Carbon monoxide (CO) is a toxic gas that is emitted into the atmosphere as a result of incomplete combustion of carbon-containing components. Even at high concentrations, it is challenging to detect due to its colorless, tasteless, and odorless nature.Reference Tomaszewski, Nelson, Howland, Lewin, Smith, Goldfrank and Hoffman 1 The 2022 Annual Report of the National Poison Data System (NPDS) by the American Association of Poison Control Centers revealed that there were 13 760 isolated cases of CO poisoning, with 11 857 being accidental. Among these cases, 5750 individuals received treatment at health centers and 63 resulted in death.Reference Gummin, Mowry and Beuhler 2 Although headache, dizziness, weakness, nausea, vomiting, and chest pain are common symptoms, patients may also present with nonspecific symptoms. This could lead to a misdiagnosis or a delayed diagnosis. The primary cause of poisonings in residential settings is the use of gasoline-powered appliances, including heating systems, cooking appliances, and electric generators.Reference Sircar, Clower and kyong 3
Another important feature of CO in the air is that it affects greenhouse gases associated with global warming and climate change. Greenhouse gases can lead to higher soil and water temperatures, which can result in severe weather conditions or storms.Reference Emberson, Pleijel and Ainsworth 4 The negative consequences of air pollution make it a top concern in the modern world, posing threats to both humans and the natural world. The World Health Organization (WHO) report identifies 6 primary air pollutants that contribute to air pollution, including particulate matter (PM2.5, PM10), sulfur dioxide (SO2), nitrogen dioxide (NO2), CO, and ozone (O3). The substantial amount of these substances presents a danger to the well-being of living creatures, as it can have severe impacts on both air quality and the surrounding environment, including soil and groundwater resources. 5 Air quality standards and guidelines have been adopted by the WHO and the Environmental Protection Agency (EPA) as tools for managing air quality and controlling different pollutants. 6 , Reference Newlands 7 In concordance with this aim, the Ministry of Environment, Urbanization and Climate Change in Turkey has instituted a continuous monitoring center on the online platform. Its principal role is to facilitate easy retrieval of information for the populace on the air quality they are exposed to and to promote the comprehension of relevant data. The air quality index (AQI) was developed to classify the air quality of a particular location as good, moderate, unhealthy for sensitive groups, unhealthy, very unhealthy, or dangerous. This information is updated hourly based on data collected from the field. 8
The purpose of this study was to determine the link between outdoor air pollution and the incidence of CO poisoning among patients admitted to emergency departments in 2 distinct cities in Turkey.
Methods
Study Design and Setting
This study was conducted prospectively at tertiary hospitals in 2 different cities. Patients in Adana province were labeled as Group 1, while patients in Gaziantep province were labeled as Group 2. The study was started after the approval of the local ethics committee. The study was conducted in accordance with the Declaration of Helsinki and good clinical practice. Written informed consent was obtained from the patients to participate in the study.
Selection of Study Patients
The study included individuals who visited both emergency medicine clinics for CO poisoning and had COHb levels greater than 5% (for nonsmokers) and 10% (for smokers) in their blood gas results. The study did not include patients who were under 18 years old, pregnant, experiencing poisoning from multiple substances (cyanide, etc.), lost to follow-up, deceased upon arrival at the emergency department from CO poisoning, admitted more than 24 hours after exposure, intentionally poisoned, or had a history of nervous system disease (Figure 1).
Figure 1. Flowchart of study.
Data Collection
The study data were documented in the pre-established data collection form by 6 esteemed emergency medicine experts, namely MS, MG, SS, CY, AFY, and SZ. In addition to the demographic data of the patients, their complaints, time of poisoning, CO source, vital signs, blood gas and laboratory parameters, COHb levels, length of stay in the emergency department, and outcomes were recorded. Hyperglycemia (>200 mg/dL), leukocytosis (>11.0x10^9/L), myocardial involvement (conditions affecting the heart, such as myocardial infarction, dysrhythmia, and heart failure), acute renal failure (an increase in serum creatinine level by 0.3 mg/dL or more within 48 hours), central nervous system depression, hypoxemia (<92%), and rhabdomyolysis complications were also recorded. Venous blood gas COHb level was measured with a Radiometer ABL90 flex (Radiometer, Copenhagen, Denmark) brand blood gas analyzer.
