Asthma Flashcards
Why are children with asthma more susceptible to respiratory failure?
- They have lower acquired immunity to organisms
-Have smaller upper and lower airways that are easily obstructed by mucosal swelling, secretions, foreign body causing increased resistance
-Infants and young children have a small surface area for gaseous exchange and increase in ventilation-perfusion mismatch
What are the four steps in respiration?
1- Ventilation (inspiration and expiration)
2-Exchange between alveoli and pulmonary capillaries (external respiration)
3- Transport of gases in blood
4- Exchange between blood and cells- internal respiration and cellular respiration; use of oxygen in ATP synthesis
What is the role of nerve impulses in control of breathing?
-The respiratory centre in the brainstem controls respiration by transmitting impulses
-Nerve impulses are transmitted from brainstem to respiratory muscles by phrenic and intercostal nerves to initiate breathing
-Medulla oblongata sets basic respiratory rate
-Pons smooths out the rhythm of inspiration and expiration is set by the medulla
How are acid levels effected by control of breathing?
-In the case of increased CO2 levels, there is an increase in carbonic acid therefore a lower pH
-Both breathing rate and volume will increase to attempt to buffer the effects of blood acidosis
-Changes in CO2 blood levels change the pH in the cerebral spinal fluid- that acts directly on the medulla
What is the role of stretch receptors in control of breathing?
-They are a protective reflex
-Bronchioles and alveoli have stretch receptors that respond to overinflation
-These send impulses to the medulla oblongata via the vagal nerve- to slow down these respirations
What is the role of chemoreceptors in control of breathing?
-Peripheral chemoreceptors in aortic branch and carotid body are sensitive to changes in paCO2 and pH
-They detect a drop in oxygen and an increase of carbon dioxide
-As a result, impulses are sent to the medulla to increase respiratory rate (to breathe in more oxygen and to breathe out more CO2)
What is the definition of asthma?
A chronic inflammatory disorder of the airways characterised by episodic, reversible bronchospasm resulting from an exaggerated bronchoconstrictor response to various stimuli
What are the 3 conditions in the atopic triad?
Atopic dermatitis
Asthma
Allergic Rhinitis
List some asthma triggers
- Food
-Dust
-Mould
-Pollution
-Smoke
-Temperature changes
What are the most common asthma symptoms?
Shortness of breath
Wheeze
Chest tightness
Dry irritating cough
What are signs that someone is having an exacerbation of asthma?
Breathlessness
Chest recession
Accessory muscle use
Tachypnoea/tachycardia
Low sats
Cyanosis
Wheeze
Silent chest
Exhaustion
Abdominal pain
What are the four main characteristics of asthma attacks?
Inflammation
Bronchoconstriction
Mucous Production
Broncho-hyperresponsiveness
Define airway modelling
An ongoing structural change caused by asthma that leads to thickened airway walls and the narrowing of the airways. Untreated inflammation leads to long-term airway damage that is irreversible.
What specifically in children with asthma causes changes?
Epithelial shedding and hyperplasia in the airway smooth muscles
What are the inflammatory cells present in the pathophysiology of asthma?
IgE
Mast Cells
T-Helper (1 and 2)
Dendritic Cells
Cytokines
Eosinophils
Beta Cells
Neutrophils
What is the role of IgE in the inflammatory response?
Attaches to the mast cell and causes degranulation upon response to the allergen
What is the role of the mast cell in the inflammatory response?
Recognises the allergen and starts releasing inflammatory mediators- histamine, leukotrienes and prostaglandins
What are the mediator effects?
Mucous secretion from goblet cells
Airway smooth muscle constriction (bronchospasm)
Oedema from increased permeability
What is the role of dendritic cells in the inflammatory response?
They detect the antigen and present it to TH2 cells to produce cytokines
What is the role of cytokines in the inflammatory response?
They cause Beta-cells to further produce IgE
Eosinophil activation
Act as antigen presenting cells
What is the role of eosinophils in the inflammatory response?
They are a type of WBC that help fight disease and release histamine. They damage the respiratory epithelium
What is the role of neutrophils in the inflammatory response?
