asthma Flashcards
epidemiology of asthma
- Asthma is the most common chronic respiratory disorder encountered in clinical practice.
- It affects over 10% of children and around 5-10% of adults, with the prevalence of asthma increasing.
- Not only does asthma account for a significant morbidity burden it should be remembered that around 1,000 people die in year from asthma in the UK, 30-40 of whom are children.
what is asthma
Asthma may be defined as a chronic inflammatory disorder of the airways secondary to hypersensitivity.
The symptoms are variable and recurring and manifest as reversible bronchospam resulting in airway obstruction.
Asthma may present at any age although it typically develops in childhood.
For many of these children their symptoms improve or resolve with age, and patients often report ‘growing out’ of their childhood asthma.
It should be remember that it is common for young children to wheeze when they develop a virus (‘viral-induced wheeze’).
This makes the diagnosis of asthma in younger children difficult.
RFs
A number of factors can increase the risk of a person developing asthma:
- personal or family history of atopy
- antenatal factors: maternal smoking, viral infection during pregnancy (especially RSV)
- low birth weight
- not being breastfed
- maternal smoking around child
- exposure to high concentrations of allergens (e.g. house dust mite)
- air pollution
- ‘hygiene hypothesis’: studies show an increased risk of asthma and other allergic conditions in developed countries. Reduced exposure to infectious agents in childhood prevents normal development of the immune system resulting in a Th2 predominant response
Focusing on atopy, patients with asthma also suffer from other IgE-mediated atopic conditions such as:
- atopic dermatitis (eczema)
- allergic rhinitis (hay fever)
A number of patients with asthma are sensitive to aspirin. Patients who are most sensitive to asthma often suffer from nasal polyps. Remember the nose is part of the respiratory tract from a histological point of view.
Finally around 10-15% of adult asthma cases are related to allergens in the workplace. Occupational asthma is usually diagnosed by observing reduced peak flows during the working week with normal readings when not at work. Examples of common occupational allergens include isocyanates and flour.
s/s
- Symptoms
- cough: often worse at night
- dyspnoea
- ‘wheeze’, ‘chest tightness’
Signs
- expiratory wheeze on auscultation
- reduced peak expiratory flow rate (PEFR)
Investigation
Spirometry is a test which measures the amount (volume) and speed (flow) of air during exhalation and inhalation. It is helpful in categorising respiratory disorders as either obstructive (conditions where there is obstruction to airflow, for example due to bronchoconstriction in asthma) or restrictive (where there is restriction to the lungs, for example lung fibrosis). Key metrics include:
💜 FEV1: forced expiratory volume - volume that has been exhaled at the end of the first second of forced expiration
💜 FVC: forced vital capacity - volume that has been exhaled after a maximal expiration following a full inspiration
Typical results in asthma
- FEV1 - significantly reduced
- FVC - normal
- FEV1% (FEV1/FVC) < 70%
Peak expiratory flow (PEF)
- simple and widely available and can be used in a wide variety of circumstances including acute severe asthma
- more useful in the monitoring of patients with established asthma than in making the initial diagnosis
- PEF is effort dependent and not repeatable
- change in PEF more meaningful than absolute value
- a peak flow recorded when symptomatic (eg during the assessment of an asthma attack) may be compared to a peak flow when asymptomatic (eg after recovery from an asthma attack) in order to confirm variability
- >60 l/min increase in PEF suggested as best criteria for defining reversibility
- peak flow records should be interpreted with caution and with regard to the clinical context
Fractional exhaled nitric oxide (FeNO)
- nitric oxide is produced by 3 types of nitric oxide synthases (NOS).
- one of the types is inducible (iNOS) and levels tend to rise in inflammatory cells, particularly eosinophils
- levels of NO therefore typically correlate with levels of inflammation.
Other investigations to consider
- chest x-ray: particular in older patients or those with a history of smoking
- allergic status
skin prick testing or measurement of a specific immunoglobulin E (IgE) in serum (less sensitive and more expensive) to assess the allergic status and identify possible asthma triggers
diagnosis
NICE guidance has radically changed how asthma should be diagnosed. It advocates moving anyway from subjective/clinical judgements are more towards objective tests.
There is particular emphasis on the use of fractional exhaled nitric oxide (FeNO). Nitric oxide is produced by 3 types of nitric oxide synthases (NOS). One of the types is inducible (iNOS) and levels tend to rise in inflammatory cells, particularly eosinophils. Levels of NO therefore typically correlate with levels of inflammation.
Other more established objective tests such as spirometry and peak flow variability are still important.
All patients >= 5 years should have objective tests. Once a child with suspected asthma reaches the age of 5 years objective tests should be performed to confirm the diagnosis.
Diagnostic testing
Patients >= 17 years
- patients should be asked if their symptoms are better on days away from work/during holidays. If so, patients should be referred to a specialist as possible occupational asthma
- all patients should have spirometry with a bronchodilator reversibility (BDR) test
- all patients should have a FeNO test
Patients 5-16 years
- all patients should have spirometry with a bronchodilator reversibility (BDR) test
- a FeNO test should be requested if there is normal spirometry or obstructive spirometry with a negative bronchodilator reversibility (BDR) test
Patients < 5 years
- diagnosis should be made on clinical judgement
Specific points about the tests
FeNO
in adults level of >= 40 parts per billion (ppb) is considered positive
in children a level of >= 35 parts per billion (ppb) is considered positive
Spirometry
FEV1/FVC ratio less than 70% (or below the lower limit of normal if this value is available) is considered obstructive
Reversibility testing
in adults, a positive test is indicated by an improvement in FEV1 of 12% or more and increase in volume of 200 ml or more
in children, a positive test is indicated by an improvement in FEV1 of 12% or more
Management
The vast majority of patients are maintained on inhalers which allow drug therapy to be delivered locally to the airways.
