Smoke inhalation is the breathing in of harmful fumes (produced as by-products of combusting substances) through the

respiratory tract The respiratory tract is the subdivision of the respiratory system involved with the process of respiration in mammals. The respiratory tract is lined with respiratory epithelium as respiratory mucosa. Air is breathed in through the nose to th ...

. This can cause smoke inhalation injury (subtype of acute inhalation injury) which is damage to the

caused by chemical and/or heat exposure as well as possible systemic toxicity after smoke inhalation. Smoke inhalation can occur from fires of various sources such as residential, vehicle, and wildfires. Morbidity and mortality rates in fire victims with burns are increased in those with smoke inhalation injury. Victims of smoke inhalation injury can present with cough, difficulty breathing, low oxygen saturation, smoke debris and/or burns on the face. Smoke inhalation injury can affect the upper respiratory tract (above the larynx), usually due to heat exposure, or the lower respiratory tract (below the larynx), usually due to exposure to toxic fumes. Initial treatment includes taking the victim away from the fire and smoke, give 100% oxygen at high flow through face mask (non-rebreather if available), and check the victim for injuries to the body. Treatment for smoke inhalation injury is largely supportive with varying degrees of consensus on benefits of specific treatments.

Epidemiology

The U.S. Fire Administration reported almost 1.3 million fires in 2019 causing 3,704 deaths and almost 17,000 injuries. Residential fires were found to be most often cooking related and resulted in the highest amount of deaths when compared to other fire types such as vehicle and outdoor fires. It has been found that men have higher rates of fire-related death and injury than women do, and that African American and American Indian men have higher rates of fire-related death and injury than other ethnic and racial groups. The age group with the highest rate of death from smoke inhalation is people over 85, while the age group with the highest injury rate is people of ages 50–54. Some reports also show increased rates of death and injury in children, due to their lower physical and mental capabilities. In 2019, the overall U.S. national fire death rate was 10.7 people per million population and the injury rate was 50.6 people per million population. Smoke inhalation injury is the most common cause of death in fire victims. Fire victims with both burns to their body and smoke inhalation injury have increased mortality rate and length of hospital stay compared to those with burns alone.

Signs and symptoms

Some of the signs and symptoms of smoke inhalation injury include recent fire exposure followed by cough, wheezing, stridor, confusion, difficulty breathing, low oxygen saturation, smoke debris (especially on face and/or in saliva), burns (especially of the face), singed facial or nose hairs, and/or hoarse voice. A careful history can be helpful in determining where the fire occurred and therefore, what chemical fumes could have been inhaled with accompanying systemic toxicities. Smoke inhalation injury can lead to respiratory complications ranging from minor to major.

Acute Respiratory Distress Syndrome Acute respiratory distress syndrome (ARDS) is a type of respiratory failure characterized by rapid onset of widespread inflammation in the lungs. Symptoms include shortness of breath (dyspnea), rapid breathing (tachypnea), and bluish skin colo ...

(ARDS) is a relatively delayed complication of smoke inhalation injury caused by chemical fumes inducing an inflammatory response in the lung tissue especially the small air sacs known as alveoli where critical gas exchange occurs. Another potential complication is swelling of the upper airway from both heat and chemical damage and can become profound enough to obstruct breathing. The onset of airway swelling can be relatively delayed making it difficult to intubate later on thus endotracheal intubation should be considered early in certain patients. Other possible complications include pneumonia, vocal cord damage and/or dysfunction, and tracheal stenosis (usually delayed).

Mechanism

Inhalation of chemical toxins produced by combusting materials can cause damage to tissues of both the upper (above larynx) and lower respiratory tract (below larynx). Damage to lower airways, air sacs, and lung tissue is due to an inflammatory cascade in response to the noxious chemicals which causes a variety of downstream effects such as increased secretions and exudative material thus clogging the airways and/or air sacs, collapse of air sacs (

atelectasis Atelectasis is the collapse or closure of a lung resulting in reduced or absent gas exchange. It is usually unilateral, affecting part or all of one lung. It is a condition where the alveoli are deflated down to little or no volume, as distinct ...

), vascular permeability leading to

pulmonary edema Pulmonary edema, also known as pulmonary congestion, is excessive edema, liquid accumulation in the parenchyma, tissue and pulmonary alveolus, air spaces (usually alveoli) of the lungs. It leads to impaired gas exchange and may cause hypoxemia an ...

(fluid in the lungs),

bronchoconstriction Bronchoconstriction is the constriction of the airways in the lungs due to the tightening of surrounding smooth muscle, with consequent coughing, wheezing, and shortness of breath. Causes The condition has a number of causes, the most common be ...

, activation of the

coagulation cascade Coagulation, also known as clotting, is the process by which blood changes from a liquid to a gel, forming a blood clot. It potentially results in hemostasis, the cessation of blood loss from a damaged vessel, followed by repair. The mechanism o ...

