Burns and smoke: airway, CO and cyanide

A fifty-year-old man is pulled from a burning apartment after a few minutes in a closed, smoke-filled room. He has burns on his arms, soot on his face and a slightly hoarse voice. On arrival at the emergency department, he is drowsy, with low blood pressure, and the pulse oximeter shows excellent saturation. The team focuses on the burns, which are the most visible finding. The scene is fictional and was written for teaching. This text uses that picture as a clinical reasoning scenario: why a fire victim in a closed space has three problems at the same time, why normal saturation can mislead and how the visible burn can hide what kills first.

NEXO is a daily medical diagnosis game: one clinical case a day, up to six progressive clues, and ICD-10 proximity feedback across five levels.

The text avoids being a protocol. Care for burn victims and for smoke inhalation follows the guidelines and routines of each service, and management depends on local resources. The interest here is reasoning: how to organize the hypotheses in a fire victim, which clues point to carbon monoxide and cyanide, and how to keep a striking finding from closing the case. If you play the case of the day on NEXO, you will recognize the move: the most visible clue is not always the most important one.

Key points

• A fire victim in a closed space may have, at the same time, thermal injury of the airway, carbon monoxide poisoning and cyanide poisoning, in addition to skin burns.
• Signs such as soot on the face, hoarse voice, singed hair and cough with dark sputum call for airway assessment right on arrival, because edema can worsen in the following hours.
• A standard pulse oximeter overestimates true saturation in carbon monoxide poisoning, and confirmation depends on measuring carboxyhemoglobin.
• Fire in a closed space, altered consciousness, unexplained low blood pressure and raised lactate suggest cyanide poisoning.
• The visible burn draws attention, but what threatens life in the first hours is usually the airway and the poisoning.

Why the fire victim is a clinical reasoning scenario

Anseeuw and colleagues, in a consensus of European experts, describe smoke inhalation as a common cause of cyanide poisoning in fires, with the potential to cause injury and death, and point out that diagnosis remains difficult (Anseeuw and colleagues, 2013). Hampson and colleagues, in practical recommendations on carbon monoxide, describe this poisoning as common and associated with major morbidity and mortality (Hampson and colleagues, 2012).

For clinical reasoning, the fire victim is an example of a patient with several conditions at the same time, each with signs that overlap. Drowsiness may come from carbon monoxide, from cyanide, from hypoxia due to airway obstruction, from head trauma during the escape or from alcohol. Low blood pressure may come from cyanide, from fluid loss through the burn or from bleeding. The challenge is not to choose one explanation too early, when several may be present together.

Guidelines for different settings

The International Society for Burn Injury has published burn care guidelines designed both for services with few resources and for well-equipped services, with recommendations based on evidence and expert opinion (ISBI, 2016). This attention to different contexts is useful for reasoning: the same victim may arrive at a burn center or at a small hospital, and the sequence of priorities has to work in both places.

Other victims as a clue

When several people come out of the same fire, the whole group becomes a source of information. If other victims from the same room have headache, confusion or vomiting, the probability of gas poisoning rises for all of them. If one victim with few burns is much drowsier than the others, it is worth asking whether they were exposed longer, hit their head during the escape or used alcohol or medications beforehand. Comparing patients with one another is a simple way to calibrate the severity of each one.

This comparison also helps organize resources. In fires with many victims, the team must decide who receives attention first. Extensive burns draw attention, but the quiet, drowsy victim with no visible burns may be more severely ill. A triage that asks about consciousness, breathing and blood pressure, and not only about the extent of the injuries, protects that patient.

What the scene tells you

The history of the fire is part of the examination. A closed or open space, exposure time, materials that burned, an explosion or a fall during the escape and other victims with similar symptoms change the probability of each hypothesis. Whoever brings the patient, whether a rescue team or a family member, usually has information that will not be available later. Asking early and writing it down helps all the care that follows.

Three problems at the same time

The table below organizes the main problems of a fire victim in a closed space in a didactic way. It simplifies a complex field and should be read together with the sources cited in the text.

Problem	What it suggests	What helps confirm or monitor it
Airway injury	Soot on the face, hoarse voice, singed nasal hairs, stridor	Direct airway assessment, serial observation
Carbon monoxide	Headache, confusion, nausea, several victims in the same place	Carboxyhemoglobin measurement on blood gas analysis
Cyanide	Closed space, altered consciousness, unexplained low blood pressure	Raised lactate, acidosis, clinical course
Skin burn	Visible injuries, pain, variable extent	Estimate of the burned body surface area
Associated trauma	Fall, explosion, escape through a window	Complete examination, imaging as indicated

The order of priorities

The order recalls that of any trauma care: airway, breathing, circulation, neurological status and exposure. In the fire victim, each step has a particularity. The airway can worsen in the following hours. Breathing can be compromised by toxic gases that the pulse oximeter does not show. Circulation can drop because of cyanide or fluid loss. Neurological status can reflect intoxication, hypoxia or trauma. And exposure reveals the extent of the burns, which guides fluid replacement.

