RF electrode sleeve

Abstract

A cannula comprising a cannula tube and a cannula tip is described herein. The cannula comprises a proximal end, a distal end, a cannula tube lumen, a sidewall, and a sidewall opening extending through the sidewall, the sidewall opening having a proximal end and a distal end. The cannula tip is secured to the distal end of the cannula tube and comprises a proximal tip portion inserted into the cannula tube lumen and a distal tip portion extending beyond the distal end of the cannula tube. The cannula tip is configured to permit fluid flow therethrough and is configured to eject the distal tip of an elongated device through the sidewall opening of the cannula tube when the elongated device is inserted through the cannula tube from the proximal end.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of U.S. Provisional Application No. 62 / 926,683, filed on October 28, 2019, and entitled “RF ELECTRODE SHOULDERS,” the entire contents of which are incorporated herein by reference. Technical Field

[0003] The present disclosure relates to novel cannulas and to systems and methods employing such cannulas. Background Art

[0004] Cannula and electrode assemblies are known and have been used for tissue ablation for some time. Among these are cannula and electrode assemblies in which the cannula is provided with a side opening a short distance from the distal end of the cannula, through which the electrode is guided so that the distal end of the electrode protrudes from the side opening. When current is supplied to such an assembly, the ablation current flows through a volume of the assembly that is larger than the volume affected by the electrode protruding from the distal end of the cannula. Summary of the Invention

[0005] In some aspects, the present disclosure relates to a cannula comprising (a) a cannula tube comprising a proximal end, a distal end, a cannula tube lumen, a sidewall, and a sidewall opening extending through the sidewall, the sidewall opening having a proximal end and a distal end; and (b) a cannula tip secured to the distal end of the cannula tube, the cannula tip comprising a proximal tip portion inserted into the cannula tube lumen and a distal tip portion extending beyond the distal end of the cannula tube, the cannula tip being configured to permit fluid flow therethrough, and the cannula tip being configured to eject the distal tip of an elongated device through the sidewall opening when the elongated device is inserted through the cannula tube from the proximal end of the cannula tube.

[0006] In some embodiments, the casing tip is secured to the casing pipe by welding.

[0007] In some embodiments, which may be used in combination with any of the above aspects and embodiments, the distal end of the sidewall opening is beveled.

[0008] In some embodiments, which may be used in combination with any of the above aspects and embodiments, the sidewall opening extends an angle ranging from 120 to 160 degrees around the circumference of the cannula tube.

[0009] In some embodiments, which may be used in combination with any of the above aspects and embodiments, the cannula conduit is bent at an angle ranging from 5 to 45 degrees at the proximal end of the sidewall opening.

[0010] In some embodiments that may be used in combination with any of the above aspects and embodiments, the proximal tip portion has a first outer diameter and the distal tip portion has a second outer diameter that is larger than the first outer diameter, and there is a gradual increase in diameter between the proximal tip portion and the distal tip portion such that the proximal tip portion is inserted into the distal end of the cannula tube and such that the proximal end of the distal tip portion is adjacent to the distal end of the cannula tube portion.

[0011] In some embodiments, which may be used in combination with any of the above aspects and embodiments, the distal tip portion has an outer diameter that is the same as an outer diameter of the cannula conduit.

[0012] In some embodiments that may be used in combination with any of the above aspects and embodiments, the cannula tip includes a lumen allowing fluid to flow therethrough, a channel allowing fluid to flow therethrough, a slot allowing fluid to flow therethrough, a combination of a lumen and a slot allowing fluid to flow therethrough, a combination of a lumen and a channel allowing fluid to flow therethrough, a combination of a channel and a slot allowing fluid to flow therethrough, or a combination of a lumen, a channel, and a slot allowing fluid to flow therethrough.

[0013] In some embodiments, which may be used in combination with any of the above aspects and embodiments, the proximal tip portion includes a slot, and the distal tip portion includes a distal tip lumen in fluid communication with the slot.

[0014] In some embodiments that may be used in combination with any of the above aspects and embodiments, the proximal portion of the cannula tip includes a ramp at its proximal end, the ramp having a proximal end and a distal end. In some of these embodiments, the slot bisects the ramp, and / or the distal end of the ramp terminates proximate to the distal end of the sidewall opening.

[0015] In some embodiments, which may be used in combination with any of the above aspects and embodiments, the slot does not extend to the distal end of the proximal tip portion.

