Patent Description:
Epidural anesthesia is widely used during labour/childbirth, lower limb and pelvic surgeries, and steroid injections for pain relief. Both single injection and catheter techniques can be used to inject medication into the epidural space. The ability to maintain continuous anesthesia after placement of an epidural catheter makes epidurals suitable for long duration surgeries and useful in the postoperative period for analgesia.

Typically, methods for placing the needle in the correct location rely on a loss of resistance to detect the epidural space (i.e., to determine when the epidural needle has entered the space). Once the needle tip is in the thick ligaments of the back, the anesthesiologist will apply constant or intermittent pressure to the plunger of an air or saline filled syringe. The anesthesiologist will commonly use a glass syringe or low resistance plastic syringe. Due to the dense and fibrous nature of the ligaments (supraspinous ligament, interspinous ligament and ligamentum flavum) leading up to the epidural space, saline or air will not be easily injected into the tissue and the syringe will maintain its pressurized state. The exact technique can vary, but generally, the epidural needle is advanced with one hand while pressure is maintained on the syringe plunger with the other hand. When the epidural needle tip enters the epidural space, the anesthesiologist senses the loss of pressure by depression of the syringe plunger. To confirm the location of the epidural space, additional saline can be injected into the space with ease. At this point, the syringe is removed and medication can be injected or a catheter can be fed through the needle. In an alternative, "incremental" method, the needle is advanced a millimeter or two, then the plunger is pressed to confirm the needle tip is still within the ligament. This occurs repeatedly until the plunger depresses with ease, releasing saline or air into the epidural space.

When using the incremental method, it is possible that between checks the needle can advance significantly through the epidural space and puncture the dura. The above-mentioned procedures rely upon the anesthesiologist to observe or sense the loss of pressure, process that information, and stop the forward progress of the needle without accidental additional forward motion of the needle. Poor technique, such as inadvertent angling of the plunger against the syringe walls, can create undesirable friction making it difficult to recognize the small changes in pressure needed to detect the epidural space. Furthermore, glass syringes typically have very low friction but will occasionally stick, creating a false negative signal for the doctor, resulting in the needle being advanced too far.

A risk of the epidural procedure is the accidental puncture of the dura. When the dura is punctured, the patient can suffer from post-dural puncture headache, spinal abscess, spinal hematoma, or permanent neurological damage in severe cases. Furthermore, when these complications arise, additional costs are incurred.

Current practice requires the anesthesiologist to observe the detection of the epidural space and simultaneously halt needle progression to prevent advancement that could cause dura puncture. Devices have been developed to provide a visual or auditory cue to alert the user of loss of pressure, thereby assisting the practitioner in detection of the epidural space. However, those devices are not configured to automatically inhibit or prevent further advancement of the needle once it has reached the epidural space.

<CIT> discloses a pressure depending clutching device for safely positioning a needle in a body cavity.

In view of the foregoing, it is desirable to provide an improved epidural device.

The following describes an epidural device configured to detect the entry of an epidural needle tip into the epidural space and to inhibit or prevent further progression upon entry. The device may be filled with fluid (e.g. saline or air), and connected to the epidural needle when the needle is inserted into a patient's back and the needle tip has been positioned in the ligamentum flavum. The device can be pressurized using the resistance of the dense ligament to prevent fluid flow from the needle. This pressurization may be used by a mechanism to lock a sliding pusher in place (relative to the body of the construct and the needle connected to it) such that the anesthetist can then use the pusher to advance the needle. Once the epidural space is reached, the fluid enters the epidural space, and the release of pressure may trigger the mechanism within the device, causing the pusher to disengage from the body of the construct. At this point if the sliding pusher is pushed, it may slide over the device without significant or any further advancement of the needle. The device may provide both the ability to detect the epidural space using pressure loss and to automatically substantially or completely prevent further progression of the needle once it has entered the epidural space. Surgical methods are not claimed.

In one aspect, there is provided an epidural device having an elongate body with a longitudinal axis, an inlet and an outlet, the epidural device comprising: a sleeve slidably disposed about an outer surface of the body; a first chamber defined in the body, the first chamber being configured to receive a fluid; a second chamber defined in the body, the second chamber being configured to convey the fluid to the outlet, the outlet being removably attachable to an epidural needle; a flow restrictor between the first and second chambers for providing fluid communication therebetween, wherein the flow restrictor has a smaller diameter than a diameter of the outlet; the first chamber having a first biasing mechanism positioned therein for pressurizing the first chamber; the second chamber having a piston provided therein, the piston being movable between: a primed position, where the piston is moved away from the flow restrictor, and the fluid can pass between first and second chambers; and a triggered (or unprimed) position, where the piston covers the flow restrictor, and the fluid can exit the second chamber via the outlet; wherein: in the primed position, the sleeve is engageable by an extension of the piston to inhibit the sleeve from moving axially toward the outlet; and in the triggered position, the sleeve is not engageable by the extension of the piston and the sleeve is movable axially toward the outlet.

In an implementation, the first chamber is configured to receive the fluid from the inlet, has an opening therein opposite the flow restrictor, and the device further comprises a plunger extending into the chamber through the opening, the plunger having: a flow port defined therein for providing fluid communication between the inlet and the first chamber; a distal end positioned within the first chamber; and a proximal end positioned outside of the chamber and being adapted to engage the inlet.

