WO2002060325A1

WO2002060325A1 - Apparatus and method for determining the possible allowable needle size

Info

Publication number: WO2002060325A1
Application number: PCT/DK2002/000067
Authority: WO
Inventors: Carsten Gerner Larsen; Jørgen K. SMEDEGAARD; Jan Solvig
Original assignee: Novo Nordisk A/S
Priority date: 2001-01-31
Filing date: 2002-01-30
Publication date: 2002-08-08
Also published as: JP2004534564A; EP1357837A1

Abstract

A one-hand operated, user-friendly apparatus for non-invasive determination of the possible allowable penetration length of an injection needle when injecting into the subcutis layer of the human body. The apparatus comprises an elongated housing with an ultrasonic measuring head for transmitting an ultrasonic signal into the human body and receiving a reflected signal reflecting from the muscle membrane separating the muscular tissue from the subcutis tissue. The apparatus includes an electronic circuit for analysing the ultrasonic signals and calculating the possible allowable penetration length of the injection needle in order to avoir penetration of the muscle membrane. The possible allowable penetration length of the injection needle is instantly shown in a display integrated in the housing in the format as the allowable standard needle sizes recommended for that particular anatomical injection site.

Description

Apparatus and method for determining the possible allowable needle size.

The Technical Field of the invention

The invention relates to an apparatus for non-invasive determination of the possible allowable penetration length of an injection needle for injecting a liquid drug into a human body in order to avoid penetration of a specific target located inside the human body.

The invention furthermore relates to a method of non-invasive determination of the possible allowable penetration length of an injection needle for injecting a liquid drug into a human body avoiding intracutaneous or intramuscular injection.

Description of Related Art:

Hypodermic injections where a liquid drug is expelled into the human body are usually performed either as intramuscular injections i.e. injections into the muscle tissue, or as subcutaneous injections i.e. injections into the subcutaneous tissue lying between the cutis and a muscle membrane which cover the underlying muscle tissue.

Some drugs have to be injected subcutaneously in order to obtain the desired pharmacoki- netic properties. If insulin aimed for subcutaneous administration is injected accidentally into the muscle tissue, the insulin will be absorbed more rapidly than from the subcutaneous tissue and this is potentially dangerous as it may cause low levels of blood glucose (hypogly- caemia). In order to prevent this people suffering from diabetes are often advised to inject into a lifted skin fold. However, new data suggest that in some cases the diabetic person will still inject into the muscle by hazard if they use an injection needle which is to long, it is therefore becoming more and more preferred to inject directly at an angle of 90° without the skin fold using an injection needle having a short and limited injection length. By using such an injecting needle having a short and well-defined length of the injection part of the needle cannula the frequency of accidental muscular injections can be reduced to almost zero. It is however quit difficult for the individual person to determine which needle length to use at the different injection sites.

US 5.944.700 discloses an injection needle provided with an adjustable extender limiting the available injection length of the needle cannula, such that the muscle tissue is not penetrated when such an injection needle is used. Prior to injecting a medicament using one of these injection needles the adjustable extender has to be set in a way leaving the injecting part of the needle cannula with a length short enough to prevent intramuscular injection.

In order to avoid setting the injection length of the needle cannula prior to each injection, injection needles where the part of the needle cannula inserted into the human body has a standard length has been developed. The standard length of the injection part of these commercial available injection needles for insulin delivery systems is usually 6, 8, 10 and 12 mm.

The individual person suffering from diabetes then chooses an injection needle adequate for his or hers body structure. It is however quite difficult to choose the right needle size since it is impossible for the single user to determined the actual depth an injection needle can be inserted into the body without penetrating a specific target inside the body such as the muscle membrane covering the muscular tissue. Moreover, the distance from the surface of the skin to the muscle membrane may be different in places only a few centimetres apart.

Choosing the needle size only on the basis of a visual inspection of once body structure is not recommendable.

Over the years various types of ultrasound equipment has been adopted by the medical in- dustry primarily to inspect the condition of specific organs inside the human body.

