A positron emission tomography study of patients with acute carbon monoxide poisoning treated by hyperbaric oxygen

Relation between brain temperature and white matter damage in subacute carbon monoxide poisoning

In the previous studies, carbon monoxide (CO) poisoning showed an imbalance between cerebral perfusion and metabolism in the acute phase and the brain temperature (BT) in these patients remained abnormally high from the acute to the subacute phase. As observed in chronic ischemic patients, BT can continuously remain high depending on impairments of cerebral blood flow and metabolism; this is because heat removal and production system in the brain may mainly be maintained by the balance of these two factors; thus, cerebral white matter damage (WMD) affecting normal metabolism may affect the BT in patients with CO poisoning. Here, we investigated whether the BT correlates with the degree of WMD in patients with subacute CO-poisoning. In 16 patients with subacute CO-poisoning, the BT and degree of WMD were quantitatively measured by using magnetic resonance spectroscopy and the fractional anisotropy (FA) value from diffusion tensor imaging dataset. Consequently, the BT significantly correlated with the degree of WMD. In particular, BT observed in patients with delayed neuropsychiatric sequelae, a crucial symptom with sudden-onset in the chronic phase after CO exposure, might indicate cerebral hypo-metabolism and abnormal hemodynamics like “matched perfusion,” in which the reduced perfusion matches the reduced metabolism.

Neuroimaging, Cognitive, and Neurobehavioral Outcomes Following Carbon Monoxide Poisoning

Carbon monoxide is a colorless, odorless gas produced as a byproduct of combustion. Carbon monoxide is the leading cause of poisoning injury and death worldwide. Morbidity following CO poisoning includes neurologic sequelae, neuropathologic abnormalities on brain imaging, neurobehavioral changes, and cognitive impairments. It is estimated that as high as 50% of individuals with carbon monoxide poisoning will develop neurologic, neurobehavioral, or cognitive sequelae. Carbon monoxide related cognitive impairments included impaired memory, attention, executive function, motor, visual spatial, and slow mental processing speed. Given the high rate of brain related morbidity and the fact that the majority of carbon monoxide is avoidable, awareness and prevention of carbon monoxide poisoning is warranted.

Brain temperature measured by 1H-magnetic resonance spectroscopy in acute and subacute carbon monoxide poisoning

INTRODUCTION

Brain temperature (BT) is associated with the balance between cerebral blood flow and metabolism according to the "heat-removal" theory. The present study investigated whether BT is abnormally altered in acute and subacute CO-poisoned patients by using (1)H-magnetic resonance spectroscopy (MRS).

METHODS

Eight adult CO-poisoned patients underwent 3-T magnetic resonance imaging in the acute and subacute phases after CO exposure. MRS was performed on deep cerebral white matter in the centrum semiovale, and MRS-based BT was estimated by the chemical shift difference between water and the N-acetyl aspartate signal. We defined the mean BT + 1.96 standard deviations of the BT in 15 healthy controls as the cutoff value for abnormal BT increases (p < 0.05) in CO-poisoned patients.

RESULTS

BT of CO-poisoned patients in both the acute and subacute phases was significantly higher than that of the healthy control group. However, BT in the subacute phase was significantly lower than in the acute phase. On the other hand, no significant difference in body temperature was observed between acute and subacute CO-poisoned patients. BT weakly correlated with body temperature, but this correlation was not statistically significant (rho = 0.304, p = 0.2909).

CONCLUSIONS

The present results suggest that BT in CO-poisoned patients is abnormally high in the acute phase and remains abnormal in the subacute phase. BT alteration in these patients may be associated with brain perfusion and metabolism rather than other factors such as systemic inflammation and body temperature.

