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

Carboxyhemoglobin half-life toxicokinetic profiles during and after normobaric oxygen therapy: On a swine model

Investigations on acute carbon monoxide (CO) poisoning struggle to highlight a relevant discriminant criterion related to CO poisoning severity for predicting complications, such as delayed neurological syndromes. In this context, it remains difficult to demonstrate the superiority of one method of oxygen (O2) administration over others or to identify the optimal duration of normobaric 100% oxygen (NBO) treatment. Myoglobin, as hemoglobin, are a potential binding site for CO, which could be a source of extravascular CO storage that impacts the severity of CO poisoning. It is not possible in routine clinical practice to estimate this potential extravascular CO storage. Indirect means of doing so that are available in the first few hours of poisoning could include, for example, the carboxyhemoglobin half-life (COHbt1/2), which seems to be influenced itself by the level and duration of CO exposure affecting this store of CO within the body. However, before the elimination of CO can be assessed, the COHbt1/2 toxicokinetic model must be confirmed: research still debates whether this model mono- or bi-compartmental. The second indirect mean could be the assessment of a potential COHb rebound after COHb has returned to 5% and NBO treatment has stopped. Moreover, a COHb rebound could be considered to justify the duration of NBO treatment. On an experimental swine model exposed to moderate CO poisoning (940 ppm for ±118 min until COHb reached 30%), we first confirm that the COHb half-life follows a bi-compartmental model. Secondly, we observe for the first time a slight COHb rebound when COHb returns to 5% and oxygen therapy is stopped. On the basis of these two toxicokinetic characteristics in favor of extravascular CO storage, we recommend that COHbt1/2 is considered using the bi-compartmental model in future clinical studies that compare treatment effectiveness as a potential severity criterion to homogenize cohorts of the same severity. Moreover, from a general toxicokinetic point of view, we confirm that a treatment lasting less than 6 hours appears to be insufficient for treating moderate CO poisoning.

Association of Cigarette Smoking History With Drug Abuse History and Arterial Carboxyhemoglobin in Trauma Activation Patients: A Retrospective Study

Introduction The relationship between cigarette smoking and arterial carboxyhemoglobin (CoHb) in trauma activation patients has not been investigated. The aim was to determine if cigarette smoking is associated with drug abuse history and arterial CoHb levels. Methodology This is a retrospective review of level I trauma center activations aged 18-60 during 2018-2020. A medical record audit was performed to assess each patient's cigarette smoking and drug abuse history and admission arterial CoHb level. The CoHb levels and smoking history for each patient were used to construct a receiver operating characteristic curve. Results Of the 742 trauma activations aged 18-60, 737 (99.3%) had a documented cigarette smoking history. Smoking history was positive in 49.7% (366) and negative in 50.3% (371). The positive smoking proportion was greater in patients with a drug abuse history (63.9% (234/366)) than those with a negative history (31.0% (115/371); p<0.0001; odds ratio=4.0). In 717 patients with a CoHb value, the CoHb was higher in smokers (3.9±2.2%) than in non-smokers (0.5±0.4%; p<0.0001; Cohen d=2.2). A CoHb >1.5% was higher in smokers (93.3% (333/357)) than non-smokers (1.7% (6/360); p<0.0001; odds ratio=818.6). The receiver operating characteristic curve for the relationship between CoHb and cigarette smoking history showed an area under the curve of 0.980 (p<0.0001). Using an arterial CoHb level >1.5% to predict a positive smoking history and a CoHb level ≤1.5% to predict a non-smoking history, sensitivity was 93.3% (333/357), specificity was 98.3% (354/360), and accuracy was 95.8% (687/717). Conclusion Cigarette smoking in trauma activations aged 18-60 is associated with drug abuse history and increased arterial CoHb levels on trauma center arrival.

Unexpected carboxyhemoglobin half-life during cardiopulmonary resuscitation: a case report

BACKGROUND

Cardiac arrest (CA) following CO poisoning (CO-induced CA) exposes patients to an extremely high risk of mortality and remains challenging to treat effectively. Terminal carboxyhemoglobin elimination half-life (COHbt_1/2) is critically affected by ventilation, oxygen therapy, and cardiac output, which are severely affected conditions in cases of CA.

