Carbon monoxide in the pregnant mother and fetus and its exchange across the placenta

Neonatal/perinatal diagnosis of hemolysis using ETCOc

Hemolysis is a pathological shortening of the red blood cell lifespan. When hemolysis occurs in a neonate, hazardous hyperbilirubinemia and severe anemia could result. Hemolysis can be diagnosed, and its severity quantified, by the non-invasive measurement of carbon monoxide (CO) in exhaled breath. The point-of-care measurement is called "End-tidal CO corrected for ambient CO" (ETCOc). Herein we explain how ETCOc measurements can be used to diagnose and manage various perinatal/neonatal hemolytic disorders. We provide information regarding five clinical situations; 1) facilitating a precise diagnosis among neonates presenting with anemia or jaundice of unknown etiology, 2) monitoring fetal hemolysis with serial measurements of mothers during pregnancy, 3) measuring the duration of hemolysis in neonates with hemolytic disease, 4) measuring neonates who require phototherapy, to determine whether they have hemolytic vs. non-hemolytic jaundice, and 5) measuring all neonates in the birth hospital as part of a jaundice-detection and management program.

Effect of environmental air pollutants on placental function and pregnancy outcomes: a molecular insight

Air pollution has become a major health concern, particularly for vulnerable populations such as the elderly, children, and pregnant women. Studies have reported a strong association between prenatal exposure to air pollutants and adverse pregnancy outcomes, including lower birth weight, reduced fetal growth, and an increased frequency of preterm births. This review summarizes the harmful effects of air pollutants, such as particulate matter, on pregnancy and outlines the mechanistic details associated with these adverse outcomes. Particulate pollutant matter may be able to cross the placenta barrier, and alterations in placental functions are central to the detrimental effects of these pollutants. In addition to associations with preeclampsia and gestational hypertension, air pollutants also induce oxidative stress, inflammation, and epigenetic alteration in the placenta. These pollutants can also affect placental homeostasis and endocrine function, contributing to pregnancy complications and possible transgenerational effects. Prenatal air pollution exposure has been linked to reduced cognitive and motor function in infants and newborns, increasing the predisposition to autism spectrum disorders and other neuropsychiatric disorders. This review also summarizes the use of various animal models to study the harmful effects of air pollution on pregnancy and postnatal outcomes. These findings provide valuable insight into the molecular events associated with the process and can aid in risk mitigation and adopting safety measures. Implementing effective environmental protocols and taking appropriate steps may reduce the global disease burden, particularly for developing nations with poor regulatory compliance and large populations of pregnant women.

Carbon Monoxide as a Potential Therapeutic Agent: A Molecular Analysis of Its Safety Profiles

Carbon monoxide (CO) is endogenously produced in mammals, with blood concentrations in the high micromolar range in the hemoglobin-bound form. Further, CO has shown therapeutic effects in various animal models. Despite its reputation as a poisonous gas at high concentrations, we show that CO should have a wide enough safety margin for therapeutic applications. The analysis considers a large number of factors including levels of endogenous CO, its safety margin in comparison to commonly encountered biomolecules or drugs, anticipated enhanced safety profiles when delivered via a noninhalation mode, and the large amount of safety data from human clinical trials. It should be emphasized that having a wide enough safety margin for therapeutic use does not mean that it is benign or safe to the general public, even at low doses. We defer the latter to public health experts. Importantly, this Perspective is written for drug discovery professionals and not the general public.

Carbon Monoxide Poisoning: From Occupational Health to Emergency Medicine

Carbon monoxide poisoning remains a leading cause of accidental poisoning worldwide (both at home and at work), and it is also a cause of suicidal poisoning. Such poisoning can arise following prolonged exposure to low levels of CO or following brief exposure to high concentrations of the gas. In fact, despite exposure limits, high safety standards, and the availability of CO alarms, nearly 50,000 people in the United States visit the emergency department each year due to poisoning. Additionally, CO poisoning in the United States causes up to 500 deaths each year. Despite the widespread nature of this form of poisoning, known about for centuries and whose damage mechanisms have been recognized (or rather hypothesized about) since the 1800s, early recognition, especially of late complications, and treatment remain a medical challenge. A well-designed therapeutic diagnostic process is necessary so that indication for hyperbaric or normobaric therapy is correctly made and so that patients are followed up even after acute exposure to diagnose late complications early. Furthermore, it is necessary to consider that in the setting of emergency medicine, CO poisoning can be part of a differential diagnosis along with other more frequent conditions, making its recognition difficult. The last thirty years have been marked by a significant increase in knowledge regarding the toxicity of CO, as well as its functioning and its importance at physiological concentrations in mammalian systems. This review, taking into account the significant progress made in recent years, aims to reconsider the pathogenicity of CO, which is not trivially just poisonous to tissues. A revision of the paradigm, especially as regards treatment and sequelae, appears necessary, and new studies should focus on this new point of view.

