WO1995012351A1

WO1995012351A1 - Fetal probe

Info

Publication number: WO1995012351A1
Application number: PCT/GB1994/002393
Authority: WO
Inventors: Jason Otto Gardosi; Simon William Horton Thomas; William Robert Pruehsner
Original assignee: Jason Otto Gardosi; Simon William Horton Thomas; William Robert Pruehsner
Priority date: 1993-11-01
Filing date: 1994-11-01
Publication date: 1995-05-11
Also published as: GB9322519D0; AU8001394A

Abstract

A fetal probe has an inflatable balloon (114) positioned so as on inflation to hinge open a leaf (110) carrying an ECG electrode (130) or other sensor. Wedging action ensures that the probe is reliably and reproducibly positioned in the uterus. The balloon is interconnected with a pressure monitor so that intrauterine activity can be mesured.

Description

FETAL PROBE

This invention relates to obstetrics and in particular to probes for monitoring intrauterine pressure during labour.

It is standard procedure to monitor contractions during labour, using either internal or external methods. One external method of assessing contractions is that of manual assessment. This method is qualitative only and no permanent record is obtained. A second external method is tocography, the qualitative assessment of the frequency and duration of contractions by means of a tocodynamometer or external contraction transducer. These are usually held on by a belt which may cause discomfort to the labouring mother and needs to be disconnected before she can mobilise and ambulate during the first stage of labour. It is difficult to obtain a good contraction trace in obese women or those who are restless. The transducer may be easily dislodged and needs frequent readjustment by the attending midwife or physician to obtain a trace of satisfactory quality.

For labours which are high risk from outset, or develop difficulties such as slow progress, or are artificially induced or augmented with drugs, . internal tocography and measurement of intrauterine pressure is recommended (1. Gordon AJ - Commentary: Measurement of uterine activity - a useful clinical tool? B J Obstet Gynaecol 1984;91 :209-210; 2.

'Dystocia' - ACOG Technical Bulletin 137, Dec 1989). This is currently achieved by one of two methods: 1. Fluid filled catheter: this is an open system which has the added advantage of providing a canula for amnioinfusion should this be considered to become advisable as labour progresses. The catheter comprises a water column connected to an external pressure transducer. However, the fluid filled system is difficult and time consuming to set up and may require frequent flushing or readjustment during labour. Blockage of the end of the tube due to vernix or meconium - or direct mechanical pressure - may cause the readings to be inaccurate. 2. Catheter tip pressure transducers: these are either reusable and considered fragile with the need for careful sterilisation to ensure that there is no transmission of infection, or single-use and expensive. They usually also have the disadvantage of not providing a simultaneous canula for amnioinfusion.

Further problems with intrauterine pressure catheters are that the clinician does not know where exactly the tip of the catheter lies after insertion. Different locations may cause variation in the amplitude or quality of pressure recordings. This lack of reproducibility may cause problems within a single labour or in comparison between different labours.

Furthermore, complications may arise from the insertion of such catheters, such as uterine perforation, placental damage and fetal compromise (Chan WH, Paul RH, Toews J. Obstet Gynecoi 1973;41 :7-13; Trudinger BJ, Pryse-Davies J. BrJ Obstet Gynaecol 1978;85:567-72). It is an object of this invention to overcome the aforementioned disadvantages and drawbacks and to provide a safe, easy and reliable method of qualitative and quantitative measurement of uterine activity.

In co-pending application PCT/GB90/01708 there is described a probe for fetal monitoring which can be inserted through the vagina into a cervical opening of 1 cm or more dilation, with the most distal part of the probe extending into the lower part of the uterus only, inside the cervix and just above the presenting part of the fetus.

The probe, which carries fetal sensor means, can be a vehicle for a variety of monitoring functions, and the probe sensor means can take a variety of forms. The probe of PCT/GB90/01708 can be secured non- invasively by an inflatable semi-cuff or balloon at the distal end of the probe. Inflation of the balloon will result in the fetal surface of the probe being apposed to the fetal skin, thus ensuring good contact for the sensors which are located on this surface. The inflated balloon also stops the probe from slipping out of the cervix and vagina during maternal movement, contractions and fetal descent, until such time that the fetal presenting part is delivered or the balloon is deflated for probe removal. Uterine pressure acts upon the exposed surface of the balloon to hold it securely in place. As the balloon is above the presenting part, it does not interfere with its descent during labour.

Another advantage of the balloon at the distal end of the probe is that after probe insertion and balloon inflation, gentle traction on the probe will reliably find a point of optimal contact between the main sensor area of the probe and the contact surface of the presenting part, which is usually the head.

The probe of PCT/GB90/01708 optionally includes one or more channels running the whole length of the probe which can be used for access into the uterus around the present part, without the need for an additional vaginal examination. For example, an access channel may be used to introduce surgical instruments and/or additional probes.

