GB2216804A

GB2216804A - Intrauterine probe

Info

Publication number: GB2216804A
Application number: GB8906582A
Authority: GB
Inventors: Ian Alexander Sutherland; Nigel John Randall; Philip James Steer
Original assignee: ST MARYS HOSPIT MED SCHOOL
Current assignee: ST MARYS HOSPIT MED SCHOOL
Priority date: 1988-03-29
Filing date: 1989-03-22
Publication date: 1989-10-18
Anticipated expiration: 2009-03-22
Also published as: GB8906582D0; GB2216804B

Abstract

An improved intrauterine probe for monitoring the condition of the fetus, e.g. the fetal and maternal heart rates during labour comprising an elongate, flexible, flattened body member having at least one sensor mounted in each flat face of the body member, the body member being sufficiently directionally stable to be inserted into the vaginal tract and through the cervical OS and capable of being guided around the fetus without twisting. The sensors may be electrodes, a temperature sensor, or a pressure transducer. <IMAGE>

Description

IMPROVED INTRAUTERINE PROBE This invention relates to an intrauterine probe which is suitable for use in monitoring the condition of the fetus and of the mother during labour.

In our co-pending U.K. Patent Application No. 8723605 (Publication No. 2195897), there is described an intrauterine probe which enables fetal heart rate (FHR) and other parameters to be monitored non-invasively.

The probe described in our above-mentioned prior application is characterised by a flattened form which is floppy and comfortable enough to be inserted into the vaginal tract and through the cervical OS without discomfort, to take up a disposition where it lies alongside the fetus in utero, but at the same time, can be directed along a desired path and has sufficient transverse stiffness so as not to twist or turn over during or after insertion.

Electrodes for measuring the fetal heart rate (FHR) may be embedded in the body of the probe and in a preferred form, the surfaces of the electrodes lie approximately in the plane (or slightly below the plane) of one face of the body member of the probe. As also described in our prior application, the probe may additionally or alternatively incorporate a sensor, e.g. a pressure sensor, so that the intrauterine pressure (IUP) can be monitored.

As alluded to in our prior application, one of the problems in using any intrauterine probe to monitor FHR is to distinguish fetal signals from maternal signals and from background noise. In the case of fetal scalp clips, it is hoped that the direct physical attachment will mean that the fetal signal "drowns" the maternal and background signals. Although close contact can be achieved to enhance signal detection, using the probe described in our prior application, it was recognised that this was not essential for its operation. Because the amniotic fluid is an effective electrical conductor it can provide the necessary electrical path from the fetal skin to the electrodes. While this results in lower maternal and fetal signal levels they can be discriminated by 'R' wave width recognition using the signal processing technique described in our above prior application.

It has now been realised that the 'directionality' of the intrauterine probe described in our prior application can be further exploited by providing electrodes (or other types of sensors) on both of its flat surfaces.

According to one aspect of the present invention there is provided an intrauterine probe for monitoring the condition of the fetus during labour which comprises an elongate flexible, flattened body member having a rounded distal endthaving at least one sensor mounted in each flat face of the body member, said body member being sufficiently directionally stable to be insertable into the vaginal tract and through the cervical OS and capable of being guided around the fetus without twisting.

Thus, for example, an electrode for detecting fetal heart rate (FHR) may be located in one face of the sensor, while an electrode located in the other face can be arranged to detect maternal heart rate (MHR). Because of the directional stability of the probe during and after insertion, it is a simple matter to ensure that the electrodes intended for detecting FHR will face the fetus, while the electrodes for detecting MHR will face away from the fetus. A predominate MHR signal will be detected by the electrodes facing away from the fetus and the wave form of this known MHR signal can be used to assist in discriminating the FHR from the mixed FHR and MHR signals picked up by the electrodes facing the fetus.

It may be advantageous to locate sensors for other parameters via the probe, either in addition to electrodes for detecting FHR and MHR or as an alternative. For example, it may be desirable to monitor maternal and fetal temperature. This can be done independently by locating fetal and maternal temperature sensors on opposite sides of the probe so that a temperature change in the mother or fetus can be rapidly detected independently.

Alternatively, an optical sensor may be employed to detect, e.g. meconium and/or fetal blood oxygen levels when used as a trans-cutaneous oximeter. The probe may include one or more pressure transducers.

The construction of the probe may be similar to that described in our above-identified co-pending application.

The construction of one example of an intrauterine probe in accordance with this invention will be apparent from the following description and accompanying drawings in which: Figure 1 is a perspective view of an embodiment of a probe in accordance with the invention, Figure 2 is a cross-sectional view taken on the line II-II in Figure 1 and Figure 2A is a cross-sectional view taken on the line IIA-IIA in Figure 1.