In another implementation, the first chamber has an opening therein opposite the flow restrictor, and the device further comprises a plunger extending into the chamber through the opening, the plunger having: a distal end positioned within the first chamber; and a proximal end positioned outside of the chamber.

In yet another implementation, the first biasing mechanism is a spring provided within the chamber and around the plunger intermediate the distal end thereof and the opening of the chamber.

In yet another implementation, a filling port for filling the first chamber extends between the first and second chambers, the filling port including a one-way valve to permit flow from the second chamber to the first chamber.

In yet another implementation, the flow restrictor is sized such that, when the device is in the primed position, at least some of the fluid can exit the second chamber through the outlet without triggering the device.

In yet another implementation, a second biasing mechanism is located within the second chamber, the second biasing mechanism being weaker than the first biasing mechanism.

In yet another implementation, the second biasing mechanism is a spring.

In yet another implementation, the piston includes a disk extending radially therefrom, the disk dividing the first chamber into trigger and reservoir chambers and having first and second annular surfaces in the trigger chamber and the reservoir chamber, respectively, the reservoir chamber being capable of fluid communication with the first chamber via a flow channel extending therebetween, wherein: when the device is in the primed position, the disk is positioned intermediate the flow channel and the flow restrictor and the trigger chamber can fluidly communicate with the first chamber and the outlet; and when the device is in the triggered position, the disk covers the flow restrictor and the trigger chamber cannot fluidly communicate with the first chamber.

In yet another implementation, the first annular surface has a greater surface area than a surface area of the second annular surface such that a force differential can be created between the trigger and reservoir chambers.

In yet another implementation, the piston includes, on an end thereof opposite the extension, a button pressable by a user in a direction toward the extension to prime the device.

In yet another implementation, the sleeve includes a protrusion extending therefrom toward the body of the device, the protrusion being configured to prime the device by depressing a button of the piston when the sleeve slides thereover, the button being attached to an end of the piston opposite the extension.

In another aspect, there is provided an epidural device having an elongate body with a longitudinal axis, an inlet and an outlet, the epidural device comprising: a sleeve slidably disposed about an outer surface of the body; a fluid passage defined in the body, the fluid passage being configured to receive a fluid from the inlet; a pressure chamber defined in the body, the chamber being configured to convey the fluid to the outlet, the outlet being removably attachable to an epidural needle; a flow restrictor between the fluid passage and the pressure chamber for providing fluid communication therebetween, the flow restrictor having a smaller diameter than a diameter of the outlet; the pressure chamber having a piston provided therein, the piston being movable between: a primed position, where the piston is moved away from the flow restrictor, and the fluid can pass between the fluid passage and the pressure chamber; and a triggered position, where the piston covers the flow restrictor, and the fluid can exit the pressure chamber via the outlet; wherein: in the primed position, the sleeve is engageable by an extension of the piston to inhibit the sleeve from moving axially toward the outlet; and in the triggered position, the sleeve is not engageable by the extension of the piston and the sleeve is movable axially toward the outlet.

In yet another aspect, there is provided an epidural device having an elongate body with a longitudinal axis, an inlet and an outlet, the epidural device comprising: a sleeve slidably disposed on an outer surface of the body; the body having a chamber defined therein for communicating a fluid between the inlet and the outlet, the outlet being removably attachable to an epidural needle; a biasing mechanism for pressurizing the chamber; a trigger mechanism for engaging the sleeve, the trigger mechanism being contained at least partially within the chamber and being movable between a first position and a second position by a decrease in pressure in the chamber; wherein: in the first position, the sleeve is engageable by the trigger mechanism to inhibit the sleeve from moving axially toward the outlet; and in the second position, the sleeve is not engageable by the trigger mechanism and the sleeve is movable axially toward the outlet.

In an implementation, the trigger mechanism comprises at least one piston having first and second ends, the first end being positioned in the chamber such that the first end can be acted on by the biasing mechanism, the second end extending radially outward through the body, wherein: in the first position, the second end protrudes radially from the body to an extent that the sleeve is engageable by the second end; and in the second position, the second end is positioned closer to the body than when the device is the first position, such that the sleeve is not engageable by the second end.

In another implementation, the trigger mechanism comprises an inflatable membrane that can be inflated by the biasing mechanism, wherein: in the first position, the inflatable membrane is inflated to an extent that the sleeve is engageable by the membrane; and in the second position, the inflatable membrane is deflated to an extent that the sleeve is not engageable by the membrane.

In yet another implementation, the trigger mechanism comprises a compliant component that can be expanded by the biasing mechanism, wherein: in the first position, the compliant component is expanded to an extent that the sleeve is engageable by the component; and in the second position, the compliant component is retracted to an extent that the sleeve is not engageable by the compliant component.

In yet another aspect, provided herein is a device for epidural procedures that can be filled with fluid and pressurized by means of an internal spring. The device further comprises: a sliding pusher on the external frame of the device, and a mechanism configured to have two positions. In one position, the sliding pusher is free to travel along the length of the device. In the other position, the pressure of the fluid holds the mechanism in place, and the sliding pusher is limited in movement as it interferes with the mechanism, allowing the user to advance the needle by means of pushing forward on the sliding pusher; when depressurized, such as when the needle tip enters the epidural space, the mechanism reverts to its other position and disengages from the sliding pusher, allowing the pusher to travel along the body of the device such that the user is unable to advance the needle further.

