Cardiovascular manifestations of moderate to severe carbon monoxide poisoning

OBJECTIVES

We describe the cardiovascular manifestations of carbon monoxide (CO) poisoning.

BACKGROUND

Carbon monoxide poisoning is a common cause of toxicologic morbidity and mortality. Although the neurologic sequelae of CO poisoning have been well described, the cardiovascular consequences are limited to isolated case reports.

METHODS

We reviewed the cardiovascular manifestations of 230 consecutive patients treated for moderate to severe CO poisoning in the hyperbaric oxygen chamber at Hennepin County Medical Center (HCMC), a regional center for treatment of CO poisoning.

RESULTS

The mean age was 47.2 years with 72% men. Ischemic electrocardiogram (ECG) changes were present in 30% of patients, whereas only 16% had a normal ECG. Cardiac biomarkers (creatine kinase-MB fraction or troponin I) were elevated in 35% of patients. In-hospital mortality was 5%.

CONCLUSIONS

Cardiovascular sequelae of CO poisoning are frequent, with myocardial injury assessed by biomarkers or ECG in 37% of patients. Patients admitted to the hospital with CO poisoning should have a baseline ECG and serial cardiac biomarkers.

Trial of normobaric and hyperbaric oxygen for acute carbon monoxide intoxication

The value of hyperbaric oxygen in the treatment of acute carbon monoxide intoxication was assessed in 629 adults who had been poisoned at home in the 12 h before admission to hospital. In patients without initial impairment of consciousness (group A) the effect of 6 h of normobaric oxygen (NBO) (group A0, n = 170) was compared with that of 2 h of hyperbaric oxygen (HBO) at 2 atmospheres absolute (ATA) plus 4 h NBO (group A1, n = 173). At the 1 month follow-up 66% of A0 and 68% of A1 patients had recovered. In patients with initial impairment of consciousness the effect of one session of HBO (group B1, n = 145) was compared with that of two sessions (group B2, n = 141); all group B patients also received 4 h of NBO. At 1 month of follow-up 54% group B1 and 52% group B2 patients had recovered. The 7 patients left with neuropsychiatric sequelae (3 B1, 4 B2) and the 4 who died (2 B1, 2 B2) had all presented with coma. HBO was not useful in patients who did not lose consciousness during carbon monoxide intoxication, irrespective of their carboxyhaemoglobin level, nor were two sessions of HBO in patients who sustained only a brief loss of consciousness. The prognosis is poorest for those presenting with coma; the trial needs to be pursued in this group of patients until the power of the study is sufficient to demonstrate the value or otherwise of HBO.

Toxicity of fire smoke

This review is an attempt to present and describe the major immediate toxic threats in fire situations. These are carbon monoxide, a multitude of irritating organic chemicals in the smoke, oxygen depletion, and heat. During the past 50 years, synthetic polymers have been introduced in buildings in very large quantities. Many contain nitrogen or halogens, resulting in the release of hydrogen cyanide and inorganic acids in fire smoke as additional toxic threats. An analysis of toxicological findings in fire and nonfire deaths and the results of animal exposures to smoke from a variety of burning materials indicate that carbon monoxide is still likely to be the major toxicant in modern fires. However, the additional toxic threats mentioned above can sometimes be the principal cause of death or their addition can result in much lower than expected carboxyhemoglobin levels in fire victims. This analysis also revealed that hydrogen cyanide is likely to be present in appreciable amounts in the blood of fire victims in modern fires. The mechanisms of action of acute carbon monoxide and hydrogen cyanide poisonings are reviewed, with cases presented to illustrate how each chemical can be a major contributor or how they may interact. Also, lethal levels of carboxyhemoglobin and cyanide in blood are suggested from an analysis of the results of a large number of fire victims from different fire scenarios. The contribution of oxygen depletion and heat stress are more difficult to establish. From the analysis of several fire scenarios, they may play a major role in the room of origin at the beginning of a fire. The results in animal studies indicate that when major oxygen depletion (<10%) is added to lethal or sublethal levels of carbon monoxide or hydrogen cyanide its major role is to substantially reduce the time to death. In these experiments the carboxyhemoglobin level at death was slightly reduced from the expected level with exposure to carbon monoxide alone. However, blood cyanide was reduced by a factor of ten from the expected level with exposure to hydrogen cyanide alone. This is another factor (among many other presented) complicating the task of establishing the contribution of cyanide in the death of fire victims, from its analysis in their blood. Finally the role of ethanol intoxication, as it may influence carboxyhemoglobin levels at death, is reviewed. Its role is minor, if any, but the data available on ethanol in brain tissue and blood of fire victims confirmed that brain ethanol level is an excellent predictor of blood ethanol.