[0016] In some embodiments, which may be used in combination with any of the above aspects and embodiments, the distal end of the slot includes a circular recess that is axially aligned with and has the same diameter as the distal tip lumen.

[0017] In some embodiments, which may be used in combination with any of the above aspects and embodiments, the cannula further comprises a hub attached to the proximal end of the cannula tubing.

[0018] In some aspects, the present disclosure also provides a system comprising: (a) a cannula according to any of the above aspects and embodiments, and (b) an electrode having a distal electrode tip, wherein the electrode is configured to be inserted into the proximal end of the cannula and passed through the cannula tube, and wherein the cannula tip is configured to eject the distal electrode tip through a sidewall opening of the cannula tube when the electrode is inserted through the cannula tube from the proximal end of the cannula. In some embodiments, the distal electrode tip is rounded.

[0019] In some aspects, the present disclosure also provides an assembly comprising: (a) a cannula according to any of the above aspects and embodiments, and (b) a stylet having a stylet tip, wherein the stylet is configured to be inserted into the proximal end of the cannula and through the cannula channel so that when fully inserted, the stylet tip is proximate to the side wall opening.

[0020] In some embodiments, the cannula further comprises a needle hub attached to the proximal end of the cannula tube, wherein the stylet comprises a stylet cap attached to the proximal end of the stylet. In some of these embodiments, the stylet cap engages the trocar hub.

[0021] These and other aspects, embodiments and advantages of the present disclosure will become apparent to those of ordinary skill in the art upon reading the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 is a schematic diagram of the distal end of a cannula according to an embodiment of the present disclosure.

[0023] Figure 2 is a schematic diagram of the distal end of a cannula conduit according to an embodiment of the present disclosure.

[0024] Figure 3 is a schematic diagram of a casing tip according to an embodiment of the present disclosure.

[0025] Figure 4A and Figure 4B is a schematic diagram of a distal end of a system including a cannula and electrodes according to an embodiment of the present disclosure.

[0026] Figure 5 is a schematic diagram of a distal end of a system including a cannula and electrodes according to another embodiment of the present disclosure.

[0027] Figure 6 is a schematic diagram of a casing tip according to an embodiment of the present disclosure.

[0028] Figure 7 is a schematic diagram of a casing end according to another embodiment of the present disclosure.

[0029] Figure 8 is a schematic diagram of a casing end according to yet another embodiment of the present disclosure.

[0030] Figures 9A to 9C 1 are photographic images of a system including a cannula and an electrode at different points of advancement of the electrode within the cannula according to an embodiment of the present disclosure.

[0031] Figures 10A to 10C is a schematic diagram of an assembly including a cannula with a trocar hub and a stylet with a stylet cap according to an embodiment of the present disclosure. DETAILED DESCRIPTION

[0032] As discussed in more detail below, in one aspect, the present disclosure relates to a cannula that can be used to guide an elongated internal device such that the elongated internal device ejects through a sidewall opening in the cannula, rather than extending through the distal end of the cannula. In various embodiments described herein, the elongated internal device is an RF electrode. However, it should be understood that the cannula described herein can be used in systems that include internal devices other than RF electrodes.

[0033] A cannula according to the present disclosure includes (a) a cannula conduit comprising a proximal end, a distal end, a cannula conduit lumen, a sidewall, and a sidewall opening extending through the sidewall, and (b) a cannula tip secured to the distal end of the cannula conduit, the cannula tip having a proximal tip portion inserted into the cannula conduit lumen and a distal tip portion extending beyond the distal end of the cannula conduit. The cannula tip is configured to allow fluid to flow through the cannula tip and is further configured to eject the distal tip of an elongated device (e.g., an electrode) through the sidewall opening when the device (e.g., an electrode) is inserted through the cannula conduit from the proximal end of the cannula conduit. In this manner, the cannula of the present disclosure allows fluid injected through the lumen of the cannula conduit to be dispensed from the distal end of the cannula while not allowing the electrode to advance to the distal end of the cannula through the side port.

[0034] Referring now to the accompanying drawings, Figure 1 A bushing 100 according to the present disclosure is shown in FIG. Figure 1 The sleeve shown in FIG is made of Figure 2 The casing pipe 110 shown and the Figure 3 A variety of materials may be used to form the cannula conduit 110 and cannula tip 120, including various metals and polymeric materials.