In an implementation, the mechanism consists of a piston that is movable vertically within the device and while in its first position may allow the sliding pusher to freely move; while in its second position it may inhibit the pusher component by way of one end of the piston engaging the pusher. The piston may be biased to be in its first position by means of a spring, and held in its second position by means of the fluid pressure within the device.

In an implementation, the sliding pusher component has flanges or wings which extend from its front end to provide a pushing surface when advancing the needle.

In another implementation, the flanges or wings are connected to the pusher by extensions, allowing the pushing surface to be closer to the patient, improving stability of the device and hand placement for the user.

In yet another implementation, the piston mechanism is movable into its second position by means of sliding the pusher forward (toward the patient). A ramp within the pusher may depress the piston mechanism as the pusher is advanced. When depressurized, the piston can move into a space within the pusher, allowing the pusher to slide freely.

In yet another implementation, the piston mechanism is movable into its second position by means of sliding the pusher back (away from the patient). A ramp within the pusher can depress the piston mechanism as the pusher is pulled back. When depressurized, the piston can move into a space within the pusher, allowing the pusher to slide freely.

In yet another implementation, the device may be filled with fluid by means of using a connector within the plunger of the device. A one-way valve within the plunger prevents fluid from exiting the chamber by the same path.

In yet another implementation, the device may be filled with fluid from the front of the device through a fluid path containing a one-way valve between the trigger mechanism and fluid reservoir.

In yet another implementation, the device may be filled with fluid from the front of the device by means of forcing the trigger mechanism into a position to allow fluid to pass and holding it in this position during the filling procedure.

In yet another implementation, the triggering mechanism does not contain a spring. In this aspect, the trigger piston may use differential forces from the pressurized on the two faces to drive the piston down or up, or hold it in place (down or up). The two faces may be of different sizes to enhance the differential forces. When depressurized, such as when entering the epidural space, the two faces of the piston mechanism may be subjected to differing forces, which can drive the piston up and allow the pusher to slide freely.

In yet another implementation, the trigger mechanism uses at least one and preferably two pins or two pistons which may interfere with the sliding pusher and in yet another implementation, the two pistons may provide equal and balanced force to the sliding pusher.

In another implementation, the device further comprises a flexible or inflatable membrane for engaging the sliding pusher when the membrane is pressurized. When depressurized, such as when entering the epidural space, the membrane may deflate and allow the sliding pusher to slide freely.

In yet another implementation, the device further comprises a compliant or flexible mechanism for engaging the sliding pusher when the mechanism is pressurized. When depressurized, such as when entering the epidural space, the compliant mechanism may retract and disengage from the sliding pusher, allowing the pusher to slide freely.

Embodiments will now be described with reference to the appended drawings wherein:.

One or more of the terms "vertical", "vertically", "horizontal", "horizontally", "top", "bottom", "upwardly", "downwardly", "upper", "lower", "right", "left", "forward" and "backward" are used throughout this specification. It will be understood that these terms are not intended to be limiting. These terms are used for convenience and to aid in describing the features herein, for instance as illustrated in the accompanying drawings.

The term "fluid" as used herein with respect to operation of the epidural device refers to a liquid or gas, e.g., saline or air, for filling and pressurizing the device.

An object of the following is to provide an epidural device capable of detecting the entry of the needle into the epidural space and simultaneously inhibiting or substantially preventing further forward motion of the needle. Such functionality may reduce the likelihood of dural puncture which can occur while carrying out the conventional loss of resistance technique. In a preferred aspect, the device is configured to prevent premature triggering when there is a slow flow of fluid from the epidural needle into surrounding tissue.

The epidural devices described with reference to <FIG> include trigger mechanisms that rely on differential forces between a spring force and a force from chamber pressure in the trigger barrel. These devices are configurable between "primed" and "triggered" (i.e., unprimed) positions or states. The devices can be primed (i.e., shifted from unprimed to primed) manually by a user, such as a physician, when attached to a needle which is positioned in a patient's back, and subsequently automatically triggered upon entry of the epidural needle into the epidural space. The unprimed (triggered) state is the default state for the epidural devices. Step-by-step operation of these devices will be described following the below description of their structure.

<FIG> illustrates an epidural device <NUM> comprising a syringe body <NUM> having a first, or open end <NUM> and a second, or needle connector end <NUM>. The syringe body <NUM> can have a substantially uniform shape with a rectangular cross-section, as shown in <FIG>. The syringe body <NUM> may be shaped differently. For example, the body <NUM> may be an elongate body having a different (i.e., not rectangular) polygonal cross-section, e.g., hexagonal. In <FIG>, the epidural device <NUM> is shown in the unprimed position, with the reservoir partially filled with a fluid (not shown). The body <NUM> may include a reservoir chamber <NUM> shaped to slidably receive and retain a plunger <NUM> for filling and pressurizing the reservoir chamber <NUM>. The reservoir plunger <NUM> can be movable parallel to a longitudinal axis of a filling port <NUM> extending through the plunger <NUM>. The body <NUM> may include a fluid flow restrictor <NUM> extending between the reservoir chamber <NUM> and a trigger barrel <NUM>. The restrictor <NUM> may induce a pressure drop between the reservoir chamber <NUM> and the trigger barrel <NUM> when fluid flow occurs therebetween. The diameter of the restrictor <NUM> may be smaller than that of the exit port <NUM>. In the unprimed position shown in <FIG>, fluid flow between the reservoir chamber <NUM> and the trigger barrel <NUM> may be blocked by a pair of disk seals <NUM> and <NUM>. The device further comprises a sleeve, or pusher <NUM> by which a user can advance an epidural needle <NUM> (see <FIG>) connected to the needle connector end <NUM>. The pusher <NUM> can be slidably disposed over the syringe body <NUM>. The pusher <NUM> can optionally have external flanges or wings <NUM>, and/or texture or shape for ergonomic purposes. As discussed further below, the pusher <NUM> can be configured to interact with a trigger mechanism of the device <NUM>.

