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EMJ Online First, published on October 15, 2013 as 10.1136/emermed-2012-201712 Original article
Carbon monoxide poisoning in patients presenting to the emergency department with a headache in winter months Nilay Zorbalar, Murat Yesilaras, Ersin Aksay Department of Emergency Medicine, Izmir Tepecik Research and Educational Hospital, Izmir, Turkey Correspondence to Dr Ersin Aksay, Department of Emergency Medicine, Izmir Tepecik Research and Educational Hospital, Izmir, Turkey; [email protected] Received 5 July 2012 Revised 11 March 2013 Accepted 21 September 2013
ABSTRACT Background Carbon monoxide (CO) poisoning is an important reason for emergency department (ED) visits during winter months, but because there are no specific symptoms it can be difficult to diagnose. We aimed to determine the frequency of CO poisoning in patients presenting to the ED with headaches during winter months and evaluate the ability of non-invasive carboxyhaemoglobin measurement (SpCO) to screen for CO poisoning in these patients. Methods SpCO measurement values of adult patients were measured non-invasively with a Rad-57 Pulse COOximeter. Patients whose initial SpCO reading was over 10% underwent a venous blood draw for laboratory determination of invasive carboxyhaemoglobin (COHb) measurement. Patients with a invasive COHb level of over 10% were diagnosed with CO poisoning. Percentage of screened patients with suspected and occult CO poisoning, the distribution of patients with CO poisoning by time of day of the ED visit and the screening sensitivity of SpCO to detect CO poisoning were calculated. Results 483 patients presenting with headaches were screened with SpCO measurement. Thirty-eight had a mean SpCO value of over 10%, 31 (6.4% of the study population) of which had elevated COHb confirmed by laboratory determination. SpCO measurement, therefore, had a screening sensitivity of 82% for CO poisoning. Twenty-four (77%) of the CO poisoning cases were suspected and seven (23%) were occult. CO poisoning was detected more frequently in patients visiting the ED after midnight and during morning hours. Conclusions CO poisoning should be kept in mind in patients presenting to the ED with a headache. SpCO is an effective screening tool to detect CO poisoning in these patients.
INTRODUCTION
To cite: Zorbalar N, Yesilaras M, Aksay E. Emerg Med J Published Online First: [ please include Day Month Year] doi:10.1136/ emermed-2012-201712
As signs and symptoms of carbon monoxide (CO) poisoning are often vague, it is difficult to diagnose in patients presenting to the emergency department (ED). Headaches are the most common symptom of CO poisoning (37–85%) and so may be the best single indicator to prompt screening for suspected and occult CO poisoning. Clinical research and case studies reveal that the incidence of occult CO poisoning in patients visiting ED is more frequent than expected.1–3 There are only a small number of studies on ED frequency of occult CO poisoning in the literature.4 5 We aimed to determine the frequency of CO poisoning in patients presenting to the ED with headaches during winter months, and to test the utility of non-invasive carboxyhaemoglobin (SpCO) as a
Zorbalar N, et al. Emerg Med J author 2013;0:1–5. doi:10.1136/emermed-2012-201712 Copyright Article (or their employer) 2013.
method of screening for CO poisoning in these patients.
METHODS This is a prospective cross-sectional study conducted on patients who presented to the ED due to headache symptoms between 1 February and 31 March 2011. Our hospital (Izmir Tepecik Traning and Research Hospital) is a tertiary facility with over 200 000 patients being treated in 2011. Approval from the local ethics committee was obtained before the start of the study and all patients signed an informed consent form before being included in the study. Inclusion criteria included consecutive patients 14 years and older with one of their chief symptoms being headache. Patients were excluded from the analysis if three consecutive SpCO’s could not be performed for any reason or if an invasive SpCO could not be performed for any reason. COHb and methaemoglobin levels of the patients were measured non-invasively using an adult or paediatric reusable finger probe (rainbow DCI or rainbow DCIP, rev G) connected to a Rad-57 Pulse CO-Oximeter (software V.1713; Masimo Corp, Irvine, California, USA). The Rad-57 and probes were obtained from Masimo Corporation and returned after the data collection. Emergency residents who performed the measurements received standardised training in the proper use of the device before the study. Step-by-step directions for non-invasive measurements on patients were developed and proper use of the equipment and use of the correct technique were enforced. When feasible, the third or fourth finger of the patient’s non-dominant hand was used for the measurement site. The thumb and little fingers, finger nails with nail polish or fingers with henna were not used. Demographic information, measurement time, accompanying symptoms, vital signs and values measured by Rad-57 (carboxyhaemoglobin and methaemoglobin) were recorded on standardised study forms. Two additional SpCO measurements were performed sequentially on patients whose initial SpCO values were greater than 10% within 5 min after arrival. The mean of three consecutive measurements was recorded as the COHb value in those patients. Furthermore, patients whose mean COHb values were more than 10% underwent an invasive measurement in which a sample of venous blood was taken by a nurse from the brachial vein of the same arm which was used for the SpCO. COHb and lactate levels in venous blood were measured using a
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1
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Original article blood gas analyser (GEM Premier 3000-GEM OPL CO-Oximeter; Instrumentation Laboratory), within 5 min of the SpCO measurement by the physician. Calibration of the CO-Oximeter was performed every 15 days by the distributor for the manufacturer, according to the manufacturer’s recommendations. In cases in which there was inconsistency between results of the SpCO and the invasive COHb measurements, the values obtained from venous blood samples were taken as gold standard to diagnose CO poisoning. Patients with a COHb level greater than 10% were diagnosed with CO poisoning irrespective of their smoking status. All patients enrolled in the study were treated based on their individual clinical conditions. All data were recorded on a computer using Microsoft Office Excel 2007. Statistical analyses were performed using the statistics for biomedical research software (Med Calc Software, V.12, Belgium). Quantitative data were summarised with frequencies and percentages, whereas qualitative data were presented with mean±SD. Fisher’s exact test was used for the analysis of the difference between syncope frequencies in patients with and without CO poisoning. Student’s t test was used for analysis of the difference between invasive COHb levels of the patients with and without syncope, the difference between lactate levels in false-positive patients and true-positive patients and the difference between venous blood carboxyhaemoglobin levels of smoking patients and non-smoking patients. All analyses were conducted within 95% CI and a p value of less than 0.05 was considered significant. The screening sensitivity of SpCO to detect CO poisoning, defined as the percentage of cases of SpCO level greater than 10% when COHb level was greater than 10% was determined.