Express and release cytokines amplifying inflammatory reactions by several other cell types
What is a V/Q mismatch?
A V/Q mismatch happens when part of your lung receives oxygen without blood flow or blood flow without oxygen. There is less efficient gaseous exchange and could lead to respiratory failure
Where is gaseous exchange most efficient?
Areas of the lung where perfusion and ventilation are similar (matching)
What is an area termed shunt showing?
V/Q of 0
An area with perfusion but no ventilation
What is an area termed dead space showing?
V/Q undefined
An area with ventilation but no perfusion
What are the consequences of a lower V/Q ration?
Impairs pulmonary gas exchange and causes low arterial paO2. Causes an impairment of CO2 excretion
What are the main causes of airway obstruction in an asthmatic child?
Smooth muscle contraction (bronchoconstriction) and increased mucous production
What affect does airway obstruction have on the lungs?
When an obstruction is present, there is an increased resistance to airflow and therefore a decreased flow rate. As a result, there is impaired expiration leading to hyperinflation and increased work of breathing.
As a response to the increased lung volume and obstruction, hyperventilation is triggered causing air trapping
What is the effect of air trapping?
There is an increased in alveoli pressures leading to decreased perfusion of the alveoli
What leads to a V/Q mismatch?
Increased alveolar pressure, decreased ventilation and decreased perfusion- leading to hypoxaemia
What are the effects of hypoxaemia?
An increase in hyperventilation causing paCO2 to decrease and pH to increase leading to a respiratory alkalosis
What happens in a severe obstruction?
Number of alveoli that are inadequately ventilated increases. The lungs and thorax become hyperinflated putting extra mechanical effort on respiratory muscles
What is the consequence of lung and thorax hyperinflation and extra respiratory effort?
CO2 retention causing a decrease in pH- leading to respiratory acidosis and hypoxia. This is a precursor to respiratory failure
Describe the series of events in reference to the pathophysiology of an asthma attack
1- IgE response triggered by an allergen
2- Inflammatory cells are released leading to vasodilation, capillary permeability, mucous production, oedema and generalised inflammation
3- Lower airway obstruction leading to wheezing- wheezing generated by turbulent airflow causing oscillation of the bronchial wall
4-The airways eventually become hyper-responsive and narrow easily in reaction to a wide range of stimuli.
5- Bronchospasm occurs
6- Bronchoconstriction, oedema, airway obstruction, epithelial shredding, increased lung volume and abnormal gaseous exchange occurs
7- Areas of atelectasis
What contributes to narrowing of the airways?
Invasion of mucosa, sub-mucosa and muscle tissues by inflammatory cells
Mucous
What is the role of stretch receptors in response to asthma?
They are triggered due to bronchoconstriction and oedema and send signals to the brain
What is the difference between hypoxia and hypoxaemia?
Hypoxaemia is low blood oxygenation
Hypoxia is where the body or a particular region of the body is deprived of adequate oxygenation at tissue level
Why does impaired cellular metabolism occur?
Impaired O2 delivery. Without oxygen, cells change from aerobic to anaerobic metabolism. As a consequence, there is lactic acid production
What causes increased intrathoracic pressure?
Hyperventilation- causing an increase in the left ventricular afterload
What are the 5 treatments for asthma?
Continuous O2 saturation monitoring
High flow O2
Beta-2 agonists (bronchodilators) (repeat every 20mins and review after an hour)
Ipratropium bromide
Oral steroids
?Fluid
What treatment may you consider in more severe asthma?
IV magnesium and aminophylline
?IV salbutamol
Why would you administer oxygen
To increase oxygen levels
What is the purpose of steroids?
To reduce inflammation, swelling and mucous production in the airways
What is the purpose of salbutamol, aminophylline and IV magnesium?
They are bronchodilators therefore dilate the airways to improve airway flow and consequently oxygenation levels
What is the purpose of using ipratropium bromide as a treatment?
Helps control bronchospasms
Why may you give fluids as a treatment for asthma?
As it is likely the child will have low oral intake due to increased respiratory rate/vomiting. Not to give full fluid maintenance to prevent further oedema
