Frostbite and non freezing cold injuries

Question 1

Describe freezing injury cascade

Answer 1

Occurs only when tissue supercools well below 0 degrees. The required temperature is at least -4 andmay be as low as -10

Three phases

1) prefreeze phase
- superficial tissue cooling
- increased viscosity of vascular contents
- microvascular constriction
- endothelial plasma leakage

2) Freeze-thaw phase
- extracellular fluid ice cyrstal formation
- water movememtn across cell membrnae
- intracellular dehydration and hypoerosomolality
- cell membrane denaturation or disurption
- cell shrinkage and collapse

3) Vascular stasis and progressive ischameia
- vasospasticity and stasis coagulation
- AV shunting
- vascular endothelial cell damage and prostanoid release
- interstitial leakage and tissue hypertension
- necorsis, demarcation, mummifications or slough

Question 2

Describe frostnip

Answer 2

Refers to superficial freezing injury manigested by transient numbness and tingling that resolves after rewarming. No tissue destruction occurs.

Question 3

Describe clinical features of frostbite

Answer 3

The most common presenting complaint of frostbite ie numbness which is nearly universal. All patients have initial sensory deficits in light touch pain or temperautre.

Anaethesis is produced by intence vasoconstrictive ischaemia and neurapraxia usually in acral areas and distal extremities. Fingers, toes nose ears and penis are the specific areas at risk.

Initial presentation can be deceptively benign. Most patients do not arrive with a frozen insensate tissue. Frozen tissue feels hard and appears mottled or violaceous hwite.

Rapid rewarming results in an initial hyperemia even in severe cases- after thawing there is usually partial return of sensation until blebs form. A residual violaceous hue after rewarming is ominous. Early formation of large blebs with clear fluid is more favourable then a delated appearance of smaller more proximal haemorrhagci vesciles.

Lack of oedema formation suggest signifiacnt tissuye damage. In severe cases frostbitten skin forms a black dry eschar that mummifies with appraent demarcation

Differentiated into superfical frost bite which does not lead to tissue loss and deep frost bite which does

Question 4

Discuss management of frost bite

Answer 4

Constricting or wet clothing should be removed and affected areas insulated and immobilised.
Massage is not efficacious and increases tissue loss
Frozen parts should be kept away from dry heat sources such as heated forced air during transport.

Thawing should not happen in the field if there is a chance of refreezing - tissue refreezing is disastrous.

ED

1) prethaw
- stabiize hypothermia and other life threats prior to warming frostbitten extremities.
- most patient are volume depleted partly due to poor intake and hypothermia induced cold diuressis and should receive fluid

2) Thaw
- frozen tissue should be rapidly rewarmed by immersion in gently circulating water that is carefully maintained at a temp of 37-39 degrees
- whirlpool is ideal
- do not let affected tissue bump against container during rewarming
- should continue until distal erythema is noted. the part should feel pliable which usually required 10-30 minutes of re-warming
- parenteral analgesai is often needed as rewarming is painful
- the acute thawing of large amounts of distal musculature extinguishes peripehral vasoconstriction resulting in a sudden return of cold, hyperkalaemia, acidotic blood to the central cirucaltion - this can produce what is termed core temperature afterdrop with VF.
- ECMO can be considered

3) Post-thaw
- Elevate injured extremities to minimize oedema, apply steril dressing loosely and handle gently
- monitor for compartment syndrome but fasciotomies are usually not necessary
- large clear blisters can be debrided
- small haemorrhagic blisters should be aspirated rahter than debrided as secondary desiccation of deep dermal layers occurs extending the injury
- Nil prophylactic Abs
- consider Thrombolytic therapy for severe injury

Question 5

Describe re-warming techniques

Answer 5

Passive Rewarming

• moved from cold environment and cold or wet clothes removed
• They can be covered by a blanket or sleeping bag and ahve their head covered to reduce heat loss
• Mild hypothermia in patients who can still shiver
  0. 5-2 degrees per hour

Active external rewarming

• Heat packs, lamps, blankes , forced air systems
• Rewarming rates approach 1-2.5 degrees/hour

Active core rewarming 
-warmed IV fluids 
-warmed humidified o2 to 42-44%
-Cavity lavage ( gastric, b ladder, peritoneal pleural_
2-3 degrees per hour

extra corp
VV -5degree/hour
Bypass - 9