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Respiratory > Tests and biochemistry > Flashcards

Tests and biochemistry Flashcards

1
Q

Define accuracy

A

How close the result is to the true value

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2
Q

Define precision

A

The reproducibility of an analytical result

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3
Q

What are the three types of variation?

A
  • pre analytical variation
  • analytical variation
  • intrinsic biological variation
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4
Q

Name some contributors to pre-analytical variation

A
  • time of day
  • posture
  • fasting status
  • recent exercise
  • time in transit to laboratory
  • temperature during transit
  • anticoagulant or preservative used
  • centrifugation time and force
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5
Q

Why is bircarbonate so important?

A
  • other buffer systems reach equilibrium
  • carbonic acid (H2CO3) is removed as CO2
  • so the only limit is the initial concentration of HCO3-
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6
Q

Define acidosis

A

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

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7
Q

Define alkalosis

A

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

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8
Q

Define acidaemia

A

Increased [H+]

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9
Q

Define alkalaemia

A

Decreased [H+]

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10
Q

Define respiratory acidosis

A

Increased [H+] due to increased pCO2

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11
Q

Define respiratory alkalosis

A

Decreased [H+] due to decreased pCO2

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12
Q

Define metabolic acidosis

A

Increased [H+] due to decreased HCO3-

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13
Q

Define metabolic alkalosis

A

Decreased [H+] due to increased HCO3-

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14
Q

How does the respiratory system compensate for metabolic acidosis?

A

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

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15
Q

How does the metabolic system compensate for respiratory acidosis?

A

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

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16
Q

What does compensation aim to do?

A

Restore the ratio opposite to normal

17
Q

Name some causes of acidosis

A
  • choking
  • bronchopneumonia
  • COAD
  • increased H+ production or ingestion
  • impaired H+ excretion
  • loss of HCO3-
18
Q

Name some causes of alkalosis

A
  • hysterical overbreathing
  • mechanical over-ventilation
  • raised intracranial pressure
  • loss of H+ in vomit
  • alkali ingestion
  • potassium deficiency
19
Q

Name some effort dependant tests

A
  • Forced expiratory volume / flow rates

- spirometry

20
Q

Name some effort independent tests

A
  • relaxed vital capacity - spirometry
  • helium / N2 washout static lung volumes
  • whole body plethysmography
  • impulse oscillometry
  • exhaled breath nitric oxide
21
Q

Describe the FVC in asthma

A

FVC is usually reached except in patients with airway remodelling

22
Q

What is a normal FEV1/FVC ratio

A

More than 75% is normal

23
Q

Describe the FVC in COPD

A

Decreased FVC

24
Q

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

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

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

25
Q

Describe exercise testing

A
  • 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
26
Q

Describe the measurement of airway resistance

A
  • 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
27
Q

Describe pH testing

A
  • 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
28
Q

Describe PaO2

A
  • 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
29
Q

Describe PaCO2

A
  • 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)
30
Q

Describe base excess (BE)

A
  • 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)
31
Q

A decreased PO2 suggests what?

A

Hypoxia

Respiratory (7 decks)

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