Spirometry and ABGs

Question 1

Pattern of disease in Obstructive airways disease

Answer 1

Fall sin FEV1, can falls FVC. FEV1/FVC is always reduced.
Severity of disease is characterise by the FEV1% Very severe <35%. Flow volume loops tend to show a scalloping of the final stages of inhalation

Question 2

Pattern of disease in restriction of airways disease

Answer 2

FVC affected more than FEV1. Ratio tends to go UP. Weirdly - the severity is still measured by the FEV1 despite the FVC being more affected

Question 3

Extra throacic-fixed airway obstruction pattern

Answer 3

Flow volume loop appears like a baguette due to the air being unable to pass in or out in a swift manor

Question 4

Intra-thoracic variable obstruction pattern

Answer 4

Flow volume loop appears like lips whereby the expiration is pushing against the obstruction, worsening the outlet but in inspiration the intrathoracic obstruction is alleviated somewhat

Question 5

Extra-thoracic variable airway obstruction pattern

Answer 5

During expiration the loop is somewhat unchanged as air can force its way past the obstruction, but inspiration causes extrapleural forces to contrict down and cause a shallow inspiratory side of the loop.

Question 6

Henderson-Hasselbach equation for concentration of H+

Answer 6

24x (PaCO2/conc HCO3)

H = 100 pH = 7
H= 80 pH = 7.1 
60 pH = 7.2 
50
40
30
25 = pH7.6
20 = 7.7

Question 7

Calculate A-a gradient

Answer 7

= (FiO2 (Patm - 47) - 1.25 x PaCo2 ) - PaO2 i.e. at standard body temp and FiO2 .21 (sea level)

= (150 - 1.25(PaCO2)) - PaO2
Normal is around Age/4 + 4

Question 8

Resp acidosis rules

Answer 8

Bicarb 1 for ever 10 CO2 Acute

4 for 10 in chronic

Question 9

Resp alkalosis rules

Answer 9

Bicarb 2 for every 10 drop

5 for every 10 Drop

Question 10

Metabolic alkalosis rules

Answer 10

0.7 increase for each 1increase in HCO3

Question 11

Metabolic acidosis rules

Answer 11

1.2 for each mmol decrease in HCO3

Question 12

Anion gap measurement

Answer 12

NA + K - (CL + HCO3)

Normal anion gap : Physiologic loss of HCO3 or H
HAGMA: unmeasured anion e.g. lactate, ketosis