|This article does not cite any references or sources. (December 2009)|
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 a pulmonary or breath powered resuscitator. The first appearance of the second type was the White Pulmonary Resuscitator or W.P.R. introduced in 1981. 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 1960's, 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 40 pounds per-square-inch in delivered oxygen pressure(275.79 kPa). Once the unit reached this limit, it ceased to pump oxygen. For patients suffering from chronic obstructive pulmonary disease (COPD), 40 pounds of pressure was insufficient pressure to fill the lungs with oxygen, meaning that, for patients with any sort of obstructive lung disease, units that cycled did more harm than good. 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.
Both the Pulmotor and the Emerson depended upon the patient's ability to breathe the oxygen in order to be beneficial. Due to the limitations imposed by the cycling feature, this meant that patients in need of rescue breathing benefited little from the application of these devices. The Emerson and Pulmotor were utilized until the mid-1960's, when a breakthrough in the history of oxygen delivery was made: the demand valve.
The demand valve was a revolutionary new piece of equipment. At the simple push of a button, high-flow oxygen could be delivered into the lungs of the patient without the worry of the device cycling and, thus, ceasing to pump oxygen. Any amount of pressure that might be required to inflate the lungs could be achieved, and the demand valve was better able to detect obstructions in the lungs and more able to "work with the patient" than the Emerson and Pulmotor could. The demand valve could also provide oxygen at any flow rate required to a conscious patient in respiratory distress. Conserving the often limited reserves of oxygen was easier with a demand valve, as oxygen was designed only to flow when either the button was depressed or the casualty inhaled.
The ambu-bag was a further advancement in resuscitation. Introduced in the 1960's by the Danish company Ambu, this device allowed two rescuers to perform CPR and ventilation on a non-breathing patient with an acceptable chance of success. The ambu-bag has now mostly replaced the demand valve as the primary method of ventilation, largely due to concerns of potential over-inflation with the demand valve by untrained rescuers. The ambu-bag, unlike the demand valve, has a "pop-off" valve to prevent inflation at greater than 40 pounds -per-square-inch (275.79 kilo-pascals), with the result being that it is generally more common in the pre-hospital setting than the demand valve. Having said that, the demand valve remains popular with BLS providers, and in situations where conserving supplies of oxygen is of paramount importance. The demand valve, while less popular today than it was previously, still remains in service, albeit with important safety features added, including the addition of a pressure-relief valve to prevent over-inflation and the restriction of its flow to 40 liters a minute.
Even newer products have been developed and are now available. Once such product is the Oxylator EM-100. This device, able to function as either a resuscitator or inhalator, is completely automatic. It combines the ability of the demand valve to provide any pressure required through use of a dial, enabling the operator to adjust the flow rate, with the safety of an ambu-bag; with features built into the device that ensure that excess pressure is not delivered when it is not required. A revolutionary feature of this device, besides the fact that it is hands-free, requiring the operator only to turn on the switch and hold the mask in place, is that it automatically synchronizes its flow rate to coincide with chest compressions. Previously, the only device able to do this was the ambu-bag, which required a person to operate it. The Oxylator is the first device to be able to both synchronize its flow with chest compressions and be truly hands-free. It is also the first resuscitator that is able to be safely used in hazardous environments where the air is not safe to breathe, because of its positive-pressure function.
A manual resuscitator should be used on a victim only in an environment where the air is unquestionably safe to breathe.