WO2011058289A1

WO2011058289A1 - Surgical devices and methods for assisting fetal delivery

Info

Publication number: WO2011058289A1
Application number: PCT/GB2009/002479
Authority: WO
Inventors: Graham Tydeman
Original assignee: Guy's And St Thomas' Hospital Nhs Foundation Trust
Priority date: 2008-10-18
Filing date: 2009-10-19
Publication date: 2011-05-19
Also published as: GB0819157D0

Abstract

Methods and surgical devices for assisting fetal delivery by caesarean section are disclosed. According to one disclosed embodiment, the surgical device comprises an elongated stem having an axially proximal end and an axially distal end; and a fetus engaging portion comprising a concave surface for engagement against a portion of a fetus, said concave surface having a concave form when not in use during fetal delivery and being connected to said axially distal end of said elongated stem, wherein said elongated stem and said fetus engaging portion have an internal lumen running continuously from a proximal opening at said proximal end of said elongated stem to a distal opening in said concave surface.

Description

Surgical Devices and Methods for Assisting Fetal Delivery

The present invention relates to surgical devices and methods for assisting fetal delivery by caesarean section.

Currently 1 in 4 babies in the UK are delivered by caesarean section. A recent survey showed 29% of caesareans are undertaken in the late first or second stage of labour (accounting for more than 40,000 births annually). Difficulty in delivering the impacted fetal head is a common obstetric problem encountered frequently in every obstetric labour ward (Bergholt T et al (2003) Intraoperative surgical complication during caesarean section: an observational study of the incidence and risk factors. Acta Obstet Gynecol Scand 82: 251-6). Furthermore, when caesarean section is performed in late labour, all reports show significantly increased rates of maternal and neonatal complications (Thomas J, Paranjothy S (2001) The RCOG: clinical effectiveness support unit national sentinel caesarean section audit report and Alexander JM et al for the National Institute of Child health and Human Development (NICHD) Maternal-Fetal Medicine Units Network (MFMU) (2007) Comparison of Maternal and Infant Outcomes From Primary Cesarean Delivery During the Second Compared with the First Stage of Labour AmJOG 109 (4): 917-21).

Since 1955, various techniques have been described (Donald I (1955) Practical Obstetric Problems p 448 Lloyd-Luke (Medical Books Ltd) London) to attempt to deal with the problem including: different uterine incisions (T or J vs normal transverse) (Fong YL, Arulkumaran S (1997) Breech extraction - the alternative method of delivering a deeply engaged head at caesarean section. International Journal of Gynaecology and Obstetrics 56: 183-4); the pull and push methods (Fasubaa OB, Ezechi OC, Orji EO et al (2002) Delivery of the impacted head of the fetus at caesarean section after prolonged obstructed labour: a randomised comparative study of two methods. Journal of Obstetrics and Gynaecology 22: 375-378); the surgeon's use of the non dominant hand for delivering the head (Lippert TH (1983) Bimanual delivery of the fetal head at caesarean section with the fetal head in midcavity Archives of Gynaecology 234: 59-60 and Landesman R, Graber EA (1984) Abdominovaginal delivery: modification of the caesarean section operation to facilitate delivery of the impacted head. AmJOG 148: 707-10) and recently the Fetal Disimpaction Device (Reducing Complications associated with a deeply engaged head at caesarean section: a simple instrument. Singh M, Varma R. TOG 2008; 10:38-41).

The above techniques have been associated with adverse outcomes for the mother, such as increased blood loss; wound extension and infection. They have also been associated with: higher rates of special care unit admissions, lower APGAR scores (Towner D et al (1999) Effect of mode delivery in nulliparous women on intracranial injury. N Eng J Med 341 : 1709-14); other short and long term health implications for the babies (Murphy DJ et al, (2003) Cohort study of operative delivery in the second stage of labour and standard obstetric care. BJOG 110: 610-5)

In caesarean sections, before the fetal head can be delivered from the pelvis through the maternal abdominal wound, air has to enter the space that was previously occupied by the head. In normal circumstances this air has to enter through the wound itself, around the surgeon's hand and the fetal head. When a head is deeply impacted in the pelvis the air has to travel further and through a narrower space than when the head is just below the wound, as is the case in an elective caesarean or one performed in early labour. Therefore, the force required to deliver a deeply impacted head has to be sufficient to not only lift the head out of the pelvis but also to overcome the partial vacuum that is created beneath the fetal head.

