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July 5, 1985

Mechanical Ventilatory Support

Author Affiliations

From the Department of Anesthesia, Northwestern University Medical School, Chicago.

JAMA. 1985;254(1):87-92. doi:10.1001/jama.1985.03360010093034

SUCCESSFUL techniques for mechanically supporting ventilation have been available since the 1920s. Positive-pressure ventilation was initially utilized in conjunction with anesthesia and surgery, while negative-pressure ventilators (iron lungs) were most commonly employed outside the operating room. The efficacy of negative-pressure techniques for supporting acutely ill patients was seriously questioned during World War II, and positive-pressure ventilation was firmly established as the superior technique by 1955.1,2 The advantages of positive-pressure ventilation are the ability to ventilate adequately despite increased airway resistance and/or decreased lung compliance, patient accessibility since the ventilator is not "encasing" the patient, and provision of adequate bronchial hygiene via endotracheal tube suctioning

The disadvantages of positive-pressure ventilation are directly related to pulmonary physiology. Gas moves into the lungs in response to transairway (tracheal to alveolar) pressure gradients. Spontaneous ventilation produces a transairway pressure gradient by decreasing pleural pressures, thereby creating transpulmonary pressure (tracheal to pleural pressure) gradients.