This week, second-year fellow Elen Gusman presented a case of non-expanding lung (NEL) which presented as a post-thoracentesis hydropneumothorax. Ouch!
Representative clip of a right-sided hydropneumothorax
What are 3 causes of NEL?
- Endobronchial lesion –> lobar collapse
- Chronic atelectasis
- Trapped lung
What is trapped lung?
- A commonly encountered cause of non-expandable lung (NEL)
- Fibrinous, restrictive layer on visceral pleura
- Caused by remote inflammatory pleural process
- Often p/w chronic pleural effusion (ex vacuo physiology)
When to suspect trapped lung?
- Chronic/recurrent effusion
- Pain with thoracentesis
- CT with visceral pleural thickening & loculations
- Fluid characteristics: low LDH, protein in exudative range, paucicellular & mononuclear
How do we diagnose?
- Gold standard is pleural manometry & elastance
- Pel = change in pleural pressure [CWP] / volume fluid removed [L]
- 14-25 CWP/L associated with trapped lung
Below is a YouTube video walking through three commonly utilized methods of transducing pleural pressure:
Lung ultrasound (LUS) may also predict trapped lung with an absent “sinusoid sign”
How to obtain:
- 2D mode U/S with indicator oriented towards head
- Switch to M mode with indicator through effusion into atelectatic lung
- Assess for respirophasic variation in position of atelectatic lung (sinusoidal pattern)
How to distinguish trapped lung from lung entrapment?
- Entrapment – active disease, exudative effusion, directly restricts expansion
- Trapped – chronic disease, transudative (except protein) effusion, visceral pleural thickening restricts
StatPearls 2022 “Trapped Lung” (link)
Annals ATS 2019;16(4):506-508. (link)
Semin Respir Crit Care Med 2001;22(6):631-6. (link)