Carboxyhemoglobin half-life in carbon monoxide-poisoned patients treated with 100% oxygen at atmospheric pressure

STUDY OBJECTIVES

There are large reported differences for the carboxyhemoglobin (COHb) half-life (COHb t(1/2)) in humans breathing 100% atmospheric O(2) following CO inhalation in tightly controlled experiments compared to the COHb t(1/2) observed in clinical CO poisoning (range, 36 to 131 min, respectively). Other reports have suggested that the COHb t(1/2) may be affected by gender differences, age, and lung function. We wished to test the hypothesis that the COHb t(1/2) might also be influenced by CO poisoning vs experimental CO exposure, by a history of loss of consciousness (LOC), concurrent tobacco smoking, and by PaO(2). The purpose of the present study was to measure the COHb t(1/2) in a cohort of CO-poisoned patients and to determine if those listed factors influenced the COHb t(1/2).

DESIGN

Retrospective chart review from 1985 to 1995. We calculated the COHb t(1/2) of CO-poisoned patients who were treated with high-flow supplemental atmospheric pressure O(2) delivered by nonrebreather face mask or endotracheal tube.

SETTING

Hyperbaric medicine department of a tertiary-care teaching hospital.

PATIENTS

Of 240 CO-poisoned patients, 93 had at least two COHb measurements > 2% (upper limit of normal) with recorded times of the measurements, permitting calculation of the COHb t(1/2).

RESULTS

The COHb t(1/2) was 74 +/- 25 min (mean +/- 1 SD) with a range from 26 to 148 min. By stepwise multiple linear regression analysis, the PaO(2) influenced the COHb t(1/2) (R(2) = 0.19; p < 0.001), whereas the COHb t(1/2) was not influenced by gender, age, smoke inhalation, history of LOC, concurrent tobacco smoking, degree of initial metabolic acidosis (base excess), or initial COHb level.

CONCLUSIONS

The COHb t(1/2) of 93 CO-poisoned patients treated with 100% O(2) at atmospheric pressure was 74 +/- 25 min, considerably shorter than the COHb t(1/2) reported in prior clinical reports (approximately 130 +/- 130 min) and was influenced only by the patient's PaO(2).

Subacute sequelae of carbon monoxide poisoning

From January 1980 to August 1983, 213 patients with carbon monoxide poisoning were seen; 131 received hyperbaric oxygen and had no sequelae. Eighty-two patients were treated with normobaric oxygen; ten (12.1%) returned with clinically significant sequelae. The specific neurological sequelae included headaches, irritability, personality changes, confusion, and loss of memory. This recurrent symptomatology developed within one to 21 days (mean, 5.7 days) after the initial exposure, although no reexposure occurred. These recurring symptoms resolved rapidly with hyperbaric oxygen therapy. We recommend that hyperbaric oxygen therapy be used whenever CO poisoning symptoms recur.

Treatment of acute carbon monoxide poisoning with hyperbaric oxygen: a review of 115 cases

From January 1978 through March 1984, 115 cases of acute carbon monoxide poisoning were treated with hyperbaric oxygen. Exposure resulted from accidental sources (n = 39), attempted suicide (n = 47), and smoke inhalation (n = 29). Forty-one victims were never unconscious, 30 victims were unconscious at the scene but awoke before arriving at the hospital, and 44 victims were unconscious in the ED. Eleven patients (9.6%) died, and two victims (1.9% of the survivors) experienced major sequelae. All these patients were comatose on arrival. The remaining 102 patients recovered fully. Carboxyhemoglobin levels did not correlate with clinical findings, thereby demonstrating the variability between carbon monoxide exposure and impairment of the cellular cytochrome system. Hyperbaric oxygen therapy facilitates the rapid removal of carbon monoxide from the hemoglobin and cytochrome systems while reoxygenating compromised tissues, and it can be an effective treatment in reducing mortality and morbidity.

Pulse oximetry in severe carbon monoxide poisoning

STUDY OBJECTIVES

To evaluate the accuracy and quantitate the error of pulse oximetry measurements of arterial oxygenation in patients with severe carbon monoxide (CO) poisoning.