Detailed weather forecast (temperature, humidity, and average wind speed) and climate parameters (AQI, PM2.5, PM10, CO, SO2, NO2, and O3) were collected for the days that the patients were admitted. In accordance with the Ministry of Environment, Urbanization, and Climate Change of the Republic of Turkey, the data were sourced from the subsequent websites: https://www.mgm.gov.tr/tahmin/il-ve-ilceler.aspx?il= and https://www.havaizleme.gov.tr, correspondingly (Figure 2).
Figure 2. National Air Quality Monitoring Network and a sample of data pertaining to the province of Gaziantep on any given day.
Outcomes
The primary outcome of the study was the prediction of the development of cardiac complications arising from CO poisoning by analyzing meteorological and air pollutant parameters.
The secondary outcome was the estimation of the correlation between meteorological and air pollutant parameters with blood COHb levels in patients who had CO poisoning.
Statistical Analysis
The statistical evaluation of the data obtained in the study utilized the SPSS 22 software package (SPSS Inc, Chicago, Illinois, USA). Variables were divided into 2: categorical and continuous. Categorical data were presented as numbers and percentages and compared using the chi-square test. Whether continuous variables were normally distributed was determined using the Kolmogorov-Smirnov test. Continuous variables were presented with mean and standard deviation. The Kolmogorov-Smirnov test was used to compare the averages of the parameters examined. The paired sample t test was used to compare 2 groups when the variables were normally distributed in the evaluations made with the histogram, and the Mann-Whitney U test was used when the variables were not normally distributed. Multivariate analysis of air pollution and air temperature parameters was performed to predict the need for hospitalization of patients and to estimate the risk of developing cardiac complications. Pearson correlation analysis was used to explain the relationship between COHb level and meteorological and air pollutant parameters. The statistical significance level was set at P < 0.05.
Results
Eighty-three patients were included in the study. 50.6% (n = 42) of the patients were male, and the average age was 45.4 ± 18.6 years. Patients were most frequently admitted in January, 44.6% (n = 37) (P < 0.001), and equally during the day shift 39.8% (n = 33), and night shift, 39.8% (n = 33) (P = 0.260). The stove used for heating was the most common cause of poisoning, accounting for 78.3%. The most common presenting symptoms were headache (53%, n = 44), nausea and vomiting (48.2%, n = 40), and dizziness (37.3%, n = 31). The most common comorbidity was hypertension (27.3%, n = 12) vs. 5.1%, n = 2), P = 0.007). When vital signs were examined, heart rate (96.2 ± 18.3 vs. 87.6 ± 17.4, P = 0.032), mean arterial pressure (93.4 ± 12.6 vs. 86.5 ± 11.1, P = 0.01), and respiratory rate (18.6 ± 3.4 vs. 16.9 ± 2.9, P = 0.016) were significantly higher in Group 1. The most common complications were hyperglycemia (25.3%, n = 21), leukocytosis (24.1%, n = 20), and myocardial involvement (24.1%, n = 20). The complication of acute renal failure was statistically significantly higher in Group 1 (15.9% vs. 2.6%, P = 0.04). The length of stay in the emergency department (5.1 ± 2.3 vs. 3 ± 1, P < 0.001) and the ICU admission rate (22.7% vs. 5.1%, P = 0.023) were statistically significantly higher in Group 1 (Table 1).
Table 1. Distribution of demographic and clinical data of CO poisoning cases by provinces
Group 1: Patients from Adana province. Group 2: Patients from Gaziantep province.
CO = carbon monoxide; COPD = chronic obstructive pulmonary disease; HR = heart rate; MAP = mean arterial pressure; RR = respiratory rate; SO2 = oxygen saturation; CNS = central nervous system; GCS = Glasgow Coma Scale; ICU = intensive care unit.
Bold values indicates a statistically significant difference with a p value <0.05.
