Infections, immune

Question 1

Acute pneumonia

presentation

Answer 1

• Classically cough (productive or non-productive), fever, breathlessness, chest pain, abnormal CXR. There may be prodromal symptoms of coryza, headache, and muscle aches.

• The aetiological agent cannot be predicted from the clinical features (see Box 2.1).
  
  • Immunocompromised patients may present with agitation, fever, tachypnoea, ↓ routine oximetry readings. CXR abnormalities may be subtle.
  • Patients with right-sided endocarditis (e.g. IV drug users) may present with haemoptysis, fever, and patchy consolidation ± cavitation.

Question 2

Causes of pneumonia

Answer 2

Community acquired

• Strep. pneumoniae (40%)

** • H. influenzae (5%)**

** • S. aureus (2%)**

** • Moraxhella catarrhalis (2%)**

• Gram −ve bacteria/anaerobes 1%

** • Influenza A&B (11%)**

* Other viruses (2%)
* Mixed pathogens (14%)
* No organism identified.

Atypicals

* *• Mycoplasma (11%)**
* *• Legionella pneumophila (4%)**
* *• Chlamydia pneumoniae (13%)**

• Other Chlamydia species (4%).

Question 3

pneumonia severity assessment

Answer 3

• Severity assessment is the key to deciding the site of care (i.e. home, medical ward, or critical care ward) and guiding general management and antibiotic treatment.

• The ‘CURB-65’ score may be used as a severity assessment tool :
  * CURB-65 score ≥ 3: high risk of mortality; should be admitted and managed as having severe pneumonia.
  * CURB-65 score of 2: ↑risk of mortality, need short stay in-patient treatment or hospital supervised outpatient treatment.
  * CURB-65 score of 0–1: low risk of mortality, may be suitable for home treatment.

Question 4

CURB-65

Answer 4

CURB-65 score is a 6 point scale (0–5)—one point for each of the following on the initial assessment):

** • Confusion (defined as Mental Test Score ≤8**, or new disorientation in time, person, or place)

** • Urea >7mmol/L**

**• Respiratory rate (≥30/min)**

• **Blood pressure, low systolic (\<90mmHg) or diastolic (≤ 60mmHg)**

** • Age ≥ 65 years.**

Question 5

Investigations for pneumonia

Answer 5

• ABGs (on air and O2)

** • FBC, U&Es, LFT, ESR, CRP**

**• ECG**

• **CXR** (see Fig. 2.1)

** • Blood cultures**

* **Sputum culture,** Gram stain, ZN stain (if suspicious of TB), cytology
* Pleural fluid aspiration (if present) for MC&S, protein, and pH
* **Pneumococcal antigen**: urine, sputum, or blood
* Serology (acute and convalescent)
* Cold agglutinins (Mycoplasma day 7–14)
* Urine for Legionella antigen, sputum for Legionella culture, and direct immunofluorescence.

Question 6

Sarcoidosis

intro

Answer 6

A multisystem granulomatous disorder of unknown cause. Prevalence highest in Northern Europe, eg uk: 10–20/10’5 population. Usually affects adults aged 20–40yrs, more common in women. AfroCaribbeans are affected more frequently and more severely than Caucasians, particularly by extra-thoracic disease. Associated with hla-drb1 and dqb1 alleles.

Question 7

clinical features of sarcoidosis

Answer 7

In 20–40%, the disease is discovered incidentally, after a routine cxr, and is thus asymptomatic. Acute sarcoidosis often presents with erythema nodosum (fig 1, [link])1 ± polyarthralgia. It usually resolves spontaneously.

PULMONARY

90% have abnormal cxrs with bilateral hilar lymphadenopathy (bhl, fig 1) ± pulmonary infiltrates or fibrosis; see below for staging. Symptoms: Dry cough, progressive dyspnoea, ↓exercise tolerance and chest pain. In 10–20% symptoms progress, with concurrent deterioration in lung function.

NON-PULMONARY

are legion: lymphadenopathy; hepatomegaly; splenomegaly; uveitis; conjunctivitis; keratoconjunctivitis sicca; glaucoma; terminal phalangeal bone cysts; enlargement of lacrimal & parotid glands (fig 5 on [link]); Bell’s palsy; neuropathy; meningitis; brainstem and spinal syndromes; space-occupying lesion; erythema nodosum (fig 1, [link]); lupus pernio; subcutaneous nodules; cardiomyopathy; arrhythmias; hypercalcaemia; hypercalciuria; renal stones; pituitary dysfunction

Question 8

CAUSES OF BILATERAL HILAR LYMPHADENOPATHY

Answer 8

** • Sarcoidosis**

** • Infection** eg tb, mycoplasma

* **Malignancy,** eg lymphoma, carcinoma, mediastinal tumours
* **Organic dust disease**, eg silicosis, berylliosis
* **Extrinsic allergic alveolitis**
* Histocytosis x

Question 9

Extrinsic Allergic Alveolitis

Answer 9

In sensitized individuals, inhalation of allergens (fungal spores or avian proteins) provokes a hypersensitivity reaction. In the acute phase, the alveoli are infiltrated with acute inflammatory cells. With chronic exposure, granuloma formation and obliterative bronchiolitis occur.

Causes

* Bird-fancier’s and pigeon-fancier’s lung (proteins in bird droppings).
* Farmer’s and mushroom worker’s lung (Micropolyspora faeni, Thermoactinomyces vulgaris).
* Malt worker’s lung (Aspergillus clavatus).
* Bagassosis or sugar workers’ lung (Thermoactinomyces sacchari).

Question 10

OXYGEN ADMINISTRATION

Answer 10

Oxygen is usually given via a facemask or nasal cannulae. It is good practice to prescribe it—this avoids inadvertent administration of too much or too little. Titrate the amount guided by the SaO2: aim for ~ 94–98% (or 88–92% if, or at risk of, hypercapnia); and the clinical condition of the patient. Humidification is only required for longer-term delivery of O2 at high flow rates, tracheostomies, but may ↑ expectoration in bronchiectasis. Be careful in those with copd ([link]).

Nasal cannulae:

preferred by patients, but O2 delivery is relatively imprecise and may cause nasal soreness. The flow rate (1–4L/min) roughly defines the concentration of O2 (24–40%). May be used to maintain SaO2 when nebulizers need to be run using air eg copd.

Simple face mask:

delivers a variable amount of O2 depending on the rate of inflow. Far less precise than venturi masks - so don’t use if hypercapnia or type 2 respiratory failure. Risk of CO2 accumulation (within the mask and so in inspired gas) if flow rate <5L/min.

Venturi mask:

provide a precise % of O2 (FiO2) at high flow rates.

Colour codes:

24% BLUE

28% WHITE

35% YELLOW

40% RED

60% GREEN

Start at 24–28% in copd.

Non-rebreathing mask:

these have a reservoir bag and deliver high concentrations of O2 (60–90%), determined by the inflow (10–15L/min) and the presence of flap valves on the side. They are commonly used in emergencies, but are imprecise and should be avoided in those requiring controlled O2 therapy.

Promoting oxygenation

Other ways to ↑ oxygenation to reach the target SaO2 (this should be given as a number on the drug chart):

* Treat anaemia (transfuse if essential)
* Improve cardiac output (treat heart failure)
* Chest physio to improve ventilation/perfusion mis-match.