Carbon Monoxide and Cyanide Poisoning in the Burned Pregnant Patient: An Indication for Hyperbaric Oxygen Therapy

Carbon monoxide (CO) is a small molecule poison released as a product of incomplete combustion. Carbon monoxide binds hemoglobin, reducing oxygen delivery. This effect is exacerbated in the burned pregnant patient by fetal hemoglobin that binds CO 2.5- to 3-fold stronger than maternal hemoglobin. With no signature clinical symptom, diagnosis depends on patient injury history, elevated carboxyhemoglobin levels, and alterations in mental status. The standard of care for treatment of CO intoxication is 100% normobaric oxygen, which decreases the half-life of CO in the bloodstream from 5 hours to 1 hour. Hyperbaric oxygen (HBO2) is a useful adjunct to rapidly reduce the half-life of CO to 20 minutes and the incidence of delayed neurologic sequelae. Because of the slow disassociation of CO from hemoglobin in the fetus, there is a far stronger indication for HBO2 in the burned pregnant patient than in other burn patient populations.Cyanide intoxication is often a comorbid disease with CO in inhalation injury from an enclosed fire, but may be the predominant toxin. It acts synergistically with CO to effectively lower the lethal doses of both cyanide and CO. Diagnosis is best made in the presence of high lactate levels, carboxyhemoglobin concentrations greater than 10%, injury history of smoke inhalation from an enclosed fire, and alterations in consciousness. While treatment with hydroxocobalamin is the standard of care and has the effect of reducing concomitant CO toxicity, data indicate cyanide may also be displaced by HBO2.Carbon monoxide and cyanide poisoning presents potential complications impacting care. This review addresses the mechanism of action, presentation, diagnosis, and treatment of CO and cyanide poisonings in the burned pregnant patient and the use of HBO2 therapy.

Health Effects of Indoor Air Pollution

Exposure to indoor-generated air pollution causes a large number of deaths and cases of disease. These effects are found, largely, in developing countries where people, especially women and young children, are exposed to high concentrations of smoke produced by biomass burning for cooking. Approximately 3 million deaths occur each year. In developed countries, the problem is much less acute: accidental exposure to high concentrations of carbon monoxide is the main cause of death. It should be remembered, however, that much of people's exposure to pollutants generated outdoors occurs in the indoor environment. Indoor exposure to particulate matter has the same effects as outdoor exposure: the cardiovascular system is most affected, with deaths being due to ischaemic heart disease and stroke. Exposure to particulate matter may also contribute to the development of chronic obstructive pulmonary disease (COPD). Exposure to high concentrations of nitrogen dioxide, although perhaps not having a great effect on measures of lung function, may contribute to the development of emphysema and reduce the resistance of the body to bacterial and viral infections. Lung cancer, due to exposure to carcinogens in wood smoke, also occurs. Efforts to reduce levels of indoor air pollution in developing countries, for example by providing flued cooking stoves, have been shown to reduce the prevalence of disease.

The implications of high carbon monoxide levels in early pregnancy for neonatal outcomes

OBJECTIVES

The aim of this study was to examine the implications of increased maternal Breath Carbon Monoxide (BCO) levels at the first antenatal visit for subsequent birthweight (BW) and neonatal outcomes.

STUDY DESIGN

Secondary analysis of a prospective, observational study. Pregnant women aged ≥18years who understood English were recruited (n=250). However, only women who delivered a normally formed baby weighing ≥500g were analysed (n=234). At the first antenatal visit, a research questionnaire was completed and a BCO test was performed. Obstetric and neonatal data computerised by midwives at the first antenatal visit and updated after delivery were also analysed.

RESULTS

Results from the receiver operating characteristic (ROC) curve indicated the highest combined sensitivity and specificity for smoking was observed at a BCO cut-off level of 3ppm (sensitivity 85%, specificity 90%). Of the 234 women, 53 (22.6%) had a BCO ≥3ppm but only 36 (15.4%) disclosed smoking to the midwife on routine questioning. A further 23 (9.8%) were classified as non-disclosers based on a research questionnaire and/or a BCO measurement ≥3ppm. No relationship was found between the self-reported number of cigarettes daily in early pregnancy and BW (r=0.05, p=0.78). However, an inverse relationship was found between maternal BCO levels and BW (r=-0.31, p<0.001). BCO levels ≥3ppm in early pregnancy were associated with an increased risk of emergency caesarean section, low birth weight, BW <25th centile, fetal distress and having two or more adverse pregnancy events (all p<0.05). Smoking non-disclosers had babies with decreased BWs (-400.1g, 95% CI 141.1-659.0g, p<0.001), and higher rates of BW <25th centile (56.5% versus 25.3%, p<0.001), small-for-gestational-age (21.7% versus 9.1%, p<0.001) and fetal distress (39.1% versus 16.0%, p<0.01) compared to non-smokers Non-disclosers at the first antenatal visit also had a 22% higher rate of having two or more adverse pregnancy events (p<0.05).

CONCLUSION

The results showed that an increased BCO level was associated with a lower BW and increased risk of adverse pregnancy and neonatal outcomes. This strengthens the case for universal BCO screening at the first antenatal visit. A high BCO reading should be an indication for referral to stop smoking services referral and close fetal surveillance.

Carbon Monoxide Exposure During Pregnancy

IMPORTANCE

Carbon monoxide (CO) is the leading cause of poisoning in the United States and is associated with high maternal and fetal mortality rates. Given the nonspecific signs and symptoms of toxicity, cases may go unsuspected or attributed to other etiologies. As CO adversely affects both mother and fetus, it is important for practitioners to recognize and treat poisoning in a timely manner.