Upon admission, patients were evaluated for meteorological, pollutant, laboratory, and blood gas parameters, all of which are listed in Table 2. According to the meteorological parameters, the air temperature (7.8 ± 4.7 vs. 4.8 ± 3, P = 0.001) and wind speed (12.3 ± 6.9 vs. 6.2 ± 4.8, P < 0.001) of the center where Group 1 patients applied were statistically significantly higher than those in Group 2. The AQI cutoff values, which are determined based on the concentrations of pollutants in the air, are shown in Table 3. When the AQI was evaluated, the air quality in Group 2 (61.7 ± 27.7) (moderate AQI) was significantly higher than that in Group 1 (47.3 ± 26.4) (good AQI) (P = 0.018). The data indicate that Group 2’s AQI has a higher level of dirtiness. When the 2 groups were compared in terms of pollutant parameters, Group 2 showed significantly higher levels of NO2 (89 ± 38.5 vs. 43.5 ± 36.6, P < 0.001) and SO2 (81.6 ± 60.7 vs. 22 ± 21.9, P < 0.001) and lower levels of O3 (41.7 ± 22.5 vs. 27.9 ± 22.2, P = 0.006) than Group 1. In Table 2, the analysis of air pollutants (CO, PM10, and PM2.5) in different provinces is presented.
Table 2. Distribution of meteorological parameters, pollutant parameters, and laboratory and blood gas parameters of CO poisoning cases by province
Group 1: Patients from Adana province. Group 2: Patients from Gaziantep province.
WBC = white blood cell; Hs-cTn = high sensitive cardiac troponin; CRP = C-reactive protein; HCO3 = bicarbonate; COHb = carboxyhemoglobin; CO = carbon monoxide; So2 = sulfur dioxide; NO2 = nitrogen dioxide; PM = particulate matter; O3 = ozone.
Normal range of the parameters: WBC: 3.7-8.7x103 /μL, glucose: 74-106 mg/dL, Hs-cTn: 0-11.6 ng/L, CRP: 0-5 mg/L, pH: 7.35-7.45, COHb: 0.5-1.5%, HCO3: 21,8-26,2 mmol/L, lactate: 0.5-1.6 mmol/L.
National cutoff values: Air quality index: good (0-50), moderate (50-100), unhealthy for sensitive groups (100-150), unhealthy (150-200), very unhealthy (200-300), hazardous (300-500) CO: 10.000 μg/m3 (8h average) SO2: 350 μg/m3 (1h average), NO2: 250 μg/m3 (1h average), PM10: 50μg/m3 (24h average), O3: 120 μg/m3 (8h average).
Bold values indicates a statistically significant difference with a p value <0.05.
Table 3. Air Quality Index (AQI) cut-off values*
* The national air quality index (AQI) was created by adapting the Environmental Protection Agency (EPA) AQI to our national legislation and limit values. AQI is calculated for 6 basic pollutants: particulate matter (PM2.5, PM10), carbon monoxide (CO), sulfur dioxide (SO2), nitrogen dioxide (NO2), and ozone (O3).
Multivariate analysis of meteorological and pollutant parameters to predict the need for hospitalization and the need for cardiac complications is shown in Table 4. It has been determined that the AQI is a reliable predictor for hospitalization (OR = 1.192, 95% CI: 1.036 - 1.372, P = 0.014) and the risk of developing cardiac complications (OR = 1.060, 95% CI: 1.017 - 1.104, P = 0.005) (Table 4).
Table 4. Multivariate analysis to predict the need for hospitalization of patients and the risk of developing cardiac complications
OR = odds ratio; CI = confidence interval; COHb = carboxyhemoglobin; CO = carbon monoxide; So2 = sulfur dioxide; NO2 = nitrogen dioxide; PM = particulate matter; O3 = ozone.
National cutoff values: Air quality index: good (0-50), moderate (50-100), unhealthy for sensitive groups (100-150), unhealthy (150-200), very unhealthy (200-300), hazardous (300-500) CO:10.000 μg/m3 (8h average) SO2: 350 μg/m3 (1h average), NO2: 250 μg/m3 (1h average), PM10:50μg/m3 (24h average), O3: 120 μg/m3 (8h average).
