GB2410442A

GB2410442A - Foetal scalp electrode with orientation marking

Info

Publication number: GB2410442A
Application number: GB0501628A
Authority: GB
Inventors: Stephen George Trotman
Original assignee: Surgicraft Ltd
Current assignee: Surgicraft Ltd
Priority date: 2004-01-28
Filing date: 2005-01-27
Publication date: 2005-08-03
Anticipated expiration: 2025-01-27
Also published as: GB0501628D0; GB2410442B

Abstract

A foetal scalp electrode (fig 1) has a connector 1 and a head member 2 connected via an electrically conductive helical spring 3 preferably having an outer insulator 18. The head 2 has a cavity 9 in which an arcuate needle 10 may emerge to connect with the head of a foetus for monitoring. The connector 1 can be rotated such that the torsion in the spring can rotate the needle 10 which is mounted to the spring 3 via a radial conductive arm 11 such that the needle can be retracted or extended. The head 2 has a flat side 13 from which the needle 10 emerges via two holes (12, 14 figs 4, 5). An insulated wire 6 is connected to the needle 10 and passes through the spring 3 to the connector 1. Leads 24, 27 to monitoring equipment enter the connector and are connected to the spring 3, 4 and to the wire 6, 7 at terminals. The connector 1 is provided with a orientation marker 31 (fig 1, 6, 7) so that the orientation of the flat side of the head can be easily known when placing the electrode on the foetal scalp.

Description

241 0442 l

FETAL SCALP ELECTRODES

This invention relates to foetal scalp electrodes, e.g of the type described in GB-A-1316072 comprising an electrical connector, a head member of electrically insulating material, an electrically conductive helical spring with a terminal at one end in the electrical connector and with the other end secured to the head member, and an electrically conductive wire with a terminal at one end in the electrical connector, the wire extending through an insulating sheath inside the helical spring and the other end of the wire being in a cavity in the head member and provided with an electrically conductive arcuate needle on an electrically conductive arm extending radiallyfrom the l () wire, with the arcuate needle normally urged, by torsion in the helical spring through a hole between the cavity and the outside of the head member, and with the point of the needle looping back to the head member; or as described in GB-A-1523263 in which the outside of the head member is provided with a concave surface facing oppositely to the flat surface containing the hole through which the arcuate needle is urged.

With the head member of such an electrode held (as by forceps In one hand, in the case of GB-A-1316072, or by one hand with a finger resting in the concave surface described in GB-A-1523263) with its flat surface in close proximity to the foetal scalp, the electrical connector is rotated (by the other hand), with respect to the head member in opposition to the torsion in the helical spring whereby the arcuate needle is withdrawn through the hole into the cavity in the head member, the head member then being held against the foetal scalp, and the electrical connector returned relative to the head member, whereby the arcuate needle is forced back out through the hole and through the foetal scalp, the looping of the point of the needle back to the head member of the electrode and the torsion applied by the helical spring ensuring secure attachment of the electrode to the foetal scalp Then, with the electrical connector connected to monitoring equipment, the wire carries the signal picked up by the needle hooked in the foetal scalp, and the helical spring serves (in a secondary role) as a screen for the signal carrying wire.

To release the electrode from the foetal scalp, the electrical connector is rotated with respect to the head member in opposition to the torsion in the helical spring while the head member is held as before, whereby the arcuate needle is withdrawn from the foetal scalp and into the cavity, and the head member is moved away from the foetal scalp before being released for the arcuate needle to spring back to its position partly outside the head member.

A second hole has been provided between the cavity and the outside of the head member for the point of the needle to enter when in said normal position looping back to the head member, to afford greater secureness when in use and shielding of the point when not In use.

The tubular torsional spring member has consisted of an outer electrically conductive wire in the form of a helical spring with a terminal at one end in the electrical connector and with an insulating sheath (e.g. of polytetrafluoroethylene, so as to afford self-lubrcation) inside the helical spring to insulate it from the central wire. The helical spring served both to make electrical contact with the mother and as a screen for the central signal-carrying wire.

The connector has comprised a generally cylindrical two-part body of electrically insulating material with a spigot and socket coupling, with a pair of axial holes In one of the body parts (conveniently the one with the spigot) for passage of the central and outer wires, which have been electrically joined to insulated leads passing through an axial hole in the other body part by means of pins pressed into the holes with the central and outer wires before fitting and sealing together of the body parts.

