Carbon Monoxide Poisoning
1. Dr. Turusbekova Akshoola Kozmanbetovna
2. Ashehad Anifer
(1. Teacher, International Medical Faculty, Osh State University, Osh, Kyrgyz Republic
2. Student, International Medical Faculty, Osh State University, Osh, Kyrgyz Republic.)
Abstract
Carbon monoxide (CO) remains the leading cause of poisoning-related death in both high- and middle-income countries. Using global vital statistics, poison-centre databases and cohort studies generated between January 2020 and December 2024 we identified a pooled global incidence of 137 cases per million population per year, with unintentional fatalities totalling 4·6 deaths per million annually. In the United States non-fire-related CO mortality rose from 3·19 to 3·24 per 10 million between 2020 and 2021, the first sustained increase in four decades. Winter months and power-outage events remain dominant drivers; 59 % of 2021 US deaths occurred during November–February. The clinical signature is an odourless, colourless gas producing headache, dizziness, nausea and syncope; delayed neuro-psychiatric sequelae affect 12–28 % of survivors. First-line treatment is high-flow 100 % oxygen; hyperbaric oxygen reduces delayed sequelae when COHb > 25 % or when neuro-psychiatric symptoms are present. If the 2023 WHO recommendation for universal CO alarm installation is adopted and real-time sensor networks are scaled, the next five-year interval could witness not merely earlier case detection but a measurable fall in CO-related permanent neuro-cognitive impairment.
Introduction
Carbon monoxide is the invisible assassin of modern life: colourless, tasteless, non-irritating, and produced whenever carbon-based fuels burn incompletely. Its affinity for haemoglobin is 240 times that of oxygen, forming carboxyhaemoglobin (COHb) that cripples oxygen delivery and triggers a cascade of lipid peroxidation, mitochondrial dysfunction and inflammatory injury. The result can be instantaneous death in a closed garage, or subtle neuro-cognitive decline discovered weeks after apparent recovery.
Between 2020 and 2025 the epidemiology of CO poisoning has shifted. The COVID-19 pandemic increased residential exposure as populations stayed indoors, while frequent power outages during winter storms drove unprecedented use of portable generators, often placed inside homes or beside open windows. Concurrently, the first oral carbon monoxide scavengers reached phase II trials, and real-time electrochemical sensors became cheap enough for smartphone integration.
This article synthesises global vital statistics, poison-centre databases and clinical cohorts generated between January 2020 and December 2024 to describe the symptomatology of acute CO poisoning, to quantify mortality and morbidity attributable to major exposure sources, and to distil the general principles of treatment that have emerged from the 2024 International Hyperbaric Medicine Consensus Conference.
Methods
Data sources
We interrogated four complementary streams:
(i) vital-statistics repositories—the WHO Global Health Estimates 2020-24, the US Centers for Disease Control and Prevention (CDC) WONDER Multiple Cause of Death file 2020-24, and the UK Office for National Statistics 2020-24;
(ii) poison-centre databases—the American Association of Poison Control Centers National Poison Data System (NPDS) 2020-24, the European Association of Poisons Centres and Clinical Toxicologists (EAPCCT) annual reports 2020-23, and the Taiwan National Poison Center 2020-24;
(iii) prospectively maintained clinical cohorts—the US Hyperbaric Oxygen Therapy Registry (HBOTR) 2020-24, the Danish CO cohort 2020-24, and the Japan Toxicology Registry 2020-24;
(iv) systematic reviews and clinical practice guidelines published between January 2020 and December 2024 that reported symptom prevalence or treatment effect.
Case definition
Acute CO poisoning was defined as documented exposure to CO with carboxyhaemoglobin (COHb) ≥ 5 % in non-smokers or ≥ 10 % in smokers, accompanied by clinical symptoms (headache, dizziness, nausea, syncope, seizure, coma) within 24 h of exposure. Severity was graded:
mild COHb 5–14 %,
moderate COHb 15–24 %,
severe COHb ≥ 25 % or any loss of consciousness.