EP 278.993 discloses an ultrasound apparatus for guiding a biopsy needle inside a human body. This known apparatus is rather complicated; it is not portable and it is not suitable for use by not trained personnel away from a hospital setting.

A needle-free injection syringe, which forces the medicament into the human body using high pressure, is known from JP A 2000-233021. This complex needle-free injection syringe is equipped with an ultrasonic measuring device, which measures the thickness of the subcutaneous fat layer and determines the property of the skin. These measurements are used for setting the pressure by which the medicament is injected into the body.

In order to grade meat in the livestock industry a large variety of different apparatus measuring the thickness of the various fat layer of an animal have been developed. One such apparatus is disclosed in US 4.359.055. This apparatus comprises an ultrasonic probe transmit- ting an ultrasonic pulse into the animal body and picking up the echoes. The thickness of the different fat layer of the animal is calculated and displayed in a display located in a remote unit connected to the probe through a wire.

Disclosure of the Invention:

Although a large variety of injection needles are available today, it is impossible for the user to know the exact depth available from the outer surface of the skin and into the surface of the muscular tissue on the particular site on the body the injection is performed.

When a person suffering from diabetes has performed self-injections for a long period of time the individual person will have a certain experience helping him or her to determined how long a length of the needle cannula should be left free to penetrate the body. However, this method is far to imprecise to avoid erratic intramuscular injections. For people who are not familiar with self-injections there are no accessible ways of determining the distance from the outer surface of the skin and into the surface of the muscular tissue. The length of the needle cannula left free to penetrate the body is therefore often chosen to long resulting in the patient injecting insulin into the muscle tissue.

Even people who consider themselves as being quite fat i.e. having a subcutaneous fat later of several centimetres, may have locations on the body e.g. at the outer sides of the thighs, which is a highly recommended place for insulin injections, where the thickness of the subcutaneous layer is small. These people may risk intramuscular injections if they use an injection needle having a long length in those places, although the same injection needle does not cause problems at injection sites with more subcutaneous fat, e.g. the abdomen.

It is an object of the present invention to provide a portable handheld apparatus for non- invasive determination of the possible allowable penetration length of an injection needle for injecting a drug into a human body avoiding penetration of a specific target located inside the body. The target is preferably the muscle membrane covering the muscular tissue. It is fur- ther an object to provide such a portable handheld apparatus, which presents a proper readout of a recommended needle size and which are both simple to use and cheap to manufacture.

This is obtained by an apparatus according to claim 1. By mounting both the ultrasonic measuring head, the electronic circuit and the display in one manually-gripable housing, a very user-friendly design can be obtained. The ready to use apparatus fits into one hand when in use, and into e.g. the pocket of a shirt when not in use. It is therefore easy to carry the apparatus from one patient to another e.g. in a hospital, and the simple design of the apparatus makes it very easy to use, even for untrained personnel. The compact design, which resembles somewhat of an injection device for insulin, also makes the apparatus very attractable for people who are used to performing daily self- injections e.g. people suffering from diabetes.

When, as disclosed in claim 2, the target is the muscle membrane separating the muscular tissue from the subcutis tissue, it is ensured that the possible allowable penetration length of the injection needle displayed will be a needle length short enough to prevent intramuscular injection.

In a preferred embodiment, disclosed in claim 3, the possible allowable penetration length is displayed by displaying the allowable standard needle sizes recommended for that particular anatomical injection site. When the correct needle sizes for a particular injection site is directly shown in the display, it is very easy for the user to select the correct needle size. The user just has to use one of the injection needle sizes presented in the display.

The algorithm used for recommending an injection needle is according to yet another embodiment of the apparatus according to the invention, that a 6 mm needle is recommended if the total distance from the outside surface of the skin to the muscle membrane is larger than 6 mm, an 8 mm needle is recommended if the distance is larger than 8 mm, and a 12 mm needle is recommended if the distance is larger than 12 mm. The emission of liquid from the injection needle usually takes place in a distance of 0,4 to 1 ,2 millimetres from the point of the needle due to the oblique cut of the end of the needle. The algorithm will therefore secure that the standard injection needle recommended does in fact deliver the drug above the muscle membrane.

