Factors Contributing to CO Uptake and Elimination in the Body: A Critical Review

BACKGROUND

Carbon monoxide (CO) poisoning is an important public health issue around the world. Research indicates that many factors may be related to the rate of CO uptake and elimination in the human body. However, some factors related to CO uptake and elimination are considered controversial. Relatively little attention has been devoted to review and synthesis of factors affecting CO uptake and elimination.

PURPOSE

This paper provides a critical scoping review of the factors and divides them into four aspects, including environmental, demographic, physiological and treatment factors.

METHODS

We searched the scientific databases for research that has proposed a mathematical equation as a synthesis of quantities related to CO poisoning, CO elimination, CO uptake, CO half-life, CO uptake and elimination and their relationships. After excluding the studies that did not meet the study criteria, there were 39 studies included in the review and the search was completed before 16 December 2019.

RESULTS AND CONCLUSION

This review discusses most of the factors that impact the rate of CO uptake and elimination. Several factors may be related to CO uptake and elimination, such as CO concentration, the duration of exposure to CO, age, sex, exercise, minute ventilation, alveolar ventilation, total haemoglobin mass and different treatments for CO poisoning. Although some potential factors were not included in the review, the findings are useful by presenting an overview for discussing factors affecting CO uptake and elimination and provide a starting point for further study regarding strategies for CO poisoning and the environmental standard of CO.

Camera-based pulse-oximetry - validated risks and opportunities from theoretical analysis

Camera-based pulse-oximetry has recently shown to be feasible, even when the signal is corrupted by noise and motion artifacts. Earlier work showed that using three instead of the common two wavelengths improves robustness of the measurement, however without a thorough investigation on the optimal wavelength selection. We therefore performed a search to identify these wavelengths to further improve the robustness of the measurement. Besides motion, it is empirically known that there are several other factors that influence the measurement leading to falsely-low or falsely-high SpO₂ readings. These factors include the presence of dyshemoglobins or other species. In this paper, we use a theoretical skin-model to study how these factors influence the measurement, and how a proper wavelength selection can reduce the impact on the measurement. Additionally, we show that adding a third wavelength does not only improve robustness, but can also be exploited to create a reliability index for the measurement. Finally, we show that the presence of dyshemoglobins in arterial blood can not only be detected but also quantified. We illustrate this by comparing the estimated COHb levels of a small group of smokers and non-smokers, which typically have different CO-levels.

Anesthesia-Related Carbon Monoxide Exposure: Toxicity and Potential Therapy

Exposure to carbon monoxide (CO) during general anesthesia can result from volatile anesthetic degradation by carbon dioxide absorbents and rebreathing of endogenously produced CO. Although adherence to the Anesthesia Patient Safety Foundation guidelines reduces the risk of CO poisoning, patients may still experience subtoxic CO exposure during low-flow anesthesia. The consequences of such exposures are relatively unknown. In contrast to the widely recognized toxicity of high CO concentrations, the biologic activity of low concentration CO has recently been shown to be cytoprotective. As such, low-dose CO is being explored as a novel treatment for a variety of different diseases. Here, we review the concept of anesthesia-related CO exposure, identify the sources of production, detail the mechanisms of overt CO toxicity, highlight the cellular effects of low-dose CO, and discuss the potential therapeutic role for CO as part of routine anesthetic management.

Impact of cigarette smoke on T and B cell responsiveness

Although its direct effects cannot be discounted, tobacco's effects on the immune system have been proposed to play a key role in mediating its deleterious health impact. Studies in rats using high levels of smoke exposure have suggested that tobacco smoke exhausts cellular signal transduction cascades, making lymphocytes unresponsive to stimulation. In the present study, we show that purified B or T cells, and total lymphocytes from the lungs, lymph nodes and spleens of smoke-exposed mice fluxed calcium, proliferated, and secreted immunoglobulin or IFN-gamma similarly to control mice when stimulated with ligands including anti-IgM, and anti-CD3. Importantly, we recapitulated these findings in PBMCs from human smokers; cells from long-term smokers and never-smokers proliferated equivalently when stimulated ex vivo. Previous reports of lymphocyte unresponsiveness in rats are inconsistent with these findings, and may reflect a phenomenon observed only at levels of smoke exposure well above those seen in actual human smokers.

Accuracy of carbon monoxide in venous blood to detect smoking in male and female trauma patients

Background: The determination of the smoking status should be part of the initial assessment in emergency or surgery patients, as preventive measures might reduce long-term morbidity. Next to self-report (not always possible or reliable) the use of biomarkers such as carbon monoxide (CO) has been recommended. Point-of-care CO-hemoglobin (CO-Hb) determination is routinely used in trauma settings. The aim of this study was to evaluate the accuracy and the best cut-off of CO-Hb in order to determine the smoking status in minimally injured patients in the emergency department. Methods: After informed consent and ethical committee approval 1283 minimally injured patients were assessed in the emergency department immediately after admission with a computer-based questionnaire including the ‘Heaviness of Smoking Index’ questionnaire. Venous blood sampling and point-of-care oximetry, including CO-Hb, was performed. Results: Median age of all patients (smokers: males: 399, females: 176; nonsmokers: males: 420, females: 288) was 33 years. According to the receiver operating characteristics CO-Hb had an excellent ability to differentiate between smokers and nonsmokers (area under the curve: males: 0.949, females 0.932). Optimal CO-Hb cut-off was 1.8% in males (specificity 95.7%, sensitivity 85.5%) and 1.6% in females (specificity 96.9%, sensitivity 80.1%). Conclusion: CO-Hb was a good marker to detect current smoking in trauma patients. The cut-off of CO-Hb should be lowered to 1.6% in females and 1.8% in males.

