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Respiratory > Spirometry, ABGs, Pleural Fluid > Flashcards

Spirometry, ABGs, Pleural Fluid Flashcards

1
Q

Draw spirometry graphy and show on it respiratory volumes/capicites

A
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2
Q

During normal quiet breathing, how much air moves in and out of the lungs with each breath

A

500ml known as tidal volume

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3
Q

Expiratory reserve volume

A

amount of air that can be expired after a tidal expiration

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4
Q

inspiratory reserve volume

A

Amount of air that can be inspired beyond the TV

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5
Q

Residual volume

A

after the most strenous expiration, about 120ml of air reminas in the lungs (prevents atelectasis)

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6
Q

Inspiratory capacity

A

total amount of air that can be inspired after a tidal expiration

IC=TV + IRV

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7
Q

Functional residual capacity (FRC)

A

amoount of air in the lungs after a tidal expiraiton

FRC=ERV + RV

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8
Q

Vital capacity

A

Total amount of exchangeable air

VC=TV+IRV+ERV

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9
Q

Total lung capcity

A

sum of all the lung volumes and is normally around 6L

TLC+VC+RV

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10
Q

FEV1

A

Forced expiratory volume in one secod (FEV1)- the maximal volume of gas, which can be expired from the lungs in the first second of a forced expiration from full inspiration

normal is 75-80%

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11
Q

Forced vital capcity (FV\C)

A

Maximal volume of gas, which can be expired from the lungs during a forced expiration from full inspiration

reduced in restrictive

normal or increased in obstructive disorders

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12
Q

FEV1/FVC%

A

The proportion of the FVC, which can be expelled during the first second of expiration expressed as a percentage

FEC1/FVC x 100

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13
Q

Peak expiratory flow

A

Maximum epiratory flow that can be sustained for a minimum of 10 seconds

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14
Q

Spirometry process

A

Forced expiratory manoeuvre from total lung capacity followed by a full inspiration

–“take a big breath in as far as you can and blow out as hard as you can for as long as possible- then take a big breath all the way in”
–Best of 3 acceptable attempts (within 5%)

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15
Q

Spirometry pitfalls

A
  • Appropriately trained technician
  • Effort and technique dependent
  • Patient frailty
  • Pain, patient too unwell
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16
Q

What can we measure with a time/volume plot

A
  • PEFR
  • FEV1
  • FVC
  • FEV1/FVC ration (>70%)
17
Q

Interpretating a flow/volume loop?

A

Number in reverse i.e from right to left
Read bottom of graph, follow bottom line from right to left, - patient taking a deep breath in
Read top of graph, patient taking forced breath out, read from left to right

18
Q

Obstructive lung disease

A

asthma, COPD, Cystic fibrosis and bronchiectasis

Result in obstructed airways creating airway resistance to expiratory flow so the patient with struggle to get air out quickly resulting in a decreased FEV1.

A smaller FEv1 will therefore result in smaller FEV1/FVC ratio

Severity of COPD stratified by %predicted FEV1

  • mild >80%
  • mod 50-80%,
  • severe 30-50%,
  • very severe <30%
19
Q

Expected results of obstructive disease on Volume/time graph and Flow-volume curve

A

Flow time graph

Prolonged increase in air expired (because air cant be expired as quickly due to airway resistance) but ends at the same point asthe total lung volume is the same

Flow-volume Loop

Decreased peak expiratory flow rate with steeper reduction in flow rate after it peaks creating a characteristic dip

20
Q

COPD or asthma?

A

nebulised or inhaled salbutamol given

  • spirometry before and 15 min after salbutamol
  • 15% and 400ml reversibility siggests asthma
21
Q

Asthma other investigtions?