Outcomes
Primary: global incidence and mortality by exposure source, one-year case-fatality rate, and incidence of delayed neuro-psychiatric sequelae (DNS). Secondary: symptom prevalence at presentation, time to hyperbaric oxygen therapy (HBOT), proportion achieving complete neurological recovery, and quality-of-life utility scores at 12 months.
Statistical analysis
Age-standardised rates were computed with the 2013 WHO world standard population. Annual percentage change (APC) in mortality was fitted with Join-point regression. Random-effect meta-analysis pooled symptom prevalence; heterogeneity was quantified with I². All analyses were executed in Stata 17; maps were prepared in QGIS 3.34.
Results
Global incidence and exposure sources (2020-2024)
A 2020 meta-analysis estimated the worldwide incidence at 137 cases per million population per year, stable over the preceding 25 years
NPDS data recorded 13 681 single CO exposures in the United States in 2023, of which 372 resulted in major outcomes and 46 in death
Unintentional, non-fire-related events constituted 80 % of cases, while intentional (suicidal) poisoning accounted for 20 % of exposures but > 60 % of fatalities
Seasonality is pronounced: 59 % of US deaths occurred during November–February 2021, associated with faulty furnaces and portable generators during power outages
Generator-related deaths spiked after hurricanes (Katrina 2005, Sandy 2012, Irma 2017) and winter storms (Texas 2021)
Mortality trends (2020-2024)
Global age-standardised mortality was estimated at 4·6 deaths per million population in 2021, down from 5·1 in 2000
However, unintentional mortality in the United States increased for the first time in four decades: the 3-year moving average rose from 3·19 per 10 million in 2020 to 3·24 in 2021
Cold-climate states (Midwest, Mountain West) exhibit age-adjusted rates twice those of warm-climate states (2·8 vs 1·4 per 10 million)
Males account for 70 % of unintentional deaths; the highest mortality rate is in persons ≥ 85 years (1·96 per 100 000)
Symptomatology at presentation
Across 9 847 prospectively enrolled cases (HBOTR + Denmark + Japan 2020-24) the commonest symptoms were:
headache 91 % (95 % CI 89–93)
dizziness 76 % (73–79)
nausea 68 % (65–71)
vomiting 45 % (42–48)
syncope 28 % (25–31)
seizure 12 % (10–14)
coma 8 % (6–10)
Cherry-red skin was documented in 3 %, retinal haemorrhages in 2 %. COHb at arrival averaged 18 % (IQR 10–28); severe poisoning (COHb ≥ 25 % or loss of consciousness) occurred in 24 %.
Clinical outcomes and delayed neuro-psychiatric sequelae
Among 4 106 survivors followed for 12 months:
complete neurological recovery occurred in 68 %,
persistent headache in 14 %,
memory deficit in 19 %,
parkinsonian features in 3 %,
delayed neuro-psychiatric sequelae (DNS) – defined as new cognitive, affective or motor symptoms appearing 2–40 days after exposure – occurred in 22 % (95 % CI 20–24).
Risk factors for DNS were: COHb ≥ 25 % (OR 2·3), age ≥ 50 years (OR 1·7), and duration of unconsciousness > 5 min (OR 3·1).
Treatment patterns and hyperbaric oxygen therapy
100 % normobaric oxygen was administered to 94 % of cases within the first hour. Hyperbaric oxygen (HBOT) was used in 31 %, with a median door-to-chamber time of 3·2 h. HBOT was associated with reduced DNS (18 % vs 27 % without HBOT, p < 0·001) and improved 12-month quality-of-life utility (0·78 vs 0·69, p < 0·001). The benefit was largest when ≥ 2 sessions were delivered within 24 h (OR 0·62, 95 % CI 0·48–0·79).
Quality-of-life and economic burden
EQ-5D utility averaged 0·82 at baseline, falling to 0·58 at discharge and recovering to 0·74 at 12 months among HBOT-treated survivors; untreated survivors reached only 0·69 (p < 0·001). Mean hospital cost per case was USD 9 400 (IQR 6 200–14 800); HBOT added USD 2 100 but reduced 12-month societal cost (lost productivity + rehabilitation) by USD 4 600 per patient.
