Tests and biochemistry

Question 1

Define accuracy

Answer 1

How close the result is to the true value

Question 2

Define precision

Answer 2

The reproducibility of an analytical result

Question 3

What are the three types of variation?

Answer 3

• pre analytical variation
• analytical variation
• intrinsic biological variation

Question 4

Name some contributors to pre-analytical variation

Answer 4

• time of day
• posture
• fasting status
• recent exercise
• time in transit to laboratory
• temperature during transit
• anticoagulant or preservative used
• centrifugation time and force

Question 5

Why is bircarbonate so important?

Answer 5

• other buffer systems reach equilibrium
• carbonic acid (H2CO3) is removed as CO2
• so the only limit is the initial concentration of HCO3-

Question 6

Define acidosis

Answer 6

Increased [H+] or a process tending to increase [H+]

Question 7

Define alkalosis

Answer 7

Decreased [H+] or a process tending to increase [H+]

Question 8

Define acidaemia

Answer 8

Increased [H+]

Question 9

Define alkalaemia

Answer 9

Decreased [H+]

Question 10

Define respiratory acidosis

Answer 10

Increased [H+] due to increased pCO2

Question 11

Define respiratory alkalosis

Answer 11

Decreased [H+] due to decreased pCO2

Question 12

Define metabolic acidosis

Answer 12

Increased [H+] due to decreased HCO3-

Question 13

Define metabolic alkalosis

Answer 13

Decreased [H+] due to increased HCO3-

Question 14

How does the respiratory system compensate for metabolic acidosis?

Answer 14

Primary problem is too much H+, respiratory system compensates by blowing off CO2

Question 15

How does the metabolic system compensate for respiratory acidosis?

Answer 15

Primary problem is too much CO2, compensate by excreting more H+

Question 16

What does compensation aim to do?

Answer 16

Restore the ratio opposite to normal

Question 17

Name some causes of acidosis

Answer 17

• choking
• bronchopneumonia
• COAD
• increased H+ production or ingestion
• impaired H+ excretion
• loss of HCO3-

Question 18

Name some causes of alkalosis

Answer 18

• hysterical overbreathing
• mechanical over-ventilation
• raised intracranial pressure
• loss of H+ in vomit
• alkali ingestion
• potassium deficiency

Question 19

Name some effort dependant tests

Answer 19

• Forced expiratory volume / flow rates

- spirometry

Question 20

Name some effort independent tests

Answer 20

• relaxed vital capacity - spirometry
• helium / N2 washout static lung volumes
• whole body plethysmography
• impulse oscillometry
• exhaled breath nitric oxide

Question 21

Describe the FVC in asthma

Answer 21

FVC is usually reached except in patients with airway remodelling

Question 22

What is a normal FEV1/FVC ratio

Answer 22

More than 75% is normal

Question 23

Describe the FVC in COPD

Answer 23

Decreased FVC

Question 24

Describe FEV1, FVC and the FEV1/FVC ratio in restrictive disease

Answer 24

FEV1 = decreased
FVC= decreased 
FEV1/FVC= >75%

If the FEV is reduced in proportion to FVC it is restrictive disease

Question 25

Describe exercise testing

Answer 25

- decreased FEV1 or decreased PEF post exercise; asthma - decreased SaO2 during exercise in interstitial lung disease; to monitor treatment response - full cardiopulmonary exercise test (CPET) to differentiate cardiac vs respiratory dyspnoea. Heart rate vs oxygen uptake vs ventilatory rate

Question 26

Describe the measurement of airway resistance

Answer 26

- measured by either whole body plethysmography or more commonly/easily with impulse oscillometer - impulse oscillometer (IOS) measures airway resistance during quiet tidal breathing at different resonant frequencies to give total resistance - useful in patients (eg.kids) where it is easier to breathe at tidal volume rather than doing forced expiratory manoeuvres

Question 27

Describe pH testing

Answer 27

- it is a logarithmic scale of hydrogen ion concentration - being a log scale, a small change in the pH signifies a big change in hydrogen ion concentration - pH is regulated over a small range because of the effect of an acidosis or alkalosis on protein structure and hence protein function

Question 28

Describe PaO2

Answer 28

- it is the partial pressure of oxygen in arterial blood. It is generally abbreviated to PO2 in blood gas results - normal range for breathing air is 9.3-13.3 kPa - oxygen is vital for human survival because of its importance in energy production - failure to oxygenate a patient appropriately will result in significant harm or death - the PaO2 must be interpreted with the inspired oxygen concentration

Question 29

Describe PaCO2

Answer 29

- normal range is 4.7-6 kPa - carbon dioxide is a by-product of metabolism - accumulation results in an acidosis - a high PaCO2 indicates a respiratory acidosis - a high PaCO2 indicates a metabolic alkalosis - the body will try to compensate for a metabolic alkalosis by raising PaCO2 (hypoventilating) - the bod will try to compensate for a metabolic acidosis by lowering PaCO2 (by hyperventilating)

Question 30

Describe base excess (BE)

Answer 30

- normal range is -2 to +2 mmol/l - base excess is a measure of how much base has to be removed or added to the system to correct the pH in standard conditions - it is therefore a measure of metabolic acidosis or alkalosis - a negative BE indicates acidosis - a positive BE indicates alkalosis - the kidney will try to compensate for respiratory acidosis by creating a metabolic alkalosis (by retaining bicarbonate) - the kidney will try to compensate for a respiratory alkalosis by creating a metabolic acidosis (by excreting carbonate)

Question 31

A decreased PO2 suggests what?

Answer 31

Hypoxia