A Case of Smoke Inhalation Injury – A Medical Student Clinical Pearl

Emmanuel Hebert

MD Candidate, Class of 2022

Dalhousie Medicine New Brunswick

Reviewed by Dr. Matthew Greer

Copyedited by Dr. Mandy Peach

Case

 A 54-year-old Male presents to the emergency room via EMS. He woke up at nighttime to his house on fire. He says he woke up coughing due to the smoke and was able to crawl out of the house while ablaze and called EMS. He was then transported to the hospital. He also reports that his voice is more rough than usual and that he has pain on his back.

Past Medical History: Unremarkable

Medications: No prescriptions medications.

Physical Examination: Patient is seen wearing a non-rebreather mask with an oxygen rate of 12L/min. He appears well and is in no acute distress. He has singed scalp hair and appears flushed. The patient’s vitals are HR-110, BP-125/80, Temp-36.5, O2 sat- 99%. Patient weighs 130 kg. His back appears very red but there are no open lacerations or blisters. There is good air entry bilaterally with no adventitious sounds or wheeze.  There is soot in the mouth as far back as can be visualized. The oropharynx is dry and mucous contains soot.

Figure 1: First degree burns on the back.

Initial bloodwork:

• WBC: 10×10^9/L
• Hgb: 135
• Plt: 300×10^9/L
• Na: 135
• K: 4
• Glu: 6
• Carboxyhemoglobin: 5%
• EtOH: Neg

What is the differential diagnosis of dysphonia?

-Acute laryngitis

-Functional dysphonia

-Tracheal Injury

-Injury to recurrent laryngeal nerve

-Caustic ingestion, smoke inhalation injury, blister chemical agents

-Neck masses (benign and malignant) [5,7]

Smoke Inhalation Upper Respiratory Tract Injury

Definition: Inhalation injury refers to damage to the respiratory tract or lung tissue from heat, smoke, or chemical irritants carried into the airway during inspiration [1].

Damage to the airway can be broken into three different affected zones with their own clinical consequences:

Upper Airway

• The leading injury in the upper airway (above the vocal cords) is thermal injury due to heat exchange in the oro- and nasopharynx.
• Injuries occurring early include erythema, ulcerations, and edema.
• It is for this reason that aggressive fluid resuscitation should be avoided as the edema resulting from the heat transfer, can be compounded with fluid resuscitation, resulting in a further compromised airway. [2]

Tracheobronchial

• Injuries to the tracheobronchial system occurs due to the chemical makeup of the smoke. When smoke stimulates the vasomotor and sensory nerve endings, neuropeptides get released which cause bronchoconstriction and vasodilation. Due to this inflammatory response, a loss of plasma proteins and fluid from the intravascular space into the alveoli and bronchioles ensues. This causes alveolar collapse and causes a VQ mismatch resulting in hypoxia. [3]

Parenchymal Injury

• Injuries to the parenchyma occur because of the above mechanism resulting in alveolar collapse, which then cause increased transvascular fluid flux, a decrease in surfactant, and a loss of hypoxic vasoconstriction and therefore impaired oxygenation. [3]

Figure 2. Mechanisms of smoke inhalation injury in tracheobronchial area [4]

Management

Patients with smoke inhalation injuries are also at risk for carbon monoxide poisoning. It is for this reason that carboxyhemoglobin is used to assess degree of carbon monoxide toxicity. The treatment for this is 100% oxygen via non-rebreather. Another treatment that can be used is hyperbaric therapy. Choice of hyperbaric therapy should be made in consultation with a hyperbaric specialist and patient must be stable prior to transport. [3]

One of the earliest decisions to make in the management of patients with suspected smoke inhalation injuries is whether to secure the airway. In patient whom the airway is non-patent or there is an obstruction, the decision is easy to either attempt intubation via endotracheal tube or secure a surgical airway. The decision is less straight forward when the patient does not seem to be having any difficulties with ventilation and oxygenation. In the case of smoke inhalation injury, early intubation can be lifesaving. [6] This is due to the delayed fashion of bronchoconstriction in addition to the thermal changes that result from heat/smoke inhalation. Clinical judgement must be used however, to avoid intubating everyone prematurely. There are several red flag symptoms that physicians can use to assess whether a patient with smoke inhalation injury requires prophylactic intubation. [5]

Indications for early intubation:

• Signs of airway obstruction: hoarseness, stridor, accessory respiratory muscle use, sternal retraction
• Extent of the burn (TBSA burn > 40-50%)
• Extensive and deep facial burns
• Burns inside the mouth
• Significant edema or risk for edema
• Difficulty swallowing
• Signs of respiratory compromise: inability to clear secretions, respiratory fatigue, poor oxygenation or ventilation
• Decreased level of consciousness where airway protective reflexes are impaired
• Anticipated patient transfer of large burn with airway issue without qualified personnel to intubate en route

Back to the case:

Due to our patient having progressive hoarseness, as well as soot throughout his oropharynx, the decision was made to secure his airway before it became too difficult to do so. A discussion was had with the patient about the risks and benefits to intubation and sedation while the inflammatory response could take its course and he consented to the procedure. Using rapid sequence intubation, rocuronium, a paralytic was used at a dose of 1mg/kg=130mg and propofol was used as a sedative at 1mg/kg=130mg. Fentanyl was used for analgesia at a dose of 1mcg/kg= 130mcg.

Due to the complexity of intubating a patient with possible impending upper airway collapse, it is important to have the best person available for intubation with one pass and ENT should be consulted so that a surgical airway can be obtained. One should also consider awake intubation due to high risk of upper airway occlusion. With this patient, a video laryngoscope was used to place the endotracheal tube.

Figure 3: Video laryngoscopy of an airway with smoke inhalation injury

During the intubation, it was seen that the tissue surrounding the airway was quite edematous with black soot present as well. This was an impending airway collapse! The endotracheal tube was placed, and the patient was monitored in the ICU overnight. As expected, edema ensued and oropharynx, tongue became edematous. The patient was stabilized on propofol drip over the next 2 days and was extubated on the third day post intubation.

Key Takeaways

• Early identification of smoke inhalation injury is critical to survival.
• The longer delay of intubation is, the harder it becomes. Consider awake intubation.
• Red flag symptoms: Respiratory distress, respiratory depression, or altered mental status, Progressive hoarseness, Supraglottic or laryngeal edema/inflammation on bronchoscopy or NPL, Full thickness burns to face or perioral region, Circumferential neck burns, Major burns over 40-60% of body surface
• Early intubation=lower mortality

References:

1. Woodson CL. Diagnosis and treatment of inhalation injury. In: Total Burn

Care, 4 ed, Herndon DN (Ed), 2009.

2. Sheridan RL. Fire-Related Inhalation Injury. N Engl J Med 2016; 375:1905.
3. Rehberg S, Maybauer MO, Enkhbaatar P, et al. Pathophysiology, management and treatment of smoke inhalation injury. Expert Rev Respir Med 2009; 3:283.
4. Herndon, D. N. (2018). 16. In Total burn care (pp. 174–183). essay, Elsevier.
5. ABLS Provider Manual. (2019). Ameriburn.org
6. Cioffi WG, Mason AD Jr, et al. The risk of pneumonia in thermally injured patients requiring ventilatory support. J Burn Care Rehabil 1995; 16:262.
7. Reiter R, Hoffmann TK, Pickhard A, Brosch S. Hoarseness-causes and treatments. Dtsch Arztebl Int. 2015;112(19):329-337. doi:10.3238/arztebl.2015.0329