Carbon monoxide controversies: neuropsychologic testing, mechanism of toxicity, and hyperbaric oxygen

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.

Delayed Neurological Sequelae in an Infant after Carbon Monoxide Intoxication

Delayed neurological sequelae are symptoms that appear over a period of time after an acute event of carbon monoxide poisoning. The incidence of delayed neurological sequelae is lower in children than in adults and is even more uncommon in infants. Here, we present a case of a 4-month-old infant who developed delayed neurological sequelae after carbon monoxide intoxication. She presented with neurologic symptoms, including opisthotonus, athetoid movements, anterior tongue thrust, and opsoclonus. Because these symptoms are starkly different from those of adults, they should be compared with age-appropriate developmental milestones. Because of their faster metabolic rate and presence of fetal hemoglobin, infants with developing brains may be especially vulnerable to carbon monoxide toxicity. Therefore, thorough neurologic examination and prompt treatment are critical for infants who experience carbon monoxide intoxication.

Risk Factors and Outcome Analysis in Children with Carbon Monoxide Poisoning

BACKGROUND

Carbon monoxide (CO) poisoning is one of the common causes of poisoning in patients and can result in significant morbidity and mortality. However, few studies have focused on the pediatric group.

METHODS

We retrospectively reviewed children (age < 18 years) with CO poisoning from nonfire accidents at a tertiary medical center in Taiwan from 2002 to 2010. We analyzed the patients' characteristics, management, and outcome; compared the data of patients who received hyperbaric oxygen (HBO) to those who received normobaric oxygen (NBO) therapy; and identified the ri0sk factors for patients who developed delayed neurological sequelae (DNS) or permanent neurological sequelae (PNS).

RESULTS

A total of 81 children were enrolled. The annual case number increased from five cases in 2002 to 20 in 2010, particularly during the cold months (December to February). The most common source of exposure was an indoor heating system (54.3%). The most common presenting symptoms were vomiting (32.1%) and consciousness changes (30.9%). HBO treatment tended to be administered to patients with a higher initial COHb (%) (p < 0.001), an initial Glasgow coma scale change (p < 0.001), and admission to the hospital (p = 0.002). After multivariate analysis, treatment in the intensive care unit because of prolonged loss of consciousness (p = 0.002) was the only independent risk factor for patients with DNS; only rescue by a ventilator (p < 0.001) was an independent risk factor for patients with PNS. In comparison to the NBO therapy, HBO treatment did not show benefit or harm to patients according to the incidence of inducing DNS or PNS after multivariate analysis.

CONCLUSION

For those with treatment in the intensive care unit because of prolonged loss of consciousness and rescue by a ventilator, special attention should be given and follow-up should be performed to determine whether DNS or PNS occurs, particularly epilepsy and cognitive deficits.

Current concepts in the pathophysiology and treatment of inhalation injury

The opinions or assertions contained herein are the private views of the author, and are not to be construed as official or as reflecting the official views of the Department of the Army or Department of Defense. Smoke inhalation injury occurs in about 10% of patients admitted to burn centres, and increases the mortality of burn patients by up to 20% over predictions based on age and burn size alone. The primary lesion in smoke inhalation injury is localized to the small airways, with alveolar injury and pulmonary oedema exercising a less prominent role during the initial phases. Injury incites a cascade of events that include ventilation-perfusion mismatch, secondary lung injury, systemic inflammation, impaired immune function, and pneumonia. The most important recent developments in the treatment of inhalation injury have included improved methods of pulmonary care targeted at the pathophysiology of the injury, such as high-frequency percussive ventilation and gentle mechanical ventilation.

[Delayed neurological syndrome after CO intoxication of elderly female]

This article discusses the case history of an 87-year old woman with loss of consciousness following accidental CO intoxication. A few weeks later, the patient's cognitive abilities progressively deteriorated. This is hence a case of Delayed Neurological Symptoms after CO intoxication. This condition occurs in 40% of patients with CO intoxication and manifests itself 3-240 days after apparent recovery. Symptoms can linger for a long time and are in some cases even permanent. Treatment of CO intoxication usually consists of administering normobaric oxygen and in certain cases hyperbaric oxygen. The role of treatment with hyberbaric oxygen in delayed neurological symptoms after CO intoxication remains controversial, however.