Drugs used in asthma management attached.
Maintenance and reliever therapy (MART)
- a form of combined ICS and LABA treatment in which a single inhaler, containing both ICS and a fast-acting LABA, is used for both daily maintenance therapy and the relief of symptoms as required
- MART is only available for ICS and LABA combinations in which the LABA has a fast-acting component (for example, formoterol)
Management of asthma has changed following the 2017 NICE asthma guidelines. The main take home points are that all patients are:
- patients on a SABA + ICS whose asthma is not well controlled should be offered a leukotriene receptor antagonist, not a LABA
- MART is now an option for patients with poorly controlled asthma
stepwise asthma mx in adults
NICE do not follow the stepwise approach of the previous BTS guidelines. However, to try to make the guidelines easier to follow we’ve added our own steps.
Maintenance and reliever therapy (MART)
- a form of combined ICS and LABA treatment in which a single inhaler, containing both ICS and a fast-acting LABA, is used for both daily maintenance therapy and the relief of symptoms as required
- MART is only available for ICS and LABA combinations in which the LABA has a fast-acting component (for example, formoterol)
It should be noted that NICE does not advocate changing treatment in patients who have well-controlled asthma simply to adhere to the latest guidance.
Table showing examples of inhaled corticosteroid doses
Frustratingly, the definitions of what constitutes a low, moderate or high-dose ICS have also changed. For adults:
- <= 400 micrograms budesonide or equivalent = low dose
- 400 micrograms - 800 micrograms budesonide or equivalent = moderate dose
- > 800 micrograms budesonide or equivalent= high dose.
types of inhalers
What kinds of reliever/preventer inhalers are there?
Usually blue, short-acting reliever inhalers contain medicine that relaxes the airways and makes it easier for you to breathe. For example:
- Metered dose inhalers (MDIs) give the medicine in a spray form (aerosol), for example Ventolin, Airomir and Salamol.
- Breath actuated inhalers (BAIs), such as Easi-breathe, Airmax, and Autohaler, automatically release a spray of medicine when you begin to inhale.
- Dry powder inhalers (DPIs), such as Accuhaler, give the medicine in a dry powder instead of a spray.
combination inhaler examples: Seretide, Symbicort or Fostair,
acute severe asthma mx
Patients with acute severe asthma are stratified into moderate, severe or life-threatening
moderate:
- PEFR 50-75% best or predicted
- Speech normal
- RR < 25 / min
- Pulse < 110 bpm
severe:
- PEFR 33 - 50% best or predicted
- Can’t complete sentences
- RR > 25/min
- Pulse > 110 bpm
life-threatening:
- PEFR < 33% best or predicted
- Oxygen sats < 92%
- Silent chest, cyanosis or feeble respiratory effort
- Bradycardia, dysrhythmia or hypotension
- Exhaustion, confusion or coma
Note that a patient having any one of the life-threatening features should be treated as having a life-threatening attack.
British Thoracic Society guidelines
- magnesium sulphate recommended as next step for patients who are not responding (e.g. 1.2 - 2g IV over 20 mins)
- little evidence to support use of IV aminophylline (although still mentioned in management plans)
- if no response consider IV salbutamol
[see alaisdair scott notes on mx upon acute hosp admission etc.]
stepwise asthma mx in kids aged 5-16yo
Children and young people aged 5 to 16
NICE do not follow the stepwise approach of the previous BTS guidelines. However, to try to make the guidelines easier to follow we’ve added our own steps:
stepwise asthma mx in kids: <5yo
Children aged less than 5 years
Clearly, it can be difficult to definitively diagnose asthma in young children. NICE acknowledge the greater role for clinical judgement in this age group.
Again, the stepwise approach is our own rather than NICE’s:
Other points
Maintenance and reliever therapy (MART)
- a form of combined ICS and LABA treatment in which a single inhaler, containing both ICS and a fast-acting LABA, is used for both daily maintenance therapy and the relief of symptoms as required
- MART is only available for ICS and LABA combinations in which the LABA has a fast-acting component (for example, formoterol)
It should be noted that NICE does not advocate changing treatment in patients who have well-controlled asthma simply to adhere to the latest guidance.
Table showing examples of inhaled corticosteroid doses
Frustratingly, the definitions of what constitutes a low, moderate or high-dose ICS have also changed. In contrast to the BTS guidelines NICE also have different definitions for adults and children. For children:
- <= 200 micrograms budesonide or equivalent = paediatric low dose
- 200 micrograms - 400 micrograms budesonide or equivalent = paediatric moderate dose
- > 400 micrograms budesonide or equivalent= paediatric high dose.
Asthma in children: assessment of acute attacks
[severe attack]
- SpO2 < 92%
- PEF 33-50% best or predicted
- Too breathless to talk or feed
- Heart rate
- >125 (>5 years)
- >140 (1-5 years)
- Respiratory rate
- >30 breaths/min (>5 years)
- >40 (1-5 years)
- Use of accessory neck muscles
Asthma in children: assessment of acute attacks
[life threatening attack]
- SpO2 <92%
- PEF <33% best or predicted
- Silent chest
- Poor respiratory effort
- Agitation
- Altered consciousness
- Cyanosis
mx of acute attack in kids
Children with severe or life threatening asthma should be transferred immediately to hospital.
steroid doses in kids w/ mild-mod asthma :)
