WO2010089523A1

WO2010089523A1 - Medico-surgical tubes

Info

Publication number: WO2010089523A1
Application number: PCT/GB2010/000007
Authority: WO
Inventors: Christopher Stratton Turnbull
Original assignee: Smiths Medical International Limited
Priority date: 2009-02-06
Filing date: 2010-01-05
Publication date: 2010-08-12
Also published as: GB0902002D0

Abstract

A tracheostomy tube (1) has a wall (14) of a silicone rubber and a helical reinforcement element (15) moulded within its thickness. The reinforcement element (15) is formed from a low iron alloy containing predominantly cobalt and nickel. In particular, the alloy may be MP35N alloy containing substantially 34 wt% cobalt, 20.56wt% chromium, 34.68 wt% nickel and 9.53 wt% molybdenum. The tube (1) can be used with MRI scanners (17, 18) with little distortion of the image.

Description

MEDICO-SURGICAL TUBES

This invention relates to medico-surgical tubes of the kind having a wall of a plastics or rubber material and a metal helical reinforcement element affixed with the wall along a part at least of the length of the tube.

Medico-surgical tubes are used for a variety of different purposes and are usually made from a plastics material, such as PVC, polyurethane or a silicone material. The tubes may be straight or formed with a bend or curvature along their entire length or along only a part of their length. In some circumstances, the tube may be reinforced by means of a helical reinforcement element embedded in the wall of the tube. For example, where it is desired to provide a highly flexible tracheal tube, this can be made of a soft, highly flexible plastics or silicone rubber, and reinforced with a helical wire to give the tube sufficient radial strength to prevent it being kinked or compressed during use. The wire reinforcement is typically of a stainless steel material, which has the desired resilience and strength and is biologically acceptable. US6148818 describes a PVC endotracheal tube reinforced with a harder plastics filament. EP950424 also describes a tube reinforced with a plastics filament. US5429127 describes an endotracheal tube reinforced with Nitinol wire, which is a nickel titanium SME alloy. US5546936 describes an endotracheal tube with a reinforced portion including a filament of steel, copper, nickel, aluminium, brass, plastic or graphite. WO2008/083286 describes an airway reinforced with a titanium or tungsten alloy.

Although wire-reinforced tubes are very useful, they have various disadvantages. Some may not be suitable when used in situations where an MRI scan may be needed because the magnetic properties of a ferrous wire can cause significant distortion of the MRI image. Often, when the patient is intubated, such as with a tracheostomy tube, it may not be known that the patient will need an MRI scan later. Before the scan, therefore, it may be necessary to replace the tube with a non-reinforced tube, which is traumatic for the patient and necessitates interruption of the patient ventilation. Some tubes are available with non-metallic reinforcements, made from a stiff helical plastics filament but these do not have the same resiliency properties as metal reinforcements and, if crushed, can remain in a distorted shape leading to at least partial occlusion of the passage along the tube. Other metal materials may not have acceptable mechanical properties, be difficult to manufacture, have corrosion or toxicity problems, or be expensive.

It is an object of the present invention to provide an alternative medico-surgical tube and method of imaging.

According to one aspect of the present invention there is provided a medico-surgical tube of the above-specified kind, characterised in that the metal is a low iron alloy containing predominantly cobalt and nickel.

The metal is preferably a nickel-cobalt-chromium-molybdenum alloy. It preferably contains approximately 34 wt % cobalt, 20.56 wt% chromium, 34.68 wt% nickel and 9.53 wt% molybdenum. The metal is preferably MP35N metal alloy. The wall material may be a silicone rubber. The tube is preferably a ventilation tube such as a tracheal tube, for example a tracheostomy tube. The reinforcement element is preferably moulded within the thickness of the tube wall.

According to another aspect of the present invention there is provided a method of imaging a patient comprising the steps of intubating the patient with a plastics or rubber tube reinforced helically with a wire of a low iron alloy containing predominantly cobalt and nickel and subsequently imaging a part at least of the patient with an MRI scanner.

The method preferably includes intubating the patient with a tracheal tube.

A paediatric tracheostomy tube and its use in an imaging method according to the present invention will now be described, by way of example, with reference to the accompanying drawings, in which:

Figure 1 is a side elevation view of the tube;

Figure 2 is an enlarged cross-sectional view of the tube along the line H-II; Figure 3 illustrates the tube in use in an imaging method.

With reference first to Figures 1 and 2, the tube 1 comprises a tubular shaft 10 and a flange and hub assembly 12 fixed at the machine end 13 of the shaft.

