Trauma

Burns: Inhalation Injuries

Background

1. Definition
   • Due to smoke inhalation or superheated air secondary to fire in an enclosed space
2. Synopsis
   • Inhalational Injuries significantly increase mortality in burn patients
   • Can be caused from both thermal and chemical exposure
     • Thermal injury
       • Typically isolated to the upper airway due to reflex closure of the larynx
       • Can lead to significant swelling and airway obstruction
       • Intubation if respiratory distress or concern for airway edema
         • Swelling can worsen during fluid resuscitation
     • Chemical injury
       • Can occur throughout respiratory tract
       • Leads to damage of epithelial and capillary endothelial cells
       • May also develop damaged mucociliary transport
         • Inability to clear secretions and bacteria
   • All Inhalational Injuries should be referred to a burn center

Pathophysiology

1. Mechanism
   • Inhalation of smoke or superheated air secondary to fire in an enclosed space
     • Results in damage by 3 mechanisms
       • Local thermal injury (upper airway)
       • Chemical injury from toxins (lower airway)
       • Inhalation of asphyxiants (CO, CN, etc)
   • Upper Airways
     • Heat displaced/absorbed by upper airways
     • Results in swelling/inflammation with potential loss of airway
     • Hoarse voice second to vocal cord swelling
   • Lower Airways
     • Damaged by cooled particles of smoke/toxins
     • Causes inflammatory cascade
     • Edema prevents alveolar exchange
     • Airway exudates coalesce to fibrin casts and act as "ball valve" during mechanical ventilation, resulting in barotrauma
   • Asphyxiants
     • Toxic by-products of combustion include carbon monoxide (CO), CN, ammonia, and aldehydes
       • CO inhalation is most common, seen in up to 30%
     • Burning plastics and foam associated with other gases
2. Etiology/Risk Factors
   • Factors that contribute to poor outcomes
     • Extremes of age (particularly elderly)
     • Medical comorbidities (eg., chronic lung disease, obesity, diabetes)
   • Causes of Inhalational Injury
     • House/Building fires account for majority
3. Epidemiology
   • Incidence/Prevalence
     • Tri-modal distribution with infants/children, young adults, and elderly being at greatest risk
     • Overall decreasing in number due to prevention campaigns
   • Mortality/Morbidity
     • Inhalational injury has been shown to increase burn mortality in multiple studies
     • Mechanical ventilation increases risk of pneumonia, barotrauma, ARDS, sepsis

Diagnostics

1. History/Symptoms
   • Suspect Inhalational Injury if presenting after structure fire (+/- obvious burns)
     • History of closed space entrapment
     • History of syncope
       • Increased suspicion if syncope or decreased level of consciousness
     • Carbonaceous sputum
     • Arterial PaO2 < 60 mmHg
     • Metabolic acidosis
     • Carboxyhemoglobin > 15%
     • Bronchospasm/wheezing
     • Facial burns
   • Common complaints
     • Shortness of breath
     • Cough
     • Throat pain/irritation
     • Throat swelling sensation
     • Neurologic symptoms
2. Physical Exam/Signs
   • General appearance/Vitals
     • Decreased level of consciousness
       • Especially if CO or CN inhalation
     • Hypoxemia
     • Tachypnea
     • Distress
   • HEENT
     • Singed nasal/facial hairs
     • Facial or oral burns
     • Soot in nose/mouth or carbonaceous sputum
   • Pulmonary/Chest
     • Wheezing
     • Rhonchi
     • Stridor
     • Hoarse voice
3. Labs/Tests
   • ABG with measured (not calculated) O2 sat
     • ABG with co-oximetry (measured Hgb saturation, CO-Hgb and met-Hgb)
   • Serum lactate (rule out CN toxicity)
   • Routine trauma labs per institutional policy
4. Imaging
   • Baseline Chest X-rays
     • May be normal for first 24-48 hours after severe inhalation
   • Bronchoscopy (View image)
     • Can reveal inflammatory changes
       • Such as erythema, edema, ulceration, mucosal sloughing, and prominent vascularity
5. Other Tests/Criteria
   • RADS (Radiologist's Score) for Smoke Inhalation Injury (Open Calc)
   • Pulmonary function tests, peak flow if available
   • Inhalation Grading
     • Grade 0: No injury
       • No carbonaceous deposits, erythema, edema, bronchorrhea, obstruction
     • Grade 1: Mild
       • Minor/patchy areas of carbonaceous deposits, erythema, edema, bronchorrhea, obstruction
     • Grade 2: Moderate
       • Moderate degree of carbonaceous deposits, erythema, edema, bronchorrhea, obstruction
     • Grade 3: Severe
       • Severe inflammation, friability, copious carbonaceous deposits, bronchorrhea, obstruction
     • Grade 4: Massive
       • Evidence of extensive mucosal sloughing tissue necrosis, endoluminal obstruction
6. Differential Diagnosis
   • Chemical inhalation
   • ARDS
   • COPD
   • Emphysema
   • Pneumonia
   • Anaphylaxis
   • Pulmonary embolism
   • Aspiration pneumonitis
   • Pneumothorax

