Pneumothorax in the Emergency Department – Part 1

Pneumothorax is a relatively rare emergency department presentation with a number of controversies existing regarding its management. Over the last decade, the standard of care has shifted from invasive strategies to more conservation management approaches. What factors should you consider in managing the next pneumothorax you see on shift, and what do we really know from the existing evidence?

In part one of our two-part grand round series on pneumothorax, Dr. Simon Wells covers the varying definitions, epidemiology, diagnostic criteria, and imaging findings of pneumothorax including on point of care ultrasound (POCUS).

Part two of the series will focus on pneumothorax treatment and management options, as well as a summary of the 2020 NEJM publication ‘Conservative versus Interventional Treatment for Spontaneous Pneumothorax’.

Definitions

Pneumothorax refers to air in the pleural cavity. It was first described in medical literature in 1803 as a complication of tuberculosis infection.¹ It was not until 1932 that the first case of “pneumothorax simple”, or pneumothorax in someone with no apparent underlying lung disease, was reported.² This type of pneumothorax would come to be known as a primary spontaneous pneumothorax (PSP).

Secondary spontaneous pneumothorax (SSP) occurs in patients with clinically apparent underlying lung disease. They are both important to differentiate from traumatic pneumothoraces, which can be either iatrogenic or caused by blunt or penetrating traumatic injuries.

PSP vs. SSP

The concept of PSP occurring in patients with “no underlying lung disease” is traditionally taught, but this concept is in-fact outdated.³

• Advances in chest imaging demonstrate underlying emphysema-like changes, most notably blebs and bullae, in most cases of PSP.^3,4
• Pathologic assessments of underlying lung also show less visible changes, such as disrupted areas of mesothelial cells, underlying inflammation, and pores 10-20 microns in diameter. ⁵
• These findings suggest that the distinction between PSP and SSP is an artificial construct.⁶
• Future study is needed to determine if patients are well served by this traditional differentiation and whether it should influence management.

Epidemiology

• PSP incidence:
  • 7-28/100 000 /year (males), 1.2-9.8/100 000 /year (females) ^7–9
• PSP is much more common in males.
  • Male/Female ratio ~ 5:1
• PSP typically occurs in younger adults, as opposed to SSP typically occur later in life.
• The incidence of SSP is similar to that of PSP.
• SSP are still more frequent in men, but at a lower ratio of 3:1.

Smoking and PSP

• The majority of patients with PSP are smokers.
• A Swedish population study found that there was a direct dose dependent relationship between the number of cigarettes smoked and the relative risk of pneumothorax, as indicated in the following table.⁷

• Smokers have higher recurrence rates.¹⁰
• Smoking cessation is the only evidence-based modifiable risk factor for PSP recurrence.¹¹
• One systematic review, including 29 pooled studies looking at recurrence risk of pneumothorax found smoking cessation was associated with a four-fold decrease in risk (OR 0.26, 95% CI 0.10–0.63).¹²
• All patients with pneumothorax should be counselled on the importance of smoking cessation and referred to appropriate support services.

Cannabis smoking and pneumothorax

• Cannabis smoking has been shown to be associated with emphysema-like changes in the lungs.¹³
• Regular cannabis smoking increases the risk of PSP.¹⁴
• Underlying cause assumed to be related to both parenchymal damage from smoke, and the longer breath-holds manoeuvres often used in cannabis smoking.¹⁵
• All patients with PSP should be questioned about cannabis use and counselled to stop.

Other risk factors for pneumothorax

• Increased height (in men)
  • Thought to be due to an increased pleural pressure gradient from the lung base to the apex in taller individuals, causing increased apical distending pressures that potentially lead to the formation of subpleural blebs.¹⁶
• Low BMI & caloric restriction
  • There is conflicting data on these potential risk factors.¹¹
• Up to 5-10% of individuals have a family history.¹⁷
  • Some are eventually found to have hereditary syndromes such as Birt-Hogg-Dube syndrome, Marfan syndrome, Ehler-Danlos syndrome, Cutis laxa.
  • These should then be considered cases of SSP, not PSP.
• Sudden atmospheric pressure changes, diving.^18–20

Causes of SSP

• Nearly every lung disease can be complicated by SSP.
• The most commonly associated disease is COPD.²¹
• In endemic areas, tuberculosis (TB) is a common cause.

Catamenial pneumothorax

• Occurs in women around the time of menstruation.
• Due to pleural endometriosis implant or defect in the diaphragm.
• Treatment: ovulatory suppression or surgery.²²
• ~5% of all pneumothoraces in women.
• Tend to be recurrent; multiple typically occur before a diagnosis is made.²³

Traumatic pneumothorax

• The current rate of traumatic pneumothorax seems to be greater than the rate of spontaneous pneumothorax. ²⁴
• Can occur iatrogenically from procedures, including transbronchial biopsy, central venous catheterization, thoracentesis and mechanical ventilation.
• Penetrating wounds can lead to open pneumothorax.
• With blunt traumatic mechanisms, rib fractures or sudden increases in alveolar pressure from chest compression with a closed glottis can cause pneumothorax.

Tension pneumothorax

• A one-way valve mechanism allows air to enter the pleural space during inspiration but not exit fully during expiration
• Air in the pleural space builds up enough pressure to interfere with venous return, leading to hypotension, tachycardia, low cardiac output, and cardiac or respiratory failure
• Tension pneumothorax is very rare in both PSP and SSP.
• More common in traumatic pneumothorax and in patients on mechanical ventilation.
• Needs immediate treatment with finger thoracostomy or needle decompression, followed by large bore chest tube placement.

