QuestionSBA
QuestionChoice
A pulmonary embolism of the size needed to cause respiratory accessory muscle usage would be expected to cause a decrease in oxygen saturation and arterial oxygen levels
32341
d
Pulmonary embolism
QuestionChoice
Poorly maintained gas and heating appliances are a common cause of carbon monoxide poisoning. Presenting symptoms can include headache, confusion, nausea, shortness of breath and chest pain. Carbon dioxide binds preferentially with haemoglobin to form carboxy-haemoglobin, thereby reducing haemoglobin's carrying capacity of oxygen. Saturation probes cannot differentiate between oxy-haemoglobin and carboxy-haemoglobin, meaning that oxygen saturations are misleadingly normal. Arterial oxygen levels are also normal as there is no ventilation-perfusion mismatch. Elevated carboxy-haemoglobin levels on an ABG can confirm the diagnosis
32338
a
Carbon monoxide poisoning
QuestionChoice
Methaemoglobinaemia is a condition in which the iron in haemoglobin is oxidised from the ferrous to the ferric state, thereby rendering it unable to bind to oxygen. It usually presents with cyanosis, oxygen saturations between 85-90% and normal arterial oxygen levels. Cyanosis is not usually seen in carbon monoxide poisoning as carboxy-haemoglobin has a bright red colour
32339
b
Methaemoglobinaemia
QuestionChoice
Normal findings on auscultation and normal oxygen saturations would make a pneumothorax an unlikely explanation for the significant symptoms that this patient has presented with
32340
c
Pneumothorax
QuestionChoice
A subarachnoid haemorrhage is an important differential in this context, given the history of severe headache and reduced GCS. However, he is not in the right age range for a subarachnoid haemorrhage. In any case, you will likely get a CT Head for this patient but this is not the single best answer
32342
e
Subarachnoid haemorrhage
QuestionComment
wouldnt his wife have it too usually
11071
User
subscriber
Myopathy Qwave
QuestionComment
Would the oxygen saturations be wrongly high at 100%?

12130
QuestionComment
O2 sats are supposedly falsely high in CO poisoning as the sats probe detects 'bound' haemoglobin, which is the case of CO it strongly binds.
24193
User
subscriber
Witzelsucht
User
subscriber
Anterior Jaundice
QuestionComment
So much wrong. Similarly an Arterial ABG would also show MetHB - wtf

15147
User
subscriber
Loose Contusion
QuestionComment
QUESENG(ineering)
24065
User
subscriber
Amaurosis Fugaxlegomenon
QuestionComment
for the love of all that is fuck, WHY does he have a severe headache?????????????????
26463
User
subscriber
Imran
Concept
Chapter
# Summary

Carbon monoxide is a tasteless, odourless and invisible gas that may be produced by fires, faulty gas appliances and fuel-burning heaters. Signs and symptoms include confusion, nausea, vomiting, hypotension and dizziness. Pulse oximetry typically shows close to 100% oxygen saturations as monitors cannot differentiate between haemoglobin bound to oxygen or carbon monoxide. A blood gas will show high levels of carboxyhaemoglobin, and breath tests can be used to measure exhaled carbon monoxide. High-flow oxygen is the mainstay of treatment, with hyperbaric oxygen considered for certain high risk patients. 
 

# Definition
 
Carbon monoxide poisoning is a serious and potentially fatal condition caused by acute or chronic inhalation of carbon monoxide gas. This gas is colourless and odourless, and can only be detected by equipment such as carbon monoxide alarms. It is produced by the incomplete combustion of fuel (when insufficient oxygen is present), for example in faulty heaters or cooking equipment.
 
# Epidemiology
 
In England, there are approximately 4000 A&E attendances per year with carbon monoxide poisoning and approximately 40 deaths. Around half of cases are due to accidental exposure and around 40% are due to self-harm (e.g. from intentional inhalation of exhaust fumes in an enclosed space). 

Poisoning is more common in winter when heating equipment is more likely to be used, and is more common in groups affected by socio-economic deprivation.

Some patient groups are more sensitive to the effects of carbon monoxide poisoning, including:

- The elderly
- Young children
- Pregnant women 
- People with anaemia
- People with cardiovascular disease

# Aetiology

Inhaled carbon monoxide binds to haemoglobin with a much greater affinity than oxygen, forming carboxyhaemoglobin. This causes tissue hypoxia, especially affecting organ systems with a high oxygen demand such as the central nervous system and the cardiovascular system.