The filling port <NUM> may provide fluid communication between a filling connector <NUM> and the reservoir chamber <NUM>. A one-way valve <NUM> is provided within the filling port <NUM> to inhibit or substantially prevent backflow and to allow the reservoir chamber <NUM> to be filled from the back end, thereby obviating the need to fill the reservoir chamber <NUM> from the needle connector end <NUM> through an exit port <NUM>, which may require having to manually hold the device in the primed position during filling. A widened portion <NUM> of the plunger <NUM> may include a seal <NUM> and an annular shoulder <NUM>.

The device <NUM> further comprises a trigger mechanism <NUM> designed to respond to pressure of the fluid in the trigger barrel <NUM>, which in turn is affected by the pressure of the fluid in the reservoir chamber <NUM>. A biasing mechanism, particularly a reservoir spring <NUM> is disposed around the plunger <NUM> and in a space <NUM> formed between a reservoir cap <NUM>, which may cover the open end <NUM>, and an annular shoulder <NUM>. Other biasing mechanisms such as flexible rubber (e.g. elastic band) or compressed air can be implemented instead of a spring. The reservoir spring <NUM>, anchored against the reservoir cap <NUM>, can bias the reservoir plunger <NUM> in a direction toward the restrictor <NUM> and thereby pressurize the fluid within the reservoir chamber <NUM>.

The trigger mechanism <NUM> may comprise a trigger piston <NUM> having a trigger piston core <NUM> therein. The trigger piston <NUM> may be provided within the trigger barrel <NUM>, and a first, or lower disk seal <NUM> and a second, or upper disk seal <NUM> may be provided on the outer circumference of the trigger piston <NUM>. The trigger piston core <NUM> can be directly connected to the trigger piston <NUM> such that these components can move together in unison. A third circumferential priming seal <NUM> may be disposed around the trigger piston <NUM>. A space defined by the priming seal <NUM>, the disk seal <NUM> and between a wall <NUM> of the trigger barrel and the trigger piston <NUM>, may be referred to as a trigger chamber <NUM>. The trigger piston core <NUM> may have a priming, or trigger button <NUM> and a trigger pin <NUM> extending from upper and lower surfaces, respectively, of the trigger barrel <NUM>. The trigger piston <NUM> is slidable within the trigger barrel <NUM>. The priming seal <NUM>, and the disk seal <NUM> may substantially prevent leaking of fluid from the trigger chamber <NUM> out of the top and bottom ends thereof. The two disk seals <NUM> and <NUM> of the trigger piston <NUM> may create sliding seals between the trigger barrel wall <NUM> and the trigger piston <NUM>. The priming seal <NUM> may create a sliding seal between the trigger piston <NUM> and a narrower section of the trigger barrel wall <NUM>. The trigger <NUM> cap may connect to and close an open end of the trigger barrel <NUM>.

The exit port <NUM> may be provided at the "forward" end (i.e., near the needle connector end <NUM> of the device <NUM>) of the trigger barrel <NUM>. The exit port <NUM> leads to the needle connector end <NUM> which can be removably attachable to a needle connector <NUM> (<FIG>) for connecting to an epidural needle <NUM> (<FIG>). The exit port <NUM> can allow fluid to exit the trigger barrel <NUM>, and ultimately to exit the device <NUM> through the needle <NUM>.

A trigger spring <NUM> can be positioned around and concentric with the trigger pin <NUM> and may bias the trigger piston <NUM> away from the trigger cap <NUM>. The trigger cap <NUM> may include a trigger pin hole <NUM> and a vent hole <NUM>. The vent hole <NUM> can be optional as the trigger pin hole <NUM> may double as a vent hole. The vent hole <NUM> in the trigger cap <NUM> may substantially prevent air that is stuck between the trigger cap <NUM>, trigger barrel <NUM>, and trigger piston <NUM> from impeding the sliding motion of the trigger mechanism <NUM>. As such, the trigger piston core <NUM> and the trigger pin <NUM> can fit inside the trigger piston <NUM> and the trigger barrel <NUM> such that the trigger pin <NUM> can slide vertically through the trigger pin hole <NUM>.

<FIG> illustrate the epidural device <NUM> in various states or alternative views. For clarity, relative to <FIG>, fewer elements are labeled in <FIG>. <FIG> illustrates the device <NUM> in the unprimed, filled state, wherein the reservoir plunger <NUM> is held away from the restrictor <NUM> by fluid in the reservoir chamber <NUM>. As shown, in the filled state, the reservoir spring <NUM> is at least partially compressed and thus may pressurize the fluid within the reservoir chamber <NUM>. In this state, fluid communication between the trigger chamber <NUM> and the reservoir chamber <NUM> can be inhibited and preferably substantially prevented by the upper disk seal <NUM>. The lower disk seal <NUM> may prevent fluid from leaking out the bottom of the trigger barrel <NUM> through the trigger cap <NUM>.

