Burns

Question 1

Define a burn

Answer 1

A coagulative destruction of the skin and its structures

Question 2

What are the main mechanisms of a burn?

Answer 2

Thermal (note, scalding confers greater thermal energy than dry heat)
Electrical
Chemical
Mechanical

Question 3

At what total body surface area (TBSA) is a burn considered “Major”?

Answer 3

15%

Question 4

At what total body surface area (TBSA) is a burn likely to produce a SIRS response

Answer 4

25%

Question 5

What are the main determinants of survival in burns?

Answer 5

%TBSA
Age
Inhalation injury

These are packaged into the modified Baux score

Question 6

What is the name given to the pathological model of burns. Please describe it.

Answer 6

Jackson’s burn wound model. Describes 3 zones: 1) zone of coagulation, 2) Zone of stasis, 3) zone of hyperaemia and vasodilatation

Question 7

How are burns classified?

Answer 7

Epidermal (no involvement of the dermis, red and painful, self limiting)
Superficial partial thickness (upper dermis)
Deep partial thickness (lower dermis)
Full thickness (extends through the dermis into underlying tissue)

Note: this is the UK model of description.

Question 8

What is the modified Baux Score

Answer 8

Age + %TBSA + (17 x inhalation injury)

Question 9

What is the current limit of survivability of the Baux score

Answer 9

160

Question 10

List some burns prognostication scores other than the Baux score

Answer 10

Belgian outcome in burn injury score
Abbreviated burn severity index
Rockwood clinical frailty score (this last one isn’t burns specific, but may be helpful in contextualising the prognostication of burns patients)

Question 11

Describe the appearance and sensation of a superficial partial thickness burn

Answer 11

Pale, pink and moist
Blisters form with fluid leak from blood vessel damage
They are very painful because of exposed nerve endings

Question 12

Describe the appearance and sensation of a deep partial thickness burn

Answer 12

Drier than a superficial partial thickness burn. Tend to be red and non-blanching as the dermal plexus is coagulated by the heat
Less painful than superficial partial thickness

Question 13

Describe the appearance and sensation of a
full thickness burn

Answer 13

Waxy and white
Not painful

Question 14

Describe the main features of the “Zone of coagulation” in the Jackson burn model

Answer 14

Irreversibly dead tissue that acts as a nidus of infection and a reservoir of inflammatory products that can lead to systemic injury

Question 15

Describe the main features of the “Zone of stasis” in the Jackson burn model

Answer 15

Hypoperfused, vasocontricted, alive but at risk tissue in proximity to the zone of coagulation. This tissue is at high risk of ischaemia, infection and necrosis. For this reason, burns may widen and deepen if this zone dies

Question 16

Describe the main features of the “Zone of hyperaemia” in the Jackson burn model

Answer 16

Inflammatory mediators released from the zone of coagulation cause local vasodilatation, increased vascular permeability and oedema within this zone. When %TBSA exceeds 25%, the whole body effectively becomes the zone of hyperaemia and a profound SIRS response occurs

Question 17

What is a key early surgical priority in the management of burns?

Answer 17

Early burn excision is aimed at reducing the nectrotic tissue load, infection risk and SIRS response. It is associated with improve survival

Question 18

Burns is often described in two phases. What are these phases, and over what time frame do they occur?

Answer 18

The Acute Phase: occurs over the first 48 hours following burn during which vasodilatation, hypovolaemia and myocardial depression contribute to burns shock.
The Hypermetabolic Phase: occurs from 48 hours to around 1 year

Question 19

If a burns patient is hypotensive at presentation to hospital, what is the most likely cause

Answer 19

It is almost certainly not from the burn itself; burns shock takes some time to manifest. If there are no overt other injuries, consider inhalation injury (carbon monoxide/Hydrogen Cyanide poisoning). Otherwise look for other trauma related injuries on the secondary survey and consider blood loss.

Question 20

Which poisons should one always consider in tandem with Burns?

Answer 20

Carbon monoxide
Hydrogen cyanide

One might also argue that you could consider recreational drugs or paracetamol if there is a suspicion that a depressed conscious level led to the injury

Question 21

At what level of COHb should you be concerned?

Answer 21

At 10% COHb patients are symptomatic
At 50% COHb patients generally enter coma

Levels over 30% are unambiguously considered “severe”

Question 22

What is the mechanism of action of carbon monoxide toxicity?

Answer 22

There are three mechanisms:
1) CO binds to Hb with x250 greater affinity than O2, blocking the binding of O2
2) CO causes a left shift of the OHDC inhibiting oxygen delivery at the tissues
3) CO causes competitive inhibition of michondrial cytochrome oxidase, inhibiting cellular utilisation of oxygen

Question 23

What are the indicators of severe CO poisoning?

Answer 23

New objective neurological signs (increased muscle tone, up-going planters)
Coma
ECG indications of ischaemia
Clinically significant acidosis
Initial COHb > 30%

Question 24

What is the half life of COHb at an FiO2 of 0.21?

Answer 24

6 hours

Question 25

What is the half life of COHb at an FiO2 of 1

Answer 25

90 minutes

Question 26

What is the standard treatment for carbon monoxide poisoning?

