Mechanical ventilation is used in most of the aeroevacuations of critically ill patients. Patients and mechanical ventilators suffer from variations in the environmental pressure, partial pressure of oxygen, humidity, luminosity, accelerations and vibrations. We describe briefly the history of Mechanical Ventilation and aeromedical transport: Vesalius was the first author to describe one method of ventilation with positive pressure; 400 years later the method was applied for the first time to a patient. Robert Hook in 1667 applied continuous flow ventilation to a dog. Woillez in 1876 made the first mechanical ventilator with negative pressure over the thorax, but the first iron lung was built in 1928 by Drinker and Shaw and later modified by Kroghs and Emerson. In 1955 the poliomyelitis epidemic was the main factor affecting the great success of the mechanical ventilation, with the device of the Emerson Company (Boston, Massachusetts) applying Mechanical Ventilation with positive pressure for the respiratory treatment of the patients affected by poliomyelitis. These innovations could represent the beginning of Mechanical Ventilation and possibly Critical Care treatment also.