Carbon monoxide intoxication

Carbon monoxide (CO) is a colorless, odorless, nonirritant gas that accounts for numerous cases of CO poisoning every year from a variety of sources of incomplete combustion of hydrocarbons. These include poorly functioning heating systems, indoor propane-powered forklifts, indoor burning of charcoal burning briquettes, riding in the back of pick-up trucks, ice skating rinks using propane-powered resurfacing machines, and gasoline-powered generators that are not in correct locations. Once CO is inhaled it binds with hemoglobin to form carboxyhemoglobin (COHb) with an affinity 200 times greater than oxygen that leads to decreased oxygen-carrying capacity and decreased release of oxygen to tissues leading to tissue hypoxia. Ischemia occurs with CO poisoning when there is loss of consciousness that is accompanied by hypotension and ischemia in the arterial border zones of the brain. Besides binding to many heme-containing proteins, CO disrupts oxidative metabolism leading to the formation of free radicals. Once hypotension and unconsciousness occur with CO poisoning, lipid peroxidation and apoptosis follow. Because COHb has a short half-life, examination of other biomarkers of CO neurotoxicity that reflect inflammation or neuronal damage has not demonstrated consistent results. The initial symptoms with CO exposure when COHb is 15-30% are nonspecific, namely, headache, dizziness, nausea, fatigue, and impaired manual dexterity. However individuals with ischemic heart disease may experience chest pain and decreased exercise duration at COHb levels between 1% and 9%. COHb levels between 30% and 70% lead to loss of consciousness and eventually death. Following resolution of acute symptoms there may be a lucid interval of 2-40 days before the development of delayed neurologic sequelae (DNS), with diffuse demyelination in the brain accompanied by lethargy, behavior changes, forgetfulness, memory loss, and parkinsonian features. Seventy-five percent of patients with DNS recover within 1 year. Neuropsychologic abnormalities with chronic CO exposure are found even when magnetic resonance imaging (MRI) and magnetic resonance spectroscopy are normal. White-matter damage in the centrum semiovale and periventricular area and abnormalities in the globus pallidus are most commonly seen on MRI following CO exposure. Though not as common, toxic or ischemic peripheral neuropathies are associated with CO exposure in humans and animals. The cornerstone for treatment for CO poisoning is 100% oxygen using a tight-fitting mask for greater than 6 hours. The indications for treatment with hyperbaric oxygen to decrease the half-life of COHb remain controversial.

Basal ganglia lesions following carbon monoxide poisoning

PRIMARY OBJECTIVES

Carbon monoxide (CO) is the most common cause of poisoning and may result in basal ganglia lesions. This study reviewed the literature of carbon monoxide poisoning and basal ganglia lesions and prospectively assessed the prevalence of basal ganglia lesions in a cohort of patients with CO poisoning.

RESEARCH DESIGN

Literature review and prospective cohort study.

METHODS

This study conducted a comprehensive review of the literature and assessed 73 CO-poisoned patients for basal ganglia lesions on sequential MR scans. Magnetic resonance scans were obtained on day 1, 2 weeks and 6 months post-CO poisoning.

RESULTS

The literature review found basal ganglia lesions occur in 4-88% of subjects. Only one patient was found with globus pallidus lesions at 2 weeks and 6 months following CO poisoning, that were not present on the initial day 1 MR scan.

CONCLUSIONS

Basal ganglia lesions, including lesions of the globus pallidus, may be less common than previously reported.

Affective outcome following carbon monoxide poisoning: a prospective longitudinal study

OBJECTIVE

To longitudinally assess the prevalence of depression and anxiety following carbon monoxide (CO) poisoning and to assess the contributions of mode of poisoning (accidental versus suicide attempt), cognitive sequelae, and oxygen dose (hyperbaric oxygen versus normobaric oxygen) to depression and anxiety.

BACKGROUND

CO is the most common cause of poisoning in the United States and may result in neuropathologic changes and cognitive and neurologic sequelae, yet little is known regarding affective outcomes.

METHOD

We prospectively assessed affect in 127 CO-poisoned patients. Self-report inventories of depression and anxiety were administered at 6 weeks and at 6 and 12 months post CO poisoning. The primary outcome was prevalence of depression and anxiety at 6 weeks. To determine the effect of mode of poisoning, cognitive sequelae, and oxygen dose, odds ratio estimates were calculated at all three times using logistic regression.

RESULTS

Depression and anxiety were present in 45% of patients at 6 weeks, 44% at 6 months, and 43% at 12 months. Patients with suicide attempt and cognitive sequelae had higher prevalence of depression and anxiety at 6 weeks. At 12 months, there were no differences in depression or anxiety regardless of mode of poisoning, presence of cognitive sequelae, or oxygen dose.

CONCLUSIONS

CO poisoning results in significant depression and anxiety that persist to at least 12 months. Patients with cognitive sequelae and suicide attempt had a higher rate of depression and anxiety at 6 weeks but not at 12 months. Clinicians need to be aware of affective morbidity following CO poisoning and remain vigilant about CO prevention.