<FIG> shows the device <NUM> in the filled, primed position, wherein the button <NUM> has been manually pressed down, moving the trigger piston <NUM> against the trigger cap <NUM>, thereby shifting the trigger pin <NUM> such that same extends out of the trigger pin hole <NUM>. When the device is in the primed position, the axial movement of the sliding pusher <NUM> can be limited by the trigger pin <NUM>. More particularly, when moved advanced axially toward the needle connecter end <NUM>, the pusher <NUM> will, at a certain point, abut the trigger pin <NUM>, thereby substantially preventing further sliding of the pusher <NUM> with respect to the body <NUM>. When the pusher <NUM> abuts the trigger pin <NUM>, most or substantially all force can be transferred from the pusher <NUM> through the device <NUM> to the epidural needle <NUM> (see below discussion regarding operation).

<FIG> shows the device <NUM> in the partially filled, triggered position, as would be expected after the epidural needle <NUM> has become "unblocked" by entering the epidural space, resulting in pressure drop across the restrictor <NUM> and subsequent upward movement of the trigger piston <NUM> to return to the unprimed state. In this triggered state, the trigger pin <NUM> does not prevent sliding of the pusher <NUM> and preferably does not at all impede sliding of the pusher. Thus, force transfer (in the axial direction), with the exception of frictional force between the pusher <NUM> and body <NUM>, may be substantially reduced and preferably prevented between the pusher <NUM> and the needle <NUM>, thereby preventing further advancement of the needle <NUM> into the epidural space.

<FIG> and <FIG> illustrates exploded views of the component part of device <NUM>, with <FIG> showing a cross-sectional exploded view.

<FIG> illustrates an isometric view of the assembled device <NUM>.

The devices depicted in <FIG> are functionally similar to the device <NUM> shown in <FIG>. Thus, similar elements will retain the same reference numbers.

<FIG> illustrates an isometric view of a similar epidural device <NUM> in the assembled state, wherein the pusher <NUM> has extended wings <NUM>. In this configuration, the wings are closely aligned with the needle connector (<NUM>, not shown in this image), and may provide improved handling for the user.

<FIG> illustrates an epidural device <NUM> similar to device <NUM>, but the device <NUM> can be primed differently in that the pusher can be used to depress the trigger piston to prime the device. <FIG> shows the device <NUM> in the unprimed position. The device <NUM> comprises a trigger piston <NUM> which is a single component in this example embodiment, and a pusher <NUM> having a priming ramp <NUM> and a reset ramp <NUM>. The trigger piston <NUM> may function similarly to the trigger mechanism <NUM> above. The device <NUM> can be primed by sliding the pusher <NUM> forward, whereby a priming ramp <NUM> may engage with a priming button <NUM> of the trigger piston <NUM> and thereby push it down into the primed state, shown in <FIG>. As described above, the trigger pin <NUM> extends out of the trigger hole <NUM> and may prevent forward sliding of the pusher <NUM>, thus transferring force from the pusher <NUM> through the device <NUM> to the epidural needle <NUM> (not shown). <FIG> shows the device in the triggered state, where the trigger piston <NUM> is permitted to move upwards and thus the trigger pin <NUM> is not engaged with the pusher <NUM>, allowing the pusher <NUM> to slide forward without significantly or preferably at all advancing the needle <NUM>. The device can be reset by sliding the pusher back across the trigger mechanism, utilizing the reset ramp <NUM> to manipulate the trigger piston <NUM> as needed.

<FIG> illustrate another epidural device <NUM> that is similar to devices <NUM> and <NUM>. The device <NUM> comprises a pusher <NUM> that can be used to prime the trigger piston <NUM>, in this case by pulling the sliding pusher <NUM> away from the needle connector end <NUM>. <FIG> shows the device in the primed position, at the moment that the sliding pusher <NUM> has been pulled back and the priming ramp <NUM> has engaged a priming button <NUM> of the trigger piston <NUM> to push it down into the primed state thereby causing the trigger pin <NUM> to extend outwardly from the trigger pin hole <NUM> such that the trigger pin <NUM> can abut a shoulder <NUM> defined in the pusher <NUM>. <FIG> is also in the primed state, but with the sliding pusher <NUM> pushed forward to the extent that the trigger pin <NUM> engages the pusher <NUM> at the shoulder <NUM> such that further movement of the pusher <NUM> toward the needle connector end <NUM> is inhibited or prevented. In this state, a majority of a pushing force can be transferred from the pusher <NUM> through the device <NUM> to the epidural needle <NUM> (not shown), thereby enabling advancement of the needle <NUM> toward the epidural space. <FIG> shows the device in the triggered state, where a decrease in pressure resulting from entry of the needle <NUM> into the epidural space has caused the pin <NUM> to move upwardly such that the trigger pin <NUM> may no longer engage the shoulder <NUM>. As a result, the pusher <NUM> may slide further toward the needle connector end <NUM> and advancement of the needle <NUM> is thus inhibited or prevented. In <FIG>, the pusher <NUM> has been moved toward the needle connector <NUM> to its full extent.