Housing and child health

The connection between housing and health is well established. Physical, chemical, and biological aspects of the child's home, such as cleanliness, moisture, pests, noise, accessibility, injury risks, and other forms of housing environmental quality, all have the potential to influence multiple aspects of the health and development of children. Basic sanitation, reduced household crowding, other improvements in housing and expanded, and improved housing regulations have led to advances in children's health. For example, lead poisoning prevention policies have profoundly reduced childhood lead exposure in the United States. This and many other successes highlight the health benefits for families, particularly children, by targeting interventions that reduce or eliminate harmful exposures in the home. Additionally, parental mental health problems, food insecurity, domestic violence, and the presence of guns in children's homes all are largely experienced by children in their homes, which are not as yet considered part of the Healthy Homes agenda. There is a large movement and now a regulatory structure being put in place for healthy housing, which is becoming closely wedded with environmental health, public health, and the practice of pediatrics. The importance of homes in children's lives, history of healthy homes, asthma, and exposures to lead, carbon monoxide, secondhand/thirdhand smoke, radon, allergy triggers is discussed, as well as how changes in ambient temperature, increased humidity, poor ventilation, water quality, infectious diseases, housing structure, guns, electronic media, family structure, and domestic violence all affect children's health.

Carbon monoxide poisoning

Carbon monoxide (CO) poisoning is the leading cause of death as a result of unintentional poisoning in the United States. CO toxicity is the result of a combination of tissue hypoxia-ischemia secondary to carboxyhemoglobin formation and direct CO-mediated damage at a cellular level. Presenting symptoms are mostly nonspecific and depend on the duration of exposure and levels of CO. Diagnosis is made by prompt measurement of carboxyhemoglobin levels. Treatment consists of the patient's removal from the source of exposure and the immediate administration of 100% supplemental oxygen in addition to aggressive supportive measures. The use of hyperbaric oxygen is controversial.

The totality of burn care

The overall improvement in mortality following severe burns has dramatically increased in the last half century with enhanced methods of resuscitation, treatment of inhalation injury, control of infection, early wound excision and novel methods of skin resurfacing. Although burn care begins at the onset of injury, reconstruction and rehabilitation feature highly throughout the various stages of treatment. Ultimately, we will have achieved little if the patient cannot be integrated back into society. For descriptive purposes burn care has been considered chronologically under the following headings: (1) First Two Minutes (Prehospital Care/First Aid), (2) First Two Hours (Emergency Room care), (3) First two days (resuscitation), (4) First Two Weeks (surgical excision and grafting), (5) First Two Months (rehabilitation and psychology), (6) First Two Years (reconstruction).

Emergency hospital admissions for cardiovascular diseases and ambient levels of carbon monoxide: results for 126 United States urban counties, 1999-2005

BACKGROUND

Evidence on risk of cardiovascular disease (CVD) hospitalization associated with short-term exposure to outdoor carbon monoxide (CO), an air pollutant primarily generated by traffic, is inconsistent across studies. Uncertainties remain on the degree to which associations are attributable to other traffic pollutants and whether effects persist at low levels.

METHODS AND RESULTS

We conducted a multisite time-series study to estimate risk of CVD hospitalization associated with short-term CO exposure in 126 US urban counties during 1999-2005 for >9.3 million Medicare enrollees aged > or =65 years. We considered models with adjustment by other traffic-related pollutants: NO2, fine particulate matter (with aerodynamic diameter < or =2.5 microm), and elemental carbon. We found a positive and statistically significant association between same-day CO and increased risk of hospitalization for multiple CVD outcomes (ischemic heart disease, heart rhythm disturbances, heart failure, cerebrovascular disease, total CVD). The association remained positive and statistically significant but was attenuated with copollutant adjustment, especially NO2. A 1-ppm increase in same-day daily 1-hour maximum CO was associated with a 0.96% (95% posterior interval, 0.79%, 1.12%) increase in risk of CVD admissions. With same-day NO(2) adjustment, this estimate was 0.55% (0.36%, 0.74%). The risk persisted at low CO levels <1 ppm.

CONCLUSIONS

We found evidence of an association between short-term exposure to ambient CO and risk of CVD hospitalizations, even at levels well below current US health-based regulatory standards. This evidence indicates that exposure to current CO levels may still pose a public health threat, particularly for persons with CVD.

