What is the primary cause of death from tension pneumothorax and what is the most important element in the history of an infant with vomiting?

Tension Pneumothorax and Infant Vomiting Assessment

Tension Pneumothorax

Death from tension pneumothorax is primarily caused by decreased venous return to the heart, which leads to cardiovascular collapse and death. 1, 2

Tension pneumothorax occurs when intrapleural pressure exceeds atmospheric pressure throughout both inspiration and expiration. This pathophysiology involves:

• A one-way valve mechanism that allows air to enter the pleural space during inspiration but prevents its escape during expiration 1
• Progressive increase in intrapleural pressure leading to:
  • Mediastinal shift
  • Compression of the vena cava
  • Impaired venous return to the heart
  • Reduced cardiac output
  • Cardiovascular collapse

Evidence Supporting Decreased Venous Return as Primary Cause

The British Thoracic Society guidelines clearly state that tension pneumothorax leads to "impaired venous return, reduced cardiac output, and hypoxemia" 1. This is further supported by animal studies showing:

• 67% decrease in cardiac output at 10 mmHg of tension pressure 3
• 82% decrease in cardiac output at 15 mmHg of tension pressure 3
• Increasing central venous pressure with simultaneous decrease in pulmonary artery diastolic pressure 3

While hypoxia and hypercapnia can occur with tension pneumothorax, they are not the primary mechanisms of death. Cardiac arrhythmias may develop as a consequence of hypoxemia and acidosis but are not the initial cause of death.

Clinical Presentation

Tension pneumothorax presents with:

• Progressive respiratory distress
• Tachycardia and hypotension
• Decreased or absent breath sounds on affected side
• Possible subcutaneous emphysema
• Jugular venous distention 1, 2

Contrary to common teaching, tracheal deviation is not a reliable sign and intervention should not be delayed waiting for this finding 2.

Infant Vomiting Assessment

The most important element in the history of an infant with vomiting is whether the vomiting is bile stained.

Bile-stained (green) vomiting in an infant is a surgical emergency until proven otherwise, as it indicates obstruction distal to the ampulla of Vater. This finding requires immediate evaluation to rule out conditions like:

• Malrotation with midgut volvulus
• Intestinal atresia
• Meconium ileus
• Hirschsprung's disease

Other elements in the history, while important, do not carry the same urgency:

• Projectile vomiting suggests pyloric stenosis but is not immediately life-threatening
• Frequency and amount of vomiting may indicate severity but don't differentiate surgical from medical causes
• Presence of fever may indicate infection but doesn't necessarily point to surgical emergencies
• Non-bilious vomiting has a broader differential diagnosis including medical causes

Clinical Approach to Infant Vomiting

When evaluating an infant with vomiting:

1. First determine if vomiting is bile-stained
2. Assess for signs of dehydration and shock
3. Evaluate for abdominal distension or tenderness
4. Consider other associated symptoms (fever, diarrhea, lethargy)

Bile-stained vomiting requires urgent surgical consultation, abdominal imaging, and possible surgical intervention to prevent intestinal necrosis, especially in cases of malrotation with volvulus.