DESIGN

Retrospective review of patient clinical records.

SETTING

Regional referral center for hyperbaric oxygen therapy.

PATIENTS

Thirty patients referred for treatment of acute severe CO poisoning who demonstrated carboxyhemoglobin (COHb) levels >25%, with simultaneous determinations of arterial hemoglobin oxygen saturation by pulse oximetry (SpO2) and arterial blood gas (ABG) techniques.

MEASUREMENTS AND RESULTS

COHb levels and measurements of arterial oxygenation from pulse oximetry, ABG analysis, and laboratory CO oximetry were compared. SpO2 did not correlate with COHb levels. SpO2 consistently overestimated the fractional arterial oxygen saturation. The difference between arterial hemoglobin oxygen saturation (SaO2) calculated from ABG analysis and SpO2 increased with increasing COHb level.

CONCLUSIONS

Presently available pulse oximeters overestimate arterial oxygenation in patients with severe CO poisoning. An elevated COHb level falsely elevates the SaO2 measurements from pulse oximetry, usually by an amount less than the COHb level, confirming a prior observation in an animal model. Accurate assessment of arterial oxygen content in patients with CO poisoning can currently be performed only by analysis of arterial blood with a laboratory CO-oximetry.

Cardiovascular effects of carbon monoxide poisoning

Carbon monoxide (CO) poisoning is an important health problem. Cardiac abnormalities may occur in patients with CO poisoning; however, the severity and duration of cardiac abnormalities are not well known. In this study, cardiac structures and function in CO poisoning were evaluated prospectively. Twenty patients were enrolled in the study. Echocardiographic examination was performed in all patients on admission, at 24 hours, and within the first week. B-type natriuretic peptide and carboxyhemoglobin levels were measured. Patients with increased cardiac markers underwent coronary angiography. Cardiac markers were high in 6 patients. Patients with high cardiac markers had significantly higher carboxyhemoglobin levels and longer exposure to CO. Left ventricular ejection fraction (LVEF) was <45% in 8 patients (group I) on admission and >55% in 7 patients in group I 24 hours after echocardiography. A significant negative correlation was found between B-type natriuretic peptide and LVEF on admission (r = -0.586, p <0.01). The decrease in LVEF was also negatively correlated with carboxyhemoglobin level and CO exposure duration. All angiograms showed normal coronary arteries. In conclusion, despite normal coronary arteries, myocardial dysfunction may occur in patients with CO poisoning. LV systolic function might be normal or mildly to severely impaired. However, most of the myocardial dysfunction dissipates at 24 hours in patients with CO poisoning.

The relationship between exposure duration, carboxyhemoglobin, blood glucose, pyruvate and lactate and the severity of intoxication in 39 cases of acute carbon monoxide poisoning in man

The relationship between exposure duration, COHb, blood glucose, pyruvate and lactate and the severity of intoxication was investigated in a group of 39 cases of acute CO poisoning treated in the Clinical Toxicology Center in Lódź, Poland. On the basis of clinical criteria the patients were classified into cases of mild, moderate, severe and very severe CO poisoning. COHb and carbohydrate metabolites were estimated in venous blood taken immediately after admission of the patient to hospital prior to treatment. The severity of intoxication did not correlate with blood COHb; variation in exposure duration seems to be responsible for this phenomenon. Severe and very severe poisonings were associated with longer exposures and were accompanied by a markedly higher blood lactate level, compared to mild and moderate cases. Blood pyruvate depended less than lactate on the severity of intoxication. Blood glucose depended neither on exposure duration nor on the severity of intoxication. Among the carbohydrate metabolic parameters studied, blood lactate determination can be helpful in the evaluation of the severity of CO poisoning in man.

Analysis of carbon monoxide

The degree of exposure to carbon monoxide is most often assessed by measuring the blood carboxyhaemoglobin saturation. This measurement is relevant to investigations of acute accidental or deliberate poisoning and of chronic exposure in a domestic or work place environment. Simple spectrophotometric methods based on differential protein precipitation or dithionite reduction are prone to interference from other haemoglobin pigments and are imprecise for low-level estimations. Automated spectrophotometric devices (CO-oximeters) that estimate simultaneously total haemoglobin, percentage oxyhaemoglobin and percentage carboxyhaemoglobin have acceptable accuracy for carboxyhaemoglobin saturation levels of > 5% and are recommended for most clinical purposes. For the investigation of low-level exposure and the detection of increased haemolysis in neonates, more sensitive methods involving the release of carbon monoxide and its measurement by gas chromatography are required. Gas chromatographic methods are also appropriate when examining post-mortem blood samples where putrefaction or heat stress has resulted in a significant change in haemoglobin composition.