Hyperbaric oxygen and carbon monoxide poisoning: a critical review

CO is likely to be the most common cause of poisoning worldwide and often results in persistent neuropathologic and cognitive sequelae. While the displacement of oxygen from hemoglobin by CO has overshadowed the myriad mechanisms by which CO causes injury, mere oxygen displacement has endured as the etiology of CO poisonings and perpetuated a cascade of misdiagnosis, misunderstandings and confusion regarding how and when to treat CO poisoning. Hyperbaric oxygen benefits the brain more than normobaric oxygen by, e.g. improving energy metabolism, preventing lipid peroxidation and decreasing neutrophil adherence. Randomized controlled trials have definitively shown hyperbaric oxygen as the only efficacious therapy for acute CO poisoning if delayed neurological sequelae are to be minimized. Normobaric oxygen should not be used between multiple hyperbaric oxygen treatments as this can contribute to toxicity. Hyperbaric oxygen seems to also have potential in the delayed treatment of CO poisoning using multiple treatments of low dose of oxygen; however, oxygen dosing issues are not yet fully understood for either acute or delayed treatment. It would behoove medical decision-makers to embrace this important tool and make it more accessible as well as helping to disseminate to the medical community what is now known from the available literature.

Myocardial dysfunction and potential cardiac hypoxia in rats induced by carbon monoxide inhalation

BACKGROUND

Results from both animal and human being studies provide evidence that inhalation of concentrations of carbon monoxide (CO) at around 100 ppm has antiinflammatory effects. These low levels of CO are incriminated in ischemic heart diseases experienced by cigarette smokers and, in some cases, from air pollution. Although neurologic mechanisms have been investigated, the effects of CO on cardiovascular function are still poorly understood.

METHODS AND RESULTS

The effects of CO (250 ppm; 90 min) inhalation on myocardial function were investigated in isolated heart of rats killed immediately, and 3, 24, 48, and 96 h after CO exposure. CO exposure at 250 ppm resulted in an arterial carboxyhemoglobin (HbCO) level of approximately 11%, which was not associated with changes in mean arterial pressure and heart rate. CO exposure induced coronary perfusion pressure increases, which were associated with endothelium-dependent and -independent vascular relaxation abnormalities. CO-induced coronary vascular relaxation perturbations were observed in the presence of increased heart contractility. Spontaneous peak to maximal Ca(2+)-activated left ventricular pressure ratio was markedly increased in CO-exposed rats, indicating increases in myofilament calcium sensitivity. Heart cyclic guanosine monophosphate/cAMP ratio and myocardial permeabilized fiber respiration (complex intravenous activity) were reduced in CO-exposed rats, which lasted after 48 h of reoxygenation in air.

CONCLUSIONS

These findings suggest that CO deteriorates heart oxygen supply to utilization and potentially may induce myocardial hypoxia through mechanisms that include increased oxygen demand due to increased contractility, reduced coronary blood flow reserve, and cardiomyocyte respiration inhibition.

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.

Hyperbaric oxygen for carbon monoxide poisoning

BACKGROUND

Poisoning with carbon monoxide (CO) remains an important cause of accidental and intentional injury worldwide. Several unblinded non-randomized trials have suggested that the use of hyperbaric oxygen (HBO) prevents the development of neurological sequelae. This has led to the widespread use of HBO in the management of patients with carbon monoxide poisoning.

OBJECTIVES

To examine randomized trials of the effectiveness of hyperbaric oxygen (HBO) compared to normobaric oxygen (NBO) for the prevention of neurologic sequelae in patients with acute carbon monoxide poisoning.

SEARCH STRATEGY

We searched MEDLINE (1966-present), EMBASE (1980-present), and the Controlled Trials Register of the Cochrane Collaboration, supplemented by a manual review of bibliographies of identified articles and discussion with recognized content experts.

SELECTION CRITERIA

All randomized controlled trials involving non-pregnant adults acutely poisoned with carbon monoxide (regardless of severity), with adequate or unclear allocation concealment.

DATA COLLECTION AND ANALYSIS

Two reviewers independently extracted from each trial information on: the number of randomized patients, types of participants, the dose and duration of the intervention, and the prevalence of neurologic symptoms at follow-up.

MAIN RESULTS

Seven randomized controlled trials of varying quality were identified; one was excluded because it did not evaluate clinical outcomes. Of the six remaining trials, two represent incomplete publications (one interim analysis, one abstract). Of these six trials, four found no benefit of HBO for the reduction of neurologic sequelae, while two others did. Although pooled analysis does not suggest a benefit from HBOT (OR for neurological deficits 0.78, 95%CI 0.54 to 1.12, p=0.18), significant methodologic and statistical heterogeneity was apparent among the trials, and this result should be interpreted cautiously. Moreover, design or analysis flaws were evident in all trials. Importantly, the conclusions of one positive trial may have been influenced by failure to adjust for multiple hypothesis testing, while interpretation of the other positive trial is hampered by apparent changes in the primary outcome during the course of the trial.