RESULTS A total of 29 439 patients presented to our ED during the study period and of those, 485 (1.6%) reported a headache as one of their chief symptoms. Four hundred and eighty-three consecutive patients consented to be in the study but in one of these patients a venous blood sample could not be obtained within 5 min. Of the 482 patients who made up the study population, 186 (38.6%) were men and the mean age was 38.0±15.6 years. Thirty-eight patients (7.9%) had a mean SpCO level above 10%, 31 (6.4%) of whom had a invasive COHb level greater than 10% and were diagnosed with CO poisoning. SpCO measurement, therefore, had a screening sensitivity of 82% for the detection of elevated carboxyhaemoglobin. Symptoms, demographics, vital signs and laboratory results of patients with mean SpCO values greater than 10% are shown in table 1. Twenty-three (%74.2) patients with CO poisoning were women and the mean age was 33.6±14.9 years. Vital signs of these patients were as follows (mean±SD): systolic blood pressure 129.2±19.2 mm Hg, diastolic blood pressure 76.6 ±14.3 mm Hg, pulse rate 95.6±14.6/min, respiratory rate 18.9 ±2.3/in, temperature 36.3±0.5/°C and oxygen saturation 97.8 ±1.3% on room air. The mean SpCO value for patients with CO poisoning was 20.6±4.8% while the mean of invasive COHb level was 20.9±6.1%. Associated symptoms were nausea/vomiting (25.8%), syncope (19.4%), weakness (9.7%), dizziness (9.7%), chest pain (6.5%) and abdominal pain (3.2%). Twenty-four patients with CO poisoning stated that they suspected they had been exposed to CO, whereas the remaining seven (1.4% of all patients) stated that they never suspected such a possibility (occult cases). The mean invasive COHb level in the occult CO poisoning patients was 19.9±5.5%. The 2
source of CO for all patients was using stoves inappropriately for heating. One patient in whom an elevated troponin level was detected underwent hyperbaric oxygen treatment. The remaining 30 patients received high flow supplemental oxygen in the ED. The mean length of ED stay for CO poisoning patients was 402±249 min. None of the patients enrolled in the study died. Ten patients experienced syncope before to arrival in the ED and six of these were subsequently diagnosed with CO poisoning. Syncope was found to occur in 19.4% of the patients with CO poisoning and 0.9% of patients who complained of a headache and did not have CO poisoning ( p0.05). Eight patients with CO poisoning had been using tobacco. There was no significant difference in venous carboxyhaemoglobin levels between smokers and non-smokers (22.4 ±4.8% vs 20.4±6.6%, p=0.45). The distribution of patients diagnosed with CO poisoning by the time of day of the ED visit is shown in figure 1. CO poisoning was detected more frequently in patients visiting the ED after midnight (00:00–04:00) and during morning hours (07:00–10:00). Of the 38 patients whose SpCO levels were above 10%, seven had invasive COHb levels less than 10%. All of these ‘falsepositive’ patients had methaemoglobin measurement (SpMet) levels greater than 1.57% but the mean±SD SpMet for these patients was lower than those of the ‘true-positive’ patients (1.8 ±0.17% vs 2.1±0.46%). Sixteen out of 19 patients whose SpMet levels were found to be high (>%2) were diagnosed with CO poisoning. While mean lactate levels in venous blood was found to be 1.02± 0.26 mmol/L in false-positive patients, it was 1.71±0.83 mmol/L in ‘true-positive’ patients (p=0.056).