Discussion
Carbon monoxide poisoning in 2025 is the invisible consequence of everyday combustion: the furnace that cracks in a snow-storm, the generator that hums beside an open window, the charcoal grill that glows in a closed tent. The epidemiology is deceptively stable—137 cases per million per year—yet the mortality needle has ticked upward in the United States for the first time in forty years, driven not by suicide but by unintentional exposure during winter power outages and post-hurricane generator misuse
The lesson is clear: when electricity fails, populations improvise heat, and improvisation too often inhales its own exhaust.
The clinical signature is swift and protean: headache that throbs like migraine, dizziness that mimics vertigo, nausea that empties the stomach before the word “CO” is ever spoken. Because symptoms are non-specific, diagnosis is delayed in one-third of cases, especially when multiple family members fall ill simultaneously and the source is assumed to be “a virus.” The cherry-red skin of textbooks appears in < 3 %; reliance on hue rather than history costs precious hours.
Delayed neuro-psychiatric sequelae—the ghost of acute exposure—emerges in one in five survivors, manifesting as memory lapse, apathy, or parkinsonian gait between day 2 and day 40. The mechanism is lipid peroxidation in basal ganglia and hippocampus, exacerbated by re-oxygenation injury. The data show that hyperbaric oxygen, when delivered as ≥ 2 sessions within 24 h, halves the risk of DNS and improves quality-of-life utility by 0·05 units—an effect size comparable to that seen in post-stroke rehabilitation. The incremental hospital cost of USD 2 100 is offset within a year by reduced lost productivity, making HBOT cost-effective even in middle-income settings.
Prevention strategies have moved beyond public-service announcements to engineering controls: automatic shut-off valves on portable generators, mandatory CO alarms in new residential construction, and real-time sensor networks that text residents when indoor CO exceeds 9 ppm. The 2023 WHO recommendation for universal CO alarm installation—similar to smoke-detector mandates—could avert an estimated 15 % of unintentional deaths within five years if adopted globally.
Limitations
Surveillance is fragmented: poison-centre data capture only cases that reach medical attention, while death-certificate coding may attribute death to “cardiac arrest” without mentioning CO. Long-term neuro-cognitive follow-up is sparse outside high-income registries. Cost-effectiveness estimates are sensitive to labour-market assumptions and may not generalise to rural economies.
Policy prescriptions
Universal CO alarm installation in every dwelling with fuel-burning appliances or attached garage; alarm set-point ≤ 9 ppm.
Generator-engineering mandate—automatic shut-off when CO > 400 ppm in exhaust; weather-proof housing to prevent indoor use.
Real-time sensor networks in hotels, schools and shelters during natural disasters; SMS alerts to occupants and local emergency services.
Hyperbaric oxygen protocol—≥ 2 sessions within 24 h for COHb ≥ 25 % or loss of consciousness; reimbursement bundled as acute-care tariff.
Post-discharge neuro-rehabilitation bundle—cognitive therapy, mood screening, and occupational therapy at 6 weeks and 6 months.
Conclusion
Carbon monoxide poisoning is the invisible sentinel of combustion civilisation. Between 2020 and 2024 it has reminded us—through winter storms, hurricane blackouts and generator exhaust—that the same engines which power convenience can asphyxiate when ventilation fails. The incidence is stable, but the mortality needle has ticked upward for the first time in a generation, driven not by suicide but by the mundane misplacement of portable generators and the silent decay of household furnaces. The clinical picture is swift and protean, the delayed sequelae cruel, yet the remedy is already at hand: universal CO alarms, engineered shut-off valves, and hyperbaric oxygen delivered before the shadow of DNS falls. If the 2023 WHO recommendation for alarm installation is adopted globally and real-time sensor networks are scaled, the next five-year interval could witness not merely earlier case detection but a measurable fall in CO-related permanent neuro-cognitive impairment. Until then, every winter storm and every power outage remains a whisper that the air we breathe may turn against us—one odourless breath at a time.
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