AUTHORS' CONCLUSIONS

Existing randomized trials do not establish whether the administration of HBO to patients with carbon monoxide poisoning reduces the incidence of adverse neurologic outcomes. Additional research is needed to better define the role, if any, of HBO in the treatment of patients with carbon monoxide poisoning. This research question is ideally suited to a multi-center randomized controlled trial.

Hyperbaric Oxygen for Carbon Monoxide Poisoning

Poisoning with carbon monoxide (CO) is an important cause of unintentional and intentional injury worldwide. Hyperbaric oxygen (HBO) enhances CO elimination and has been postulated to reduce the incidence of neurological sequelae. These observations have led some clinicians to use HBO for selected patients with CO poisoning, although there is considerable variability in clinical practice. This article assesses the effectiveness of HBO compared with normobaric oxygen (NBO) for the prevention of neurological sequelae in patients with acute CO poisoning. The following databases were searched: MEDLINE (1966 to present), EMBASE (1980 to present), and the Controlled Trials Register of the Cochrane Collaboration, supplemented by a manual review of bibliographies of identified articles and discussion with recognised content experts. All randomised controlled trials involving people acutely poisoned with CO, regardless of severity, were examined. The primary analysis included all trials from which data could be extracted. Sensitivity analysis examined trials with better validity (defined using the validated instrument of Jadad) and those enrolling more severely poisoned patients. Two reviewers independently extracted from each trial, including information on the number of randomised patients, types of participants, the dose and duration of the intervention, and the prevalence of neurological sequelae at follow-up. A pooled odds ratio (OR) for the presence of neurological symptoms at 1-month follow-up was calculated using a random effects model. Bayesian models were also investigated to illustrate the degree of certainty about clinical effectiveness. Eight randomised controlled trials were identified. Two had no evaluable data and were excluded. The remaining trials were of varying quality and two have been published only as abstracts. The severity of CO poisoning varied among trials. At 1-month follow-up after treatment, sequelae possibly related to CO poisoning were present in 242 of 761 patients (36.1%) treated with NBO, compared with 259 of 718 patients (31.8%) treated with HBO. Restricting the analysis to the trials with the highest quality scores or those that enrolled all patients regardless of severity did not change the lack of statistical significance in the outcome of the pooled analysis. We found empiric evidence of multiple biases that operated to inflate the benefit of HBO in two positive trials. In contrast, the interpretation of negative trials was hampered by low rates of follow-up, unusual interventions for control patients and inclusion of less severely poisoned patients. Collectively, these limitations may have led negative trials to overlook a real and substantial benefit of HBO (type II error). There is conflicting evidence regarding the efficacy of HBO treatment for patients with CO poisoning. Methodological shortcomings are evident in all published trials, with empiric evidence of bias in some, particularly those that suggest a benefit of HBO. Bayesian analysis further illustrates the uncertainty about a meaningful clinical benefit. Consequently, firm guidelines regarding the use of HBO for patients with CO poisoning cannot be established. Further research is needed to better define the role of HBO, if any, in the treatment of CO poisoning. Such research should not exclude patients with severe poisoning, have a primary outcome that is clinically meaningful and have oversight from an independent data monitoring and ethics committee.

Lesão por inalação de fumaça

A lesão inalatória é hoje a principal causa de morte nos pacientes queimados, motivo pelo qual se justifica o grande número de estudos publicados sobre o assunto. Os mecanismos envolvidos na gênese da lesão inalatória envolvem tanto os fatores de ação local quanto os de ação sistêmica, o que acaba por aumentar muito as repercussões da lesão. Atualmente, buscam-se ferramentas que permitam o diagnóstico cada vez mais precoce da lesão inalatória e ainda estratégias de tratamento que minimizem as conseqüências da lesão já instalada. Esta revisão aborda os mecanismos fisiopatológicos, os métodos diagnósticos e as estratégias de tratamento dos pacientes vítimas de lesão inalatória. Ressalta ainda as perspectivas terapêuticas em desenvolvimento.

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.

Supervisory attentional control following carbon monoxide poisoning

This study tested the hypothesis that carbon monoxide poisoning would produce a deficit of attentional control, the supervisory attention system, as indexed by attention switching and attentional scheduling, and that routine attentional orienting would be unaffected. Seventy-three cases of carbon monoxide poisoning were assessed at 3 days and 1 month post poisoning on tasks of attentional orienting, and tasks of the supervisory attention system. The results were compared to a group of 53 healthy community participants. A deficit of the supervisory attentional system was documented on a task of attention switching in survivors of both deliberate and accidental CO poisoning, leaving attentional scheduling intact. There was no deficit of attentional orienting in the current study. Alteration of consciousness was found to predict subsequent supervisory attention system impairment in correlation analyses, and the deficit was persistent for a 1 month follow-up period.

