CASE REPORT

I"7, Lpidemic of Accidental Carbon Monoxide

Poisonings Caused by Snow-Obstructed Exhaust Systems

From the Emergency Medicine Residency* and the Department of Emergency Medicine ~, Albert Einstein College of Medicine; and the Hyper- baric Medicine Program ~, Jacobi Medical Center, Bronx, New York.

Received for publication February 19, 1996. Revision received October 4, 1996. Accepted for publi- cation October 19, 1996.

Copyright © by the American College of Emergency Medicine.

Rama Rao, MD* Michael Touger, MD* Paul Gennis, MD* Jim Tyrrell, CH~ Joseph Roche, RN s E John Gallagher, MD*

We report a case series of accidental carbon monoxide poisonings caused by snow-obstructed automobile exhaust systems. Accum- ulation of more than 24 inches of snow contributed to the poison- ing of 25 patients who were subsequently treated with hyperbaric oxygen therapy. Two illustrative cases are presented in greater detail, illustrating a life-threatening hazard associated with heavy snow accumulations.

[Rao R, Touger M, Gennis P, Tyrrell J, Roche J, Gallagher E J: Epidemic of accidental carbon monoxide poisonings caused by snow-obstructed exhaust systems. Ann Emerg Med February 1997;29:290-292.]

INTRODUCTION

Beginning January 8, 1996, the New York City metropolitan area experienced a blizzard that resulted m snow accumula- tion of more than 24 inches. 1 During the next 5 days, 25 patients were referred to the Jacobi Medical Center for hyperbaric oxygen treatment of carbon monoxide (CO) poisoning. Eighteen of these patients were treated during the first 24 hours of the blizzard. Each patient had been exposed to CO in a stationary automobile with the engine running when the exhaust system became obstructed by accumulated snow. This case series describes the relevant features of this unusual epidemic.

CASE REPORTS

Patients rescued from snowbound automobiles and treated for CO poisoning at the Jacobi Medical Center hyperbaric chamber between January 8 and January 12, 1996, were included in the series. Jacobi Medical Center is the main hyperbaric treatment center CO poisoning reported to the New York City Emergency Medical Service and the New York City Poison Control Center. It is likely that this series include all identified serious cases of CO poisoning in the metropolitan area during the blizzard. Serious cases were considered to be those with significant cardiovascular or

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neurologic dysfunction, including initial loss of conscious- ness. Environmental carboximetry measurements from the vehicles were not available; cases were identified on the basis of clinical findings, as well as arterial carboxyhemoglobin level. Venous and arterial carboxyhemoglobin levels were considered equivalent. 2 Hospital records were reviewed for pertinent demographic and clinical information and the circumstances leading to the exposure. Telephone follow-up was conducted 2 weeks after exposure for the two illustrative cases presented in greater detail below.

Case 1 A 67-year old hypertensive man with a history of stroke was shoveling snow while warming his car. He decided to rest for a few minutes inside the car and was found unconscious 1 hour later. Prehospital care included endotracheal inmbation and IV glucose, thiamine, and nal- oxone, with no improvement in mental status. In the emer- gency department, he remained comatose, with episodes of decorticate posturing. His vital signs included a pulse of 90, blood pressure of 170/120 mm blg, and temperature of 98.6 ° E His pupils were equal and reactive to light, and his corneal and gag reflexes were intact. No focal neurologic deficits were noted, and other physical examination findings were unremarkable. His ECG showed a sinus rhythm with- out evidence of ischemia. Arterial blood gas on t00% oxy- gen-assisted ventilation revealed a pH of 7.15, P c o 2 of 40 mm Hg, and Po 2 of 363 mm Hg. The arterial carboxy- hemoglobin level was 35.1%. Noncontrast computed tomo- graphy of the head yielded normal findings. Emergency management included hyperventilation and treatment with hyperbaric oxygen at 2.8 atmospheres absolute for 46 min- utes. The patient regained consciousness the day after ad- mission, was able to follow commands~ and was extubated without complication. During his hospital stay, he was intermittently confused but was able to carry on meaningful conversation. He required assistance walking, which he did with a shuffling gait. He was discharged home on hospital clay 6 with a walker. Two weeks after discharge, his wife reported that he continued to require a walker and that he was frequently confused about time. He was described as markedly lethargic, sleeping frequently and requiring con- stant supervision at home.

Case 2 A 5-year-old girl with a history of developmental delay was playing while her father shoveled snow from around their car. He started the engine while the rear of the vehicle was still encased in a snowbank and allowed the child to sit in the car for warmth. She was noted to be unresponsive within 5 minutes. She was removed from the car and awoke shortly thereafter. She was given 100% oxy- gen by face mask and vomited once before arriving in the ED. in the ED, she was awake and crying. Her blood pres-

sure was 100/70 mm Hg, heart rate 156, and respiratory rate 28. Arterial blood-gas analysis revealed a pH of 7.24, Pco 2 of 34 mm Hg, and Po 2 of 358 mm Hg with a 100% nonrebreather mask. The arterial carboxyhemoglobin level was 18.5%. Although the patient's carboxyhemogtobin level was not markedly increased, she was considered a candidate for hyperbaric therapy because her age and history of devel- opmental delay precluded accurate assessment of central nervous system dysfunction. She underwent hyperbaric oxygen treatment without complications. Telephone follow- up 2 weeks later revealed that she had returned to her base- line level of function. Her sister was similarly exposed and treated, with a favorable outcome.

D I S C U S S I O N

Hospital records were available for 22 of the 25 patients included in this series. Relevant features of this cohort are summarized in the Table. The median age was 44 years (interquartile range, 11.5 to 58.5 years). Eight patients were younger than 18 years, and six were older than 65 years. Fourteen patients were male. In no case was exposure intentional.

