GB2226496A

GB2226496A - Epidural space location device

Info

Publication number: GB2226496A
Application number: GB8824309A
Authority: GB
Inventors: Abdul Rahman Osman Ziko
Original assignee: Individual
Current assignee: Individual
Priority date: 1988-10-18
Filing date: 1988-10-18
Publication date: 1990-07-04
Anticipated expiration: 2008-10-18
Also published as: GB8824309D0; GB2226496B

Abstract

A device functioning as an epidural space location aid comprises a rotor-containing chamber fitted on to the end of a syringe vessel and with the syringe needle projecting from the end of the chamber and in fluid-flow communication via the chamber with the syringe vessel. The negative pressure experienced at the tip of the needle as it enters the epidural space of a patient, in use, is transmitted via the needle to the chamber and causes the rotor to rotate. The rotation is visible through the transparent walls of the chamber and as soon as it is seen it tells the practitioner that he has found the epidural space. The device, consisting of rotor-containing chamber with needle projecting from one end thereof, and with the other end of the device fitting on to the syringe vessel in use, may be manufactured as a self-contained unit; or it may form an inherent extension of the syringe vessel and be constructed as part of the syringe from the outset. <IMAGE>

Description

EPIDURAL SPACE LOCATION DEVICE Field of the Invention The invention relates to a device for aiding the correct location of the tip of a needle within the epidural space.

A number of anaesthetics and analgesics are introduced into the body most effectively in the epidural space. The epidural space is also used for the introduction of other substances such as dyes for diagnostic purposes. The epidural space is a space that runs along the length of the spine between an inner wall called the 1dura' which separates the space from the subdural space which contains the spinal cord and the cerebral fluid and a dense layer of tissue called the 'ligamentum flavum' which lies on the outer wall of the epidural space.

The spinal cord ends between the lumbar 1 and the lumbar 2 vertebrae. The epidural space is a region of loosely bound tissue which has within it a negative pressure. When an injection is made into the epidural space it is very important that the tip of the needle passes through the ligamentum flavum but does not puncture the dura. If the needle does not pass through the ligamentum flavum the anaesthetic will have little effect. If the dura itself is punctured there is danger of spinal anaesthetic with subsequent headache and other complications.

The correct location of the needle can be very difficult because the needle has to pass through 1u-2 inches (3.175-6.35 centimetres) of flesh and then be correctly located within a space which is a few millimetres wide. Clearly, for the student, this is a daunting task. An experienced anaesthetist will become used to the change in resistance as the needle tip passes from tissues of high resistance to those of low resistance and will know, with a degree of certainty, that the needle tip is within the epidural space. However, until this degree of experience is achieved, great care has to be taken to ensure that the needle tip is in the correct location.

It should be noted that whenever an epidural anaesthetic is given, even by the most experienced operator, a test dose is always used of a very small dosage to ensure that the correct effect is achieved.

Review of the Prior Art A number of different techniques have been developed to aid the inexperienced anaesthetist. A number of indicators have been developed which depend upon the negative pressure within the epidural space. The commonest of these is known as the 'hanging drop test' which entails the insertion of an open ended needle having a liquid drop hanging from its open end.

When the tip of the needle enters the epidural space, the negative pressure causes the drop to be sucked inwards. Unfortunately this method is not 100% effective and can give a false indication. Moreover, the method can only be used for thoracic and cervical epidural injections and cannot be used effectively in the lumbar regions. Other indicators include a 'balloon indicator' which has a balloon which is inflated and attached to the end of the open ended needle. This balloon deflates quickly when the tip of the needle enters the epidural space.

A similar method includes a liquid between the balloon and the needle so that as the tip of the needle enters the epidural space the gas within the balloon is sucked through the liquid causing it to froth which is a visual effect. Other indicators include auditory devices which cause a hiss as the epidural space is entered.

The other type of method is to apply pressure on the plunger of a syringe as the needle is passed towards the epidural space. When the operator feels a loss of resistance due to the passage of the needle tip from tissues of high resistance into the epidural space, the operator will know that the needle is in the correct location. However, because it depends on feel it is a method which is difficult to use in teaching.