The devices described above each include a reservoir chamber that can be filled with a fluid which can be pressurized by a biasing mechanism in the reservoir chamber. A reservoir chamber may not be needed to pressurize the fluid before the restrictor. Instead, for example, the filling port <NUM> could extend from the valve <NUM> to the restrictor <NUM> and be integrated physically with the body <NUM> (i.e., the port <NUM> could extend through a length of the body <NUM> to the restrictor <NUM>). The filling port <NUM> could be pressurized by, for example, being connected to a pressurized fluid line (i.e., leading to the <NUM>-way valve <NUM>). This could obviate the need for a reservoir chamber <NUM>.

<FIG> illustrates another epidural device <NUM> that is similar to device <NUM>. In this version, the reservoir chamber is filled through the port <NUM> at the front of the device, instead of through the filling port <NUM> as is described with respect to <FIG>. The device <NUM> thus may include a plunger <NUM> that does not have such a filling port <NUM> defined therein. It follows that the one-way valve <NUM> and the filling connector <NUM> are not needed in the device <NUM>. Fluid may enter the reservoir <NUM> through the trigger chamber <NUM> and through a one-way valve <NUM>, by means of pulling back on the reservoir plunger <NUM>. Functionally, this device is otherwise similar to the device <NUM>.

<FIG> illustrate another epidural device <NUM> that can utilize a differential pressure trigger mechanism <NUM>, but is otherwise similar to device <NUM>. In this example embodiment, the trigger spring has been replaced by a trigger reservoir <NUM>, which is connected to the syringe reservoir chamber <NUM> by a relatively wide reservoir connector <NUM>. The trigger piston <NUM> is moveable vertically and may be constrained by the trigger cap <NUM> at the bottom. Similar to device <NUM>, the trigger chamber <NUM> may be bound by the priming seal <NUM> and the upper disk seal <NUM>. The trigger reservoir <NUM> may be bound by the lower disk seal <NUM> and the trigger reservoir seal <NUM>, as well as the trigger cap <NUM> and its associated trigger cap seal <NUM>.

The operation of the differential pressure device <NUM> relies upon the differential forces on the trigger piston <NUM> from the trigger chamber <NUM> and trigger reservoir <NUM>. The size of the horizontal faces on the trigger piston <NUM> can be relatively large for the trigger chamber face <NUM>, and can be relatively smaller for the trigger reservoir face <NUM>, which can create differential forces when the chambers <NUM> and <NUM> are at the same or nearly equivalent pressures. Details of the operation of this device are explained below.

<FIG> show another epidural device <NUM> that is functionally similar to the device <NUM> shown in <FIG> but uses two piston pins <NUM> that when pressurized can move outwardly from both the top and bottom of the device <NUM> and inhibit or substantially prevent forward movement of the pusher <NUM> once the pusher <NUM> abuts the pins <NUM>. The contact angle between the pins and the pusher may be such that the piston pins can move up and down in response to pressure changes in the chamber. When the epidural space is reached, the device can depressurize, allowing the piston pins <NUM> to slide inward and the pusher <NUM> to slide forward.

<FIG> shows the device <NUM> in an unprimed state, with the piston pins <NUM> retracted. <FIG> shows the device <NUM> in a primed state, with the piston pins <NUM> extended and stopping the forward travel of the pusher <NUM>. <FIG> shows the device <NUM> in a triggered state and with the pusher slid fully forward. When the primed device is unblocked, (e.g., resulting from entry of the epidural needle <NUM> (not shown) into the epidural space), pressure in the internal chamber may be reduced and the piston pins <NUM> can move inwardly, allowing the pusher <NUM> to move forward.

<FIG> depict another epidural device <NUM> that is functionally similar to device <NUM>. The epidural device <NUM> comprises a syringe body <NUM> having slits <NUM> defined therein. The body <NUM> has a tube <NUM> provided coaxially therein. The slits <NUM> may permit longitudinal movement of a pusher <NUM> that is at least partially contained within the body <NUM>. The pusher <NUM> comprises a ring <NUM> provided on an outer circumference of the tube <NUM>. The ring <NUM> is slidable in the axial direction along the tube <NUM> and may have two wings <NUM> connected thereto that extend out of the body <NUM> through the slits <NUM>. The pusher <NUM> is slidable coaxially to and within the body <NUM> by applying force to the wings <NUM>. The tube <NUM> can have at least one hole <NUM> defined therein for permitting fluid communication between can exit the tube <NUM> and enter a membrane <NUM> surrounding the hole. The membrane can expand and deflate in response to pressurization, and is shown in its inflated (pressurized) state in <FIG>.

When the epidural needle <NUM> (not shown) enters the epidural space, loss of pressure may cause the membrane <NUM> to deflate, thereby enabling movement of the ring <NUM> and thus the pusher <NUM>. As the pusher <NUM> slides over the deflated membrane as shown in <FIG>, a majority of the force exerted on the pusher <NUM> will not be transferred to the needle <NUM> and thus further advancement of the needle <NUM> can be inhibited.