[0035] Now go to Figure 2 (For example, in Figures 4A to 4B), which schematically illustrates a distal portion of a cannula conduit 110 according to an embodiment of the present disclosure. The cannula conduit 110 comprises a cannula conduit lumen 1101, a sidewall 110s, and a sidewall opening 110o having a proximal end 110op and a distal end 110od. The outer diameter of the cannula conduit will vary widely depending on the application and may range, for example, from 16 gauge (1.651 mm) to 23 gauge (0.6414 mm), among other values. The thickness of the sidewall 110s and the diameter of the inner lumen 1101 will depend on the gauge selected. Typically, the sidewall 110s thickness can range from 0.229 mm (e.g., for 16 gauge regular wall) to 0.102 mm (e.g., for 23 gauge thin wall), among other values. Typically, the diameter of the inner lumen 1101 can range from 1.194 mm (e.g., for 16 gauge regular wall) to 0.432 mm (e.g., for 23 gauge thin wall), among other values. The length 11001 of the sidewall opening will also vary depending on the gauge selected. In some embodiments, the length 11001 of the sidewall opening can range, for example, from 1.5 mm to 4.0 mm, such as 2.425 mm (based on an 18 gauge prototype) to 2.88 mm (based on a 20 gauge prototype), among other values.

[0036] The sidewall opening 110o will extend around the circumference of the casing conduit 110 at various angles 110oa, such as from 45 to 240 degrees, preferably from 100 to 180 degrees, more preferably from 120 to 160 degrees, among other values, around the circumference of the casing conduit 110.

[0037] The sidewall opening 110o can be formed by any suitable process, including machining, wire EDM, grinding, or laser cutting. Once formed, the edges of the sidewall opening 110o can be beveled via grinding and / or electropolishing processes. In various embodiments, the distal end 110od of the sidewall opening 110o can be provided with a bevel angle that matches the angle of the slope of the cannula tip 120 (described below).

[0038] In some embodiments, the distal end of the cannula tube 110 may be angled at 110a (see Figure 4B ) bend to aid in discharging the electrode. For example, the cannula tube 110 may be bent at an angle 110a ranging from 5 degrees to 45 degrees, typically ranging from 10 degrees to 30 degrees, among other values.

[0039] In certain embodiments, the material for the cannula tube 110 may be formed of metallic materials including iron-chromium alloys such as stainless steel, nickel-titanium alloys such as Nitinol, and nickel-chromium alloys such as Inconel.

[0040] Now go to Figure 3 (See also Figures 4A to 4B ), schematically illustrating a cannula tip 110 according to an embodiment of the present disclosure. The cannula tip 120 has a proximal end 110p and a distal end 110d. The cannula tip 120 is configured to allow fluid to flow therethrough, as discussed in more detail below. The cannula tip 120 also includes a ramp 122 at a proximal portion 120p thereof that is configured to assist in ejecting internal devices, such as electrodes, from the sidewall opening 110o of the cannula 100 by gently pushing the tip of the electrode in the direction of the sidewall opening 110o. In some embodiments, the proximal side of the ramp is provided with a ramp angle 122a relative to the longitudinal axis of the cannula tip 120 (see Figure 4B For example, the slope 122 may be provided with a slope angle 122a ranging from, for example, 15 degrees to 60 degrees, typically ranging from 25 degrees to 35 degrees, and other values.

[0041] Furthermore, the cannula tip 120 typically includes a bevel 124 at its distal tip that is configured to enhance the ability of the cannula 100 to penetrate tissue.

[0042] In certain embodiments, the material for cannula tip 120 may be formed from metallic materials including iron-chromium alloys (such as stainless steel), nickel-titanium alloys (such as Nitinol), and nickel-chromium alloys (such as Inconel).

[0043] As from Figure 1 As can be seen, when the cannula tube 110 and the cannula tip 120 are assembled, the distal end 110od of the sidewall opening 110o will be a predetermined distance 100d from the distal-most end of the cannula tip 120. In some embodiments, the distance 100d may range from 2 to 10 mm.

[0044] In the illustrated embodiment, the cannula tip 120 mates with the distal tip 110dt of the cannula tube 110. To provide this feature, the proximal portion 120p of the cannula tip 120 is formed such that the diameter of the proximal portion 120p is smaller than the inner diameter of the cannula tube 110 at the distal end of the cannula tube 110d (i.e., the diameter of the lumen 110l), so that the proximal portion 120p of the cannula tip 120 can be inserted into the distal end 110d of the cannula tube 110.