The primary object of the present invention is to improve the aforesaid foetal scalp electrodes from a user viewpoint while a secondary object is to improve them from a manufacturing viewpoint.

According to one aspect of the present invention a foetal scalp electrode comprises an electrical connector, a head member of electrically insulating material, an electrically conductive helical spring with a terminal at one end in the electrical connector and with the other end secured to the head member, and an electrically conductive wire with a terminal at one end in the electrical connector, the wire extending through an insulating sheath inside the helical spring and the other end of the wire being in a cavity in the head member and provided with an electrically conductive arcuate needle on an electrically conductive arm extending radially from the wire, with the arcuate needle normally urged, by torsion in the helical spring through a hole between the cavity and the outside of the head member, and with the tip of the needle looping back to the head member, the connector also being provided with an indicator of its orientation with respect to the head member. Thus, with the connector held in one hand with the indicator visible, a finger of the other hand can press the non-visible head member to the foetus confidently with the flat surface towards the foetal scalp.

For best visibility, the indicator is preferably located at least at the end of the connector nearest to the head member, and may be formed by a projection (such as a fin or web) on the connector disposed symmetrically to each side of a plane orthogonal to the flat surface of the head member; whereby, with the indicator projecting upwards it is evident that the flat surface of the head member faces downwards However, the indicator may be provided at each end of the connector body or it may extend along the whole length of the connector body.

According to another aspect of the present invention, the connector may have a cross-section having one dimension appreciably greater than another cross-sectional dimension, whereby the connector can be held with greater security than a generally cylindrical connector as In GB-A- 1316072 or GB-A-1523263, especially when the surface of the connector is made slippery by fluids, e.g. amniotic fluid. However, the connector is preferably also provided with rounded longitudinal ribs (e.g. similarto those on the connectors in GB-A-1316072 and GB-A-1523263) to enhance the grip.

l O The larger cross-sectional dimension Is preferably in the plane orthogonal to the flat surface of the head member, as this makes for convenience in gripping the connector between thumb and forefinger applied to 'flatter' sides of the connector.

According to a further aspect of the present invention, the connector body may be formed in two parts with a longitudinal interface, at least one of which parts has l 5 longitudinal channels within which are housed the connected ends of the helical spring and central wire and of the leads for connection to monitoring equipment, and between the respective channels are provided longitudinal formations for effecting alignment of the two parts before securing by adhesive. Integral projections may also be provided on each part to fit in holes in the other part to effect Initial location of the two parts together Semi-cylindrical portions at the ends of the parts provide for entry, at one end, of the helical spring and the insulating sheath between the helical spring and the central wire, and, at the other end, of the insulated leads for connection to montonng equipment The connections between the ends of the helical spring and central wire and of the leads for connection to monitoring equipment may be effected by specalised bonding, e.g., resistance welding under pressure and high temperature thus improving manufacture by reducing the number of components e.g. removing the need for connecting pins in the connector as in GB-A-131 6072 or GB-A-1523263, and permitting the bonded connections to be inserted mechanically into the channels in one connector body part A second advantage is the improved performance of the electrode by providing a clearer heartbeat trace by reducing the level of electrical noise by reducing the number of interface surfaces and dissimilar materials in the joint. Reduced noise is also achieved by the resistance welding vaporising any trapped impurities in the l O connections, not achieved in mechanical or low temperature joints such as soldering.

The resistance welding also affords very strong connections significantly reducing the risk of accidental separation during the manufacturing process, which being machine controlled can be mechanised and ensures the process conditions are continually within specification thus guaranteeing a good connection every time. For added secureness, l S end portions of the central wire and the helical spring within the channels are bent at right angles and are engaged in slots perpendicular to the respective channels.

Although the arcuate needle may be provided with a point so as to pass through the scalp, the tip of the needle may be blunt, e.g., rounded, so as to merely nip a small portion of scalp between itself and the flat underside of the head member, in which case a second hole between the cavity and the outside of the head member need not be provided.

