Basic Information About Subcutaneous Injection

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Advantages and Disadvantages of subcutaneous injection

Some medications are best administered into the subcutaneous tissue by a needle.  R is route has the advantage of almost complete absorption, providing the patient’s circulation is good; therefore an accurate measure of the amount of the drug absorption is possible.  Medicines administered in this manner are not affected by gastric disturbances (although it should be remembered that the medicines may themselves cause gastrointestinal disturbances), nor is their administration dependent upon the consciousness or rationality of the patient.

The chief disadvantage of this method is that by introducing a needle through skin one of the body’s barriers against infection is broken.  It is therefore important that aseptic technique be used for all needle injections.

Site of subcutaneous injection

The subcutaneous tissue is just below the cutaneous tissue or skin.  It is aerolar tissue which has fewer pain receptors than the skin itself; therefore once a needle is through the skin an injection is relatively painless.  Some drugs sting upon injection, but an isotonic solution can usually be administered painlessly.  Isotonic refers to a concentration that is the same as a normal saline solution.

The exact site for a subcutaneous injection is dependent upon the need of the specific patient and to some extent upon the policy of the institution.  Since drugs administered subcutaneously (hypodermically) are usually given for their systemic effect, the site is irrelevant with respect to any local effect.  Areas in the upper arms, anterior and lateral aspects of the thigh and the lower ventral abdominal wall are suggested.  The skin and subcutaneous tissue should be in good condition, that is, free of irritation such as itching and free from any signs of inflammation such as redness, heat, edema, tenderness or pain.  Areas where there is scar tissue should not be used.  A common practice is to choose the outer aspect of the patient’s upper arm about one-third of the distance down between the shoulder and the elbow.  Other sites are the anterior aspect of the thigh, the loose tissue f the abdomen and the subscapular region of the back.  Actually the subcutaneous tissue in any area can be injected provided that is not over bony prominences and if free of large blood vessels and nerves.  If a patient is receiving a series of injections the sites are rotated and the site is charted receiving a series of injections the sites are rotated and the site is chartered each time so that two consecutive doses are not given in the same area.  Sometimes a map is drawn on the patient’s skin to indicate the sites for rotating injections, or a chart may be attached to the nursing care plan for the patient.

Equipment for subcutaneous injection

Subcutaneous (hypodermic) injections involve the use of sterile equipment and supplies.  These include a syringe, a needle, the medication and a swab and disinfectant to cleanse the skin.  Syringes vary in size from 1 cc to 50 cc.  The 2 cc. syringe, commonly used for subcutaneous injections is calibrated in cubic centimeters and minims.  For administration of insulin, special 1 cc. syringes are often used.  Insulin syringes usually have an 80 unit scale and 40 unit scale to correspond to the strength of the particular insulin.  They are calibrated in units.

A syringe has two parts, the barrel or outer part and the plunger or inner part.  Most syringes are manufacture so that their parts are interchangeable, but if they are not they bear corresponding numbers on the plunger and barrel.

Syringes are made of glass or plastic.  The latter, which are usually disposable, are increasingly being used in hospitals offices and clinics. A 2 cc. syringe is usually used for subcutaneous injections.  The maximum volume of solution which can be given comfortably by this route is thought to be 20 minims.  Certainly anything greater than 2 cc. 930 minims) will cause pressure on surrounding tissues and therefore be painful.

A needle has a hub and a stem or cannula.  The hub is the larger part that connects to the barrel of the syringe; the cannula is the long narrow part.  At the end of the cannula is the bevel or slanted portion where the fluid is ejected.  A short or small bevel is used when there is a danger that a larger bevel would become occluded, as in intravenous injections in which the bevel could rest against the side of the vein.  The longer bevel provides the sharper needle and is used for subcutaneous and intramuscular injections.

The needle used for subcutaneous injection is usually 24, 25 or 26 gauge.  The larger the number; the smaller the diameter of the needle.  The length that required varies anywhere from 3/8 inch to 1 inch depending upon the obesity and hydration of the patient.  A longer needle is needed for the obese patient, a shorter needle for the hydrated person.  Generally a No. 24 needle 5/8 inch in length is used for average adult.

The needle used for any injection should be straight and sharp.  As disposable needles are increasingly being used, the problem of the bent or dull needle is disappearing. If disposable needles are not used, the needles are checked for sharpness and the presence of barbs before they are sterilized.  A needle may be checked for the presence of barbs by passing the tip lightly over a piece of absorbent cotton.  If the needle does catch on the cotton, it may have a barb and will be uncomfortable for a patient.  Needles that are bent should not be used, because of the danger that they will break off in a patient.  The weakest point in a needle is where the cannula joins the hub.

A word of caution on the use of disposable needles and syringes: after use they should be discarded in the designated containers, never where they can be used again.  These practices also help to protect the housekeeping staff from injury.