OBJECTIVE

We seek to assist practitioners with understanding the physiology and recognizing the presentations of both acute and chronic CO poisoning, as well as provide information on diagnosis and treatment options. We also conducted a review of cases described in the literature during the past half century to show varying presentations and treatment methodologies.

EVIDENCE ACQUISITION

A qualitative literature search was conducted using PubMed and Google Scholar for articles published between 1970 and 2014 that assessed cases of CO poisoning during pregnancy. Excluded studies were not in English or contained nonhuman subjects.

RESULTS

Nineteen published reports of CO poisoning during pregnancy described in varying levels of detail were found in the literature from 1971 to 2010.

CONCLUSIONS AND RELEVANCE

Carbon monoxide poisoning requires a high degree of suspicion. Diagnosis is made based on initial history and physical evaluation and assessment of environmental CO levels; presenting carboxyhemoglobin levels may be poor indicators of severity of disease. Oxygen therapy should be initiated promptly in all possible cases with consideration of hyperbaric oxygen therapy in cases of significant maternal exposure. Treatment requires a longer duration for fetal CO elimination than in the nonpregnant patients. Importantly, practitioners should educate pregnant patients on prevention.

Prenatal carbon monoxide impairs migration of interneurons into the cerebral cortex

Prenatal exposure to carbon monoxide (CO) disrupts brain development, however little is known about effects on neocortical maturation. We exposed pregnant mice to CO from embryonic day 7 (E7) until birth. To study the effect of CO on neuronal migration into the neocortex we injected BrdU during corticogenesis and observed misplaced BrdU+ cells. The majority of cells not in their proper layer colocalized with GAD65/67, suggesting impairment of interneuron migration; interneuron subtypes were also affected. We subsequently followed interneuron migration from E15 organotypic cultures of mouse neocortex exposed to CO; the leading process length of migrating neurons diminished. To examine an underlying mechanism, we assessed the effects of CO on the cellular cascade mediating the cytoskeletal protein vasodilator-stimulated phosphoprotein (VASP). CO exposure resulted in decreased cGMP and in a downstream target, phosphorylated VASP. Organotypic cultures grown in the presence of the phosphodiesterase inhibitor IBMX resulted in a recovery of the leading processes. These data support the idea that CO acts as a signaling molecule and impairs function and neuronal migration by acting through the CO/NO-cGMP pathway. In addition, treated mice demonstrated functional impairment in behavioral tests.

Carbon monoxide pollution and neurodevelopment: A public health concern

Although an association between air pollution and adverse systemic health effects has been known for years, the effect of pollutants on neurodevelopment has been underappreciated. Recent evidence suggests a possible link between air pollution and neurocognitive impairment and behavioral disorders in children, however, the exact nature of this relationship remains poorly understood. Infants and children are uniquely vulnerable due to the potential for exposure in both the fetal and postnatal environments during critical periods in development. Carbon monoxide (CO), a common component of indoor and outdoor air pollution, can cross the placenta to gain access to the fetal circulation and the developing brain. Thus, CO is of particular interest as a known neurotoxin and a potential public health threat. Here we review overt CO toxicity and the policies regulating CO exposure, detail the evidence suggesting a potential link between CO-associated ambient air pollution, tobacco smoke, and learning and behavioral abnormalities in children, describe the effects of subclinical CO exposure on the brain during development, and provide mechanistic insight into a potential connection between CO exposure and neurodevelopmental outcome. CO can disrupt a number of critical processes in the developing brain, providing a better understanding of how this specific neurotoxin may impair neurodevelopment. However, further investigation is needed to better define the effects of perinatal CO exposure on the immature brain. Current policies regarding CO standards were established based on evidence of cardiovascular risk in adults with pre-existing comorbidities. Thus, recent and emerging data highlighted in this review regarding CO exposure in the fetus and developing child may be important to consider when the standards and guidelines are evaluated and revised in the future.

Involvement of the Heme Oxygenase System in the Development of Preeclampsia and as a Possible Therapeutic Target

The enzyme heme oxygenase (HO) is an important regulatory molecule present in most nucleated mammalian cells which functions to break down the pro-oxidant molecule heme into three products, carbon monoxide (CO), biliverdin and free iron. The HO system has been associated with many physiologic functions, including vascular tone, regulation of inflammation and apoptosis, angiogenesis and antioxidant capabilities. Deficiencies in HO are associated with several pregnancy disorders, including preeclampsia. With no present cure, this disorder continues to affect 5–7% of all pregnancies worldwide, leading to maternal and fetal morbidity and mortality. Researchers continue to strive for therapeutic potentials and this review will outline the possible use of the HO/CO system as a target treatment/prevention of preeclampsia in the future.