The pulse oximetry gap in carbon monoxide intoxication

STUDY OBJECTIVE

Pulse oximetry has been reported to be falsely elevated in the presence of carbon monoxide (CO). However, the degree to which pulse oximetry overestimates measured oxyhemoglobin saturation (O2Hb) has not been investigated in patients with CO exposure. This study quantifies the effect of CO on pulse oximetry and O2Hb in a series of patients with elevated carboxyhemoglobin (COHb) levels.

METHODS

A prospective case series of 25 pulse oximetry measurements, with concurrent arterial blood gas sampling, were obtained on 16 adults with CO exposure.

RESULTS

COHb levels (mean, 16.1%; SD, 11.6%; range, 2.2% to 44%) did not significantly correlate with pulse oximetry saturation (mean, 97.7%; SD, 1.5%; range 96% to 100%) (r = .45; P = .1 [NS]). Compared with COHb, a pulse oximetry gap (mean, 17.5%; SD, 1.5%; range, 2.3% to 42%), defined as pulse oximetry saturation minus O2Hb, yielded a linear regression model: pulse oximetry gap = 1.82 + 0.94 x COHb (SEM = 0.07; F = 204; R2 = .90; P < .0001).

CONCLUSION

Oxygen saturation as measured by pulse oximetry failed to decrease to less than 96% despite COHb levels as high as 44%. Regression between the pulse oximetry gap and COHb suggests that pulse oximetry overestimates O2Hb by the amount of COHb present. Pulse oximetry is unreliable in estimating O2Hb saturation in CO-exposed patients and should be interpreted with caution when used to estimate oxygen saturation in smokers.

Relationship between venous and arterial carboxyhemoglobin levels in patients with suspected carbon monoxide poisoning

STUDY OBJECTIVE

To test the hypothesis that venous carboxyhemoglobin (V-COHb) levels accurately predict arterial (A-COHb) levels.

DESIGN

Prospective comparison of A-COHb and V-COHb levels in patients with suspected carbon monoxide (CO) poisoning.

SETTING

Municipal hospital emergency department with contiguous multiplace hyperbaric chamber staffed 24 hours a day.

PARTICIPANTS

Unselected convenience sample of 61 adults with suspected CO toxicity.

INTERVENTION

Simultaneous sampling of arterial and venous blood.

RESULTS

Correlation between V-COHb and A-COHb showed an r value of .99 (95%CI, .99 to .99), and an r2 value of .98. Agreement between V-COHb and A-COHb levels was examined by use of a plot of arteriovenous differences against the mean of the two measurements. The mean arteriovenous difference was .15% COHb (95%CI, .13% to .45%), with 95% of the differences ranging from 2.4% COHb to -2.1% COHb.

CONCLUSION

Venous COHb levels predict arterial levels with a high degree of accuracy. Patients with suspected CO poisoning can be screened with the use of venous blood, without the need for arterial puncture.

Nitric oxide released by platelets inhibits neutrophil B2 integrin function following acute carbon monoxide poisoning

Carbon monoxide (CO) poisoning has been reported to temporarily inhibit B2 integrin adherence molecules on leukocytes in previous studies in a rat model. The aim of this study was to investigate the mechanism for this effect. Studies were conducted using blood obtained from rats after they were exposed to CO and also with blood cells exposed to CO in vitro. Initial investigations indicated that inhibition of neutrophil (polymorphonuclear leukocyte, PMN) B2 integrin function was linked to the platelets in blood, as the effect was resolved by decreasing platelet number before PMN adherence was tested. The platelet effect could also be shown by incubating either platelet-rich plasma or whole blood with CO in vitro. The effect of platelets was blocked by superoxide radicals and by NG-nitro-L-arginine methyl ester, an inhibitor of nitric oxide (NO) synthase. These observations suggested that CO caused platelets to release NO, an agent known to inhibit the function of B2 integrins. The concentration of NO measured in suspensions of platelets from rats poisoned with CO according to the established model (exposure to 1000 ppm CO for 40 min and 3000 ppm CO for 20 min) was 47 nmol/10(8) platelets, in contrast to only 0.3 nmol NO/10(8) platelets from control rats. Enhanced NO release occurred despite a 60% inhibition of NO synthase activity, assessed by measuring conversion of [14C]L-arginine to citrulline. Exposure to only 1000 ppm CO for 1 hr caused platelets to release 74 nmol NO/10(8) platelets, and no inhibition of NO synthase occurred. Enhanced NO release, and inhibition of PMN adherence, did not occur after platelets were exposed to light from a quartz lamp to photodissociate CO from heme proteins. The data suggest that the NO flux from platelets increased when CO became bound to heme-containing platelet proteins, which normally scavage intraplatelet NO and thus prevent diffusion beyond the platelet membrane.