The present invention seeks to overcome problems associated with the prior art.

According to an embodiment of the invention, there is provided a surgical device for assisting fetal delivery by caesarean section, comprising: an elongated stem having an axially proximal end and an axially distal end; and a fetus engaging portion comprising a concave surface for engagement against a portion of a fetus, said concave surface having a concave form when not in use during fetal delivery and being connected to said axially distal end of said elongated stem, wherein said elongated stem and said fetus engaging portion have an internal lumen running continuously from a proximal opening at said proximal end of said elongated stem to a distal opening in said concave surface.

The surgical device as claimed helps to prevent or reduce the formation of partial vacuum under the fetal head during caesarean section, when the head is lifted from the maternal pelvis. The forces required to remove the fetus are thereby reduced, thus speeding up delivery and/or reducing maternal and/or neonatal trauma.

The concave surface may be configured so as to be inserted in use between the fetal head and the maternal tissue.

Preferably, the fetus engaging portion (i.e. the concave surface and/or the rim or lip region around the concave surface) are configured to engage matingly against the fetal head. This helps to ensure that air is supplied to the correct region. In addition, the cooperation between the complementary surfaces (i.e. the part of the fetal head in contact with the fetus engaging portion and the corresponding part or parts of the fetus engaging portion) helps to ensure that the fetus engaging portion remains in place once it has been appropriately inserted, and minimizes the need for supervision of the placement and/or repeated re-insertion or re-positioning of the device.

The concave surface may be inclined to face at an oblique angle relative to a longitudinal axis of the axially distal end of said stem, when not in use. Preferably, the oblique angle should be chosen so as to correspond as much as possible with the angle that the concave surface will make relative to the stem when the device is fully inserted in use. Typically, the oblique angle will be in the range of 0 to 90 degrees, or more particularly in the range of 20 to 60 degrees.

By minimizing the difference between the angle of the concave surface relative to the stem when not in use to the angle of the concave surface relative to the stem when the device is fully inserted in use, distortions in the region where the fetus engaging portion meets the stem are reduced, which minimizes the chances of pinching of the internal lumen and/or of excessive mechanical wear in this region.

The fetus engaging portion may comprise a lip region laterally delimiting the concave surface, said lip region being configured to engage matingly against a head of a fetus and being sufficiently rigid such that when the fetus engaging portion is positioned between the fetal head and the maternal tissue in use, a gap is maintained between the fetal head and at least a portion of said concave surface. The gap maintained by the lip region helps to prevent or at least reduce the extent of blocking of the distal openings in the concave surface.

The concave surface may be formed so as to be sufficiently flexible as to mould against the fetal head when positioned in use between the fetal head and the maternal tissue, such that the majority of the concave surface is in contact with the fetal head. This arrangement helps to ensure that as many as possible of the openings in the concave surface are in close proximity to the fetal head in use, such that the partial vacuum relief is provided uniformly and/or over a wide area.

The concave surface may be formed so as to have a shape that is approximately complementary to the average form of a fetal head when not in use. This arrangement ensures that the concave surface can be brought into close proximity to the fetal head over a relatively large area without requiring significant deformation of the concave surface. Wear is thus reduced, and the distortion of the openings in use, which might deleteriously affect the ease with which air can flow through the openings and/or the susceptibility to blocking by non-gaseous fluids present in the region of the fetus, is reduced.

The concave surface may comprise a plurality of openings. This arrangement increases the throughput of air for a given size of opening and driving pressure difference across the opening, while at the same time helping to avoid complete blockage by nongaseous fluids in the region of the fetus. If some of the openings become blocked, others may remain unblocked and continue to perform their function. The increased pressure behind the openings caused by the blockage of some of the openings will lead to an increase in the rate of flow through the remaining openings which should at least partially compensate for the blockages.

A pressurization system for controllably increasing a pressure within the lumen may be provided. Preferably, the pressurization system comprises a bellows connected at the proximal end of the stem. A system of valves may be provided to control the flow of air into and out of the bellows, to allow the bellows to be expanded without sucking air out of the stem, and to allow the bellows to be compressed to force air into the stem in a controllable fashion. The bellows may be resiliently biased towards a compressed state. These arrangements ensure that a small positive pressure can be applied reproducibly, safely and/or conveniently.