[0045] In various embodiments, the distal portion 120d of the cannula tip 120 is formed to have a larger diameter than the inner diameter of the cannula conduit 110 at the distal end 110d of the cannula conduit 110 (i.e., the diameter of the lumen 110l). In other words, there is a gradual increase in the diameter of the cannula tip 120 at the point where the distal portion 120d of the cannula tip 120 transitions to the proximal portion 120p of the cannula tip 120. In this manner, the proximal portion 120p of the cannula tip 120 can be inserted into the distal end 120d of the cannula conduit 110, but only to the point where the proximal tip 120dp of the distal portion 120d of the cannula tip 120 abuts the distal tip 110dt of the cannula conduit 110. In various embodiments, the outer diameter of the distal portion 120 d at the proximal end 120 dp matches the outer diameter of the cannula tube 110 at the distal end 110 dt of the cannula tube 110 .

[0046] The cannula tip 120 may be secured to the distal end 110d of the cannula tube 110 by a variety of methods, including, for example, by friction fit welding (eg, laser welding), or by use of a suitable adhesive, among other methods.

[0047] As previously mentioned, in various embodiments, the cannula 100 according to the present disclosure is configured to allow fluid to flow therethrough, such that the fluid exits the distal end of the cannula 100. First, note that in order to provide this feature for the cannula described herein, some mechanism must be provided to allow fluid to flow through and / or around the cannula tip 120. The inventors of the present disclosure have developed various strategies to provide this feature for the cannula described herein, including lumens, channels, slots, and combinations of these features.

[0048] For example, refer to Figure 6 In one embodiment, a cannula tip 120 is provided having a lumen 1201 extending therethrough. Although the lumen 1201 is shown as having an increase in diameter between the proximal portion 120p of the cannula tip 120 and the distal portion 120d of the cannula tip 120, other designs are possible in which the lumen 1201 decreases in diameter between the proximal portion 120p of the cannula tip 120 and the distal portion 120d of the cannula tip 120, or in which the lumen 1201 has a constant diameter within the proximal portion 120p of the cannula tip 120 and the distal portion 120d of the cannula tip 120.

[0049] As another example, Figure 7 As can be seen, a cannula tip 120 can be provided having a channel 120c extending along a proximal portion 120p of the cannula tip 120 and a distal portion 120d of the cannula tip 120.

[0050] As another example, Figure 8As can be seen, a cannula tip 120 may be provided having a channel 120c within a proximal portion 120p of the cannula tip 120 and a lumen 1201 within a distal portion 120d of the cannula tip 120.

[0051] exist Figure 1 、 Figure 3 、 Figure 4A 、 Figure 4B and Figure 5 In other embodiments shown in FIG, a cannula tip 120 having a slot 120s in a proximal portion 120p of the cannula tip 120 and a lumen 120ld in a distal portion 120p of the cannula tip 120 may be provided. Figure 5 The slot 120s extends along the entire length of the proximal portion 120p of the cannula tip 120 (that is, all the way to the proximal end 120dp of the distal portion 120d of the cannula tip 120 where there is a gradual increase in diameter of the cannula tip 120).

[0052] On the other hand, Figure 3 、 Figures 4A to 4B In the embodiment shown, the slot 120 does not extend all the way to the proximal end 120dp of the distal portion 120d (that is, the slot 120s terminates near the point where the diameter of the cannula tip 120 gradually increases). Thus, the proximal portion 120p of the cannula tip 120 includes a lumen 1201p that opens into the slot 120s and is an extension of the lumen 1201d in the distal portion 120p of the cannula tip 120. In other embodiments (not shown), the slot 120s may extend only the axial length of the ramp 122. A potential advantage of terminating the slot 120s near the point where the diameter of the cannula tip 120 gradually increases is that potential problems that may arise when the cannula tip 120 is welded to the cannula conduit 110 can be avoided.

[0053] As from Figure 3 and Figure 4B As can be further seen in the illustrated design, a circular recess 120r is formed at the distal end of the slot 120s that is axially aligned with and has the same diameter as the lumen 1201p / 1201d.

