Smoke inhalation is a caustic event that can be lethal. In the United States, there are more than 23,000 cases and between 5,000 and 10,000 deaths from smoke inhalation each year. Thirty percent of patients treated at burn centers have experienced smoke inhalation.
The presence of burns should increase the provider’s level of suspicion for inhalational injury. In more than half of the cases in which a patient has burns to the nose, lips, eyebrows and neck area, there is some form of respiratory injury. In situations that involve a structure fire and burns to a patient, it is estimated that more than three-quarters of related deaths are due to smoke inhalation and not the burns. In cases where a patient sustains a burn but does not experience smoke inhalation, the mortality rate is less than 2%. When burns and smoke inhalation are both present, mortality rates can exceed 25%.1–3
Overview of Smoke Inhalation
Smoke is a product of combustion (fire) that consists of a mixture of heated particles, chemicals and gases. The specific contents of smoke will vary, depending on location of the fire and what is burned. Examples include: vegetation in forest fires, wood and synthetic material in enclosed structure fires, plastics and metals in burning cars or Dumpsters, and toxic chemicals in industrial fires. In the prehospital setting, it can be difficult to determine the exact makeup of smoke, as many factors contribute to its composition. This not only includes the material being burned, but also availability of oxygen and the fire’s maximum temperature.1–3
Smoke inhalation occurs when an individual inhales smoke through their nose, mouth or both. The effects of smoke inhalation include simple asphyxiation, chemical asphyxiation, simple and chemical irritation, and thermal damage. Because of this, it is important to recall that smoke is more than the visible gray or ashen-white cloud that is associated with a fire. Smoke includes particles of the incinerated material and extreme heat associated with the fire. The heat alone can cause very serious injury.1–3
In addition to recognizing the potential for smoke inhalation, providers should not underestimate the potential effects and impact of inhalation injuries. It has been noted that smoke inhalation injuries can influence patient outcomes more than the patient’s age or burned body surface area. When responding to incidents that may involve smoke inhalation, providers will need to recall the mechanisms that are involved, as well as the associated signs and symptoms in an effort to rapidly identify potential smoke inhalation cases.3
In many situations, the oropharynx, nasopharynx and upper airway can help limit the inhalation of particulate materials and diffuse the heat of the inspired air. The upper airway provides structures (e.g., nasal hair) and mechanisms (e.g., sneezing) to remove solid particles before they can pass deeper into the airway. The upper airway can also limit the exposure to heat. In most situations, such as when participating in physical activity during an athletic event in hot weather, this mechanism is effective. However, because the heat associated with the smoke from a fire can be extreme, normal protective mechanisms are often overwhelmed and extensive airway anatomy damage can occur, including tissue irritation, injury and complete destruction. For these reasons, always anticipate that excessive heat was involved. Providers will need to remain attentive to the potential for immediate and delayed airway compromise.1–8
Asphyxiation involves complex events that result in tissue hypoxia, which occurs when there is a reduced delivery of oxygen to the tissues. For example, in simple asphyxia, fire in an enclosed room may consume the majority of oxygen available in the room’s air. There will therefore be less oxygen available for the individual to inhale. The individual may have adequate or sufficient circulation and oxygen-carrying capability; however, the reduced concentration of oxygen in the room’s air can lead to an insufficient amount for the body’s tissues and cells.2,3,7
Chemical asphyxiation is more complex than simple asphyxiation. Chemical asphyxiation may occur despite adequate oxygen in ambient air at the time of exposure and may continue after the initial exposure despite the availability of normal air and administration of supplemental oxygen (e.g., 100% oxygen by face mask). In this situation, the chemical or toxin may prevent the normal use of oxygen by binding to sites that oxygen would normally bind to in the victim’s blood and tissue. Examples of toxins producing chemical asphyxiation are carbon monoxide and cyanide.9
Carbon monoxide must be considered in all cases of smoke inhalation. Commonly referred to as “CO,” carbon monoxide is a tasteless, odorless gas that should not be confused with natural gas (methane) used for household energy. When used for domestic energy, natural gas has an additive that provides a rotten cabbage odor, allowing for easy detection.9,10