Statistical parametric mapping in brain single photon computed emission tomography after carbon monoxide intoxication

The purpose of this retrospective study was to assess regional cerebral blood flow in patients after carbon monoxide intoxication by using brain single photon emission computed tomography and statistical parametric mapping. Eight patients with delayed neuropsychiatric sequelae and ten patients with no neuropsychiatric symptoms after carbon monoxide intoxication were studied with brain single photon emission tomography imaging with 99mTc-hexamethyl-propyleneamine oxime. Forty-four control subjects were also studied. We used the adjusted regional cerebral blood flow images in relative flow distribution (normalization of global cerebral blood flow for each subject to 50 ml x 100 g(-1) x min(-1) with proportional scaling) to compare these groups with statistical parametric mapping. Using this technique, significantly decreased regional cerebral blood flow was noted extensively in the bilateral frontal lobes as well as the bilateral insula and a part of the right temporal lobe in the patients with delayed neuropsychiatric sequelae as compared with normal volunteers (P< 0.005). In the patients with no neuropsychiatric symptoms, significantly decreased regional blood flow in the bilateral frontal lobes particularly on the left side was detected. There was a significantly decreased regional cerebral blood flow in the right frontal lobe and insula in the patients with delayed neuropsychiatric sequelae as compared to those with no neuropsychiatric sequelae. It is concluded that statistical parametric mapping is a useful technique for highlighting differences in regional cerebral blood flow in patients following carbon monoxide intoxication as compared with normal volunteers. The selectively reduced blood flow noted in this investigation supports the contention that the decrease following carbon monoxide intoxication may be prolonged and further worsen in the frontal lobe. In addition, the present study may help to clarify the characteristics of the pathophysiological alteration underlying delayed neuropsychiatric sequelae.

Carbon monoxide poisoning--a public health perspective

Carbon monoxide (CO) may be the cause of more than one-half of the fatal poisonings reported in many countries; fatal cases also are grossly under-reported or misdiagnosed by medical professionals. Therefore, the precise number of individuals who have suffered from CO intoxication is not known. The health effects associated with exposure to CO range from the more subtle cardiovascular and neurobehavioral effects at low concentrations to unconsciousness and death after acute or chronic exposure to higher concentrations of CO. The morbidity and mortality resulting from the latter exposures are described briefly to complete the picture of CO exposure in present-day society. The symptoms, signs, and prognosis of acute CO poisoning correlate poorly with the level of carboxyhemoglobin (COHb) measured at the time of hospital admission; however, because CO poisoning is a diagnosis frequently overlooked, the importance of measuring COHb in suspicious settings cannot be overstated. The early symptoms (headache, dizziness, weakness, nausea, confusion, disorientation, and visual disturbances) also have to be emphasized, especially if they recur with a regular periodicity or in the same environment. Complications occur frequently in CO poisoning. Immediate death is most likely cardiac in origin because myocardial tissues are most sensitive to the hypoxic effects of CO. Severe poisoning results in marked hypotension, lethal arrhythmias, and electrocardiographic changes. Pulmonary edema may occur. Neurological manifestation of acute CO poisoning includes disorientation, confusion, and coma. Perhaps the most insidious effect of CO poisoning is the development of delayed neuropsychiatric impairment within 2-28 days after poisoning and the slow resolution of neurobehavioral consequences. Carbon monoxide poisoning during pregnancy results in high risk for the mother by increasing the short-term complication rate and for the fetus by causing fetal death, developmental disorders, and chronic cerebral lesions. In conclusion, CO poisoning occurs frequently; has severe consequences, including immediate death; involves complications and late sequelae; and often is overlooked. Efforts in prevention and in public and medical education should be encouraged.

Adaptive responses and apoptosis in endothelial cells exposed to carbon monoxide

Prior studies have shown that exposure to carbon monoxide (CO) will elevate the steady-state concentration of nitric oxide ((.)NO) in several cell types and body organs and that some toxic effects of CO are directed toward endothelial cells. Studies reported in this paper were conducted with bovine pulmonary artery endothelial cells exposed to 10 to 100 ppm CO to achieve concentrations between 11 and 110 nM in air-saturated buffer. Exposure to 11 nM CO increased synthesis of manganous superoxide dismutase and conferred resistance against the lethal effects of 110 nM CO. At concentrations of 88 nM CO or more, exposures for 1 h or longer caused cell death that became apparent 18 h after the exposure ceased. Caspase-1 was activated in response to CO, and cell death was inhibited by a caspase-1 inhibitor. Alteration of proteolytic pathways by CO was indicated by the presence of ubiquitin-containing intracellular inclusion bodies. Morphological changes and caspase activation indicated that cell death was an apoptotic process. Cells exposed to 110 nM CO had higher concentrations of manganous superoxide dismutase and heme oxygenase-1 but no changes in glutathione peroxidase, glucose-6-phosphate dehydrogenase, thiols, or catalase. Elevated levels of antioxidant enzymes and apoptosis were inhibited by the nitric oxide synthase inhibitor, S-isopropylisothiourea, and the peroxynitrite scavenger, selenomethionine. These results show that biochemical effects of CO occur at environmentally relevant concentrations, that apoptotic cell death follows exposure to relatively high concentrations of CO, and that these actions of CO are mediated by nitric oxide.

