Surgery – Respiratory method or device – Means for supplying respiratory gas under positive pressure
Reexamination Certificate
1998-05-22
2001-02-27
Weiss, John G. (Department: 3761)
Surgery
Respiratory method or device
Means for supplying respiratory gas under positive pressure
C128S205240, C128S205250, C128S206210, C128S206280
Reexamination Certificate
active
06192884
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a device and method for providing supplemental oxygen to a living body during respiration. More particularly, the invention relates to an improved supplemental oxygen delivery device and method therefore that is simpler in construction and utilizes less oxygen to achieve a given oxygen level in breathing than devices and methods known heretofore.
BACKGROUND ART
Supplementary oxygen is of critical importance in many situations, including use (1) as a first aid measure, (2) treatment of chronically ill patients, and (3) prevention of hypoxemia (lack of oxygen in arterial blood) at high altitudes. The therapeutic effects of supplementary O
2
include: elimination of nitrogen bubbles in tissue or blood vessels, oxygenation of plasma to increase physically dissolved oxygen, reduction of tissue edema, and increase O
2
saturation of hemoglobin. In each of these examples, the user of a supplementary oxygen delivery system desires to maintain a certain inspired O
2
percentage for a given duration of time. However, in some situations such as in remote locations, the supply of available oxygen is limited. This makes the efficiency of the delivery system an important factor. Also, the percentage of oxygen required may differ according to the situation. For example, in many emergency applications as close to 100% inspired O
2
as possible is desired.
On the other hand, for high altitude applications, a percentage only high enough to achieve 90% arterial O
2
saturation may be sufficient. Therefore, control of the percentage of oxygen delivered to an individual is significant in making a system versatile as well as efficient. Applicants' invention provides a system with improved efficiency for delivering a given percentage of O
2
for the longest duration.
EMERGENCY APPLICATIONS OF SUPPLEMENTAL OXYGEN
In many emergency situations, paramedics will administer oxygen to a patient until he reaches a treatment center. Typically, oxygen is delivered via a nasal cannula or oro-nasal mask with a constant flow. This allows the patient to inhale about 40-50% O
2
, depending on the flow from the oxygen tank. Often it is sufficient to increase the O
2
concentration only slightly, but in many situations, 100% O
2
or as close as possible is the most important treatment. Emergency Normobaric Oxygen Therapy (NBO) administers 100% O
2
at normal atmospheric pressure. NBO is indispensable in air embolism and decompression sickness from diving or altitude exposure, cardiac arrest/cardiovascular insufficiency, and carbon monoxide intoxication and smoke inhalation. It is important to begin with oxygen as soon as possible since delay can negatively affect the final outcome.
In diving accidents, gas bubbles composed primarily of nitrogen form in the blood or tissues. By eliminating all nitrogen in the lungs with 100% oxygen, the nitrogen gradient between the blood and tissues is increased and causes accelerated resolution of the bubbles. With carbon monoxide poisoning, the CO competes with and is 200 times more stable when bound to hemoglobin than is oxygen. Since the arterial O
2
tension of a person breathing 100% O
2
can approach 700 mmHg (as opposed to about 100 mmHg when breathing air), this elevated O
2
tension displaces CO from hemoglobin and replaces it with O
2
In emergencies such as these, oxygen administration as a first aid measure may be of critical importance.
The principle behind using supplemental oxygen as a first aid measure is to deliver the highest concentration possible until arrival at a medical center. The device most often used to accomplish this is a non-rebreathing mask attached to a reservoir bag (see FIG.
1
). This device functions similarly to a demand regulator used in SCUBA. The oxygen supply flows constantly into the reservoir, and when the patient inhales, 100% O
2
is drawn from the reservoir through a non-return (one-way) valve. The flow must be high enough so that the reservoir bag is not completely deflated during inhalation. The patient then exhales the used O
2
to the atmosphere through a second one-way valve that prevents the inspiration of air. This system requires an O
2
flow rate equal to the breathing rate (minute ventilation), so it is very difficult to maintain a high O
2
percentage for very long without exhausting the O
2
supply. In situations such as diving accidents, the nearest treatment facility may be hours away, and the supply of oxygen may be very limited.
APPLICATION OF SUPPLEMENTAL OXYGEN FOR CHRONIC ILLNESS IN REMOTE AREAS
While sufficient environmental oxygen is present at normal atmospheric pressures, trauma or disease may interfere with oxygenation of the blood in the lungs or with the delivery of oxygenated blood by the heart and circulatory system. In such situations, it may be desirable to achieve an inspired O
2
fraction above the 20.9% in air. Chronically ill patients with poor gas exchange in the lungs due to pulmonary disease or poor blood circulation due to cardiovascular disease are often administered an elevated percentage of oxygen in order to raise the O
2
in their arterial blood nearer to normal. (The normal arterial oxygen tension in the blood is about 100 mmHg; however, for patients suffering from cardiopulmonary disease, this level may be difficult to achieve). A supplemental oxygen system with an adjustable flow is used in these cases to maintain the desired O
2
level in the blood. Administration of Normobaric Oxygen is without hazard for less than about 8 hours as used during immediate first aid. Exposure to 100% oxygen for longer periods, however, can cause chronic irritations known as pulmonary oxygen toxicity. The first noticeable signs of pulmonary toxicity are chest soreness and sore throat which occur after about 8 hours, but potentially serious damage does not occur until after about 48 hours. Patients may be treated with 40 to 50 percent oxygen for an extended duration since this percentage is low enough to avoid the danger of pulmonary oxygen toxicity.
In medical treatment centers with a virtually unlimited supply of oxygen, maintaining 40-50% oxygen is not difficult. However, for military casualties and patients who live in rural areas, the oxygen supply must be used more conservatively. Under these circumstances, an efficient O
2
delivery system is also required. Presently, a non-rebreathing mask without a reservoir (
FIG. 2
) is the most commonly used system. This system supplements air inspired from the atmosphere with a low but constant flow of oxygen, and one-way valves prevent rebreathing.
HIGH ALTITUDE APPLICATIONS OF SUPPLEMENTAL OXYGEN
For mountain climbers, aviators, and high altitude parachutists, supplemental oxygen is very important. At high altitudes, atmospheric pressure decreases causing the partial pressure of oxygen to decrease. Although the percentage of oxygen in the atmosphere is the same at high altitude as at sea level (the amount of oxygen in air is 20.93% up to 110 km), the reduced atmospheric pressure makes the air less dense, and a smaller mass of oxygen enters the lungs with each inhalation. The effect is equivalent to breathing a lower percentage of oxygen at sea level. This situation can result in a deficiency of oxygen in the blood, or hypoxemia. The symptoms of hypoxemia include heavy breathing, lightheadedness, euphoria, overconfidence, apathy, fatigue, visual disturbances, chest pain, unconsciousness, seizures, and even death. These symptoms become apparent when the arterial oxygen saturation drops below about 87% (arterial O
2
tension of about 55 mmHg), and below 65% (arterial O
2
tension of about 35 mmHg) the symptoms become severe and the subject may lose consciousness.
There are two types of high altitude exposure which require supplemental oxygen: aviation and mountaineering. Military combat aviators, for example, are susceptible to acute hypoxia when they ascend to altitude rapidly. Nonetheless, they must maintain their capabilities for judgment, decision making, and physical performance. Since an error in judgment
Muza, Jr. Stephen R.
Vann Richard D.
Duke University
Jenkins & Wilson, P.A.
Weiss John G.
Weiss, Jr. Joseph F.
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