Multiple-Patient CO Incident Yields Lessons

By Brandon Johnson and Mike McEvoy

On August 16, 2007, at 10:30 a.m., the Hebron (KY) Fire Protection District was dispatched to an unknown gas problem in a private residence. The dispatch center advised it had lost contact with the caller but still had an open line. Initial response included an engine, an ambulance, a chief, and a sheriff’s patrol.

Arriving units found an ashen, 15-year-old male sitting in the driveway. He was alert but disoriented and complained of a headache. He had been inside the residence and was awakened by his ringing cell phone and then noticed the smell of “propane or something.” He proceeded to phone a nearby relative and then unsuccessfully tried to awaken three other people inside the residence. After calling 911, he left the house to await the fire department’s arrival.

Fire crews on-scene donned breathing apparatus and made entry into the residence to locate the three others and an additional relative, who had arrived prior to the fire department and apparently had entered the residence. Firefighters located and removed four individuals including two 17-year-olds, a 19- and a 45-year-old, as well as two cats and a dog from the home. All had been sleeping; two of the animals were unconscious. Apparently, the 19-year-old had been listening to the vehicle radio in the garage when he became tired and went to bed, forgetting to turn off the running vehicle. He was unsure of what time this occurred.

(1) The CO poisoning scene. A vehicle was found running inside the garage. [Photos courtesy of the Hebron (KY) Fire Protection District.]

Returning to the residence with a four-gas monitor, firefighters encountered 800 ppm of carbon monoxide (CO) at the front door. A search of the home found a running vehicle in the garage with the garage door closed. The highest CO reading obtained was 936 ppm with volatile organic compounds (VOCs) at 2.6, lower explosive limit (LEL) six percent, and oxygen 19.1 percent. Fresh animal feces and vomit from the cats and dog were scattered throughout the home. The vehicle engine was barely operating, probably because of the oxygen-deficient atmospheric conditions. There were no working CO detectors inside the residence.

(2) Firefighters used a four-gas monitor to evaluate atmospheric conditions inside the residence.

EMS examined the five patients who had been in the residence. All had difficulty walking and complained of severe headaches. Using a pulse CO-oximeter, EMS measured each patient’s blood carbon monoxide levels. CO in the body binds to red blood cells (hemoglobin), forming carboxyhemoglobin, referred to as SpCO when measured with an oximeter. SpCO was measured at 40 percent for the two 17-year-olds and 45 percent for the 19-year-old. The 15-year-old who met the fire department outside had an SpCO of 35 percent, and the relative who arrived and entered the home some 10 minutes prior to the firefighters measured 20 percent SpCO. All victims were placed on 100 percent oxygen by nonrebreather mask, effectively lowering SpCO levels during treatment and transport.

The fire department contacted animal control to care for the animals while the occupants of the home were transported to local hospitals. The four individuals who had been in the residence for the longest time were transported to a hyperbaric oxygen (HBO) therapy-capable facility at the regional university teaching medical center hospital. The 19-year-old, who had the highest SpCO and the most significant symptoms, was treated with HBO. Despite this, he suffered long-term neurological deficits. Interestingly, staff at the receiving hospital were unfamiliar with noninvasive CO-oximetry and somewhat skeptical of the firefighter paramedic assessments of CO toxicity in the patients.


This incident illustrates several important lessons.

  • CO is an incredibly dangerous gas. Colorless, odorless, and invisible, CO is a poison that poses a major threat to firefighter health and safety. Firefighters on this alarm had no idea they were responding to a CO incident. Had they elected to enter the residence without the protection of breathing apparatus, any member entering the garage area (where the highest CO readings were obtained) most likely would have been overcome by the combined CO level and resultant oxygen-deficient atmosphere. Maintaining a high index of suspicion for CO is imperative. It is also practical, since CO is the leading cause of poisoning and poisoning deaths in virtually every industrialized nation. Given the increasing frequency of fire department responses to CO alarms, expected to average one response every five minutes in the United States1 during 2008, every fire department must have a standard operating guideline for response to CO alarms and incidents.