Selection criteria utilized for hyperbaric oxygen treatment of carbon monoxide poisoning

Medical directors of North American hyperbaric oxygen (HBO) facilities were surveyed to assess selection criteria applied for treatment of acute carbon monoxide (CO) poisoning within the hyperbaric medicine community. Responses were received from 85% of the 208 facilities in the United States and Canada. Among responders, 89 monoplace and 58 multiplace chamber facilities treat acute CO poisoning, managing a total of 2,636 patients in 1992. A significant majority of facilities treat CO-exposed patients with coma (98%), transient loss of consciousness (LOC) (77%), ischemic changes on electrocardiogram (91%), focal neurologic deficits (94%), or abnormal psychometric testing (91%), regardless of carboxyhemoglobin (COHb) level. Although 92% would use HBO for a patient presenting with headache, nausea, and COHb 40%, only 62% of facilities utilize a specified minimum COHb level as the sole criterion for HBO therapy of an asymptomatic patient. When COHb is used as an independent criterion to determine HBO treatment, the level utilized varies widely between institutions. Half of responding facilities place limits on the delay to treatment for patients with only transient LOC. Time limits are applied less often in cases with persistent neurologic deficits. While variability exists, majority opinions can be derived for many patient selection criteria regarding the use of HBO in acute CO poisoning.

Predictors of occult carbon monoxide poisoning in patients with headache and dizziness

Headache and dizziness occur at carboxyhemoglobin levels of greater than 10%. We studied 89 patients with headache or dizziness for evidence of carbon monoxide exposure. The mean carboxyhemoglobin level was 2.87%. Number of cigarettes smoked per day (r = 0.471; p less than 0.00002), use of gas kitchen stoves for heating purposes (r = 0.252, p less than 0.02), problems with the home heating system (r = 0.278, p less than 0.01), and cohabitants with concurrent headache or dizziness (r = 0.427, p less than 0.01) correlated with carboxyhemoglobin levels. Multiple regression analysis identified number of cigarettes smoked daily, use of stoves for heat, and concurrently symptomatic cohabitants as significant predictors of carboxyhemoglobin level (F = 13.939 [3, 85]; p less than 0.01). Obtaining carboxyhemoglobin levels from patients who used stoves for heat or had similarly affected cohabitants identified 4 of 4 patients with levels greater than 10% (sensitivity, 100%) and excluded 47 of 85 patients with lower levels (specificity, 55.3%). The 4 patients with carboxyhemoglobin levels in excess of 10% may represent occult carbon monoxide poisoning in this population.

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.

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.

"First pass phenomenon" of inhaled gas in the fire victims

We investigated the differences in the levels of carboxyhemoglobin (COHb), cyanide (HCN) and petroleum fuels (gasoline and kerosene) between left and right ventricular bloods from fire victims. COHb was slightly, and HCN and petroleum fuels were markedly higher levels in the left than those in the right. These effects were so called 'first pass phenomena' due to the circulation, diffusion and metabolization before the deaths of fire victims.

Pediatric carbon monoxide toxicity

We report a series of 28 pediatric carbon monoxide exposures. Sixteen patients (57%) were judged to have potentially toxic carboxyhemeglobin (COHb) levels (greater than 15%). In this group the range of COHb blood levels was 16.7% to 44.0% (mean = 26.5%). An unusually high incidence of syncope (56.3%, 9/16) and lethargy (68.7%, 11/16) was observed. Every patient with a COHb level greater than or equal to 24% experienced syncope; a marked departure from published adult values. Lethargy was reported at a mean COHb concentration of 25.9%. All patients with levels over 25% COHb, neurologic findings, acidosis, or syncope were considered candidates for hyperbaric oxygen therapy (HBOT). No morbidity from HBOT was encountered. Eighty-nine percent (25/28) of the patients are reportedly doing well, with no late sequelae identified. Delayed neurologic sequelae in three patients include chronic headaches, memory difficulties, or decline in school performance.