Chronic carbon monoxide inhalation during pregnancy augments uterine artery blood flow and uteroplacental vascular growth in mice

End-tidal breath carbon monoxide (CO) is abnormally low in women with preeclampsia (PE), while women smoking during pregnancy have shown an increase in CO levels and a 33% lower incidence of PE. This effect may be, in part, due to lowered sFLT1 plasma levels in smokers, and perhaps low-level CO inhalation can attenuate the development of PE in high-risk women. Our previous work showed maternal chronic CO exposure (<300 ppm) throughout gestation had no maternal or fetal deleterious effects in mice. Our current study evaluated the uteroplacental vascular effects in CD-1 maternal mice that inhaled CO (250 ppm) both chronically, gestation day (GD) 0.5 to 18.5, and acutely, 2.5 h on each of GD 10.5 and 14.5. We demonstrated, using microultrasound measurements of blood velocity and microcomputed tomography imaging of the uteroplacental vasculature, that chronic maternal exposure to CO doubled uterine artery blood flow and augmented uteroplacental vascular diameters and branching. This finding may be of benefit to women with PE, as they exhibit uteroplacental vascular compromise. The ratio of VEGF protein to its FLT1 receptor was increased in the placenta, suggesting a shift to a more angiogenic state; however, maternal circulating levels of VEGF, sFLT1, and their ratio were not significantly changed. Doppler blood velocities in the maternal uterine artery and fetal umbilical artery and vein were unaltered. This study provides in vivo evidence that chronic inhalation of 250 ppm CO throughout gestation augments uterine blood flow and uteroplacental vascular growth, changes that may protect against the subsequent development of preeclampsia.

Effects of chronic carbon monoxide exposure on fetal growth and development in mice

BACKGROUND

Carbon monoxide (CO) is produced endogenously, and can also be acquired from many exogenous sources: ie. cigarette smoking, automobile exhaust. Although toxic at high levels, low level production or exposure lends to normal physiologic functions: smooth muscle cell relaxation, control of vascular tone, platelet aggregation, anti- inflammatory and anti-apoptotic events. In pregnancy, it is unclear at what level maternal CO exposure becomes toxic to the fetus. In this study, we hypothesized that CO would be embryotoxic, and we sought to determine at what level of chronic CO exposure in pregnancy embryo/fetotoxic effects are observed.

METHODS

Pregnant CD1 mice were exposed to continuous levels of CO (0 to 400 ppm) from conception to gestation day 17. The effect on fetal/placental growth and development, and fetal/maternal CO concentrations were determined.

RESULTS

Maternal and fetal CO blood concentrations ranged from 1.12- 15.6 percent carboxyhemoglobin (%COHb) and 1.0- 28.6%COHb, respectively. No significant difference was observed in placental histological morphology or in placental mass with any CO exposure. At 400 ppm CO vs. control, decreased litter size and fetal mass (p < 0.05), increased fetal early/late gestational deaths (p < 0.05), and increased CO content in the placenta and the maternal spleen, heart, liver, kidney and lung (p < 0.05) were observed.

CONCLUSIONS

Exposure to levels at or below 300 ppm CO throughout pregnancy has little demonstrable effect on fetal growth and development in the mouse.

Association between maternal exposure to ambient air pollution and congenital heart disease: A register-based spatiotemporal analysis

Recent studies have linked maternal exposure to air pollution with a range of adverse pregnancy outcomes. However, the available evidence linking this exposure to congenital anomalies is still limited and controversial. The present case-control study tested the hypothesis that maternal exposure to ambient black smoke and sulfur dioxide is a risk factor for the occurrence of congenital heart disease. The authors used registry-based data on congenital heart disease for the population of the northeast of England in 1985-1996. A 2-stage spatiotemporal model was developed to predict weekly black smoke and sulfur dioxide levels at each maternal place of residence. Controls were frequency-matched to cases by year of birth (control-to-case ratio of 4:1). Two sets of analyses were performed, using predicted mean values of exposure and 1,000 simulated scenarios of exposure. The analyses were adjusted for birth year, socioeconomic status, infant sex, season of conception, and degree of urbanity. The authors found a weak association between maternal exposure to black smoke and congenital malformations of cardiac chambers and connections only when using exposure as a continuous variable. When the authors used quartiles of exposure, odds ratios did not show a dose-response relation for consecutive quartiles. For sulfur dioxide, the results were not indicative of any association.

Endogenous carbon monoxide production in disease

Carbon monoxide (CO) in tissues and cells can originate from inhalation of CO or endogenously. Endogenous production, carboxyhemoglobin (COHb) formation, and exhaled CO levels are influenced by physiological factors, including disease. It is suggested that endogenous CO production can be used as a biomarker for oxidative and inflammatory processes. Also, endogenous CO can contribute to increased body burden of CO, which may both disrupt normal CO signaling cascades and increase the risk of CO toxicity.

Toxicity Associated with Carbon Monoxide

Carbon monoxide is an insidious poison that accounts for thousands of deaths each year in North America. Clinical effects maybe diverse and include headache, dizziness, nausea, vomiting,syn-cope, seizures, coma, dysrhythmias, and cardiac ischemia. Children, pregnant women, and patients who have underlying cardiovascular disease are particularly at risk for adverse out-comes. Treatment consists of oxygen therapy, supportive care, and, in selected cases, hyperbaric oxygen therapy.

Carbon monoxide poisoning

CO is an ubiquitous poison with many sources of exposure. CO poisoning produces diverse signs and symptoms that are often subtle and may be easily misdiagnosed. Failure to diagnose CO poisoning may result insignificant morbidity and mortality and permit continued exposure to a dangerous environment. Treatment of CO poisoning begins with inhalation of supplemental oxygen and aggressive supportive care. HBOT accelerates dissociation of CO from hemoglobin and may also prevent DNS. Absolute indications forHBOT for CO poisoning remain controversial, although most authors would agree that HBOT is indicated in patients who are comatose or neurologically abnormal, have a history of LOC with their exposure, or have cardiac dysfunction. Pregnancy with an elevated CO-Hgb level(>15%-20%) is also widely, considered an indication for treatment.HBOT may be considered in patients who have persistent symptoms despite NBO, metabolic acidosis, abnormalities on neuropsychometric testing, or significantly elevated levels. The ideal regimen of oxygen therapy has yet to be determined, and significant controversy exists regarding HBOTtreatment protocols. Often the local medical toxicologist, poison control center, or hyperbaric unit may assist the treating physician with decisions regarding therapy.

