Typically, most awake spontaneously breathing patients have
pleuritic chest pain and dyspnoea. In patients with underlying lung
disease, dyspnoea is severe and significant hypoxaemia can occur,
even with a small pneumothorax. Arterial blood gas measurements
typically show an increase in the alveolar–arterial oxygen gradient
and acute respiratory alkalosis.
The diagnosis of pneumothorax in critical illness or in the ventilated
patient is suggested by deterioration in the patient’s respiratory
and cardiovascular variables, and physical examination. It is
confirmed by radiological investigation or ultrasound. Patients with
a small pneumothorax (,15% of the hemithorax) often have a
normal physical finding on examination. Tachycardia is the most
common physical finding. In patients with a larger pneumothorax,
examination shows decreased movement of the chest wall, a hyperresonant
percussion note, tracheal shift, and decreased or absent
breath sounds on the affected side. The physical findings are often
subtle and may be masked by the underlying lung disease, particularly
in patients with chronic obstructive pulmonary disease.
Systemic hypotension and central cyanosis should raise the suspicion
of a tension pneumothorax. Ventilator parameters will show
decreased tidal volumes and compliance.
Chronic lung conditions give rise to adhesions between parietal
and visceral pleura restricting lung collapse. In such situations, a
pneumothorax may be loculated and localized rather than spreading
throughout the pleural space. In established adult respiratory distress
syndrome (ARDS), a pneumothorax is often present without the
lung completely collapsing as a result of the stiff, non-compliant
nature of the lungs that are filled with fluid and cellular debris and
associated pleural inflammation. Similarly, such affected lungs may
be slow to re-expand (Fig. 1). Therefore, a tension pneumothorax
may exist without total lung collapse or mediastinal shift.5 Once a
pneumothorax has occurred, the high pressures generated during
mechanical ventilation cause the pneumothorax to tension producing
respiratory and haemodynamic effects. If suspected, it should be
confirmed with a chest X-ray or other investigations without delay