Is elevated plasma lactate a useful marker in the evaluation of pure carbon monoxide poisoning?

OBJECTIVE

To examine whether CO poisoning induces a significant increase in plasma lactate concentration.

DESIGN AND SETTING

Prospective observational clinical study in the emergency department and intensive care unit in a university-affiliated teaching hospital.

PATIENTS

146 pure CO poisonings resulting from dysfunction of gas cookers or water heaters.

MEASUREMENTS AND RESULTS

Patients were classified into four neurological impairment groups: 37% were severely, 8% moderately, and 45% mildly intoxicated, while 1% were asymptomatic. We found only very mild increases in plasma lactate concentration (median 2.30 mmol/l) which, however, was significantly correlated with the severity of neurological impairment and blood CO concentration (1.41 mmol/l, Spearman's test r=0.3).

CONCLUSIONS

Plasma lactate is mildly elevated in pure CO-exposed patients. This mild increase and the extensive overlap between the groups of neurological impairment severity do not suggest the usefulness of systematic plasma lactate measurement in pure CO poisoning.

Are arterial blood gases of value in treatment decisions for carbon monoxide poisoning?

Traditionally, the carboxyhemoglobin (HbCO) level has been used to estimate the severity of carbon monoxide (CO) poisoning. Through extensive clinical experience, we have found this to be an inaccurate correlation; thus, other variables such as pHa or psychometric abnormalities have been assessed to determine severity from CO poisoning. In a 5-yr experience with 247 patients, on admission 114 had an arterial blood gas and HbCO determinations, and 88 also had psychometric testing. The data were evaluated to determine any relationship between pH and HbCO level; a weak correlation (r approximately equal to -0.3) was discovered. A comparison of psychometric testing with HbCO level showed a much stronger statistical relationship. The definition of HbCO poisoning severity may be better determined by psychometric testing than by the HbCO level because psychometric testing measures actual neurologic disability. The weak correlation between both psychometric testing and the HbCO level with pHa reinforces the clinical impression that patients with acidosis, alkalosis, or normal blood gases could have equally severe neurologic symptomatology at HbCO levels ranging from 1% to 62%.

Rate of formation of carboxyhemoglobin in exercising humans exposed to carbon monoxide

The purpose of this study was to test the CFK equation for its prediction of the rate of formation of carboxyhemoglobin (HbCO) in exercising humans by use of measured values of the respiratory variables and to characterize the rate of appearance of HbCO with frequent blood sampling. Ten nonsmoking male subjects were exposed to carbon monoxide (CO) on two separate occasions distinguished by the level of activity. Steady-state exercise was conducted on a cycle ergometer at either a low (approximately 45 W) or moderate (approximately 90 W) power output. Each experiment began with an exposure of 3,000 ppm CO for 3 min during a rest period followed by three intermittent exposures ranging from 3,000 ppm CO for 1 min at low exercise to 667 ppm CO for 3 min at moderate exercise. Increases in HbCO were normalized against predicted values to account for individual differences in the variables that govern CO uptake. No difference in the normalized uptake of CO was found between the low- and moderate-exercise trials. However, the CFK equation underpredicted the increase in HbCO for the exposures at rest and the first exposure at exercise, whereas it overpredicted for the latter two exposures at exercise. The net increase in HbCO after all exposures (approximately 10% HbCO) deviated by less than 1% HbCO between the measured and predicted values. The rate of appearance of HbCO fits a sigmoidal shape with considerable overshoot at the end of exposure. This can be explained by delays in the delivery of CO to the blood sampling point (dorsal hand vein) and by a relatively small blood circulation time compared with other regions of the body. A simple circulation model is used to demonstrate the overshoot phenomenon.

