Carbon monoxide screening in ED patients with headache

Plain English summary of protocol

Background and study aims
Carbon monoxide (CO) exposure is an important but often overlooked cause of headaches. Many patients who come to the emergency room with headaches are not routinely checked for CO exposure, and how common it is or which patients are most at risk is not fully understood. Being better at recognising headaches caused by CO could help doctors diagnose the problem earlier, stop people from being exposed to more CO, and prevent long-term brain and health issues. Low-level CO exposure often goes unnoticed, especially indoors, where appliances like boilers or fireplaces may not be working properly or may lack good ventilation. People exposed to these low levels of CO repeatedly often have headaches that do not have an obvious cause, but improve once they are away from the source of CO.

To find out how often CO exposure causes headaches, two main methods have been used: testing CO levels in the blood and checking for sources of CO in a person’s environment. During this study, CO levels will be measured in patients coming to the emergency room with headaches using two methods: a quick, non-invasive finger sensor called CO-oximetry, and a standard blood test. The finger sensor gives fast results without needing a blood sample, and research suggests it can be useful in emergency settings. It might also be cheaper and easier to use, especially in places where blood tests aren’t always possible. Since CO leaves the blood quickly, this quick test could be more effective at catching recent exposure. The study will also collect information about the patients’ environments to see if they are exposed to CO at home. Previous research found that many people do not have CO alarms or are not aware that they do, which puts them at risk of undetected CO exposure. To help track this, a portable CO monitor will be given to each patient to take home for one week. These monitors detect much lower levels of CO than regular alarms.

This study aims to evaluate the feasibility, acceptability, and operational practicality of the one-week home CO monitoring in identifying environmental CO exposure. It will also explore the number of patients attending the Emergency Department (ED) with a simple headache who have been exposed to carbon monoxide, as well as assessing the agreement between different CO measurement methods (blood tests, CO-oximetry, and home monitoring) and how they relate to patient symptoms. The team will also assess the impact of the time of year on CO exposure in homes, and recruitment, retention, data completeness, and participant adherence information will also be analysed. This will lead to the development of draft clinical guidance for identifying and managing CO exposure in patients with headache, suitable for future testing in further research.

Who can participate?
Adult patients aged 18 and over attending the ED with a headache, but are unlikely to be admitted to the hospital.

What does the study involve?
The study is made up of various data collection points outlined below:
During ED visit - Baseline (Day 0):
Whilst in ED, patients will receive two procedures to measure the carbon monoxide levels in their blood (known as carboxyhaemoglobin, or COHb). The first procedure is a routine test that would take place within usual care, which involves a member of the clinical team taking a blood sample and processing it using a device known as a blood gas machine. The second procedure involves a painless finger probe test, where a device will be placed on the tip of a finger to measure COHb levels. Before the participant is discharged from ED, a member of the research team will provide them with a transportable carbon monoxide alarm and instructions on how to use it. All participants will receive a stamped, addressed envelope to return the monitor to the research team after 7 days.

7-day home monitoring phase, post-discharge:
After discharge, the 7-day home monitoring period will begin. Participants will be asked to put the carbon monoxide alarm in their kitchen, as far as possible from the boiler/stove. Participants will receive a daily message or email from the research team each evening with a link to the daily home monitoring questionnaire measuring symptoms, alongside a paper copy.

Day 8:
Participants will be asked to return the monitor to the research team using the stamped, addressed envelope provided. Participants will be given an optional £10 bank transfer upon the return of the monitor.

Day 14 follow-up (± 7 days):
The research team will follow up at 14 days post-discharge to recheck symptoms. If the CO monitor has been received, participants will get the results of the 7-day home monitoring period, and if high levels of CO are detected, they will receive information on corrective measures and may be referred to the National Emergency Gas Service.

[OPTIONAL] CO monitoring follow-up:
For patients who return their CO monitor later than day 14, participants will receive a follow-up telephone call after the symptom check to provide results.

Day 42 follow-up (± 7 days):
All participants will receive a final follow-up at 6 weeks (± 7 days) to recheck symptoms. If the research team detects abnormal levels of CO during the analysis, they will take note of any corrective measures made by participants.

What are the possible benefits and risks of taking part in this study?
The information obtained from this study will help the research team to understand if the study method is feasible among patients with headaches in the ED. This will then inform a larger main trial across multiple centres.

The study will be beneficial to people who have high environmental CO levels recorded, as it will highlight the potential cause of headaches and enable participants to take corrective actions.

There are no anticipated risks or disadvantages to taking part in this study.

Where is the study run from?
St George’s Emergency Department Collaborative Research Group, St George's University Hospitals NHS Foundation Trust, UK

When is the study starting and how long is it expected to run for?
September 2025 to June 2027

Who is funding the study?
The CO Research Trust (CORT), UK

Who is the main contact?
Kathryn Willis (study co-ordinator), EDCOstudy@stgeorges.nhs.uk

Contact information

Study information

Eligibility

Locations

Countries of recruitment

• United Kingdom
• England

Study participating centre

Results and Publications

Study outputs

Editorial Notes

23/09/2025: Study's existence confirmed by the CO Research Trust, UK.