Answer
Concepts that the military developed during World War II to deliver oxygen and gas volume to fighter pilots operating at high altitude were incorporated into the design of the modern positive-pressure ventilator. With the development of safe endotracheal tubes with high-volume, low-pressure cuffs, positive-pressure ventilation replaced the iron lung.
Intensive use of positive-pressure mechanical ventilation gained momentum during the polio epidemic in Scandinavia and the United States in the early 1950s. In Copenhagen, the patient with polio and respiratory paralysis who was supported by manually forcing 50% oxygen through a tracheostomy had a reduced mortality rate. However, this heroic intervention required the continuous activity of 1400 medical students recruited from the universities. The overwhelming manpower needed, coupled with a decrease in mortality rate from 80% to 25%, led to the adaptation of the positive-pressure machines used in the operating room for use in the ICU.
Positive-pressure ventilation means that airway pressure is applied at the patient's airway through an endotracheal or tracheostomy tube. The positive nature of the pressure causes the gas to flow into the lungs until the ventilator breath is terminated. As the airway pressure drops to zero, elastic recoil of the chest accomplishes passive exhalation by pushing the tidal volume out.
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An example of the Drinker and Shaw negative-pressure ventilator (iron lung).
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The pressure, volume, and flow to time waveforms for assist-control ventilation.
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The pressure, volume, and flow to time waveforms for controlled ventilation.
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The components of mechanical ventilation inflation pressures. Paw is airway pressure, PIP is peak airway pressure, Pplat is plateau pressure.
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The effects of decreased respiratory system compliance (A) and increased airway resistance (B) on the pressure-time waveform.
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Determination of the lower inflection point to estimate the best (optimal) positive end-expiratory pressure (PEEP) from the pressure-volume hysteresis curve.
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The effect of positive end-expiratory pressure (PEEP) on the pressure-time inflation curve.
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The pressure, volume, and flow to time waveforms for synchronized intermittent mandatory ventilation (SIMV).
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The pressure, volume, and flow to time waveforms for synchronized intermittent mandatory ventilation (SIMV) with pressure-support ventilation.
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The flow to time waveform demonstrating auto–positive end-expiratory pressure (auto-PEEP).
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The pressure, volume, and flow to time waveforms for pressure-regulated volume-controlled ventilation.
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The pressure, volume, and flow to time waveforms for proportional-assist ventilation.
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The pressure, volume, and flow to time waveforms for airway pressure–release ventilation.
