Chest Trauma: Pneumothorax, Haemothorax, Flail Chest, and Cardiac Tamponade

Definition / Overview

Thoracic trauma accounts for a significant proportion of trauma-related mortality, with immediate life-threatening injuries detectable and treatable during the primary survey. The four injuries covered here represent the most time-critical thoracic diagnoses and are tested heavily in viva and MCQ formats. Each disturbs the fundamental mechanics of breathing and circulation in a distinct way, and each demands a specific management response, often before radiological confirmation.

Pneumothorax

Pathophysiology

Air enters the pleural space, disrupting the sub-atmospheric intrapleural pressure ($P_{pl} \approx -5\,\text{cmH}_2\text{O}$ at rest) that maintains lung expansion. The degree of lung collapse and haemodynamic consequence depends on volume of air, rate of accumulation, and whether a one-way-valve mechanism exists.

Tension pneumothorax develops when a ball-valve defect, in lung parenchyma or the chest wall, allows progressive air accumulation with no route of escape. Intrapleural pressure rises above atmospheric, resulting in:

• Ipsilateral lung collapse
• Mediastinal shift away from the affected side
• Compression of the contralateral lung
• Kinking of the superior vena cava (SVC) and inferior vena cava (IVC) at the thoracic inlet and diaphragm, reducing preload catastrophically

The net effect is obstructive shock: cardiac output falls despite a normal or even elevated heart rate.

Open pneumothorax arises from a chest wall defect ≥ two-thirds the diameter of the trachea; air preferentially enters through the wound rather than the upper airway because resistance is lower, producing ineffective ventilation.

Clinical Features and Diagnosis

Tension pneumothorax is a clinical diagnosis, do not wait for imaging:

Tracheal deviation is a late sign and is often subtle, palpate at the sternal notch.

EFAST (Extended Focused Assessment with Sonography in Trauma): absence of lung sliding and the absence of a "comet-tail" artefact strongly suggest pneumothorax. Sensitivity of ultrasound exceeds that of supine chest X-ray for pneumothorax detection.

On chest X-ray, tension pneumothorax produces mediastinal shift, depression of the ipsilateral hemidiaphragm, and hypo-opacification with absent lung markings.

Occult pneumothorax is identified on CT but not on plain film; may be managed conservatively if $<35\,\text{mm}$ in widest dimension and the patient is haemodynamically stable, even in the intubated patient.

Management

1. Tension pneumothorax: Immediate needle decompression (14-16G cannula, second intercostal space, mid-clavicular line, or fourth/fifth intercostal space, anterior axillary line) followed without delay by tube thoracostomy.
2. Simple pneumothorax: Tube thoracostomy in the fourth or fifth intercostal space, anterior axillary line. A 14Fr pigtail catheter placed by Seldinger technique is equally effective and less painful for uncomplicated pneumothorax.
3. Open pneumothorax: Apply a three-sided occlusive dressing (flutter-valve effect) immediately; insert a tube thoracostomy through a separate incision; definitive operative closure of the chest wall defect.
4. Occult pneumothorax: Serial clinical reassessment and repeat imaging; intervention guided by symptoms or radiological progression.

Haemothorax

Pathophysiology

Blood accumulates in the pleural cavity, most commonly from intercostal vessel, lung parenchyma, or great vessel injury. Haemodynamic compromise arises from two parallel mechanisms:

• Haemorrhagic shock: volume loss from ongoing bleeding
• Restrictive physiology: mechanical compression of the ipsilateral lung reduces functional residual capacity (FRC) and impairs gas exchange

A massive haemothorax is defined as $>1500\,\text{mL}$ of blood in the chest (or $>200\,\text{mL/hr}$ on drainage). At this volume, mediastinal shift and obstructive physiology can co-exist with haemorrhagic shock.

Clinical Features and Diagnosis

• Reduced or absent breath sounds ipsilaterally
• Dullness to percussion (distinguishes from pneumothorax)
• Haemodynamic compromise (tachycardia, hypotension, flat neck veins)
• Trachea remains midline unless tension physiology supervenes

Chest X-ray shows opacification of the hemithorax; approximately $300\,\text{mL}$ is detectable on an erect film, but considerably more is required for detection on a supine film. Ultrasound is highly sensitive even for small haemothoraces.