<FIG> depict yet another example embodiment of an epidural device <NUM>. Similar to the device <NUM>, the device <NUM> comprises a syringe body <NUM> having slits <NUM> defined therein. The body <NUM> has a tube <NUM> provided coaxially therein. The slits <NUM> may permit longitudinal movement of a pusher <NUM> contained at least partially within the body <NUM>. The pusher <NUM> comprises a sleeve <NUM> slidably disposed on an outer circumference of the tube <NUM>. The sleeve <NUM> is slidable in the axial direction along the tube <NUM> and may have two wings <NUM> connected thereto that extend out of the body <NUM> through the slits <NUM>. The pusher <NUM> is slidable coaxially to and within the body <NUM> by applying force to the wings <NUM>. The tube <NUM> may have at least one hole <NUM> through which fluid can exit the tube <NUM> toward a flexible or compliant section <NUM> of the tube <NUM> surrounding the hole. The flexible section <NUM> can be made from plastic or another flexible material and may bend and bow outwardly when exposed to an increase in fluid pressure. As discussed with respect to the previous example embodiments, pressure within the tube <NUM> can increase when the device <NUM> is filled with fluid and there is no flow or substantial resistance to flow out the needle <NUM> (not shown). When pressurized, the flexible section <NUM> can expand to press against a pusher sleeve <NUM> surrounding the section <NUM>, thereby forming a frictional bond between the pusher sleeve <NUM> and the flexible section <NUM> which can allow advancement of the needle in response to force application on the wings <NUM> extending radially out from the pusher <NUM>. This state is shown in <FIG>, and can be seen in detail in <FIG>.

When the epidural space is reached, pressure within the device <NUM> is reduced, causing the flexible portion <NUM> to collapse and thereby disengage the sleeve <NUM>. The device <NUM> in this triggered state is shown in <FIG>, and can be seen in detail in <FIG>. The sleeve <NUM>, and thus the pusher <NUM>, now disengaged, can move freely of the needle <NUM> and thus further advancement of same is stopped.

Rather than being removably attachable, the needle <NUM> can be physically integrated with any of the devices of the present disclosure.

The operation of the epidural device <NUM> will be described below. As indicated above, the devices <NUM>, <NUM>, <NUM> and <NUM> have a number of similar features; thus, their operation is similar. The discussion of the devices <NUM>, <NUM> and <NUM> is limited to features not included in the device <NUM>.

When the trigger piston <NUM> is at the upper end of the trigger barrel <NUM>, the trigger pin <NUM> is retracted within the exterior surface of the trigger cap <NUM> and thus may not impede the sliding motion of the pusher <NUM>. This is the unprimed or triggered position and is the default state for the device. In this position the restrictor <NUM> is substantially aligned with the space between the two disk seals <NUM> and <NUM> of the trigger piston <NUM>, and fluid flow between the reservoir chamber <NUM> and the trigger chamber <NUM> may be substantially or completely prevented.

When the trigger piston <NUM> is at the bottom end of the trigger barrel <NUM> the trigger pin <NUM> extends beyond the exterior surface of the trigger cap <NUM> and may impede the forward sliding motion of the pusher <NUM>. This is referred to herein as the primed position. To move the trigger piston <NUM> to this position in the devices <NUM> and <NUM>, one may compress the trigger spring <NUM> by pressing on the priming button <NUM>. The piston can be moved to such position in the devices <NUM> and <NUM> by moving the pusher forward and sliding the pusher back, respectively. In this position the restrictor <NUM> is aligned with the trigger chamber <NUM>, allowing fluid communication between the reservoir and trigger chambers <NUM> and <NUM>, respectively.

When the device is mostly or completely filled with fluid and the epidural needle <NUM> attached to the exit port <NUM> at the needle connector end <NUM> is blocked or sufficiently resistant to outflow of fluid (e.g. when the needle <NUM> is in a dense ligament), there may be little or no flow through the restrictor <NUM> and therefore no pressure drop from the reservoir chamber <NUM> to the trigger chamber <NUM>. In this state, the forces due to the chamber pressure in the trigger chamber <NUM> may keep the trigger mechanism <NUM> in the primed position. When the epidural needle <NUM> is "unblocked" (i.e., when resistance to fluid outflow decreases sufficiently), flow through the restrictor may occur and result in a corresponding pressure drop across the restrictor <NUM>, reducing the pressure in the trigger chamber <NUM> relative to the reservoir chamber <NUM>. When the pressure in the trigger chamber <NUM> drops below the pressure required to keep the trigger spring <NUM> compressed and the trigger piston <NUM> in the primed position, the trigger spring <NUM> can push the trigger piston <NUM> into the triggered position. In such position, the trigger pin <NUM> may disengage the sliding pusher <NUM>. This, in turn, may automatically inhibit or prevent further advancement of the epidural needle <NUM> into the epidural space.

Preferably, the restrictor <NUM> is sized such that a slow outflow of fluid from the needle <NUM> can occur without triggering the device. This may prevent the device <NUM> from triggering before the needle <NUM> enters the epidural space.