The fetus engaging portion may be switchable between an axially compact state for insertion through a birth canal and an axially expanded state for engagement against said portion of said fetus. This arrangement helps to ensure that the device can be inserted effectively but with a minimum of risk or discomfort for the patient.

According to an alternative aspect of the invention, there is provided a surgical device for assisting fetal delivery by caesarean section, comprising: an elongated stem having an axially proximal end and an axially distal end; and a fetus engaging portion comprising a plurality of stems branching out from the distal end of said elongated stem, wherein said elongated stem and said fetus engaging portion have an internal lumen running continuously from a proximal opening at said proximal end of said elongated stem to a plurality of openings in each of said plurality of stems branching out of said elongated stem.

In other words, according to this arrangement, the fetus engaging portion comprises a plurality of stems with openings instead of a single concave portion with openings. Many of the advantages associated with the concave surface embodiments discussed above are also directly applicable to this arrangement. In particular, the openings in the branches when positioned in proximity to the fetal head help to relieve partial vacuum formation behind the fetus as the fetus is extracted from the mother. The fact that there are a plurality of stems branching out at different angles to the main stem axis means that the partial vacuum release can be achieved over a wide area and in a flexible manner.

According to an alternative aspect of the invention, there is provided a method of assisting fetal delivery by caesarean section, comprising: providing a surgical device comprising: an elongated stem with an axially proximal end and an axially distal end; and a fetus engaging portion connected at said axially distal end, said elongated stem and said fetus engaging portion having an internal lumen running continuously from a proximal opening at said proximal end of said elongated stem to a distal opening at said fetus engaging portion; and inserting said surgical device into a patient such that said distal opening is adjacent to the fetus, said proximal opening is outside of said patient, and said internal lumen provides a continuous connection for air to travel between the external environment and the fetus.

As discussed above with reference to the apparatus embodiments, the provision of a path by which air can travel from the outside environment to the region behind the fetus helps to avoid or reduce the extent of partial vacuum formation in the region behind the fetus during extraction of the fetus from the mother. The risk of injury and/or discomfort for the fetus and/or mother can thereby be reduced.

The invention is described further hereinafter, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 is a schematic sectional side view of a tube for use in a method of assisting fetal delivery by caesarean section;

Figure 2 is a schematic side view of a tube with a branched fetus engaging portion for use in a method of assisting fetal delivery by caesarean section;

Figure 3A is a schematic top view of a surgical device having a fetus engaging portion comprising a concave surface;

Figure 3B is a schematic side view of the surgical device of Figure 3 A;

Figure 4A is a schematic view of a bellows system in an expanded state; and

Figure 4B is a schematic view of a bellows system in a compressed state.

Figure 1 shows a surgical device 100 for assisting with fetal delivery by caesarean section. The surgical device 100 comprises an elongate stem 102 having an axially proximal end 104 and an axially distal end 106, and a fetus engaging portion 108. In this embodiment, there is no compositional or structural junction between the fetus engaging portion 108 and the stem 102; they are defined as different integral parts of the same length of tube. However, the fetus engaging portion 108 and stem 102 could alternatively be formed from different materials. The fetus engaging portion 108 is a region at the distal end of the tube that will be positioned adjacent to the fetus during the caesarean section operation, while the stem 102 represents the part of the tube that will lead out through the birth canal from the fetus to the external environment. It is envisaged that the stem will normally take this route, but it is also possible to insert the device via the incision, in which case the stem 102 would exit the body through the incision.

The stem 102 and fetus engaging portion 108 together have an internal lumen 1 16 running longitudinally so as to provide a continuous connection between a longitudinal proximal opening 110 at the proximal end of the stem 102 and a longitudinal distal opening 112 in the fetus engaging portion 108. In the example shown, the area of the proximal and distal openings 1 10 and 112 are approximately the same as the cross-sectional area of the lumen 116, but either or both of these openings 1 10/112 could be arranged to be larger or smaller than this. In addition, in the example shown the proximal and distal openings 110/1 12 are arranged so as to face in a longitudinal direction relative to the axis of the stem 102, but other orientations are also possible.

Additional openings 114 may also be provided. In the example shown, these additional openings 1 14 open out laterally, perpendicular to the axis of the stem 102. The additional openings 114 are arranged so as to be longitudinally and circumferentially spaced relative to each other so as to allow the suction (partial vacuum) releasing function of the device to operate over a large area and in different directions, without the stem 102 having to be twisted to change its orientation and/or pushed and/or pulled to change its position.