Carbon-monoxide poisoning, behavioural changes and suicide: an unusual industrial accident

We report a case of CO intoxication caused by a motor vehicle's faulty heating-system. A truck driver experienced severe mental deterioration, behavioural changes and delirium after acute CO intoxication and committed suicide 15 months later. This report examines the pathogenetic mechanism of CO, the immediate and delayed consequences of CO intoxication, diagnostic difficulties and current treatment options. The medical-legal aspects of the case are discussed.

Carbon monoxide load in indoor carting

Personal experience and reports of colleagues made the authors aware of a possible problem of carbon monoxide exposure in indoor carting arenas. Symptoms such as nausea, headache and altered coordination are not uncommon. This prompted us to register carbon monoxide levels in 15 healthy volunteers in a recreational carting event in a random arena. After two sessions of 10 min and a finale of 20 min we measured a clear increase in carboxyhaemoglobin levels, up to a 16.5-fold increase. The mean rise in the carboxyhaemoglobin level (expressed as a percentage) was 2.06 (mean start carboxyhaemoglobin 0.49%, mean end carboxyhaemoglobin 2.55%). Nausea was noted in 53% of the drivers, headache and altered coordination in 33%, and 13% had a vague abdominal pain. The effects of carbon monoxide exposure during indoor carting should thus not be underestimated, and healthcare workers should be aware of the possible risks.

Twenty-nine years after carbon monoxide intoxication

Carbon monoxide (CO) is a worldwide environmental toxin and a leading cause of deliberate or accidental poisoning. There is an extensive literature devoted to the clinical features and treatment of those victims who have survived acute CO poisoning for a short length of time. The long-term sequelae of non-fatal poisoning have received scanty references, and the prospects for the long-lasting survivors of acute CO intoxication are less clear. Literature review uncovered reports of only three patients who were followed for a considerable period of time. We present a case of CO poisoning with progressive neurological and psychological deterioration that began 17 years after recovery from a severe, accidental CO asphyxia. The patient was examined in the neurology out patient clinic 29 years after the initial CO intoxication. We believe the unique status of this patient, her similarity to one other case in the literature and the circumstances allowing correlation of the clinical picture to the CO poisoning warrants emphasis.

Sevoflurance: approaching the ideal inhalational anesthetic. a pharmacologic, pharmacoeconomic, and clinical review

Sevoflurane is a safe and versatile inhalational anesthetic compared with currently available agents. Sevoflurane is useful in adults and children for both induction and maintenance of anesthesia in inpatient and outpatient surgery. Of all currently used anesthetics, the physical, pharmacodynamic, and pharmacokinetic properties of sevoflurane come closest to that of the ideal anesthetic (200). These characteristics include inherent stability, low flammability, non-pungent odor, lack of irritation to airway passages, low blood:gas solubility allowing rapid induction of and emergence from anesthesia, minimal cardiovascular and respiratory side effects, minimal end-organ effects, minimal effect on cerebral blood flow, low reactivity with other drugs, and a vapor pressure and boiling point that enables delivery using standard vaporization techniques. As a result, sevoflurane has become one of the most widely used agents in its class.

Characteristics and outcome of children with carbon monoxide poisoning with and without smoke exposure referred for hyperbaric oxygen therapy

OBJECTIVES

To describe the clinical characteristics and outcome of children with carbon monoxide (CO) poisoning with and without smoke exposure referred for hyperbaric oxygen therapy (HBOT), and to determine the association between any of these characteristics and death.

SETTING

Regional hyperbaric referral center.

PATIENTS

The medical records of 150 children with CO poisoning (COP) who were treated with HBOT between August 92 and September 95 were reviewed.

