6.3 Superficial & Deep Heat / Cold
Key Takeaways
- Hot packs are applied with 6-8 layers of terry-cloth toweling for 15-20 minutes; vasodilation and increased tissue extensibility are reached at a depth of about 1-2 cm.
- Paraffin baths are kept at 52-54 degrees C (125-130 degrees F); the dip-wrap-bag technique with 6-10 layers of paraffin transfers heat for about 15-20 minutes, mostly to the hands and feet.
- Cryotherapy (ice pack, ice massage, cold pack) is typically applied 10-20 minutes and produces vasoconstriction, decreased nerve conduction velocity, decreased muscle spasm, and reduced acute inflammation.
- Heat is contraindicated over insensate skin, acute injury or inflammation, peripheral vascular disease with arterial insufficiency, active bleeding, and malignancy; cold is contraindicated in cold hypersensitivity, Raynaud's phenomenon, and cryoglobulinemia.
- The PTA monitors skin response and the patient's report at least every 5 minutes during any heat or cold application and stops immediately for mottling, severe pain, or wheals.
Superficial Heat and Cold
These modalities are some of the safest and most-tested in the PTA scope. Most NPTE-PTA items test (1) the correct delivery technique, (2) the appropriate clinical stage (acute vs subacute vs chronic), and (3) absolute contraindications screened during setup. All four mechanisms of heat transfer appear here: conduction (hot pack, paraffin, cold pack), convection (whirlpool, fluidotherapy), conversion (ultrasound, diathermy), and evaporation (vapocoolant spray).
Hot Packs
Hydrocollator hot packs sit in a water bath at 70-80 degrees C (158-176 degrees F). They are far too hot to apply directly.
- Layering: 6-8 layers of terry-cloth toweling between the pack and the patient (some sources cite 8-10 layers for older clay packs, or when the patient lies on the pack, which adds compression and heat transfer).
- Duration: 15-20 minutes.
- Depth of heating: approximately 1-2 cm; primarily superficial tissue.
- Effects: vasodilation, increased tissue extensibility, decreased muscle spasm, mild analgesia.
- Use: chronic pain, pre-stretch warm-up, muscle guarding, subacute injury after the acute phase has settled.
The PTA checks the skin after 5 minutes for excessive redness, mottling, or blanching. The patient must have a call light or other way to signal if the pack becomes too hot, and should never lie directly on the pack without extra layers.
Paraffin
Paraffin wax baths are kept at 52-54 degrees C (125-130 degrees F) and are used primarily on hands and feet where contoured surface contact matters.
| Technique | Description | Typical use |
|---|---|---|
| Dip-wrap-bag | Patient dips 6-10 times, then the limb is wrapped in plastic and a towel | Most common; comfortable and effective |
| Dip-immersion | Continuous immersion in the bath after dipping | More aggressive heating; less common |
| Brush-on | Painted on for areas that cannot be dipped | Rare in PTA practice |
Patients remove jewelry and wash and dry the limb first. The bath has a layer of mineral oil that lowers the perceived heat and keeps the wax pliable. Sessions last about 15-20 minutes. The wax can be peeled off cleanly and returned to the bath for reuse.
Paraffin is favored in chronic arthritis, scleroderma, post-immobilization stiffness, and chronic hand tendinopathy. It is contraindicated over open wounds, infections, recent surgery, impaired sensation, severe peripheral vascular disease, and over hardware close to the skin surface.
Cryotherapy
Cold modalities lower tissue temperature to reduce metabolic rate, inflammation, edema, pain, and muscle spasm. Common options include cold packs, ice massage, ice immersion, vapocoolant sprays, and contrast baths.
- Cold pack duration: 10-20 minutes; longer applications increase the risk of skin and nerve injury.
- Ice massage duration: 5-10 minutes over a small area, moved continuously in overlapping circles.
- Effects: vasoconstriction, decreased nerve conduction velocity, decreased muscle spindle activity, reduced acute inflammation.
- Patient sensation (CBAN sequence): Cold, Burning, Aching, then Numbness; numbness signals the analgesic phase and is the cue to stop ice massage.
Use for acute injury (sprain, strain, post-exercise inflammation), acute flare-ups of chronic conditions, post-surgical edema, and acute spasticity reduction before stretch. Cold is the first-line agent in the early inflammatory phase (first 24-72 hours). A useful technique caution: applying ice for more than about 20 minutes can trigger a rebound vasodilation reflex (the hunting response, or cold-induced vasodilation), so the PTA should stay within the time window.
Whirlpool and Fluidotherapy (Convection)
Convective agents move warm or cool water or particles across the skin. Whirlpool temperatures are matched to the goal: a warm whirlpool of 36-40 degrees C (96-104 degrees F) for general heating, a hot whirlpool only for small distal areas, and a cool whirlpool of 26-33 degrees C for acute conditions. Open wounds are treated at neutral or tepid temperatures (33-35 degrees C) to avoid maceration, and additives such as antiseptics are now used cautiously because of cytotoxicity concerns.
Fluidotherapy circulates warmed cellulose particles at 38-48 degrees C, providing dry heat plus a desensitizing massage that suits hand rehabilitation and hypersensitivity. Both allow active motion during heating, which contrast packs and paraffin do not.
Heat vs Cold: Selection Logic
| Clinical picture | Best initial modality |
|---|---|
| Acute ankle sprain, less than 48 hours, swollen and warm | Cold pack with elevation and compression |
| Chronic upper trapezius pain and tightness before stretching | Hot pack |
| Acute lateral epicondylitis flare with marked tenderness | Cold (ice massage) |
| Stiff arthritic hands in the morning | Paraffin |
| Subacute hamstring strain at day 5 with reduced swelling | Mild heat or contrast |
| Acute post-op TKA on day 2 | Cold |
Contraindications and Precautions
| Modality | Absolute contraindications |
|---|---|
| Hot pack / paraffin | Acute injury or inflammation, impaired or absent sensation, peripheral vascular disease with arterial insufficiency, active bleeding or hemorrhagic disorder, malignancy in the treatment area, infection, recent radiation therapy, deep vein thrombosis |
| Cold pack / ice massage | Cold hypersensitivity (cold urticaria), Raynaud's phenomenon or disease, cryoglobulinemia, paroxysmal cold hemoglobinuria, severe peripheral vascular disease, regenerating peripheral nerves, areas of impaired sensation |
A frequent NPTE-PTA distractor pairs a Raynaud's patient with "acute wrist sprain" and asks for the modality. The correct answer is not ice in a Raynaud's patient; switch to compression, elevation, and possibly mild heat once the acute phase resolves, after consulting the supervising PT.
PTA Documentation
For every heat or cold application, document: modality, area, duration, layers or temperature, the patient's report of intensity, the skin check at 5 minutes and post-treatment, and the patient's functional response (pain rating, range of motion).
A patient with a documented history of Raynaud's phenomenon presents 24 hours after an acute lateral ankle sprain with moderate swelling. The supervising PT's plan of care lists "thermal agent of choice" for edema management. Which modality should the PTA choose?
Which finding during a hydrocollator hot pack treatment requires the PTA to stop the modality immediately?