, and impaired function of the

mucociliary escalator Mucociliary clearance (MCC), mucociliary transport, or the mucociliary escalator, describes the self-clearing mechanism of the airways in the respiratory system. It is one of the two protective processes for the lungs in removing inhaled partic ...

. Inhalation of hot fumes can cause thermal damage to tissues usually limited to the upper respiratory tract (above larynx). Damage in this location can result in sloughing of the damaged tissue and swelling both of which can cause obstruction of the respiratory tract, ulceration, increased secretions, and redness (

erythema Erythema (from the Greek , meaning red) is redness of the skin or mucous membranes, caused by hyperemia (increased blood flow) in superficial capillaries. It occurs with any skin injury, infection, or inflammation. Examples of erythema not assoc ...

). Systemic toxicity can occur from inhalation of chemical compounds produced as byproducts of combustion in a fire.

Carbon monoxide poisoning Carbon monoxide poisoning typically occurs from breathing in carbon monoxide (CO) at excessive levels. Symptoms are often described as "flu-like" and commonly include headache, dizziness, weakness, vomiting, chest pain, and confusion. Large e ...

is the most common systemic toxicity after smoke inhalation and can cause organ failure from lack of oxygen (often

heart attack A myocardial infarction (MI), commonly known as a heart attack, occurs when blood flow decreases or stops to the coronary artery of the heart, causing damage to the heart muscle. The most common symptom is chest pain or discomfort which may tr ...

Carbon monoxide Carbon monoxide (chemical formula CO) is a colorless, poisonous, odorless, tasteless, flammable gas that is slightly less dense than air. Carbon monoxide consists of one carbon atom and one oxygen atom connected by a triple bond. It is the simple ...

is a common byproduct of combusting substances in fires and is colorless and odorless. It has a much higher binding affinity for hemoglobin compared to oxygen and thus can block oxygen from binding to

hemoglobin Hemoglobin (haemoglobin BrE) (from the Greek word αἷμα, ''haîma'' 'blood' + Latin ''globus'' 'ball, sphere' + ''-in'') (), abbreviated Hb or Hgb, is the iron-containing oxygen-transport metalloprotein present in red blood cells (erythrocyte ...

causing hypoxia. Additionally, carbon monoxide decreases the ability of oxygen to dissociate from hemoglobin to diffuse into tissues thus causing hypoxia.

Treatment

First responders often take the victim away from the fire and smoke, give 100% oxygen at high flow through a face mask (non-rebreather if available), assess level of consciousness, and check the victim for burns and/or injuries to the body for initial care. Upper respiratory tract injury due to heat exposure often results in swelling. Intubation should be considered early given that the swelling can have a slow, delayed onset but once present, will make intubation very difficult. Lower respiratory tract injury due to exposure to noxious fumes often consists of supportive measures such as intubation and ventilator support if indicated, suctioning of the airways (

pulmonary hygiene Pulmonary hygiene, formerly referred to as pulmonary toilet, is a set of methods used to clear mucus and secretions from the airways. The word ''pulmonary'' refers to the lungs. The word ''toilet'', related to the French ''toilette'', refers to ...

), and other supportive measures. Intravenous fluids are a mainstay in treatment of fire victims with extensive burns to the body, however, there are differing perspectives on the risks/benefits of IV fluids in fire victims with both burns and smoke inhalation injury due to the potential worsening of pulmonary edema with large amounts of IV fluids typically given in burn victims. Other treatments with differing perspectives and study findings on utility in smoke inhalation injury include nebulized

bronchodilator A bronchodilator or broncholytic (although the latter occasionally includes secretory inhibition as well) is a substance that dilates the bronchi and bronchioles, decreasing resistance in the respiratory airway and increasing airflow to the lung ...

s (such as beta-2-agonists), IV

corticosteroid Corticosteroids are a class of steroid hormones that are produced in the adrenal cortex of vertebrates, as well as the synthetic analogues of these hormones. Two main classes of corticosteroids, glucocorticoids and mineralocorticoids, are involv ...

s, nebulized

epinephrine Adrenaline, also known as epinephrine, is a hormone and medication which is involved in regulating visceral functions (e.g., respiration). It appears as a white microcrystalline granule. Adrenaline is normally produced by the adrenal glands and ...

, nebulized

heparin Heparin, also known as unfractionated heparin (UFH), is a medication and naturally occurring glycosaminoglycan. Since heparins depend on the activity of antithrombin, they are considered anticoagulants. Specifically it is also used in the treatm ...

, and nebulized

N-acetylcysteine Acetylcysteine, also known as ''N''-acetylcysteine (NAC), is a medication that is used to treat paracetamol overdose and to loosen thick mucus in individuals with chronic bronchopulmonary disorders like pneumonia and bronchitis. It has been used ...

. Carbon monoxide poisoning is initially treated with high flow 100% oxygen. Hyperbaric oxygen therapy can be considered but there are differing views on its clinical benefit in terms of outcomes.

References

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