Types of Resuscitators Available And What They Are Designed to Do
A-B-C—airway, breathing, then circulation. These are the three steps in cardiopulmonary resuscitation, according to a 1973 joint statement by the American Heart Association, National Academy of Sciences and National Research Council. Breathing comes first, although the equipment technology is somewhat less complex than that of cardiac monitoring as reviewed in another article in this issue.
But here, too, the EMS technician encounters a bewildering variety of apparently similar devices. What are the basic functions of each? What standards apply? What lies ahead?
Resuscitation methods go back hundreds, if not thousands, of year. A primitive bellows was used to ventilate non-breathing patients more than four centuries ago. In this century, in the wake of gas mask developments of World War I, fire departments began to use devices which evolved over generations into the resuscitators of today.
For many years, rescue breathing apparatus generally provided a constant flow of air or oxygen, usable by breathing patients. This usually did little good unless artificial respiration methods got breathing started.
Three common types
Today, there are three common types of portable resuscitators for EMS use. One is the intermittent positive pressure (IPPB) type, such as the Rockford, with optional high flow capability. In the Kreiselman version, the maximum pressure is selected by the operator, who manually triggers oxygen flow which stops automatically when the selected back pressure is reached in the patient’s lungs. The variable pressure limit was favored by Dr. Kreiselman primarily in treating infants.
The high flow feature, initiated manually by the operator through a lever or button on the face mask valve, will supply the 100 to 150 liters per minute of oxygen needed in treatment of cardiac arrest. Physicians at one time felt that 60 liters per minute was enough, but today’s higher values are intended to allow for face mask leakage.
The second type of resuscitator is the positive/negative pressure device, such as the E & J model, which uses a factory-set value of positive pressure (typically 30 centimeters of water, or about 1/2 psi) not variable in the field. When the lung back pressure reaches that figure, the valve automatically switches to its negative pressure mode and “exhales” for the patient. Again, a manual high flow option is available.
The third type of resuscitator has a demand valve with a high flow override. The Robertshaw is typical. The demand valve is similar to that on selfcontained breathing apparatus with which most fire fighters are familiar.
Once the patient is breathing on his own, the slight negative pressure created by his inspiratory effort triggers the valve from a non-flow state to a flowing state. The greater the inspiratory effort, the higher the flow. When the inspiratory effort stops, the flow stops. Exhaling opens the valve chamber from the mask to the atmosphere, to eliminate rebreathing exhaled gases. Such valves were first developed for bail-out breathing equipment needed by World War II fliers.
Two basic functions
Resuscitator valves are complex mechanisms (see drawing) and bear many names: Flynn, Marion, Elder, Robertshaw, Globe, E & J, Isaacson, etc. The latest types generally have two basic functions in common:
First, an oxygen-powered pressure ventilation cycle is controlled by the patient’s own lung pressure. Oxygen is supplied to the mask in accordance with the lung’s ability to absorb the flow.
Second, the manual override control allows the operator to directly pressurize the lungs of a nonbreathing patient up to the limit of probable safety, usually about 50 centimeters of water column. By operating the high flow override cyclically, the operator can “breathe for the patient,” timing the flow cycles to fit in with such other rescue efforts as cardiac compression.
Resuscitators thus equipped have been available for about a decade. Demand valves were available years earlier, but they lacked a market because of the absence of trained EMS personnel to use such equipment.
We can offer no comparison of Brand X vs. Brand Y here. In choosing these devices, there is no substitute for: (1) the opinion of the medical staff with which the EMS group is training or working, and (2) the reputation of the device manufacturer, the extent of his field experience, and his acceptance in the medical community. Cost is not a major factor in the total budget of an EMS unit—demands valves are about $95, and complete resuscitators are in the $500 or less range.
With the advent of paramedics, and the generally high level of EMS training in today’s fire-rescue service, the rescuer tends to exercise more control, more feel for patient response, more on-the-spot judgment. There is less strict reliance on automatic mechanical devices with preset operating characteristics that may not fit all emergency situations. Hence, many paramedics may follow this preference in rescue breathing aids:
- Mouth-to-mouth. This does have the disadvantage of limited oxygen supply.
- Bag mask with oxygen supply capability.
- Demand-regulated resuscitators.
As one experienced paramedic views the bag mask, “The oxygen supply valve here is not a demand valve. We are getting away from that concept because the patient just may not have enough energy to demand oxygen flow and may asphyxiate when the valve remains closed. With the manual trigger on the valve, we just hit the button, and it breathes for him.
“At one time, resuscitators were made so ‘safe’ in design that there was no flexibility left to keep people alive in difficult situations.
“Today, valves are more rugged and dependable. We can get three flow settings—for infant, adolescent, or adult. If the patient is ill but breathing, there is no need to substitute for his demand mechanism, so you just set the valve to provide liter flow only.”
A paramedic instructor in another state had this comment: “We prefer the bag mask. You can feel directly the patient’s compliance, which you can’t do with the mechanical resuscitator. The fancy valves are OK in a hospital setting, where the operator may may have at least two years of training as an inhalation therapist. But in the field, the bag mask is better for us.”
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Again, what is acceptable to the physician must govern what is used.
Standards to be written
What standards apply to resuscitation equipment? So far, Almost none. But last June 1, the medical device amendments to the Food Drug and Cosmetic Act became effective, requiring national standards to be written. Groups such as the General Hospital Panel of the Food and Drug Administration are expected to oversee development of standards under contract by outside research firms.
Devices may be classified into one of three groups. For example, Class I, which will probably cover bag mask equipment, requires only that “good manufacturing practice” be monitored by quality assurance procedures to yield a good product. Other types of resuscitators may fall into Class III, requiring “pre-market clearance,” performance standards, and clinical data proving efficacy.
How long it will take to get the standards will depend on the priority assigned, but could take years. In the medical device field more than 2000 separate standards are expected eventually, so they won’t be completed overnight.
Meantime, there is the performance standard developed by the May 1973 National Conference on Cardiopulmonary Resuscitation. This was later published as a February 1974 supplement to the Journal of the American Medical Association, and reprints of it should be available from local Heart Association offices. Here are some brief quotations:
“Conventional pressure-cycled automatic resuscitators (IPPB respirators, positive-negative pressure resuscitators, resuscitators-inhalators) should not be used in conjunction with external cardiac compression because effective . . . compression prematurely triggers termination of the inflation cycle so inadequate ventilation results . . . Manually triggered (time cycled) devices are easier to use effectively. They have high instantaneous flow rates that allow them to be used for artificial ventilation alone. The devices also allow breaths to be interposed between compressions during CPR. Most will function as inhalators, too, for patients who are breathing spontaneously but require oxygen. “Manually triggered, oxygen-powered resuscitators should be able to provide instantaneous flow rates of 100 liters/ minute or more.. .”
Glance toward future
Are there any radically new wrinkles in resuscitation equipment to be expected?
Says one manufacturer of several types, “There is only so much you can do to a lung. We have some difficulty in finding consensus among doctors on such matters as the proper oxygen flow rates . . . Valve design depends on flow and pressures to be used, and what do you do if you find 20 percent of the market wanting one set of numbers, another 20 percent something different, and so on? We work closely with medical groups, especially in anaesthesiology, and we do field testing, and changes in approved techniques are going to continue to arise. But nothing drastically new in valve design seems likely-”
Although changes in both function and electronics are reducing the size and weight of cardiac monitoring equipment, such change seems unlikely for resuscitators. The limitation, as with demand mask equipment, is in the air/oxygen cylinders. A basic change in these must come about to significantly cut resuscitator weight from the 40-pound package typical today.