DISCUSSION The main aim of the study is to determine the frequency of CO poisoning in patients presenting to the ED with headaches during winter months using non-invasive SpCO as a screening tool. 6.4% of our study population was diagnosed with CO poisoning. The screening sensitivity of SpCO was found to be 82%. CO poisoning is one of the leading causes of death resulting from accidental poisoning worldwide.6 The use of fossil fuels as a heating source is common in Izmir (which is the third biggest city in Turkey, its population is over 3 900 000), frequent ED visits due to CO poisoning in winter months are observed. Patients who do not suspect exposure to CO can be difficult to diagnose because symptoms are variable and sometimes vague. Lack of a timely diagnosis can delay treatment in those patients or worse, patients discharged with an incorrect diagnosis can be re-exposed to CO. Among the most common symptoms of CO poisoning are headache (37–85%), ataxia (18–69%), weakness (9–69%) and vomiting (18–52%).1 7 A headache typically presents when the COHb level is between 10% and 20%.3 The mean venous blood COHb level in our patients was 20.9%. The majority of our patients experienced a mild to moderate level of CO poisoning. Suner et al5 performed SpCO using aRAD-57 in 10 856 patients presenting to the ED irrespective of their symptoms. They reported that the sensitivity and specificity of SpCO using invasive COHb as the gold standard test were 94% and 54%, respectively. In that study, occult CO toxicity was defined as a Zorbalar N, et al. Emerg Med J 2013;0:1–5. doi:10.1136/emermed-2012-201712
Symptoms, demographics, vital signs and laboratory results of patients with mean SpCO greater than 10% Mean SpMet (%)
Occult poisoning
99
17.33
12.5
1.93
+
39.7
94
16
0
2.1
NP
36 36.8 36.4 36 36 36.8 36.1 36 37.3 36.1 37.5 36 37.5 36.4 36.4 36 36.7 36 36.2 36.8 36.7 36.2 36.1 36 36 36 36 36.1 37 36 36 37.6 36 36 36 36
97 100 97 98 96 98 100 97 97 99 97 97 97 98 98 97 99 99 99 96 97 99 97 100 98 95 97 97 98 99 98 99 96 98 98 97
22.8 22.4 23.9 24.4 18 0 16.8 30 5 2.2 12 13.1 0 21.2 13.2 17.7 20.1 23.8 16.6 32 31 19 31.2 20 24.2 25.7 24.7 0 19 16.5 32 10.9 12.4 0.7 22.3 19.4
2.23 1.2 2.63 2.93 2.53 1.57 2.13 1.8 1.73 1.93 1.67 1.63 1.83 2.63 2.33 2.27 1.83 1.73 2.17 1.6 1.37 1.97 2.63 2.20 2.80 2.07 2.37 1.67 1.93 1.97 2.77 1.73 1.27 1.8 2.33 2.57
− + − − − NP − + NP NP − − NP − − + + − + − − − − + − − − NP − − − − − NP − −
88
16
36
56
104
19
102 70 74 82 85 83 78 67 69 67 93 86 69 71 90 71 78 68 82 97 47 56 80 81 64 103 105 72 70 80 65 50 63 74 74 75
112 65 94 96 127 77 99 86 142 81 120 90 83 90 81 124 85 85 79 101 107 81 99 78 93 105 112 98 111 90 96 88 106 110 77 100
19 16 19 19 20 18 19 14 16 18 19 20 14 23 20 18 22 18 19 20 18 18 20 18 19 19 18 19 17 20 27 19 18 18 15 19
Associated symptoms
Smoking status
Systolic blood pressure (mm Hg)
Diastolic blood pressure (mm Hg)
1
F
36
−
124
68
2
F
33
+
124
139 165 177 245 246 247 261 293 294 295 308 309 310 319 320 361 362 363 375 376 377 378 379 380 399 400 405 406 415 450 451 452 453 474 482 485
F F M F F F M F F M M F M M F F F F F F F F M F M F F F F M F F F F M F
38 38 31 68 39 68 32 22 14 27 28 25 27 68 40 14 16 28 40 45 22 14 15 31 44 16 43 44 31 36 69 17 38 45 28 29
Vomiting chest pain Vomiting chest pain weakness syncope – Syncope Vomiting – Vomiting weakness – – Vomiting dizziness Syncope – – Vomiting Weakness – Dizziness Vomiting Syncope Syncope Abdominal pain – – Syncope – Syncope Weakness – – – – Nausea Syncope vomiting Weakness – – Dizziness –
+ − − − − − − − − − − − − − − − − + + − + − − − + − + + − + − − − + − +
163 110 132 151 171 177 135 107 109 125 134 144 128 126 150 161 110 121 135 147 106 100 160 125 106 122 115 132 121 130 105 118 139 143 119
3
F, female; M, male; NP, patients without poisoning; SpCO, carboxyhaemoglobin measurement; SpMet, methaemoglobin measurement.
Oxygen saturation (%)
24.33 15.33 25.33 28.67 19.67 15.67 22.67 16.67 14 14 16.33 14.67 13.67 25.67 23.33 21.33 17 19.67 20.33 16.67 11.67 19.33 26.33 21 29.33 21.67 23.67 10.67 19 18 26 17 12 11.67 23.67 25.33
Original article
Venous carboxyhaemoglobin (%)
Body temperature (°C)
Age Gender (years)
Pulse rate (/dk)
Mean SpCO (%)
Respiratory rate (/dk)
Patient no.
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Zorbalar N, et al. Emerg Med J 2013;0:1–5. doi:10.1136/emermed-2012-201712
Table 1
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Original article Figure 1 The distribution of cases according to the hours. CO, carbon monoxide.
