Cerebral oxygenation monitor

Details Cerebral oxygenation monitor Cerebral oxygenation monitor

2000-04-10

2002-09-17

Winakur, Eric F. (Department: 3736)

Surgery

Diagnostic testing

Measuring or detecting nonradioactive constituent of body...

C600S323000, C600S338000

Reexamination Certificate

active

06453183

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a method and apparatus for monitoring cerebral oxygenation (i.e., a Cerebral Oxygenation Monitor or COM), particularly in the intrauterine environment. The method includes measuring light scattering parameters of light directed through the cerebral cortex.
BACKGROUND
Fetal brain injury resulting from hypoxia and ischemia during labor is an important cause of death and long-term disability. However, little is known about fetal brain oxygenation and hemodynamics because there are currently no satisfactory clinical techniques for fetal monitoring. There is a need for a new method to assess fetal deep brain oxygenation.
With the United States experiencing unacceptably high infant mortality rates, national health objectives have targeted reductions in infant mortality, fetal death, low birth weight, and severe complications of pregnancy, along with reduction in severe mental retardation, as important goals to be achieved in this decade. However, the attainment of these goals has remained elusive, even with the rising cost of health care.
Obstetrical care continues to be more technology oriented than many other areas of health care. Risk factors are quickly identified, and patients are followed with an array of tools including electronic fetal monitoring (EFM), ultrasound, amniocentesis, and laboratory tests which were virtually unknown 20 years ago. Yet perinatal morbidity and mortality have not yielded to this intensive investment of resources. At least one form of neurologic handicap (cerebral palsy) may be on the rise. An example of perhaps the most obvious unintended and undesirable consequence of the use of surveillance methods has been the drastic increase in the cesarean delivery rate. While the rate is falling, there is still general agreement that the rate is too high and should be lowered if possible. In fact, the national health objectives now include a targeted reduction in the cesarean delivery rate.
As indicated, increasing expenditures for perinatal care have not led to a corresponding reduction in infant mortality, low birth weight deliveries, severe mental retardation, or birth defect rates in the United States. A principal explanation for this lack of progress is the scientific uncertainty surrounding the provision of perinatal care. Significant variation in the practice of medicine, and concomitant variation in health care costs, arise when there is insufficient scientific knowledge to support one alternative over another. Such is the case with the most feared aspect of perinatal morbidity: neurologic handicap, principally cerebral palsy, but also including mental retardation, learning disabilities and epilepsy. For over 100 years, the medical profession has assumed that the circumstances of birth predict which infants will develop cerebral palsy. Until recently, rigorous analyses had failed to confirm this assumption. A recent comprehensive review concluded that it is not possible to predict which babies are at risk for brain disorders and which of the at-risk babies will actually experience problems. Although a 1996 study found that there was an association between abnormal findings on EFM and the risk of cerebral palsy, the false-positive rate was very high.
Regrettably, there is currently no highly sensitive and specific technology to assess fetal well being. Therefore, a method that accurately and reliably categorizes fetal status has the potential to significantly improve perinatal outcomes while managing health care costs.
Intrapartum fetal evaluation is used to prevent neonatal illness and death as well as intrapartum fetal death. Intermittent auscultation was originally utilized for this purpose, and remains acceptable for monitoring “low risk” patients. EFM subsequently was touted as a method of evaluation that would lead to decreased cerebral palsy, neonatal and intrapartum death rates. Although it places less of a demand on nursing staff, allows continuous and objective recording of information (fetal and uterine), and allows improved detection of patterns of fetal distress that are missed by auscultation, its benefit over no monitoring has not been proven.
Fetal heart rate patterns of distress may be associated with fetal acidemia, hypoxemia and acidosis. Abnormal fetal heart rate patterns, although a good predictor of fetal distress, are not good predictors of cerebral palsy. EFM is reassuring when normal. When abnormal, correct diagnosis of the problem requires an attendant skilled in EFM interpretation and ancillary procedures such as fetal scalp stimulation and scalp pH monitoring, vibroacoustic stimulation, ultrasound, etc.
The drawback in these methods is that they do not provide a direct assessment of fetal brain oxygenation, which is ultimately the most important variable in determining whether an infant will suffer from long-term neurologic injury or succumb to death. A method of fetal evaluation for those infants with a distress pattern that would allow detection of cerebral hypoxia is needed. The EFM is a screening test. The diagnostic tests detailed above have lead to increasing cesarean section rates with no reduction in cerebral palsy and a minimal reduction in intrapartum death.
A testing modality that would allow clinicians a more direct method of evaluating cerebral oxygenation would target the hypoxic fetus and thus reduce the number of unnecessary cesarean sections performed for the misperception of “fetal distress,” and in turn decrease maternal morbidity and mortality, as well as length of hospital stay and, thus, lower medical costs.
An instrument according to different aspects of the present invention addresses at least three different clinical needs. The first is continuous non-invasive monitoring of fetal cerebral oxygenation during labor and delivery. This requires a small, unobtrusive, bedside instrument.
A second aspect of the invention is a postpartum imager. The imager has a position sensor on the probe and a high resolution video display. Images will resemble diagnostic ultrasound B-scans. The technology used in the postpartum imager utilizes identical laser light sources, detectors and signal processing as the COM. A three dimensional image is produced by overlaying many individual COM readings taken from different volumes of the newborn head on a display. The different sample volumes can be obtained in two ways. First, a source-detector pair can be positioned at different locations on the head similar to an ultrasound B-scan. Alternatively, an array of source-detector pairs can take a sequence of sample volumes similar to computed tomography.
The third aspect of the invention is an antepartum monitor. Because the instrument can penetrate 8-10 cm of tissue, fetal cerebral oxygenation images can be obtained through the mothers abdomen. The principle of the antepartum imager is identical to the postpartum imager. The specially conditioned laser light penetrates the additional soft tissue of the mother and the same banana shaped sample volume is measured. Roughly 50% of the middle of the sample volume is fetal cerebral tissue. Fetal tissue is differentiated from maternal tissue on the resulting three dimensional image by the dark outline of the fetal skull.
Comparison of the Present Invention with Fetal Pulse Oximeters
Fetal pulse oximeters have been in development for several years. This device utilizes a modification of adult finger probe transmission technology to perform reflectance pulse oximetry on intrauterine fetal cheeks. The probe is attached to the fetal cheek and held in place by pressure from the uterine wall. However, investigators outside of the United States have been evaluating fetal pulse oximeters for several years and conclude that the current generation of fetal pulse oximetry sensors is not improving the quality of combined monitoring of fetal heart rate and fetal scalp blood analysis. This is not the case for a COM according to the present invention as shown in the following comparison with the fetal pulse oximeter.
Feature
COM
Fetal Pulse Oxi

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