It is suggested that one possible use for such an access channel is the insertion of an intrauterine pressure catheter or transducer. Thus, when, during labour, it becomes apparent that such a catheter needs to be inserted for pressure monitoring, an often distressing additional digital vaginal examination for this insertion can be avoided and the access channel of the in-situ probe can be used to guide the tip of the catheter around the presenting part into the uterus.

Whilst this approach offers important advantages, it has limitations and it is an object of this invention to provide an improved probe which overcomes these limitations.

According to one aspect of the present invention there is provided a fetal probe comprising an elongate body portion, adapted for insertion into the cervix around the presenting part of the fetus and expandable means at the distal end of the body portion, the expandable means comprising at least one inflatable balloon inflatable from an orientation facilitating insertion of the body portion to an expanded orientation in which: a fetal surface of the expandable means is urged into contact with the fetus, a maternal surface of the expandable means is urged into contact with maternal tissue and an exposed surface of the inflatable balloon is presented towards the uterus, such that the application of pressure to said exposed surface tends to urge the fetal surface into still closer contact with the fetus, wherein the balloon is connected to a pressure monitor such that intrauterine activity can be measured. Thus, intrauterine activity can be measured quantitatively without the need for separate probes. The use, in accordance with the present invention of the inflatable balloon as in effect the pressure sensing element, has further important advantages. The fluid environment of the uterus during labour is complex and dynamic, and it is found that pressure measurements vary as the site of the pressure sensing element varies with respect to the uterine wall and with respect to the fetus. In the present invention, as has been described above and in the cited reference, the inflatable balloon is held firmly in position by the wedging action between the fetal presenting part and maternal tissue and by the action of interuterine pressure on the balloon itself. Accordingly, the site at which pressure is measured in accordance with the present invention is likely to remain fixed during labour. Changes in measured pressure can therefore be directly related to uterine activity, rather than to variation in the placement of the pressure sensing element. There is another aspect to this relatively fixed positioning of the pressure sensing element. The probe of the present invention and particularly the manner of insertion by which, after inflation of the balloon, gentle traction is applied to draw the balloon back in a wedging action between the fetal presenting part and the uterine wall, provides a well defined position in the nuchal space just beyond the largest diameter of the presenting part, usually the fetal head. This means that measures of uterine activity are likely not only to be reproducible during the course of a labour but also more comparable between different labours.

Further advantages of the probe of the present invention include: having the probe for fetal monitoring in place when, during labour, it becomes necessary to measure intrauterine activity avoids the time delay before inserting an additional probe; the external pressure transducer may be used again thereby reducing costs; and the problems associated with known fluid filled catheters, such as blockage, are obviated. Further the lack of an intrauterine transducer reduces costs and reduces the risk of damage.

The present invention will now be described by way of example with reference to the accompanying drawings, in which:-

Figure 1 is a plan view of a fetal probe according to this invention;

Figure 2 is a side view of the probe shown in Figure 1 ;

Figures 3, 4 and 5 are enlarged scale sections on respectively lines 3-3, 4-4 and 5-5 of Figure 2; Figure 6 is a plan view of a fetal probe according to another embodiment of the invention including a diagrammatic representation of the manner in which an interconnection is made to the probe;

Figure 7 is a side view of the probe shown in Figure 6, showing the inflated orientation of the probe, to a reduced scale; Figure 8 is an end view corresponding to Figure 7; and

Figure 9 is a diagrammatic representation of the probe of Figures 6, 7 and 8, when positioned in the uterus.

Referring initially to Figures 1 and 2, the probe 10 comprises a strip like body portion 12. This carries on one surface a reference electrode 14 and, on the opposite surface and towards the distal end of the probe, fetal sensor means 16. In this example, the sensor means 16 takes the form of an ECG electrode 18, a photodiode 20 and LED's 22 (red and IR). In known fashion, the photodiode 20 and LED's 22 can be used to determine the oxygenation levels of fetal blood. In Figures 1 and 2 the ECG electrode 18, the photodiode 20 and the LED's 22 are illustrated as being adjacent to one another across the width of the body portion 12. However, it will be understood that the electrode, photodiode and photosensor may be arranged in any suitable manner and may, for example, be spaced longitudinally along the body portion 12. At the distal end of the body portion 12 is formed an inflatable balloon or sac 24 which, for ease of reference, will hereinafter be referred to as a balloon. This balloon, which may be made of thin plastics material or synthetic-rubber material, may be of any suitable shape, including spherical, frusto-conical and hemi-sphericai.

As seen more clearly in Figures 3, 4 and 5, a lozenge shaped channel 26 may extend through the length of the body portion 12. The purpose of this channel 26 will be described in more detail later. A bore 28 in the probe body communicates between the inflatable balloon 24 and a coupling 30 at the proximal end of the body portion. Passages 32 and 34 carry leads communicating between the external lead 36 and, respectively, the photodiode 20 and LED'S 22. Passage 38 similarly carries a lead connecting with the fetal electrode 18.

