Gate Control Theory of Pain
The gate control theory is the basis for the design of Buzzy®. The premise is that when nerves receive non-painful signals such as vibration or cold, the brain closes the gate on pain signals. For example, if you hit your finger with a hammer, you might instinctively begin to rub it, shake it, or run it under cold water. You are sending non-pain signals through your nerves to close the gate on the pain signals.
Descending Inhibitory Controls
The second part of Buzzy® efficacy, and the reason it can help even when distant from the site of procedural pain, is something called Descending Noxious Inhibitory Control, or DNIC. While gate control happens locally (confusing nerves right where the pain happens) another effective mechanism of pain control uses the brain’s ability to dampen out unwanted signals. Instead of happening right where the nerves are, though, an intense degree of cold can work anywhere on the body.
The idea is like putting your hand in a bucket of ice water. Whoa, it’s cold! But you can handle the amount of cold initially. Studies have found that when someone’s hand is in ice water, they can handle more intense pain everywhere else in the body, probably because the sensation of ice is so intense it doesn’t leave as much room for the brain to notice pain as sharply other places.
It is as if when one sensation is very intense, the brain turns the volume down on sensations anywhere in the body. In scientific terms, intense cold activates a supraspinal modulation raising the body’s overall pain threshold. There have now been over 50 independent clinical trials proving the effectiveness of Buzzy® and VibraCool®.
The gate control theory is the basis for Buzzy®, a reusable device that provides natural injection pain relief. “Gate control” is the term used to describe pain relief by causing sensations other than pain, and then sending them down the same pathway where pain gets blocked at the “gate”. Sharp pain, itching, and burning are transmitted on the same Aδ nerve to a transmission system in the dorsal (sensory) horn of the spinal cord. Motion signals travel alongside pain fibers on Abeta nerves, as do temperature and pressure nerves (C fibers). A single summary signal is then transmitted up the spinal cord, thus excess vibration or cold can overwhelm or dilute the sharp pain from shots, itching, or burning from medications.
Using the body’s own nervous system, the gate control theory invokes the concept that the final common pathway for sharp pain to the brain can be shut out by the nerves that transmit cold and vibration senses. Just as running a burn under cold water stops the sharp pain, or rubbing a bumped elbow stops the pain, simultaneously stimulating vibration and cold receptors can dull or eliminate pain.
Other ways besides Buzzy® to stimulating C [cold] and Abeta [vibration] fibers prior to sticking with a needle include compressed fluoroethane gas, which becomes cold as it expands on the skin. Cold spray has been used for shots, but research has been equivocal concerning efficacy. While Mawhorter found it effective for adult immunization in a travel clinic,1 Ramsook et al found increased distress in small children undergoing IV sticks.2 The cold also caused vasoconstriction, making threading the vein difficult. 2 Pain relief with cold spray for pediatric immunization has been mixed, as this study shows when comparing prior pain ratings to pain with cold spray or placebo.3,4
Most likely, the sub-freezing temperature penetrates the thinner stratum corneum in children, injuring epidermis and causing pain, while in adults it slows transmission of Aδ substance P release while non-noxiously stimulating C fibers. Children experience heat thermal burns in ¼ the time of adults; freezing spray could damage tissues in a similar manner.
Certainly, cold applied directly over a vein can cause vasoconstriction; however, applying a cold pack proximal to the site of puncture (as with Buzzy®) will delay or avoid development of vasoconstriction. With the application of the gate control theory, as with other areas of science and medicine, children are not just little adults. In a randomized controlled trial, Buzzy® with ice pack increased venipuncture success on the first try compared to vapocoolant (OR: 3.05, 95%CI 1.05 – 9.15).5 In a smaller study without ice packs, 81% of phlebotomists found access easier with Buzzy®.6
Optimal use of cold packs proximal to the site of injection has not been studied for children. Placing the pack at least 15 seconds prior to sticking seems to increase pain relief, and placing the pack as close as possible to the site of puncture is helpful. The pack needs to be in place during the stick, so make sure it is out of the way of the zone to be prepped. Leaving the pack in place longer than 2-3 minutes may be distressing to the child and likely will not improve pain management. In addition, prolonged cold can trigger cold agglutinins which can falsely lower white blood cell counts in approximately 10% of patients.
Buzzy® applied appropriately uses the gate control theory without these side effects and has been proven effective for IV starts in adults and children ages 4+.(7, 8)