A
  • PEFR testing
    • Look for diurnal variation and variation over time
    • Response to inhaled corticosteroid
    • Occupational asthma
  • Bronchial provocation
  • Spirometry before and after trial of inhaled/ oral corticosteroid
22
Q

Restrictive lung disease

A

restrictive disease such as pulmonary fibrosis/ILD, obesity, neuromuscular and chest/spine disorders

  • restrict lung expansion, reducing the amount of air the lungs can hold (the vital capacity) resulting in a decreased FVC
  • as there is decreased lung complance and elasticity it is also harder for the lungs to force air out quicky resulting in a decreased FEV1
  • as both Fev1 and FVC the FEv1/FVC ratio will be near normal
23
Q

Result of restrictive disease on volume-time graph and flow-volume loop

A

volume time graph

rapid increase as normal, but reaches plateou much ssoner (because total volume of lungs is restricted)

Flow-volume curve

curve looks normal just smaller due to proportionally reduced flow rates (because total volume of lungs is restricted

24
Q

Spirometry interpretation

A
  1. First look at FEV1/ FVC ratio
  2. If <70%, obstruction
  3. If obstructed, look at % predicted FEV1 (severity) and any reversibility (COPD vs asthma)
  4. If FEV1/ FEV ratio normal, look at % predicted FVC (if low, suggests restrictive abnormality)
  5. Can also get mixed picture, eg obesity and COPD
25
Q

Transfer factor test

A
  • Single breath of a very small concentration of carbon monoxide
  • CO has very high affinity to Hb
  • Measure concentration in expired gas to derive uptake in the lungs
26
Q

Transfer factor affeced by and reduced by

A

Affected by:
–Alveolar surface area
–Pulmonary capillary blood volume
–Haemoglobin concentration
–Ventilation perfusion mismatch

Reduced in:
–Emphysema
–Interstitial lung disease
–Pulmonary vascular disease
–Anaemia (increased in polychthaemia)

27
Q

How to measure lung volume?

A

2 methods of measuring:

  • Helium dilution (inspire known quantity of inert gas)
  • Body plethysmography (respiratory manoevures in a sealed box lead to changes in air pressure- can derive lung volumes. Archimedes principle!)

Lung volumes reduced in

  • restrictive lung disease

Increased RV and RV/TLC in

  • obstructive lung disease
28
Q

oximetry

A

•Non-invasive measurement of saturation of haemoglobin by oxygen
•Depends on oxyhaemoglobin and deoxyhaemoglobin absorbing infrared light differently
•Depends on adequate perfusion (shock, cardiac failure)
•Does NOT measure carbon dioxide, so no measurement of ventilation
False reassurance in a patient on oxygen with normal saturations (acute asthma, COPD, hypoventilation

29
Q

Main causes of hypoaemia

A

–Hypoventilation (eg drugs, neuromuscular disease)
–Ventilation/ perfusion mismatch (eg COPD, pneumonia)
–Shunt (eg congenital heart disease)
–Low inspired oxygen (altitude, flight)

30
Q

Ventillation perfusion mismatch

A
  • Happens to a degree in normal lungs
  • Main cause of hypoxaemia in medical patients
  • Areas of lung that are perfused but not well ventilated (eg pneumonic consolidation)
  • Mixing of blood from poorly ventilated and well ventilated parts of the lung causes hypoxaemia
  • Does not fully correct with oxygen administration
  • Shunt an “extreme” form of V/Q mismatch where blood bypasses the lungs entirely. Does not correct with oxygen administration
31
Q

Blood gas analysis

A
  • Always look at the pO2 first
    • Is the patient in respiratory failure requiring additional oxygen?
  • Then look at the PCO2 (type 1 vs type 2 respiratory failure)
  • Then consider acid base balance
    • Acute respiratory acidosis- elevated pCO2, normal bicarbonate, acidosis
    • Compensated respiratory acidosis- elevated pCO2, elevated bicarbonate (renal compensation), not acidotic
    • Acute on chronic respiratory acidosis- elevated pCO2, elevated bicarbonate, acidotic
32
Q

Pleural effusion analysis

A

Can be transudate or exudate

Transudate

  • hydrostatic/oncotic forces cause extravasation of fluid through a normal membrane
  • causes: heart failure, hypoalbuminaemia (liver failure, nephrotic syndroem)
  • <30g/l of pleural fluid protein

Exudate

  • inflammation causes increased permeability of leural surface/capillaries leaking intravascular fluid
  • Exudate causes
    • inflammation
    • Infection
    • infarction (PE)
    • malignancy
  • Plerual fluid protein >30g.L
  • or LDH high

Respiratory (18 decks)

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