# Situation: A 40-year-old woman weighing 55 kg is rescued after being trapped for 20 minutes in a closed room of a burning house, where furniture and plastic items were burning. She has partial-thickness burns of the face, neck, anterior trunk, and both arms, estimated at 30% of total body surface area. She does not smoke. On arrival she has a headache, nausea, and confusion. Her results are: Pulse oximetry: 98% on room air Arterial oxygen tension: 92 mmHg Carboxyhemoglobin: 26% (normal in a nonsmoker < 3%) Which interpretation is correct?

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> subject: Nursing Practice V — Care of Clients with Maladaptive Patterns of Behavior; Care of Clients with Life-Threatening Conditions, Acute Multi-Organ Problems, High Acuity and Emergency Situations

## 문제

Situation: A 40-year-old woman weighing 55 kg is rescued after being trapped for 20 minutes in a closed room of a burning house, where furniture and plastic items were burning. She has partial-thickness burns of the face, neck, anterior trunk, and both arms, estimated at 30% of total body surface area. She does not smoke.

On arrival she has a headache, nausea, and confusion. Her results are:
Pulse oximetry: 98% on room air
Arterial oxygen tension: 92 mmHg
Carboxyhemoglobin: 26% (normal in a nonsmoker < 3%)
Which interpretation is correct?

## 보기

1. The pulse oximeter is faulty and should be replaced before acting
2. Her confusion comes from burn pain, since her oxygen values are normal
3. Oxygenation is adequate, since oximetry and arterial oxygen are normal
4. Oxygen delivery to tissues is poor even though oximetry reads normal **✔ 정답**

**정답: 4**

## 해설

Carbon monoxide binds hemoglobin in place of oxygen, so a carboxyhemoglobin of 26% means much of her hemoglobin cannot carry oxygen. Standard pulse oximetry reads carboxyhemoglobin as oxygenated hemoglobin, and arterial oxygen tension reflects dissolved oxygen, so both look normal while tissue oxygen delivery is poor. Her headache, nausea, and confusion fit carbon monoxide poisoning, treated with 100% oxygen.

## 심화 해설

Why the “normal” numbers are misleading
This patient was trapped in a closed room with burning furniture and plastics, which produces large amounts of carbon monoxide (CO). CO binds to hemoglobin with an affinity roughly 200–250 times greater than that of oxygen [1]. The result is carboxyhemoglobin (COHb), a hemoglobin species that cannot carry oxygen effectively and also shifts the oxyhemoglobin dissociation curve, impairing oxygen unloading at the tissue level [1][4]. A COHb of 26% in a nonsmoker is markedly elevated, since baseline is normally below 2–3% [1].

Pulse oximetry and PaO₂ can look falsely reassuring
Standard two-wavelength pulse oximetry cannot distinguish COHb from oxyhemoglobin. It reads COHb as if it were oxygenated hemoglobin, so the displayed SpO₂ of 98% is misleading [2][3]. Arterial oxygen tension, or PaO₂, measures only dissolved oxygen in plasma, not the oxygen bound to hemoglobin. Therefore, a PaO₂ of 92 mmHg can be normal while total oxygen-carrying capacity is severely reduced [1][4]. Normal pulse oximetry and normal PaO₂ do not rule out clinically significant carbon monoxide poisoning.

Clinical picture matches tissue hypoxia, not burn pain alone
Headache, nausea, and confusion are classic early neurologic symptoms of CO poisoning [1][2][4]. The brain is especially vulnerable because CO also interferes with mitochondrial respiration and promotes oxidative stress and inflammation beyond simple hypoxemia [4]. Symptoms correlate poorly with the exact COHb percentage, so the clinical presentation must guide urgency even when the number seems only moderately elevated. In a burn patient, pain can cause agitation, but the combination of a fire in an enclosed space, neurologic symptoms, and a high COHb level points to CO poisoning as the primary driver.

Diagnosis and immediate management
Definitive diagnosis is made by blood co-oximetry, which directly measures COHb and methemoglobin, unlike standard pulse oximetry [2][3]. Initial treatment is high-flow 100% oxygen via a nonrebreather mask, which shortens the half-life of COHb and improves oxygen delivery [2][3]. Watch out! A normal SpO₂ on a standard pulse oximeter does not exclude CO poisoning; co-oximetry is required when exposure is suspected.

