Mechanical ventilation historical perspective

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief: Vishnu Vardhan Serla M.B.B.S. [2]

Overview

Vesalius was the first person to describe mechanical ventilation by inserting a reed or cane into the trachea of animals and then blowing into this tube. The iron lung, also known as the Drinker and Shaw tank, was developed in 1929 and was one of the first negative-pressure machines used for long-term ventilation.

Historical Perspective

Vesalius was the first person to describe mechanical ventilation by inserting a reed or cane into the trachea of animals and then blowing into this tube.

Negative Pressure Machines

Iron Lung

• The iron lung, also known as the Drinker and Shaw tank, was developed in 1929 and was one of the first negative-pressure machines used for long-term ventilation.
• It was refined and used in the 20th century largely as a result of the polio epidemic that struck the world in the 1950s.
• The machine is effectively a large elongated tank, which encases the patient up to the neck.
• The neck is sealed with a rubber gasket so that the patient's face (and airway) are exposed to the room air.

• Gaseous exchange in the lungs takes place by process of simple diffusion, however, air must be drawn into the lungs to make it available for exchange.
• In spontaneous breathing, a negative pressure is created in the pleural cavity by the muscles of respiration, and the resulting gradient between the atmospheric pressure and the pressure inside the thorax generates air flow.

• In the iron lung, vacuum is created inside a tank by pumping out the air, thus generating a pressure gradient to allow flow of air.
• This negative pressure leads to expansion of the chest, which causes a decrease in intrapulmonary pressure and flow of ambient air into the lungs. *As the vacuum is released, the pressure inside the tank equalizes to that of the ambient pressure, and the elastic coil of the chest and lungs leads to passive exhalation.
• However, when the vacuum is created, the abdomen also expands along with the lung, cutting off venous flow back to the heart, leading to pooling of venous blood in the lower extremities.
• There are large portholes for a nurse or home assistant access.
• The patients can talk and eat normally and can see the world through a well-placed series of mirrors.
• Some could remain in these iron lungs for years at a time quite successfully.

• Today, negative pressure mechanical ventilators are still in use, notably with the Polio Wing Hospitals in England such as St Thomas' (by Westminster in London) and the John Radcliffe in Oxford.
• The prominent device used is a smaller device known as the cuirass.
• A cuirass is a shell-like unit, creating negative pressure only to the chest using a combination of a fitting shell and a soft bladder. Its main use is in patients with neuromuscular disorders who have some residual muscular function.
• However, it was prone to falling off and caused severe chafing and skin damage and was not used as a long-term device.
• In recent years this device has re-surfaced as a modern polycarbonate shell with multiple seals and a high-pressure oscillation pump in order to carry out biphasic cuirass ventilation.

Positive Pressure Machines

Mechanical ventilator

• The design of the modern positive-pressure ventilators was mainly based on technical developments by the military during World War II to supply oxygen to fighter pilots at high altitude.
• Such ventilators replaced the iron lungs as safe endotracheal tubes with high volume/low pressure cuffs were developed.
• The popularity of positive-pressure ventilators rose during the polio epidemic in the 1950s in Scandinavia and the United States.
• Positive pressure through the manual supply of 50% oxygen through a tracheostomy tube led to a reduced mortality rate among patients with polio and respiratory paralysis.
• However, because of the sheer amount of manpower required for such intervention, positive-pressure ventilators became increasingly popular.

• Positive-pressure ventilators work by increasing the patient's airway pressure through an endotracheal or tracheostomy tube. The positive pressure allows air to flow into the airway until the ventilator breath is terminated.
• Subsequently, the airway pressure drops to zero, and the elastic recoil of the chest wall and lungs push the tidal volume out through passive exhalation.