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Flashcards in Respiratory - Asthma Deck (18):

What is asthma?

Asthma is an obstructive respiratory disease characterised by recurrent SOB, wheeze or cough caused by REVERSIBLE narrowing of the airway lumen and airflow obstruction.

Asthma is sometimes classified into extrinsic and intrinsic categories, although the treatment is the same.


What is the underlying pathophysiology of asthma?

The main cause of airflow obstruction and increased airways resistance is contraction of bronchial smooth muscle cells as a result of hypersensitivity to many different stimuli - e.g. cold air, smoke, exercise and emotion as well as antigens and some drugs (esp. NSAIDs).

Thickening of the airways by oedema and cellular infiltrates as well as blockage of airways by mucus and secretions also contributes.


What are the clinical features of acute asthma attacks?

These may be fairly abrupt in onset and brief in duration (hours) or longer (a week or two)and occur on a background of chronic asthma. Longer severe asthma attacks are called "status asthmaticus".

In an attack, the patient feels tightness in the chest and both inspiratory and expiratory effort are difficult. There may be a cough that is initially dry but later becomes productive, particularly if there is infection.

The patient usually sits up with an overinflated chest, an audible expiratory wheeze using the accessory muscles of respiration.

The pulse is rapid.


What triggers an acute asthma attack?

Attacks are precipitated by specific allergens (e.g. pollens or house dust mite), exertion, cold air, respiratory infection and beta blockers.


What is recurrent asthma?

Mild asthmatics (particularly with extrinsic asthma) usually have normal respiratory function between attacks but those with long standing severe asthma tend to develop a degree of dyspnoea and persistent airway obstruction between acute attacks.


How should asthma be investigated?

This somewhat depends on how the patient presents. Investigation includes chest X ray (for regional collapse, pneumonia, pneumothorax) and measurement of ventilatory function (FEV1 or PEFR, preferably several times a day on several days at home) and the response to bronchodilators.

Variability through the day, especially with morning "dips" in PEFR is characteristic.

Skin hypersensitivity tests performed by pricking standard allergens into the skin can help the patient recognise and avoid environmental precipitants.

Bronchial reactivity may be more precise but should be done in a controlled environment with adrenaline (1:1000) to hand.


What precipitating factors should the patient be asked about as part of the management of chronic asthma?

- season (grass pollen and funal spores, esp. Aspergillus)
- cold
- exercise
- food
- house dust (contains the mite Dermatophagoides)
- smoke
- emotion
- drugs (e.g. aspirin, NSAIDs, beta blockers)


Describe the stepwise management of asthma?

This is a guideline published by the BTS. A cumulative drug regimen is prescribed for each step - stepping up if necessary to achieve control and stepping down when control is good.

Step 1: Inhaled SABA (e.g. salbutamol) prn

Step 2: Add inhaled steroid 200-800mcg/day

Step 3: Add inhaled long acting beta 2 agonist (e.g. salmeterol) and assess response
- Good response - continue LABA
- Benefit but control still inadequate - increase inhaled steroid up to 800mcg per day
- No response - stop LABA and increase inhaled steroid up to 800mcg/ day (if not done so already)

Step 4: Consider trial of increased dose of inhaled steroid up to 2000mcg/day; addition of fourth drug - e.g. leukotriene receptor antagonist SR theophylline, beta 2 agonist tablet

Step 5: Addition of a daily steroid tablet in lowest dose providing adequate control; maintain high dose of inhaled steroid; consider other treatments to minimise use of oral steroids; REFER


What is acute severe asthma?

Acute severe asthma is a life threatening condition. It typically occurs in poorly controlled individuals whose condition has been deteriorating over days or weeks, but death can be sudden and sometimes unexpected as the patient may NOT appear severely ill.

Most patients have some degree of respiratory failure at presentation.


What are the features of severe life threatening asthma?

These are part of the BTS guidelines for managing acute severe asthma.

Clinically the patient is:
- breathless (unable to complete sentence in one breath)
- exhausted, confused
- tachycardia, bradycardia or arrhythmia
- hypotension
- cyanosis
- respiratory rate >25bpm
- poor respiratory effort (use PEF metre)
- silent chest

- PaO2 < 8kPa
- oxygen saturation <92%


How should acute severe asthma be investigated?

ABGs provide the most useful guide to the severity of the attack and to the success of treatment.

The following values indicate a very severe attack:
- SaO2 < 92%
- PaO2 < 8kPa
- PaCO2 > 5.0kPA

A chest X ray is useful if pneumothorax, pneumomediastinum or consolidation are suspected. It should also be performed if there is a failure to respond to treatment and if asthma is life threatening.


Outline the management of acute severe asthma?

1) Continuous high flow oxygen - i.e. 15L

2) Bronchodilators: beta 2 agonists (e.g. salbutamol, terbutaline) plus ipratropium by oxygen driven nebuliser or IV infusion if inhaled therapy cannot be used

3) Corticosteroids: give ORAL prednisolone or IV hydrocortisone if unable to swallow (or speak in full sentences)
- continue oral prednisolone 40-50mg daily for at least 5 days or until recovery

4) IV fluids: required to make up the initial dehydration and for as long as oral fluids are not taken. Monitor urine output

5) Bacterial infection: is a RARE trigger but antibiotics are given if it is present or strongly suspected. The usual organisms are Strep pneumoniae and Haemophilus

6) Mechanical ventilation: persistent or increasing elevation of PaCO2 or worsening hypoxia especially with accompanying exhaustion indicates need for artifical ventilation


When can a patient be safely discharged following an acute severe asthma attack?

This depends on the PEFR.
Discharge from hospital after PEFR returns to > 75% of best, with daily variability of < 25%.
Early clinic follow up is recommended.


What variation in PEFR is needed to diagnose chronic asthma?

Diurnal variation of >20% on >3 days a wk for 2wks


What improvement in FEV1 is needed to suggest reversible airflow obstruction?

Usually a >15% improvement in FEV1 following beta 2 agonists or steroid trial suggests reversibility


What are the differential diagnosis of asthma?

- pulmonary oedema ("cardiac asthma")
- COPD (may co-exist)
- large airway disease (e.g. foreign body, tumour)
- SVC obstruction (wheeze/ dyspnoea but not episodic)
- Pneumothorax
- PE
- bronchiectasis
- obliterative bronchiolitis


What diseases are associated with asthma?

- Acid reflux
- Churg-Strauss


What is the distribution of V/Q inequality in asthma?

The V/Q inequality causes abnormal arterial gases, although in asthma the PaO2 is only slightly reduced and is not severe, whilst the PCO2 is usually normal because of increased ventilation.

The distribution of V/Q inequality is very abnormal:
1) Before bronchodilator - substantial amount of blood flow to units with low V/Q ratios - i.e. completely obstructed airways

2) After bronchodilator - big increase in amount of blood flow to units with low V/Q ratios and large decrease in PaO2! Possibly explained by inflammatory mediators causing vasoconstriction which is relieved (i.e. vasodilation) by bronchodilator

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