Carbon monoxide is produced when combustion (burning) is incomplete. It is often associated with specific events, such as malfunctioning furnaces, automobile exhaust, hot water heaters and kerosene heaters. It is an unfortunate and preventable cause of death in campers who use stoves in their tents without adequate ventilation.11
Carbon monoxide acts as a chemical asphyxiant by decreasing the ability of the blood to carry oxygen to the body’s tissues. Hemoglobin has more than 100 times greater affinity for carbon monoxide than for oxygen. Carbon monoxide combines with hemoglobin to form carboxyhemoglobin—an abnormal form of hemoglobin that is inefficient in transporting oxygen. When hemoglobin is saturated by carbon monoxide, oxygen is unable to adequately attach to the hemoglobin, leading to tissue and cellular hypoxia.9,11
Symptoms of carbon monoxide poisoning can be vague, nonspecific and elusive. Examples include headache, shortness of breath, nausea, vomiting, general weakness, diaphoresis (excessive sweating), lack of coordination, lethargy and drowsiness, altered mental status from confusion to coma, seizures and cardiopulmonary arrest (see Table I).4,9,11
Cyanide gas is at least 15 times as toxic as carbon monoxide and can be produced by burning a variety of substances, including plastics, wool, nylon, rubber and paper products. Cyanide can enter the body through several routes, including contact with skin, contact with the eyes, being swallowed, and being inhaled as a pure gas or smoke from fire associated with the previously mentioned substances. Cyanide gas is sometimes described as having a bitter almond smell, but this is not a reliable indicator, as it is not always present and not everyone is able to detect the scent.12
Cyanide gas acts as a chemical asphyxiant by interrupting respiration at the cellular level. When cellular function ceases, anaerobic metabolism begins and lactic acid is produced. Continued anaerobic metabolism and increased acidosis can have a lethal outcome. As with carbon monoxide, the symptoms of cyanide toxicity may be vague and include dizziness, weakness, nausea, vomiting, headache, palpitations and respiratory distress. Severe cases may present with coma or cardiac arrest.12
Other Chemical Asphyxiants
The inhalation of smoke from nitrogen-containing products may produce methemoglobinemia (a condition in which the iron within hemoglobin is unable to support hemoglobin and oxygen-binding, leading to deficiencies of oxygen transport). Similar to carboxyhemoglobin, methemoglobin (metHb) is inefficient in transporting oxygen and results in tissue hypoxia. The symptoms of hypoxia from methemoglobinemia are similar to those of carbon monoxide poisoning. Additional clinical findings may include chocolate brown-color blood and cyanosis (despite normal pulse oximetry) that is not responsive to oxygen therapy.13
Carbon Monoxide and Cyanide Considerations
The severity of respiratory distress can vary significantly between carbon monoxide and cyanide. Although chemical asphyxiants can continue to produce hypoxia even after the victim has been removed from the source, the patient with cyanide poisoning is likely to continue experiencing moderate to severe “air hunger,” while the patient with carbon monoxide exposure is more likely to experience rapid improvement of symptoms after being removed from the source. In metropolitan and industrial smoke-inhalation cases, it is possible victims have been exposed to both cyanide and carbon monoxide.9,12,14,15
It has been noted that the signs and symptoms of carbon monoxide poisoning and cyanide poisoning can be subtle and sometimes difficult to distinguish. In addition, there may be no respiratory signs or symptoms, despite the patient having had a potentially fatal exposure. This is especially true in the prehospital setting. Other signs may also be important to recognize. For example, cherry red skin has been reported in cases of both carbon monoxide and cyanide poisoning.9,12,14,15
Providers should note that even after a fire has been extinguished, the smoke associated with smoldering materials can still contain chemical asphyxiants like cyanide and carbon monoxide. Also, inhalation victims of industrial fires may be exposed to more than one chemical asphyxiant. Because symptoms can overlap, providers are encouraged to have a high index of suspicion and carefully assess and monitor patients who have been exposed to smoke, as their conditions can change within minutes.2,9,12,14,15
Any chemical that is present in a fire, or occurs as a byproduct of mixing chemicals like chlorine and ammonia in a fire, may be present in smoke. If chemical irritants are inhaled, significant pulmonary injury can occur. This can be similar to injuries sustained when there is an exposure that involves direct contact with the individual’s skin or mucous membranes. Many irritants can produce caustic injury to the respiratory system. Certain chemicals, such as chlorine, can have rapid and devastating effects on the airway by producing acute or delayed airway edema (swelling), airway collapse, bronchospasm, deep tissue injury and activation of the body’s inflammation response.16
