frostbite
Enable an AI agent to recognise a suspected frostbite episode, record evolving tissue injury and support timely, evidence-based escalation and care decisions.
Research draft, second pass
A second pass drafted this model: the structure a model of this thing needs, and what is known about it in the world. The line under this one says how the second half was obtained - researched against sources, or recalled without web access, in which case nothing here was read anywhere and every claim is a lead to verify. Unreviewed either way.
Researched by: Codex + Grok
Purpose and description
Enable an AI agent to recognise a suspected frostbite episode, record evolving tissue injury and support timely, evidence-based escalation and care decisions.
Frostbite, also called freezing cold injury, is localized destruction of living tissue that occurs when tissue is cooled below 0 °C so that ice forms in the extracellular (and, if cooling continues, intracellular) space, damaging cells directly and then producing endothelial injury, microvascular stasis, thrombosis and a reperfusion inflammatory cascade that can progress to necrosis of skin and, when deep, of subcutaneous tissue, muscle, tendon or bone.
It can be Assemble a site-specific frostbite assessment while flagging missing evidence and alternative diagnoses; Construct a freeze-thaw timeline with explicit uncertainty; Compare serial examinations without overwriting earlier severity judgments; Check proposed protection, rewarming and transport actions against recorded conditions and an applicable clinical protocol; Prepare an urgent clinical handoff containing affected sites, timing, perfusion findings and unresolved questions; Track tissue outcomes and frostbite-related functional limitations.
Distinguishing features
Require evidence supporting tissue freezing rather than cold exposure alone; frostbite is a freezing injury. [CDC frostbite overview](https://www.cdc.gov/winter-weather/prevention/preventing-frostbite.html)
Compare with frostnip: rapid resolution after warming without tissue injury supports frostnip, whose freezing does not extend into tissue. [WMS frostbite summary](https://wms.org/magazine/1250/frostbite-cgp/default.aspx)
Distinguish local tissue injury from systemic hypothermia and allow both to coexist. [CDC frostbite overview](https://www.cdc.gov/winter-weather/prevention/preventing-frostbite.html)
Test whether the exposure history and clinical assessment support freezing rather than nonfreezing cold injury or primary vascular ischemia; numbness or discoloration alone must not settle attribution.
Scope
+ Suspected or confirmed freezing injury at individually identified anatomical sites
+ Exposure, freezing, thawing and refreezing chronology
+ Local examination, tissue perfusion and evolving injury classification
+ Frostbite-specific protection, rewarming and specialist referral decisions
+ Tissue survival, healing and persistent functional consequences
- Whole-person hypothermia assessment and treatment, referenced as a concurrent condition
- Frostnip, chilblains and nonfreezing cold injury except as diagnostic alternatives
- Primary vascular disease and unrelated causes of limb ischemia
- General weather forecasting, expedition planning and protective equipment specifications
- Full medication, surgical procedure and rehabilitation models
Characteristics
- Diagnostic status
- suspected | clinically diagnosed | excluded | unresolved Separates an actionable concern from an established diagnosis and preserves competing explanations.
- Affected anatomical territory
- person, body part, laterality, digit and proximal extent Allows different sites in the same episode to carry different assessments and outcomes.
- Exposure mechanism
- environmental cold | cold-object contact | refrigerant or cryogenic exposure | mixed | unknown Records the proposed freezing mechanism and flags cases needing a boundary decision.
- Freeze-thaw phase
- suspected frozen | partially thawed | thawed | refrozen | unknown Makes examination findings and care decisions interpretable in their thermal context.
- Exposure and thawing intervals
- timestamps and elapsed minutes or hours, with uncertainty bounds Preserves the timing needed to evaluate progression and protocol-specific treatment eligibility.
- Local examination pattern
- documented color, firmness, sensation, swelling and blister appearance; unassessed allowed Retains observed evidence separately from inferred injury depth.
- Perfusion assessment
- preserved | impaired | absent | indeterminate | unassessed, with method and time Supports reassessment and specialist review without treating different examination methods as equivalent.
