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Introduction

The historical evolution of mechanical ventilation is rich and built on advances in many fields, including endeavors by anatomists, chemists, explorers, physiologists, and clinicians.1 In 1543, Vesalius demonstrated that positive-pressure ventilation could be used to resuscitate a dying animal. Bellows ventilation was advocated by various lay bodies in the resuscitation of near-drowning victims late in the 18th century. In 1827, however, Leroy demonstrated that overzealous bellows inflation could result in pneumothoraces. Official bodies condemned the technique, and, thus, early in its infancy, positive-pressure ventilation was banned from use. Around this time, negative-pressure ventilators were developed and later popularized as a panacea for a wide variety of ailments.

The modern era of mechanical ventilation was ushered in by Bjorn Ibsen in response to epidemic of bulbar poliomyelitis in Copenhagen in 1952. In the first 3 weeks of the epidemic, 31 patients had been treated with negative-pressure respirators, and 27 had died. Ibsen advised immediate tracheostomy and the use of positive-pressure ventilation with manual positive pressure from a rubber bag, as was then customary in the operating room. Hundreds of medical students worked in relays, delivering bag ventilation during the epidemic; shortly thereafter, machines were introduced to deliver positive-pressure ventilation. Over the following 40 years, ventilators changed enormously in appearance, becoming more sophisticated and versatile and having enhanced capabilities for monitoring and alarming.

Objectives and Indications for Mechanical Ventilation

The objectives of mechanical ventilation are listed in Table 148-1.2 In isolation, hypoxemia of mild-to-moderate severity can be managed by administration of oxygen (O2) through a face mask. With more severe hypoxemia secondary to shunt or ventilation–perfusion V̇a/Q̇ mismatching, it is difficult to guarantee the delivery of a high fractional inspired oxygen concentration (FiO2) through a face mask. Moreover, these patients are commonly in considerable distress. Thus, intubation helps by ensuring delivery of the required FiO2, and positive-pressure ventilation helps by recruiting collapsed lung units, leading to improved matching of ventilation and perfusion.

Table 148-1Objectives of Mechanical Ventilation

Acute progressive respiratory acidosis is a major indication for mechanical ventilation, although simpler measures can sometimes reverse the process.3 For example, among patients with acute severe asthma and hypercapnia, hypercapnia resolves with standard bronchodilator therapy, without the need for mechanical ventilation, in more than 90% of patients.4 If a patient has severe respiratory depression that is expected to be ...

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