Resuscitator

A resuscitator is a device using positive pressure to inflate the lungs of an unconscious person who is not breathing, in order to keep them oxygenated and alive. There are three basic types: a manual version (also known as a bag valve mask) consisting of a mask and a large hand-squeezed plastic bulb using ambient air, or with supplemental oxygen from a high-pressure tank. The second type is the Expired Air or breath powered resuscitator. The first appearance of the second type was the Brooke Airway introduced in 1957. The third type is an oxygen powered resuscitator. These are driven by pressurized gas delivered by a regulator, and can either be automatic or manually controlled. The most popular type of gas powered resuscitator are Time Cycled, Volume Constant Ventilators. In the early days of pre-hospital emergency services, pressure cycled devices like the Pulmotor were popular but yielded less than satisfactory results. One of the first modern resuscitation ventilators was the HARV, later called the PneuPac 2R or Yellow Box. Most modern resuscitators are designed to allow the patient to breathe on his own should he recover the ability to do so. All resuscitation devices should be able to deliver >85% oxygen when a gas source is available.

Resuscitators began in 1907 when Heinrich Dräger, owner of the Drägerwerk AG Company, produced the "Pulmotor" Resuscitator. Considered to be the first practical device for delivering oxygen to unconscious patients or patients in respiratory distress, the Pulmotor influenced resuscitators for many years.

When ambulance services began to form in major cities around the world, such as in London, New York and Los Angeles, Emergency medical services or EMS was developed. In these early days, perhaps the most advanced piece of equipment carried on these ambulances were devices for delivering supplemental oxygen to patients in respiratory distress. The Pulmotor and later models, such as the Emerson Resuscitator, utilized heavy tanks of oxygen to power a device which forced air into the patient's lungs. While better than no oxygen at all, these old units were problematic. Aside from often failing to sense obstructions in the airway, the Emerson, and to a lesser degree the Pulmotor, were large, bulky and heavy. The Emerson Resuscitator required two strong men to carry it from the ambulance to the victim. Perhaps the greatest defect, however, was the fact that these units "cycled".

Cycling was a feature that was built into most resuscitators built before the 1960s, including the Pulmotor and Emerson models. To ensure that the victim's lungs were not injured from being over-inflated, the resuscitator was pre-set to provide what was considered a safe pressure of oxygen. Once the unit reached this limit, it ceased to pump oxygen. For patients suffering from chronic obstructive pulmonary disease (COPD), or any form of obstructive lung disease, the delivered pressure was insufficient pressure to fill the lungs with oxygen, meaning that, for patients with any sort of obstructive lung disease, units that pressure cycled did more harm than good. Pressure cycling also meant that cardiopulmonary resuscitation was impossible to perform if a patient's respiration was being supported by one of these units. If chest compressions were to be done, the cycle would be retarded and the resuscitator would be unable to provide oxygen as long as the chest was being compressed. For victims of smoke inhalation and drowning, however, the benefits outweighed the negatives, so these units found a home on ambulances around the world. The devices that cycled on the basis of upper and lower pressure limits are known as pressure cycled automatic resuscitators. In the UK the introduction of BS6850:1987 Ventilatory Resuscitators confirmed that "....automatic pressure-cycled gas-powered resuscitators are not considered suitable for such use (closed chest cardiac compression)..." and confirmed the standards required for gas powered resuscitators and operator powered resuscitators. The following year a similar ISO standard was introduced. Around this date most manufacturers supplied or introduced time - volume cycled resuscitators and pressure cycled devices were discontinued.

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