Surgery – Respiratory method or device – Respiratory gas supply means enters nasal passage
Reexamination Certificate
1999-01-28
2002-07-23
Dawson, Glenn K. (Department: 3761)
Surgery
Respiratory method or device
Respiratory gas supply means enters nasal passage
C128S207140, C128S204180
Reexamination Certificate
active
06422240
ABSTRACT:
FIELD AND BACKGROUND OF THE INVENTION
The present invention relates to a nasal cannula and to an oral
asal cannula, and, more particularly, to a nasal cannula and an oral
asal cannula which permits both delivery of oxygen and accurate sampling of carbon dioxide.
For purposes of description, the discussion herein is focused on cannulas for use with human patients, it being understood that the present invention is not limited in scope only to use with patients and can beneficially be used in various other contexts.
Different types of oral
asal cannulas are used to deliver oxygen to hospital patients who require assistance to breathe properly, to collect carbon dioxide samples from patients to monitor respiration, or to perform both functions. Such cannulas are used when direct ventilation is not provided. The term “oral
asal” refers to the adaptable configuration of such cannulas which can be in close proximity to the oral cavity or inserted into the nasal cavity of the patient. In either arrangement, a sidestream of the patient's exhaled breath flows through the cannula to a gas analyzer to be analyzed. The results of this non-invasive analysis provide an indication of the patient's condition, such as the state of the patient's pulmonary perfusion, respiratory system and metabolism.
The accuracy of this non-invasive analysis of exhaled gases depends on the ability of a sampling system to move a gas sample from the patient to the gas analyzer while maintaining a smooth, laminar flow of gases, such that there are as few alterations to the waveform and response time of the concentration of the gases as possible. The waveform of the concentration of the gas is critical for accurate analysis. As the gas mixtures travels from the patient to the gas analyzer, the concentration of the gases can be affected by mixing of the component gases, which reduces the accuracy of the analysis of the sample by the gas analyzer, and reduces the amount of information obtained from that analysis.
Prior art nasal or oral
asal cannulas unfortunately have caused significant alterations to these important features of the internal structure of the stream of exhaled gases. Such alterations have especially arisen as the result of attempts to combine the delivery of oxygen with the sampling of the exhaled breath of the patient. For example, the simplest nasal cannula design, consisting of a tube with two double hollow prongs for insertion into the nostrils, allows significant mixing of the oxygen which is delivered from the end of one tube, and the exhaled breath which is collected from the end of the second tube. Such mixing occurs when oxygen is delivered in a stream with strong force, so that the oxygen stream penetrates deeply into the nasal cavity even during expiration, thereby artifactually altering the composition of the exhaled gases.
However, attempts to prevent mixing between delivered oxygen and exhaled gases have resulted in other alterations to the exhaled gases. For example, one type of prior art nasal cannula (Salter Labs, Arvin, Calif. USA) consists of a tube with two openings at either end, and two hollow prongs projecting perpendicularly from the center of the tube with a partition between them. Oxygen enters the tube from one end and exhaled breath leaves the tube from the other end. The two hollow prongs are inserted into the nasal cavity of a patient, one prong in each nostril, so that oxygen could be delivered to, and exhaled breath collected from, the patient. Unfortunately, the reliance of this cannula on a single nasal prong for collection of exhaled gases does not prevent the strong flow of delivered oxygen from the other nostril mixing with exhaled gases deep in the nasal cavity, above the nasal septum. Such mixing of delivered oxygen with exhaled gases reduces the accuracy of gas analysis.
In addition, this type of cannula usually has significant “void volume”, or space in which mixing of gases and concurrent alteration of the gas waveform, can occur. Such space is often referred to as “void volume” because it is not part of the pathway for the flow of gases and hence is unproductive. For example, void volume arises in this cannula between the septum dividing the main tube and the junction of each prong with that tube. The presence of such void volume is a significant hindrance to the accurate analysis of exhaled gases. Thus, this prior art nasal cannula has a reduced efficiency for the collection of exhaled gases for analysis.
Another design for a nasal cannula (Hospitak, Lindenhurst, N.Y., USA) has two parallel overlapping tubes, one for delivering oxygen and one for receiving exhaled gases. The tube which receives exhaled gases has two nasal prongs, while the tube which delivers oxygen has two holes parallel to these prongs. Both tubes have two holes, such that the gases can flow freely from the prongs to the holes. This configuration allows delivered oxygen to easily mix with expired gases, even at the end of the expiration period, thereby reducing the accuracy of the gas analysis.
U.S. Pat. No. 5,046,491 discloses another type of nasal cannula which also includes a first tube with two double nasal prongs and a septum placed between the prongs. One prong delivers oxygen and the second prong collects exhaled gases. A second tube is attached to the first tube and has two holes which are placed in or near the oral cavity of the patient for collecting exhaled breath. One problem with this cannula is that the exhaled gases are collected through two outputs, which are then connected to two separate tubes. These separate tubes then join together before delivering the gases to the capnograph. If gases are not flowing at exactly the same rate through both tubes, for example due to condensation, then the waveform of the gas concentration is altered and the results of the analysis are affected. In addition, this cannula has significant void volume because of the large dimension of the tubes and because there are two outputs for collecting the exhaled gases. The large void volume also causes mixing of the gases. Thus, the cannula of U.S. Pat. No. 5,046,491 does not solve the prior art problems for accurate gas analysis by nasal cannulas.
Furthermore, none of these prior art cannulas is a true oral
asal cannula, which can be placed in either the oral or nasal cavities of the patient interchangeably. Such prior art oral
asal cannulas, which are described below in the “Description of the Preferred Embodiments”, also have significant problems regarding the collection of gases for accurate analysis, but offer the desirable feature of flexibility concerning the respiratory cavity from which exhaled gases are collected. Patients often alternately exhale through the nasal cavity and the oral cavity. The advantage of the oral
asal cannula is that exhaled gases can be automatically collected from either cavity. The disadvantage is that many prior art oral
asal cannulas are susceptible to the intake of ambient air through that portion of the cannula which is not receiving exhaled air. For example, if the patient exhales through the oral cavity, ambient air can be sucked into the cannula through the opening provided for the nasal cavity. Such ambient air can dilute the concentration of gas in the exhaled breath of the patient, thus giving misleading results for the gas analysis.
Hereinafter, the term “respiratory cavity” refers to the oral cavity, the nasal cavity, or both cavities, of a patient.
In addition, the effectiveness of oxygen delivery by a cannula is determined by two principles, neither of which is completely fulfilled by prior art cannulas. The first principle is that the distribution of the delivered oxygen stream should be equal between the two nostrils of the patient. In most prior art cannulas, one nostril receives 1.2-2.0 times as much oxygen as the other. However, an equal distribution of oxygen is preferably for the following reasons. First, if one of the nostrils is blocked, the second will continue to deliver oxygen. Second, even flow rates for both nos
Brown Sanford
Colman Joshua L.
Levitsky Gershon
Dawson Glenn K.
Hoffman Wasson & Gitler
Oridion Medical Ltd.
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