Preferably, the stem 102 should be long enough to reach from alongside the fetal head, through the birth canal to the external environment and be accessible for removal from the vagina once the baby has been delivered, by an assistant, without disrupting the sterile operating field. More preferably the stem 102 measures approximately 1 meter in length.

Preferably, the internal lumen 116 must be large enough to allow free passage of air into the vagina even if some of its length is occupied by liquid. The tensile strength of the tube material, outer diameter and wall thickness must be sufficient to prevent collapse resulting from pressure between the fetal head and the maternal tissues, but soft and flexible enough to be placed into the vagina without causing trauma to mother or fetus. The internal diameter of the lumen within the stem may be in the range of 5mm to 25mm. More preferably, the diameter of the internal lumen is approximately 12mm and the external diameter of the tube is approximately 14 mm.

The additional openings 1 14 provided in the circumference of the tube at the fetus engaging portion 108 are approximately 6mm in diameter. Preferably, the additional openings 114 should extend over a length that is approximately 150mm from the distal end 106 of the stem 2.

The stem 102 and/or fetus engaging portion 108 are formed from any suitable flexible material such as soft plastics or rubber. Preferably, the flexible material is formed of a sterilised or sterilisable material, or the flexible material is coated with a sterilised or sterilisable material.

Alternatively the additional openings 114 may be situated along a longer section of the tube and perhaps along the entire length.

Figure 2 shows a surgical device 200 that is similar to the embodiment shown in Figure 1 except that the stem 202 splits into a plurality of branches 218 at the distal end 206 of the stem 202. Each of the branches 218 has a longitudinal opening 212 at the end thereof and lateral additional openings 214 running along its length. However, other arrangements are possible. For example, the longitudinal openings 212 may be omitted and/or additional openings may be provided at various positions along the lengths of the branches 218 and at various positions around the circumference of the branches 218. In general, this arrangement facilitates application of the suction releasing functionality over a larger and more flexible range of positions and orientations.

Figures 3A and 3B show an alternative embodiment of the surgical device 300, in which the fetus engaging portion 308 comprises a concave surface 320. The concave surface 320 may correspond to a portion of a spherical surface, for example a hemisphere. The radius of curvature of the undeformed concave surface (i.e. prior to insertion through the birth canal) may be in the range of 20mm to 200mm, more preferably in the range of 20mm to 100mm, and preferably 60mm. Alternatively, the curvature of the concave surface 320 may not correspond to a portion of a single sphere (for which the radius of curvature is constant by definition), and may be describable instead by a radius of curvature that varies over the concave surface 320.

The shape of the undeformed concave surface may be arranged (shaped and dimensioned) so as to correspond with the average shape of a fetal head (at birth) so that in use as much as possible of the concave surface 320 can be brought into contact with the fetal head, with a minimum of deformation to the concave surface 320. Alternatively or additionally, a plurality of concave surfaces 320 may be provided to correspond with different sized fetuses (i.e. a plurality of different devices may be provided, each having a differently shaped and/or dimensioned concave surface 320, or the stem may be configured so as to be usable interchangeably with one of a plurality of different fetus engaging portions 308 with different concave surfaces). For example, the plurality of different sized concave surfaces may have different average radii of curvature and/or different outer diameters and/or surface areas.

The concave surface 320 may be delimited by an outer rim or lip region 322. The shape of the concave surface 320 and lip region 322 may be arranged so that substantially all of the lip region 322 can come into contact with the fetus's head during use. The body of the fetus engaging portion 308 may be formed so as to be sufficiently rigid that the rim substantially keeps its form when the fetus engaging portion 308 is inserted into position adjacent to the fetus's head, such that, optionally, there is a small gap between some or all of the concave surface and the fetus's head. This arrangement may help to keep 328 openings in the fetus engaging portion 308 open (unblocked) during use and spread the partial vacuum releasing effect more uniformly over the part of the fetus against which the fetus engaging portion 308 is engaged.

The lip region 322 and concave surface 320 may be considered to constitute a "front" side of the fetus engaging portion 308. The opposite or "rear" side 324 of the fetus engaging portion 308 is spaced apart from the concave surface 320 so as to provide a cavity 326 which provides a connection to the lumen 316 of the stem 302. A plurality of openings 328 are provided in the concave surface 320 that lead through into the cavity 326 such that there is a continuous connection between the lumen 316 and each of the openings 328.