Once the device <NUM> is filled with fluid and primed, and when the epidural needle <NUM> is at least partially blocked as described above, such as by the needle tip being in ligament, there is no or little flow and thus no (or a negligible) pressure drop across the restrictor <NUM> so the trigger reservoir <NUM> and trigger chamber <NUM> pressures are approximately equal. When the chamber (<NUM> and <NUM>) pressures are equal there may be a greater force on the trigger chamber <NUM> side of the trigger piston <NUM> due to the larger area of the trigger chamber face <NUM>, and thus the device <NUM> may remain in the primed position. In this position, the trigger pin <NUM> may impede axial movement the pusher. When the epidural needle is "unblocked" (i.e., when resistance to fluid outflow decreases sufficiently) while the device is filled or nearly filled with fluid there may be fluid flow and a pressure drop across the restrictor <NUM> so the trigger reservoir <NUM> pressure may be greater than the trigger chamber <NUM> pressure. If the difference in pressure is great enough the force on the smaller face <NUM> (trigger reservoir) of the trigger piston will overcome the force on the larger face <NUM> (trigger chamber) and the trigger piston <NUM> can move to the triggered position where the trigger pin <NUM> may not impede the pusher from sliding axially toward the needle connector end <NUM>.

However, if there is a sufficiently slow flow of fluid from the epidural needle <NUM> (e.g. into muscle tissue), the pressure drop across the restrictor may be negligible, and the resulting forces on the trigger piston <NUM> may not cause pre-mature triggering. If the epidural needle <NUM> becomes "blocked" again and there is still pressurized fluid in the reservoir <NUM>, the trigger piston <NUM> may be returned to the primed position by pressing the priming button <NUM>. If the device runs out of fluid, the forces on each the faces of the trigger piston can both decrease to zero, and the trigger piston <NUM> may stay in its last, or most recent position because there will be no fluid pressure driving it in either direction. In this case, the device <NUM> may fail to trigger even if the needle <NUM> reaches the epidural space. This may be overcome by incorporating a slanted pin (not shown) within the reservoir plunger <NUM> that can interact with the piston <NUM> to force the piston <NUM> upwardly when the reservoir <NUM> runs out of fluid, thereby disengaging the trigger pin <NUM> from the pusher <NUM>.

Each of the devices <NUM>, <NUM>, and <NUM>, are operated in a similar fashion as described above, using variations on the trigger mechanism and pusher configuration. While not shown, the trigger mechanisms in devices <NUM>, <NUM> and <NUM> could be combined with features similar to those described with reference to <FIG> and <FIG> to achieve similar triggering responses, e.g., limiting fluid flow out of the exit port into the patient to reduce the likelihood of premature triggering.

The automatic disengaging mechanism of the epidural device described herein may have other applications not discussed above. Without being held to any theory, it is believed that a needle and syringe device including a disengaging mechanism according to the present disclosure could be configured for other medical applications. More generally, the automatic disengaging mechanism described herein may be applied when it is desirable to pass a needle through one or more materials having a relatively high resistance to outflow from the needle into a material having a relatively lower resistance to outflow, and to ultimately inhibit or prevent unwanted advancement of the needle beyond the low resistance material. The present description is not limited to any particular triggering mechanism for causing the pushing means to disengage from the epidural needle.

For simplicity and clarity of illustration, where considered appropriate, reference numerals may be repeated among the figures to indicate corresponding or analogous elements. In addition, numerous specific details are set forth in order to provide a thorough understanding of the examples described herein. However, it will be understood by those of ordinary skill in the art that the examples described herein may be practiced without these specific details. In other instances, well-known methods, procedures and components have not been described in detail so as not to obscure the examples described herein. Also, the description is not to be considered as limiting the scope of the examples described herein.

It will be appreciated that the examples and corresponding diagrams used herein are for illustrative purposes only. Different configurations and terminology can be used without departing from the principles expressed herein. For instance, components and modules can be added, deleted, modified, or arranged with differing connections without departing from these principles.

Claim 1:
An epidural device (<NUM>) comprising:
an elongate body (<NUM>) with a longitudinal axis;
an inlet;
an outlet (<NUM>) being removably attachable to a needle (<NUM>) having a passage therethrough;
a sleeve (<NUM>) slidably disposed about an outer surface of the body (<NUM>) ;
a first chamber (<NUM>) defined in the body (<NUM>) , the first chamber (<NUM>) being configured to receive a fluid; characterised in that the epidural device further comprises:
a second chamber (<NUM>) defined in the body (<NUM>), the second chamber (<NUM>) being configured to convey the fluid to the outlet (<NUM>);
a flow restrictor (<NUM>) between the first and second chambers for providing fluid communication therebetween, wherein the flow restrictor (<NUM>) has a smaller diameter than a diameter of the outlet (<NUM>);
the first chamber (<NUM>) having a first biasing mechanism (<NUM>) positioned therein for pressurizing the first chamber (<NUM>) ;
the second chamber (<NUM>) having a piston (<NUM>) provided therein, the piston (<NUM>) being movable between:
a primed position, where the piston (<NUM>) is moved away from the flow restrictor (<NUM>), and the fluid can pass between first and second chambers; and
a triggered position, where the piston (<NUM>) covers the flow restrictor (<NUM>), and the fluid can exit the second chamber (<NUM>) via the outlet (<NUM>);
wherein:
in the primed position, the sleeve (<NUM>) is engageable by an extension (<NUM>) of the piston (<NUM>) to inhibit the sleeve (<NUM>) from moving axially toward the outlet (<NUM>); and
in the triggered position, the sleeve (<NUM>) is not engageable by the extension (<NUM>) of the piston (<NUM>) and the sleeve (<NUM>) is movable axially toward the outlet (<NUM>).