The present disclosure is directed to medical sensing devices. More specifically, the present disclosure is directed to a sensor device and method of use for measuring vital parameters of a fetus during birth.
Fetal monitoring has been used to prevent injury to the most vital and sensitive organs, such as the brain and the heart, by detecting a decreased oxygen supply to these organs before the onset of cell damage. Some causes of fetal hypoxia are umbilical cord compression, placental insufficiency or hypertonia of the uterus. Early examples of fetal monitoring are intermittent auscultation of fetal heartbeat, electronic monitoring of fetal ECG and heart rate, and scalp blood pH. These techniques are based on the assumption that fetal hypoxia, leads to fetal acidemia and also to specific pathologic fetal ECG and heart rate patterns. These indirect techniques, however, are unsatisfactory because it is only after hypoxia has occurred for some time that it is reflected in adverse changes in the heart rate or blood pH.
Fetal assessment has evolved to the direct measurement of fetal oxygen status using pulse oximetry. Pulse oximetry instrumentation, which provides a real-time measurement of arterial oxygen saturation, has become the standard of care for patient vital sign monitoring during anesthesia and in neonatal and adult critical care. A pulse oximetry system consists of a sensor attached to a patient, a monitor, and a lead connecting the sensor and monitor. The sensor typically has red and infrared light emitting diodes that illuminate a tissue site and a photodetector that measures the intensity of that light after absorption by the pulsatile vascular bed at the tissue site. From these measurements, the oxygen saturation of arterial blood can be calculated.
Pulse oximetry as applied to fetal intrapartum monitoring must overcome several significant and interrelated obstacles not faced by pulse oximetry as applied to adults, children, infants and neonates. These obstacles include attaching the sensor to a readily accessible tissue site, obtaining a representative measurement of central arterial oxygen saturation at that site, and calibrating the sensor. Pulse oximetry sensors are conventionally attached, for example, to an adult finger or a neonate foot using a self-adhesive mechanism that wraps around the tissue site. Sensor attachment to a fetus in this manner is impractical if not impossible. Further, the presenting portion of the fetus is typically the crown of the head, which yields only the fetal scalp as a readily accessible tissue site. A number of mechanisms have been developed to overcome these impediments to attachment of a pulse oximetry sensor to the fetus. These include suction cups, spiral clamps and vacuum devices for scalp attachment. There are also devices that slide beyond the fetus presenting portion, wedging between the uterine wall and the fetus.
U.S. Pat. Nos. 5,529,064; 5,911,690 and 5,865,737, incorporated by reference herein, by Rall and Kintza, disclose a scalp attachment mechanism used in conjunction with a fetal ECG sensor. The sensor assembly consists of a fetal sensor, a driver within a guide tube to facilitate placement, and interconnecting conductors for communication signals to a monitor. The fetal sensor has a spiral probe attached to a sensor base. The probe is utilized to attach the sensor to the fetal scalp and also functions as an ECG probe. The sensor base is removably connected to the driver. The driver is movably contained within the guide tube. The interconnecting wires are attached at one end to the sensor base, and one of the conductors is electrically connected to the probe.
The present invention is directed to a medical sensor device configured to be temporarily secured at a tissue field, such as a fetal skull, via a spiral probe. The spiral probe functions to both secure the sensor in place and provide an electrode for ECG purposes. The sensor device also includes a housing carrying a light detector and light source utilized during a pulse oximetry process. In some embodiments the spiral probe is non-uniform and includes portions with different diameters and different spiral pitches. In one embodiment, the spiral probe includes a stop element which limits the extent to which a drive rod can be inserted into the probe. In another embodiment, the spiral probe includes a cross bar which engages a portion of the drive rod during placement of the sensor probe. In yet another embodiment, the spiral probe includes a collapsed portion adapted to engage tissue after a predetermined rotation of the probe into the tissue field. The collapsed portion can provide an increased rotational resistance to the drive rod leading to rotational disengagement of the drive rod from the spiral probe. In one embodiment, the spiral probe is directly coupled to an end of the drive rod. The probe diameter can expand with an increase in torque applied to the drive rod, leading to a disengagement of the drive rod from the probe. In one embodiment a spiral probe and drive rod define a detent mechanism whereby upon reaching a predetermined torque the drive rod is disengaged from the probe and rotates without further entry of the probe into the tissue field.
The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims. The novel features which are believed to be characteristic of the invention, both as to its organization and method of operation, together with further objects and advantages will be better understood from the following description when considered in connection with the accompanying figures. It is to be expressly understood, however, that each of the figures is provided for the purpose of illustration and description only and is not intended as a definition of the limits of the present invention.
For a more complete understanding of the present invention, reference is now made to the following descriptions taken in conjunction with the accompanying drawing, in which:
Fetal sensor 10 includes a sensor housing 14 which carries a spiral probe 15, light emitter 16 and light detector 17, which may be a photodiode. Spiral probe 15 is attached to a front end of sensor housing 14 and extends away from the housing 14. Lead 11 is connected at one end to sensor housing 14 and connects to monitor 12 at the other end. Lead 11 transmits signals between monitor 12 and sensor 10. Monitor 12 controls operation of sensor 10 and processes light intensity signals from the light detector 17, providing a display and/or record of the resulting oxygen saturation, pulse rate and plethysmograph. In one embodiment, monitor 12 receives ECG signals from sensor device 10 and provides an interface to a remote fetal ECG monitor, such as via lead 18 (
Lead 11 is in one embodiment a series of wires that are connected to a remote monitoring device. The remote monitoring device can be in the same room as the patient or can be located elsewhere. However, in some embodiments a wireless communication component may be provided upon or within sensor device 10 to wirelessly communicate to a remote monitor via, for example, one of many known medical device wireless protocols (e.g., BLUETOOTH).