The fetus engaging portion 308 may be formed from a material that is strong enough that the compressive forces likely to be encountered when the device is inserted into position next to the fetus's head will not be sufficient to disrupt the continuous connection between the stem lumen 316 and each of the openings 328. On the other hand, the material should be chosen so as to be sufficiently soft and flexible that it can be inserted into position without risk of damage to the mother or fetus. For example, the fetus engaging portion 308 may be arranged to have a Shore A hardness in the range of 30 to 70 and the stem 302 may be arranged to have a Shore A hardness in the range of 50 to 90. In general, the mechanical requirements for the fetus engaging portion 308 are substantially different to those of the stem 302, so that their properties may advantageously be chosen to be different. They may, for example, be formed from different materials and/or different thicknesses, in order to perform their respective functions optimally. Generally, it will be desirable for the stem 302 to have a higher stiffness and/or tensile strength than the fetus engaging portion 308. This could be achieved by making the walls of the stem 302 thicker than the walls of the fetus engaging portion 308. Alternatively or additionally, the stem 302 could be made of a material that is intrinsically stiffer and/or which has a higher tensile strength than the material of the fetus engaging portion 308. In this way, the stem 302 can be made more compact (because the walls will not have to be thickened to the same extent), which may help with insertion of the device in use and/or may minimize discomfort associated with the presence of the inserted device. Manufacturing costs may also be reduced. Alternatively or additionally, the stem 302 may be provided with a reinforcement structure, for example a braid, to provide additional stiffness and/or tensile strength. Again, such an arrangement can help keep the stem 302 compact and facilitate manufacture. For example, the stem 302 and fetus engaging portion 308 could be made from the same material, which may be convenient from the point of view of manufacture and longevity, with the required difference in mechanical properties being provided partly or exclusively by the reinforcing structure.

The concave surface 320 may be configured so as to be deformable to the extent necessary to fit matingly against the fetus's head in use, such that at least a portion of the concave surface 320 substantially follows the contours of the fetus's head, without the continuous connection between the stem lumen 316 and the openings 328 being compromised. In an embodiment, the fetus engaging portion 308 is configured such that when it is fitted against the fetus's head in use, a finger may be inserted between the fetus's head and the concave surface 320. For example, the lip region 322 that delimits the concave surface 320 may be beveled or chamfered. This allows a finger to lift the lip and to be inserted easily between the fetus's head and the concave surface 320.

In all of the above embodiments, the stem 102/202/302 needs to be formed so that it is sufficiently strong in tension that it can be inserted and removed from the patient reliably. The stem 102/202/302 must also be sufficiently resistant to radial compression that the lumen 116/216/316 remains open along its length and maintains the continuous connection between proximal end of the stem 102/202/302 and the fetus engagement portion 108/208/308.

In all of the above embodiments, the various openings in the fetus engaging portion 108/208/308 need to be sufficiently large to resist becoming blocked by viscous fluids (e.g. meconium) present near the fetus and to provide an effective connection for air to enter the space between the fetal head and maternal tissue and thereby alleviate suction effects, but sufficiently small that fluids are prevented from entering the device to such an extent that the passage of air is blocked or disrupted too severely within the stem. Providing a large number of relatively small openings is effective because even if some of the openings do become blocked, the others can still provide a sufficiently good link for the air to flow through and help to alleviate suction. Preferably, an average of between 1 and 5 openings per square centimetre may be provided, more preferably about 1.2 openings per square centimetre, the average being taken over the surface area of the concave surface 326. For example, in the case of 1.2 openings per square centimetre, this would mean having 24 openings in a concave surface area of 20 square centimetres.

Means may be provided for preventing certain viscous fluids, such as meconium, from reaching at least some of the openings 108/208/308. For example, a woven mesh may be provided over some of the openings 108/208/308 that has gaps between the threads of the weave that are too small for viscous fluids to penetrate through.

A system of one-way valves could be employed to help prevent unwanted fluids from entering the lumen 1 16/216/316. For example, one-way valves could be positioned in one or more of the openings 1 12/1 14/212/214/314 in the fetus engaging portion 308. Alternatively or additionally, the openings themselves may be structured so as to themselves function as one-way valves. The one-way valves could be configured only to allow passage of air outwards through the openings 1 12/114/212/214/314 and block passage of air and/or other fluids in the other direction (into the lumen 1 16/216/316).