Answer 26

An FiO2 of 1 until COHb falls to < 3%. This needs to be weighted up against the negative impacts of breathing high concentrations of O2.

Question 27

What is the treatment for hydrogen cyanide poisoning?

Answer 27

Hydroxycobalamin

Question 28

What is the mechanism of action of hydrogen cyanide poisoning?

Answer 28

Binds to the Ferric ion of mitrochondrial cytochrome A3 oxidase leading to: Histotoxic hypoxia (oxygen is present, but cannot be utilised) Lactic acidosis Essentially it prevents aerobic respiration Other mechanisms include: Biogenic amine release leading to pulmonary and coronary vasoconstriction --> pulmonary oedema and cardiac failure Stimulates neurotransmitter release causing neurotoxicity and seizures

Question 29

What indicators can be used to prompt to treat for hydrogen cyanide poisoning

Answer 29

Generally, have a low threshold to treat. However, the following should make the decision unambiguously: Lactate > 7 Raised anion gap acidosis (presumably from the lactate) Reduced AV oxygen gradient (oxygen cannot be used) Haemodynamic instability in the context of an elevated lactate

Question 30

What is the mechanism of action of hydroxocobalamin?

Answer 30

Binds to HCN and forms non-toxic cyanocobalamin which is then renally excreted

Question 31

What is the treatment dose of hydroxocobalamin (cyanokit)

Answer 31

Adults: 5g over 15 minutes (repeat once if necessary) Paediatrics: 70 mg/kg (up to 5 g max)

Question 32

What are the side effects of hydroxocobalamin treatment?

Answer 32

Transient hypotension Reddish brown skin/membranes for up to 15 days Urine discolouration for up to 35 days Note, these discolourations can impact on equipment: colorimetric laboratory tests can be error. Haemofiltration blood in line alarms can be triggered. COHb will be falsely elevated by around 5%

Question 33

List a couple of methods of estimating %TBSA

Answer 33

Lund and Browder chart Wallace rule of nines

Question 34

How long should you irrigate an acid burn for?

Answer 34

45 minutes

Question 35

How long should you irrigate an alkali burn for?

Answer 35

1 hour

Question 36

What might prompt you to intubate a burns patient?

Answer 36

Reduced conscious level Evidence of deep neck, peri-oral or intra-oral burns Respiratory distress Generally have a low threshold to intubate. It's better to intubate and extubate a few days later following a successful leak test, than to try and intubate in a crisis with a closing airway.

Question 37

You are looking after a burns patient with 40% TBSA coverage. Their temperature is 35 degrees. How should you proceed?

Answer 37

Do whatever you can to prevent further heat loss, and warm the patient actively (warm fluids etc.). However, this is a loosing battle and you need to prioritise getting them to the burns centre where they have specialised equipment and heated rooms. Do not delay transfer in order to try and rewarm them as it is likely their body temperature will only continue to drop.

Question 38

Is suxamethonium safe to use in burns?

Answer 38

For the first 48 hours, yes. After that, no.

Question 39

What is an escharotomy, when is it required, and how should it be performed?

Answer 39

These are cuts made into the burn to release constrictive tissue. They are mandatory in any circumferential burn of the chest, abdomen or limbs. They should be performed by a surgeon, prior to transfer to the burns unit and with diathermy. Ventilation may be impossible without them. Don't forget antibiotics.

Question 40

Are there situations where a non-circumferential burn may require an escharotomy?

Answer 40

Clearly. In children, non-circumferential burns to the chest and abdomen by impair ventilation and still require escharotomy

Question 41

How should you calculate the fluid requirement for a burns patient?

Answer 41

By the parkland formula

Question 42

Define the parkland formula, and when and how to apply it?

Answer 42

Total requirement in first 24 hours = 2-4 mL x actual body weight (kg) x %TBSA Using 3 mL is a sensible middle ground to start. Start the clock from the time of the burn Give half in the first 8 hours, and the other half in the next 16 hours. Subtract any fluid already given. Use a warmed isotonic balanced crystalloid Aim for a urine output of 0.5-1 mL/kg/hr. Some are concerned that this formula may over-do it slightly. Hence the use of urine output as a physiological marker.

Question 43

If urine output drops during burns fluid resuscitation, how should you proceed?

Answer 43

Consider other causes besides hypovolaemia (such as Rhabdo). Increase the rate of fluid administration to the full 4 mL of the parkland. If still not improving, consider "colloid" rescue with 1/3 of the crystalloid regimen being replaced by 4.5% albumin

Question 44

What are the criteria for diagnosing sepsis in burns?

Answer 44

Temp > 39 or < 36.5 HR > 110 RR > 25 or MV > 12L Thrombocytopenia < 100 Glucose > 11.1, or insulin > 7 units/hr Intolerence to enteral feed Generally, biomarkers like CRP are not useful. PCT may be of use.

Question 45

How does the basal metabolic rate of burns patients change?

Answer 45

It is much higher than their non-burn counterparts. At 40% TBSA it is double.

Question 46

Which respiratory marker is correlated with outcome following inhalation injury?

Answer 46

P/F ratio

Question 47

What is the role of bronchoscopy in inhalation injury?

Answer 47

Diagnose and grade inhalation injury Early clearance of particular matter and washout