Effects of carbon monoxide inhalation during experimental endotoxemia in humans

Data show that carbon monoxide (CO) exerts direct antiinflammatory effects in vitro and in vivo after LPS challenge in a mouse model. We hypothesized that CO may act as an antiinflammatory agent in human endotoxemia. The aim of this trial was to study the effects of CO inhalation on cytokine production during experimental human endotoxemia. The main study was a randomized, double-blinded, placebo-controlled, two-way cross-over trial in healthy volunteers. Each volunteer inhaled synthetic air (as placebo) and 500 ppm CO for 1 hour in random order with a washout period of 6 weeks and received a 2-ng/kg intravenous bolus of LPS after inhalation. Carboxyhemoglobin levels were assessed as a safety parameter. CO inhalation increased carboxyhemoglobin levels from 1.2% (95% confidence interval, 1.0 to 1.4%) to peak values of 7.0% (95% confidence interval, 6.5 to 7.7%). LPS infusion transiently increased plasma concentrations of tumor necrosis factor-alpha, interleukin (IL)-6 (approximately 150-fold increases), and IL-8, as well as IL-1alpha and IL-1beta mRNA levels (an approximately 200-fold increase). These LPS-induced changes were not influenced by CO inhalation. Inhalation of 500 ppm CO for 1 hour had no antiinflammatory effects in a systemic inflammation model in humans, as 250 ppm for 1 hour did in rodents.

Urban CO exposure and its health effects on traffic policemen in Ankara

Carbon monoxide (CO) is an important component of air pollution caused by traffic exhaust fumes. CO can cause chronic poisoning which shows its first symptoms as headaches, blurry vision, difficulty in concentration, and confusion. With the increasing number of vehicles in metropolitan areas of Turkey, the CO level has also increased in the city air as is the case in the capital city of Ankara, especially at certain locations. As far as the effects of CO on humans are concerned, traffic policemen are the population group under risk due to their inhalation of CO-rich air while on duty at the crowded cross-sections of the city. The traffic policemen on duty at these cross-sections are exposed to these high levels of CO for at least 6 h. This study was performed to investigate the traffic policemen (traffic organizers) who are exposed to high concentrations of CO at crowded cross-sections of Ankara City and to find out if chronic CO intoxication exits among this risk group. The CO levels in the ambient air at these cross-sections have also been compared to, and correlated with measurements of CO in the expired air of the target population. Additional factors like smoking, general health status, type of heating systems used at home, etc., have been taken into consideration by evaluating special questionnaires filled out by the policemen. A control group of clerk policemen, who were not engaged in street traffic activities was formed for comparative purposes.

Angiographic changes in saphenous vein grafts and atherosclerosis risk factors. A 5-year study with serial measurements of serum lipids and lipoproteins

The association between cardiovascular risk factors and stenosis or occlusion of saphenous vein grafts was analysed in a prospective 5-year study of 176 unselected patients with coronary artery bypass grafting (CABG). Methods included serial measurements of serum lipids and lipoproteins, determination of apolipoprotein E phenotype, lipoprotein (a) levels 5 years postoperatively, and subcutaneous fat biopsy to determine the fatty acid composition before and one year after CABG. Graft angiography with quantitative analysis of angiograms was performed at the end of follow-up. A coronary artery with diameter < or = 1.5 mm was associated with occlusion of vein grafts (p < 0.01). The mean levels of serum lipids and lipoproteins, other traditional risk factors for atherosclerosis, and subcutaneous fatty acid composition were similar in patients with and without graft occlusion, and similar when the maximum diameter of non-occluded grafts was < 50% vs > or = 50%, and < 25% vs > or = 25%. High lipoprotein (a) concentration tended to be associated with obstructive changes in vein grafts. Our data indicate that, because lipids, lipoproteins and other traditional cardiovascular risk factors do not predict occlusion or stenosis of saphenous vein grafts five years after CABG, it is not currently possible to predict directly from the levels of these risk factors which patients are likely to benefit from pharmacological or other interventions.

[Reference values for carboxyhemoglobin]

INTRODUCTION

The reference values (RV) of biological indicators are used in the interpretation of the results of such indicators in individuals occupationally exposed to chemical agents. The Brazilian Group for the Establishment of Reference Values has worked on these definitions for the purpose of establishing RVs for several bioindicators in various regions of the country. In the present study, the RV for carboxyhemoglobin (COHb) was determined for the South of Minas Gerais.

MATERIAL AND METHOD

The COHb was analyzed by the Beutler and West (1984) spectrophotometric method, optimized in our laboratory. In all the samples, analyses of some biochemical and hematological parameters were made to evaluate the health condition of a population of 200 volunteer non-smokers occupationally not exposed to CO. Each individual answered a questionnaire to obtain data pertinent to the interpretation of the results. The reference values were expressed as mean values +/- standard deviation, with a 95% confidence interval, and an upper reference value. The statistical distribution of the results was made so as to enable comparisons between the results of groups of workers, rather than individual evaluations, to be made.

RESULTS AND CONCLUSIONS

The mean value +/- standard deviation was 1.0% +/- 0.75; the 95% confidence interval was 0.9-1.1% and the upper reference value was 2.5%. By the t Student test (p < or = 0.05), no difference was detected between the values related to sex, age or ingestion of alcoholic beverages. The reference values obtained were close to those reported for others countries.