Summary of the Invention According to the invention there is provided an epidural space location device comprising a syringe consisting of an elongate outer vessel including a chamber, at least partially transparent, and which in use is fluid-filled, and coupled to one end of the chamber a plunger housing portion of substantially constant internal cross-section, a plunger slidably mounted within the plunger housing portion, the plunger having a cross-section substantially equal to the internal cross-section of the plunger housing portion, and a needle mounted at the end of the chamber opposite the plunger housing portion, the needle being mounted at a position off-set from an axis extending centrally along the vessel, the device also comprising a rotor mounted within the chamber to rotate about an axis perpendicular to the central axis of the vessel, and substantially perpendicular to a line passing through the position of the needle and the central axis, the rotor including at least one blade which lies across a plane perpendicular to the axis of rotation such that negative pressure applied to the needle causes rotation of the rotor.

The fluid with which the chamber is filled may be any gas or liquid but typically will be air which will not inhibit the rotation of the rotor.

The resulting system is one which is ideal for teaching purposes since an instructor can readily monitor the progress of the needle and notice immediately rotation of the rotor. Once rotation occurs the instructor and student will know that the needle tip has reached the epidural space due to the change in pressure between the needle and the chamber.

In order to readily see the movement of the rotor preferably it is brightly coloured so that the movement will easily be noticed. Alternatively the rotor may be coloured in stripes of contrasting colours to emphasize the rotation.

It is for this reason that the chamber must be transparent.

In most cases, the whole syringe vessel will be transparent since many syringes are made of glass or clear plastics. In this case it is preferred that the syringe is a plastics syringe since this allows for the friction between the plunger and the plunger housing to be kept to a minimum to allow smooth movement of the plunger within the syring vessel.

Preferably the rotor is of a material which is light and has a low coefficient of friction so that it will rotate easily within the vessel. The shape of the blades of the rotor may be planar but lie off-set from the plane perpendicular to the axis of rotation so that they present a surface on to which negative pressure can be applied by the needle. Alternatively the blades may be non-planar, for instance, aerofoil shape. The choice of shape of rotor will be readily apparent to the skilled addressee of the specification.

The outer vessel of the syringe may comprise one continuous vessel of constant cross-section so that the chamber just forms one end of the vessel. However, it is preferred that the chamber is of smaller internal cross-section than the plunger housing region to help increase the pressure within the chamber. This increases the differential between the pressure in the chamber and the negative pressure in the epidural space to produce a marked effect. Thus the syringe vessel may have one area of larger outer cross-section than the end. However, it is preferred that the outer cross-section of the vessel is constant to aid the operator in handling the syringe. In this case, the walls of the chamber may be thickened to reduce the internal crosssection. However, this may cause difficulty in seeing the rotor.

To overcome this the chamber may include inner walls which act as partitions to reduce the internal cross-section.

The pressure within the chamber may be further increased by the placing of a diaphragm within the chamber having a hole aligned with the position of the needle. The choice of material for the diaphragm will be readily apparent to the skilled addressee of the specification.

The rotor may be permanently mounted within the chamber of the syringe since it will not interfere with the use of a syringe to apply the anaesthetic or analgesic. However, the rotor may be disposable and only temporarily mounted within the chamber of the syringe until the epidural space has been correctly located.

The whole syringe may also be arranged to be disposable.

Brief Description of the Drawings An epidural space location device in accordance with the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a longitudinal section of the device; and, Figure 2 is a view in direction A in Figure 1.

Description of the Preferred Embodiment An epidural space location device 1 comprises a syringe 3 consisting of an elongate outer vessel 5 including a chamber 7 at least partially transparent and which in use if fluid-filled. The fluid here is air. Coupled to the end of the chamber 7 is a plunger housing portion 9 of substantially constant internal cross-section.

Slidably mounted within the plunger housing portion 9 is plunger 11 which has a cross-section substantially equal to the internal cross-section of the plunger housing portion 9.