Limiting iron availability confers neuroprotection from chronic mild carbon monoxide exposure in the developing auditory system of the rat

Iron deficiency and chronic mild carbon monoxide (CO) exposure are nutritional and environmental problems that can be experienced simultaneously. We examined the effects of chronic mild CO exposure and iron availability on auditory development in the rat. We propose that chronic mild CO exposure creates an oxidative stress condition that impairs the spiral ganglion neurons. The CO-exposed rat pups had decreased neurofilament proteins and increased copper, zinc-superoxide dismutase (SOD1) in the spiral ganglion neurons. We conclude that the increased amount of SOD1 causes an increase in hydrogen peroxide production that allows the Fenton reaction to occur. This reaction uses both iron and hydrogen peroxide to generate hydroxyl radicals and leads to the development of oxidative stress that impairs neuronal integrity. However, rat pups with decreased iron and CO exposure (ARIDCO) exhibited in their cochlea an up-regulation of transferrin, whereas their expression of neurofilament proteins and SOD1 were similar to control. Consequently, reduced iron availability and the normal expression of SOD1 do not promote oxidative stress in the cochlea. By using basal c-Fos expression as a marker for cellular activation we found a significant reduction in c-Fos expression in the central nucleus of the inferior colliculus in iron-adequate rat pups exposed to CO. By contrast, rather than being reduced, c-Fos expression in the ARIDCO group is the same as for controls. We conclude that the cochlea of rat pups with normal iron availability is selectively affected by mild CO exposure, causing a chronic oxidative stress, whereas limiting iron availability ameliorates the effect caused by mild CO exposure by averting conditions that facilitate oxidative stress.

Carbon monoxide poisoning

CO is an insidious poison with many sources of exposure. CO poisoning produces diverse signs and symptoms, which often are subtle and can be misdiagnosed easily. Failure to diagnose CO poisoning may result insignificant morbidity and mortality and allow continued exposure to a dangerous environment. In the ED, a high index of suspicion must be maintained for occult CO exposure. Headache, particularly when associated with certain environments, and flulike illness in the wintertime with symptomatic cohabitants should raise the index of suspicion in the ED significantly for occult CO poisoning. Emergency treatment of CO poisoning begins with inhalation of supplemental oxygen and aggressive supportive care. HBOT accelerates dissociation of CO from hemoglobin and may prevent DNS. Absolute indications for HBOT for CO poisoning remain controversial, although most would agree that HBOT is indicated in patients who are comatose, are neurologically abnormal, have a history of loss of consciousness with their exposure, or have cardiac dysfunction. Pregnancy with an elevated CO-Hgb level (>15-20%) also is widely considered an indication for treatment. HBOT may be considered in patients who have persistent symptoms despite NBO, metabolic acidosis, abnormalities on neuropsychometric testing, or significantly elevated levels. The ideal regimen of oxygen therapy has yet to be determined, and significant controversy exists regarding HBOT protocols. The emergency physician may be confronted with the difficult decision regarding disposition and even transfer to a hyperbaric facility. Often the local medical toxicologist, poison control center, or hyperbaric unit can assist the emergency physician with the decision-making process.

Molecular aspects of embryonic hemoglobin function

In order to provide the appropriate level of oxygen transport to respiring tissues, we need to produce a molecular oxygen transporting system to supplement oxygen diffusion and solubility. This supplementation is provided by hemoglobin. The role of hemoglobin in providing oxygen transport from lung to tissues in the adult is well-documented and functional characteristics of the fetal hemoglobin, which provide placental oxygen exchange, are also well understood. However the characteristics of the three embryonic hemoglobins, which provide oxygen transport during the first three months of gestation, are not well recognized. This review seeks to describe the state of our understanding of the temporal control of the expression of these proteins and the oxygen binding characteristics of the individual protein molecules. The modulation of the oxygen binding properties of these proteins, by the various allosteric effectors, is described and the structural origins of these characteristics are probed.

Smoking cessation in pregnant women

Cigarette smoking is considered the most significant modifiable cause of adverse pregnancy outcomes in US women. Smoking cessation in pregnant patients is one of the most effective ways to reduce negative pregnancy outcomes of fetal growth retardation, preterm delivery, and perinatal mortality. Research evidence documenting the effectiveness of health care provider interventions in smoking cessation has led to the PHS recommendation to screen and counsel every patient. Materials from the PHS and NCI are available to assist health care providers in developing a brief office-based intervention. Patient materials for distribution are also available. Increased use of office-based cessation strategies, of cessation programs in community-based interventions, and of pharmacologic therapies is necessary to remedy the public health burden of fetal exposure to tobacco. Relapse prevention methods using office-based and social support systems are important to improve long-term maintenance of cessation in women who quit smoking during pregnancy.

