Respiratory

Question 1

Normal pH

Answer 1

7.35 - 7.45

Question 2

Normal PaO2

Normal PaCO2

Answer 2

11-13kPa (note this is for room O2 - 21%)

4.7-6.0kPa

Question 3

Rule of thumb to estimate PaO2 using the inspired O2 concentration

Answer 3

Ten less
i.e. if inspiring 21% O2 as in the air then PaO2 estimate around 11 kPa

If 60% O2 then 50kPa and so on

This is why PaO2 must always br interpreted with FiO2 in mind

Question 4

Type 1 Respiratory failure PaO2 & PaCO2

Answer 4

PaO2 under 8kPa
PaCO2 under 6.5 kPa

(T1 only 1 abnormality)

Question 5

Type 2 Respiratory failure PaO2 & PaCO2

Answer 5

PaO2 under 8kPa
PaCO2 over 6.5 kPa

(T2 only 2 abnormality)

Question 6

Causes of T1RF (All the P’s)

Answer 6

Pulmonary oedema
Pneumonia
PE
Pulmonary fibrosis

Due to VQ mismatch

Question 7

Causes of T2RF (more to do with mechanics of breathing)

Answer 7

COPD
Resp centre depression
Resp muscle weakness
Abnormal chest wall

Question 8

What is quicker, resp or metabolic compensation

Answer 8

For resp pH problems, metabolic compensation occurs but this takes some time

For metabolic pH problems, resp compensation occurs and this is quick (resp rate change)

Question 9

Steps of determining cause of pH imbalance

Answer 9

Look at pH (acid or alkali)
Assess PaCO2

If normal / high in alkalosis or normal / low in acidosis then go on to look at HCO3 as the potential cause of imbalance

Question 10

pH acidic and bicarb low

Answer 10

Metabolic acidosis

Question 11

pH alkaline bicarb high

Answer 11

Metabolic alkalosis

Question 12

pH acidic and CO2 high

Answer 12

Resp acidosis (resp failure)

Question 13

pH alkaline and CO2 low

Answer 13

Resp alkalosis (hyperventilation)

Question 14

What is anion gap and when is it used

Answer 14

(Na+ + K+) - (Cl- + HCO3-) used to determine cause of metabolic acidosis

Question 15

Normal anion gap metabolic acidosis causes

Answer 15

HCO3- loss from gut (e.g. diarrhoea)

Renal tubular acidosis

Na and K not increased (may be lost in diarrhoea)

Question 16

Raised anion gap metabolic acidosis causes

Answer 16

Ketoacidosis (high K)
Renal failure
Lactic acidosis
Salicylate toxicity
Methanol ingestion
Antifreeze ingestion

All factors are where extra metabolites are added or ingested

Question 17

Metabolic alkalosis causes

Answer 17

Loss from gut (e.g. vomiting causes hypochloraemic met alk)

Hyperaldosteronism (due to lower levels of potassium in blood + more H+ excretion)

Question 18

What is PEFR compared against

Answer 18

Predictive value using age, sex and height

Question 19

FEV1 / FVC use in spirometry

Answer 19

Distinguish between obstructive (COPD and Asthma) and Restrictive (Pulmonary fibrosis) lung disease

(less than 70% = obstructive, over 80% = restrictive)

Question 20

What is Kco

Common causes of a low Kco

Answer 20

This measures the ease of diffusion of carbon monoxide into capillary blood

Interstitial lung disease
Emphysema
Pulmonary oedema
PE
Anaemia (lower binding capacity - this will also have normal spirometry)