A needle 13 is mounted at the end of the chamber 7 opposite the plunger housing portion 9 and is mounted at a position 15 off-set from an axis 17 extending centrally along the vessel 5.

The device 1 also comprises a rotor 19 which is mounted within the chamber 7 to rotate about an axle 21 which is perpendicular to the central axis 17 of the vessel and substantially perpendicular to a line 23 passing through the position 15 of the needle and the central axis 17. The rotor includes six non-planar blades 25 arranged such that negative pressure applied to the needle 13 causes rotation of the rotor 21. The blades 25 lie across the plane lying perpendicular to the axis of rotation 21. The axis of rotation 21 is formed by a cylindrical pin which is rotable with respect to the walls 27 of the chamber 7.

Here the vessel 5 has a constant cylindrical cross-section but the internal cross-section of the chamber 7 and plunger housing portion 9 are different. The walls of the chamber 7 are formed by partitions 27 which reduce the internal cross-section of the chamber 7. A diaphragm 29 extends across the body of the chamber to further increase the pressure within the chamber 7. The diaphragm 29 is of clear plastics and includes a hole 31 aligned with the position 15 of the needle 13. The plunger 11 and the vessel 5 are made from a low-friction plastics which is lightweight and transparent. The rotor 19 i-..c!jAes six blades 25 which are aerofoil shaped such that pressure applied at position 15 cause rotation of the rotor. The blades 25 are all of different colours so that the rotation of the rotor 19 is very easy to see.

In use the chamber 7 is filled with air and pressure is applied by the plunger 11 to ensure that a high pressure exists within the chamber 7. As the needle 13 is advanced through the flesh, once it has passed from the dense tissue of the ligamentum flavum into the epidural spaace, the negative pressure within the epidural space applies negative pressure to the needle 13 and thus a sucking action is applied at position 15. This pressure differential immediately causes rotation of the rotor 19 which is readily visible.

Because such a positive effect is produced the system is ideal for use in teaching where the student has not yet reached the stage where feel alone is enough for him to be sure he has reached the epidural space correctly.

Claims

1. A device functioning as an epidural space location aid and comprising an elongate and at least partially transparent chamber, fitting on to the end of a syringe vessel in use, and an epidural needle projecting in use from that end of the chamber remote from the plunger-housing portion of the vessel; the chamber having a rotor so mounted within it that rotation thereof is visible through the transparent ~ portion of the chamber; the chamber, when fitted on to the syringe vessel, putting the needle into fluidflow communication with both the rotor and the syringe vessel; and the relative arrangement and intercommunication of needle, chamber and rotor, and syringe vessel thereby being such that the negative pressure experienced at the tip of the needle as it enters the epidural space in use is transmitted via the needle to the chamber and causes the rotor to rotate.

2. A device according to Claim 1 and in which'the needle axis is offset from the rotor axis.

3. A device according to Claim 1 or Claim 2 and in which the needle axis is offset from the axis of the syringe vessel in use.

4. An epidural space location device comprising a chamber, one end of which can fit in use on to the end of a syringe vessel; an epidural needle projecting from the other end of the chamber; and a rotor mounted within the chamber, the construction and arrangement of the device being substantially as described herein with reference to and as illustrated in Figure 1 of the accompanying drawings.

5. A device according to Claim 4 when modified substantially as described herein with reference to and as illustrated in Figure 2 of the accompanying drawings.

6. A syringe fitted with a device in accordance with any of the preceding claims.

7. A syringe according to Claim 6 and in which the chamber is of smaller internal cross-section than the plunger-housing portion of the syringe vessel.

8. A syringe according to Claim 6 or Claim 7 and in which the chamber is of substantially the same external shape and cross-section as the portion of the syringe vessel on to which the chamber fits or of which it forms an extension.

9. A syringe, fitted with or incorporating as part of its construction a rotor-containing chamber and with the syringe needle projecting from the end of said chamber, the syringe being substantially as described herein with reference to and as illustrated in Figure 1 of the accompanying drawings.

10. A syringe according to Claim 9 when modified substantially as described herein with reference to and as illustrated in Figure 2 of the accompanying drawings.