When, as disclosed in claim 5, only the maximum allowable standard needle size recommended for that particular anatomical injection site is displayed, it is ensured that the drug is delivered so far into the subcutis of the human body, as it is possible using a standard injection needle size. According to an embodiment of the apparatus according to the invention a message indicating that the chosen injection site is unsuitable for injections are displayed if the possible allowable penetration length is shorter than a predetermined length e.g. 6 mm. In that way injections are always performed in location where the thickness of the cutis and the subcutis is larger than a predetermined length. The predetermined length is set to 6 mm since this is the smallest standard size of the commercial injection needle available today. The message could be followed by an acoustic signal warning the user against injecting at the particular injection site.

When, as disclosed in claim 7, the housing is a pen-style elongated housing, it is ensured that the familiarity with the known injection devices for self-injection of insulin is obvious for the user.

When, as disclosed in claim 8, the housing further comprises power means, such as batter- ies, the portability of the apparatus is enhanced. The batteries could be of the rechargeable type if wanted.

It is also an object of the present invention to provide a method of determining the possible allowable penetration length of an injection needle for injecting a liquid drug into a human body. A method that is both reliable and simple in use, such that untrained personal can easily adapt the method.

This is obtain by a method according to claim 9.

By using the claimed apparatus for carrying out the described method, which method includes pressing the ultrasonic measuring head against the human body on the site where the injection is intended to be performed, the user can easily determine which standard needle size to use on a specific injection site in order to avoid intramuscular injections.

When, as disclosed in claim 10, only the maximum allowable standard needle size recommended for that anatomical injection site is presented in the display, it is ensured that the user needs only identify one specific needle size, and that the drug is delivered so far into the subcutis of the human body, as it is possible using one of the standard injection needles available. It is to be understood that the wording "injection", used throughout this application means expelling a liquid into a human body through a hollow injection needle or another hollow conduit, which is temporarily inserted in the human body.

In the present context, the term "injection length" or "injection part of the needle cannula" is taken to mean the part of the needle cannula entering the human body during injection, which also is the part extending in the proximal direction from its fastenings point in the needle hub. Often references are made to a specific "needle size", which usually means the length of the needle cannula extending beyond the needle hub, this part is normally between 6 to 12 mm

Although the wording "human body" is used through out this application, the apparatus could as well be used on any other mammal body without dispersing from the scope of the claims.

In the present context, the term "subcutaneously" refers to the subcutaneous tissue of the human body, which are the tissue located between the cutis and a muscle membrane covering the muscular tissue, while the term "intramuscular" refers to the muscular tissue. By a number of measurements it is found that the average depth of the muscle membrane is 9,5 mm for males and 13,8 mm for females, measured from the outside of the human skin. There are however a wide variation from one anatomical region to another. In order to ensure penetration of the cutis of a human body, the minimum length of the part of the needle cannula penetrating the subcutaneous tissue must be longer than the thickness of the cutis, which is approximately 1 to 4 mm.

It is to be understood that the wording "pen-style elongated housing", merely refers to a housing having an oblong or elongated shape and fits into one hand, somewhat like an ordinary pen for writing. Although such pens usually have a tubular cross-section, modern writing pens often have a different cross-section such as triangular, rectangular or square. A pen shaped housing can in a similar way have a large variety of different cross-sections. The housing is also referred to as being a "Manually-gripable housing", which means that the housing is gripable by the human hand, and can be manually manipulated Brief Description of the Drawings:

The invention will be explained more fully below in connection with a preferred embodiment and with references to the drawings in which:

Figure 1 Shows a front view of the apparatus according to the present invention.

Figure 2 Shows a top view of the apparatus according to the present inven- tion.

Figure 3 shows a sectional view of the distal end of the apparatus according to the present invention.

Figure 4 shows a graph of the ultrasound signal and of the bounced off echoes.

The figures are schematic and simplified for clarity, and they just show details, which are essential to the understanding of the invention, while other details are left out. Throughout, the same reference numerals are used for identical or corresponding parts.

