flashcards
When does slow vital capacity differ from forced vital capacity (FVC)
dynamic airway collapse
What happens to FEV1 in obstructive lung disease?
low, gets worse with increasing disease severity
What happens to FVC in obstructive lung disease?
normal in mild disease, decreased in more severe disease
Can spirometry diagnose restrictive airways disease?
No, spirometry can only suggest restriction, must be confirmed with lung volumes
What happens to FEV1 in restrictive airway disease?
Initially normal, becomes decreased with disease severity
What happens to FVC in restrictive airway disease?
reduced, gets worse with increasing disease severity
What happens to FEV1/VC in restrictive airway disease?
initially may be normal, increases with disease severity
How is severity of restrictive lung disease graded?
based on FEV1 percentage predicted
What happens to the flow volume loop in a fixed large airway obstruction?
plateauing of the expiratory loop and inspiratory loop
What happens to the flow volume loop in an intrathoracic variable obstruction?
plateauing of the expiratory loop but a normal inspiratory loop
What happens to the flow volume loop in an extrathoracic variable obstruction?
normal expiratory loop but a plateauing of the inspiratory loop
What is the use of an A-a gradient?
if normal then it is unlikely that there is significant lung disease and its more likely just hypoventilation
How do you calculate A-a gradient?
(150-(1.25PaCO2))-PaO2
What is the normal A-a gradient?
(age / 4) + 4
How much do you expect the bicarbonate to increase by in acute compensation for a 10mmHg rise in PaCO2?
1mmol/L
How much do you expect the bicarbonate to increase by in a chronic compensation for a 10mmHg rise in PaCO2?
4mmol/L
What is the normal anion gap?
11mmol/L
How do you calculate the anion gap?
(Na + K) - (Cl + HCO3)
What causes an elevated anion gap acidosis?
lactate
toxins
ketones
renal failure
What causes a normal anion gap acidosis?
diarrhoea
renal tubular necrosis
chloride (e.g. too much n.saline)
What causes metabolic alkalosis?
vomiting
burns
diuretics