  • Any response to known CO or unknown odors in an occupied structure requires EMS. A significant reason CO remains a leading killer is the frequency with which it is misdiagnosed by the fire service, EMS, and physicians. Sadly, up to half of all cases of CO poisoning are missed.2 With symptoms that cleverly resemble viral illness, food poisoning, the flu, migraines, or coronary syndromes, CO toxicity very often masquerades as a minor medical problem instead of the life-threatening poison it really is. Medical journals and textbooks list common symptoms that can be expected as levels of CO (COHb), yet every attempt to translate these signs and symptoms into a screening tool that might be useful for medical providers to pick out patients with CO poisoning has failed to work.3 The reason no accurate CO screening tool has been created is simple: Symptoms of CO poisoning vary incredibly from person to person, with no relationship whatsoever between severity of poisoning and degree of illness experienced. This is an absolute no brainer: If physicians cannot consistently pick out CO-poisoned patients, then patients themselves certainly are not capable of telling a fire dispatcher whether they are poisoned or not. EMS must be sent to every CO alarm and unknown odor call.

  • If signs and symptoms are insufficient to detect CO poisoning in patients, then measuring COHb (CO level in the blood) is the only reliable means of diagnosing CO poisoning. In a hospital setting, this can be done by measuring the gas content of a venous blood sample. Prehospital (and hospital) providers have noninvasive devices such as the one Hebron firefighters used on this alarm that provide rapid, continuous, and reliable measurements of COHb with the same degree of accuracy as a laboratory blood gas analyzer. The Centers for Disease Control and Prevention (CDC), in an effort to reduce deaths and injuries from CO poisoning, recently advised clinicians that patients with suspected exposure to CO and those with symptoms of CO should have their COHb measured using either blood or a noninvasive CO-oximeter.4 The implication for fire service response to CO alarms and incidents is that every occupant was potentially exposed and must be evaluated either at a hospital or by a noninvasive test administered in the field. This is a fact: Without measuring CO in patients, poisonings will be missed.

    How many unfounded CO alarms have you responded to? Keep this in mind: A structure can be ventilated in seconds; CO remains bound to hemoglobin in the blood of an exposed patient for days. Why not take advantage of the ability to measure CO in occupants to make certain that we’re not falsely reassuring homeowners they can safely return to their residence?

    A CO-oximeter can be incredibly useful when confronted with a symptomatic CO-poisoned patient. Quantifying a COHb level helps EMS providers select an appropriate transport destination, especially given our present knowledge of the benefits of HBO for certain subsets of CO-poisoned individuals.5 In multiple patient situations such as this incident, a CO-oximeter allows rapid screening of large numbers of potentially exposed individuals. When confronted with tens or hundreds of potentially CO exposed patients, the ability to screen on-scene can avoid overwhelming local hospital emergency department resources.

  • Firefighters need to know their equipment and understand the data generated. CO and unknown odor responses require use of an atmospheric gas meter for assessing environmental conditions. The four-gas monitor used on this response reported CO, VOCs, hydrogen sulfide, LEL, and O2. To properly use any gas meter, firefighters should understand how it operates, know that zeroing must be done well away from fire apparatus exhaust and the structure they plan to enter, and be able to interpret the readings obtained. Most humans would collapse and die within one to two minutes in a 12,800-ppm CO environment, within 10 to 15 minutes at 6,400 ppm, 30 minutes at 3,200 ppm, and at least lose consciousness after one hour at 1,000 ppm.6 Likewise, SpCO readings obtained from a CO-oximeter require interpretation by EMS providers according to a medically developed protocol. Nonsmokers normally have SpCO readings of zero to five percent; smokers from five to 10 percent; and, depending on local medical practice, CO-poisoned patients will have readings above 12 to 15 percent. HBO treatment is typically considered for symptomatic patients with SpCO readings above 25 percent, also depending on local medical protocols. (5) EMS increasingly employs some technologies that are more sophisticated or cutting edge than those used in emergency departments (EDs) or hospitals. Educating ED staff about medical devices used in the field is an important component of smoothly transitioning care. The time to conduct training on EMS medical devices is before using them on patients, a lesson that Hebron Fire learned from this incident.