Association of fetal and maternal carboxyhemoglobin levels in normal and Rh-alloimmune pregnancies

OBJECTIVE

To compare paired antepartum fetal/maternal COHb ratios in whole blood from control and alloimmunized pregnancies and to examine the relationships between fetal and maternal COHb.

METHODS

COHb levels were measured in paired fetal and maternal blood samples obtained at cordocentesis in 47 control and 16 Rh-alloimmunized pregnancies. COHb was determined by gas chromatography. Results were analyzed by t-test, regression and analysis of covariance.

RESULTS

Although fetal/maternal COHb ratios for control and alloimmunized pregnancies were not statistically significantly different, i.e. 1. 11+/-0.04 and 1.26+/-0.09, respectively (P=0.09), fetal COHb levels were higher in Rh-alloimmunized fetuses (P=0.0002). Fetal COHb levels were also higher than paired maternal levels among the alloimmunized group (P=0.011), but not among the control group (1. 04+/-0.04, P=ns). In univariate regression analysis, fetal and maternal COHb levels were significantly correlated with one another in both control (r=0.52, P=0.0002) and alloimmunized pregnancy groups (r=0.52, P=0.05). Comparison of the slopes of the fetal versus maternal COHb plots for the two groups showed a significant difference (P=0.02), with the alloimmunized group having the steeper slope.

CONCLUSION

Differences in the antepartum fetal-maternal COHb relationships in control and alloimmunized groups likely reflect increased endogenous CO production among alloimmunized fetuses as a result of pathologic hemolysis.

Impact of addictive and harmful substances on fetal brain development

Animal models of alcohol, nicotine, and cocaine exposure have provided convincing evidence for prenatal effects on brain development caused by alterations in cell migration, signal transduction, and neurotransmitter function. The extrapolation to effects on the human nervous system is confounded by the multiplicity of factors affecting central nervous system development.

Effects of prenatal exposure to low concentrations of carbon monoxide on sexual behaviour and mesolimbic dopaminergic function in rat offspring

1. Inhalation of low concentrations of carbon monoxide (CO) by pregnant rats (75 and 150 p.p.m. from day 0 to day 20 of gestation) leads to changes in mesolimbic dopaminergic transmission associated with an impairment of sexual behaviour in male offspring. 2. Eighty day old males exposed in utero to CO (150 p.p.m.) exhibited a significant increase in mount/ intromission latency as well as a significant decrease in mount/intromission frequency. A significant decrease in ejaculation frequency was also found in CO (150 p.p.m.)-exposed animals. 3. The acute administration of amphetamine, at a dose (0.5 mg kg(-1) s.c.) stimulating copulatory activity in control rats, failed to reduce mount/intromission latency and did not increase mount frequency in 80-day offspring exposed to CO (150 p.p.m.) during gestation. 4. These behavioural alterations were paralleled by neurochemical changes (in vivo microdialysis) showing that prenatal CO exposure, at concentrations (150 p.p.m.) that did not affect basal extracellular levels of dopamine in the nucleus accumbens, blunted the amphetamine (0.5 mg kg(-1) s.c.)-induced increase in dopamine release in 80-day old male rats. 5. No significant changes in either behavioural or neurochemical parameters were observed in 10-month old rats exposed prenatally to CO. 6. Since the alterations in sexual behaviour and dopaminergic transmission have been produced by prenatal exposure to CO levels resulting in maternal blood carboxyhaemoglobin concentrations equivalent to those maintained by human cigarette smokers, the present data further point out the large risk that the smoking mother poses for her offspring.

Pathogenicity of carbon monoxide

The effects of carbon monoxide, one of the most commonly encountered toxic agents in forensic practice, have been known for a long time, but the nature of its bonding to the heme prosthetic group of hemoproteins has only recently been elucidated. In addition to reducing the oxygen capacity of the blood and the consequent systemic hypoxia, carbon monoxide interferes with the dissociation of oxyhemoglobin and the removal of carbon dioxide. Carbon monoxide also produces a direct cytotoxic effect by inactivating some intracellular respiratory enzymes, but the relative importance of these various mechanisms often remains uncertain, particularly with regard to the lesions in the brain and myocardium.

Prenatal exposure to carbon monoxide and vascular responsiveness of rat resistance vessels

The aim of the present study was to investigate the influence of prenatal exposure to carbon monoxide (CO) on vascular reactivity of rat resistance vessels, in different stages of neurogenesis. Both prenatally CO-exposed and control male Wistar pups (5-7, 9-11, 14-16, 20-22 days) were tested vs respective 60 day adult rats. The results showed that: (i) at 5-7 days of age, TTX caused a more marked inhibition of perivascular nerve stimulation (PNS)-evoked vasoconstriction in CO-exposed animals with respect to controls; (ii) the NO-related relaxant effect by ACh in CO-exposed group appeared earlier (5-7 days) than in control group (9-11 days); (iii) the contractile response evoked by ACh on resting tone disappeared earlier (after 14-16 days) than in control group (after 20-22 days). These observations suggested that CO-exposure might induce changes in nerve electrophysiological properties and might cause a precocious maturation of the NO-related enzymatic mechanism implicated in ACh-relaxation.

