Chapter 5 How to Inject Local Anesthetic With Minimal Pain
LOCAL ANESTHESIA DOES NOT HAVE TO HURT
We easily teach all of our medical students and residents how to inject local anesthetic for carpal tunnel surgery so that all the patient consistently feels is the first stick of a 27- or 30-gauge needle.1 Patients will greatly appreciate the doctor who has invested the time required to learn the ten simple rules listed below.2 The most important are rules 7, 8, 9, and 10. Our patients are constantly amazed and delighted at how little pain they feel from our medical students’ and residents’ injections.
RULE 1. BUFFER 1% LIDOCAINE AND 1:100,000 EPINEPHRINE WITH 10:1 8.4% SODIUM BICARBONATE
1% lidocaine with 1:100,000 epinephrine has an average pH of 4.2, with a range of 3.3 to 5.5.3 This can be 1000 times more acidic than the normal body pH of 7.4. This is one reason that it hurts when you inject it unbuffered.
A bottle of 50 ml of 8.4% sodium bicarbonate costs less than $10.
RULE 2. DO NOT USE REFRIGERATED LOCAL ANESTHETIC
Refrigerated local anesthetic will result in a more uncomfortable injection for the patient than room-temperature local anesthetic.4 We store our lidocaine with epinephrine at room temperature. Some centers keep their lidocaine and epinephrine refrigerated so that it lasts longer. This is not necessary if you simply adhere to the expiration dates on the bottle.
RULE 3. INJECT LOCAL ANESTHESIA WITH SMALL-BORE 27- OR 30-GAUGE NEEDLES
Bigger needles hurt more. Stop using 25-gauge or larger needles.
Injecting large volumes quickly causes pressure pain. Use smaller 27-gauge needles, which will remind you to slow down, which will decrease injection pain.
Use 30-gauge needles for children or patients who are particularly sensitive.
RULE 4. CREATE SENSORY NOISE IN THE AREA OF INJECTION
Simply pressing firmly on the skin proximal to where you will insert the needle can create sensory input “noise” that decreases the pain felt by the patient. This is like hearing a baby cry in a crowd versus hearing it cry in your room at 2 AM.
It may hurt the patient more if he or she watches the needle go in.5 Ask the patient to look away.
You can also move loose skin into the needle tip instead of moving the needle into the skin.
RULE 5. STABILIZE THE SYRINGE WITH BOTH HANDS AND HAVE YOUR THUMB READY ON THE PLUNGER TO AVOID THE PAIN OF A MOVING NEEDLE
It can take up to a minute for the needle site to numb after you place the needle under the skin, especially if you inject an insufficient bleb right under the dermis. In this time, the patient will feel the sting with every little wobble of the needle moving in the skin.
If you stabilize the syringe with two hands, and if your thumb is on the plunger ready to inject before the needle penetrates, you will minimize painful needle movement in unanesthetized skin.
RULE 6. INJECT 0.5 ML WITH A PERPENDICULAR NEEDLE JUST UNDER THE DERMIS AND THEN PAUSE UNTIL THE PATIENT SAYS THE NEEDLE PAIN IS GONE
Nerves in the dermis are like trees with sensitive leaves, and in the fat are like branches and trunks. Injections in the dermis hurt more than in subcutaneous fat, because you irritate more “leaves” with the pressure of intradermal injection.8 Inject just under the dermis instead of in the dermis.
Inserting the needle perpendicular (90 degrees) to the skin hurts less than if you come in parallel to it, because you pierce fewer nerve endings with the sharp needle tip on the way to the subcutaneous fat.9
Begin by injecting a visible bleb (0.5 ml) just under the dermis, then pause until the patient tells you the pain is all gone. You will be able to start to count the number of subsequent times the patient feels pain. You can then score yourself as per rule 9 and improve your injection technique, because you will be able to count the total number of times the patient feels pain during the injection process.
When the patient tells you the sting of the needle site is gone, inject an additional 1.5 ml very slowly without moving the needle.
If you start to inject quickly or move the needle tip out of the numb zone, the patient will feel pain. After you have injected the initial 2 ml of anesthetic, you can change the angle from 90 perpendicular degrees to parallel to the skin without causing pain.