The balloon 24 is preferably inflated using saline or other suitable fluid, which is preferably sterile, supplied from a syringe or other suitable means connected with coupling 30.

In use, the probe, with the balloon 24 deflated, is introduced through the cervix passing between the presenting part of the fetus (which will usually be the fetal head) and the opposing uterine wall. When the probe has been inserted to a suitable length, which is preferably of approximately 15 cm, the balloon 24 is inflated.

Slight traction applied to the probe by the attendant will then ensure that the sensor is reliably positioned and securely held against the fetal scalp with the inflated balloon 24 wedged between the maternal tissues and the fetal head. Continuous baseline intrauterine pressure and the increased pressure during contractions is transferred to the inflated balloon and serves to keep the probe in good surface contact with fetal skin and maternal tissue.

It will be recognised that uterine pressure through a mechanical wedging action will maintain the position of the fetal sensor, even in the face of contraction, maternal or fetal movements, and descent in the birth canal. Indeed, the probe should remain in position even if the parturient were to stand up and walk during labour.

With the balloon 24 positioned to the maternal side of the probe body portion 12, and because of the shape of the balloon being, generally convex to the maternal tissues and flat toward the body portion, the effect is to urge the body portion and thus the fetal sensor into still closer contact with the fetal skin, and to maintain that contact.

Once the balloon 24 is inflated, the syringe, or other means, is removed and a pressure monitor, not shown, is connected to the balloon 24 via the bore 28. Alternatively, where the bore 28 is connected to a syringe or other means via a first line and to a pressure monitor via a second line, the first and second lines being connected to coupling 30 via a valve or valves, the valves are adjusted to isolate the balloon from the syringe or other means and to connect it to the pressure monitor.

Because the balloon is held in constant position in the nuchal space just beyond the largest diameter of the fetal presenting part, reliable and reproducible measures of uterine activity can be expected.

Further, since the probe extends only a relatively short distance into the uterus and is located just above the presenting part of the fetus, the possibility of the probe becoming entangled with the fetus, the uterine wall being perforated and/or placental vessels being damaged, is avoided. A further advantage of the present invention is that intrauterine pressure can be measured whether or not the amniotic membrane is intact. Thus, unlike the probe described in US 4 543 965 measurement of contractions may continue even after the membrane has ruptured.

The channel 26 can be used to pass appropriate instruments into the uterine cavity in a straightforward manner and with minimum discomfort to the parturient. Examples of instruments which may be inserted include those for amniotomy. Thus a small hooked or sharp-tipped flexible trochar can be inserted to perforate the membranes. Alternatively, a special cannula to apply localised suction or contact-glue before rupturing the membrane by traction. The channel 26 itself may also be used to apply localised suction to the membrane. In this case, a vacuum is applied directly through the channel 26.

The access channel can then be left open to allow sample amounts of amniotic fluid to escape even when the presenting part would otherwise, due to a tight fit, be sealing the pelvic outlet; thus meconium would still be noted in circumstances where the presence of meconium would otherwise remain hidden up to delivery.

Alternatively, or additionally, the channel 26 may be used as a means of taking a sample of amniotic fluid from the upper uterus, ie before it is tainted by blood or mucous. The sample may then be visually examined by the attendant or sent for further examination, such as by microbiological analysis.

The channel 26 may also be used for the insertion of a canula (or used itself as a canula) for amnioinfusion should this become desirable as labour progresses.

A further embodiment of this invention will now be described with reference to Figures 6,7,8 and 9.

The probe 100 comprises a probe head 102 from which extend three leads 104, 106 and 108 which are joined side by side to present a generally flat cross-section. The probe head 102 contains an integral, hinged leaf 110 which, in the closed position shown in Figure 6, is received within a complementariiy formed recess 112 in the probe body 102. Between the leaf 110 and the recess 112 is disposed an inflatable balloon 114. As best seen in Figure 8, the balloon 114 comprises two interconnected balloon lobes 114(a) and 114(b). The balloon lobes are secured to the hinged leaf 110 and act in tandem, as inflation progresses, to urge the free end of the hinged leaf 110 away from the probe head 102. A fluid channel, not seen in the drawings, connects the balloon lobes 114(a) and 114(b) with the lead 104. As shown in Figure 6, this lead 104 provides communication alternatively - via a fluid valve 120 - with either a syringe 122 or a pressure monitor 124. It will be recognised that the syringe 122 can be replaced by a wide variety of alternative means for inflating the balloon with saline or other appropriate fluids. Such alternative means might include a bladder or an electromechanically powered device. Also, the simple manometer shown at 124 is to be regarded as an example of a wide range of devices which can serve to monitor the pressure within the balloon. Lead 106 communicates, as seen in Figure 8, with an orifice 126 in leaf 110. Because of the bi-lobal balloon arrangement, this orifice is situated in a region which has, through the inflation procedure, been "cleared". The likelihood of the orifice being blocked or obstructed is therefore very slight. This provides for simple and reliable amniotic fluid sampling or amnioinfusion, whenever required.