[0054] In certain embodiments, a cannula tip 120 according to the present disclosure can be machined from a solid bar of material, for example, by drilling a hole in the distal end of the material, forming a bevel in the distal end of the material, reducing the diameter of the proximal end of the material, grinding a bevel in the proximal end of the material, and forming a slot in the proximal end of the material.

[0055] For example, from Figure 1 、 Figure 4A and Figure 5As can be seen in FIG, the length of the proximal portion 120p of the cannula tip 120 is advantageously sized such that when the proximal portion 120p of the cannula tip 120 is inserted into the distal end 110d of the cannula tube 110, the ramp 122 is positioned such that the distal end 122d of the ramp 122 is located at or just proximate to the distal end 110od of the sidewall opening 110o (see, for example, FIG. Figure 4A ). Moreover, as described above, in certain advantageous embodiments, the distal end 110 od of the sidewall opening 110 o may be beveled at an angle that substantially matches the angle of the ramp 122 .

[0056] Now go to Figures 10A to 10C In various embodiments, a cannula 100 according to the present disclosure can be provided with a trocar hub 140 attached to the proximal end 110p of the cannula conduit 110. In various embodiments, an assembly 160 can be provided that further includes a stylet 150 having a stylet cap 152. According to the present disclosure, the stylet 150 can be inserted into the trocar hub 140 and the cannula conduit 110 of the cannula 100. Moreover, the stylet cap 152 can be configured to engage with the trocar hub 140, as shown. The materials used to form the stylet cap 152 and the trocar hub 140 include any suitable materials, with plastics (e.g., acrylic polymers and polycarbonates) being particularly beneficial in some embodiments. Materials used to form the stylet 150 include polypropylene, polycarbonate, acrylonitrile butadiene styrene (ABS), and ABS / polycarbonate blends. The stylet 150 can provide structural rigidity to the cannula 100 during insertion into the patient. Furthermore, by having the distal tip of the stylet 150 terminate in the sidewall opening 110 o (but not extend therefrom), coring of tissue during insertion of the cannula 100 may be reduced or prevented.

[0057] Now turn Figure 4A 、 Figure 4B 、 Figure 5 and Figures 9A to 9C In some aspects, the present disclosure provides a system comprising a cannula 100 according to the present disclosure and an electrode 125 insertable into the cannula 100, as shown schematically in FIG. In some of these embodiments, the electrode 125 is provided with a rounded (e.g., hemispherical) distal tip 125d. In some of these embodiments, the electrode 125 is straight and not curved. Materials used to form the electrode 125 include metals and metal alloys, such as stainless steel, Inconel, or Nitinol.

[0058] In some embodiments, the electrode 125 can be operated in a monopolar manner, for example, in conjunction with one or more return electrodes positioned on the patient's body. In some embodiments, the electrode 125 can be operated in a bipolar manner, for example, with the distal tip 120 of the cannula 100 serving as the other member of a bipolar pair, in which case the electrode 125 and / or the cannula 100 will be appropriately insulated to avoid shorting the electrode 125 and the cannula 100.

[0059] When the distal tip 125d of the electrode 125 has been inserted through the cannula tube 110 from the proximal end of the cannula 100 according to the present disclosure (eg, by inserting the distal tip 125d of the electrode 125 through the cannula tube 110 at the proximal end 110p of the cannula tube 110) Figures 10A to 10C When the needle hub 140 (shown in FIG. 1 ) has advanced through the cannula tube 110 to the point where the distal tip 125d reaches the ramp 122 of the cannula tip 120, the ramp 122 serves to deflect the electrode distal tip 125d out through the sidewall opening 110o of the cannula tube 110, rather than allowing the electrode distal tip 125d of the electrode 125 to continue advancing into the cannula tip 120. In these embodiments, the width of the electrode 125 is narrower than the width of the lumen 110l of the cannula tube 110 and wider than the slot formed in the ramp 122 (or, in other embodiments, the channel or hole formed in the ramp 122). In this regard, Figure 9A FIG. 1 shows a top view of a casing 100 according to the present disclosure, wherein the sidewall opening 110o of the casing pipe 110 and the ramp 122 of the inserted casing tip 120 can be seen. In the right-hand portion of the photograph, the weld W securing the casing tip 120 to the casing pipe 110 can be seen. Figure 9B and Figure 9C As can be seen, when the electrode 125 that has been inserted into the proximal end of the cannula 100 reaches the ramp 122 , the ramp is used to deflect the distal tip 125 d of the electrode 125 out through the sidewall opening 110 o of the cannula tube 110 .