The correlations between COHb levels and meteorological and air pollutant parameters are outlined in Table 5. When meteorological parameters were examined, it was found that the COHb levels of the patients had a statistically significant but weak correlation with air humidity (r = 0.276, P = 0.011). When the pollutant parameters were examined, it was found that the COHb levels of the patients had a statistically significant but weak negative correlation with the air O3 level (r = –0.218, P = 0.048).
Table 5. Correlation values between COHb levels and meteorological and pollutant parameters
r: Correlation coefficient
COHb = carboxyhemoglobin; CO = carbon monoxide; So2 = sulfur dioxide; NO2 = nitrogen dioxide; PM = particulate matter; O3 = ozone.
Bold values indicates a statistically significant difference with a p value <0.05.
Discussion
This study reveals that AQI, calculated based on the concentration of pollutants in the air, is an independent predictor for determining the probability of hospitalization and cardiac complications in emergency department patients with CO poisoning.
The cause of CO poisoning cannot be attributed to a single factor. The severity of CO poisoning depends on the amount of CO exposure, the concentration of CO in the air breathed in, the duration of exposure, and the patient’s breathing rate.Reference Ruan, Deng and Wang 9 –Reference Scherer 11 Both outdoor pollution (ambient air pollution) and indoor pollution (pollution produced by indoor fuels, exhaust, poor ventilation, leakage of outdoor air pollutants) affect the concentration of CO in inhaled air.Reference Manisalidis, Stavropoulou and Stavropoulos 12 , 13 The presence of indoor smoke may result in an elevation of basal COHb levels.Reference Varon, Marik and Fromm 10 , Reference Scherer 11 This study indicates that despite the lower AQI in Adana province (Group 1), patients are prone to extended stays in the emergency department and prolonged hospitalization due to the prevalence of indoor pollution.
The National AQI was developed by modifying the EPA AQI to national legislation and limit values. The AQI is calculated based on six basic pollutants: PM2.5, PM10, CO, SO2, NO2, and O3. 8 Particulate matter often forms in the atmosphere as a result of chemical reactions between various pollutants.Reference Wilson and Suh 14 Particles with aerodynamic diameters of 2.5 μm (PM2.5) or 10 μm (PM10) seem to be the main cause of the cardiovascular effects observed from air pollution.Reference Dennekamp, Akram and Abramson 15 The review of several studies revealed that the cardiovascular death rates increased by about 1% for every 10 μg/m3 rise in PM2.5.Reference Pope and Dockery 16 The penetration of particles generally depends on their size. Particulate matter comprises small liquid or solid droplets that can be breathed in.Reference Cheung, Daher and Kam 17
After inhaling, particles with a diameter of 10 micrometers (PM10) can enter the lungs and even reach the circulatory system. Fine particles (PM2.5) pose a greater risk to health.Reference Kelishadi and Poursafa 18 , Reference Zhang, Yang and Li 19 While it causes nasopharyngitis in the short term, it has been associated with cardiovascular diseases and infant deaths in the long term.Reference Manisalidis, Stavropoulou and Stavropoulos 12 , Reference Dennekamp, Akram and Abramson 15 Individuals with asthma, pneumonia, diabetes, respiratory, and cardiovascular diseases may be more vulnerable to the effects of PM because it affects respiratory health and the immune system. 20 Ozone is a gas created from oxygen through high voltage electrical discharge.Reference Bezirtzoglou, Alexopoulos and Bakker 21 It is taken by inhalation. It affects the upper layers of the skin, tear ducts, and lungs.Reference Amann, Derwent and Forsberg 22 , Reference Hatch, Slade and Harris 23 Ozone increases DNA damage in epidermal keratinocytes, leading to biochemical, morphological, functional, and immunological disorders.Reference McCarthy, Pelle and Dong 24 Automobile engines emit NO2, a harmful pollutant associated with traffic.Reference Richmond-Bryant, Chris Owen and Graham 25 , Reference Hesterberg, Bunn and McClellan 26 Inhaling at high levels (above 0.2 ppm) can cause coughing, wheezing, difficulty breathing, bronchospasm, and even pulmonary edema. In addition, high concentrations may have an effect on T-cells that play a crucial role in immune response, including CD8+ cells and natural killer cells. Chronic exposure can lead to chronic lung disease.Reference Chen, Kuschner and Gokhale 27 The release of SO2 is a hazardous byproduct commonly associated with the burning of fossil fuels or industrial processes. The level of the annual SO2 standard is 0.03 ppm. 28 Inhaling can cause shortness of breath, wheezing, acute bronchitis, and increased mucus secretion. It can cause urticaria, lacrimation, corneal opacity, and worsening of pre-existing cardiovascular diseases.Reference Chen, Kuschner and Gokhale 27 Air quality index is calculated based on the proportions of these 6 harmful gases in the air.