An embodiment of the invention and a modification thereof will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a general view of a foetal scalp electrode in accordance with the invention; Figure 2 is a fragmentary elevation showing the other side of the head member of the electrode of Figure 1; Figure 3 is an enlarged fragmentary section taken from the line 3-3 of Figure 2; Figure 4 is a section on the line 4-4 of Figure 3, Figure 5 corresponds to Figure 4 but shows the arcuate needle of the electrode withdrawn into the head member; Figure 6 Is an enlarged fragmentary section taken from the line 6-6 of Figure 1; and Figure 7 is an enlarged (about four times actual size) isometric view of a modified form of connector viewed from one end; Figure 8 is an elevation of the other end of the connector of figure 7; figure 9 is an elevation of the inside of one part of the connector of Figures 7 and 8; Figure 10 is an elevation of the inside of the other mating part of the connector, and Figure 11 corresponds to Figure 9 but twice the size and shows the ends of the helical spring and central wire secured to the leads of a cable for connection to the monitoring equipment.

The foetal scalp electrode shown in Figures 1 to 6 comprises an electrical connector 1, a head member 2 of electrically insulating material (e.g nylon), an outer electrically conductive wire in the form of a helical spring 3, with a terminal 4 in the electrical connector constituted by a straightened end portion of the spring, and with another straightened end 5 secured to the head member, and a central electrically conductive wire 6 with a terminal 7 at one end in the electrical connector, the central wire extending through an insulating sheath 8 (e.g. of polytetrafluoroethylene, so as to be self-lubricating) inside the helical spring 3, and the other end of the wire being in a cavity 9 In the head member and provided with an electrically conductive arcuate needle 10 on an electrically conductive arm 11 radial to the wire 6, with the arcuate needle normally urged, by torsion in the helical spring, out of the cavity through a hole 12 between the cavity and a flat surface 13 on the outside of the head member 2, and l O with the point of the needle looping back into the head member through a second hole 14 provided between the cavity 9 and the flat surface 13 for the point of the needle to enter, to afford greater secureness when in use (as will be described presently) and shielding of the point when not in use.

The outside of the head member 2 is also provided with a concave surface 15 l 5 facing oppositely to the flat surface 13, and the concave surface is formed with the ribs 16 extending transversely with respect to the axis of the helical spring 3, which ribs deter a finger engaged therewith from sliding along the head member in a direction away from the electrical connector 1 when the adjacent fingers engage the sides 17 of the head member.

The helical spring 3 is covered with insulating material 18 over most of its length, to prevent abrasion, the exposed portion of the helical spring, for making contact with the mother, being adjacent the head member 2.

The connector 1, (see figure 6) comprises a two-part body of electrically insulating material (e g. nylon), with a spigot 19 on one body part 20 and a socket 21 in the other body part 22 for coupling the body parts together, and with a pair of axial holes 23 in the body part 20 for passage of the central and outer wire terminals 7 and 4, which are electrically joined to insulated leads 24 passing through an axial hole 25 in the body part 22 by means of pins 26 pressed into the holes 23 before fitting and sealing together of the body parts. The pins 26 are preferably gold-plated, so as to ensure excellent electrical joints, and the pins are tubular, to enable bared ends 27 of the leads 24 to be led through them and bent back before insertion into the holes containing the central and outer wires Relative rotation of the body parts 20, 22 is prevented, whilst sealing of them together is being effected, by means of a projection l O 28 on the body part 20 engaged with a notch 29 in the body part 22 Ribs 30 extending longitudinally of the body parts of the connector 1 assist in gaining a good grip The leads 24 are for connection to monitoring equipment (not shown).

With the head member 2 of the electrode held, by one hand with a finger resting in the concave surface 15 with the ribs 16 and the adjacent fingers gripping the sides l 5 17, in close proximity to the foetal scalp, the electrical connector 1 is rotated, by the other hand with respect to the head member, in opposition to the torsion in the helical spring 3, whereby the arcuate needle 10 is withdrawn through the hole 12 into the cavity in the head member, which then has its flat surface 13 held against the foetal scalp by pressing with the finger resting in the concave surface 15, and the electrical connector 1 returned relative to the head member 2, whereby the arcuate needle 10 is forced back out through the hole 12 and through the foetal scalp, the looping of the point of the needle 10 back to the head member and through the hole 14, and the torsion applied by the helical spring 3, ensuring secure attachment of the electrode to the foetal scalp To release the electrode from the foetal scalp, the head member 2 is held (as before) and the electrical connector 1 is rotated with respect to the head member in opposition to the torsion in the helical spring 3, whereby the arcuate needle 10 is withdrawn from the foetal scalp and into the cavity 9, and the head member is moved away from the foetal scalp before being released for the arcuate needle to spring back to its position partly outside the head member In accordance with one aspect of the present invention, the connector 1 is provided with an Indicator of its orientation with respect to the head member 2 comprising web-like projections 31, 32 (see Figures 1 and 6) at respective ends of the connector body disposed symmetrically to each side of a plane orthogonal to the flat surfaces 13 of the head member; whereby, with the indicator projections 31, 32 projecting upwards it is evident that the flat surface of the head member faces downwards; and thus, with the connector 1 held in one hand with the indicator projections visible, a finger of the other hand can press the non-vsble head member to the foetus confidently with the flat surface towards the foetal scalp.