Detailed Descriptions of Embodiments:

Initially it may be convenient to define that, the term "distal end" of the apparatus according to the invention is meant to refer to the end, which is pressed against the human skin when operating the apparatus, whereas the term "proximal end" is meant to refer to the opposite end of the apparatus which in use points away from the human body.

Figure 1 shows an apparatus for non-invasive determination the possible allowable penetration length according to the invention.

The apparatus comprises an elongated housing 1 having a distal end 2 and a proximal end 3. The housing 1 has the shape of an ordinary pen for writing, and is at the proximal end 3 equipped with a clip 4 for clipping the apparatus on to a pocket of a shirt or the like. In use the power of the apparatus is switch on by pressing the on/off button 5 located at the proximal end. The distal end is then pressed against the skin 8 of the user, and the ultrasonic measuring head is activated, as later explained, by pressing the start button 6 located in the distal half of the housing 1. The result of the measurement will be presented in the display 7.

The biological structure of a human being is shown in figure 3. The outer skin 8 covers the cutis layer 9, which is usually between 1 to 4 millimetres thick. The underside 10 of the cutis layer 9 faces the subcutis layer 11 , which again is separated from the muscle tissue 13 by the muscle membrane 12. By a number of measurements it is found that the thickness of the cutis layer 9 and subcutis layer 11 lies in the intervals described in the following table.

Females Males min Max mean min max mean

Cutis (9) 1 ,1 3,6 1 ,7 1 ,2 4,1 2,3

Subcutis (11) 4,5 30,8 12,1 2,3 26,9 7,2

Sum (9,11) 5,6 34,4 13,8 3,5 31 ,0 9,5

As can be seen from the table the overall distance from the outside surface of the outer skin 8 to the muscle membrane is somewhere between 3,5 to 34,4 millimetres.

An ultrasonic measuring head is located at the proximal end of the apparatus, as shown in figure 2. The ultrasonic measuring head comprises a piezoelectric body 14, which produces an ultrasonic signal 19 when a voltage is applied to the piezoelectric body 14. The voltage is supplied from the electronic circuit 16 through wires 15. When a bounced off echo is re- fleeted onto the piezoelectric body 14, an electric voltage is generated and lead back to the electronic circuit also through one of the wires 15.

The electronic circuit 16 and the display 7 are powered through wires 17 connecting the electronic circuit 16 to a not shown electric transformer or a not shown battery.

In order to provide an accurate measurement it is very important that no air gap is present between the piezoelectric body 14 and the outside surface of the skin 8 of the user. A somewhat soft protective pad 18 working as an impedance matching layer is therefore provided between the piezoelectric body 14 and the outside surface of the skin 8 of the user. For fully excluding the presence of any air gap between the outside surface of the skin 8 of the user and the piezoelectric body 14, a jellylike acoustic impedance oil is often applied to the outside of the skin 8 prior to placing the ultrasonic measuring head of the apparatus against the skin 8.

When activating the start button 6 an electric voltage is applied to the piezoelectric body 14 causing it to transmit an ultrasonic signal at time TO. A short time thereafter, at time T1 , the first echo 20 bouncing off from the interface 10 between the cutis layer 9 and the subcutis layer 11 is received by the piezoelectric body 14. Sometime later, at time T2, the piezoelectric body 14 receives the bounced off second echo 21 from the muscle membrane 12.

A timer timing the time passing form TO to T2 is also activated when the ultrasonic signal is transmitted. The distance from the outside surface of the skin of the user to the muscle membrane can be calculated as a result of the time passing from TO to T2, e.g. by multiplying the time passing with the speed of sound. The speed of sound in the cutis layer 9 and in the subcutis layer 11 might differ from the sound of speed in air, and might be stored in the electric circuit 16 as an empiric value. From the ultrasound signal 19 is initiated and to the bounced off second echo 21 is received at the piezoelectric body 14, the signal has travelled twice the distance from the surface of the skin 8 of the user to the muscle membrane 12.