Carbon monoxide concentrations usually range from 0.02 to 1.0 ppm in clean air. However, in urban areas, CO concentrations can increase 10-fold during periods of atmospheric stagnation, such as when temperature inversions occur in winter or in situ air masses form in summer. 29 , Reference Campbell, Benson and Muir 30 Research in the literature has extensively explored the impact of meteorological factors such as temperature, humidity, and wind speed on CO poisoning.Reference Lin and Liao 31 In recent years, studies have been evaluating cases of out-of-hospital cardiac arrest and CO poisoning, as well as air pollutants such as PM2.5, PM10, CO, SO2, NO2, and O3, along with meteorological factors.Reference Ruan, Deng and Wang 9 –Reference Dennekamp, Akram and Abramson 15 In the study on CO poisoning, the researchers attempted to estimate the elevated risk of poisoning by creating models that incorporated both meteorological and pollutant parameters. The model, which considers both atmospheric conditions and pollutant variables, is effective in predicting cases of CO poisoning. It outperforms the model based only on weather factors in terms of precision and forecasting potential for severe poisoning levels.Reference Ruan, Deng and Wang 9 This study differs from previous studies in that it examined the potential of meteorological factors and air pollution to predict the onset of complications and the likelihood of hospitalization. This study concluded that AQI was a significant factor in predicting both hospitalization and myocardial involvement. This discovery has the potential to be advantageous in mitigating unintentional CO poisoning, which carries a significant fatality risk. By including AQI value estimates in weather forecasts, public awareness of potential CO poisoning can be heightened.Reference Gijsenbergh, Vispoel and Poppe 32 Moreover, the dissemination of public service warnings through public transportation, news releases, and government surveillance can effectively reduce the occurrence of poisoning incidents, particularly during storms.Reference Hampson, Piantadosi and Thom 33 Additionally, imparting training in schools to heighten cognizance about CO poisoning and techniques for diminishing CO production in both indoor and outdoor settings will serve as an efficacious measure in preventing both atmospheric pollution and CO poisoning in its nascent stages. In the event of poisoning, the primary objective is to reduce the number of fatalities by promptly and precisely identifying and treating the condition.
Limitations
This study had some limitations. The first limitation regards the sample group. The study gathered data from 2 tertiary hospitals situated in 2 distinct provinces. These 2 hospitals rank among the biggest in the area. Nevertheless, other hospitals in the same area may have also seen instances of poisoning. This situation might have impeded the availability of a comprehensive dataset. The second limitation was related to continuous monitoring centers. Meteorological observation stations provide information by collecting average measurements of specific districts within each metropolis. The data were procured from the surveillance hubs within the vicinities of the patient’s residence or the immediate vicinity.
Conclusion
This study highlights the critical importance of air pollution in emergency department visits due to CO poisoning. The identification of the AQI as an independent predictor for hospitalization necessity and cardiac complications in patients with CO poisoning presenting at the emergency department highlights the significant impact of environmental factors on public health. These findings provide a fundamental guide for the development of public health strategies and the implementation of measures to improve air quality. Combating air pollution is urgent not only for the environment but also to protect the health of individuals.
Data availability statement
The datasets generated and/or analyzed during the current study are available from the corresponding author on reasonable request.
Acknowledgments
None.
Author contribution
MG, MS: Concept, review, data searching, design, statistical extractions, analysis, and final approval. SS, CY, AFY, SZ: Concept, review, analysis, data searching, analysis, and final approval.
Competing interest
The authors have no conflicts of interest to declare.
Ethical standard
The Ethics Committee of Gaziantep University of Medical Sciences, (Meeting date: February 23, 2022, Ethics committee decision no:2022/09) approved this study.