In accordance with another aspect of the present invention, the connector 1X shown in Figures 7 and 8 has one cross-sectional dimension appreciably greater than another cross-sectonal dimension, whereby the connector 1 X can be held with greater security than a generally cylindrical connector such as the connector 1 seen in Figures 1 and 6. However, the connector 1X is also provided with rounded longitudinal ribs 30 to enhance the grip The larger cross-sectional dimension of the connector 1 X is seen to lie in the plane about which the projections 31, 32 lie symmetrically orthogonal to the flat surface 13 of the head member 2, as this makes for convenience in gripping the connector 1X between thumb and forefinger applied to 'flatter' sides of the connector In accordance with a further aspect of the present invention, the connector body 1 X is formed in two parts 33,34 (see also Figures 9 and 10) with a longitudinal interface (conveniently coincident with the aforesaid orthogonal plane) part 33 of which has channels 36, 37 within which are housed (as can be seen In Figure 11) the connected ends 4,7 of the helical spring 3 and central wire 6 and 27,27 of the Insulated leads 24 for connection to monitoring equipment (not shown), and between the channels are provided longitudinal formations 38, 39 for effecting alignment of the two parts 33, 34 before securing with adhesive (not shown). Integral projectors 40 are also provided on each part to fit in holes 41 in the other part to effect initial location of the two parts together. Semi-cylndrical portions 42, 43 at the ends of the parts 33, 34 provide for l 0 entry, at one end, of the helical spring 3 and the insulating sheath 8 between the helical spring and the central wire 6, and, at the other end, of the insulated leads 24 for connection to monitoring equipment The connections between the ends 4, 7 of the helical spring 3 and the central wire 6 and 27, 27 of the leads 24 are preferably effected by resistance welding under pressure and high temperature, for the reasons stated above. For added secureness, end portions 44,45 of the central wire 6 and helical spring 3 within the channels 37,36 are bent at right angles and are engaged In slots 46, 47 respectively perpendicular to the respective channels.

It is to be noted that the insulating sheath 18 seen in Figures 1 to 3 and 6 is not included in Figure 11, because it has been found not to be necessary to prevent abrasion, while enabling the helical spring 3 to make contact with the mother anywhere along its length.

Claims

1 A foetal scalp electrode comprising an electrical connector, a head member of electrically insulating material, an electrically conductive helical spring with a terminal at one end in the electrical connector and with the other end secured to the head member, and an electrically conductive wire with a terminal at one end in the electrical connector, the wire extending through an Insulating sheath inside the helical spring and the other end of the wire being in a cavity In the head member and provided with an electrically conductive arcuate needle on an electrically conductive arm extending radially from the wire, with the arcuate needle normally 1() urged, by torsion in the helical spring through a hole between the cavity and the outside of the head member, and with the tip of the needle looping back to the head member, the connector also being provided with an indicator of its orientation with respect to the head member.

2. A foetal scalp electrode as in Claim 1 wherein the indicator is located at least at the end of the connector nearest to the head member

3. A foetal scalp electrode as in Claim 2, wherein the indicator is formed by a projection on the connector disposed symmetrically to each side of a plane orthogonal to the flat surface of the head member.

4. A foetal scalp electrode as in Claim 2 or Claim 3, wherein the indicator is provided at each end of the connector body.

A foetal scalp electrode as in Claim 2 or Claim 3, wherein the indicator extends along the whole length of the connector body.

6. A foetal scalp electrode as in any one of Claims 1 to 5, wherein the connector has a cross-section having one dimension appreciably greater than another cross sectional dimension.

7. A foetal scalp electrode as in Claim 6, wherein the connector is provided with rounded longitudinal ribs.

8 A foetal scalp electrode as in Claim 6 or Claim 7, wherein the larger cross-sectional dimension is in the plane orthogonal to the flat surface of the head member.