SpCO value of 9% or greater for non-smokers and 13% or greater for smokers. Twenty-eight cases of CO poisoning were detected (0.26% of all patients screened), 11 of which (39%) were unsuspected. Only three out of those 11 patients had a headache among their list of chief symptoms. A number of studies in the literature evaluate the frequency of CO poisoning in patients presenting to the ED complaining of a headache.7 Eberhardt et al7 measured CO levels in the exhaled breath of patients who presented to the ED in winter months with headache symptoms in 2006. They found that 12 patients out of 170 (7.1%) had CO poisoning (cut-off value for smokers 5%, for non-smokers 2%). In their study, the mean carboxyhaemoglobin level in patients’ exhaled breath was 5%, whereas invasive COHb levels of the same patients averaged 7.2%. Patients who were suspected of being exposed to CO were excluded from the study, which left all patients they detected with CO poisoning as occult poisoning. In our study, however, we accepted carboxyhaemoglobin levels greater than 10% in venous blood as the gold standard in diagnosing CO poisoning. As the diagnostic value threshold was higher in our study, the occult CO poisoning frequency was lower. While Eberhardt et al7 presented the need for breath holding for measurement as a limitation, the non-invasive method used in our study does not have such a limitation. All of the CO poisonings observed in our study were due to the use of fossil fuels for heating. Our hospital is located in an area where the use of stoves for heating is common. Previous studies indicate that many patients with elevated carboxyhaemoglobin levels are not diagnosed in the ED because they present with non-specific symptoms, so the actual incidence of CO poisoning is greater than reported.1–3 While 6.4% of the patients in our study group were diagnosed with CO poisoning, seven (1.5%) of them had occult CO poisoning. We suggest that SpCO be used as a screening tool during the triage of patients presenting to the ED with a headache in winter months. Sixteen out of 19 patients whose SpMet levels were found to be high (>%2) were diagnosed with CO poisoning. Elevated SpMet levels should therefore alert clinicians to the presence of CO poisoning. As not all of the patients who presented to the ED during the study period had their carboxyhaemoglobin levels measured, we were not able to evaluate the specificity of SpCO (number of false-negative results). On the other hand, seven of the 38 patients with high SpCO had normal venous carboxyhaemoglobin levels (false positives). All these patients had SpMet levels greater than 1.57%. Our hospital is located in a city in the Mediterranean region where thalassaemia is common and the incidence of 4
haemoglobinopathy is 4.8%.8 Both increased methaemoglobin and haemoglobinopathies in patients may cause errors in SpCO as stated in the RAD-57 operator manual.9 We cannot rule out, therefore, that the false-positive evaluations in our study were due to the presence of haemoglobinopathies or the higher than normal methaemoglobin levels. We therefore suggest that a confirmatory blood gas measurement be made in patients who have SpCO levels greater than 10% or SpMet levels greater than 1.6%. Among the patients who presented to the ED with a headache, CO poisoning was detected more frequently in those presenting after midnight or in the morning hours and in those who had accompanying syncope. In their retrospective study, Keles et al4 reported on 323 patients diagnosed with CO poisoning between 2002 and 2003. The most commonly presented symptoms by the patients were headache (55%), vomiting (44%), syncope (28%) and epileptic seizures (4%). That study also concluded that syncope was seen more often in patients with high carboxyhaemoglobin levels. A higher possibility of CO poisoning should be carefully considered in similar patient groups.
Limitations As we did not perform invasive COHb tests in all 482 study patients, we were not able to assess the rate of false negatives from SpCO. However, despite this limitation, we were able to detect patients who had occult CO poisoning and we therefore suggest the use of SpCO as a screening tool in the ED. The carboxyhaemoglobin threshold for CO poisoning was chosen as 10% in our study. Higher and lower threshold levels for diagnosis were reported in the literature. Some studies determine separate threshold levels for smokers and nonsmokers.5 6 8 10 Our carboxyhaemoglobin threshold level is relatively high compared to others in the literature. This might have caused missing patients with carboxyhaemoglobin levels slightly under the threshold. When the half-life of CO is considered, evaluation of the time period between exposure to CO and presenting to the ED could have been appropriate. The carboxyhaemoglobin levels of some patients who had delayed a visit to the ED following the exposure could have been measured at less than 10%.
CONCLUSION Emergency physicians should bear in mind CO poisoning as a differential diagnosis in patients presenting to ED with headache. SpCO measurements provide an effective screening tool to detect occult CO poisoning in those patients. Zorbalar N, et al. Emerg Med J 2013;0:1–5. doi:10.1136/emermed-2012-201712
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Original article Acknowledgements Masimo Corporation loaned the Rad-57 Pulse CO-Oximeters and sensors used in the study. Contributors EA, MY and NZ contributed to the planning and conducting of the study. MY and EA prepared the manuscript. All authors contributed substantially to its revision. EA takes responsibility for the paper as a whole. Competing interests None. Ethics approval Ethics approval was received from the local ethics committee of Izmir Tepecik Research and Educational Hospital. Patient consent Obtained.
2 3 4 5
6
Provenance and peer review Not commissioned; externally peer reviewed.
7
Data sharing statement The authors shared the study data with Masimo Corporation before submission according to the loan agreement (see loan agreement form in the supplementary file, available online only).
8 9
REFERENCES 1
Lavonas EJ. Carbon monoxide poisoning. In: Shannon MW, et al., eds. Haddad and Winchester’s clinical management of poisoning and drug overdose. 4th edn. Chapter 87. Philadelphia, PA: Saunders Elsevier, 2007:1297.
Zorbalar N, et al. Emerg Med J 2013;0:1–5. doi:10.1136/emermed-2012-201712
10
Heckerling PS. Occult carbon monoxide poisoning: a cause of winter headache. Am J Emerg Med 1987;5:201–4. Ares BM, Casais JL, Dapena D, et al. Headache secondary to carbon monoxide poisoning. Rev Neurol 2001;32:339–41. Keles A, Demircan A, Kurtoglu G. Carbon monoxide poisoning: how many patients do we miss? Eur J Emerg Med 2008;15:154–7. Suner S, Partridge R, Sucov A, et al. Non-invasive pulse CO-oximetry screening in the emergency department identifies occult carbon monoxide toxicity. J Emerg Med 2008;34:441–50. Nikkanen H, Skolnik A. Diagnosis and management of carbon monoxide poisoning in the emergency department. Emerg Med Pract 2011;13:1–14. Eberhardt M, Powell A, Bonfante G, et al. Noninvasive measurement of carbon monoxide levels in ED patients with headache. J Med Toxicol 2006;2: 89–92. http://www.talasemifederasyonu.org.tr/pdf/tani/cansinTedavi-3.pdf (accessed 7 October 2013). http://www.medcontrol.com/omd_lib/rad%2057%20config%20operators% 20manual-%20aug2010.pdf (accessed 19 April 2012). Bland JM, Altman DG. Statistical methods for assessing agreement between two methods of clinical measurement. Lancet 1986;1:307–10.
