Surgery – Diagnostic testing – Measuring or detecting nonradioactive constituent of body...
Patent
1998-02-12
2000-08-15
Winakur, Eric F.
Surgery
Diagnostic testing
Measuring or detecting nonradioactive constituent of body...
600328, A61B 500
Patent
active
061049387
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a procedure as defined and to a measuring apparatus for non-invasive determination of fractional oxygen saturation in blood. Moreover, the invention relates to a sensor, designed for use in conjunction with the measuring apparatus of the invention to collect measurement data about the patient.
Specifically, the present invention relates to the monitoring of the oxygenation level of the body in patient monitoring systems. Measuring the oxygen saturation of arterial blood in peripheral circulation is generally sufficient to determine the oxygenation situation and sufficiency of oxygen supply in the entire body. The oxygenation level of the human body can be estimated via oxygen saturation measurement of arterial blood either in a non-invasive manner using pulse oximeters or transcutaneous oximeters/blood gas analysers or in an invasive manner either by taking a sample of arterial blood and analysing in vitro blood gases (In Vitro Blood Gas/pH Analyzers) or performing an optic measurement on the blood sample using so-called CO-oximeters or haemoximeters (In Vitro Multiwavelength Oximeters).
Partial pressure measurements of gas in arterial blood samples and optic methods based on the absorption of light by blood samples are part of long-standing tradition, but clinical use of pulse oximeters only became common in late 1980's and the measuring principle itself is relatively new. There are numerous patents and patent applications relating to pulse oximeters. The most important of these as well as the most comprehensive general descriptions of prior art are found in patent specifications U.S. Pat. No. 4,653,498, U.S. Pat. No. 4,819,752, U.S. Pat. No. 4,407,290 and U.S. Pat. No. 4,832,484.
The prior-art technology described in the above-mentioned patent specifications, which is the basis of currently used equipment, is imperfect and inadequate for continuous and non-invasive monitoring of changes in the actual oxygenation level or degree of fractional oxygen saturation in a patient's blood. Although in vitro oximeters are in principle capable of measuring fractional oxygen saturation from a normal blood sample, the measurement is neither non-invasive nor continuous. On the other hand, pulse oximeters measure continuously and non-invasively, but they are not able to measure the actual degree of fractional oxygen saturation of blood and are therefore inadequate for situations where only a part of the total amount of haemoglobin in a patient is functional. Pulse oximeters measure fractional oxygen saturation assuming that the patient's blood composition is the same as that of a healthy, non-smoking person. A high dyshaemoglobin level, i.e. a high relative amount of haemoglobin not participating in oxygen transport, always involves a danger to the patient because current pulse oximeters produce an incorrect estimate of the oxygenation level of blood.
The cause of incorrect measurement lies in the measuring principle: Since pulse oximeters use only two different wavelengths of light for the estimation of oxygen saturation, only two different kinds of blood haemoglobin, viz. oxyhaemoglobin (HbO2) and deoxyhaemoglobin (Hb), can be accurately measured by this method. All other dyeing blood components (usually dyshaemoglobins or dyes used in clinical tests) have a disturbing effect on the measurement and can only be taken into account as average amounts. This type of average correction is generally made on the composition of healthy blood. However, the composition of normal blood may change in an unforeseen manner and without a readily identifiable cause. The blood composition of a patient with a critical illness may differ from the blood composition of a healthy person as a result of medication, the nature of the illness or a medical treatment or measurement. A new and significant treatment of this type is the so-called nitrogen oxide (NO) treatment, which may cause a considerable rise in the patient's methaemoglobin (MetHb) level. Another common case of incorr
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Arterial Oxygen Saturation by Non-Invasive Oximetry Technique: An Office Test for Determining Jeopardy of Status Asthmaticus, Leonard S. Girsh and Brian J. Girsh, Annuals of Allergy, vol. 42, Jan. 1979, pp. 14-16.
Huiku Matti
Weckstrom Kurt
Instrumentarium Oy
Winakur Eric F.
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