In the arrangement of Figures 3 A and 3B, the concave surface 320 is oriented so as to face at an oblique angle A relative to the axis defined by the distal end of the stem 302. Figure 3B illustrates what is meant by the orientation of the concave surface 320 and how the oblique angle A is therefore defined. Of course, because the surface 320 is not flat, individual portions will not all "face" (i.e. be perpendicular to) the same direction. However, the average of the orientations of the individual portions can be taken to correspond to the overall orientation of the surface. Often, the direction of orientation of the concave surface 320 will be perpendicular to a plane within which all or most of the lip region 322 lies. The angle A is preferably in the range of 0 degrees to 90 degrees, more preferably in the range of 20 degrees to 60 degrees, or more preferably within the range of 20 degrees to 40 degrees. In general, the angle A should be chosen so that when the fetus engaging portion 308 is in position between the fetal head and maternal tissue, the junction between the distal end of the stem 302 and the fetus engaging portion 308 is distorted to the minimum extent. This helps to reduce the chances of the lumen 316 being pinched at this point, which might deleteriously restrict or prevent air flow into the fetus engaging portion 308.

The fetus engaging portion 102/202/302 may be configured so as to be switchable between a radially constrained state and a radially expanded state, to assist with insertion of the device during use. For example the fetus engaging portion 102/202/302 may be elastically deformable so that the concave surface can collapse inwards towards the axis during insertion and spring back out to its normal shape (e.g, to a shape that is approximately complementary to the shape of the fetal head) just prior to insertion between the fetal head and maternal tissue.

Preferably, the dimensions of the surgical device 300 shown in Figures 3A and 3B are as follows. The outer diameter of the concave surface 320 (i.e. the maximum separation between opposite sides of the rim 322) is between 20 and 100mm, more preferably about 60mm. The gap between the interior side of the concave surface 320 and the interior side of the rear surface 324 of the fetus engaging portion 308 is between 1 and 20mm, more preferably about 15mm. The size of the openings 328 in the concave surface 320 are between lmm and 20mm, more preferably about 8mm.

For all of the embodiments, the width of the stem is preferably between 5mm and 25mm and more preferably about 15mm, and the length of the stem is preferably between 200mm and 3000mm and more preferably about 800mm. The internal diameter of the lumen within the stem is preferably in the range of 5mm to 25mm.

Generally, in use, the continuous connection provided by the lumen 116/216/316 will be sufficient substantially to equalize the pressure between the external environment and the region between the fetal head and maternal tissue at which the fetus engaging portion 108/208/308 is located, or at least to reduce the pressure difference between these two regions, so as to alleviate the suction-based effects which are inhibiting delivery of the fetus and/or placing strain on the fetus and/or mother.

However, performance may be improved by the provision of means to provide a small, controlled overpressure within the lumen 116/216/316. This needs to be carried out very carefully to avoid the risk of damage to the fetus or mother. For instance, care needs to be taken to ensure that any outflow of air is sufficiently limited to ensure that the risk of introducing air bubbles into the vascular system of the mother is kept within acceptable bounds.

Figures 4 A and 4B illustrate an arrangement using a bellows 430. Figure 4 A illustrates the expansion phase and Figure 4B illustrates the compression phase. The bellows 430 is attached to the proximal end of the stem 402 and comprises a valve system for controlling the feeding of air into the bellows 430. The valve system comprises a stem valve 432 for controlling a connection between the bellows 430 and the stem 402 and an external environment valve 434 for controlling a connection between the bellows 430 and the external environment. During expansion of the bellows 43 (arrows 440), the stem valve 432 will be closed to prevent suction of air out of the stem 402 and reduction of the pressure therein, while the external environment valve 434 will be open to allow air to enter from the external environment (arrows 442). During compression of the bellows 430 (arrows 444) to drive air into the stem 402 (arrows 446) and thereby increase the pressure within the stem 402, the opposite valve configuration will be established: the stem valve 432 will be opened (at least partially) and the external environment valve 434 will be closed (at least partially).