**Prevention of carbon monoxide poisoning:**

- Carbon monoxide alarms should be fitted in the home
- Gas appliances should be correctly installed and be regularly serviced
- Vulnerable patients (e.g. disabled or elderly patients) may be entitled to free annual gas safety checks
- Landlords have a legal duty to ensure gas appliances are checked at least yearly
- Do not burn charcoal indoors for cooking or heating
- Do not use gas appliances if you suspect they may be faulty

# Signs and Symptoms

- Headache
- Dizziness
- Lethargy
- Flushing
- Myalgia and weakness
- Confusion
- Nausea and vomiting
- Cherry red skin (rare)
- Tachycardia and hypotension
- Seizures

# Differential Diagnosis
 
- **Migraine:** headache is the predominant symptom of many cases of carbon monoxide poisoning; migraine is more likely to be associated with aura, photophobia and phonophobia
- **Viral infections:** cause overlapping symptoms of headache and myalgia, may have other symptoms such as cough or fever not seen in carbon monoxide poisoning
- **Diabetic ketoacidosis:** may have similar symptoms of nausea and vomiting, lethargy and weakness; blood glucose will be high with raised ketones
 
# Investigations

**Bedside tests:**

- **Pulse oximetry** is likely to show close to 100% oxygen saturations; this is artifactual as the devices cannot differentiate carboxyhaemoglobin and oxyhaemoglobin.
- A **blood gas** (either venous or arterial) should be taken to confirm the diagnosis by measuring carboxyhaemoglobin
    - The normal level in non-smokers is 1–2%
    - In smokers 5-10% is normal (heavy smokers can tolerate up to 15%)
    - Carboxyhaemoglobin of 10% or more is usually indicative of carbon monoxide poisoning
    - Toxicity usually manifests at levels of 15-20%
    - Carboxyhaemoglobin of 20% or higher is usually associated with severe cerebral or cardiac ischaemia
- An **ECG** should be done to look for ischaemic changes
- **Capillary blood glucose** to rule out hypoglycaemia or hyperglycaemia as a cause for lethargy and confusion

**Blood tests:** 

- **FBC** for anaemia
- **U&Es** for renal impairment
- **CK** for rhabdomyolysis
- **Troponin** for myocardial ischaemia
- **Lactate** - may indicate concurrent cyanide exposure if high in the context of smoke exposure

# Management
 
- Take an **A to E approach** and ensure the airway is protected in the first instance
- Administer **100% oxygen** via a tight-fitting face mask (if high-flow nasal cannulae available these can be used to administer up to 60L/min oxygen)
- Continue high-flow oxygen until any symptoms have resolved and carboxyhaemoglobin levels are 2% or lower in non-smokers or 10% or lower in smokers
- Correct hypotension with **IV fluids**
- Contact the **National Poisons Information Service** (NPIS) if advice required
- In certain severe cases (e.g. carboxyhaemoglobin > 25%) **hyperbaric oxygen therapy** may be considered however its use is currently not recommended by the NPIS
- **Inform the local Health Protection Team** who will coordinate services to address the source of carbon monoxide poisoning

# Complications

Most patients will recover fully from carbon monoxide poisoning, although in a minority of people (generally those who have had severe or prolonged exposure) neuropsychiatric complications may develop, including:

- Emotional lability and personality change
- Difficulty concentrating
- Insomnia
- Lethargy
- Movement disorders such as chorea and Parkinsonism
- Memory impairment and dementia
- Psychosis
- Neuropathy

# NICE Guidelines

[NICE CKS - Carbon Monoxide Poisoning](https://cks.nice.org.uk/topics/carbon-monoxide-poisoning/)

# References
 
[RCEM Learning - Carbon Monoxide Poisoning](https://www.rcemlearning.co.uk/reference/carbon-monoxide-poisoning/)

[London Fire Brigade - Carbon Monoxide Safety](https://www.london-fire.gov.uk/safety/the-home/carbon-monoxide-safety/)
661
712
Emergency Management of Carbon Monoxide poisoning
Topic
39
Emergency Medicine
Video
Concept
712
Emergency Management of Carbon Monoxide poisoning
116
fyt23zP
images/videos/ED.png
Emergency Management of Carbon Monoxide poisoning
Video
Concept
712
Emergency Management of Carbon Monoxide poisoning
312
vf6znRM
images/videos/oncology.png
Quesmed Tutorial: Drug Toxicity and Overdose
6468
Carbon monoxide poisoning often presents with headache, confusion, and respiratory distress, despite normal oxygen saturation readings.
A 75-year-old man presents to the Emergency Department (ED), having been found collapsed at his home by his wife. His wife tells you that they recently moved to a new house and had been moving things into the basement.

On assessment, he reports a severe headache and has a GCS of 14. On examination, there is significant accessory muscle usage, tachypnoea and vesicular breath sounds are heard throughout both lung fields. Oxygen saturations are 96% on room air. An arterial blood gas (ABG) shows a PaO<sub>2</sub> of 11.5kPa (>11kPa) and a PCO<sub>2</sub> of 5.1kPa (4.5-6kPa).

Which of the following is the most likely diagnosis?
a