The extent and severity of the respiratory system injury sustained by inhaling a chemical irritant will be influenced by a variety of factors, including particle size, solubility in water and acidity. For example, substances that are soluble in water, such as ammonia, tend to result in upper airway injury. Substances that are less soluble, such as chlorine, tend to result in upper and lower respiratory injury. The less water-soluble the particles are, the greater the likelihood that upper and lower airway and lung tissue damage will occur. While this information is valuable for prehospital care providers to have as part of their baseline and background knowledge, time should not be invested on scene attempting to determine the temperature or specific chemical composition of the smoke. Rather, it is essential to be able to recognize when any potential airway compromise is present. If resources are available and details of the chemical’s composition involved in the fire are available, this information should be relayed to the receiving hospital as soon as possible.3
As with any EMS response, patient assessment may need to be deferred until the scene is secured and determined to be safe. Because a smoke inhalation scene is likely to involve a fire, this may require EMS to stage at a safe location until cleared for scene entry. Once cleared to enter, begin to assess the “global scene,” or big picture, as well as the patient-level situation.4,6,8,17
The global scene assessment is essential. Begin by assessing for clues as to what might be expected as you enter the scene. Think about possible causes of the incident: an explosion? Car fire? Structure fire? Are there any signs of traumatic injury? If the EMS crew is not the first to enter the scene, are the initial responders wearing protective gear, such as breathing apparatus? If yes, what kind of protective gear is being worn, why, and should everyone be wearing similar gear? Is this a potential crime scene?Are there multiple patients being removed from an enclosed space, such as a theater or concert hall, with burned and/or soot-covered clothing (i.e., signs of immediate simple asphyxiation and thermal injury)? Are the patients ambulatory without signs of direct contact with smoke, but suffering severe nausea and vomiting (i.e., chemical asphyxiation)? Or are patients vigorously coughing with signs of facial swelling and non-thermal burns (i.e., chemical irritants)?4,6,8,17
Part of the global scene assessment may include use of ambient carbon monoxide detectors, which may provide important information and can be easily purchased and installed. Many states require such detectors in construction. Ambient carbon monoxide detectors should not be confused with smoke detectors. If carbon monoxide detectors are located on the scene, they should be checked to determine if they are functioning and have been activated. If detectors are not present or are not functioning in a situation that is suggestive of CO poisoning, ambient sampling may provide the only clue that determines CO as the cause of symptoms.17–19
Depending on the availability of local resources, ambient testing devices may be available through emergency response agencies like the fire department. When residential testing is conducted, many homes will have levels less than 10 parts per million (ppm). Readings taken near inefficient combustion appliances may reach 30 ppm. This is important to note, as symptoms may occur with prolonged exposure to ambient levels of 50 ppm; death may occur with prolonged exposures to levels over 150 ppm.18–20
Once providers have entered the scene and are able to see the patient, the visual assessment can begin. When approaching, note the patient’s overall appearance. Clues noted on scene, such as medicine bottles and medical supplies, may provide insight to the patient’s medical history. Evidence of substance abuse should also be noted.4,6
When assessing a smoke inhalation patient, there are key items in the history and assessment to consider. For example, try to determine the duration of exposure and if the patient and smoke were confined to a closed room versus being in an open space. Fire and smoke in a closed space increase the risk for thermal injury, smoke inhalation and toxic chemical exposure. The presence of underlying or pre-existing medical conditions should also be considered. For example, a patient with methemoglobinemia may be at greater risk for smoke inhalation complications. Patients with a history of respiratory illness, such as chronic obstructive pulmonary disease or underlying heart disease, may be at greater risk and may have greater complications from asphyxiation and subsequent tissue hypoxia.4–6,8,21–23
A rapid yet thorough primary survey should always be conducted on any potential smoke inhalation victim. This should include assessment and management of the patient’s airway, breathing and circulation. Immediate intervention may be needed when any component of the ABCs is at risk.4,6