The bellows 430 may be constructed so as to be biased resiliently towards the compressed state, so that a user only needs to apply a force to the bellows 430 to pull it to its expanded state. A ring 436 or similar may be provided to assist with the pulling process. When the user wishes to apply the controlled positive pressure to the stem 402, he simply sets the valves in the appropriate configuration, pulls the bellows 430 outwards by the required amount and releases the bellows 430. The size of the over-pressure applied by the bellows 430 is determined by the volume of the bellows 430, the magnitude of the biasing force and the extent to which the bellows 430 were expanded by the user before release.

As a further variation, the external environment valve 434 may be configured so that the extent to which the flow of air into the bellows 430 is restricted (i.e. the flow impedance of the external valve 434) may be controlled continuously between complete restriction (blocking) and a fully open state, such that the over-pressure applied by compression of the bellows 430 can be controlled more precisely. Setting of the external environment valve 434 to an intermediate position will reduce the amount of overpressure generated by compression of the bellows 430 relative to the situation where the external environment valve is fully closed (the amount of overpressure being a function of the particular intermediate flow impedance selected) because some of the air from the bellows 430 will be allowed to escape to the external environment through the valve 434 rather than being forced up the stem 402. A similar effect could also be achieved by controlling the flow impedance through the stem valve 432 (changing the flow impedance at this valve will change the rate at which the bellows forces air into the stem 402 for a given driving force on the bellows).

Claims

1. A surgical device for assisting fetal delivery by caesarean section, comprising:

an elongated stem having an axially proximal end and an axially distal end; and a fetus engaging portion comprising a concave surface for engagement against a portion of a fetus, said concave surface having a concave form when not in use during fetal delivery and being connected to said axially distal end of said elongated stem, wherein said elongated stem and said fetus engaging portion have an internal lumen running continuously from a proximal opening at said proximal end of said elongated stem to a distal opening in said concave surface.

2. A surgical device according to claim 1, wherein said fetus engaging portion and said elongated stem are configured such that, in use, when the fetus engaging portion is inserted between a fetal head and maternal tissue, and the elongated stem feeds out to the external environment, a continuous passage for air is maintained through said lumen from said proximal opening to said distal opening.

3. A surgical device according to claim 1 or 2, wherein said fetus engaging portion is configured to engage matingly against a head of a fetus.

4. A surgical device according to claim 1 , 2 or 3, wherein said concave surface is inclined to face at an oblique angle relative to a longitudinal axis of the axially distal end of said stem, when not in use.

5. A surgical device according to claim 4, wherein said oblique angle is in the range of 0 degrees to 90 degrees, preferably within the range of 20 degrees to 60 degrees.

6. A surgical device according to any one of the preceding claims, wherein said fetus engaging portion comprises a lip region laterally delimiting said concave surface, said lip region being configured to engage matingly against a head of a fetus and being sufficiently rigid such that when the fetus engaging portion is positioned between the fetal head and the maternal tissue in use, a gap is maintained between the fetal head and at least a portion of said concave surface.

7. A surgical device according to any one of the preceding claims, wherein said concave surface is formed so as to be sufficiently flexible as to mould against the fetal head when positioned in use between the fetal head and the maternal tissue, such that the majority of the concave surface is in contact with the fetal head.

8. A surgical device according to any one of the preceding claims, wherein said concave surface is formed so as to have a shape that is approximately complementary to the average form of a fetal head when not in use.

9. A surgical device according to any one of the preceding claims, wherein at least a portion of said concave surface has a shape when not in use that corresponds to a portion of a sphere having a radius of curvature in the range of 20mm to 200mm, preferably within the range of 20mm to 100mm.

10. A surgical device according to any one of the preceding claims, wherein said concave surface comprises a plurality of distal openings.

1 1. A surgical device according to any one of the preceding claims, further comprising: a pressurization system for controllably increasing a pressure within said lumen.

12. A surgical device according to claim 1 1 , wherein said pressurization system comprises a bellows connected to said proximal end of said stem.

13. A surgical device according to claim 12, further comprising a valve system operable between a first configuration, in which a connection between said bellows and said lumen is closed and a connection between said bellows and the external environment is open, and a second configuration in which the connection between said bellows and said lumen is at least partially open and the connection between said bellows and the external environment is at least partially closed, said first configuration being suitable for expanding said bellows without a corresponding reduction in pressure in said lumen and said second configuration being suitable for increasing the pressure inside the lumen in a controlled manner through compression of the bellows.

14. A surgical device according to claim 12 or 13, further comprising resilient means configured to bias said bellows towards a compressed state.