The shaft 10 is moulded from a soft, flexible silicone rubber material 14 and has a circular section with an external diameter of 2.5mm (for paediatric use) and a curve along its length. A metal helical reinforcement element 15 is embedded within the thickness of the wall 14 of the shaft 10. The metal is a non-ferrous or low iron, nickel-cobalt-chromium- molybdenum alloy containing predominantly cobalt and nickel and is preferably MP35N alloy. MP35N is available from SPS Technologies Inc of Jenkintown, PA, USA. MP35N alloy is a nonmagnetic, nickel-cobalt-chromium-molybdenum alloy possessing ultrahigh tensile strength, good ductility and toughness. The mechanical properties of MP35N alloy are developed through work hardening, phase transformation and aging. The typical composition (Wt %) of the alloy is set out below:

Carbon 0.008

Manganese 0.01

Silicon 0.01

Phosphorus 0.001

Sulphur 0.001

Chromium 20.56

Nickel 34.68

Molybdenum 9.53

Cobalt Balance (approximately 34 wt%)

Titanium 0.75

Boron 0.009

The alloy is a low iron alloy and may contain zero or small amounts of iron, up to around 0.5 wt% but this is not enough to contribute any noticeable magnetic effect. The alloy has been used extensively in medical applications, such as pacemaker leads, orthopaedic implants and the like and has FDA approval in various devices. This material has high strength and resilience to resist deformation and to recover its original shape after any crushing of the helix. Helical springs made from stainless steel (typically stainless steel 304 as used conventionally in reinforced tracheal tubes) and from MP35N have been found to have very similar values of elastic modulus E, as follows:

E_ss = 28xl0⁶ psi (or l93Gpa) E_Mp = 33x10⁶ psi (or 227Gpa) where Ess is the elastic modulus of stainless steel and E_MP is the elastic modulus of the MP35N alloy.

The majority of the stiffness of the tube 1 is created by the silicone rubber wall material 14 so, when the MP35N helical spring 15 is incorporated within a tube 1 its mechanical properties are very similar to those of conventional stainless steel reinforced tubes.

The method of the present invention will now be described with reference to Figure 3. This involves intubating the patient 20 with the tracheostomy tube 1 in the usual way. The machine end fitting 12 of the tube 1 may be connected to a conventional ventilation circuit 16 or left open to atmosphere if the patient is breathing normally. The intubated patient 20 is then moved into a conventional MRI scanner 17 and a scan of the patient is made in the usual way for display on a screen 18 or for storage and subsequent analysis. The scan can include the region of the neck where the tube 1 is located with very little or no perceptible distortion of the image produced. The metal used for reinforcing the tube shaft 10 has excellent mechanical properties to ensure that the flexibility and radial strength of the tube 1 is not compromised. The present invention enables reinforced tubes to be used where MR imaging is required, without the disadvantages of previous reinforcing elements.

Similar metal reinforcement wires can be used in tubes made by techniques other than moulding, such as by dipping or extrusion. Where the tube is extruded, the helical reinforcement could be wound between two layers of the tube. The wire need not be embedded within the thickness of the wall of the tube but could be attached to the outer or inner surface of the shaft. The reinforcement need not extend along the entire length of the tube or might just be provided in a localized region, such as in the region of the teeth, where the tube extends through the mouth. The tube need not be a tracheostomy tube but could be alternative ventilation tubes such as endotracheal tubes, laryngeal masks or airways and could be of any size. Alternatively, the tube could be for purposes other than ventilation, such as for drainage, fluid supply or the like. The tube could be entirely implanted within the body, such as in the form of a stent or catheter extending from an implanted port.

Claims

1. A medico-surgical tube having a wall (14) of a plastics or rubber material and a metal helical reinforcement element (15) affixed with the wall along a part at least of the length of the tube, characterised in that the metal (15) is a low iron alloy containing predominantly cobalt and nickel.

2. A medico-surgical tube according to Claim 1, characterised in that the metal (15) is a nickel-cobalt-molybdenum alloy.

3. A medico-surgical tube according to Claim 2, characterised in that the metal (15) contains approximately 34 wt % cobalt, 20.56 wt% chromium, 34.68 wt% nickel and 9.53 wt% molybdenum.

4. A medico-surgical tube according to any one of the preceding claims, characterised in that the metal (15) is preferably MP35N metal alloy.

5. A medico-surgical tube according to any one of the preceding claims, characterised in that the wall material is a silicone rubber (14).

6. A medico-surgical tube according to any one of the preceding claims, characterised in that the tube is a patient ventilation tube (1).

7. A medico-surgical tube according to Claim 6, characterised in that the tube is a tracheal tube (1).

8. A medico-surgical tube according to Claim 7, characterised in that the tube is a tracheostomy tube (1).

9. A medico-surgical tube according to any one of the preceding claims, characterised in that the reinforcement element (15) is moulded within the thickness of the tube wall (10).

10. A method of imaging a patient comprising the steps of intubating the patient with a plastics or rubber tube (1) reinforced helically with a wire (15) of a low iron alloy containing predominantly cobalt and nickel and subsequently imaging a part at least of the patient with an MRI scanner (17, 18).

11. A method according to Claim 10, characterised in that the method includes the step of intubating the patient with a tracheal tube (1).