Management

1. Simultaneously: establish large-bore IV access, commence crystalloid and packed red cell resuscitation, activate massive transfusion protocol (MTP) if haemodynamically unstable.
2. Tube thoracostomy: indicated for any haemothorax $>300\,\text{mL}$, drains blood, quantifies ongoing loss, and prevents fibrothorax/trapped lung.
3. Operative indications:
   • Initial drainage $>1500\,\text{mL}$
   • Ongoing drainage $>200\,\text{mL/hr}$ for $2$-$4$ hours
   • Haemodynamic instability despite resuscitation
   • Massive or tension haemothorax
4. Decisions for surgery are primarily physiological (shock, ongoing haemorrhage) rather than based on a single drainage threshold in isolation.

Retained haemothorax (blood not evacuated by chest tube) risks fibrothorax and empyema, consider early VATS (video-assisted thoracoscopic surgery) if significant residual collection persists after $3$-$5$ days.

Flail Chest

Pathophysiology

Radiographic flail segment: two or more ribs broken in two or more places on imaging.

Clinical flail chest: paradoxical chest wall movement during respiration, the disconnected segment moves inward during spontaneous inspiration (negative intrapleural pressure pulls it in) and outward during expiration, directly opposite to the surrounding chest wall.

The primary cause of hypoxia in flail chest is underlying pulmonary contusion rather than the paradoxical movement itself. Pulmonary contusion causes:

• Alveolar haemorrhage and oedema → reduced compliance
• Ventilation-perfusion mismatch ($\dot{V}/\dot{Q}$ mismatch) → shunt physiology
• Reduced FRC

Pain from multiple rib fractures leads to splinted breathing, further reducing tidal volume, impairing secretion clearance, and predisposing to atelectasis and pneumonia.

Clinical Features

• Paradoxical segment motion is visible on inspection
• Reduced breath sounds over the contused lung
• Hypoxia, tachypnoea, tachycardia
• Associated injuries: pneumothorax, haemothorax (common co-existing diagnoses)

Severity of hypoxia is determined by the extent of pulmonary contusion, not the size of the flail segment per se.

Investigation

• Chest X-ray: may demonstrate multiple rib fractures, pulmonary infiltrates (contusion may lag 6-12 hours), associated pneumo/haemothorax
• CT chest: superior for identifying rib fractures, pulmonary contusion extent, and diaphragmatic injury
• ABG: degree of hypoxia and hypercapnia guides ventilatory support decisions
• Pulse oximetry and continuous monitoring throughout

Management

Analgesia is the cornerstone of management. Inadequate pain control → splinting → atelectasis → pneumonia → respiratory failure. Options:

• Thoracic epidural analgesia: gold standard for bilateral or extensive injuries; reduces need for mechanical ventilation and improves outcomes
• Paravertebral nerve block: effective alternative, particularly for unilateral injury; lower risk of hypotension
• Serratus anterior plane block / intercostal nerve blocks
• Systemic opioids: less preferred due to respiratory depression; adjunct role

Operative rib fixation (surgical stabilisation of rib fractures, SSRF) is increasingly used for large flail segments, particularly when thoracotomy is already planned for another indication, or in patients failing weaning from mechanical ventilation.

Cardiac Tamponade

Pathophysiology

The pericardial sac is a non-compliant fibrous envelope. Blood accumulating within it raises pericardial pressure ($P_{peri}$). When $P_{peri}$ exceeds right atrial pressure, diastolic filling is impaired:

$$\text{CO} = \text{HR} \times \text{SV}$$

Stroke volume falls as diastolic ventricular filling is restricted. Heart rate rises reflexively (compensatory tachycardia), but cardiac output ultimately falls and obstructive shock develops. As little as $150$-$200\,\text{mL}$ of acutely accumulated blood can produce tamponade because the pericardium has minimal acute compliance reserve; chronic effusions can accommodate $>1000\,\text{mL$ before haemodynamic compromise.

Causes in trauma:

• Penetrating cardiac injury (most common): wounds to precordium or in proximity to the mediastinum
• Blunt cardiac rupture: rare in survivors presenting to hospital
• Penetrating great vessel injury with pericardial extension

Clinical Features

Beck's Triad:

1. Hypotension
2. Raised jugular venous pressure (JVP) / distended neck veins
3. Muffled heart sounds

Note: in the trauma bay, muffled heart sounds are very difficult to detect, and neck veins may be flat in the presence of concurrent haemorrhage, making Beck's triad unreliable as a complete set.

