Electrical cable for use in a medical surgery environment

Abstract: An electrical cable comprises, multiple conductors (2), a dense shield (5) encircling the conductors, a sealant sheath (8) encircling the dense shield (5), an open braid armor (11) encircling the sealant sheath (8), and a sealant layer (14) covering the open braid armor (11) and entering interstices (13) in the open braid armor (11) to bond to the sealant sheath (8).

Description: The invention relates to an electrical cable and, more particularly, to an electrical cable for use in a medical surgery environment. According to US Patent No 4 761 519, an electrical cable is disclosed for linking an electronic medical instrument and a patient monitoring transducer. The transducer is applied to the body of a human patient to monitor human vital functions. A stiff and inflexible cable would apply a bias force on the transducer which would resist movement of the transducer and which would cause discomfort to the patient. An exterior of the cable must be smooth to avoid abrasion and other discomfort to the patient. An electrical cable used in a medical surgery environment must resist contamination by blood-borne viruses and other infectious contaminants. The cable core, meaning component parts of the cable in the interior of the cable, must be sealed by a sheath against incursions of such infectious contaminants, as well as other noninfectious contaminants. Such a sheath that covers the core is required to be flexible, limp and capable of sterilization in an autoclave. A concern exists that such a sealant sheath is susceptible to being damaged by contact with sharp surgical tools and by contact with other surgical apparatus. Thus, it is desirable to provide armor protection for the sheath without significantly reducing flexibility of the cable and without altering the exterior of the cable to cause discomfort to a patient. FR-A-2 254 862 (on which the pre-characterising part of claim 1 is based) describes a shielded electrical cable usable with ordinary electrical installations and comprising multiple electrical conductors in a core of the cable, an inner insulating casing covering the core, a shield embedded in an outer insulating casing, the material of which penetrates the interstices of the shield during injection so that the shield is securely anchored. The shield provides electrical shielding and also functions to relieve traction on the cable. This known electrical cable is resistant to traction, which contradicts the requirement that a cable for linking a patient monitoring transducer and a medical instrument, as described in US 4 761 519, should be flexible and limp. The present invention consists in an electrical cable comprising a core having one or more electrical conductors, a shield encircling the conductors and a sealant sheath encircling and covering the shield to seal the core, characterized in that: (i) the cable is for use in a medical surgery environment contaminated by blood-borne viruses and other infectious contaminants; (ii) the cable further comprises an armour of braided wire strands encircling the sealant sheath and a sealant layer covering the braided armour; and (iii) the sealant sheath and sealant layer are both of silicone material and fused to one another through interstices of the braided armour. Hence an electrical cable constructed in accordance with this invention has a sealant sheath that isolates an interior of the cable from contaminants and armur which is capable of protecting the sealant sheath from being damaged by contact with sharp surgical tools and other surgical apparatus. Embodiments of the invention will now be described by way of example with reference to the accompanying drawings, according to which: FIGURE 1 is an isometric view of a portion of an electrical cable comprising, in part, a sealant sheath and an open braid; FIGURE 2 is an isometric view of a portion of another electrical cable comprising, in part, a sealant sheath and an open braid;and FIGURE 3 is a plan view of a portion of an alternative construction of the cable as shown in Figs. 1 and 2. With reference to Figs. 1 and 2, an electrical cable 1 for use in a medical surgery environment comprises one or more continuous electrical conductors 2, for example, one or more insulated wires 3 or one or more coaxial cables 4, or both insulated wires and coaxial cables 4, of fine wire gauge, for example, 32 to 42 AWG. The conductors 2 comprise a core of the cable. The core of the cable further comprises, a continuous hollow sheath 6 of polytetrafluoroethylene that encircles the conductors 2. The hollow sheath 6 can be eliminated from the construction of the cable 1. The core of the cable further comprises, a continuous conductive electrical shield 5. The shield 5 encircles and covers the conductors 2, and covers the hollow sheath 6 if present. The electrical shield 5 is constructed of a dense braid of metal wire strands 7. The dense braid assures complete coverage over the conductors 2 that require the electrical shield 5 for protection from undesired RF and EMI electrical energy. To seal the core from contaminants, a hollow sealant sheath 8 encircles and covers the shield 5. The sealant sheath 8 is continuous, nonporous, and is fabricated of a flexible and limp material, for example, silicone