AY Honors/Home Nursing/Answer Key
A heating pad is a pad used for warming of parts of the body in order to manage pain. Such pads are now usually electrical or chemical, though in the past "hot water bottles" were used and sometimes still are.
Electric pads usually operate from household current and must have protections against overheating. Chemical pads employ a chemical heat reservoir (see below) or a one-time chemical reaction such as catalyzed rusting of iron.
Types
A sodium acetate heat pad is a quantity of sodium acetate (CH3COONa) that heats when you start the crystallisation process by clicking the piece of metal that is in the liquid.
Because the liquid is supercooled, i.e. the temperature of the solution is below its crystallisation point, clicking makes it crystallise suddenly thereby releasing the energy of the crystal lattice. See sodium acetate for a more technical discussion.
The heat required for crystalisation is retained when the temperature drops and the liquid gets below the melting temperature. The heat is released on solidification, which is triggered by flexing a (patented[1]) small flat disc of notched ferrous metal which releases very tiny adhered crystals of sodium acetate [2] into the solution which then act as nucleation sites for the recrystallization of the remainder of the salt solution.
To reuse the pad it is placed boiling water for 15 minutes which reliquifies the sodium acetate solution. Once the pad has returned to room temperature it can be triggered again.
A microwavable heating pad is a heating pad that is warmed by placing it in a microwave oven before use. Microwavable heating pads are typically made out of a thick insulative fabric such as flannel and filled with grains such as buckwheat or flax seed. Due to their relative simplicity to make, they are frequently sewn by hand, often with a custom shape to fit the intended area of use.
Often, aromatic compounds will also be added to the filler mixture to create a pleasant or soothing smell when heated. The source of these can vary significantly, ranging from adding essential oils to ground up spices such as cloves and nutmeg, or even dried rose petals.
Function
Many episodes of pain come from muscle exertion or strain, which creates tension in the muscles and soft tissues. This tension can constrict circulation, sending pain signals to the brain. Heat application eases pain by:
- dilating the blood vessels surrounding the painful area. Increased blood flow provides additional oxygen and nutrients to help heal the damaged muscle tissue.
- stimulating sensation in the skin and therefore decreasing the pain signals being transmitted to the brain
- increasing the flexibility (and decreasing painful stiffness) of soft tissues surrounding the injured area, including muscles and connective tissue.
As many heating pads are portable, heat may be applied as needed at home, at work, or while traveling. Some physicians recommend alternating heat and ice for pain relief. As with any pain treatment, a physician should be consulted prior to beginning treatment.