There is situated on the exterior surface of the leaf 110, an ECG electrode 130. A reference electrode 132 is positioned on the interior surface of the leaf 110. The arrangement of a hinged leaf opening on inflation of the balloon lobes conveniently provides a region which is infused by amniotic fluid and the reference electrode can be located anywhere in this region. Electrical connection to the electrodes is established through lead 108 to an external ECG monitor and recorder.

It should be understood that other forms of contact sensors can be positioned on the exterior, fetal surface of the leaf 110 whether in addition to or in place of the described ECG electrode. Indeed, there may be applications where the fetal probe is used solely for the measurement of intrauterine activity, and no further sensor is provided.

There is shown in Figure 9, the usual position of the probe, posterior to the fetal head which is in the transverse position. The arrow 140, indicates the site of the ECG contact. It will be apparent that the nature of the described probe encourages and promotes accurate placement of the probe. Moreover, with a similar fetus position, reproducible probe positions are likely to be achieved across a range of patients. This enables meaningful comparisons between measures of uterine activity.

As the balloon of all embodiments of the present invention is located above the presenting part of the fetus, it does not interfere with its descent during labour and indeed is held in position by the action of uterine pressure. Removal of the probe may be effected by deflating the balloon. Alternatively, the probe may be left in position during the birth and will thus be delivered with the baby. It is therefore possible to monitor intrauterine activity up until the moment of birth.

Claims

1. A fetal probe comprising an elongate body portion, adapted for

insertion into the cervix around the presenting part of the fetus and expandable means at the distal end of the body portion, the expandable means comprising at least one inflatable balloon inflatable from an orientation facilitating insertion of the body portion to an expanded orientation in which: a fetal surface of the expandable means is urged into contact with the fetus, a maternal surface of the

expandable means is urged into contact with maternal tissue and an exposed surface of the inflatable balloon is presented into the uterine cavity, such that the application of intrauterine pressure to said exposed surface tends to urge the fetal surface into closer and continuous contact with the fetus, wherein the balloon is connected to a pressure monitor such that intrauterine activity can be measured.

2. A fetal probe according to Claim 1 , wherein a fetal sensor is provided on said fetal surface of the expandable means.

3. A probe according to Claim 1 or 2, further comprising a channel extending through the length of the elongate body portion enabling the introduction of instruments or the removal of samples through the fetal probe.

4. A fetal probe according to any one of Claims 1 to 3, wherein the inflatable balloon comprises two or more balloon lobes.

5. A fetal probe according to Claim 3 and Claim 5, wherein said balloon lobes define between them a free space into which said channel opens.

6. A fetal probe according to Claim 2, wherein the fetal sensor comprises an ECG electrode.

7. A fetal probe according to Claim 2 or Claim 6, wherein the fetal sensor comprises means for transcutaneous fetal oximetry.

8. A fetal probe according to any one of the preceding claims, wherein the expandable means includes a hinged leaf positioned as to be hinged open on inflation of the expandable means.

9. A method of measuring intrauterine activity comprising the use of a fetal probe comprising an elongate body portion, adapted for insertion into the cervix around the presenting part of the fetus and expandable means at the distal end of the body portion, the expandable means comprising at least one inflatable balloon inflatable from an orientation facilitating insertion of the body portion to an expanded orientation in which: a fetal surface of the expandable means is urged into contact with the fetus, a maternal surface of the expandable means is urged into contact with maternal tissue and an

exposed surface of the inflatable balloon is presented into the uterine

cavity, such that the application of intrauterine pressure to said exposed surface tends to urge the fetal surface into closer and continuous contact with the fetus, wherein the balloon is connected to a pressure monitor such that intrauterine activity can be measured.

10. A method of measuring intrauterine activity according to Claim 9, wherein traction on the body portion serves to urge the expandable means into wedging engagement between the fetal presenting part and maternal tissue.

11. A fetal probe comprising an elongate body portion, adapted for insertion into the cervix around the presenting part of the fetus; at least one inflatable balloon at the distal end of the body portion inflatable from an orientation facilitating insertion of the body portion to an expanded orientation in which a wedging action serves to urge the body portion into closer engagement with the fetal presenting part; and a channel extending through the length of the elongate body portion, wherein the balloon is formed in at least two lobes which when inflated define between them a free space, the channel opening into said free space.

12. A fetal probe according to Claim 11 , wherein the balloon is connected to a pressure monitor such that intrauterine activity can be

measured.