Pneumothorax: High-Risk Characteristics, Conservative Care and the Tension Emergency

Introduction

A pneumothorax is air within the pleural space. Normally the intrapleural pressure is negative relative to the atmosphere, and it is this negative pressure that keeps the lung expanded against the chest wall. Once air enters, the pressure equalises, the elastic recoil of the lung is unopposed, and the lung collapses inwards.

Risk factors

• Smoking - increases the risk in men roughly twentyfold, and the risk is dose-dependent
• Tall, thin body habitus - greater apical alveolar distending pressure predisposes to bleb formation
• Male sex and age 15 to 34 for primary disease
• Underlying lung disease, particularly COPD with bullae
• Connective tissue disorders - Marfan syndrome, Ehlers-Danlos syndrome
• Family history - and rare inherited causes such as Birt-Hogg-Dube syndrome
• Cannabis and other inhaled drug use
• Previous pneumothorax - recurrence risk is around 30% after a first primary spontaneous event

Clinical features

Symptoms

• Sudden onset pleuritic chest pain - typically unilateral, often at rest
• Breathlessness - the degree depends far more on the underlying lung function than on the size of the pneumothorax. A small pneumothorax in severe COPD may be devastating; a large one in a healthy 20 year old may cause only mild symptoms.
• Dry cough
• In tension pneumothorax, rapidly worsening breathlessness, agitation and collapse

Signs

• Reduced chest expansion on the affected side
• Hyper-resonant percussion note
• Reduced or absent breath sounds
• Reduced vocal resonance and tactile vocal fremitus
• Tachycardia and tachypnoea
• Surgical emphysema - crackling under the skin of the chest wall and neck
• A small pneumothorax may produce no abnormal signs at all

Investigations

Chest radiograph

An erect posteroanterior chest radiograph is the first-line investigation in a stable patient. Look for:

• A visible visceral pleural edge - a thin white line, with no lung markings peripheral to it
• Mediastinal shift away from the affected side - indicating tension
• Depression of the hemidiaphragm on the affected side
• A fluid level, suggesting haemopneumothorax
• In a supine patient (for example on a trauma or intensive care unit), air collects anteriorly rather than apically, producing the deep sulcus sign - an abnormally deep and lucent costophrenic angle - which is easily overlooked

Other imaging and tests

• CT thorax - the gold standard, and used where the radiograph is equivocal, where there is complex or bullous lung disease (in which a large bulla can closely mimic a pneumothorax, with disastrous consequences if drained), in trauma, and for surgical planning
• Thoracic ultrasound - more sensitive than a supine radiograph and increasingly used in trauma. Absence of lung sliding and of comet-tail artefact, with a lung point, are the diagnostic findings.
• Arterial blood gas - if saturations are below 92% or the patient has underlying lung disease
• ECG - to consider alternative causes of chest pain
• Expiratory films are no longer recommended - they add little and delay diagnosis

Management

The 2023 British Thoracic Society pleural disease guideline substantially changed the approach.¹ Management is no longer driven primarily by measuring the size of the pneumothorax on a film. Instead, it asks two questions: is the patient significantly symptomatic, and are there high-risk characteristics?

The pathway

1. Is the patient in extremis with suspected tension? Immediate needle decompression, then a chest drain.
2. Are there high-risk characteristics, and is it safe to intervene? Insert a chest drain.
3. No high-risk characteristics and symptoms tolerable? The patient has a genuine choice between conservative observation, needle aspiration and an ambulatory device, guided by their priorities - avoiding a procedure, avoiding admission, or fastest resolution.
4. Significant symptoms without high-risk characteristics? Intervene, choosing between aspiration and an ambulatory device according to local expertise and patient preference.

Conservative management

Observation has moved from a fallback to a legitimate first-line option for primary spontaneous pneumothorax with minimal symptoms, following a randomised trial that showed conservative management to be non-inferior to interventional management for lung re-expansion, with fewer adverse events and fewer recurrences.³ Air is reabsorbed from the pleural space at around 1 to 2% of the hemithorax volume per day. High-flow oxygen speeds reabsorption by increasing the nitrogen gradient, and is used in admitted patients where not contraindicated by CO2 retention.