  • A growing body of evidence is teaching us that there are serious long-term consequences from CO exposures. One of the most significant and more common is delayed neurologic syndrome (DNS),7 a life-changing constellation of brain and cognitive symptoms seen in one of the patients following this incident. DNS affects between 11 and 33 percent of CO-poisoned patients, with devastating consequences including memory loss, intelligence decline, seizures, concentration difficulties, and speech problems.8 Of equal importance are studies showing a substantially increased risk of major cardiovascular events such as stroke or heart attack (often leading to earlier death) following even a single moderate to severe CO exposure.9 The more we learn about long-term effects of exposure to CO, the more apparent it becomes that merely surviving an exposure may not be enough. Further research is imperative to refine our treatment protocols to reduce long-term effects, and much more work needs to be done to prevent CO poisonings.

    The fire service can play a key role in prevention and response to CO incidents. This incident illustrates the use of technology and safety equipment to protect the responders and best assess, evaluate, and transport the affected civilians. Using all the tools available to the fire service can dramatically reduce the misdiagnosis of CO poisoning and provide comprehensive assessment of not only property but also the valuable lives of the occupants inside.


    1. Flynn, J, “CO Deaths,” NFPA Journal; 2008:102(1) January/February, 32-5.

    2. Grace TW, FW Platt, “Subacute carbon monoxide poisoning: Another great imitator,” JAMA; 1981:246(15), 1698-700.

    3. Heckerling PS, JB Leiken, A Maturen, “Occult carbon monoxide poisoning: validation of a prediction model,” American Journal of Medicine; 1988:84(2),251-6.

    4. Centers for Disease Control and Prevention, “Carbon Monoxide Poisoning Prevention Clinical Education,” September 20, 2007, clinician training Web cast. Archived at

    5. Weaver LK, RO Hopkins, KJ Chan, S Churchill, CG Elliott, TP Clemmer, JF Orme Jr, FO Thomas, AH Morris, “Hyperbaric oxygen for acute carbon monoxide poisoning,” New England Journal of Medicine; 2002:347(14),1057-067.

    6. NFPA 720, Standard for the Installation of Carbon Monoxide (CO) Warning Equipment in Dwelling Units (2005 edition). National Fire Protection Association.

    7. Abelsohn, A, MD Sanborn, BJ Jessiman, E. Weir, “Identifying and managing adverse environmental health effects: 6. Carbon monoxide poisoning,” Canadian Medical Association Journal; 2002:166 (13), 1685-90.

    8. Kao LW, KA Nanagas, “Carbon monoxide poisoning,” Emergency Medicine Clinics of North America; 2004:22(4), 985-1018.

    9. Henry CR,D Satran, B Lindgren, C Adkinson, C Nicholson, TD Henry, “Myocardial Injury and Long-Term Mortality Following Moderate to Severe Carbon Monoxide Poisoning,” JAMA; 2006:295(4), 398-402.

    Brandon Johnson is the assistant director and toxmedic coordinator for the Northern Kentucky Regional WMD Hazmat Response Unit, a firefighter/paramedic with the Hebron (KY) Fire Protection District, and a paramedic instructor with the University of Cincinnati Paramedic Education Program.

    Mike McEvoy is the EMS technical editor for Fire Engineering, a critical care nurse, an instructor in critical care medicine, and a co-chair of the Resuscitation Committee at Albany (NY) Medical Center. He is also the EMS coordinator for Saratoga County, New York, and chief medical officer for the West Crescent (NY) Fire Department.

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