SEPT 10 Built from the handwritten pages you uploaded on 10 September 2026.

CO poisoning & burns

Carboxyhaemoglobin levels and half-lives, cyanide, and the Parkland formula.

Carbon monoxide

Affinity for haemoglobin is about 240 times that of oxygen, so even a low inspired concentration produces a high carboxyhaemoglobin level.
It does two things at once: it reduces oxygen carrying capacity, and it shifts the dissociation curve LEFT, so the oxygen that is carried is not released to tissue. Tissue hypoxia is therefore worse than the level alone suggests.
It also binds cytochrome oxidase, impairing cellular respiration directly.
Cherry red skin is the classic sign — but it is late, uncommon, and often a post-mortem finding. Do not rely on it.

COHb (%)	Symptoms
0–15	None. Smokers sit here — up to about 10–15%
15–20	Headache, mild confusion
20–40	Nausea and vomiting, disorientation, fatigue
40–60	Hallucinations, ataxia, fits, coma
> 60	Death

Carboxyhaemoglobin absorbs light at 660 nm almost identically to oxyhaemoglobin, so the oximeter reads falsely NORMAL or HIGH while the patient is profoundly hypoxic.
PaO₂ is also normal — it measures dissolved oxygen, which CO does not affect.
You must use a co-oximeter, which uses four or more wavelengths and measures COHb directly.
Suspect it in any enclosed-space fire, faulty boiler or generator, or a group of people from one house with headache and nausea.

Room air: about 4 hours
100% oxygen: about 1 hour
Hyperbaric oxygen: about 30 minutes
So the treatment is simply high-flow 100% oxygen, continued for far longer than the patient looks like they need it. Hyperbaric oxygen is considered for loss of consciousness, neurological signs, cardiac involvement, COHb above about 25%, or pregnancy (fetal Hb binds CO even more avidly).

Released by combustion of plastics, polyurethane foam, wool and silk — so it accompanies CO in almost every enclosed-space house fire.
It inhibits cytochrome oxidase, halting oxidative phosphorylation.
Suspect it when there is a severe metabolic (lactic) acidosis with a HIGH mixed venous oxygen saturation — the tissues cannot extract oxygen, so venous blood stays bright red. Also: a normal PaO₂ with a normal A–a gradient in a collapsing patient.
Treatment: hydroxocobalamin (binds cyanide to form cyanocobalamin — safe, and does not compromise oxygen carriage). Sodium thiosulphate is an alternative.
Avoid nitrite-based antidotes in a fire victim — they generate methaemoglobin, which worsens oxygen carriage in a patient already carrying CO.

4 ml × body weight (kg) × %TBSA burned, given as Hartmann's in the first 24 hours.
Half in the first 8 hours, half over the next 16.
The clock starts at the TIME OF INJURY, not the time of arrival. If the patient took 3 hours to reach you, the first half must be given over the remaining 5 hours.
Worked example: 70 kg, 30% TBSA → 4 × 70 × 30 = 8400 ml in 24 hours; 4200 ml in the first 8 hours from the burn.
The formula is a starting point only. Titrate to urine output 0.5–1 ml/kg/h in adults, 1–1.5 ml/kg/h in children. Over-resuscitation ("fluid creep") causes compartment syndrome, ARDS and oedema.

The patient's own palm with fingers is about 1% — useful for scattered or patchy burns.
Count only partial and full thickness burns — second and third degree. Superficial erythema (simple sunburn) is excluded.
Children have proportionately larger heads and smaller legs, so the adult rule overestimates the legs and underestimates the head.

Adult: 9 (head) + 9 + 9 (arms) + 18 + 18 (torso) + 18 + 18 (legs) + 1 (perineum) = 100.
Infant: 18 (head) + 9 + 9 (arms) + 18 + 18 (torso) + 14 + 14 (legs) + 1 (perineum) = 101 — the figures are conventionally rounded, and the leg is strictly 13.5%, which gives exactly 100.
The head–leg trade-off is the whole point: as a child grows, the head loses roughly 1% per year of age and each leg gains about 0.5%, until the adult proportions are reached at about 10 years.

Airway: facial burns, singed nasal hair, soot in the mouth, hoarseness or stridor mean early intubation — oedema develops fast and later intubation may be impossible. Use an uncut tube.
Suxamethonium is contraindicated from about 24–48 hours after the burn and remains so for a year or more — extrajunctional receptor proliferation causes catastrophic hyperkalaemia. It is safe in the first 24 hours.
Resistance to non-depolarising blockers develops for the same reason — higher doses are needed.
Expect hypothermia (no skin barrier), a hypermetabolic state, difficult vascular access and difficult monitoring, and high analgesic requirements with tolerance.
Escharotomy may be needed for circumferential limb or chest burns compromising perfusion or ventilation.

Caffeine and theophylline LOWER the seizure threshold — which is exactly why they are used in electroconvulsive therapy to lengthen an inadequate seizure.
In ECT the aim is a seizure of adequate duration. Agents that shorten it (propofol, benzodiazepines) reduce efficacy; those that lengthen it are used deliberately.
Etomidate and hyperventilation (hypocapnia) both increase seizure duration and are used for the same purpose.
Methohexital was traditionally the induction agent of choice for ECT for this reason.

CO 240× affinity, left shift

SpO₂ falsely normal

4 h · 1 h · 30 min COHb t½

↑SvO₂ + acidosis cyanide

4 × kg × %TBSA Parkland

From injury not arrival

Head 9→18 Legs 18→14 in infants

Palm+fingers ≈ 1%

Sux unsafe after 24–48 h

Caffeine lowers seizure threshold

Built from your CO, burns and ECT pages. See also Acute poisoning.