Local Anesthesia Sheet 5 by Ibrahim Murad

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Today we will continue talking about the armamentarium for administration of local anesthesia.



We will talk about three things today:

1- syringes

2- needles

3- carpools







* Components of the syringe:

1- Barrel

2- Thumb ring

3- Finger grip

4- Hub: where u load the needle

5- Piston (Plunger): u can advance it forward or backward

6- Harpoon: metallic part of the piston & it’s look like (الحربة) to penetrate the diaphragm (rubber plunger) of the carpool

7- Needle adaptor (screw hub): to which the double ended needle is fixed









- Now we all know that the carpool has 2 parts:

1- Metallic part: has a diaphragm which should be penetrated by the needle

2- Rubber part: this side should be penetrated by the harpoon of the syringe

* Types of the syringes:



A- Non-disposable:



1- Breech-loading, Metallic, Cartridge-type, Aspirating:

- Breech-loading means à the cartridge is inserted from the side

- Top-loading when u open the joint and insert the needle from above

- Metallic part is NON disposable

- Most commonly used in dentistry

- Before u give the injection u should do aspiration especially in block types injections to make sure that u r NOT in a blood vessel (BV) cuz if u give the injection in a BV; there will be a high toxicity & the patient may encounter a vasovagal attack ( is a malaise mediated by the vagus nerve. When it leads to syncope or "fainting", it is called a vasovagal syncope, which is the most common type of fainting.wiki) cuz u give a large bolus of anesthesia into the circulation & we don’t this to happen



- So, aspiration means à to release ur thumb backward to create a positive pressure in the carpool & a negative pressure in the surrounding tissues and when u start to inject in the tissues, there will be a difference in the pressure between the carpool & the surrounding, so if u r in a BV small droplets of blood will come out toward the carpool so change the position of the needle (NOTE: don’t replace the carpool with a new one just change the position of the needle)



- Question asked by a student: why patients mouth swell when we give anesthesia??



- Answer: cuz u are injecting a large volume of anesthesia (1.8 ml) corresponding to the area that u r injecting in, that’s why u have to inject slowly



- In conclusion what u r making in aspiration is a negative pressure around the tissue (pulling out)



- We said that aspiration is v.imp in block types (like ID) anesthesia cuz the possibility to be in a BV is 15%, so it’s a high percentage BUT in infiltration types the percentage is very minimal



- You don’t do a backward pressure unless u r sure that the carpool is within the piston (harpoon is engaged within the diaphragm of the carpool)



- In aspiration we depend on the harpoon which is attached to the piston & is used to penetrate the rubber plunger



- Positive pressure applied to the piston force the LA into the needle lumen then into the patient’s tissue, then negative pressure is exerted on the thumb ring so the blood will enter the needle lumen & become visible in the carpool if it was in a BV





2- Breech-loading, Plastic, Cartridge-type, Aspirating:

- Disposable syringes, there are some types that are reusable so we classified it in the non-disposable category

- Expensive

- Lighter weight so we can handle it more easily (tactile sensation is better)

- This type doesn’t accept a carpool so we use bottles

- In major surgeries they still use bottles

- In our clinics we use this syringe for irrigation





3- Breech-loading, Metallic, Cartridge-type, Self-Aspirating:

- These syringes use the elasticity of the rubber diaphragm of the carpool to obtain the required negative pressure for aspiration

- The diaphragm rest on a metal projection inside the syringe that direct the needle into the carpool, when the pressure is released sufficient negative pressure develops within the cartridge (that means when u give injection a pressure difference will develop)

- Pressure on thumb increases the pressure within the carpool (positive pressure)

- Releases of pressure on thumb disk produces self-aspiration



4- Pressure Syringes:

- They invented this type cuz we have new techniques of anesthesia

- In PDL (periodontal ligament) or ILI (intraligamentary injection) u inject around the tooth itself in the intraligamental space or the septal bone

- There are lots of indications for this type and especially in PEDO clinics

- It’s considered a highly painful type of anesthesia so they invented a special type for this injection

- The syringe give anesthesia in a certain force & in a slow motion (high force with a slow motion)

- They enclose the glass carpool totally cuz we apply a high force and the carpool may fracture and there will be a glass shatter, so this envelop will protect us & the children

- We may use in adults if the ID block wasn’t successful

- Question: why we use it mainly in children?

- Answer: cuz we don’t like to give them ID block cuz a trauma may happen to them (very common) after giving the ID the lip become numb & they start biting their lip & causes trauma to the lip (sometimes it’s huge) so we give a localized anesthesia to the PDL in addition to that the bone in children is more porous so when I give ILI it will be easier & the dose will be less

- We don’t give more than 2 carpools in children

- In pressure syringes u give a certain amount of anesthesia per unit time that’s why we have new techniques in the armamentarium depends on the computer (computer aided anesthesia), here the computer itself calculate the amount of the anesthesia & inject in a controlled manner

- This type is very expensive

- Pin like grip that inject with a controlled force per unit time & it will be more accurate if it’s connected with the computer


- There is an old type pressure syringe called the Wilcox-jewett Obtunder, but we don’t use it anymore cuz it’s heavy & the child will be afraid when he see this




B- Disposable syringes:

- We encourage the use of this type of syringes

- Light weight so better tactile sensation (but u me feel awkward the first time u use it)

- Decontamination so better cross-infection control

- Expensive





C- Safety syringes:

- Mainly designed to protect u from needle stick injury

- There is a mechanism (by using one or 2 hands) that after when u give the anesthesia there will be capping or sheathing for the needle