- Injury severity assessment
- named classification, assigned grade, assessment phase and assessor; unclassified allowed Prevents unsupported conversion between classification systems or premature certainty.
- Refreezing exposure
- possible | controlled | occurred | unknown Records a central constraint on thawing and transport planning.
- Functional impact
- task-specific ability or named scale, recorded against baseline Connects tissue injury to mobility, dexterity and recovery needs.
Also called
Where this came from
wikidata · CC0 1.0
Drafted structure
Bundle to layer to finding to question, as the second pass will find it: 6 bundles · 11 layers · 18 findings · 28 questions.
Freezing injury recognition Establish whether the episode represents frostbite and identify the injured territory.
Cold exposure and altered skin appearance do not independently establish tissue freezing.
Freezing evidence
Separate reported exposure, observed signs and diagnostic interpretation.
Basis for frostbite attribution
Record why freezing injury is suspected or diagnosed, with the observer, examination time and supporting record.
- What exposure and examination evidence supports tissue freezing at this site? definition
- Who supplied each observation, and was it recorded before or after thawing? provenance
Territory and alternatives
Locate each affected area and retain plausible neighbouring conditions.
Site-specific diagnostic boundary
Identify laterality and anatomical extent while distinguishing frostbite from frostnip, nonfreezing injury and other causes of ischemia.
- Which body parts, digits and proximal boundaries are affected or still unexamined? measurement
- Which findings support or weaken frostnip, nonfreezing cold injury or vascular ischemia as alternatives? boundary
Freeze-thaw history Represent the exposure and thermal transitions that frame the injury.
An examination and a care decision require a shared account of when tissue was exposed, thawed or refrozen.
Cold exposure context
Capture the local exposure mechanism and factors affecting heat loss or circulation.
Injurious exposure account
Record exposure duration, cold medium, wetness, protection and reported local circulation constraints without inferring tissue temperature from air temperature.
- What cold medium contacted the site, for how long, and with what protection or wetness? measurement
- Which exposure details were measured, recalled or inferred, and how uncertain are they? provenance
Thermal transition sequence
Track freezing, spontaneous or deliberate thawing, and subsequent cold exposure.
Thawing and refreezing timeline
Preserve separate thermal events and uncertain intervals rather than compressing them into one injury time.
- When did suspected freezing, each thawing attempt and any refreezing occur? measurement
- What evidence establishes the current thermal phase at each affected site? provenance
Tissue state and severity Describe local injury and how confidence in depth and viability changes.
Severity can vary within one extremity, and classification is difficult before rewarming. [WMS frostbite summary](https://wms.org/magazine/1250/frostbite-cgp/default.aspx)
Serial local examination
Keep comparable observations tied to anatomical sites and thermal phases.
Local injury pattern
Record sensation, color, firmness, swelling, blister characteristics and perfusion findings, including limitations of examination.
- What local signs are present, absent or unassessed, and how were they examined? measurement
- How have those signs changed since the last examination relative to thawing and treatment? measurement
Depth and viability interpretation
Keep clinical grades and tissue-survival predictions distinct from raw observations.
Supported severity judgment
Attach the classification system, assessor, evidence and uncertainty to each severity or viability judgment.
- Which classification was used, at what assessment phase, and which findings support the assigned grade? definition
- What remains uncertain about depth or viability, and what reassessment could resolve it? action
Protection and care decisions Represent the conditions and clinical authority governing immediate protection, thawing and referral.
Refreezing after thawing worsens injury, so the ability to maintain a thawed state matters to care planning. [CDC Yellow Book](https://www.cdc.gov/yellow-book/hcp/environmental-hazards-risks/heat-and-cold-illness-in-travelers.html)
Field care feasibility
Link local protection and rewarming proposals to shelter, resources and evacuation conditions.
Protection and thawing constraints
Record refreezing exposure, unavoidable use of injured tissue and the protocol supporting a proposed field action.
- Can the affected tissue remain thawed and protected throughout the expected evacuation? boundary
- What protection or rewarming action is supported by the applicable protocol, available resources and responder competence? action
Clinical escalation
Capture referral urgency and evidence needed for clinician-led treatment decisions.