MRI, quantitative MRI, SPECT, and neuropsychological findings following carbon monoxide poisoning

Carbon monoxide (CO) poisoning has been shown to result in neuropathologic changes and cognitive impairments due to anoxia and other related biochemical mechanisms. The present study investigated brain-behaviour relationships between neuropsychological outcome and SPECT, MRI, and Quantitative magnetic resonance imaging (QMRI) in 21 patients with CO poisoning. Ninety-three per cent of the patients exhibited a variety of cognitive impairments, including impaired attention, memory, executive function, and mental processing speed. Ninety-five per cent of the patients experienced affective changes including depression and anxiety. The results from the imaging studies revealed that 38% of the patients had abnormal clinical MRI scans, 67% had abnormal SPECT scans, and 67% had QMRI findings including hippocampal atrophy and/or diffuse cortical atrophy evidenced by an enlarged ventricle-to-brain ratio (VBR). Hippocampal atrophy was also found on QMRI. SPECT and QMRI appear to be sensitive tools which can be used to identify the neuropathological changes and cerebral perfusion defects which occur following CO poisoning. Cerebral perfusion defects include frontal and temporal lobe hypoperfusion. Significant relationships existed between the various imaging techniques and neuropsychological impairments. The data from this study indicate that a multi-faceted approach to clinical evaluation of the neuropathological and neurobehavioural changes following CO poisoning may provide comprehensive information regarding the neuroanatomical and neurobehavioural effects of CO poisoning.

The significance of cobalt-55 positron emission tomography in ischemic stroke

Cobalt-55 ((55)Co) has been shown to be an interesting positron emission tomography (PET) tracer that may reflect calcium (Ca) influx in damaged cerebral tissue. Because Ca load is important in the ischemic cascade, the exact meaning of (55)Co PET in stroke patients has to be shown. The present study compares the degree of (55)Co uptake to regional cerebral blood flow (rCBF) and regional cerebral metabolic rate for oxygen (rCMRO(2)) values in brains of patients with ischemic stroke. Eighteen patients with an ischemic event in the middle cerebral artery territory were examined with PET using, in the same session, (55)Co and the (15)O steady state technique. The (55)Co ratio was assessed in ischemic and infarcted regions and compared with the corresponding rCBF and rCMRO(2) values. The average (55)Co ratio is inversely correlated to the rCBF and rCMRO(2) values. Also (55)Co accumulation tends to increase during the weeks after the onset of stroke and decreases down to normal levels after 6 months. The degree of (55)Co uptake corresponds to the severity of the ischemic damage within the first month after stroke. As it increases with time, it probably reflects the Ca accumulation caused by the progression of the inflammatory response within and around the infarct core.

Magnetic resonance imaging and 11C-N-methylspiperone/positron emission tomography studies in a patient with the interval form of carbon monoxide poisoning

Magnetic resonance (MR) and (11)C-N-methylspiperone ((11)C-NMSP)/positron emission tomography (PET) imagings were repeatedly performed in a 50-year-old man with the interval form of carbon monoxide (CO) poisoning. In MR images obtained when delayed neuropsychiatric symptoms developed (two months after poisoning), the inner segments of the bilateral globus pallidus appeared as high signal intensities in the T1-weighted and low signal intensities in the T2-weighted images, suggesting prior focal hemorrhage in these areas. A PET study with (11)C-NMSP performed at that time showed an increase in dopamine D2 receptor binding in the caudate and putamen. Treatment with bromocriptine was very effective and five months after the poisoning, MR and (11)C-NMSP/PET images showed improvement, concomitantly with the disappearance of the neuropsychiatric symptoms.

Pathophysiology and treatment of carbon monoxide poisoning

Carbon monoxide poisoning is the leading cause of poisoning deaths in the US, and published reports of carbon monoxide related morbidity and mortality can vary widely. Common morbidity involves myocardial and/or neurologic injury including delayed neurologic sequelae. The pathophysiology of this entity is complex, involving hypoxic stress on the basis of interference with oxygen transport to the cells and possibly impairing electron transport. Carbon monoxide can also affect leukocytes, platelets and the endothelium, inducing a cascade of effects resulting in oxidative injury. Carboxyhemoglobin levels are valuable for confirming carbon monoxide exposure but cannot be used to stratify severity of poisoning, predict prognosis, or indicate a specific treatment plan. Oxygen therapy is the key treatment of carbon monoxide intoxication, and hyperbaric oxygen has been shown to interdict and improve clinical outcome in some patients. Immediate treatment with a high fraction of inspired oxygen and careful clinical evaluation are mandatory. Timely referral for hyperbaric oxygen is indicated for patients with any history of unconsciousness, cardiovascular instability or ischemia, and persistent mental and/or neurologic deficits. Hyperbaric oxygen should also be considered in certain other patient subsets.