Treatment

1. Initial/Prep/Goals
   • ABCs, IV access, monitors
     • 100% O2 during evaluation
     • Secure airway
       • Early intubation if suspected airway involvement
     • If suspected CO or CN poisoning and not intubated, begin 100% FIO2 by NRB
   • Management of inhalation injury directed at
     • Maintaining open airways
     • Clearing secretions
     • Maximizing gas exchange
   • Bronchoscopy
     • Should be performed within 24 hrs of admission
   • Treat burns and other injuries accordingly
2. Medical/Pharmaceutical
   • For bronchospasm
     • Inhaled beta agonists (albuterol nebulizer)
   • N-acetylcysteine added to nebulized heparin (to decrease cast formation) and albuterol
     • Should be initiated and continued for 7 days post-inhalation injury
   • CO poisoning
     • If CO-Hgb > 5-10%
       • Give 100% O2 by face mask
     • Consider hyperbaric oxygen chamber if
       • CO-Hgb levels > 25%
       • Neurologic deficits or loss of consciousness
       • Pregnant patients
       • Cardiac ischemia
       • Marked metabolic acidosis
   • CN poisoning treatment
     • Sodium Nitrate and Sodium Thiosulfate
       • Caution: Sodium nitrate will increase hypoxia by increasing methemoglobinemia
     • Hydroxocobalamin
       • Consider in burn injuries sustained in an enclosed space with suspected cyanide toxicity and ≥ 1 of the following criteria:
         • Hypotension without clear etiology
         • Altered mental status or seizure
         • Cardiopulmonary arrest
       • DO NOT give ascorbic acid therapy with hydroxocobalamin
         • Higher risk for calcium oxalate nephropathy
3. Surgical/Procedural
   • Frequent suctioning and chest physiotherapy
     • May be helpful in intubated patients
   • Frequent bronchoscopy
     • May be needed to clear secretions
   • Ventilation
     • Settings that minimize barotrauma
4. Complications
   • Intubated patients particularly sensitive to barotrauma secondary to airway casts and increased airway pressures
   • Intubated burn patients have higher susceptibility to pneumonia and systemic infection due to decreased protective barrier and impaired immune system
   • Inhaled asphyxiants can produce cardiac ischemia, neurologic deficits, and death
5. Prevention
   • Widespread safety campaigns and regulations have significantly reduced the incidence and prevalence of burns

Disposition

1. Admission Criteria
   • All Inhalational Burns
2. Consults
   • Burn unit, trauma surgery
3. Discharge/Follow-up instructions
   • Asymptomatic exposed patients with a normal exam, ABG, and Chest X-ray
   • Consider Bronchoscopy and/or 4-6 hour emergency dept observation if uncertain

References

1. DuBose JA, O'Connor JV, Scalea TM. Lung, Trachea, and Esophagus. In: Mattox KL, Moore, EE, Feliciano DV; (eds). Trauma, 7th ed., McGraw-Hill, Inc, 2013;Chapter 25
2. Pham TN, Cancio LC, Gibran NS. American Burn Association Practice Guidelines: Burn Shock Resuscitation. J of Burn Care and Research Jan-Feb 2008;29(1):257-266
3. Schlosser A, Cheatham ML. BURN INHALATION INJURY TREATMENT. Available at: http://www.surgicalcriticalcare.net/Guidelines/Burn%20Inhalation%20Injury%202019.pdf. [Accessed January 2022]
4. Shubert J, Sharma S. Inhalation Injury. StatPearls [Internet]. Available at: https://www.ncbi.nlm.nih.gov/books/NBK513261/. [Accessed January 2022]

Contributor(s)

1. Latham, Douglas E., MD

Updated/Reviewed: January 2022