Lung Ultrasound in the Evaluation of Pleural Infection
Resident Clinical Pearl (RCP) July 2019
Yazan Ghanem – PGY5 Internal Medicine, Dalhousie University
SJRHEM PoCUS Elective
Reviewed and edited by Dr. David Lewis.
CASE: MR. WHITE
83 year old male with known past medical history of mild cognitive impairment (lives alone in assisted living). Two weeks prior to current presentation, he was admitted with community acquired pneumonia and discharged after 2 nights of hospital stay on oral antibiotics.
He is now presenting with 5 days history of worsening dyspnea, fever, fatigue and reduced oral intake. Vital signs are: Temperature 38.4 C; heart rate 80/min; Blood pressure 121/67; Respiratory rate 28/ minute; Oxygen saturation 90% on room air. His chest exam showed reduced air entry and dullness to percussion in the right hemithorax.
CXR:
Bedside POCUS:
Pleural fluid analysis:
• WBC – 22,000 cells per uL
• LDH – 1256 Units / L
• Glc – 2.2 mmol / L
• pH – 7.18
• Gram Stain – Neg
Next steps in management?
A – 14 Fr pleural drain + Start IV Levofloxacin
B – 28 Fr pleural drain + Start Ceftriaxone / Azithromycin
C – 14 Fr pleural drain + Start Piperacillin – Tazobactam
D – Start Ceftriaxone / Azithromycin + Repeat CXR in 1 week
(See end of page for answer )
Normal Thoracic Ultrasound:
Thoracic Ultrasound is limited by bony structures (ribs and scapulae) as well as by air within lungs (poor conductor of sound waves).
With the transducer held in the longitudinal plane:
1 – Ribs are visualized as repeating curvilinear structures with a posterior acoustic shadow.
2 – Overlying muscle and fascia are seen as linear shadows with soft tissue with soft tissue echogenicity.
3 – Parietal and visceral pleura is visualized as a single echogenic line no more than 2 mm in width which “slides” or “glides” beneath the ribs with respiration. Two separate lines can be seen with a high frequency transducer.
4 – Normal aerated lung blocks progression of sound waves and is characterized by haphazard snowstorm appearance caused by reverberation artifact.
5 – Diaphragms are bright curvilinear structures which move with respiration. Liver and spleen have a characteristic appearance below the right and left hemi diaphragms respectively.
Pleural Effusion:
Ultrasound has higher sensitivity in detecting pleural effusions than clinical examination and chest X-Ray.
On Ultrasound, pleural effusions appear as an anechoic or hypoechoic area between the visceral and parietal pleura that changes in shape with respiration. Atelectatic lung tissue appear in the far field as flapping or swaying “tongue-like” echodensities.
Ultrasound morphology:
1- Anechoic Effusion: Totally echo-free (Could be transudative or exudative)
2- Complex Non-septated: Echogenic appearing densities present (fibrinous debris). Always exudative.
3- Complex Septated: Septa appear in fluid. Always exudative.
Parapneumonic Effusions and Empyema:
Ultrasound is superior to CT in demonstrating septae in the pleural space. However, CT is recommended for evaluation of complex pleuro-parenchymal disease and loculated pleural collections if drainage is planned: There is no correlation between ultrasound appearance and the presence of pus or need for surgical drainage; however, the presence of a septated appearing parapneumonic effusion correlate with poorer outcomes (longer hospital stay, longer chest tube drainage, higher likelihood for need for fibrinolytic therapy and surgical intervention.
Parapneumonic effusions appear as hyperechoic (with or without septae) on ultrasound.
Pulmonary Consolidation:
Pulmonary consolidation is sonographically visible in the presence of a pleural effusion that acts as an acoustic window or if directly abutting the pleura.
It appears as a wedge-shaped irregular echogenic area with air or fluid bronchograms.
Back to Mr. White
Next steps in management?
A – 14 Fr pleural drain + Start IV Levofloxacin
B – 28 Fr pleural drain + Start Ceftriaxone / Azithromycin
C –14 Fr pleural drain + Start Pipercillin- Tazobactam
D – Start Ceftriaxone / Azithromycin + Repeat CXR in 1 week
Rationale:
Complicated parapneumonic effusions should be managed with drainage and antibiotics that will treat anaerobic infection. An alternative would be a combination of Ceftriaxone and Metronidazole (No pseudomonas coverage). Levofloxacin alone does not add any anaerobic coverage. Azithromycin has poor penetration into loculated pleural collections.
References
British Thoracic Society – Pleural Disease Guideline – 2010
https://thorax.bmj.com/content/65/8/667