Clinical Presentation

• Common symptoms: sudden chest tightness, pain and SOB.
• Onset does not usually occur during exertion.
• SSP has been traditionally associated with more morbidity and mortality, as well as more severe symptoms. However, the evidence for this is largely anecdotal.
• In mechanically ventilated patients, pneumothorax should manifest as a sudden decrease in pulmonary compliance.
  • Volume control ventilation = elevation in both peak and plateau pressures.
  • Pressure control ventilation = decreased tidal volume.

Diagnosis and Imaging

• The first issue in the imaging and management of pneumothorax is that there is no international consensus as to what quantifies a large pnemothorax.
• Available guidelines from the American College of Chest Physicians (ACCP) and British Thoracic Society (BTS) are below.^25,26 However, they agree less than 50% of the time in clinical settings based available data.²⁷
• This is an important issue, as guidelines currently recommend different management options for large vs small pneumothoraces.

The Light Index²⁸

• • % Pneumothorax = 100 – [(lung diameter³/hemithorax diameter³) x 100]
  • One study found strong correlation with volume of air removed²⁹
  • Poor correlation with CT volumetrics found in another study³⁰
  • Overall seems to be inaccurate, especially seems to underestimate size for moderate/large pneumothoraces.³¹

The Collins Method³²

• • % Collins = 4.2 + 4.7(A+B+C)
  • It is obtained by getting measurements in centimetres at three locations and inputting them into the formula above.
  • Seems to be better at estimating the size of larger pneumothoraces.²⁷

Overall however, neither of these methods is routinely used in clinical practice. Additionally, at present, it is reasonable to choose either the BTS or ACCP definition of large pneumothorax.

X-ray criteria for diagnosing pneumothorax

1. Displacement of the pleural line
2. Absence of lung markings peripheral to the pleural line

Inspiratory vs expiratory views

• Thomsen et al. found that pneumothoraces during inspiration demonstrate a greater width than during expiration, contrary to widely held but unstudied assumptions.³³
• Inspiratory and expiratory views have been shown to perform similarly.^34,35
• Guidelines recommend inspiratory views alone; no need for expiratory views!
• Measurement standards are based on views obtained during inspiration.

Signs of pneumothorax on supine x-rays

• Deep sulcus sign – a deep and sometimes lateral costophrenic sulcus
• Double diaphragm sign – visualization of the anterior costophrenic sulcus
• Increase in sharpness of the cardiac borders, adjacent mediastinal margin, or diaphragm
• Visualization of inferior edge of collapsed lung
• Increased lucency on affected side
• Depression of the ipsilateral hemidiaphragm
• X-ray mimics: skin fold, bullae, gastric herniation

CXR vs PoCUS

• Most studies comparing the two modalities are in trauma and use supine x-rays.³⁶
• Meta-analysis, 8 studies, traumatic and iatrogenic pneumothorax:³⁷
• PoCUS: 9% sensitive (95% CI, 86.5-93.9), 98.2% specific (95% CI, 97.0-99.0)
• CXR (almost all supine): 50.2% sensitive (95% CI, 43.5-57.0), 99.4% specific (95% CI, 98.3-99.8)
• PoCUS significantly outperforms supine CXR for diagnosing pneumothorax in trauma.
• PoCUS is faster and less disruptive to care/resuscitation.³⁸
• E-FAST with bilateral lung assessments should be the standard of care in trauma assessments to add assessment for pneumothorax.
• Cannot make accurate size estimates based on PoCUS as of yet.

PoCUS findings of pneumothorax

• Absence of Pleural sliding
• Absence of Comet tails or B-Lines
• Presence of a lung point
• Absence of lung pulse
• Should be assessed using an 8-zone technique

Check out this excellent video on POCUS assessment for pneumothorax from EM cases for more information:

Lung sliding

• Lack of sliding at the pleural line on POCUS is indicative of pneumothorax, however multiple other conditions can cause loss of sliding.
• This means we need to combine the loss of lung sliding with other signs and not limit our assessment purely to the pleural line.

Comet tails and B-lines

• Comet tails and B lines are normal reverberation artefacts that occur in the presence of lung parenchyma in contact with the pleural line.
• In patients with no lung sliding, the presence of B lines or comet tails can essentially rule out pneumothorax.
• If they are absent and there is no lung sliding, this combination improves the specificity and PPV of lung ultrasound for pneumothorax detection.

Lung point

• The lung point is where lung starts to be in contact with pleural line – this is defined as a transition between an area of active lung sliding and an area without any sliding.
• The presence of a lung point, with the absence of lung sliding and comet tails, improves the specificity of POCUS to 100%.
• Location of lung point can help to roughly estimate size –  if found more laterally or posterior then pneumothorax is larger.

Lung Pulse

• This is the slight movements of the pleural line corresponding with heart beats (In the absence of normal lung sliding) – looks like a slight shimmering at the pleural line.
• Indicates normal visceral-parietal pleura interface – not seen in pneumothorax.
• Can be seen in conditions like atelectasis and mainstem intubation.

Potential pneumothorax mimics on POCUS

• Pleural scarring: Previous pleurodesis, radiation changes, infectious/inflammatory pleural disease
• Lung volume loss: atelectasis, mucus plug, right mainstem intubation
• COPD (bullous emphysema)
• Pulmonary fibrosis
• Phrenic palsy

Conclusions

In this post, we explored the varying definitions of pneumothorax, including whether a PSP truly occurs in the absence of any underlying lung disease. We discussed risk factors, including cannabis smoking, and the different sub-typing of pneumothorax described in the literature. Finally, we reviewed imaging findings of pneumothorax and POCUS clinical pearls to help sharpen your bedside skill-set.

Our next post, part two of the series, will focus on treatment and management options, as well as a summary of the 2020 NEJM publication entitled ‘Conservative versus Interventional Treatment for Spontaneous Pneumothorax’. Stay tuned!