Spirometry, ABGs, Pleural Fluid

Question 1

Draw spirometry graphy and show on it respiratory volumes/capicites

Answer 1

Question 2

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

Answer 2

500ml known as tidal volume

Question 3

Expiratory reserve volume

Answer 3

amount of air that can be expired after a tidal expiration

Question 4

inspiratory reserve volume

Answer 4

Amount of air that can be inspired beyond the TV

Question 5

Residual volume

Answer 5

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

Question 6

Inspiratory capacity

Answer 6

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

IC=TV + IRV

Question 7

Functional residual capacity (FRC)

Answer 7

amoount of air in the lungs after a tidal expiraiton

FRC=ERV + RV

Question 8

Vital capacity

Answer 8

Total amount of exchangeable air

VC=TV+IRV+ERV

Question 9

Total lung capcity

Answer 9

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

TLC+VC+RV

Question 10

FEV1

Answer 10

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%

Question 11

Forced vital capcity (FV\C)

Answer 11

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

Question 12

FEV1/FVC%

Answer 12

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

FEC1/FVC x 100

Question 13

Peak expiratory flow

Answer 13

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

Question 14

Spirometry process

Answer 14

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%)

Question 15

Spirometry pitfalls

Answer 15

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

Question 16

What can we measure with a time/volume plot

Answer 16

• PEFR
• FEV1
• FVC
• FEV1/FVC ration (>70%)

Question 17

Interpretating a flow/volume loop?

Answer 17

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

Question 18

Obstructive lung disease

Answer 18

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%

Question 19

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

Answer 19

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

Question 20

COPD or asthma?

Answer 20

nebulised or inhaled salbutamol given

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

Question 21

Asthma other investigtions?

Answer 21

• 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

Question 22

Restrictive lung disease

Answer 22

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

Question 23

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

Answer 23

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

Question 24

Spirometry interpretation

Answer 24

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

Question 25

Transfer factor test

Answer 25

* 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

Question 26

Transfer factor affeced by and reduced by

Answer 26

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)

Question 27

How to measure lung volume?

Answer 27

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

Question 28

oximetry

Answer 28

•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

Question 29

Main causes of hypoaemia

Answer 29

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

Question 30

Ventillation perfusion mismatch

Answer 30

* 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

Question 31

Blood gas analysis

Answer 31

* 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

Question 32

Pleural effusion analysis

Answer 32

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