Thinking together

In practice, these steps happen almost at the same time, with teams dividing tasks. The risk is that each person looks only at their own part. A brief pause to gather the information, asking whether all the findings are explained by the current hypotheses, helps to see what was left out. The post on diagnostic pause discusses how to fit this moment into the routine.

Airway: decide early

Thermal and chemical injury of the upper airway causes edema that can increase in the hours after the fire. The International Society for Burn Injury guidelines note that edema continues to form for many hours, that delaying intervention carries a risk of obstruction later and that late intubation can be dangerous because of pharyngeal edema (ISBI, 2016). A patient who arrives speaking, with only a hoarse voice, may have difficulty breathing a few hours later, when intubation becomes much more difficult. For this reason, the decision about the airway is usually made early, based on the clues and the course, and not only on the current state.

The clues that call for attention

Some signs increase concern about the airway:

• soot on the face, mouth or nose;
• singed nasal hairs or eyebrows;
• hoarse voice or voice change;
• cough with dark sputum;
• stridor or difficulty breathing;
• extensive burns on the face and neck.

Each of these signs, on its own, carries little weight in management. Together, and added to a history of exposure in a closed space, they change the probability of significant injury and justify assessment by someone with experience in difficult airway.

Reasoning about time

The airway is a good example of prognostic reasoning. The question is no longer only "how is the patient now?" and starts to include "how will the patient be in a few hours, and where will the patient be when that happens?". A patient who will be transferred over a long distance or who will stay in a place with few resources has a different threshold from one who is in a referral center. The post on prognostic reasoning explores this idea further.

Carbon monoxide: when oximetry misleads

Carbon monoxide binds to hemoglobin and reduces the blood's capacity to carry oxygen. The problem for reasoning is that a common pulse oximeter does not distinguish hemoglobin bound to oxygen from hemoglobin bound to carbon monoxide. Bozeman and colleagues showed that pulse oximetry stayed high even when the real oxygen saturation fell as carboxyhemoglobin rose, and they concluded that, when poisoning is suspected, oximetry should be considered unreliable until carboxyhemoglobin is measured (Bozeman and colleagues, 1997).

The patient in the scene has excellent saturation on the oximeter and is drowsy. That combination, instead of reassuring, should raise the alarm.

The symptoms of carbon monoxide poisoning are also nonspecific. Headache, nausea, dizziness, fatigue and confusion appear in many other conditions, and the cherry-red skin described in textbooks is rare in practice (Hampson and colleagues, 2012). So suspicion comes more from the exposure history than from the exam. Every smoke victim in an enclosed space deserves the question, even when they seem well and talk normally on arrival. A simple question, asked early, can change the whole course of care that follows.

The noninvasive devices

There are handheld devices that try to measure carboxyhemoglobin without drawing blood. Touger and colleagues compared one of these devices with the laboratory measurement and found that it correctly identified 11 of 23 patients with raised levels, concluding that the reading cannot replace the laboratory measurement (Touger and colleagues, 2010). For reasoning, this means that a normal result on these devices does not rule out poisoning when clinical suspicion is high.

Treatment and uncertainty

High-concentration oxygen is the basis of treatment. The role of hyperbaric oxygen remains debated. Weaver and colleagues, in a randomized trial, observed fewer cognitive sequelae at six weeks with three sessions of hyperbaric oxygen within 24 hours (19 of 76 versus 35 of 76) (Weaver and colleagues, 2002). Buckley and colleagues, in a Cochrane systematic review with six trials, concluded that the existing studies do not establish whether hyperbaric oxygen reduces neurological sequelae, and they pointed to important heterogeneity among them (Buckley and colleagues, 2011). This is an example of a clinical question in which experts reach different recommendations from the same evidence.

Cyanide: the lactate and shock clue

Plastics, foams, synthetic fabrics and other materials release cyanide when they burn. Anseeuw and colleagues list four findings that suggest cyanide poisoning: a history of fire in an enclosed space, any change in level of consciousness, cardiovascular changes, especially unexplained low blood pressure, and raised plasma lactate (Anseeuw and colleagues, 2013).

The patient in the scene has at least three of these clues: fire in an enclosed space, drowsiness and low blood pressure. There is no rapid and widely available blood cyanide test, and the decision to treat is based on the history and the clinical signs (European Medicines Agency, Cyanokit). O'Brien and colleagues recall that cyanide is an important toxic agent in many smoke victims, but that poisoning cannot be confirmed in an emergency setting (O'Brien and colleagues, 2011).