Two variations to the traditional means of administering injections subcutaneously are the injector syringe equipped with a spring which releases the needle for rapid insertion, and the jet injector by which the medication is introduced into the subcutaneous tissue by means of high pressure rather than through a needle.  Although these methods are preferred in some instances, they have not replaced the usual subcutaneous injection by hypodermic syringe.

Preparation of subcutaneous injection

Medications for injection come in tablet, liquid and powder forms.  All these forms must be kept sterile during preparation and administration.  If a drug in tablet form is to be administered subcutaneously, it is first dissolved in a sterile solution.  The safest method is to carefully drop the tablet into a sterile container, draw up measured amount of sterile solution into the syringe (sterile normal saline is less painful to the patient than sterile water), add the solution to the tablet to dissolve it and, finally draw up the measured amount of medicated solution into the syringe ready for administration.  Another method which is being used increasingly is to mix the tablet and the solution, directly in the syringe.

Medications in a liquid form generally come in single dose ampules or multiple dose vials. To open an ampule, the nurse first taps it to shake all the medication to the bottom and then brains a sterile cotton ball which she holds behind the neck of the ampule.  Some ampules open directly upon pressure at the neck; others require filling.  The cotton ball used to protect the nurse’s fingers when breaking the glass.  After the ampule is opened, the needle is carefully inserted, the ampule is inverted, and the solution is drawn into the sterile syringe.

Multiple dose vials of medication have a sealed rubber cap at the top which makes them air tight.  The cap is first wiped off with an antiseptic solution; the plunger of the syringe is drawn back to a point which indicates the volume of solution to be withdrawn and then the needle is inserted through the rubber cap.  Air is injected into the vial to equalize the pressure and thus facilitate the removal of the solution.  The vial is held upside down with the syringe at eye level in order to obtain an accurate measure of the drug.  Incorrect holding of the vial may result in air being drawn into the syringe.

Injectable drugs that come as powders are dissolved in sterile solution before they are administered.  Generally they are directions on the label as to the amount and kind of solution that is to be added to a vial.  In order to maintain normal pressure inside the vial, air is removed in a volume that corresponds to the amount of solution that is inserted.  If a large vial is used, it is often easier to insert a second sterile needle through the rubber cap to allow the free flow of air out of the vial as the fluid flows in.

Some drugs are now being prepared commercially in two compartment vials.  One compartment contains the powdered medication and the second contains the sterile liquid for dissolving the drug.  The insertion of a sterile needle or pressure upon a rubber diaphragm releases the liquid to mix with the powder, which is then ready for injection.  Some drugs are packaged this way because they are more stable in a dry state and thus can be kept for a longer period of time than the same drug in liquid form.

Whenever a powder or tablet is prepared for injection it should be completely dissolved before it is drawn into the syringe.  Rotating a vial between one’s hand in an effective way of missing a powder and a liquid without creating bubbles on the top of the solution. Bubbles can make it difficult to ascertain an accurate measure of the drug.

Administration of subcutaneous injection

When a subcutaneous injection is to be administered, a site is selected and cleansed with an antiseptic solution.  The type of antiseptic used depends on the policy of the agency.  Isopropanol in 70 percent solution is used in many hospitals.  The antiseptic solution is allowed to dry on the skip surface prior to insertion of the needle to prevent local irritation at the site of the injection.

When the skin is dry, air is expelled from the needle.  The needle is then inserted through the skin.  The angle of insertion depends on the size of the needle used.  It is recommended that the injection should be given deeply into subcutaneous tissue.  Therefore, if a ½ inch needle is used, it is inserted at a 90 degree angle, that is perpendicular to the skin surface.  Injections with a 5/8 inch needle are inserted at a 45 degree angle. Recent research indicates that the skin should not be drawn taut, pinched or pulled into a skin fold for the injection.  Rather, it should be left in its natural state.  The nurse will find it easier to give the injection, however, if she lightly holds the area around the injection site.

After the needle is inserted the plunger is drawn back in order to determine whether the needle is in a blood vessel.  If no blood appears in the syringe, the solution is injected slowly, after which the needle is quickly withdrawn.  If blood does appear in the syringe, the needle is immediately withdrawn and another medication prepared.  After the needle is withdrawn the area is massaged gently with an antiseptic sponge to facilitate dispersion of the solution.  If there is any sign of bleeding from the site of the injection, firm pressure over the area for a few minutes will usually stop the bleeding and thus prevent bruising.

Recording of subcutaneous injection

A subcutaneous injection is recorded on the patient’s record as in any medication but in addition, the word “subcutaneous” or the abbreviation “H” follows the dosage of the drug to indicate the route.  Sometimes the site of the injection is also recorded.


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