5
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Carbon monoxide poisoning in patients presenting to the emergency department with a headache in winter months Nilay Zorbalar, Murat Yesilaras and Ersin Aksay Emerg Med J published online October 15, 2013
doi: 10.1136/emermed-2012-201712
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References
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EMJ Online First, published on October 15, 2013 as 10.1136/emermed-2012-201712 Original article
Carbon monoxide poisoning in patients presenting to the emergency department with a headache in winter months Nilay Zorbalar, Murat Yesilaras, Ersin Aksay Department of Emergency Medicine, Izmir Tepecik Research and Educational Hospital, Izmir, Turkey Correspondence to Dr Ersin Aksay, Department of Emergency Medicine, Izmir Tepecik Research and Educational Hospital, Izmir, Turkey; [email protected] Received 5 July 2012 Revised 11 March 2013 Accepted 21 September 2013
ABSTRACT Background Carbon monoxide (CO) poisoning is an important reason for emergency department (ED) visits during winter months, but because there are no specific symptoms it can be difficult to diagnose. We aimed to determine the frequency of CO poisoning in patients presenting to the ED with headaches during winter months and evaluate the ability of non-invasive carboxyhaemoglobin measurement (SpCO) to screen for CO poisoning in these patients. Methods SpCO measurement values of adult patients were measured non-invasively with a Rad-57 Pulse COOximeter. Patients whose initial SpCO reading was over 10% underwent a venous blood draw for laboratory determination of invasive carboxyhaemoglobin (COHb) measurement. Patients with a invasive COHb level of over 10% were diagnosed with CO poisoning. Percentage of screened patients with suspected and occult CO poisoning, the distribution of patients with CO poisoning by time of day of the ED visit and the screening sensitivity of SpCO to detect CO poisoning were calculated. Results 483 patients presenting with headaches were screened with SpCO measurement. Thirty-eight had a mean SpCO value of over 10%, 31 (6.4% of the study population) of which had elevated COHb confirmed by laboratory determination. SpCO measurement, therefore, had a screening sensitivity of 82% for CO poisoning. Twenty-four (77%) of the CO poisoning cases were suspected and seven (23%) were occult. CO poisoning was detected more frequently in patients visiting the ED after midnight and during morning hours. Conclusions CO poisoning should be kept in mind in patients presenting to the ED with a headache. SpCO is an effective screening tool to detect CO poisoning in these patients.
INTRODUCTION
To cite: Zorbalar N, Yesilaras M, Aksay E. Emerg Med J Published Online First: [ please include Day Month Year] doi:10.1136/ emermed-2012-201712
As signs and symptoms of carbon monoxide (CO) poisoning are often vague, it is difficult to diagnose in patients presenting to the emergency department (ED). Headaches are the most common symptom of CO poisoning (37–85%) and so may be the best single indicator to prompt screening for suspected and occult CO poisoning. Clinical research and case studies reveal that the incidence of occult CO poisoning in patients visiting ED is more frequent than expected.1–3 There are only a small number of studies on ED frequency of occult CO poisoning in the literature.4 5 We aimed to determine the frequency of CO poisoning in patients presenting to the ED with headaches during winter months, and to test the utility of non-invasive carboxyhaemoglobin (SpCO) as a
Zorbalar N, et al. Emerg Med J author 2013;0:1–5. doi:10.1136/emermed-2012-201712 Copyright Article (or their employer) 2013.
method of screening for CO poisoning in these patients.
METHODS This is a prospective cross-sectional study conducted on patients who presented to the ED due to headache symptoms between 1 February and 31 March 2011. Our hospital (Izmir Tepecik Traning and Research Hospital) is a tertiary facility with over 200 000 patients being treated in 2011. Approval from the local ethics committee was obtained before the start of the study and all patients signed an informed consent form before being included in the study. Inclusion criteria included consecutive patients 14 years and older with one of their chief symptoms being headache. Patients were excluded from the analysis if three consecutive SpCO’s could not be performed for any reason or if an invasive SpCO could not be performed for any reason. COHb and methaemoglobin levels of the patients were measured non-invasively using an adult or paediatric reusable finger probe (rainbow DCI or rainbow DCIP, rev G) connected to a Rad-57 Pulse CO-Oximeter (software V.1713; Masimo Corp, Irvine, California, USA). The Rad-57 and probes were obtained from Masimo Corporation and returned after the data collection. Emergency residents who performed the measurements received standardised training in the proper use of the device before the study. Step-by-step directions for non-invasive measurements on patients were developed and proper use of the equipment and use of the correct technique were enforced. When feasible, the third or fourth finger of the patient’s non-dominant hand was used for the measurement site. The thumb and little fingers, finger nails with nail polish or fingers with henna were not used. Demographic information, measurement time, accompanying symptoms, vital signs and values measured by Rad-57 (carboxyhaemoglobin and methaemoglobin) were recorded on standardised study forms. Two additional SpCO measurements were performed sequentially on patients whose initial SpCO values were greater than 10% within 5 min after arrival. The mean of three consecutive measurements was recorded as the COHb value in those patients. Furthermore, patients whose mean COHb values were more than 10% underwent an invasive measurement in which a sample of venous blood was taken by a nurse from the brachial vein of the same arm which was used for the SpCO. COHb and lactate levels in venous blood were measured using a
Produced by BMJ Publishing Group Ltd under licence.
