Sponsors

You're browsing as an anonymous user. Join the community today to view notes at your university, edit pages, and share knowledge!

Asthma

From Mediwikis

Overview

Asthma attack.PNG

Asthma is a respiratory condition that is characterised by chronic airway inflammation and reversible airway narrowing. It is part of a triad of atopic conditions, and along with Hayfever and Eczema generally indicates immune overactivity.

Signs & Symptoms

Symptoms of asthma include:

  • Coughing
  • Wheezing
  • Chest tightness
  • Shortness of Breath on Exertion (SOBOE)
  • Diurnal variation in symptoms
  • Sensitivity to airborne allergens

Patients may present in a primary care setting describing one or more of the above symptoms. They may also present acutely to emergency care with an 'asthma attack' - an acute episode of severe (and sometimes life-threatening) bronchospasm often precipitated by exercise or contact with an allergen. Patients can often find 'asthma attack's very distressing, causing them to increase their own oxygen requirement and compounding symptoms.

Asthma has two phases: An immediate and a late phase. The immediate phase is essentially a short term immune response. Mast cells in the airways are activated and release spasmogens, Leuktrienes and prostoglandins which cause bronchospasm (resulting in bronchoconstriction). The mast cells also release chemotaxins and chemokines which activate the late phase. This is the infiltration of cytokine releasing cells, monocytes and eosinophils. This causes airway damage, airway inflammation and airway hyper reactivity.

There are several histological changes to the airways. The smooth muscle hypertophises, there is oedema in both the mucosa and sub mucosa caused by inflammatory response, blood vessels nearby are dilated and mucus plugs form, partially blocking the airway. The mucus plugs, apart from mucus, contain eosinophils and disquamated epithelial cells (epithelial cells which have broken off from their layer).

Investigation

Acute attack: PEF, sputum culture, FBC, U&E, ABG analysis (normal or slightly low PaO2 but low PaCO2 due to hyperventilation)[1]

Chronic asthma: PEF monitoring, spirometry

Assessment of Severity

Severity of acute severe asthma can be broken down into Moderate, Severe and Life-threatening. These labels help to guide the level and aggression of required treatment.

Classification PEFR Ventilation Features Other Features
Moderate >50-75% predicted Normal or hyper- ventilation None
Severe 33-50% predicted Inability to speak in full sentences Respiratory Rate > 25, Heart Rate > 110
Life-threatening <33% predicted Poor respiratory effort SpO2 < 92%

Paediatric types

Transient Early Wheezing

  • Common, often self resolving
  • Episodic, no reduced function between episodes
  • Viral Associated Wheeze
  • No family link
  • Risk increased by maternal smoking

Persistent & Recurring Wheeze

  • Frequent exacerbations triggered by multiple stimuli
  • May have history of atopy (IgE mediated disease)
  • Persistent symptoms between episodes

Management

Acute Asthma: Status Asthmaticus

'O SHIT ME':

  • Oxygen (high dose: >60%)
  • Salbutamol- 5 mg via oxygen-driven nebuliser
  • Hydrocortisone (IV)/ Prednisalone (oral)
  • Ipratropium bromide (anti muscarinic)
  • Theophylline/ Aminophylline
  • Magnesium
  • Escalate care (should be done before giving theophylline)

Long term management

Done via a step treatment with you moving up to the minimum step at which the asthma is controllable.

  1. Short Acting β Agonist PRN- Salbutamol, Terbutaline
  2. Add Inhaled Corticosteroid regularly
  3. Add Long Acting β Agonist/ tailor Inhaled Corticosteroid Dose
  4. Increase dose of ICS/ Add Leukotriene antagonists/ SR Theophylline
  5. Oral Steroids, need specialist care referral
  • Allergen avoidance
  • Teach and check correct inhaler technique

Pharmacology

B2 Agonists

These are either short acting or long acting. They stimulate Beta 2 adrenergic receptors in the smooth muscle, the same ones stimulated by the sympathetic nervous system. They cause bronchodilation and will relieve the immediate phase of asthma.

  • Short Acting: Salbutamol and Terbutaline
  • Long Acting: Salmeterol and Formoterol
  • Side effects: Headaches, tremors, nausea and increased heart rate

Methylxanthines

These are phosphodiesterase inhibitors. They act by inhibiting the enzyme, phosphodiesterase, which breaks down cyclic AMP. cAMP is a key signalling molecule produced by the pathway connected to the beta 2 adrenergic receptors mentioned above. If it is not removed from the cell then it continues to stimulate bronchodilation. This will mean that any sympathetic response in the airways will have increased effect.

The most commonly used one is theophylline. Side effects include chronotropic and inotropic effects on the heart, dysrthythmias, seizures and tremors.

Anti Muscarinics

These inhibit the M3 muscarinic acetylcholine receptors in the airways. If these receptors are stimulated they cause bronchoconstriction and by inhibiting them one stops the reflex action which causes bronchoconstriction on contact with cold air, allergens and irritants as in asthmatics this can be dangerous.

The most commonly used one is ipatropium bromide and principle side effects are dry mouth and bladder pain and disruption. These are less common as the drug is absorbed very poorly so often does not have large quantities of it in the bloodstream.

Corticosteroids

These are hormones derived from cholesterol. They diffuse across the cell membrane of the epithelial cells and other cells in the lungs. They then act as transcription factors and alter gene expression to make cells respond more to the sympathetic nervous system than the parasympathetic nervous system. They also minimise the immune response in the airways. They have a large amount of side effects such as suppressing adrenaline, reducing bone minerals, anxiety, headaches and nausea.

Examples include: Cortisol, Hydrocortisone, aldesterone, budesonide, beclometasone. In general if it has -one or cort- as part of it's name it is probably a corticosteroid for the purposes of year 1 exams.

Leukotriene Receptor Antagonists

These arrest the effect of cys leukotrienes released by mast cells in the immediate phase of asthma. This makes the patient less breathless on exercise and exhibit a less drastic response to allergens

Examples include montelukast and zafirlukast

References:

  1. Test