8.0 pneumothorax

A pneumothorax occurs when there is the presence of air within the pleural space,

the potential space between the parietal and visceral pleura.

A pneumothorax is a collection of air outside the lung

but within the pleural cavity.

It occurs when air accumulates between the parietal + visceral pleurae inside the chest which can apply pressure onto the lung → its collapse,

the degree of collapse determining the clinical presentation.

Figure 1: Presentation of a pneumothorax

Air can enter the pleural space by two mechanisms:

1. Trauma causing communication through the chest wall

2. Rupture of the visceral pleura. 

There are two types of pneumothorax;

• traumatic

• and atraumatic

  •  primary

  • and secondary. 

Under normal physiological conditions pleural pressure is maintained by the balance between two opposing forces that generate a negative pressure of approximately -5 cmH₂O (centimetres of water) within the pleural space,

this ensures that the lungs remain expanded against the chest wall.

These forces are:

1. Hydrostatic Pressure

2. Oncotic Pressure

hydrostatic pressure

pulmonary capiliary hydrostatic repssure is the force of fluid pushing against the walls of the pulmonary capiliaries normally 8-10mmHg

oncotic pressure

the osmotic pressyre exerted by proteins in the plasma that are too large to pass thru the pulmonary capiliaries

In addition, maintenance of pleural pressure is facilitated by the presence of pulmonary surfactants

that allow for the smooth movement of the lungs during respiration while maintaining a negative pressure relative to the atmosphere.

Pneumothorax results in a change in the pressure gradient inside the thorax.

The standard negative pressure (compared to athmospheric pressure) usally present in the pleural space

allows for the lungs to collapse due to elastic recoil during breathing.

 When there is communication between the alveoli and the pleural space, air fills this space and results in a change of the pressure gradient,

allowing for lung collapse unit equilibrium, i.e. a collapsed lung.

The pneumothorax then enlarges, and the lung gets smaller due to this vital capacity,

and oxygen partial pressure decreases. 

Clinical presentation of a pneumothorax can range anywhere from

asymptomatic → chest pain + shortness of breath

A tension pneumothorax can cause

severe hypotension (obstructive shock) and even death.

tension pneumothorax

a life threatening emergency wherein a large air collection in the pleural space compromises respiration and cardiac function this condition can arise from events like trauma or aggressive emchanical ventilation or resucitation