Lactate as a clue

Raised lactate reflects the oxygen-free metabolism that cyanide causes in cells. The European consensus includes raised plasma lactate among the clues of cyanide poisoning (Anseeuw and colleagues, 2013). For reasoning, lactate works as an indirect clue: it does not confirm the diagnosis on its own, because shock and seizures also raise lactate, but a high value without another clear explanation increases the probability of cyanide.

Treat before confirming

Anseeuw and colleagues report that empiric treatment with hydroxocobalamin in smoke inhalation victims has feasibility and safety described in the literature (Anseeuw and colleagues, 2013). Borron and colleagues, in an observational study, reported that hydroxocobalamin was well tolerated and that 28 of 42 patients with confirmed poisoning later survived after administration (Borron and colleagues, 2007). The decision to treat based on suspicion is a classic example of reasoning under uncertainty, in which the risk of waiting for confirmation may be greater than that of treating.

Burned surface and fluid replacement

After the airway and poisonings, the skin burn moves to the center of attention. Estimating the burned body surface guides fluid replacement, the need for transfer and the prognosis. The International Society for Burn Injury guidelines address these points with recommendations applicable to different resource levels (ISBI, 2016).

Common errors in estimation

Estimating the burned area is subject to error. Areas that are only reddened, without blisters, are often included by mistake. Areas on the back, which are hidden when the patient is lying down, may be forgotten. Overestimation leads to excess fluids, with edema and other complications. Underestimation leads to insufficient replacement. Reassessing the area after cleaning the skin and examining the whole patient help reduce both errors.

The response as a guide

Fluid replacement starts with an estimate and is adjusted by the patient's response. Urine output, blood pressure, heart rate, mental status and lactate are monitored over the hours. For the reasoning, the calculated volume is an initial hypothesis, and the patient's response is the test of that hypothesis. A patient who remains hypotensive despite adequate replacement calls for a return to the differential: cyanide, occult bleeding, associated injury.

When to transfer

Major burns, burns on the face, hands, feet and genital areas, inhalation injuries and patients with other serious conditions usually benefit from specialized centers. The decision to transfer involves the patient's severity, the distance to the referral center, transport conditions and airway safety during the journey. For the reasoning, transferring is also a prognostic decision: the team must estimate how the patient will be in the coming hours, not only how the patient is now.

Communication with the referral center follows the same principle as any case handover. Tell the story of the fire, the exposure time, the airway findings, the signs of poisoning, the estimate of the burned area, what has already been done and what still worries the team. A well-organized handover prevents important information, such as suspected cyanide poisoning, from being lost along the way. The post on clinical decision-making discusses how to think about actions as choices with risks and benefits.

The bias of looking only at the burn

Croskerry described how cognitive errors lead to diagnostic errors and proposed strategies to reduce them (Croskerry, 2003). Graber and colleagues showed that cognitive factors, such as premature closure, are present in a good part of diagnostic errors in internal medicine (Graber and colleagues, 2005). In the fire victim, one bias stands out.

The most visible clue

Burns are striking. They take up the team's attention, create immediate tasks and explain part of the signs, such as pain and tachycardia. The risk is that they explain too much. Drowsiness comes to be attributed to pain or medication. Low blood pressure comes to be attributed only to fluid loss. Along this path, carbon monoxide and cyanide go uninvestigated. The post on heuristics in clinical reasoning shows how the salience of a finding distorts judgment.

The number that reassures

Normal oxygen saturation on the pulse oximeter is another anchor point. A number that looks good tends to end the discussion about oxygenation. In a smoke inhalation victim, that number must be read with suspicion, as Bozeman and colleagues showed (Bozeman and colleagues, 1997). The post about pretest probability helps interpret a test in light of the context.

Questions that protect

Some questions help you escape bias:

1. What does the burn not explain in this patient?
2. Is consciousness altered beyond what pain and medication would justify?
3. Is the blood pressure lower than fluid loss would explain at this point?
4. Are there other victims from the same location with similar symptoms?
5. Could some "normal" test be misleading in this context?

How NEXO helps train this reasoning

In NEXO, the case of the day is fictional, with a real clinical presentation and up to six progressive clues. You propose a diagnosis by searching for the ICD-10 code and receive proximity feedback in five levels, which shows whether your guess landed on the exact code, the same category, the same group, the same chapter or a different chapter. This format connects with the theme of this text: when the most visible clue seems to solve everything, the proximity feedback shows whether you stayed in the right chapter.

