Saline solution was the first liquid used as a respiratory medium
Saline effectively eliminates the gas-liquid interface within the lung.
Saline has been fundamental in understanding factors that influence alveolar structure, distensibility, stability, ventilation, and pulmonary blood flow.
The detergent-like action of saline solution has proved useful in removing pulmonary debris,however  it also removes pulmonary surfactant, which is necessary for lung stability.
Low respiratory gas solubility and excessive diffusion gradients at atmospheric conditions have limited the applicability of saline solution to support pulmonary gas exchange.
Because the O2 content of saline solution saturated at 1 atm is only approximately 3 vol%, it cannot support oxygenation under atmospheric conditions.
In 1950, it was suggested that saline solution saturated with O2 dissolved under pressure could potentially sustain submersed mammals. Practical application of this concept was first demonstrated in 1962.
Additional studies demonstrated that mammals submerged in hyperbaricoxygenated saline solution could breath liquid and resume gas breathing.
These studies demonstrated adequate oxygenation however, CO2 retention and profound acidosis occurred, thus rendering saline ventilation physiologically unsound during either normobaric or hyperbaric conditions
Shaffer, T.H. and M.R. Wolfson, Liquid Ventilation, in Fetal and Neontal Physiology, R.A. Polin, W.W. Fox, and S.H. Abman, Editors. 2011, Elsevier: Philadelphia, PA. p.1063.
Neonatal Liquid Ventilation