CASE PRESENTATION

Asystole occurred in an 18-year-old woman after unintentional exposure to CO in her bathroom. Cardiopulmonary resuscitation (CPR) was started immediately, including mechanical ventilation with a fraction of inspired oxygen (FiO₂) of 1.0 and external chest compressions with a LUCAS® device. CPR was stopped after 101 min, as it was unsuccessful. During this period, we calculated a COHbt_1/2 of 40.3 min using a single compartmental model.

CONCLUSIONS

This result suggests that prolongation of CPR time needed to back COHb at 10%, a level more compatible with successful return of spontaneous circulation (ROSC), could be compatible with a realistic CPR time. Calculating COHbt_1/2 during CPR may help with decision-making regarding the optimal duration of resuscitation efforts and further with HBO₂ or ECLS. Further evidence-based data are needed to confirm this result.

Heme Oxygenase-1 and Blood Bilirubin Are Gradually Activated by Oral D-Glyceric Acid

It has been shown that small doses of oral D-glyceric acid (DGA) activate mitochondrial metabolism and reduce inflammation among 50-60-year-old healthy volunteers. The present results with the same small doses reveal that after a 4-day DGA regimen, a dose of DGA activated the HO-1 pathway acutely, while enhanced inflammatory status after the 4-day DGA regimen seemed to be able to downregulate the HO-1 pathway in non-acute measurement. Blood bilirubin was strongly upregulated towards the end of the altogether 21-day study period with positive associations towards improved inflammation and reduced blood triglycerides. After the 4-day DGA regimen, hepatic inflow of blood bilirubin with albumin as the carrier was clearly upregulated in the lower-aerobic-capacity persons. At the same time also, blood triglycerides were down, pointing possibly to the activation of liver fatty acid oxidation. The combination of activated aerobic energy metabolism with transient HO-1 pathway activation and the upregulation of blood bilirubin may reduce the risks of chronic diseases, especially in aging. Furthermore, there exist certain diseases with unsatisfactorily-met medical needs, such as fatty and cholestatic liver diseases, and Parkinson's disease, that can be possibly ameliorated with the whole-body mechanism of the action of the DGA regimen.

Can Exhaled Carbon Monoxide Be Used as a Marker of Exposure? A Cross-Sectional Study in Young Adults

Carbon monoxide (CO) poisoning is a major public health issue worldwide. People are exposed to CO in their daily lives, with one of the common sources of CO being cigarette smoking. Inhalation of CO leads to elevated carboxyhaemoglobin (COHb) levels in the blood and also in exhaled CO concentration. Several factors have been shown to affect COHb concentration and COHb half-life. However, factors affecting exhaled CO concentration and exhaled CO half-life are not well understood. The present study aimed to investigate the potential factors related to baseline exhaled CO concentration and exhaled CO half-life among smokers. A cross-sectional study was conducted between 26 January and 30 June 2019, and young adults were recruited into the study. A total of 74 participants (mean age: 27.1 years, 71.6% males and 28.4% females) attended the study. They were invited to complete a questionnaire, including demographic, physiological, and behavioural factors. Then, exhaled CO measurements were taken. These measurements were taken before and after smoking a single cigarette for smokers and only once for non-smokers. The average baseline exhaled CO concentration was 6.9 ± 4.9 ppm for smokers and 1.9 ± 0.5 ppm for non-smokers. The mean of exhaled CO half-life was around 273.3 min (4.6 h) for smokers. No difference was seen in exhaled CO half-life between light smokers and heavy smokers in the smoking group. Gender and cigarettes smoked weekly affected baseline exhaled CO in smokers. Even though height seemed to positively associate with exhaled CO half-life, the relationship disappeared when adjusting by gender and weight. Therefore, exhaled CO could be used as a marker of CO exposure, but we cannot ignore the factors mentioned in the study. For future study, considering factors related to smoking habits and smoking style are recommended as these may affect total inhaled CO.

