Smoke Inhalation Injury

Description

Smoke inhalation can result in
- Injury to the airway due to superheated air, steam, or particulate matter
- Systemic toxicities from by-products of combustion
Patients can present to the anaesthetist for initial airway management, surgery for burns and other injuries, as well as pain management. Additionally, smoke inhalation injury can result from operating room or airway fires.

Epidemiology

Incidence

Found in 5–35% of patients with burn injuries.
In the US, there are 700,000 burn injuries per year (1).

Mortality

Thermal burn injury (all-cause mortality): 25–65%
Smoke inhalation injury accounts for the majority of fire-related deaths.

Etiology/Risk Factors

Closed space fire
Gas, electrical, chemical, steam, or scalding injuries.

Physiology/Pathophysiology

Smoke inhalation injury describes thermal injury to the airways, particulate irritation, and gaseous-related injury.
- Presentation involves significant airway swelling and edema; and may be delayed
- Animal models suggest that calcitonin gene-related peptide (CGRP) plays a role in increasing airway hyperemia, transvascular fluid flux, and respiratory malfunction. Attenuation with an antagonist was shown to decrease edema and alveolar inflammation. Future efforts may target this gene.
- Interleukin-8 (IL-8) also appears to play a role in the inflammatory pathogenesis. In animal models, pretreatment with anti-IL-8 demonstrated attenuation of lung permeability, suggesting another potential therapeutic target.
- Inducible nitric oxide synthase (NOS) also increases the effects of smoke inhalation injury; inhibition of NOS has been shown to improve pulmonary gas exchange and reduce pulmonary shunt fraction compared to controls.
Particulate irritation to the airways can be seen with gas or flame burns. The pathogenesis involves impaired motility of respiratory cilia. Additionally, it may also dissolve into harmful substances.
Gaseous-related Injury
- Carbon monoxide (CO) is a product of incomplete combustion that binds to ferric atoms in hemoglobin to form carboxyhemoglobin. CO has a 260–300 times greater affinity to hemoglobin compared to oxygen; thus it "displaces" oxygen and prevents binding and impairs oxygen delivery to tissues. As a result, tissues resort to anaerobic metabolism with resultant lactic acid production.
- Hydrogen cyanide is a by-product of burning synthetic polymer materials. Cyanide binds to ferric ions in the mitochondrial electron transport chain; it prevents the final electron transfer to oxygen and halts adenosine triphosphate (ATP) production. Tissues resort to anaerobic metabolism, with resultant lactic acid production.
- Acrolein results from burning wood and petroleum products and causes protein denaturation along the airways.
- Hydrochloric acid is formed from burning plastics and polyvinylchloride (PVC); it can cause pulmonary edema and lethal arrhythmias.
- Toluene diisocyanate is produced from burning foam products, furniture, and insulating materials; it causes severe bronchospasm upon exposure to lower airways.

Anesthetic GOALS/GUIDING Principles

Maintain a high index of suspicion for smoke inhalation injury based on history and physical exam. There should be a low threshold for securing the airway if thermal injury to the airways is suspected or present. Similarly, CO or cyanide toxicity, if suspected, should be confirmed and treated.
In the event of an operating room fire, or rescue scene, make sure as a healthcare provider, you do not become a victim. Evacuate yourself and the patient from the area of smoke or fumes before initiating any care.

Diagnosis ⬆ ⬇

Symptoms

Coughing, nausea, headache, confusion, somnolence

History

Type of fire
Duration of exposure
Events leading to exposure
Determine whether the fire was in an enclosed structure such as a building or vehicle

Signs/Physical Exam

Facial burns, carbonaceous sputum, soot in the mouth, singeing of facial hair, and second or third degree burns elsewhere on the body correlate strongly with associated airway injuries (2).
"Cherry Red" colored skin and mucosal surfaces are very late findings and are often noted post-mortem.

Treatment History

Intubation if airway edema is suspected
High-frequency oscillatory ventilation (HFOV) has been shown to significantly improve oxygenation in burn injury patients, but not in patients with smoke inhalation injury (3) [A].
High concentrations of oxygen are required for the treatment of CO toxicity as a bridge therapy until hyperbaric treatment can be provided. Hyperbaric oxygen therapy is the delivery of 100% oxygen at increased atmospheric pressures. By providing an overabundance of oxygen, CO is displaced from hemoglobin molecules.

Medications

Hydroxocobalamin for cyanide toxicity; the cyanide antidote kit should be avoided because nitrites can result in a methemoglobinemia that could be fatal if the patient also has high levels of carboxyhemoglobin.

Diagnostic Tests & Interpretation

Labs/Studies

Arterial blood gas (ABG) with carboxyhemoglobin level
Electrocardiogram (EKG)
Lactate levels (4)

CONCOMITANT ORGAN DYSFUNCTION

Acute respiratory failure from burn injury
Acute renal failure from rhabdomyolysis
Severe fluid redistribution in burn patients

Circumstances to delay/Conditions

Due to significant associated morbidity and mortality, only emergency surgery should be contemplated in the patient with suspected smoke inhalation.
Carboxyhemoglobin levels >25% should be strongly considered for hyperbaric oxygen therapy prior to any operative procedure.

