Asthma Flashcards
Describe the typical clinical features of asthma (stable and during exacerbations) seen in an acute medical setting and formulate and appropriate investigation and management plan
What are the symptoms of asthma?
Shortness of breath (Dyspnoea)
Wheeze
Cough
Chest tightness
What factors contribute towards the airway obstruction in asthma?
Oedema
Increased mucous production
Increased smooth muscle tone/ bronchoconstriction
These are due to the underlying inflammatory process which is IgE mediated and a type I hypersensitivity reaction.
What are some features that increase the likelihood of dyspnoea being due to asthma?
Wheeze, SOB, chest tightness
Diurnal variation (Worse in morning)
Triggers- Cold weather, allergen, exercise, symptoms after Beta Blocker/NSAID
History of Atopy- Atopic Dermatitis, Hay Fever, Allergy
Family history of atopy/asthma
Expiratory polyphonic wheeze
PEF improvement in FEV1 of 12% or more with Salbutamol or steroid trial (NICE say 12 for salbutamol)
FEV1/FVC<0.7
What peak flow findings suggest asthma is more likely?
Reduced FEV1
FEV1/FVC <0.7
Improvement in FEV1 of 12% or more with salbutamol or steroids
What should you ask about for potential triggers for asthma?
Cold weather Exercise Salbutamol NSAIDs Known allergens Smoking Infection Occupational Exposures- does it improve at weekend/during holidays? (Common for paint sprayers, food processors, welders and animal handlers)
What features would you want to know about for a patient presenting with acute asthma/exacerbation?
Prodrome- preceding symptoms that could indicate a cause e.g. Cough, Wheeze, GI Symptoms, Rhinorrhoea, Fevers
Speed of onset- How quickly has it worsened?
When did it first start?
Previous diagnosis with asthma?
Treatment of asthma? Compliance to this
Previous exacerbations?
Previous admission to ITU/intubation for asthma?
Possible triggers- e.g. allergen exposure, dust, building work
PEFR- Best for them
What are the findings from an asthma exacerbation on respiratory examination?
Wheeze- polyphonic expiratory wheeze
Tachypnoea
Tachycardic
Hyperinflated chest
Use of accessory muscles of respiration- SCM
Inability to complete sentences (bad sign)
What is the mechanism that leads to hyperinflation of the chest?
Premature airway closure during expiration causes inspiratory volumes to become greater than expiratory volumes- this leads to hyperinflation
What changes are seen in spirometry values during an acute exacerbation of asthma?
FEV1/FVC decreases FVC decreases RV increases FRC and TLC increase (Static volumes increase)
What PEFR % ranges guide wether the exacerbation is severe or moderate?
Moderate- PEFR 50-75%
Acute Severe Asthma- PEFR 33-50%
(Both of best predicted)
What four clinical features indicate acute severe asthma?
PEFR 33-50%
Inability to complete sentences
Tachypnoea- RR>25
HR>110
What ABG findings would you expect to see in acute severe asthma? How would this change as the patient fatigues due to the increased effort of breathing?
Low PaO2 and a Normal/Low PaCO2
Initially Type I Respiratory failure would be seen due to V/Q mismatch. The patient is hypoxic but PaCO2 is normal/low as the patient is hyper ventilating and breathing off carbon dioxide.
Progression to Type II Respiratory Failure as PaO2 <8kPA and PaCO2>6kPa. This occurs when the patient fatigues and alveolar ventilation begins to reduce. it is a very bad sign.
Why do patients with severe acute asthma fatigue when breathing?
Airway obstruction and a hyper inflated chest (meaning the chest wall is less compliant) mean the effort of breathing is increased
What is a silent chest?
This occurs when no breath sounds can be heard, the wheeze is no longer audible. This is a bad clinical sign.
What are some features of life threatening asthma?
Cyanosis Silent chest Fatiguing patient Reduced consciousness Hypotension
What measurements (ABG, O2 Sats, PEFR) indicate life threatening asthma?
Type I Respiratory Failure
O2 Sats less than 92%
PEF <33%
Why is a raised PaCO2 a very bad clinical sign?
A raised PaCO2 in addition to a PaO2 less than 8 indicates Type II respiratory failure and is a marker of near-fatal asthma. PaCO2 starts to rise when the patients ventilation reduced due to fatigue.
In an acute asthma attack what investigations should be requested?
CXR (Rule out pneumonia, pneumothorax) ABG PEFR Other Bloods Bloods- FBC, CRP, ESR, U+Es, Blood culture if appropriate Sputum culture (if suspecting infection)
For a patient presenting in GP with features of asthma (not acute severe asthma) what tests should be done to diagnose asthma?
PEFR- and PEFR monitoring over 2 weeks (A diurnal variation of more than 20 % on at least three days a week for 2 weeks is suggestive of asthma)
Spirometry- FEV1:FVC less than 0.7 suggests asthma. Usually improvement in FEV1 when salbutamol given. NICE say to regard a 12% improvement or more as a positive test.
Fractional Exhaled Nitric Oxide- 40 parts per billion is a positive finding. Produced by eosinophils in the airways and so higher levels indicate greater activity.
Skin prick tests may be done to identify potential allergens if thought to be a trigger.
What percentage FEV1/FVC indicates obstructive spirometry?
70% or less
What percentage improvement in FEV1/FVC following salbutamol is suggestive of asthma?
12% or more according to NICE
How long should patients monitor their peak flow results for to check for variability?
2-4 weeks
When should patients peak flow variability be checked for?
NICE say to monitor for peak flow variability over 2-4 weeks if there is diagnostic uncertainty after FeNo testing and they have either normal spirometry or obstructive spirometry (FEV1:FVC <0.7), reversible airway obstruction (12% or more improvement)
What percentage peak flow variability indicates a positive test)?
20%