Effects of carbon monoxide and hypoxia on cleft lip in A/J mice

Epidemiologic evidence indicates an increase in cleft lip with or without cleft palate [CL(P)] in infants of mothers who smoke cigarettes. It appears that the principle mechanism is through carbon monoxide (CO) decreasing the oxygen (O2) available to the embryo. Previous studies have shown that maternal respiratory hypoxia can increase the incidence of CL(P) in mice. The present investigation was designed to analyze the effects of altered levels of CO and O2 in respiratory gases on the incidence of CL(P) in genetically susceptible A/J mice. Results from blood gas analysis, after a 24-hour exposure of pregnant mice during the time of primary palate development, showed that CO levels of 180 ppm in air decrease oxyhemoglobin (%O2Hb) and increased carboxyhemoglobin (%COHb) to slightly above the high end of the range found in human studies of cigarette smokers. Interestingly, the control COHb levels were higher in our CL(P) sensitive mouse strain compared with those of the range of increases found in human smokers, versus nonsmoker studies, and that the increase for treated mice (3x) was at the low end of the range for smokers. Decreasing O2 levels to 10% from 21% (normal percentage in air) more severely decreased %O2Hb and moderately decreased %COHb. At 24 hours of exposure, the incidence of CL(P) and resorption was approximately the same for both the CO and the control groups, but there were significant increases in the incidence of resorptions in the hypoxia group and of CL(P) in relation to the CO group.(ABSTRACT TRUNCATED AT 250 WORDS)

The adverse effects of tobacco smoking on reproduction and health: a review from the literature

This paper compromises a short literary review of the adverse consequences of tobacco smoking on reproduction, as well as on infant and adult health. Furthermore, attention is drawn to the bad effects of smoking on the nutritional status.

Teratogenicity and developmental toxicity of carbon monoxide in protein-deficient mice

Experiments were carried out to determine the teratogenicity and developmental toxicity of carbon monoxide (CO) in mice fed protein-deficient diets. Pregnant CD-1 mice were fed 27 (control), 16, 8, or 4% protein diets throughout gestation and each group was exposed to 0 (control), 65, 125, 250, or 500 ppm of CO from gestation days 8-18. The CO exposure was continuous except for daily watering, feeding or cage changing. The animals were killed on gestation day 18. Pregnancy status of the dams was examined. Fetuses were examined for gross and skeletal malformations. The percentages of dead or resorbed fetuses and of grossly malformed fetuses per litter were related to the CO exposure levels and inversely related to the dietary protein levels. All levels of CO and 8 or 4% protein diets significantly decreased the fetal weight of normal fetuses. The most commonly seen gross malformations were brachygnathia accompanied by protruding tongue, microstomia, microcephaly, open mouth, or open eyes. Most of the grossly malformed fetuses also had dry, bleached and wrinkled skin. An increased incidence of skull (interparietal or supraoccipital), and jaw (mandible or premaxilla) malformation; wavy ribs and scoliosis of spine; and limb unossifications were observed in the litters of dams fed protein-deficient diet and all levels of CO exposure. Malformed litters in each protein diet were related to CO exposure levels. The data suggest that CO is teratogenic under protein-deficient conditions. Protein deficiency had additive effect on CO teratogenicity and synergistic effect on fetal mortality. Special groups at risk may include cigarette or marijuana smokers and malnourished or undernourished populations.

A multicenter, prospective study of fetal outcome following accidental carbon monoxide poisoning in pregnancy

We report the results of the first prospective, multicenter study of acute carbon monoxide (CO) poisoning in pregnancy. We collected and followed cases of CO poisoning occurring during pregnancy between December 1985 and March 1989. The sources of CO were malfunctioning furnaces (n = 16), hot water heaters (n = 7), car fumes (n = 6), and methylene chloride inhalation (n = 3). Pregnancy outcome was adversely affected in 3 of 5 pregnancies with severe toxicity; two stillbirths, and one cerebral palsy with tomographic findings consistent with ischemic damage. All adverse outcome occurred in cases treated with high flow oxygen, whereas the 2 cases of severe toxicity with normal outcomes followed hyperbaric oxygen therapy. All 31 babies exposed in utero to mild or moderate CO poisoning exhibited normal physical and neurobehavioral development. Severe maternal CO toxicity was associated with significantly more adverse fetal cases when compared to mild maternal toxicity (P less than 0.001). It is concluded that while severe CO poisoning poses serious short- and long-term fetal risk, mild accidental exposure is likely to result in normal fetal outcome. Because fetal accumulation of CO is higher and its elimination slower than in the maternal circulation, hyperbaric oxygen may decrease fetal hypoxia and improve outcome.

Fetal toxicity associated with maternal carbon monoxide poisoning

We report six cases of acute carbon monoxide poisoning during pregnancy. All of the women survived with good outcomes, but three cases were associated with fetal mortality. Two fetuses were delivered stillborn within 36 hours of exposure. One fetus remained alive in utero for 20 weeks and was delivered nonviable at 33 weeks gestation with multiple morphologic anomalies. Three pregnancies were carried to term and resulted in normal neonates. Maternal blood carboxyhemoglobin levels did not correlate with the concurrent severity of symptoms in the woman. Maternal symptoms at the site of exposure seemed to predict the risk of associated morbidity to the fetus. A single maternal carboxyhemoglobin level cannot be used to estimate fetal carboxyhemoglobin if the exposure pattern is not known.

