Spirometry, ABGs, Pleural Fluid Flashcards
Draw spirometry graphy and show on it respiratory volumes/capicites
During normal quiet breathing, how much air moves in and out of the lungs with each breath
500ml known as tidal volume
Expiratory reserve volume
amount of air that can be expired after a tidal expiration
inspiratory reserve volume
Amount of air that can be inspired beyond the TV
Residual volume
after the most strenous expiration, about 120ml of air reminas in the lungs (prevents atelectasis)
Inspiratory capacity
total amount of air that can be inspired after a tidal expiration
IC=TV + IRV
Functional residual capacity (FRC)
amoount of air in the lungs after a tidal expiraiton
FRC=ERV + RV
Vital capacity
Total amount of exchangeable air
VC=TV+IRV+ERV
Total lung capcity
sum of all the lung volumes and is normally around 6L
TLC+VC+RV
FEV1
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%
Forced vital capcity (FV\C)
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
FEV1/FVC%
The proportion of the FVC, which can be expelled during the first second of expiration expressed as a percentage
FEC1/FVC x 100
Peak expiratory flow
Maximum epiratory flow that can be sustained for a minimum of 10 seconds
Spirometry process
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%)
Spirometry pitfalls
- Appropriately trained technician
- Effort and technique dependent
- Patient frailty
- Pain, patient too unwell
What can we measure with a time/volume plot
- PEFR
- FEV1
- FVC
- FEV1/FVC ration (>70%)
Interpretating a flow/volume loop?
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
Obstructive lung disease
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%
Expected results of obstructive disease on Volume/time graph and Flow-volume curve
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
COPD or asthma?
nebulised or inhaled salbutamol given
- spirometry before and 15 min after salbutamol
- 15% and 400ml reversibility siggests asthma
Asthma other investigtions?
- 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
Restrictive lung disease
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
Result of restrictive disease on volume-time graph and flow-volume loop
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
Spirometry interpretation
- First look at FEV1/ FVC ratio
- If <70%, obstruction
- If obstructed, look at % predicted FEV1 (severity) and any reversibility (COPD vs asthma)
- If FEV1/ FEV ratio normal, look at % predicted FVC (if low, suggests restrictive abnormality)
- Can also get mixed picture, eg obesity and COPD
Transfer factor test
- 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
Transfer factor affeced by and reduced by
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)
How to measure lung volume?
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
oximetry
•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
Main causes of hypoaemia
–Hypoventilation (eg drugs, neuromuscular disease)
–Ventilation/ perfusion mismatch (eg COPD, pneumonia)
–Shunt (eg congenital heart disease)
–Low inspired oxygen (altitude, flight)
Ventillation perfusion mismatch
- 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
Blood gas analysis
- 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
Pleural effusion analysis
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