9. A foetal scalp electrode as in any one of Claims 1 to 8, wherein the connector body is formed in two parts with a longitudinal interface, at least one of which parts has longitudinal channels within which are housed the connected ends of the helical spring and central wire and of the leads for connection to monitoring equipment and l O between the respective channels are provided longitudinal formations for effecting alignment of the two parts before securing by adhesive.

10. A foetal scalp electrode as in Claim 9 wherein integral projections are also provided on each part to fit in holes in the other part to effect initial location of the two parts together.

11. A foetal scalp electrode as in Claim 9 or Claim 10, wherein semicylindrical portions at the ends of the parts provide for entry, at one end, of the helical spring and the insulating sheath between the helical spring and the central wire, and, at the 2() other end, of the insulated leads for connection to monitoring equipment.

12 A foetal scalp electrode as In any one of Claims 9 to 11, wherein connections between the ends of the helical spring and central wire and of the leads for connection to monitoring equipment Is effected by resistance welding under pressure and high temperature 13 A foetal scalp electrode as in any one of Claims 9 to 12, wherein end portions of the central wire and the helical spring within the channels are bent at right angles and are engaged in slots perpendicular to the respective channels 14. A foetal scalp electrode with a connector substantially as herenbefore described with reference to Figures 1 to 6 of the accompanying drawings A foetal scalp electrode substantially as hereinbefore described with a connector as in Figures 7 to 11 of the accompanying drawings.

11. A foetal scalp electrode as in Claim 9 or Claim 10, wherein sem'cylindrical portions at the ends of the parts provide for entry, at one end, of the helical spring and the insulating sheath between the helical spring and the central wire, and, at the other end, of the insulated leads for connection to monitoring equipment.

12 A foetal scalp electrode as in any one of Claims 9 to 11, wherein connections between the ends of the helical spring and central wire and of the leads for connection to monitoring equipment Is effected by resistance welding under pressure and high temperature 13. A foetal scalp electrode as In any one of Claims 9 to 12, wherein end portions of the central wire and the helical spring within the channels are bent at right angles and are engaged in slots perpendicular to the respective channels 14. A foetal scalp electrode with a connector substantially as hereinbefore described with reference to Figures 1 to 6 of the accompanying drawings.

15. A foetal scalp electrode substantially as hereinbefore described with a connector as in Figures 7 to 11 of the accompanying drawings.

Amendments to the claims have been filed as follows

1 A foetal scalp electrode comprising an electrical connector, a head member of electrically insulating material, an electrically conductive helical spring with a terminal at one end in the electrical connector and with the other end secured to the head member, and an electrically conductive wire with a terminal at one end in the electrical connector, the wire extending through an insulating sheath inside the helical spring and the other end of the wire being in a cavity in the head member and provided with an electrically conductive arcuate needle on an electrically conductive arm extending radially from the wire, with the arcuate needle normally urged, by torsion in the l-'elicai spring through a hole between the cavity and the outside of the head member, and with the tip of the needle looping back to the head member, the connector also being provided with an Indicator of its orientation with respect to the head member 2. A foetal scalp electrode as in Claim 1 wherein the indicator is located at least at the 1: end of the connector nearest to the head member.

3. A foetal scalp electrode as in Claim 2, wherein the indicator is formed by a projection on the connector disposed symmetrically to each side of a plane orthogonal to a flat surface of the head member containing the hole through which the arcuate needle is urged 4. A foetal scalp electrode as In Claim 2 or Claim 3, wherein the Indicator Is provided at each end of the connector body 5. A foetal scalp electrode as in Claim 2 or Claim 3, wherein the indicator extends along the whole length of the connector body 6 A foetal scalp electrode as In any one of Claims 1 to 5, wherein the connector has a pO cross-section having one dimension appreciably greater than another cross sectional dimension 7 A foetal scalp electrode as in Claim 6, wherein the connector is provided with rounded longitudinal ribs.

8 A foetal scalp electrode as in Claim 6 or Claim 7, wherein the larger cross-sectiona, dimension is In the plane orthogonal to a flat surface of the head member containing the hole through which the arcuate needle is urged.

9 A foetal scalp electrode as in any one of Claims 1 to 8, wherein the connector body is formed in two parts with a longitudinal interface, at least one of which parts has longitudinal channels within which are housed the connected ends of the helical spring and central wire and of leads for connection to monitoring equipment and between the respective channels are provided longitudinal formations for effecting alignment of the two parts before securing by adhesive A foetal scalp electrode as in Claim 9 wherein integral projections are also provided on each part to fit in holes in the other part to effect initial location of the two parts together.