Chemistry: analytical and immunological testing – Optical result – Including reagent preparation
Reexamination Certificate
1998-08-04
2004-11-09
Warden, Jill (Department: 1743)
Chemistry: analytical and immunological testing
Optical result
Including reagent preparation
C422S051000, C422S082060, C422S083000, C422S082050, C436S068000, C436S164000, C436S172000, C427S002130
Reexamination Certificate
active
06815211
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention relates to the monitoring of oxygen concentration and, more particularly, to novel, improved methods and apparatus for monitoring the concentration of oxygen in respiratory and other gases and to components of and controls for apparatus as just characterized.
In another aspect, the present invention relates to methods of manufacturing airway adapters designed for use in on-airway applications of the invention.
In a third aspect, the present invention relates to novel sensors which include an oxygen quenchable luminescable compound and methods for manufacturing sensors of the character.
BACKGROUND OF THE INVENTION
The most common cause of anesthetic and ventilator related mortality and morbidity is inadequate delivery of oxygen to a patient's tissues. Therefore, the monitoring of static inspired oxygen concentration has long been a safety standard of practice to ensure detection of hypoxic gas delivery to patients undergoing surgery and to those on mechanical ventilators and receiving supplemental oxygen therapy. However, monitoring the static inspired fraction of inhaled oxygen does not always guarantee adequate oxygen delivery to the tissues because it is the alveolar oxygen concentration that eventually enriches the blood delivered to the cells.
It is this alveolar gas phase that is interfaced with pulmonary perfusion which, in turn, is principally responsible for controlling arterial blood gas levels. It is very important that the clinician know the blood gas levels (partial pressure) of oxygen (pO
2
) and carbon dioxide (pCO
2
) as well as the blood pH. Blood gas levels are used as an indication of incipient respiratory failure and in optimizing the settings on ventilators. In addition, blood gas levels can detect life-threatening changes in an anesthetized patient undergoing surgery.
The traditional method for obtaining arterial blood gas values is highly invasive. A sample of arterial blood is carefully extracted and the partial pressure of the gases is measured, using a blood gas analyzer. Unfortunately, arterial puncture has inherent limitations: (1) arterial puncture requires a skilled health care provider and it carries a significant degree of patient discomfort and risk, (2) handling the blood is a potential health hazard to the health care provider, (3) significant delays are often encountered before results are obtained, and (4) measurements can only be made intermittently.
Non-invasive methods for estimating blood gas levels are available. Such methods include the use of capnography (CO
2
analysis). These methods employ fast gas analyzers at the patient's airway and give a graphic portrayal of breath-by-breath gas concentrations and, therefore, can measure the peak exhaled (end tidal) concentrations of the respective respired gases. Although gradients can occur between the actual arterial blood gas levels and the end tidal values, this type of monitoring is often used as a first order approximation of the arterial blood gas values.
Other techniques have been utilized for assessing patient blood gas levels with mixed results. Transcutaneous sensors measure tissue pO
2
and pCO
2
diffused through the heated skin surface. This type of sensor has a number of practical limitations including a slow speed of response and difficulty of use.
Pulse oximetry is widely used to measure the percentage of hemoglobin that is saturated with oxygen. Unfortunately, it does not measure the amount of dissolved oxygen present nor the amount of oxygen carried by the blood when hemoglobin levels are reduced. This is important because low hemoglobin levels are found when there is a significant blood loss or when there is insufficient red blood cell information. In addition, pulse oximeter readings are specific to the point of contact, which is typically the finger or ear lobe, and may not reflect the oxygen level of vital organs during conditions such as shock or hypothermia.
Oxygraphy measures the approximate concentration of oxygen in the vital organs on a breath-by-breath basis and can quickly detect imminent hypoxemia due to decreasing alveolar oxygen concentration. For example, during hypoventilation, end tidal oxygen concentration changes more rapidly than does end tidal carbon dioxide. During the same conditions, pulse oximetry takes considerably longer to respond. Fast oxygen analysis (oxygraphy) can also readily detect inadvertent administration of hypoxic gas mixtures.
Oxygraphy reflects the balance of alveolar O
2
available during inspiration minus the O
2
uptake secondary to pulmonary perfusion. An increasing difference between inspiratory and end tidal oxygen values is a rapid indicator of a supply/demand imbalance which could be a result of changes in ventilation, diffusion, perfusion and/or metabolism of the patient. This imbalance must be quickly corrected because failure to meet oxygen demand is the most common cause of organ failure, cardiac arrest, and brain damage. Oxygraphy provides the earliest warning of the development of an impending hypoxic episode.
Oxygraphy has also been shown to be effective in diagnosing hypovolemic or septic shock, air embolism, hyperthermia, excessive PEEP, CPPR efficacy, and even cardiac arrest. During anesthesia, oxygraphy is useful in providing a routine monitor of preoxygenation (denitrogenation). It especially contributes to patient safety by detecting human errors, equipment failures, disconnections, misconnections, anesthesia overdoses, and esophageal intubations.
Combining the breath-by-breath analysis of oxygen with the measurement of airway flow/volume as outlined in U.S. Pat. Nos. 5,347,843 and 5,379,650 gives another dimension to the clinical utility of oxygraphy. This combination parameter, known as oxygen consumption (VO
2
), provides an excellent overall patient status indicator. Adequate cardia output, oxygen delivery, and metabolic activity are all confirmed by oxygen consumption because all of these physiological processes are required for oxygen consumption to take place. Oxygen consumption is also useful in predicting ventilator weaning success.
A metabolic measurement (calorimetry) includes determination of a patient's energy requirements (in calories per day) and respiratory quotient (RQ). Interest in the measurement of caloric requirements has closely paralleled the development of nutritional support. For example, the ability to intravenously provide all the necessary nutrition to critically ill patients has only been accomplished within the last 25 years. Along with the realization that we need to feed patients, has come the need to know how much to feed them, what kind of nutrients (carbohydrates, lipids, protein) to feed them, and in what ratio the nutrients need to be supplied. The only true way to measure the caloric requirements of patients and to provide a non-invasive quality assessment of their response to nutrition is with indirect calorimetry. Airway O2 consumption and CO
2
production can be measured non-invasively and provide a basis for the computations needed for a measurement of indirect calorimetry, a direct measurement of the metabolic status of the patient, and the patient's respiratory quotient.
With the above clinical need in mind, it is important to ensure that clinicians have the proper equipment to monitor breath-by-breath oxygen. While there are adequate devices for measuring static levels of oxygen, the measurement of breath-by-breath (fast) airway oxygen concentration requires more sophisticated instruments. Very few of these devices can be directly attached to the patient airway. Instead, most require the use of sampling lines to acquire the gas and send it to a remote site for analysis. Fast airway oxygen monitors are typically large, heavy, fragile instruments that consume considerable power. They must sample airway gases via a small bore plastic tube (sidestream) and remotely detect the oxygen gas as it passes from the airway to the sensor. The problems associated with this type of gas sampling are well know
Apperson Jerry R.
Blazewicz Perry R.
Khalil Gamal-Eddin
Mace Leslie E.
Handy Dwayne K
NTC Technology
TraskBritt
Warden Jill
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