To use the case of the day as training, try three habits. Before each guess, list all the problems that may coexist. When a clue draws a lot of attention, ask what it leaves unexplained. After the result, note which discreet clue you let slip by.

Three exercises with cases

List in layers. For each case, write the most visible problem and, below it, the problems that may be hidden.

Distrust the normal. For each normal test, ask in what situation it could mislead.

Treat the suspicion. Identify cases in which waiting for confirmation would bring high risk, and think about what would justify acting earlier.

The post about case-based learning in clinical practice shows why training with cases helps consolidate this type of decision.

The limits on using the game are described on the NEXO economy page. If you research the teaching of clinical reasoning, the page for researchers explains how to get in touch. Professionals who write or review cases find information under curation and creators, and institutions can learn about the proposal on the partnerships page.

Frequently asked questions

Why is the airway such a concern in a fire victim?

Because thermal and chemical injury causes edema that can increase in the following hours. A patient who arrives talking may have trouble breathing later, when intubation becomes more difficult.

Why does the pulse oximeter mislead in carbon monoxide poisoning?

Because a standard oximeter reads hemoglobin bound to carbon monoxide as if it were bound to oxygen. Saturation appears high while actual oxygen is low. Measuring carboxyhemoglobin confirms the diagnosis.

Which clues suggest cyanide poisoning?

A fire in an enclosed space, altered consciousness, unexplained low blood pressure and raised lactate, according to a consensus of European experts.

Why treat cyanide before confirmation?

Because there is no rapid confirmatory test, the decision is based on the history and clinical signs, and the poisoning can progress quickly (European Medicines Agency; O'Brien and colleagues, 2011). Empirical treatment with hydroxocobalamin has feasibility and safety described in the literature for smoke inhalation victims.

What is the purpose of estimating the burned surface area?

To guide fluid replacement, the need for transfer to a specialized center and the prognosis. The estimate is adjusted afterward based on the patient's response.

What is the main bias in caring for a burn patient?

Looking only at the burn. It is the most visible finding and tends to explain too much, while the airway, carbon monoxide and cyanide call for active investigation.

Final checklist

• I asked whether the fire was in an enclosed space and how long the exposure lasted.
• I assessed the airway early and thought about how it would be in the following hours.
• I read the oximeter saturation with suspicion and requested carboxyhemoglobin.
• I looked for the cyanide clues, including lactate.
• I estimated the burned surface area with the whole patient exposed and reassessed afterward.
• I asked what the burn leaves unexplained.

Want to practice reasoning with progressive clues? Play the case of the day.

References

1. Anseeuw K, et al. Cyanide poisoning by fire smoke inhalation: a European expert consensus. Eur J Emerg Med. 2013. PMID 22828651.
2. Borron SW, Baud FJ, Barriot P, et al. Prospective study of hydroxocobalamin for acute cyanide poisoning in smoke inhalation. Ann Emerg Med. 2007. PMID 17481777.
3. Bozeman WP, Myers RA, Barish RA. Confirmation of the pulse oximetry gap in carbon monoxide poisoning. Ann Emerg Med. 1997. PMID 9360570.
4. Buckley NA, Juurlink DN, Isbister G, et al. Hyperbaric oxygen for carbon monoxide poisoning. Cochrane Database Syst Rev. 2011. PMID 21491385.
5. Croskerry P. The importance of cognitive errors in diagnosis and strategies to minimize them. Acad Med. 2003. PMID 12915363.
6. European Medicines Agency. Cyanokit (hydroxocobalamin): summary of product characteristics. ema.europa.eu.
7. Graber ML, Franklin N, Gordon R. Diagnostic error in internal medicine. Arch Intern Med. 2005. PMID 16009864.
8. Hampson NB, Piantadosi CA, Thom SR, Weaver LK. Practice recommendations in the diagnosis, management, and prevention of carbon monoxide poisoning. Am J Respir Crit Care Med. 2012. PMID 23087025.
9. ISBI Practice Guidelines Committee. ISBI Practice Guidelines for Burn Care. Burns. 2016. PMID 27542292.
10. O'Brien DJ, Walsh DW, Terriff CM, Hall AH. Empiric management of cyanide toxicity associated with smoke inhalation. Prehosp Disaster Med. 2011. PMID 22336184.
11. Touger M, Birnbaum A, Wang J, et al. Performance of the RAD-57 pulse CO-oximeter compared with standard laboratory carboxyhemoglobin measurement. Ann Emerg Med. 2010. PMID 20605259.
12. Weaver LK, Hopkins RO, Chan KJ, et al. Hyperbaric oxygen for acute carbon monoxide poisoning. N Engl J Med. 2002. PMID 12362006.