Needle aspiration

• Performed under local anaesthetic with a large-bore cannula, typically in the 2nd intercostal space in the mid-clavicular line, or in the safe triangle
• Aspirate up to a maximum of 2.5 litres; stop earlier if resistance is felt or the patient coughs excessively
• Repeat the chest radiograph afterwards. If the lung has re-expanded and the patient is well, they may be discharged with follow-up.
• If aspiration fails twice, insert a chest drain

Chest drain insertion

• Insert within the safe triangle, bounded by the lateral border of pectoralis major anteriorly, the lateral border of latissimus dorsi posteriorly, a horizontal line at the level of the 5th intercostal space (nipple level) inferiorly, and the axilla superiorly
• Pass the needle immediately above the upper border of the rib below, to avoid the neurovascular bundle running in the groove beneath each rib
• Connect to an underwater seal, which acts as a one-way valve. Swinging of the fluid level with respiration confirms the drain is in the pleural space; bubbling indicates a continuing air leak.
• Keep the bottle below the level of the patient's chest at all times, or fluid will siphon back into the pleural space
• Do not clamp a bubbling drain - this can convert an open pneumothorax into a tension pneumothorax
• Suction may be added if the lung fails to re-expand, but only on senior advice and applied at low pressure, because rapid re-expansion can cause re-expansion pulmonary oedema
• Remove the drain once it has stopped bubbling and the lung has re-expanded on the radiograph

Ambulatory management

Ambulatory devices incorporate a one-way valve and a small collection chamber, allowing selected patients to be managed as outpatients without admission. They reduce hospital stay significantly and are now an established option in patients without high-risk characteristics.

Surgical referral and recurrence prevention

• Refer to thoracic surgery if the air leak persists beyond 3 to 5 days, or if the lung fails to re-expand
• Definitive management is video-assisted thoracoscopic surgery (VATS) with resection of blebs plus pleurectomy or pleural abrasion, which reduces recurrence to around 1 to 5%
• Chemical pleurodesis (talc) is an alternative where surgery is not tolerated
• Indications for definitive intervention include a second ipsilateral pneumothorax, a first contralateral pneumothorax, bilateral spontaneous pneumothorax, persistent air leak, spontaneous haemothorax, and occupations at risk such as pilots and divers

Complications

• Tension pneumothorax - the most feared, and rapidly fatal without decompression
• Recurrence - around 30% after a first primary spontaneous pneumothorax, and higher after a secondary one, with most recurrences occurring within the first year
• Persistent air leak - a bronchopleural fistula, requiring prolonged drainage or surgery
• Re-expansion pulmonary oedema - after rapid re-expansion of a chronically collapsed lung, particularly with suction. Presents with cough, breathlessness and unilateral pulmonary oedema.
• Haemopneumothorax - from tearing of a vascular pleural adhesion, which can cause significant blood loss
• Surgical emphysema - usually benign, but rarely extensive enough to compromise the airway
• Complications of chest drain insertion - malposition, infection and empyema, damage to intercostal vessels, and injury to the lung, liver, spleen or heart
• Respiratory failure - particularly in secondary pneumothorax where reserve is already limited

Red flags

Prognosis

Primary spontaneous pneumothorax has an excellent prognosis. Most resolve without complication, and mortality is very low. The dominant issue is recurrence, at around 30% after a first event, most of it in the first year - which is why smoking cessation advice and clear safety-netting matter more than anything else at discharge.

Secondary spontaneous pneumothorax is a different disease. Mortality is around 10%, because these patients have limited reserve and a small volume of pleural air may be enough to precipitate respiratory failure. They almost always require admission, drainage and a lower threshold for definitive surgical management, and the pneumothorax should be regarded as a marker of advanced underlying lung disease.

After definitive surgical management with VATS pleurectomy, recurrence falls to around 1 to 5%, which is why surgical referral is offered readily after a second event or a first event in a high-risk occupation.