15. A surgical device according to any one of the preceding claims, wherein said stem and fetus engaging portion are configured so as to be insertable in use through a birth canal to a position at which said fetus engaging portion is engaged against said portion of said fetus.

16. A surgical device according to any one of the preceding claims, wherein said fetus engaging portion is switchable between an axially compact state for insertion through a birth canal and an axially expanded state for engagement against said portion of said fetus.

17. A surgical device according to any one of the preceding claims, wherein the internal diameter of said lumen within the stem is in the range of 5mm to 25mm.

18. A surgical device according to claim 17, wherein the internal diameter of said lumen within the stem is approximately 12mm and the external diameter of the stem is approximately 14mm.

19. A surgical device according to any one of the preceding claims, wherein said stem has a length that is sufficient to allow it reach from alongside the fetal head, through the vagina and be accessible for removal from the vagina.

20. A surgical device according to any one of the preceding claims, further comprising: a one-way valve positioned between said distal opening and said internal lumen, said one-way valve being configured to allow air to pass from the inside of said lumen to the outside of said lumen through said distal opening and to inhibit the passage of non-gaseous fluid from the outside of said lumen to the inside of said lumen through said distal opening.

21. A surgical device set, comprising:

a surgical device according to any one of the preceding claims with a plurality of different fetus engaging portions that are interchangeably attachable to said elongated stem, each of said different fetus engaging portions having a concave surface that is shaped and dimensioned so as to correspond with a different size range of fetal head; or

a plurality of surgical devices according to any one of the preceding claims, each of the surgical devices having a different concave surface that is shaped and dimensioned so as to correspond with a different size range of fetal head.

22. A surgical device for assisting fetal delivery by caesarean section, comprising:

an elongated stem having an axially proximal end and an axially distal end; and a fetus engaging portion comprising a plurality of stems branching out from the distal end of said elongated stem, wherein said elongated stem and said fetus engaging portion have an internal lumen running continuously from a proximal opening at said proximal end of said elongated stem to a plurality of openings in each of said plurality of stems branching out of said elongated stem.

23. A surgical device according to any one of the preceding claims, wherein said opening or openings in said fetus engaging portion are of a number and size that allow sufficient passage of air through them to alleviate in use suction between the fetal head and maternal tissue while substantially preventing other fluids from blocking or restricting the lumen.

24. A surgical device according to claim 23, wherein said fetus engaging portion comprises, as an average over said concave surface, between 1 and 5 openings per square centimetre.

25. A surgical device according to any one of the preceding claims, wherein said stem is formed from a different material than said fetus engaging portion, said different materials having different hardnesses, as measured by the Shore A durometer scale.

26. A surgical device according to any one of the preceding claims, further comprising a woven mesh attached to an outside surface of said fetus engaging portion and positioned so as to act as a barrier in use between said distal openings in said concave surface and non-gaseous fluids present in the region of the fetus.

27. A method of assisting fetal delivery by caesarean section, comprising:

providing a surgical device comprising: an elongated stem with an axially proximal end and an axially distal end; and a fetus engaging portion connected at said axially distal end, said elongated stem and said fetus engaging portion having an internal lumen running continuously from a proximal opening at said proximal end of said elongated stem to a distal opening at said fetus engaging portion; and

inserting said surgical device into a patient such that said distal opening is adjacent to the fetus, said proximal opening is outside of said patient, and said internal lumen provides a continuous connection for air to travel between the external environment and the fetus.

28. A method according to claim 27, wherein said surgical device is inserted through the birth canal.

29. A method according to claim 27 or 28, wherein said surgical device is as defined in any one of claims 1 to 26.

30. A method according to any one of claims 27 to 29, wherein said surgical device comprises a pressurization system and said method further comprises using said pressurization system to controllably increase a pressure within said lumen.

31. A method according to any one of claims 27 to 30, wherein said elongated stem and said fetus engaging portion are formed from a single tube.

32. A method according to any one of claims 27 to 31, wherein either or both of said elongated stem and fetus engaging portion have a plurality of additional openings formed in lateral surfaces thereof.

33. A surgical device constructed and arranged to operate substantially as hereinbefore described with reference to and/or as illustrated in the accompanying drawings.

34. A method of assisting fetal delivery by caesarean section substantially as hereinbefore described with reference to and/or as illustrated in the accompanying drawings.