known as GE 63A TUFEL, available from the General Electric Company, having a typical durometer of 63. According to Fig. 1, the core of the cable 1 further comprises, a moisture barrier sheath 9 which is fabricated, for example, of ETFE polymer, encircles the hollow sheath 6, and is interposed between the hollow sheath 6 and the electrical shield 5 of dense braid. The moisture barrier sheath is not present in the cable 1 shown in Fig. 2. With reference to Fig. 2, an alternative construction is shown of the cables 1 described in either Fig. 1 or Fig. 3, wherein the core of the cable 1 further comprises multiple filaments 10 of Kevlar that are bunched with the conductors 2 to provide the core of the cable 1 with a cross section of approximate cylindrical shape. Silicone has high elasticity and is capable of being elongated with an elastic recovery to shape. Silicone is a surgical material and has low tear strength and is easily cut with a surgical instrument. A concern exists that such a sealant sheath 8 is susceptible to being damaged by contact with a sharp surgical tool and by contact with other surgical apparatus. Thus, it is desirable to provide armor protection for the sealant sheath 8. The cable 1 must be flexible and limp, and armored against cutting and penetration of contaminants, and have bonded together layers of jacketing material with the armor. The armor protection is to be provided for a sealant sheath 8 on such an electrical cable 1 without significantly reducing flexibility of the cable 1, and without altering the exterior of the cable 1 to cause discomfort to a patient. According to a feature of the invention, an armor 11 comprises a continuous open braid of metal wire strands 12, also known as ends. The metal strands 12 are braided together in an open braid, meaning that at least fifty per cent of the area of the armor 11 is comprised of interstices 13 through the armor 11. The sealant sheath 8 need not be covered with a dense braid of metal wire, since an open braid provides a grid of wire strands 12 that will resist being penetrated by a sharp surgical tool and by other surgical apparatus. The open braid provides a flexible and limp armor 11 for protecting the sealant sheath 8 on the cable 1. Hard drawn stainless steel wire is preferred. The open braid provides a further advantage, wherein the interstices 13 receive therein an exterior sealant coating 14 that bonds to the sealant sheath 8. The exterior sealant coating 14 covers the armor 11 and enters the interstices 13 and bonds to the sealant sheath 8. For example, both the sealant sheath 8 and the exterior sealant coating 14 can be fabricated of a silicone material, for example, GE 63A TUFEL, available from the General Electric Company, having a typical durometer of 63. Such material is cured, by the application of heat at a specified temperature and time duration, according to a process that is recommended by the manufacturer. The sealant sheath 8 on the cable 1 described with reference to Fig. 2 is partially cured by interrupting the process before completion of the curing process. The exterior sealant coating 14 is applied to the cable 1, and is subsequently cured completely, according to the process recommended by the manufacturer. The partially cured sealant sheath 8 becomes fully cured, together with the exterior sealant coating 14. The sealant sheath 8 and the exterior sealant coating 14 bond by fusion during the curing process. The sealant sheath 8, fabricated of silicone for example, is partially cured, for example, 50% to 70% cured, and upon being fully cured, is converted from a putty-like consistency to a more solidified consistency. The exterior sealant coating 14 and the armor 11 comprise a unit of construction wherein they are immobile with respect to each other. The sealant coating 14 in the interstices 13 is interlocked with the armor 11 of open braid construction, and is interlocked with the sealant sheath 8. The sealant coating 14 is capable of stretching resiliently and returning to its original shape. The open braid construction allows considerable stretching of the sealant coating 14 and the sealant sheath 8, since the coverage of the braid is 50% or less. The exterior sealant coating 8 and the sealant sheath 14 are described as being fabricated of the same material. However, other materials can be selected that will bond together, whether the same or different materials are selected, such materials having physical and chemical properties that permit the materials to bond to each other. The materials are required to bond together without melting the sealant sheath. An electrical cable 1 for use in a medical surgery environment is to be sterilized, for example, in an autoclave environment, wherein the cable 1 is subjected to steam under pressure at 150 degrees Celsius for a time duration necessary for disinfection. Chemical disinfectants may be present in an autoclave environment. The interior of the cable 1 must be sealed to resist incursions of autoclave moisture and chemical contaminants from the core of the cable 1. Accordingly, another aspect of the invention resides in an electrical cable 1 constructed with materials of enhanced flexibility and limpness that can withstand an autoclave environment. The materials for fabricating the sealant sheath 