Treatment ⬆ ⬇

PREOPERATIVE PREPARATION

Premedications

Benzodiazepines and opioids can cause respiratory depression or affect hemodynamics; if administered, should be done judiciously and with monitoring.

INTRAOPERATIVE CARE

Choice of Anesthesia

General endotracheal anesthesia is commonly chosen due to the emergent nature of cases involving smoke inhalation and the need for a secured airway. Thus, regional and neuraxial blocks as a sole anesthetic are not appropriate.
Regional anesthesia such as nerve blocks and epidural anesthesia can be considered for management of pain, but factors such as the patient's ability to communicate, urgency of the procedure, and hemodynamic stability should be strongly considered.

Monitors

Standard ASA monitors
Arterial line for frequent blood gas measures and assessment of the pH
Co-oximetry for detection of CO. The standard pulse oximeter and ABG are not capable of distinguishing between carboxyhemoglobin and oxyhemoglobin (can yield falsely elevated oxygen levels).

Induction/Airway Management

If a difficult airway is anticipated, have a fiberoptic bronchoscope, indirect video laryngoscope (Glidescope), jet ventilator, or surgical airway available. Consider utilizing advanced techniques during the initial attempt.
Smaller endotracheal tubes should be available; if burns affect the lips or nose, use of an extended length, small diameter tube may be considered to accommodate swelling.
Patients are considered to have a "full stomach" for recent burns; however, rapid sequence inductions are contraindicated if a difficult airway is suspected. Consideration may need to be made for an awake fiberoptic intubation.
Succinylcholine should be avoided if the burn injury occurred >24 hours. The proliferation of extrajunctional receptors can result in profound hyperkalemia.
Etomidate is capable of maintaining good hemodynamic stability, but is associated with adrenal insufficiency. This may be of concern if multiple surgeries are anticipated

Maintenance

Volatile agents may result in further airway irritability and may even have impaired uptake and elimination with severe lung injury.
Fluid management should be guided by the associated burn injury and the time interval since the burn injury. Patients who have developed lung injury are particularly susceptible to pulmonary edema from excess fluid administration.
Hypothermia can be an issue for all burn patients, and is exacerbated by the vasodilatory effects of general anesthetics. Prevention of heat loss, the use of forced air warming blankets, and increasing the ambient room temperature of the operating room may help prevent hypothermia.

Extubation/Emergence

Use caution if recent burn injury to airways, as swelling may worsen during the first 24 hours. Consider leaving the patient intubated postoperatively with appropriate sedation.

Follow-Up ⬆ ⬇

Bed Acuity

Burn unit is the most suitable location

Medications/Lab Studies/Consults

Patient should be managed by a burn specialist and intensivist who is capable of managing difficult airways and performing repeat bronchoscopies.
Serial lactate and carboxyhemoglobin can aid with directing therapy in CO and cyanide toxicity.

Complications

Smoke inhalation may be an overlooked problem in patients with other trauma or with distracting burn injuries.
Hypoxemia is possible from progressive lung injury and systemic toxicities.
Significant airway edema can occur in the first 24 hours after exposure, even if the initial presentation appears unremarkable.

References ⬆ ⬇

Hall JR. Burns, Toxic Gases, and Other Hazards Associated with Fires: Deaths and Injuries in Fire and Non-Fire Situations. Quincy, MA:. National Fire Protection Association, Fire Analysis and Research Division, 2001.
Madnani DD , Steele NP , de Vries E. Factors that predict the need for intubation in patients with smoke inhalation injury. Ear Nose Throat J. 2006;85(4):278–280.
Cartotto R , Walia G , Ellis S , et al. Oscillation after inhalation: High frequency oscillatory ventilation in burn patients with the acute respiratory distress syndrome and co-existing smoke inhalation injury. J Burn Care Res. 2009;30:199–227.
Baud F , et al. Elevated blood cyanide concentrations in victims of smoke inhalation. N Engl J Med. 1991;325:1761–1766.

section name header

Basics ⬇

Incidence

Mortality

Diagnosis ⬆ ⬇

History

Signs/Physical Exam

Labs/Studies

Treatment ⬆ ⬇

Premedications

Choice of Anesthesia

Monitors

Induction/Airway Management

Maintenance

Extubation/Emergence

Follow-Up ⬆ ⬇

References ⬆ ⬇

Additional Reading ⬆ ⬇

Codes ⬆ ⬇

Clinical Pearls ⬆ ⬇

Author(s) ⬆

section name header

Basics ⬇

Incidence

Mortality

Diagnosis ⬆ ⬇

History

Signs/Physical Exam

Labs/Studies

Treatment ⬆ ⬇

Premedications

Special Concerns for Informed Consent

Choice of Anesthesia

Monitors

Induction/Airway Management

Maintenance

Extubation/Emergence

Follow-Up ⬆ ⬇

References ⬆ ⬇

Additional Reading ⬆ ⬇

Codes ⬆ ⬇

Clinical Pearls ⬆ ⬇

Author(s) ⬆