MEASUREMENTS/MAIN RESULTS

COP was defined as a history of probable exposure to CO, with either a carboxyhemoglobin level (COHb) > 25, or COHb < 25 with neurological, respiratory, or cardiac compromise. Major cutaneous burns were described as second degree burns over greater than 20% of the patient's total body surface area (TBSA), or third degree burns over greater than 10% of the patient's TBSA. Children extracted from a closed-space fire who had airway soot, singed facial hair/facial burns, or respiratory distress were defined as having smoke inhalation and carbon monoxide poisoning (CO/SI). CO/SI occurred in 40.1% of patients. Compared to children with COP alone, those with CO/SI were significantly more likely to have a depressed mental status upon arrival to an ED (76.3 % vs 13.6 %, P < 0.001), lower mean initial GCS (6.7 vs 14.7, P < 0.001), lower mean initial pH (7.2 vs 7.4, P < 0.001), respiratory arrest at the scene (68.5% vs 0%, P < 0.001), and cardiac arrest at the scene (25.9% vs 0%, P < 0.001). Children with CO/SI were significantly more likely to have a poor outcome (death) than children with COP alone (22.6% vs. 0%, P < 0.001). Comparing children with CO/SI who died versus survivors, there were significant differences in mean initial COHb (38.3 vs 24.3, P = 0.03), mean initial temperature upon arrival in an ED (94.9 degrees F vs 98.2 degrees, P < 0.006), respiratory arrest at the scene (92% vs 59.6%, P = 0.04), and cardiac arrest at the scene (66.7% vs 13.5%, P < 0.001). Sixty percent of children died who had a combination of risk factors of smoke inhalation, low temperature, high COHb level, and respiratory and cardiac arrest in the field.

CONCLUSIONS

These preliminary data suggest that children with COP alone who are treated with HBOT are at low risk for dying regardless of initial COHb level. Children with CO/SI have a significantly higher risk of dying than those children with COP alone. A combination of smoke inhalation, low temperature, high COHb level, respiratory arrest, and cardiac arrest is highly associated with death. Prospective studies are needed to confirm and further define these associations.

Hyperbaric oxygen for carbon monoxide poisoning

BACKGROUND

Poisoning with carbon monoxide (CO) remains an important cause of accidental and intentional injury worldwide. Several unblinded nonrandomized trials have suggested that the use of hyperbaric oxygen (HBO) prevents the development of neurological sequelae. This has led to the widespread use of HBO in the management of patients with carbon monoxide poisoning.

OBJECTIVES

To assess the effectiveness of hyperbaric oxygen (HBO) compared to normobaric oxygen (NBO) for the prevention of neurologic symptoms in patients with acute carbon monoxide poisoning.

SEARCH STRATEGY

We searched MEDLINE (1966-present), EMBASE (1980-present), and the Controlled Trials Register of the Cochrane Collaboration, supplemented by a manual review of bibliographies of identified articles and discussion with recognized content experts.

SELECTION CRITERIA

All randomized controlled trials involving non pregnant adults acutely poisoned with carbon monoxide, regardless of severity, with adequate or unclear allocation concealment were examined. Trials with a score of 3 out of 5 or higher on the validity instrument of Jadad were included in the primary analysis.

DATA COLLECTION AND ANALYSIS

Two reviewers independently extracted from each trial information on the number of randomized patients, types of participants, the dose and duration of the intervention, and the prevalence of neurologic symptoms at follow-up. A pooled odds ratio (OR) for the presence of neurologic symptoms at one month follow-up was calculated using a random effects model.

MAIN RESULTS

Six randomized controlled trials were identified. The trials were of varying quality. Three trials employing different doses of NBO and HBO were included in the primary analysis. The severity of CO poisoning was inconsistent between trials. At one month follow-up after treatment, symptoms possibly related to carbon monoxide poisoning were present in 81 of 237 patients (34.2%) treated with HBO, compared with 81 of 218 patients (37.2%) treated with NBO (O.R. for benefit with HBO 0.82; 95% CI 0.41-1.66).

REVIEWER'S CONCLUSIONS

There is no evidence that unselected use of HBO in the treatment of acute CO poisoning reduces the frequency of neurological symptoms at one month. However, evidence from the available randomized controlled trials is insufficient to provide clear guidelines for practice. Further research is needed to better define the role of HBO, if any, in the treatment of carbon monoxide poisoning. This research question is ideally suited to a multicentre, randomized, double-blind controlled trial.

Carbon monoxide poisoning

Carbon monoxide (CO) poisoning is common and frequently unrecognized since the signs and symptoms are relatively nonspecific. CO poisoning causes tissue hypoxia. Additionally, various animal studies have demonstrated that CO interferes with myoglobin, P450, and other enzyme function; causes lipid peroxidation through neutrophil activation; produces oxidative stress manifested by peroxynitrate deposition in endothelium; binds to cytochrome aa3, disrupting intracellular oxygen utilization; can cause neuroexcitotoxicity; and contributes to hippocampal cellular death through apoptosis. Emergency treatment for CO poisoning is 100% oxygen. Hyperbaric oxygen therapy (HBO2) is accepted in CO poisoning, although data from randomized clinical trials regarding the efficacy of HBO2 in CO poisoning is conflicting. CO poisoning, even when treated with supplemental oxygen can leave the patient with permanent neurocognitive or affective problems. Unfortunately, there appears to be no marker or constellation of signs or symptoms at presentation that predicts long-term outcome following CO poisoning. Given the neurocognitive sequelae following CO poisoning, increased awareness and prevention of CO poisoning is imperative.