Pulsus paradoxus: an exaggerated drop in systolic blood pressure ($>10\,\text{mmHg}$) on inspiration, due to ventricular interdependence, right ventricular filling during inspiration shifts the septum leftward and further impairs left ventricular filling.

Additional findings:

• Sinus tachycardia (early compensatory response)
• Electrical alternans on ECG (alternating QRS axis due to swinging heart)
• Kussmaul's sign unusual in acute trauma

Investigation

• FAST/EFAST ultrasound: the key investigation, pericardial effusion seen as an echo-free stripe around the heart; right ventricular diastolic collapse is the sonographic hallmark of tamponade physiology. Sensitivity is high and examination is performed simultaneously with the primary survey.
• CXR: enlarged globular cardiac silhouette (only useful if effusion $>200$-$250\,\text{mL}$; unhelpful in acute tamponade)
• ECG: tachycardia, low-voltage QRS complexes, electrical alternans

Management

1. Immediate resuscitation: IV fluid bolus maintains preload and buys time by supporting filling pressure, do not under-resuscitate while preparing for definitive intervention.
2. Haemodynamically unstable with penetrating mechanism and positive FAST: proceed directly to operative decompression.
3. Emergency department thoracotomy (EDT): indicated for penetrating thoracic trauma with witnessed cardiac arrest or extreme haemodynamic compromise (signs of life on arrival); allows open cardiac massage, release of tamponade, and direct cardiac wound control.
4. Pericardiocentesis: subxiphoid needle aspiration, temporising measure only in the trauma setting; 20mL of blood withdrawn can provide transient haemodynamic improvement. Useful as a bridge when operative facilities are unavailable.
5. Operative management: median sternotomy (preferred for penetrating anterior cardiac wounds) or anterolateral thoracotomy (better access for lateral wounds and when cardiac arrest occurs). The pericardium is opened anterior to the phrenic nerve; cardiac lacerations are controlled initially with digital pressure or a Foley catheter balloon, then repaired with interrupted sutures.

Key principle: cardiac tamponade from trauma is a surgical emergency, ultrasound confirms the diagnosis rapidly, and definitive treatment is operative.

Comparative Summary Table

Perioperative and Anaesthetic Considerations

• Positive pressure ventilation (PPV) converts a simple pneumothorax to tension pneumothorax by raising intrathoracic pressure against a one-way leak, any pneumothorax should be drained before induction of general anaesthesia where possible.
• Nitrous oxide is contraindicated when pneumothorax is present: nitrous oxide diffuses into air-containing spaces faster than nitrogen exits, expanding the pneumothorax.
• Induction of anaesthesia in tamponade causes cardiovascular collapse, sympathetically mediated compensatory tachycardia is ablated and vasodilation drops preload further. Ketamine (0.5-2 mg/kg IV) or etomidate (0.3 mg/kg IV) are preferred induction agents for their sympathomimetic profile or cardiovascular neutrality respectively.
• Thoracic epidural analgesia for rib fractures and flail chest should be commenced early; the benefits in reducing ventilator days and pneumonia are substantial, and this is a viva-favourite topic.
• Rib fractures in the elderly carry disproportionately higher morbidity; each additional rib fracture increases pneumonia risk and mortality, aggressive early analgesia and respiratory physiotherapy are mandatory in this cohort.

High-Yield GSSE Points

• Tension pneumothorax is a clinical diagnosis, treat before imaging.
• Flail chest hypoxia is driven by pulmonary contusion, not paradoxical movement.
• Cardiac tamponade presents with obstructive shock; FAST confirms the diagnosis at the bedside during the primary survey.
• Beck's triad is often incomplete in trauma, do not rely on all three components being present.
• Pericardiocentesis is temporising only; operative decompression is definitive.
• Massive haemothorax drainage thresholds are guides, not rigid rules, physiology drives operative decision-making.
• Analgesia (especially thoracic epidural) is the most important intervention in rib fractures and flail chest.

Sources

• ATLS (Advanced Trauma Life Support)
• RACS position statements & curriculum (Royal Australasian College of Surgeons)