[0060] In some embodiments, the system is further provided with a container for an injected fluid, such as an anesthetic fluid, saline, a contrast agent (including an opaque fluid), a fluid containing a dye, or a fluid containing a steroid. For example, the injected fluid may be provided in a syringe that can be engaged with the trocar hub 140. As described above, an advantage of the cannula designs of the present disclosure is that they allow the fluid injected through the lumen of the cannula conduit to be dispensed from the distal end of the cannula while preventing the inserted electrode from advancing beyond the side port to the distal end of the cannula.

[0061] Although various embodiments have been specifically shown and described herein, it will be understood that modifications and variations of the present disclosure are covered by the above teachings and within the purview of the appended claims without departing from the spirit and intended scope of the disclosure.

Claims

1. A cannula comprising: (a) a cannula conduit comprising a proximal end, a distal end, a cannula conduit lumen, a sidewall, and a sidewall opening extending through the sidewall, the sidewall opening having a proximal end and a distal end; and (b) a cannula tip secured to the distal end of the cannula conduit, the cannula tip comprising a proximal tip portion inserted into the cannula conduit lumen and a distal tip portion extending beyond the distal end of the cannula conduit, the cannula tip being configured to permit fluid flow therethrough, The proximal tip portion of the cannula tip includes a ramp at its proximal end, wherein the ramp is configured to eject the distal tip of the elongated device through the sidewall opening of the cannula tube when the elongated device is inserted through the cannula tube from the proximal end of the cannula tube.

2. The cannula according to claim 1, wherein the cannula tip is secured to the cannula tube by welding, wherein a distal end of the sidewall opening is beveled, and / or wherein the sidewall opening extends around the circumference of the cannula tube over an angle ranging from 120 to 160 degrees.

3. The cannula of claim 1, wherein the cannula tubing is bent at an angle ranging from 5 to 45 degrees at the proximal end of the sidewall opening.

4. The cannula of claim 1 , wherein the proximal tip portion has a first outer diameter and the distal tip portion has a second outer diameter that is larger than the first outer diameter, and wherein there is a step-wise increase in diameter between the proximal tip portion and the distal tip portion such that the proximal tip portion is inserted into the distal end of the cannula tubing and such that the proximal end of the distal tip portion abuts the distal end of the cannula tubing.

5. The cannula of claim 1, wherein the distal tip portion has an outer diameter that is the same as an outer diameter of the cannula tubing.

6. The cannula of claim 1, wherein the cannula tip comprises a lumen to permit fluid flow therethrough, a slot to permit fluid flow therethrough, or a combination of a lumen and a slot to permit fluid flow therethrough.

7. The cannula of claim 1, wherein the proximal tip portion comprises a slot and the distal tip portion comprises a distal tip lumen in fluid communication with the slot.

8. The cannula of claim 7, wherein the slot bisects the ramp, and / or wherein the ramp has a proximal end and a distal end, the distal end of the ramp terminating proximate the distal end of the sidewall opening.

9. The cannula of claim 8, wherein the slot does not extend to the distal end of the proximal tip portion, and / or wherein the distal end of the slot comprises a circular recess that is axially aligned with and has the same diameter as the distal tip lumen.

10. The cannula of claim 1, wherein the cannula further comprises a needle hub attached to the proximal end of the cannula.

11. An ablation system comprising a cannula according to any one of claims 1 to 10 and an electrode having a distal electrode tip, wherein the electrode is configured to be inserted into the proximal end of the cannula tube and pass through the cannula tube, and wherein the cannula tip is configured to pop out the distal electrode tip through a side wall opening of the cannula tube when the electrode is inserted through the cannula tube from the proximal end of the cannula tube.

12. The ablation system of claim 11, wherein the distal electrode tip is rounded.

13. A cannula and stylet assembly comprising a cannula according to any one of claims 1 to 10 and a stylet having a stylet tip, wherein the stylet is configured to be inserted into the proximal end of the cannula tube and through the cannula tube so that when fully inserted, the stylet tip is proximate to the side wall opening.

14. The cannula and stylet assembly of claim 13, wherein the cannula further comprises a hub attached to the proximal end of the cannula tube, wherein the stylet comprises a stylet cap attached to the proximal end of the stylet.

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