Hyperbaric or normobaric oxygen for acute carbon monoxide poisoning: a randomised controlled clinical trial

OBJECTIVE

To assess neurological sequelae in patients with all grades of carbon monoxide (CO) poisoning after treatment with hyperbaric oxygen (HBO) and normobaric oxygen (NBO).

DESIGN

Randomised controlled double-blind trial, including an extended series of neuropsychological tests and sham treatments in a multiplace hyperbaric chamber for patients treated with NBO.

SETTING

The multiplace hyperbaric chamber at the Alfred Hospital, a university-attached quarternary referral centre in Melbourne providing the only hyperbaric service in the State of Victoria.

PATIENTS

All patients referred with CO poisoning between 1 September 1993 and 30 December 1995, irrespective of severity of poisoning. Pregnant women, children, burns victims and those refusing consent were excluded.

INTERVENTION

Daily 100-minute treatments with 100% oxygen in a hyperbaric chamber--60 minutes at 2.8 atmospheres absolute for the HBO group and at 1.0 atmosphere absolute for the NBO group--for three days (or for six days for patients who were clinically abnormal or had poor neuropsychological outcome after three treatments). Both groups received continuous high flow oxygen between treatments.

MAIN OUTCOME MEASURES

Neuropsychological performance at completion of treatment, and at one month where possible.

RESULTS

More patients in the HBO group required additional treatments (28% v. 15%, P = 0.01 for all patients; 35% v. 13%, P = 0.001 for severely poisoned patients). HBO patients had a worse outcome in the learning test at completion of treatment (P = 0.01 for all patients; P = 0.005 for severely poisoned patients) and a greater number of abnormal test results at completion of treatment (P = 0.02 for all patients; P = 0.008 for severely poisoned patients). A greater percentage of severely poisoned patients in the HBO group had a poor outcome at completion of treatment (P = 0.03). Delayed neurological sequelae were restricted to HBO patients (P = 0.03). No outcome measure was worse in the NBO group.

CONCLUSION

In this trial, in which both groups received high doses of oxygen, HBO therapy did not benefit, and may have worsened, the outcome. We cannot recommend its use in CO poisoning.

Deliberate exposure to motor vehicle exhaust gas: the psychosocial profile of attempted suicide

OBJECTIVE

Deliberate exposure to motor vehicle exhaust gas has become the second most commonly used method of suicide in Australia. In an attempt to understand the factors contributing to the rise in popularity of this method, the psychosocial profiles, factors influencing method choice and circumstances of the act of self-harm were examined in a group of survivors.

METHOD

A cross-sectional cohort study of 30 patients presenting for hyperbaric oxygen treatment having survived deliberate exposure to car exhaust gas was undertaken. A structured clinical interview was administered together with scales measuring depression, hopelessness and suicidal intent. Daily assessment of mental state and cognitive function was performed.

RESULTS

Factors common to the majority of subjects included male gender, age group of 20-50 years, and alcohol abuse. Relationship discord was the most common precipitating factor. Reasons given for choice of this method included the availability and accessibility of motor vehicles, painlessness, awareness that the method was lethal, knowledge of another person's successful suicide by this method and awareness of the method through media portrayal. Most of the cars used did not have engines fitted with catalytic converters, substantially increasing the risk of toxicity. Regret of the attempt, denial of further suicidal ideation after the event, and the absence of a suicide note were common findings. Most denied excessive time spent planning. The most common diagnosis in this group was adjustment disorder with depressed mood. Suicide intent scores were not high, inconsistent with the majority of patients being aware of the lethality of the method.

CONCLUSION

Sociodemographic findings resemble those of psychological autopsy studies of subjects completing suicide by this method. Survival in this group was due to failure of the method or unexpected discovery rather than patient factors. This population described the method as highly acceptable and accessible emphasising the urgent need for reduction of access to this means of suicide in Australia.