The primary assessment maybe expanded to ABCDEs. D is for disability, a quick neurological assessment; E is for exposure to identify the presence of trauma. Remove the patient’s clothing as soon as possible, as this may limit associated thermal injury and provide decontamination from chemical exposure. It will also allow for visualization of the patient’s skin. If the patient’s clothes have been on fire and are now adhered to the skin, remove loose garments away from the wounds while leaving attached clothing in place.4,6,8
If the patient’s airway patency is at risk, intervention is critical. If cervical spine injury is suspected, the airway may need to be opened using a chin-lift or modified jaw-thrust. Additional airway management may include the use of airway adjuncts like a nasopharyngeal or oropharyngeal airway, or an advanced airway like endotracheal intubation. Early airway management can be lifesaving in smoke inhalation situations, as airway swelling can worsen over time, making the airway more difficult to manage.4,6,8
As the patient’s airway is being opened, evaluate his breathing and respiratory effort. Note the respiratory rate, quality and depth of the respiratory effort and accessory muscle use.Assess (auscultate) breath sounds as soon as practical. Auscultation may reveal a variety of findings, such as absent or diminished sounds, wheezing, rales (crackles) or rhonchi. Stridor is a high-pitched inspiratory sound often associated with upper airway obstruction.4,6,8,17,23,24
Quickly assess the patient’s circulation using common pulse locations, including the carotid (neck), brachial (elbow) or radial (wrist) pulse, evaluating for presence, rate, regularity, strength and quality. The patient’s skin can also be used to assess circulation. Skin is normally warm and dry to the touch. Abnormal findings include skin that is cool, pale, gray and/or moist. Capillary refill time, or CRT, can be evaluated to obtain a quick assessment of peripheral circulation. Providers should recall that a variety of factors can influence capillary refill time.4,6,8
A rapid assessment of the patient’s neurological status should be performed, and mental status may be evaluated and documented using the AVPU system: A—patient is alert; V—patient responds to verbal stimuli; P—patient responds to painful stimuli; U—patient is unresponsive. The Glasgow Coma Scale, or GCS, can also be used to assess the patient’s mental status. The GCS is more detailed and includes verbal, eye and extremity responses.A rapid evaluation may include assessing the patient’s ability to squeeze equally with both hands and move both arms and legs equally.4,6,8
Expose the patient to allow for a rapid visual inspection of the body. This is especially important, as clothing or other items may be covering wounds. Once exposed, visually inspect the patient for external hemorrhage, abrasions, lacerations, burns, bruising and other abnormal findings.4,6,8
In addition to the ABCDEs, assessment of the smoke inhalation patient should include awareness of the potential for trauma and looking for additional injuries. Carefully observe and note the condition of the patient’s face, paying specific attention to the mouth and nose. The nares should be inspected for the presence of soot, redness or any discoloration that may be caused by smoke inhalation, or swelling as a result of thermal injury. Inspect the oral cavity, including the mouth and posterior oropharynx, in a similar manner. Oral cavity findings such as gray color, presence of soot, carbonaceous sputum or burned mucosa should alert you to potential airway injury.4,6,8
Perform a visual inspection of the patient’s neck and chest, observing the chest’s rise and fall and noting the symmetry and accessory muscle use. Paradoxical movements (e.g., seesaw patterns of the chest and abdomen) should alert you to the potential for respiratory distress.Accessory muscle use includes nasal flaring, intercostal retractions, supraclavicular retractions and sternal retractions. An additional and potentially ominous finding is when the patient is using accessory muscles to breathe, with associated tracheal tugging.4,6,8,23,24
Note the patient’s voice or ability to speak, remembering that signs and symptoms of upper airway injury may include hoarseness, throat pain and possibly painful swallowing. Listen attentively to the patient’s speech. If he is attempting to speak but is unable, suspect significant airway involvement until proven otherwise. A coarse or raspy-sounding voice or the ability to speak only in two- or three-word sentences should be considered a significant finding and raise the concern for possible airway compromise (see Table II).4,6,8,23–25
Injury and Burns
The ability to assess and anticipate smoke inhalation is critical; however, you will also need to be simultaneously observant of other findings during the assessment. As noted earlier, the presence of burns and/or traumatic injuries will need to be considered during the assessment, as well as when forming a treatment plan. When burns or trauma are present and smoke inhalation is suspected, the general rule is to ensure that the patient’s ABCs are managed while treating the trauma first and burns second. Smoke inhalation is often assessed and managed during the assessment and management of the patient’s airway and breathing.4,6,8,25,26