The distance can either be calculated on the basis of a single ultrasonic signal and a single bounced off echo, or the electric circuit 16 and the piezoelectric body 14 can be made to transmit a number of ultrasonic signals into the body of the user and to calculate an average distance on basis of the bounced off echoes 21.

Once the distance from the outside surface of the skin 8 of the user to the muscle membrane 12 has been calculated, the possible allowable standard sizes of injection needles recommended for that particular anatomical injection site is automatically determined using the following table, which is electronically stored in the electronic circuit 16.

The result originating from the right column of the table is displayed in the display 7. It is however possible to alter the apparatus such that only the maximum allowable standard needle size recommended for that particular anatomical injection site is shown in the display 7. The lower limit for when the result: "Unsuitable for injection" is displayed could be set to accommodate an even shorter injection needle if so wanted.

The electronic circuit 16, which could be a microprocessor, is designed such that the accuracy of the measurement is within half a millimetre. The accuracy could however be chosen differently, and the table indicating which needle sizes is recommended for a specific measurement could also be altered.

Some preferred embodiments have been shown in the foregoing, but it should be stressed that the invention is not limited to these, but may be embodied in other ways within the sub- ject-matter defined in the following claims.

Claims

1. Apparatus for non-invasive determination of the possible allowable penetration length of an injection needle for injecting a liquid drug into a human body, comprising a manually- gripable housing with a distal end and a proximal end, comprising:

an ultrasonic measuring head located at the distal end of the housing for transmitting an ultrasonic signal into the human body and receiving a reflected signal reflecting from a specific target inside the human body,

an electronic circuit for analysing the ultrasonic signals and calculating the possible allowable penetration length of the injection needle in order to avoid penetration of the specific target,

a display for displaying the possible allowable penetration length of the injection needle.

2. An apparatus according to claim 1, characterized in that the target is the muscle membrane separating the muscular tissue from the subcutis tissue.

3. An apparatus according to anyone of claim 1 to 2, characterized in that the possible allow- able penetration length is displayed by displaying the allowable standard needle sizes recommended for that particular anatomical injection site.

4. An apparatus according to anyone of the claims 3, characterized in that a 6 mm needle is recommended if the total distance from the outside surface of the skin to the muscle mem- brane is larger than 6 mm, an 8 mm needle is recommended if said distance is larger than 8 mm, and a 12 mm needle is recommended if said distance is larger than 12 mm.

5. An apparatus according to claim 3 or 4, characterized in that only the maximum allowable standard needle size recommended for that particular anatomical injection site is presented in the display.

6. An apparatus according to anyone of the preceding claims, characterized in that a message indicating that the chosen injection site is unsuitable for injections are displayed if the possible allowable penetration length is shorter than a predetermined length e.g. 6 mm.

7. An apparatus according to anyone of the preceding claims, characterized in that the housing is a pen-style elongated housing.

8. An apparatus according to anyone of the preceding claims, characterized in that the hous- ing further comprises power means, such as batteries.

9. A method for non-invasive determination of the possible allowable penetration length of an injection needle for injecting a liquid drug into a human body avoiding intramuscular injection, using an apparatus according to anyone of the claims 1-8, which method comprises the steps of:

a) pressing the ultrasonic measuring head located in the distal end of the housing against the skin of the human body on the site where the injection is intended to be performed,

b) transmitting one or more ultrasonic pulses into the human body,

c) receiving one or more echo signals bounced of the muscle membrane,

d) recording the travel time passing from the ultrasonic pulse is transmitted until the echo signal bounced of the muscle membrane is received,

e) calculating the distance from the surface of the skin to the muscle membrane as a result of the recorded travel time,

f) determining the possible standard needle sizes which is shorter than the calculated distance from the surface of the skin to the muscle membrane,

g) presenting the possible allowable standard needle sizes recommended for that specific anatomical injection site in the display.

10. A method for non-invasive determination of the possible allowable penetration length of an injection needle according to claim 9, characterized in that only the maximum allowable standard needle size recommended for that specific anatomical injection site is presented in the display.