Why the other options are incorrect

| Option | Reason it is wrong |
| --- | --- |
| 1. Pulse oximeter is faulty | The oximeter is functioning normally; it simply cannot differentiate COHb from oxyhemoglobin [2][3]. |
| 2. Confusion from burn pain because oxygen values are normal | Oxygen values are falsely normal. COHb of 26% means a large proportion of hemoglobin cannot carry oxygen [1][4]. |
| 3. Oxygenation is adequate | PaO₂ reflects dissolved oxygen only, not total oxygen content or tissue delivery. With high COHb, tissue oxygenation is poor despite normal PaO₂ and SpO₂ [1][4]. |

Key point! In carbon monoxide poisoning, oxygen delivery to tissues is impaired even when pulse oximetry and arterial oxygen tension appear normal. The correct interpretation is that tissue oxygen delivery is poor, and the patient requires immediate high-flow oxygen.References (research sources)

- [1]Carbon Monoxide PoisoningResearch articleBourke M, Schaffer DH. (2026)

- [2]Carbon Monoxide Poisoning.Research articleChenoweth JA, Albertson TE, Greer MR (2021) · DOI: 10.1016/j.ccc.2021.03.010

- [3]Carbon Monoxide Poisoning: Diagnosis, Prognostic Factors, Treatment Strategies, and Future Perspectives.Research articleAfzal M, Agarwal S, Elshaikh RH, Babker AMA, Choudhary RK, Prabhakar PK (2025) · DOI: 10.3390/diagnostics15050581

- [4]Carbon Monoxide Poisoning: Pathogenesis, Management, and Future Directions of TherapyResearch articleJason J. Rose, Ling Wang, Qinzi Xu, Charles F. McTiernan, Sruti Shiva, Jesús Tejero (2016) · DOI: 10.1164/rccm.201606-1275ci

## 임상 시나리오

Carbon Monoxide Poisoning in Burn PatientsWhy Normal SpO2 and PaO2 Do Not Rule Out Tissue Hypoxia
In any patient rescued from a closed-space fire with burning furniture or plastics, assume carbon monoxide exposure until proven otherwise. CO binds hemoglobin with 200–250 times the affinity of oxygen, forming carboxyhemoglobin that cannot carry oxygen and shifts the dissociation curve left, impairing tissue unloading.

A COHb level of 26% in a nonsmoker is markedly elevated and indicates severe poisoning. Standard pulse oximetry reads COHb as oxygenated hemoglobin, so a displayed SpO2 of 98% is falsely reassuring. Similarly, PaO2 measures only dissolved oxygen, not oxygen bound to hemoglobin, so 92 mmHg can be normal despite critically reduced oxygen-carrying capacity.

Headache, nausea, and confusion are classic neurologic symptoms of CO poisoning, not merely burn pain. The brain is especially vulnerable because CO also disrupts mitochondrial respiration and promotes oxidative stress. Treat immediately with 100% oxygen via non-rebreather mask, regardless of pulse oximetry readings.

CautionDo not delay high-flow oxygen while waiting for COHb levels. Symptom severity correlates poorly with the exact COHb percentage, and normal SpO2 or PaO2 never excludes clinically significant carbon monoxide poisoning in smoke inhalation victims.

## 핵심 개념

- **Carboxyhemoglobin (COHb)** — Hemoglobin bound to carbon monoxide, which cannot carry oxygen and shifts the oxyhemoglobin dissociation curve, impairing tissue oxygen delivery.
- **Pulse oximetry limitation** — Standard two-wavelength pulse oximetry reads COHb as oxygenated hemoglobin, producing a falsely normal SpO2 in carbon monoxide poisoning.
- **PaO2** — Arterial oxygen tension reflecting only dissolved plasma oxygen, not hemoglobin-bound oxygen, so it can appear normal despite reduced oxygen-carrying capacity.
- **Carbon monoxide affinity** — CO binds hemoglobin with an affinity approximately 200-250 times greater than oxygen, displacing oxygen even at low CO concentrations.
- **Inhalation injury** — Burn patients exposed to smoke in enclosed spaces are at high risk for carbon monoxide and cyanide poisoning, requiring high-flow oxygen.

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