Occult carbon monoxide poisoning: a cause of winter headache

Headache is an early symptom of carbon monoxide (CO) poisoning, occurring at carboxyhemoglobin (COHb) levels of greater than 10%. We investigated 37 patients presenting to an emergency department during the winter-heating season with a complaint of headache for evidence of CO exposure. Seven of the 37 patients (18.9%) had COHb levels in excess of 10%, with a mean of 14.0%. Three of these seven patients (42.9%) used gas space heaters or kitchen stoves to heat their homes, and three (42.9%) had cohabitants at home with headache. Of the 30 patients with COHb levels of less than 10% (mean level, 3.2%), only four (13.3%) used gas space heaters and kitchen stoves for heat (P = NS), and none (0%) had cohabitants with headache (P = .0045). In six of the seven patients with elevated COHb levels (85.7%), gas company investigation or historical information obtained retrospectively revealed a definite or probably toxic CO exposure. In none of these patients had the diagnosis of CO poisoning been suspected by the emergency department physician or the patient prior to obtaining the result of the COHb level. Occult CO poisoning may be an important cause of winter headache.

Complications and protocol considerations in carbon monoxide-poisoned patients who require hyperbaric oxygen therapy: report from a ten-year experience

We conducted a study to determine the type, incidence, and timing of complications that occur in patients who have a carbon monoxide (CO) exposure serious enough to require hyperbaric oxygen therapy (HBOT). Complication data were retrospectively collected from a ten-year period for 297 consecutive CO-poisoned emergency department patients who received HBOT. HBOT was indicated for 41% of the patients because of an elevated carboxyhemoglobin (COHb) level alone. Central nervous system dysfunction, including loss of consciousness, and/or cardiovascular dysfunction, was the criteria for HBOT in 59% of patients, regardless of their COHb level. The mean peak COHb level was 38 mg%, with 88% of patients having a peak COHb level greater than 25 mg%. The mortality rate was 6% in this case series. Cardiac arrest occurred in 8% of patients; all experienced their first arrest prior to HBOT. The 3% of patients who sustained an isolated respiratory arrest and those who had a myocardial infarction did so prior to HBOT. Several complications, however, occurred for the first time or as a recurrent event during HBOT. These included emesis (6%), seizures (5%), agitation requiring restraints or sedation (2%), cardiac dysrhythmias or arrests (2%), and arterial hypotension (2%). No patient's level of consciousness deteriorated subsequent to the initial resuscitation except for those who later had a generalized seizure. The most significant complication attributable to HBOT was tension pneumothorax, noted in three patients (1%).(ABSTRACT TRUNCATED AT 250 WORDS)

Outcome of patients experiencing cardiac arrest with carbon monoxide poisoning treated with hyperbaric oxygen

STUDY OBJECTIVE

We sought to examine the outcome of a subgroup of patients with extreme carbon monoxide (CO) poisoning, specifically those discovered in cardiac arrest, resuscitated, and subsequently treated with hyperbaric oxygen (HBO(2)). Opinions of hyperbaric medicine physicians regarding the treatment of such patients were also sought.

METHODS

Records of patients treated with HBO(2) for acute CO poisoning at Virginia Mason Medical Center in Seattle from September 1987 to August 2000 were reviewed. Those who were resuscitated from cardiac arrest in the field before HBO(2) treatment were selected for detailed analysis. Patient demographic data and information regarding circumstances of the poisoning, resuscitation, HBO(2) treatment, and subsequent course were extracted and collated. In addition, a postal survey of medical directors of North American HBO(2) treatment facilities regarding opinions about the management and outcome of such patients was performed.

RESULTS

A total of 18 patients were treated with HBO(2) after resuscitation from CO-associated cardiac arrest. They included 10 female and 8 male patients ranging in age from 3 to 72 years. Sources of CO included house fires (10 patients) and automobile exhaust (8 patients). Patient carboxyhemoglobin levels averaged 31.7%+/-11.0% (mean+/-SD), and arterial pH averaged 7.14+/-0.19. Presenting cardiac rhythm was a bradydysrhythmia in 10 of 18 patients. HBO(2) treatment was administered an average of 4.3 hours after poisoning (< or = 3 hours in 10 patients and < or = 6 hours in 15 patients). Despite this, all 18 patients died during their hospitalizations. Medical directors of hyperbaric treatment facilities estimated a 74% likelihood of survival for a hypothetical patient with this presentation.

CONCLUSION

In this consecutive case series, cardiac arrest complicating CO poisoning was uniformly fatal, despite administration of HBO(2) therapy after initial resuscitation. Survey results suggest that physician education regarding this subset of CO-poisoned patients is needed. The prognosis of this condition should be considered when making triage and treatment decisions for patients poisoned to this severity.