1
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Original article blood gas analyser (GEM Premier 3000-GEM OPL CO-Oximeter; Instrumentation Laboratory), within 5 min of the SpCO measurement by the physician. Calibration of the CO-Oximeter was performed every 15 days by the distributor for the manufacturer, according to the manufacturer’s recommendations. In cases in which there was inconsistency between results of the SpCO and the invasive COHb measurements, the values obtained from venous blood samples were taken as gold standard to diagnose CO poisoning. Patients with a COHb level greater than 10% were diagnosed with CO poisoning irrespective of their smoking status. All patients enrolled in the study were treated based on their individual clinical conditions. All data were recorded on a computer using Microsoft Office Excel 2007. Statistical analyses were performed using the statistics for biomedical research software (Med Calc Software, V.12, Belgium). Quantitative data were summarised with frequencies and percentages, whereas qualitative data were presented with mean±SD. Fisher’s exact test was used for the analysis of the difference between syncope frequencies in patients with and without CO poisoning. Student’s t test was used for analysis of the difference between invasive COHb levels of the patients with and without syncope, the difference between lactate levels in false-positive patients and true-positive patients and the difference between venous blood carboxyhaemoglobin levels of smoking patients and non-smoking patients. All analyses were conducted within 95% CI and a p value of less than 0.05 was considered significant. The screening sensitivity of SpCO to detect CO poisoning, defined as the percentage of cases of SpCO level greater than 10% when COHb level was greater than 10% was determined.
RESULTS A total of 29 439 patients presented to our ED during the study period and of those, 485 (1.6%) reported a headache as one of their chief symptoms. Four hundred and eighty-three consecutive patients consented to be in the study but in one of these patients a venous blood sample could not be obtained within 5 min. Of the 482 patients who made up the study population, 186 (38.6%) were men and the mean age was 38.0±15.6 years. Thirty-eight patients (7.9%) had a mean SpCO level above 10%, 31 (6.4%) of whom had a invasive COHb level greater than 10% and were diagnosed with CO poisoning. SpCO measurement, therefore, had a screening sensitivity of 82% for the detection of elevated carboxyhaemoglobin. Symptoms, demographics, vital signs and laboratory results of patients with mean SpCO values greater than 10% are shown in table 1. Twenty-three (%74.2) patients with CO poisoning were women and the mean age was 33.6±14.9 years. Vital signs of these patients were as follows (mean±SD): systolic blood pressure 129.2±19.2 mm Hg, diastolic blood pressure 76.6 ±14.3 mm Hg, pulse rate 95.6±14.6/min, respiratory rate 18.9 ±2.3/in, temperature 36.3±0.5/°C and oxygen saturation 97.8 ±1.3% on room air. The mean SpCO value for patients with CO poisoning was 20.6±4.8% while the mean of invasive COHb level was 20.9±6.1%. Associated symptoms were nausea/vomiting (25.8%), syncope (19.4%), weakness (9.7%), dizziness (9.7%), chest pain (6.5%) and abdominal pain (3.2%). Twenty-four patients with CO poisoning stated that they suspected they had been exposed to CO, whereas the remaining seven (1.4% of all patients) stated that they never suspected such a possibility (occult cases). The mean invasive COHb level in the occult CO poisoning patients was 19.9±5.5%. The 2
source of CO for all patients was using stoves inappropriately for heating. One patient in whom an elevated troponin level was detected underwent hyperbaric oxygen treatment. The remaining 30 patients received high flow supplemental oxygen in the ED. The mean length of ED stay for CO poisoning patients was 402±249 min. None of the patients enrolled in the study died. Ten patients experienced syncope before to arrival in the ED and six of these were subsequently diagnosed with CO poisoning. Syncope was found to occur in 19.4% of the patients with CO poisoning and 0.9% of patients who complained of a headache and did not have CO poisoning ( p0.05). Eight patients with CO poisoning had been using tobacco. There was no significant difference in venous carboxyhaemoglobin levels between smokers and non-smokers (22.4 ±4.8% vs 20.4±6.6%, p=0.45). The distribution of patients diagnosed with CO poisoning by the time of day of the ED visit is shown in figure 1. CO poisoning was detected more frequently in patients visiting the ED after midnight (00:00–04:00) and during morning hours (07:00–10:00). Of the 38 patients whose SpCO levels were above 10%, seven had invasive COHb levels less than 10%. All of these ‘falsepositive’ patients had methaemoglobin measurement (SpMet) levels greater than 1.57% but the mean±SD SpMet for these patients was lower than those of the ‘true-positive’ patients (1.8 ±0.17% vs 2.1±0.46%). Sixteen out of 19 patients whose SpMet levels were found to be high (>%2) were diagnosed with CO poisoning. While mean lactate levels in venous blood was found to be 1.02± 0.26 mmol/L in false-positive patients, it was 1.71±0.83 mmol/L in ‘true-positive’ patients (p=0.056).