Light detector 17 and light emitter 16 are mounted on a surface of flexible circuit 30. One embodiment of flex circuit 30 is shown in
Detector 17 and emitter 16 are mounted on one side of the flex circuit 30 substrate. Detector 17 and emitter 16 may be partially enclosed in an encapsulant. Detector 17 is mounted so that the active, light collecting region of the photodiode faces the same housing side as spiral probe 15. Emitter 16 contains a pair of light emitting diodes (LEDs), one of which emits a narrow band of red wavelength light and the other of which emits a narrow band of infrared wavelength light. These emitters are mounted so that the active regions of the LEDs face the same housing side as spiral probe 15.
Spiral probe 15 includes collapsed portion 153, which in this embodiment is approximately 360 degrees, or one turn, from the sharpened end of probe 15. As described in detail hereinafter, collapsed portion 153 limits the extent to which spiral probe 15 enters the fetal tissue field. Spiral probe 15 includes a portion 154 having a greater diameter than a portion 155 proximate to the sharpened end. Enlarged portion 154 engages conductive ring 42 of flex circuit 30 to form a portion of the ECG circuit. As spiral probe 15 is rotated into engagement with the tissue field, portion 154 remains in contact with conductive ring 42 so that regardless of the rotational displacement of spiral probe 15 relative to housing 14, an electrical (ECG) circuit remains intact.
During placement of sensor 10 to a tissue field, sensor 10 is introduced through the vagina and attached to the presenting part of the fetus during labor. When sensor 10 is pressed against fetal tissue, the peripheral zone of housing base 22 undergoes elastic deformation into a depressed state. With base 22 in the depressed state, rod 26 is rotated via manipulation of handle 28. With the opposite end of rod 26 engaging spiral probe 15, this rotation of rod 26 results in a 1:1 rotation of spiral probe 15 until axial or rotational disengagement as subsequently described herein. In one embodiment, rotation of rod 26 during sensor 10 placement causes rotation of spiral probe 15 but not housing 14 or lead 11.
As the sharpened end of spiral probe 15 pierces and rotates into the fetal tissue, spiral probe 15 develops a spring force tending to retain housing 14 in place against the fetal tissue. The peripheral zone of base 22 remains engaged on the fetal tissue with surfaces of light emitter 16 and detector 17 in contact or near contact with the tissue field. In one embodiment, the spiral probe is rotated approximately 1 turn into the fetal scalp and the elastic base 22 engages the fetal scalp with an elastic preload.
The unique geometry of spiral probe 15 and rod 26 limits the extent to which spiral probe 15 engages the tissue field. For example, as spiral probe 15 is rotated into the tissue field, the tissue engages the collapsed portion 153 of spiral probe 15. Further rotation causes the tissue field to engage the tip of drive rod 26 and bias the drive rod 26 outwardly and into axial disengagement with spiral probe 15. Drive rod 26 and spiral probe 15 may also be disengaged by application of a pinch force applied to tissue engaging the collapsed portion of spiral probe 15. The pinch force can cause an increased rotational resistance. An increase in rotational resistance can also be exhibited as the spiral probe tip engages denser tissue near the skull. In either case, an increased rotational resistance can result in disengagement of spiral probe 15 from drive rod 26. For example, increased rotational resistance may cause portions of spiral probe 15 to expand radially and release engagement between cross bar 152 and channel 171 of rod 26, at which point rod 26 may rotate without further rotation of spiral probe 15, i.e., the 1:1 rotational relationship between rod 26 and spiral probe 15 is no longer present. Spiral probe 15 and drive rod 26 thus define a detent mechanism whereby upon reaching a predetermined torque, drive rod 26 is released to rotate without further entry of spiral probe 15 into the tissue field.
Upon successful placement of sensor 10 to the tissue field, rod 26 is axially disengaged from sensor 10. In one embodiment, an axial force is applied at the end of rod 26 by compression of retractor 29. Rod 26 and tube 25 can then be withdrawn leaving sensor 10 in place.
In general, the pulse oximetry sensor used in the preferred embodiment of the invention is conventional. Light from the light emitters 16 is directed into the fetal epidermis and reflected back to detector 17. The light transmitted is attenuated by the fetal tissue and then received by detector 17. Processing circuitry associated with the pulse oximetry sensor determines the oxygen saturation of the blood based on the attenuation of the red and infrared light beams. The light beams received by light detector 17 each have a pulsatile and nonpulsatile component. The nonpulsatile components are due to the attenuation of time invariant physiologic blockers such as skin and bone. This is referred to as the DC component. The pulsatile component, on the other hand, represents the attenuation of light during arterial blood flow. This signal is time varying and is often referred to as the AC component. Additionally, the pulsatile components are different for red and infrared light. This difference is due to the fact that hemoglobin and oxyhemoglobin have different optical characteristics. Both hemoglobin and oxyhemoglobin behave similarly with respect to infrared light; however, for red light, the absorption coefficient for hemoglobin is quite different than that of oxyhemoglobin. Thus, the difference in the pulsatile components can be used to derive the level of oxyhemoglobin, and the oxygen saturation of the blood can be computed based on the Lambert-Beers law. In one embodiment, sensor device 10 obtains signals.
The unique aspects of sensor 10, especially spiral probe 15 and its engagement with flex circuit 30 and drive rod 26, fulfill in an excellent manner the objects of a reliable and durable means of attachment to the fetal tissue with acceptable reception of signals for the purpose of measuring vital parameters of a fetus during labor and delivery.
Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the disclosure of the present invention, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the present invention. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.