Specialist care decision
Connect injury findings, concurrent emergencies and timing uncertainty to a documented referral or treatment assessment.
- What findings or concurrent conditions require urgent escalation, and where can appropriate care be obtained? action
- Which clinician and current protocol determine treatment eligibility, and what timing or contraindication information is missing? provenance
Tissue outcome and function Follow tissue recovery, complications and lasting effects at each injured site.
A frostbite episode needs an outcome record beyond its initial appearance or provisional severity grade.
Healing and tissue loss
Separate evolving tissue assessments from confirmed healing or loss.
Observed tissue outcome
Record healing, clinician-assessed necrosis, complications and any linked tissue-removal procedure without treating an early prediction as final.
- Which areas have healed, remain unresolved or have confirmed tissue loss, and when was each outcome established? measurement
- What new local findings prompted reassessment or a change in the care plan? action
Persistent functional effects
Track reported symptoms and practical limitations after the acute injury.
Frostbite-related recovery needs
Record changes in sensation, pain, cold tolerance, mobility or dexterity and the evidence linking them to this episode.
- Which symptoms or task limitations persist relative to the person's pre-injury baseline? measurement
- What follow-up, rehabilitation or exposure precautions has the responsible clinician recommended? action
Evidence and external alignment What the world already says about this thing, gathered so the model can be checked against it.
A model that cannot be lined up against existing standards, identifiers and practice cannot be adopted by anyone who already uses them.
Reported evidence
Findings from the breadth pass, kept separate from the structural claims.
Kinds and varieties
Reported by the breadth pass; each item needs checking against its source before it becomes normative.
- Frostnip (intense vasoconstriction without tissue ice or tissue loss; pallor and numbness reverse quickly on warming)
- First-degree frostbite (partial-thickness skin freezing: numbness, central pallor, surrounding erythema/edema, later desquamation; no gross infarction)
- Second-degree frostbite (full-dermal freezing with clear or milky blisters, erythema and edema; expected skin recovery with little tissue loss)
- Third-degree frostbite (full-thickness skin necrosis with hemorrhagic blisters extending beneath the dermal vascular plexus)
- Fourth-degree frostbite (necrosis into fat, muscle, tendon and/or bone, typically ending in mummification or loss of the part)
- Superficial versus deep field class (post-rewarming, pre-imaging: little expected tissue loss versus expected tissue loss)
- Cauchy grades 1-4 on hands and feet (extent of cyanosis after rewarming, used to predict digit versus limb amputation)
- Contact or cryogenic frostbite (direct contact with metal, fuel, dry ice or liquefied gases) versus environmental air-cold frostbite
- Which of these kinds and varieties hold for the sense of frostbite this model covers, and on what evidence? provenance
Identifiers and schemes
Reported by the breadth pass; each item needs checking against its source before it becomes normative.
- ICD-10 (WHO) - T33-T35 - T33 superficial frostbite; T34 frostbite with tissue necrosis; T35 multiple regions or unspecified frostbite.
- ICD-10-CM (United States) - T33.- / T34.- plus 7th character A, D or S - No T35 category; laterality and site in the 5th/6th characters. Type 2 excludes T68 and T69.-.
- ICD-10-CM external cause - X31 (natural cold); W93.- (man-made cold, dry ice, liquefied gas) - Cause-of-injury coding, not the injury itself.
- ICD-9-CM - 991.0-991.3 - Historic frostbite range cited in the disease infobox; superseded by ICD-10.
- MeSH - D005627 - National Library of Medicine heading Frostbite.
- MedlinePlus - 000057 - Consumer topic identifier.
- DiseasesDB - 31167 - Diseases Database record.
- NCBI Bookshelf / PMID - NBK536914 / 30725599 - StatPearls chapter identifiers, not a disease code.
- Which of these identifiers and schemes hold for the sense of frostbite this model covers, and on what evidence? provenance
Standards and regulation
Reported by the breadth pass; each item needs checking against its source before it becomes normative.