Smoking and low birth weight: absence of influence by carbon monoxide?

Fetal outcome in 77 uneventful pregnancies was examined and related to venous cord carboxyhaemoglobin (HbCO) levels. 30 women were smokers, 47 were non-smokers. Birth weight and birth weight centiles were found to be substantially reduced in children of mothers who smoked. HbCO levels were significantly elevated in venous cord blood of children of smokers compared with non-smokers. The role of fetal HbCO as a causal factor in reducing birth weight centiles of children of smoking mothers is discussed. It is concluded that carboxyhaemoglobin concentration in fetal venous cord blood did not account for fetal growth retardation in pregnant women who smoked.

Acute carbon monoxide poisoning during pregnancy

The course of a pregnant patient at term who was acutely exposed to carbon monoxide is described. A review of the fetal-maternal carboxyhemoglobin relationships and the differences in fetal oxyhemoglobin physiology are used to explain the recommendation that pregnant women with carbon monoxide poisoning should receive 100% oxygen therapy for up to five times longer than is otherwise necessary. The role of hyperbaric oxygen therapy is considered.

The cardiorespiratory effects of perfluorochemicals on acute carbon monoxide poisoning in the pregnant ewe

Studies in nonpregnant animal models of carbon monoxide poisoning have demonstrated the protective effect of perfluorochemicals. Anesthetized pregnant ewes were exposed to carbon monoxide. After symptoms of toxicity were demonstrated, group 1 animals were respired with room air. Group 2 animals respired room air and were given intravenous perfluorochemicals. Group 3 animals were administered 100% oxygen. Group 4 animals were given intravenous perfluorochemicals and respired 100% oxygen. In all ewes exposure to carbon monoxide resulted in increased cardiac output, heart rate, and carboxyhemoglobin level without a significant change in arterial oxygen tension. After carbon monoxide exposure, there was no significant difference in the carboxyhemoglobin to oxyhemoglobin conversion between groups 1 and 2 although the conversion rates were more rapid in groups 3 and 4. Fetal oxygenation was improved in groups 3 and 4. All fetal lambs exhibited a progressive increase in carboxyhemoglobin and a decrease in venous pH regardless of the maternal postexposure treatment. There was no significant increase in the fetal venous oxygen content of group 4 as compared with that of group 3, suggesting that the adjunctive administration of limited quantities of perfluorochemicals to the mother offers no apparent advantage over 100% oxygen alone for acute fetal resuscitation.

Alteration in the postnatal ontogeny of cerebellar norepinephrine content following chronic prenatal carbon monoxide

The postnatal ontogeny of norepinephrine content in the cortex and cerebellum was determined in rats exposed prenatally to a chronic low level of carbon monoxide (150 parts per million). In the cerebellum, norepinephrine concentration and total norepinephrine content among carbon monoxide-exposed rats were consistently elevated over that of control rats from the second through the sixth postnatal weeks. In the cortex, norepinephrine concentration and total norepinephrine content among carbon monoxide-exposed rats did not differ from that of control rats over the same period. These results identify the cerebellum as a region whose postnatal development is altered by prenatal exposure to low levels of carbon monoxide-induced hypoxia.

Extrapolation of the evidence on teratogenicity of chemicals between humans and experimental animals: chemicals other than drugs

Epidemiologic literature regarding the possible association between malformations and 23 exposures or occupations other than pharmaceutical products, was analysed. The qualitative level of scientific evidence was classified into four categories: high (ethanol, methylmercury, PCBs, laboratory work), limited (anesthetic gases, carbon monoxide), low (hexachlorophene, LSD, nitrous oxide, smelter work, tobacco), and inadequate (all other exposures). Human data for exposures belonging to categories "high" and "limited" were quantitatively compared to results of animal teratogenicity tests of the relevant chemicals. Ethanol, methylmercury, and PCBs have caused malformations in experimental animals, and the effective doses have ranged from 0.2 to 8.0 times the effective human doses. Ethanol and PCBs caused similar types of lesions in some animal species as have been observed in humans.

Threshold for carbon monoxide induced fetotoxicity

Carbon monoxide (CO) is said to be the most widely encountered occupational and environmental contaminant. Threshold for CO-induced fetotoxicity was studied using mouse as an experimental animal. Pregnant animals of CD-1 strain were exposed to 0, 65, 125, 250, or 500 ppm CO from gestation day 7 to 18. The animals were sacrificed on gestation day 18, and their uterine horns were examined for live or resorbed fetuses. The data suggest that maternal CO exposure to as low as 125 ppm affects fetal growth and higher levels affect viability. The data also suggest that the developing organism is sensitive to chronic CO exposure, and this sensitivity is dose dependent. The fetal mouse is influenced at levels of exposure below those found transiently for human cigarette smokers and ambient CO concentrations associated with various occupations.

Prenatal exposure to carbon monoxide: learning and memory deficits

Exposing pregnant rats to carbon monoxide (150 parts per million) produced only minor reductions in the birth weights of the pups and gave no evidence of overt teratogenesis. However, behavioral evaluation of learning and memory processes in a two-way avoidance task suggested a functional deficit in the central nervous system of the exposed offspring. Multiple dependent measures and specific control groups confirmed that this deficit was independent of nonassociative or motivational alterations.