Respiratory Flashcards
Which organisms are most likely to cause an abscess or empyema?
Group A Strep or Staph aureus
List some sequelae / complications of pneumonia
Empyema
Pleural effusion
Lung abscess
SIADH
Which is the most common bacterial cause of pneumonia?
Strep pneumoniae
Risk factors for pneumonia
Prematurity
Congenital heart disease
Immunodeficiency
Which ages are more likely to have viral VS bacterial pneumonia
Viral infections are common in younger children and bacterial infections are more frequently identified with increasing age
Causes of viral pneumonia
RSV
Parainfluenza
Influenza
Adenovirus
Rhinovirus
Human Metapneumovirus
CMV
VZV
HSV
Coronavirus
Enterovirus
List the four stages of lobar pneumonia
1) Vascular congestion and alveolar oedema with high numbers of the infective organism
2) Red hepatisation: Significant infiltration of RBCs and neutrophils. Fibrin also infiltrates into the alveolar fluid.
3) Grey hepatisation: Fibrin and RBC breakdown to form a fibrinopurulent exudate
4) Resolution: macrophages clear the exudate
Define bronchopneumonia
Involves one or more lobes and is characterised by patchy consolidation. Exudate in the bronchi spreads to the adjacent alveoli
Define interstitial pneumonia
Patchy or diffuse inflammation. The interstitium is infiltrated by lymphocytes and macrophages.
The alveoli contain minimal exudate.
Define miliary pneumonia
Spread of a pathogen from the blood to the lungs producing multiple discrete lesions with foci of necrosis
Common pathogens: TB, CMV, VZV, histoplasmosis and coccidioidomycosis
Define lobar pneumonia
Involves a single lobe of the lung
General pathophysiology of pneumonia
Alveoli and terminal airspaces become inflamed secondary to the introduction of a pathogen. A resulting inflammatory cascade causes leakage of plasma and loss of surfactant, which results in air loss and consolidation.
In viral infections, mononuclear cells accumulate in the submucosa leading to narrowing of the airways producing wheeze and crackles. Pulmonary oedema then develops due to destruction of the alveolar type 2 cells and formation of hyaline membranes.
1st line antibiotic for bacterial pneumonia
Amoxicillin for a minimum of 7 days
1st line antibiotic for atypical pneumonia
A macrolide (e.g. Clari, Azithro or Erythromycin)
*note may be added to Amoxicillin
When to treat pneumonia with Abx?
All children >2 with a clinical diagnosis of pneumonia should be treated with Abx as difficult to differentiate between bacterial/viral
Children <2 do not require Abx if they have mild Sx of LRTI
Biggest risk factor for fungal pneumonia
Chronic granulomatous disease (genetic condition) as phagocytic cells are unable to kill engulfed organisms due to defects in enzyme function
Note other risk factors: chronic malnutrition/faltering growth, chronic lung diseases such as asthma + bronchiectasis, immunosuppression
Genetic cause of CF
Mutation in the CF-transmembrane conductance regulator (CFTR) gene on chromosome 7
There are >1800 mutations identified, however most labs will test for the 34 most common mutations (>90% cases)
What does the newborn screening blood spot test detect to diagnose CF
Raised immunoreactive trypsin (IRT)
Life expectancy in CF
Mid-40s
1) Inheritance pattern of CF
2) Prevalence
1) Autosomal recessive
2) In a white population there is a carrier frequency of 1:25
List the five classes of mutation in the CFTR gene identified to cause CF
Class 1: nonsense, frame-shift or splicing mutation causes a premature termination of the messenger RNA sequence (2-5%)
Class 2: abnormal post-translational processing of CFTR protein so it is unable to move to the apical membrane. MOST COMMON EXAMPLE = Delta-F508 MUTATION.
Class 3: diminished protein activity (fully formed but non-functional protein channel)
Class 4: normal functioning protein in the correct part of the cell surface but the rate of Cl ions and stimulation of the channel are reduced
Class 5: reduced concentration of CFTR channels due to rapid degradation
Which is the most common CFTR mutation
Delta-F508 mutation (class 2 mutation which leads to defective protein folding/processing so unable to reach the apical membrane)
1) What is the primary function of the CFTR channel
2) What is the result of defective CFTR function
1) It is an ATP-responsive chloride ion channel (moves chloride from intracellular -> extracellular space). It also inhibits the epithelial sodium channel.
2) When defective the respiratory epithelium fails to secrete chloride ions and hyper-absorbs sodium ions + water (by osmosis) causing dehydration of the airway surface. This causes viscous secretions.
Brief outline of the pathophysiology of CF
Defective secretion of chloride ions and increased absorption of sodium ions/water leads to viscous secretions and a dehydrated airway surface.
This impairs mucociliary clearance and host defence. This leads to inflammatory lung damage secondary to a neutrophilic response (IL-8 and elastase released).
Which other organs are commonly effected in CF
Gut, pancreas, liver, reproductive tract
How does CF usually present?
List other presentations as well
Most commonly detected on newborn screening result
Other presentations:
- Meconium ileus (10-20%)
- Recurrent URTI/chest infections
- Jaundice
- Pseudo-Bartter syndrome (hypochloraemic, hypokalaemic alkalosis)
What percentage of CF patients are chronically infected with pseudomonas by the time they reach adolescence?
80%
List the x3 most common organisms causing recurrent respiratory infections in CF
Staph aureus
Haemophilus influenzae
Pseudomonas aeruginosa
What percentage of patients with CF will also have nasal polyps
30%
What percentage of boys with CF will have infertility
99%
What is the false negative rate for CF on the newborn screening test
3-6%
What is the “gold standard” diagnostic test for CF
Sweat test
What is a diagnostic result on sweat test for CF
> 60mmol/L chloride ions
Which infection does a faulty CFTR gene protect against
Typhoid fever (Salmonella typhi uses proteins coded by CFTR to enter the epithelium from the gut)
This may explain why the CFTR gene remains so prevalent
What bacteria causes Whooping Cough?
Bordetella pertussis
Treatment for whooping cough
Macrolide (Clarithromycin or Erythromycin)
What is tested for on the newborn blood spot test for CF?
Immunoactive trypsin levels
What are the embryonic origins of the respiratory tract?
Development of the respiratory system begins with evagination of the respiratory diverticulum from the ventral wall of the foregut which is derived from endoderm.
At what gestation do type 2 pneumocytes form?
Type 2 pneumocytes begin to form at the end of the six month (23 weeks)
What is the embryonic origin of the parietal pleura?
Somatic mesoderm.
It also forms most of the chest wall.
What is the embryonic origin of the visceral pleura?
Splanchnic mesoderm.
The cartilage, muscle and connective tissue of the respiratory system are also formed from splanchnic mesoderm.
What is the anatomical abnormality seen in laryngomalacia?
Shortened aryepiglottic folds which causes the epiglottis to be pulled into an omega shape.
The arytenoid cartilage and mucosa prolapse anteriorly into the airway.
Best antibiotic to treat Mycoplasma pneumoniae
Clarithromycin