- Wilderness Medical Society Clinical Practice Guidelines for the Prevention and Treatment of Frostbite: 2024 Update (Wilderness Medical Society; graded with ACCP methodology).
- ICD-10 / ICD-10-CM categories T33-T35 (WHO) and T33-T34 (US National Center for Health Statistics / CMS) for diagnosis coding; T68 and T69.- are excluded as different cold effects.
- NATO research task group position paper on classification of freezing cold injuries (military FCI morphology, signs and outcome classes).
- ICD-10-CM external-cause codes X31 (excessive natural cold) and W93.- (man-made cold, dry ice, liquefied gas) for how the injury was produced.
- Which of these standards and regulation hold for the sense of frostbite this model covers, and on what evidence? provenance
Real-world use
Reported by the breadth pass; each item needs checking against its source before it becomes normative.
- Diagnosed in emergency and burn services after winter outdoor exposure: mountaineering, polar and high-altitude work, hunting, skiing and other cold recreation.
- A classic military cold casualty; still coded and classified as freezing cold injury in NATO and other armed forces.
- A winter injury of people without adequate shelter, clothing or cognition (homelessness, intoxication, extremes of age).
- Occupational and industrial contact injury from metal tools, fuels, dry ice and cryogenic liquids (liquid nitrogen, liquid oxygen, other liquefied gases).
- Field care follows WMS rules: protect from further cooling, do not thaw if refreeze is likely, then rapid water-bath rewarming; hospital care may add ibuprofen, iloprost, and, for severe acral injury, tPA with heparin, plus delayed rather than immediate amputation.
- Technetium-99 bone scans or angiography are used in the first days to map non-perfusion and decide thrombolysis or the eventual amputation level.
- Which of these real-world use hold for the sense of frostbite this model covers, and on what evidence? provenance
Typical measurements
Reported by the breadth pass; each item needs checking against its source before it becomes normative.
- Tissue or ambient temperature at which freezing injury occurs - Tissue ice below 0; some environmental risk 0 to −15, risk rises below −15 - °C
- Water-bath rewarming temperature - 37-39 (WMS 2024); older hospital protocols 40-42 - °C
- Cutaneous blood flow during cooling - about 250 normally; <20-50 in frostbite; ceases below 0 °C tissue temperature - mL/min
- Core temperature to restore before extremity rewarming if hypothermic - raise above 35 before thawing the part - °C
- Time from rewarming to blister formation - 4-24 - h
- Time to mummification and a clear line of demarcation - 3-8 - week
- Window for tPA in severe (Cauchy 3-4) injury - within 24 of injury - h
- Window for iloprost in deep (Cauchy 2-4) injury - within 72 after rewarming, as early as possible - h
- Which of these typical measurements hold for the sense of frostbite this model covers, and on what evidence? provenance
Failure modes and hazards
Reported by the breadth pass; each item needs checking against its source before it becomes normative.
- Thaw-refreeze cycles, which markedly worsen ischemia and thrombosis compared with remaining frozen until definitive rewarming.
- Rewarming over fire, exhaust or other dry heat, or rubbing frozen tissue, which adds burn or mechanical injury.
- Premature surgical amputation or aggressive debridement before a line of demarcation (often weeks), removing tissue that would have survived.
- Missed concurrent hypothermia, intoxication or trauma, with systemic collapse during or after rewarming.
- Progressive microvascular thrombosis after reperfusion, compartment syndrome, secondary infection, gangrene and sepsis.
- Long-term sequelae: cold intolerance, neuropathic or phantom pain, complex regional pain syndrome, nail loss, hyperhidrosis or anhidrosis, stiffness and auto-amputation.
- Alcohol, tobacco and vasoconstricting drugs that further cut peripheral perfusion during exposure.
- Which of these failure modes and hazards hold for the sense of frostbite this model covers, and on what evidence? provenance
Regional variation
Reported by the breadth pass; each item needs checking against its source before it becomes normative.
- WHO ICD-10 retains T35 (multiple or unspecified sites); US ICD-10-CM codes only T33 and T34.
- Japanese clinical language uses 凍傷 (tōshō) and the older character 瘃 (choku); Polish coding language uses odmrożenie for the same T33-T35 block.