DISCUSSION The main aim of the study is to determine the frequency of CO poisoning in patients presenting to the ED with headaches during winter months using non-invasive SpCO as a screening tool. 6.4% of our study population was diagnosed with CO poisoning. The screening sensitivity of SpCO was found to be 82%. CO poisoning is one of the leading causes of death resulting from accidental poisoning worldwide.6 The use of fossil fuels as a heating source is common in Izmir (which is the third biggest city in Turkey, its population is over 3 900 000), frequent ED visits due to CO poisoning in winter months are observed. Patients who do not suspect exposure to CO can be difficult to diagnose because symptoms are variable and sometimes vague. Lack of a timely diagnosis can delay treatment in those patients or worse, patients discharged with an incorrect diagnosis can be re-exposed to CO. Among the most common symptoms of CO poisoning are headache (37–85%), ataxia (18–69%), weakness (9–69%) and vomiting (18–52%).1 7 A headache typically presents when the COHb level is between 10% and 20%.3 The mean venous blood COHb level in our patients was 20.9%. The majority of our patients experienced a mild to moderate level of CO poisoning. Suner et al5 performed SpCO using aRAD-57 in 10 856 patients presenting to the ED irrespective of their symptoms. They reported that the sensitivity and specificity of SpCO using invasive COHb as the gold standard test were 94% and 54%, respectively. In that study, occult CO toxicity was defined as a Zorbalar N, et al. Emerg Med J 2013;0:1–5. doi:10.1136/emermed-2012-201712
Symptoms, demographics, vital signs and laboratory results of patients with mean SpCO greater than 10% Mean SpMet (%)
Occult poisoning
99
17.33
12.5
1.93
+
39.7
94
16
0
2.1
NP
36 36.8 36.4 36 36 36.8 36.1 36 37.3 36.1 37.5 36 37.5 36.4 36.4 36 36.7 36 36.2 36.8 36.7 36.2 36.1 36 36 36 36 36.1 37 36 36 37.6 36 36 36 36
97 100 97 98 96 98 100 97 97 99 97 97 97 98 98 97 99 99 99 96 97 99 97 100 98 95 97 97 98 99 98 99 96 98 98 97
22.8 22.4 23.9 24.4 18 0 16.8 30 5 2.2 12 13.1 0 21.2 13.2 17.7 20.1 23.8 16.6 32 31 19 31.2 20 24.2 25.7 24.7 0 19 16.5 32 10.9 12.4 0.7 22.3 19.4
2.23 1.2 2.63 2.93 2.53 1.57 2.13 1.8 1.73 1.93 1.67 1.63 1.83 2.63 2.33 2.27 1.83 1.73 2.17 1.6 1.37 1.97 2.63 2.20 2.80 2.07 2.37 1.67 1.93 1.97 2.77 1.73 1.27 1.8 2.33 2.57
− + − − − NP − + NP NP − − NP − − + + − + − − − − + − − − NP − − − − − NP − −
88
16
36
56
104
19
102 70 74 82 85 83 78 67 69 67 93 86 69 71 90 71 78 68 82 97 47 56 80 81 64 103 105 72 70 80 65 50 63 74 74 75
112 65 94 96 127 77 99 86 142 81 120 90 83 90 81 124 85 85 79 101 107 81 99 78 93 105 112 98 111 90 96 88 106 110 77 100
19 16 19 19 20 18 19 14 16 18 19 20 14 23 20 18 22 18 19 20 18 18 20 18 19 19 18 19 17 20 27 19 18 18 15 19
Associated symptoms
Smoking status
Systolic blood pressure (mm Hg)
Diastolic blood pressure (mm Hg)
1
F
36
−
124
68
2
F
33
+
124
139 165 177 245 246 247 261 293 294 295 308 309 310 319 320 361 362 363 375 376 377 378 379 380 399 400 405 406 415 450 451 452 453 474 482 485
F F M F F F M F F M M F M M F F F F F F F F M F M F F F F M F F F F M F
38 38 31 68 39 68 32 22 14 27 28 25 27 68 40 14 16 28 40 45 22 14 15 31 44 16 43 44 31 36 69 17 38 45 28 29
Vomiting chest pain Vomiting chest pain weakness syncope – Syncope Vomiting – Vomiting weakness – – Vomiting dizziness Syncope – – Vomiting Weakness – Dizziness Vomiting Syncope Syncope Abdominal pain – – Syncope – Syncope Weakness – – – – Nausea Syncope vomiting Weakness – – Dizziness –
+ − − − − − − − − − − − − − − − − + + − + − − − + − + + − + − − − + − +
163 110 132 151 171 177 135 107 109 125 134 144 128 126 150 161 110 121 135 147 106 100 160 125 106 122 115 132 121 130 105 118 139 143 119
3
F, female; M, male; NP, patients without poisoning; SpCO, carboxyhaemoglobin measurement; SpMet, methaemoglobin measurement.
Oxygen saturation (%)
24.33 15.33 25.33 28.67 19.67 15.67 22.67 16.67 14 14 16.33 14.67 13.67 25.67 23.33 21.33 17 19.67 20.33 16.67 11.67 19.33 26.33 21 29.33 21.67 23.67 10.67 19 18 26 17 12 11.67 23.67 25.33
Original article
Venous carboxyhaemoglobin (%)
Body temperature (°C)
Age Gender (years)
Pulse rate (/dk)
Mean SpCO (%)
Respiratory rate (/dk)
Patient no.
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Zorbalar N, et al. Emerg Med J 2013;0:1–5. doi:10.1136/emermed-2012-201712
Table 1
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Original article Figure 1 The distribution of cases according to the hours. CO, carbon monoxide.