If burns are present, try to approximate the percentage of the patient’s body surface area (BSA) that has been burned. In the prehospital setting, the “rule of nines" and/or a Lund-Browder diagram are frequently used for estimating the extent of burns. The front of the patient’s head (face) is considered 4%, back of the head 4%, front of the neck 0.5%, back of the neck 0.5%, anterior adult chest 9%, anterior abdomen 9%, upper back (from neck to waist) 9%, buttocks 9%, front of each arm 4.5%, back of each arm 4.5%, front of each leg 9%, back of each leg 9%, and groin approximately 1% (see Table 3).26
If the patient is wearing restrictive items, such as some types of clothing or jewelry, remove them to every extent possible. This is especially important if the patient has any burns. If restrictive items are left in place, edema may occur, resulting in a variety of complications, including distal circulation compromise.4,6
Obtain a baseline assessment of the patient’s vital signs as soon as possible. Vital signs should include heart rate, respirations and blood pressure. If available, cardiac monitoring and pulse oximetry should also be used. Providers should recall that pulse oximetry may have potential limitations in cases of smoke inhalation. As discussed earlier, hemoglobin has a greater affinity for carbon monoxide than for oxygen. In cases of smoke inhalation, when excessive carbon monoxide may be present, the hemoglobin may become fully saturated with carbon monoxide instead of oxygen. Due to mechanisms involved in pulse oximetry (i.e., a light originates from the probe and is partly absorbed by hemoglobin by amounts that differ depending on whether the hemoglobin is saturated), the pulse oximetry reading may reflect carboxyhemoglobin (COHb) or methemoglobin (metHb) levels and not oxyhemoglobin saturation (O2Hb). Therefore, the pulse oximetry reading may be normal in the setting of abnormal hemoglobins and tissue hypoxia.27–31
A carbon monoxide (CO) detector can be useful in determining elevated CO levels in the patient’s blood in the prehospital setting. While they are not common in all EMS systems, consider using a CO detector when available in cases where CO might be involved. One significant benefit of a CO detector is earlier identification of high levels of CO. This in turn can assist providers and emergency department staff in determining optimal treatment plans.27–34
Newer CO oximeter devices are available for measuring abnormal hemoglobins (COHb and metHb) by prehospital providers; however, clinical application of these devices is controversial due to a lack of correlation between immediate carboxyhemoglobin levels and exposure to carbon monoxide. The accuracy of these devices continues to be reviewed and remains the topic of some debate.30–32
Vital signs should be reassessed at least every 10 minutes and more frequently when indicated by patient condition. For example, an increasing respiratory rate, tachycardia and development of hypoxia may indicate worsening respiratory function from thermal injury, inflammatory response to particulate matter or progression of chemical asphyxiation.4,6,8
Obtain the patient’s medical history when possible. This can be accomplished using the AMPLE acronym: A—allergies; M—medications; P—past medical history; L—last meal; and E—events leading to injury. In the setting of a critical smoke inhalation patient, excessive time should not be invested in obtaining a thorough medical history. Priorities should be performing a patient assessment, providing care and ensuring rapid transport to an appropriate hospital.4,6
Author’s note:This article is designed to provide a general overview of smoke inhalation. Readers interested in additional details, including cases that may be related to biological, chemical or nuclear warfare, as well as explosives, are encouraged to conduct additional research.
1. Ludwig G. NewThinking About Treating Smoke Inhalation Victims, www.emsworld.com.
2. Lafferty KA, Goett HJ. Smoke Inhalation, http://emedicine.medscape.com.
31. Barker SJ, Curry J, Redford D, Morgan S. Measurement of carboxyhemoglobin and methemoglobin by pulse oximetry: A human volunteer study. Anesthesiology 105(5): 892–897, 2006.
32. Touger M, Birnbaum A, et al. Performance of the RAD-57 pulse CO-oximeter compared with standard laboratory carboxyhemoglobin measurement. Ann Emerg Med 56(4): 382–88, Oct 2010.
Paul Murphy, MSHA, MA, is a regional sales manager with InTouch Health, with administrative and clinical experience in healthcare organizations.
Chris Colwell, MD, is medical director for Denver Paramedics and the Denver Fire Department and an attending physician in the emergency department at Denver Health Medical Center (Denver, CO).
Gilbert Pineda, MD, FACEP, is medical director for the Aurora Fire Department and Rural/Metro Ambulance (Aurora, CO) and an attending physician in the emergency department at The Medical Center of Aurora (Aurora, CO) and Denver Health Medical Center (Denver, CO).