- Nordic lay practice has used emollients as frostbite prevention; circumpolar research found no protective effect and StatPearls advises against them.
- Intravenous iloprost is used in several European and expedition protocols for deep frostbite but is not available in the United States, which leans more on tPA plus heparin where indicated.
- Case mix shifts by setting: military FCI in cold-climate armies, recreational and high-altitude frostbite in alpine regions, urban hypothermia-plus-frostbite in homeless populations, and cryogenic contact injury in industrial sites.
- Which of these regional variation hold for the sense of frostbite this model covers, and on what evidence? provenance
Neighbouring kinds and how to tell them apart
Reported by the breadth pass; each item needs checking against its source before it becomes normative.
- Frostnip - No tissue ice and no tissue loss; numbness and pallor reverse within minutes of warming. Frostbite has ice in tissue and a thaw injury that can blister or necrose.
- Non-freezing cold injury (trench foot, immersion foot/hand) - Prolonged wet cold above freezing without ice crystals; coded T69, not T33-T34. Frostbite requires actual freezing of tissue.
- Chilblains (pernio) - Inflammatory, usually itchy red-purple lesions after repeated non-freezing damp cold; no ice, no mummification. ICD-10 groups them with other reduced-temperature effects (T69), excluded from frostbite.
- Hypothermia - A fall in core temperature (T68), not a local freeze. They often coexist; core rewarming takes precedence, but the local lesion is still frostbite only if tissue froze.
- Thermal burn - Heat rather than ice; the four-degree labels are borrowed from burns. History of freezing exposure and pale, insensate, hard tissue before thaw separate frostbite.
- Raynaud phenomenon - Reversible vasospasm in the cold without ice formation or necrosis of the part, unless a separate freeze occurs.
- Dry-ice or liquefied-gas contact injury - Same freezing pathology (contact frostbite) but a man-made cold source coded W93 rather than X31; not a different disease if tissue actually froze.
- Which of these neighbouring kinds and how to tell them apart hold for the sense of frostbite this model covers, and on what evidence? provenance
Sources
- Frostbite - Definition as freezing cold injury below 0 °C; risk factors; ice-crystal and reperfusion pathophysiology; zones of coagulation/stasis/hyperemia; four-degree and Cauchy staging; skin blood-flow figures; rewarming, delayed amputation, complications and the Nordic emollient finding.
- Wilderness Medical Society Clinical Practice Guidelines for the Prevention and Treatment of Frostbite: 2024 Update - Frostnip versus frostbite; four-degree and two-tier field classifications; Cauchy table; risk rising below −15 °C; water-bath rewarming at 37-39 °C only if refreeze is unlikely; iloprost and tPA windows.
- The classification of freezing cold injuries - a NATO research task group position paper - Freezing cold injury versus non-freezing cold injury; morphological split of superficial (1st-2nd) versus deep (3rd-4th) FCI; clinical signs used in military practice.
- ICD-10-CM Codes T33-T34 Frostbite - US billing codes: T33 superficial frostbite (includes partial-thickness skin loss), T34 frostbite with tissue necrosis, anatomic 5th/6th characters, 7th-character A/D/S, and Type 2 exclusion of hypothermia (T68) and other reduced-temperature effects (T69).
- 凍傷 - Crosswalk identifiers (ICD-10 T33-T35, ICD-9-CM 991.0-991.3, MeSH D005627, MedlinePlus 000057, DiseasesDB 31167) and Japanese naming (凍傷, 瘃).
What the second pass must settle
- Does the ACT / ACT.ACT registry placement intentionally represent a human injury episode, and should veterinary frostbite share this model?
- Should contact freezing and refrigerant or cryogenic injuries remain within this entry or link to a neighbouring cold-burn model?
- Which severity systems should the publication support, and what evidence permits any mapping between them?
- Which current jurisdiction-specific protocols should govern referral and time-sensitive treatment eligibility, especially when thawing times are uncertain?
- Which follow-up measures and observation periods best establish persistent frostbite-related impairment?