- So, when give the anesthesia and withdraw the needle from the tissue u press a button that will make re-sheathing of the needle

- Ultra-Safety Plus: make re- sheathing by itself

- Very expensive

- You need to train how to load the syringe cuz it differ from other needles






D- Jet injectors:

- It’s like a pin

- It’s a needle free syringe

- It’s designed for patients who have a phobia from needles

- Expensive also (zy kol eshe b el dentistry L)

- We can’t depend on it to give anesthesia as we usually do cuz we want to give the anesthesia to the closest nerve ending or trunk

- So, it’s mainly considered as a step before injection

- Disadvantage of this syringe is that it requires more pressure so may cause sloughing of the tissues after the anesthesia cuz the oral mucosa can’t withstand a high pressure











· American Dental Association criteria for acceptance of local anesthesia syringes:

1- They must be durable

2- Can withstand repeated sterilization

3- Should load a variety of carpools & needles

4- Should be inexpensive

5- Light weight & simple to use with one hand

6- Should provide effective aspiration so that the blood will be easily observed in the carpool (the visible part in our syringes is throughout the barrel)





· Technical problems in the syringe:

1- No flow of the solution:

- The needle is bent



2- Leakage during the injection:

- Be sure that the needle penetrates the center of rubber diaphragm of the carpool

- An off-center perforation produces an ovoid puncture of the diaphragm that allows leakage of the anesthetic solution outside the needle



3- Broken carpool:

- Caused by a badly worn syringe, extra pressure, bent or dull harpoon will produce an off-center of the rubber plunger causing the plunger to rotate as it moves down the glass carpool this may cause breakage

- When u give infiltration or ID block u will not encounter resistant BUT in a palatal injection the tissues will be thick & the mucoperiosteum is in intimate relation to the bone so in this case u will that the needle is stopped so u have to inject very slowly so the carpool won’t be broken

- If u feel leakage u have to stop & check

















- Most needles used in dentistry are stainless steel & disposable

- Parts of the needle:

1- Bevel:

- Defines the point or the tip of the needle. There is long, medium and short

2- Shaft:

- One long piece running from the tip of the needle, through the hub, and continue to penetrate the cartridge

3- Hub:

- Plastic or metal piece through which the needle attaches to the syringe

- NEVER insert the needle in the tissues to this part

4- Syringe-penetrating end:

- The part which goes inside the needle adapter of the syringe & perforates the rubber diaphragm of the carpool





* There’re 2 important factors that should be considered when u choose the needle: gauge & langth



1-Gauge:

- It reflects the diameter of the lumen

- There is an inverted relationship (30-gauge needle has a smaller internal diameter than a 25-gauge needle), so the smaller the number the greater the diameter of the lumen

- Most common needle used in dentistry is the 25-gauge needle, why?

- Because the aspiration of the large needle in more, and the deflection will be less, so u will not be afraid when u inject in a thick tissues (like block anesthesia)

- 30-guage needle maybe used in infiltration cuz u have less tissue penetration & less chance for aspiration

- Again, the advantages for the large gauge needle over the small one:

1- Less penetration as the needle advanced through the tissue

2- Great accuracy in the injection

3- Less chance of needle breakage

4- Easier aspiration

- It was thought that a large gauge needle causes more severe pain than a smaller one, but they prove that there is no big difference, and even if it was more painful the other advantages will let u to choose the large one



2-length:

- Long needles range from 35-40 mm (that’s what the Dr said but in the book the longest needle is 35, so the average length will be different)

- Short needles range from 15-25

- The weakest point of the needle is the hub,that’s why u should never insert the needle to its full length

- If the needle broke in the patient’s mouth & u can see it u can try to get it out BUT if u don’t see it so never try to get it out & refer it



· General rules of using needles:

1- Never be used for more than one patient

2- Should be changed after several uses (if u give the same patient more than one injection) cuz the needle will be dull

3- Decontaminated needles should be disposed in a special container

4- Needles should NOT be inserted in the tissue to their hub

5- Long needle is preferred for the block injection & the short needle for the infiltration

6- Needles direction should NOT be changed in the tissues

7- Needle should NEVER be forced against resistance

8- Needles should NOT be bent if they are to be inserted (the only indication sometimes is when we give pulpal anesthesia)









· Parts of the carpool:

1- Plastic cylinder

2- Rubber bung

3- Diaphragm

4- Aluminum cap



- The Dr said that u have to look to the carpool before injection & check the following:

· Expiry date

· Rubber bung if its in its place or not

· Look to the cap if there is corrosion

· Carpool itself if there are air bubbles



What inside this carpool (u have to know as u know ur name):

1- LA

2- Vasopressor

3- Preservative (sodium bisulfate)

4- Sodium chloride

5- Distilled water


NOTES about the carpool:

- Glass cartridge should NOT be autoclaved

- You don’t have to warm the syringe in cold weather

- Should NOT be soaked in alcohol cuz the diaphragm is semi-permeable so the alcohol may enter the carpool & this will cause pain to the patient during injection

- Should be stored in their container at room temperature





Notes in general:

- Non-aspirating syringes are NO more in the dental use cuz they increase the risk of intravascular injection & this may lead to fainting

- Heating needles to sterilize it is FORBIDDEN

- One carpool for each patient cuz of micro-leakage (backward flow) even if u didn’t do aspiration

- When closing the needle U should use the SCOOP technique to prevent needle stick injury