Referring to the drawings, the probe comprises an elongate body 1 about 40 to 50 cms in total length and having a rounded distal end 22. As best seen in Figures 2 and 2A, the probe has a flattened configuration with rounded edges 2,3 and generally flat upper and lower faces 4,5. Typically, the probe is about 1 to 2 cm wide and about 3 mm thick. A flexible printed circuit board 6 carries spaced electrodes e.g. of stainless steel 7, 8, 9 & 10 each having a domed head 11 and is encapsulated in a soft, flexible plastics potting compound, such as a 2-part polyurethane composition. The dimensions and inherent flexibility of the plastics material are such that when the probe is inserted into the uterus with one side facing the fetus, there is no tendency for the probe to twist.

The particular potting composition employed was a 2-part polyurethane composition obtainable from Emerson & Cumming Ltd. 866 Uxbridge Road, Hayes, Middlesex, under the trade name CPC 19 flexible polyurethane potting compound or from Devcon under the trade name Devcon Flexane 80.

Probes having a stiffness (Young's Modulus) in the range of 1 to 10 mega Newtons per square metre are suitable.

As shown in Figure 2, the domed head 11 of each electrode 8 is effectively shrouded by rounded portions 12 & 13 of the insulating material of the body. The surface of the domed portion 11 preferably lies substantially in the same plane as the flat face 5a of the body or slightly above or below.

Figure 1 shows one surface of the probe, e.g. the surface which is intended to face the fetus. This surface may be marked, e.g. colour-coded, so that the obstetrician can readily identify the side which is to be inserted so that it faces the fetus.

Figure 2 shows a section through the probe of Figure 1, which passes through the electrode 8 along the line II-II.

Figure 2A shows a section through the probe along the line IIA-IIA. It will be apparent from Figure 2A that the face 5 which cannot be seen in Figure 1 is also provided with electrodes 8A. Electrodes 8A are similarly formed with domed portions 11 which preferably lie substantially in the same plane as flat face 5 of the body or slightly above or below. One or both faces 5 & 5a of the probe may have one or more electrodes and/or other sensors. In the case where the side 21 is intended in use to face the fetus, the electrodes 8A would be intended for measurement of MHR. Pressure sensor 19 may be located on either surface but may be more conveniently located on the surface which faces away from the fetus.

The construction of the probe is generally as described in our co-pending application No. 8723605 (Publication No. 2195897). Where appropriate the same reference numerals are used in the drawings as in the drawings in our co-pending application No. 8723605 and indicate equivalent parts of the probe. Thus, the electrodes 7, 8, 8A, 9 and 10 are mounted on a flexible printed circuit board and the whole structure encapsulated in a potting compound, such as 2-part polyurethane composition as described in our above co-pending application. Probes having a stiffness (Young's Modulus) in the range of 1 to 10 mega Newtons per square metre are preferred.

The probe of the present invention is used in the manner described in our co-pending patent application No.

8723605 (Publication No. 2195897). Processing of the signals from the probe is carried out as described in our co-pending application (especially in connection with Figure 6), utilising as an input, the signals derived from electrodes on each face of the probe.

Claims

1. An intrauterine probe for monitoring the condition of the fetus during labour which comprises an elongate flexible, flatte#ned body member having at least one sensor mounted in each flat face of the body member, said body member being sufficiently directionally stable to be inserted into the vaginal tract and through the cervical OS and capable of being guided around the fetus without twisting.

2. A probe according to claim 1 in which the body member has a bending stiffness about an axis transverse to the plane of the body member of between 1 and 10 mega 2 Newtons/m

3. A probe according to claim 1 or 2 in which the portions of material surrounding the sensors are formed from a resilient foam material having non-communicating cells.

4. A probe according to any one of the preceding claims in which the portions of material bounding the sensors have a rounded upper surface in cross-section.

5. A probe according to any one of the preceding claims which has at least two sensors spaced longitudinally thereof in at least one flat face of the body member.

6. A probe according to any one of the preceding claims having a distal sensor.

7. A probe according to any one of the preceding claims in which the body member is formed from an electrically insulating material.

8. A probe according to claim 8 in which the insulating material is a polyurethane.

9. A probe according to any one of the preceding claims which has a plurality of sensors in each flat face of the body member, the sensors being spaced over a distance which, in use, is sufficient to encompass the fetal head, neck and back.

10. A probe according to any one of the preceding claims having a distal sensor and two or more additional sensors located in a group, the spacing lengthwise of the body member between the distal sensor and the proximal additional sensors being greater than the spacing between additional sensors in the group.

11. A probe according to any one of the preceding claims in which said sensors comprise a pressure transducer.

12. A probe according to any one of the preceding claims in which said sensors comprise a temperature sensor.

13. A probe according to claim 10 in conjunction with a processor which is adapted to distinguish between signals representing fetal heart rate (FHR) and maternal heart rate (MHR).

14. A method of monitoring FHR during labour which comprises introducing into the cervix a probe comprising an elongate, flexible, flattened body member formed from electrically insulating material, said body member being sufficiently directionally stable to be inserted into the vaginal tract and through the cervical OS and capable of being guided around the fetus without twisting, and having at least one electrode located in each face thereto and analysing the signal output from the electrodes by discriminating the fetal heart rate from the maternal heart rate on the basis of difference in R wave signal width or frequency.