SpCO value of 9% or greater for non-smokers and 13% or greater for smokers. Twenty-eight cases of CO poisoning were detected (0.26% of all patients screened), 11 of which (39%) were unsuspected. Only three out of those 11 patients had a headache among their list of chief symptoms. A number of studies in the literature evaluate the frequency of CO poisoning in patients presenting to the ED complaining of a headache.7 Eberhardt et al7 measured CO levels in the exhaled breath of patients who presented to the ED in winter months with headache symptoms in 2006. They found that 12 patients out of 170 (7.1%) had CO poisoning (cut-off value for smokers 5%, for non-smokers 2%). In their study, the mean carboxyhaemoglobin level in patients’ exhaled breath was 5%, whereas invasive COHb levels of the same patients averaged 7.2%. Patients who were suspected of being exposed to CO were excluded from the study, which left all patients they detected with CO poisoning as occult poisoning. In our study, however, we accepted carboxyhaemoglobin levels greater than 10% in venous blood as the gold standard in diagnosing CO poisoning. As the diagnostic value threshold was higher in our study, the occult CO poisoning frequency was lower. While Eberhardt et al7 presented the need for breath holding for measurement as a limitation, the non-invasive method used in our study does not have such a limitation. All of the CO poisonings observed in our study were due to the use of fossil fuels for heating. Our hospital is located in an area where the use of stoves for heating is common. Previous studies indicate that many patients with elevated carboxyhaemoglobin levels are not diagnosed in the ED because they present with non-specific symptoms, so the actual incidence of CO poisoning is greater than reported.1–3 While 6.4% of the patients in our study group were diagnosed with CO poisoning, seven (1.5%) of them had occult CO poisoning. We suggest that SpCO be used as a screening tool during the triage of patients presenting to the ED with a headache in winter months. Sixteen out of 19 patients whose SpMet levels were found to be high (>%2) were diagnosed with CO poisoning. Elevated SpMet levels should therefore alert clinicians to the presence of CO poisoning. As not all of the patients who presented to the ED during the study period had their carboxyhaemoglobin levels measured, we were not able to evaluate the specificity of SpCO (number of false-negative results). On the other hand, seven of the 38 patients with high SpCO had normal venous carboxyhaemoglobin levels (false positives). All these patients had SpMet levels greater than 1.57%. Our hospital is located in a city in the Mediterranean region where thalassaemia is common and the incidence of 4
haemoglobinopathy is 4.8%.8 Both increased methaemoglobin and haemoglobinopathies in patients may cause errors in SpCO as stated in the RAD-57 operator manual.9 We cannot rule out, therefore, that the false-positive evaluations in our study were due to the presence of haemoglobinopathies or the higher than normal methaemoglobin levels. We therefore suggest that a confirmatory blood gas measurement be made in patients who have SpCO levels greater than 10% or SpMet levels greater than 1.6%. Among the patients who presented to the ED with a headache, CO poisoning was detected more frequently in those presenting after midnight or in the morning hours and in those who had accompanying syncope. In their retrospective study, Keles et al4 reported on 323 patients diagnosed with CO poisoning between 2002 and 2003. The most commonly presented symptoms by the patients were headache (55%), vomiting (44%), syncope (28%) and epileptic seizures (4%). That study also concluded that syncope was seen more often in patients with high carboxyhaemoglobin levels. A higher possibility of CO poisoning should be carefully considered in similar patient groups.
Limitations As we did not perform invasive COHb tests in all 482 study patients, we were not able to assess the rate of false negatives from SpCO. However, despite this limitation, we were able to detect patients who had occult CO poisoning and we therefore suggest the use of SpCO as a screening tool in the ED. The carboxyhaemoglobin threshold for CO poisoning was chosen as 10% in our study. Higher and lower threshold levels for diagnosis were reported in the literature. Some studies determine separate threshold levels for smokers and nonsmokers.5 6 8 10 Our carboxyhaemoglobin threshold level is relatively high compared to others in the literature. This might have caused missing patients with carboxyhaemoglobin levels slightly under the threshold. When the half-life of CO is considered, evaluation of the time period between exposure to CO and presenting to the ED could have been appropriate. The carboxyhaemoglobin levels of some patients who had delayed a visit to the ED following the exposure could have been measured at less than 10%.
CONCLUSION Emergency physicians should bear in mind CO poisoning as a differential diagnosis in patients presenting to ED with headache. SpCO measurements provide an effective screening tool to detect occult CO poisoning in those patients. Zorbalar N, et al. Emerg Med J 2013;0:1–5. doi:10.1136/emermed-2012-201712
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Original article Acknowledgements Masimo Corporation loaned the Rad-57 Pulse CO-Oximeters and sensors used in the study. Contributors EA, MY and NZ contributed to the planning and conducting of the study. MY and EA prepared the manuscript. All authors contributed substantially to its revision. EA takes responsibility for the paper as a whole. Competing interests None. Ethics approval Ethics approval was received from the local ethics committee of Izmir Tepecik Research and Educational Hospital. Patient consent Obtained.
2 3 4 5
6
Provenance and peer review Not commissioned; externally peer reviewed.
7
Data sharing statement The authors shared the study data with Masimo Corporation before submission according to the loan agreement (see loan agreement form in the supplementary file, available online only).
8 9
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10
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Carbon monoxide poisoning in patients presenting to the emergency department with a headache in winter months Nilay Zorbalar, Murat Yesilaras and Ersin Aksay Emerg Med J published online October 15, 2013
doi: 10.1136/emermed-2012-201712
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References
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