Respiratory

Question 1

Aspiration Pneumonia CXR

Answer 1

usually involves

• posterior segments of the upper lobes and superior segments of the lower lobes if recumbent
• basal segments of the lower lobes if erect

initial antibiotic choice

• benzylpenicillin 1.2 g IV, 6 hourly plus either
• metronidazole 500 mg IV, 12-hourly or
• metronidazole 400 mg orally, 12 hourly

•in patients with penicillin hypersensitivity use either

• clindamycin 450 mg IV or orally, 8 hourly or
• lincomycin 600 mg IV, 8 hourly

Answer 2

Location

• the left lung is more commonly affected than the right (60:40)
• the posterobasal segments of the lung are involved in 2/3 of cases

Right heart signs

• usually only present with large PE
• loud pulmonary closure sound
• wide splitting of second heart sound
• right ventricular gallop
• right ventricular heave
• JVP
• elevated
• prominent a waves

•localised rales, rhonchi, rub

Question 3

what is PERC

Answer 3

Pulmonary embolism rule-out criteria [PERC]

•parameters at initial ED assessment

• < 50 years of age
• pulse rate < 100 beats/min
• SpO2 > 94% on air
• no unilateral leg swelling
• no haemoptysis
• no surgery or trauma within 4 weeks
• no previous DVT or PE
• no oral hormone use

•the absence of all of the above criteria

-3% false negative rate for PE (LR- 0.17)

• probably not quite sensitive enough for clinical use
• would reduce need for any further testing (including D dimer) in approximately 20% of cases

Question 4

What are the CXR finding in PE

Answer 4

cardiomegaly

• elevated hemidiaphragm - common
• small pleural effusion
• transient pulmonary infiltrates, especially wedge shaped (infarction)
• Westermark’s sign
• prominent PA
• abrupt cut off of peripheral vessels
• normal vessels should be visible within 2 cm of chest wall

Hampton’s hump

• pleural based opacity (pulmonary infarction) with convex border medially
• often in costophrenic angle
• elevated hemidiaphragm
• difference in size between equivalent pulmonary vessels
• abnormal radiolucency in some lung zones
• loss of lung volume

Question 5

What are the advantages of V/Q and disadvantage

Answer 5

Diagnostic when the results are normal or indicate a high probability of PE

1. •use when CTPA is contraindicated

severe renal impairment, or iodine or contrast allergy

1. lower radiation exposure than CTPA
   - especially to the breast
   - appropriate for patients for whom radiation is undesirable
   - e.g. younger patients, women, pregnancy
2. rate of non diagnostic scan may be minimised in selected patients
   - young pregnant population with normal CXR (compared with older, non pregnant population)
3. suitable for follow up of PE

recognises small and large PE, so progression / regression may be studied

Disadvantages

1. interpretation linked to pre-test probability

•high and low probability scans have a PE likelihood of 88% and 4% respectively

• rather than the desired 100 and 0%
  1. high rate of non diagnostic scans, which then warrant further imaging
  e. g. intermediate or low-probability scan plus high clinical suspicion for PE

1. does not provide alternative diagnosis if PE absent
2. not useful if prior lung disease
3. although diffuse disease such as APO or reticulonodular disease does not cause the perfusion lung scan to be abnormal in 70% of cases
4. residual perfusion defects present in 10 - 30% of patients with previous PE
5. incomplete resolution more common in patients with underlying cardiopulmonary disease
6. not as rapid as CTPA
7. not suitable for the unstable patient
8. limited availability at some centres