Carbon Monoxide Poisoning in Kuwait: A Five-Year, Retrospective, Epidemiological Study

BACKGROUND

Carbon monoxide (CO) poisoning is a major public health concern and a common cause of death worldwide. However, to our knowledge, no studies have been conducted on CO poisoning exposure and mortality in Kuwait.

OBJECTIVES

Using epidemiological and forensic data analysis, we investigated the prevalence and characteristics of CO poisoning-associated deaths in Kuwait over five years (2014-2018), using official police data.

METHODS

The Forensic Toxicology Laboratory analyzed 203 blood specimens of deceased individuals for potential CO poisoning during the study period. We obtained demographic information of the deceased and other information regarding the source of the CO, the type of death and the seasonal and geographical distribution of fatalities. The percentage of carboxyhemoglobin (COHb%) was assessed using a CO-oximeter.

RESULTS

CO poisoning was confirmed in ~29% (59 cases) of the analyzed specimens, of which CO poisoning was accidental in the majority of cases (~95%) and homicidal in the remaining of cases (~5%), with no reported suicides. The five-year cumulative mean of COHb% in the blood specimens of the 59 confirmed cases was ~63%. Most of the deceased were males (~68%). The mean age of male and female victims per year were similar (~23-38 years). Fatalities were more common (~44%) during the winter (December-February). Uncontrolled home fires and coal stoves contributed to the primary sources of CO poisoning at 61% and 22%, respectively.

RECOMMENDATIONS

Based on our findings, we propose that the local government should mandate the installation of smoke alarms and CO detectors in residential settings and endorse health education, informing the local population about the causes of fire and potential for CO poisoning, with an emphasis on prevention. Practical measures that can be applied include proper installation and regular maintenance of home-heating appliances and appropriate ventilation. The present study could greatly benefit the government in directing efforts toward decreasing CO poisoning incidents in Kuwait in the future.

The Role of Gasotransmitters in Gut Peptide Actions

Although gasotransmitters nitric oxide (NO), carbon monoxide (CO) and hydrogen sulfide (H₂S) receive a bad connotation; in low concentrations these play a major governing role in local and systemic blood flow, stomach acid release, smooth muscles relaxations, anti-inflammatory behavior, protective effect and more. Many of these physiological processes are upstream regulated by gut peptides, for instance gastrin, cholecystokinin, secretin, motilin, ghrelin, glucagon-like peptide 1 and 2. The relationship between gasotransmitters and gut hormones is poorly understood. In this review, we discuss the role of NO, CO and H₂S on gut peptide release and functioning, and whether manipulation by gasotransmitter substrates or specific blockers leads to physiological alterations.

Variation of DNA Methylation in Newborns Associated with Exhaled Carbon Monoxide during Pregnancy

Fetal exposure to tobacco smoke is an adverse risk factor for newborns. A plausible mechanism of how this exposure may negatively impact long term health is differential methylation of deoxyribonucleic acid (DNAm) and its relation to birth weight. We examined whether self-reported gestational smoking status and maternal exhaled carbon monoxide (eCO) during early pregnancy were associated with methylation of cytosine by guanines (CpG) sites that themselves predicted birth weight. We focused first on CpGs associated with maternal smoking, and secondly, among these, on CpGs related to birth weight found in another cohort. Then in 94 newborns from the Breathing for Life Trial (BLT) DNAm levels in cord blood were determined using Infinium Methylation EPIC BeadChip measuring >850K CpGs. We regressed CpGs on eCO and tested via mediation analysis whether CpGs link eCO to birth weight. Nine smoking related CpG sites were significantly associated with birth weight. Among these nine CpGs the methylation of cg02264407 on the LMO7 gene was statistically significant and linked with eCO measurements. eCO greater than six ppm showed a 2.3% decrease in infant DNAm (p = 0.035) on the LMO7 gene. A 1% decrease in methylation at this site resulted in decreased birth weight by 44.8 g (p = 0.003). None of the nine CpGs tested was associated with self-reported smoking. This is the first study to report potential mediation of DNA methylation, linking eCO measurements during early pregnancy with birth weight.