8 and the exterior sealant coating 14 resist steam under pressure at an elevated temperature of 150 degrees Celsius, for example, when sterilized in an autoclave environment. Such an elevated temperature degrades polymer cable materials, for example, by leaching plasticizers. The materials also take a set, meaning that their shape becomes permanently deformed. The armor on the cable 1 isolates the sealant sheath 8 from cuts in the cable 1 that would allow fluids of an autoclave environment to leak into interior of the cable 1 and cause damage to the materials in the core of the cable 1. The cable 1 is constructed according to the following examples: EXAMPLE I A core of the cable 1 is constructed of conductors 2 comprising, 2 - 34/32 american wire gauge insulated wires 3 and one single coaxial cable 4. Insulation on the conductors 2 is capable of withstanding 150 degrees Celsius. Kevlar filaments 10 provide space fillers that will compress slightly to assume a cylindrical shape in the cross section of the core. The filaments 10 and the conductors 2 are bunched together in parallel to form a cylindrical bundle. Unsintered PTFE tape is helically wrapped over the conductors to provide a sheath 6 having a diameter of 1.5mm (0.06 inch). The sheath 8 is pressure extruded over with silicone to a diameter of 2.8mm (0.11 inch). The silicone is cured to seventy per cent cured, followed by applying an armor of open braid of 304 stainless steel wires 12 having 30 % coverage and a 60 degree braid angle with 3.9 pics/cm (10 pics/inch). Eight wire ends comprise the open braid of 4x4 ends per carrier. Standard braid coverage formulas, known in the industry, are followed to achieve 50% or less coverage of the sealant sheath 8 by the open braid. The open braid is partially imbedded in the partially cured, sealant sheath 8, and provides a diameter of 2.9mm (0.115 inch). A pressure extrusion of an exterior sealant coating 14 of silicone covers the open braid, and is bonded to the sealant sheath 8 within interstices in the open braid. Curing at elevated temperatures will cure not only the exterior sealant layer 14, but also will completely cure the partially cured, sealant sheath 8. The open braid becomes imbedded in the silicone material of the sheath 8 and the exterior sealant layer 14. During curing, the exterior sealant layer 14 and the sealant sheath 8 bond together by fusion. EXAMPLE 2 A finished cable 1 of 3.8mm (0.15 inch) diameter is constructed with equal thicknesses of polymer on both sides of a stainless steel braid. The braid angle of the braid pics is increased from 60 degrees braid angle to promote flexibility. An advantage of the invention resides in an electrical cable constructed with a flexible and limp armor for protecting a sealant sheath on the cable. Another advantage of the invention resides in an electrical cable constructed with an armor of open braid construction providing interstices in the armor within which an exterior sealant layer bonds to a sealant sheath that is protected from damage by the open braid. Another advantage of the invention resides in an electrical cable for use in a surgery environment, according to which, a sealant sheath of the cable is capable of sterilization, an armor is constructed of braided metal strands over the sealant sheath, at least fifty per cent of the area of the armor is comprised of interstices through the armor, and an outer sealant coating covers the armor and enters the interstices to bond to the sealant sheath. Another advantage of the invention resides in an electrical cable constructed with a flexible and limp armor for protecting a sealant sheath on the cable, interstices in the armor, and an exterior sealant coating on the armor and entering the interstices to bond to the sealant sheath.

Claims: An electrical cable (1) comprising a core having one or more electrical conductors (2), a shield (5) encircling the conductors and a sealant sheath (8) encircling and covering the shield (5) to seal the core, characterized in that: (i) the cable is for use in a medical surgery environment contaminated by blood-borne viruses and other infectious contaminants; (ii) the cable (1) further comprises an armour (11) of braided wire strands encircling the sealant sheath (8) and a sealant layer (14) covering the braided armour (11); and (iii) the sealant sheath (8) and sealant layer (14) are both of silicone material and fused to one another through interstices of the braided armour (11). An electrical cable according to claim 1, a helically wrapped tape of unsintered PTFE i.e polytetrafluoroethylene material being disposed between the electrical conductor(s) and the shield (5) which tape forms a hollow sheath (6) which encircles the electrical conductor(s). An electrical cable according to claim 1 or 2, wherein the sealant layer (14) has a durometer of at least 62. An electrical cable according to any preceding claim, the sealant sheath (8), the armour (11) and the sealant layer (14) being formed from material able to withstand the sterilising temperature present in an autoclaved of 150°C.

Inventors: BECK DORIS ARLENE, BUCK ARTHUR GLEN, CHY SOKHA, BECK, DORIS ARLENE, BUCK, ARTHUR GLEN, CHY, SOKHA
Applicants: WHITAKER CORP, THE WHITAKER CORPORATION
Application year: 1995
Main classification: H01B7
IPC codes: H01B7