A few circumstances leading to the CO exposures were evident. Attempting to keep warm inside a snow-buried vehicle was a factor in most of the cases. In some cases the

Table. Features of case ser~es.

No. of Laboratory Features Patients Abnormalities

Total included in series 22 Patient found with engine running 21 Documentation of fumes smelled 5

inside car by patient or rescuer Window or door documented to have 3

been open during event Patient unconscious on ED arrival 20 Endotracheal intubation 4 Patient unconscious on ED arrival 3 Patient awake but disoriented on 5

ED arrival Dysrhythmias or abnormal ECG 9/13

findings/total ECGs* Median % carboxyhemoglobin (IQR) Median arterial pH (IQR) Hospital discharge >24 hours 4

after hyperbaric treatment

34.3 (24.5-39£) 7.28 (7.20-7.36)

lQR, interquartile range (25th-75th percentiles), *Dysrhythmias included premature ventrioular contractions, bigeminy, runs of ventdcular tachycardia, and atrial fibrillation, all of which converted to sinus rhythm before or during hyperbaric therapy.

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tailpipe of the vehicle was obstructed with snow. In others the entire vehicle was encased in a snowdrift. Two patients were found unconscious in vehicles with the engines run- ning, apparently trapped in snowdrifts while driving. There was no apparent association of any particular vehicle manu- facturer, model, or age with these poisoning episodes.

During the period investigated, the New York City Medical Examiner's Office confirmed one death, not in- cluded in this series, by the same mechanism. A second death is still under investigation (Borakove E, Office of Chief Medical Examiner, personal communication, January 29, 1996).

CO is the most common cause of accidental death by poisoning in the United States. 3 CO exposure has been reported in a variety of settings including homes 3, engine- powered vehicles 4, recreational boats 5, and indoor ice-skat- ing rinks. 6 The main source of CO in the atmosphere is automobile exhaust) Prior studies have identified exposures and fatalities due to unintentional CO poisoning from engine exhaust 3,4, including faulty exhaust systems in stationary cars during winter months. To date, however, no series of unintentional CO poisonings resulting from snow-obstructed exhaust systems has been reported.

The confirmed fatality, as well as the significant functional sequelae noted in case 1, underscores the importance of primary prevention of CO exposures. An understanding of contributing circumstances may help educate the public about the risks of remaining in a stationary vehicle during a hea W snowfall if the engine As left running. Centralized care of these patients in a referral center--in this case our hyperbaric facility in cooperation with our regional poison control center--aided in the rapid recognition of the unusual cause of this epidemic. Prompt notification of public health authorities and the media resulted in appropriate public service announcements by the second day of the blizzard. Although we cannot prove a causal relationship, the number of poisonings markedly diminished after the first day despite the immobilization of many vehicles for several days.

In three cases, leaving a car window or door partially open evidently did not prevent CO exposure. This phe- nomenon has been reported previously. 4 Public service an- nouncements should include the warning that opening a window may be insufficient protection against CO exposure in these circumstances. The smell of engine exhaust, noted in five cases, has also been reported in association with CO poisoning, r Although CO itself is colorless and odorless, it is found in high concentration in exhaust gases, which have a more identifiable odor.

Pediatric cases of CO poisoning caused by vehicle exhaust have been reported, s-l° In our series eight expo-

sures occurred when parents were protecting their chil- dren from the cold while digging a car out of the snow. Public service announcements should address this issue.

Public education about the dangers of CO intoxication is warranted during heavy snow accumulation. Practical recommendations should emphasize visual inspection of the vehicle exhaust system before the engine is started, the importance of an unobstructed tailpipe for vehicles caught in snowdrifts, recognition of unusual odors or fumes in the car as an indication of possible exposure, warnings that an open window or door may not be sufficient to pre- vent CO toxicity, and alerts to parents to protect children from unintentional CO exposure.

R E F E R E N C E S

1. The New York Times, January 9,/996. p 33.

2. Touger M, Gallagher E J, Tyrrell J: Relationship between venous and arterial carboxyhemo- globin levels in patients with suspected carbon monoxide poisoning. Ann Emerg Med 1996;25:481-483.

3. Centers for Disease Control: Carbon monoxide intoxication: A preventable environmental health hazard. MMWR Morbid Mortal Wkty Rep 1982;31:529-531.

4. Baker SP, Fisher RS, Masemore WC, et al: Fatal unintentional carbon monoxide poisoning in motor vehicles. Am J Public Health 1972;62:463-467.

5. Silvers SM, Hampson NB: Carbon monoxide among recreational boaters. JAMA 1995; 274: 1614-1616,

6. Johnson C J, Moran JC, Paine SC, et ah Abatement of toxic levels of carbon monoxide in Seattle ice skating rinks Am JPubfic Health 1975;65:1087-1090.

7. Jaffe LS: Sources, characteristics, and fete of atmospheric carbon monoxide. Ann NYAcad Sci 1970;174:76-88.

8. Johnson C J, Moran J, Pekich R: Carbon monoxide in school buses, Am J Public Health 1975;65:1327-1329.

9. Centers for Disease Control: Fatal carbon monoxide poisoning in a camper-truck--Georgia. MMWR Morbid Mortal Wkly Rep 1991 ;40:154-155.

16. Hampson NB, Norkool DM: Carbon monoxide poisoning in children riding in the back of pickup trucks. JAMA 1992;267:538-540.

Reprint no. 47/1/79137 Address for reprints:

Michael Touger, MD

1W20 Jacobi Medical Center

Pelham Parkway South at Eastchester Road

Bronx, New York 10461

718-918-5852

Fax 718-918-7459

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