Carbon monoxide poisoning presenting as an isolated seizure

Seizures are generally regarded as a manifestation of extreme, generally near-fatal carbon monoxide poisoning. A case is described in which a seizure attributable to carbon monoxide poisoning occurred in a small child at a level not thought to be associated with serious neurologic toxicity. A literature review of the occurrence of seizures in carbon monoxide poisoning found that no particular degree of carboxyhemoglobin was correlated with the presence of seizures. A seizure with no other apparent cause occurring in circumstances in which carbon monoxide toxicity would be suspected can be attributed to carbon monoxide poisoning.

Outcome of children with carbon monoxide poisoning treated with normobaric oxygen

OBJECTIVE

To evaluate the clinical characteristics and neurologic outcome of children with carbon monoxide poisoning treated with normobaric oxygen therapy.

METHODS

We reviewed the medical records of all children with a diagnosis of carbon monoxide exposure admitted during a 10-year period. Exposures were categorized as (1) severely toxic, carboxyhemoglobin level >25%; (2) toxic, carboxyhemoglobin level 10.1 to 25%; (3) suspected toxic, carboxyhemoglobin level < or = 10% with acute neurologic manifestations; or (4) nontoxic, carboxyhemoglobin < or = 10% without acute neurologic manifestations.

RESULTS

One hundred six patients (median age, 3.5 years; range, 0.1-14.9 years) were identified, 37 with severe toxic, 37 with toxic, 13 with suspected toxic, and 19 with nontoxic exposures. The most common presenting signs or symptoms included altered level of consciousness, metabolic acidosis, tachycardia, and hypertension. All patients received normobaric oxygen for 5.5 hours (range, 0.6-44 hours). Carboxyhemoglobin levels decreased to less than 3% in 3.6 hours (range, 0-15.5 hours). Fifteen patients died, three from massive burn injury, eight from hypoxic-ischemic encephalopathy after cardiopulmonary arrest at presentation, and four from late complications of burn injury. Seven survivors did not recover their premorbid neurologic state, four of whom had respiratory arrest when rescued. Two patients had initial neurologic recovery followed by transient deterioration at 4 and 14 days after exposure. One patient developed seizures and was found to have bilateral occipital lobe infarctions 51 days after exposure.

CONCLUSION

Acute neurologic manifestations after carbon monoxide exposure are common in children. These resolve rapidly with normobaric oxygen, however. Persistent sequelae are primarily related to asphyxia. Delayed neurologic syndromes are uncommon in children treated with normobaric oxygen.

Confirmation of the pulse oximetry gap in carbon monoxide poisoning

STUDY OBJECTIVES

To demonstrate the degree to which pulse oximetry overestimates actual oxyhemoglobin (O2Hb) saturation in patients with carbon monoxide (CO) poisoning. This phenomenon has been reported in fewer than 20 humans in the English medical literature.

METHODS

A retrospective chart review of 191 patients evaluated for CO poisoning at a regional hyperbaric center identified 124 patients 10 years of age and older who had had both arterial blood gas and pulse oximetry measurements and who had received either high-flow oxygen through a nonrebreather mask or 100% inspired oxygen through an endotracheal tube. Blood gas measurements, including direct spectrophotometric determination of O2Hb and carboxyhemoglobin (COHb) saturation values, were compared with finger-probe pulse oximetry readings.

RESULTS

Measured O2Hb saturation (mean +/- SD, 88.7 +/- 10.2%; range, 51.4% to 99.0%) decreased linearly and predictably with rising COHb levels (10.7 +/- 10.4%; range, .2% to 46.4%). Pulse oximetry saturation (99.2% +/- 1.3%; range, 92% to 100%) remained elevated across the range of COHb levels and failed to detect decreased O2Hb saturation. The pulse oximetry gap, defined as the difference between pulse oximetry saturation and actual O2Hb saturation (10.5% +/- 9.7%; range, 0% to 40.6%), approximated the COHb level.

CONCLUSION

There is a linear decline in O2Hb saturation as COHb saturation increases. This decline is not detected by pulse oximetry, which therefore overestimates O2Hb saturation in patients with increased COHb levels. The pulse oximetry gap increases with higher levels of COHb and approximates the COHb level. In patients with possible CO poisoning, pulse oximetry must be considered unreliable and interpreted with caution until the COHb level has been measured.

MR enhancing brain lesions in methanol intoxication

Methanol intoxication can cause necrosis of the putamen and subcortical white matter that is evident on neuroimaging. We report a 47-year-old man with significant methanol intoxication who had enhancing lesions in the caudate nuclei, putamina, hypothalamus, and subcortical white matter by MRI. This case demonstrates that contrast enhancement of brain lesions can be observed after methanol poisoning.