Smoke inhalation injury: Diagnosis and treatment (Burn Guideline)

Smoke inhalation injury: Diagnosis and treatment (Burn Guideline)

Step  1
Initial assessment of the burn patient should include evaluation of the airway and breathing.

Considerations STEP 1
As respiratory failure is immediately life threatening, including  an evaluation of the airway and breathing in the initial  assessment of any trauma patient is unarguable. Assessment  of the airway and breathing are universally advocated  by life support training programs as the first steps in  assessment of trauma cases [58–60]. Oropharyngeal burns  can rapidly cause obstruction, and other causes of critical  respiratory failure, such as coma, require immediate diagnosis  and treatment.

Balance of benefits and harms
Loss of upper airway patency due to progressive edema from inhaled  hot gases will lead to death if insufficient cross-sectional  area of the trachea and larynx is available for respiratory  exchange. Similarly, the progression of damaged lung  parenchyma to respiratory distress syndrome following exposure  to inhaled toxicants will result in pneumonia or death.  Respiratory injury is the major cause of death in patients  injured in structure fires [61].

Values and preferences
Decentralization of care throughout many countries of the world,  especially in RLS, means that the frequency with which patients  may present with smoke inhalation injury may be quite  low in rural areas. Recognition of inhalation injury presupposes  the existence of resources for providing appropriate  treatment. In some cases, humidified supplemental oxygen  will be sufficient supportive care until upper airway edema  subsides, but the need for endotracheal intubation and ventilatory  support may exceed the capabilities of all but a few speciality  hospitals in RLS.

Evaluation of airway and breathing require only education of health  care providers; there is no need for specialized equipment  or supplies. In addition, evaluation of airway and breathing  is a standard item in all trauma care educational programs.  Therefore, no additional costs are envisaged by inclusion  of airway and breathing in the initial assessment of burn  patients.

Diagnosis of inhalation injury is suspected by a history of exposure within  a closed space to products of incomplete combustion, in the physical  examination by diminished consciousness, and by the presence  of soot in the oral cavity and by facial burns. Normal oxygenation  or chest radiographs do not exclude the diagnosis. However,  signs such as hoarseness, carbonaceous sputum, wheeze,  and dyspnea are strongly suggestive of inhalation injury.

Considerations STEP 2
Evidence for this recommendation is weak, not least because the  definition of inhalation injury is imprecise. The term ‘‘inhalation  injury’’ comprises three main components, which can  occur separately but which frequently present in combination.  These components are:
1.    Systemic poisoning due to the inhalation of gases produced  by combustion, such as carbon monoxide (CO)  and hydrogen cyanide (HCN).
2.    Obstruction of the upper airways due to the effects of heat  and subsequent edema.
3.    Injury to the lower respiratory system due to the inhalation  of noxious chemicals and particulates present in  smoke. As  each type of injury is potentially fatal, inhalation injury should  be suspected if the presenting history, symptoms or signs  suggest the possibility.
Carbon  monoxide poisoning is suggested by diminished consciousness  together with a history of exposure to fire in an  enclosed space. Hydrogen cyanide poisoning, which may also be  present, produces similar signs. The differential diagnosis includes  diminished consciousness from other causes, especially  inebriation from alcohol and other drugs, which may have  a similar presentation. (The eventuality that a fire may be caused  by a prior deterioration of consciousness should also be  considered.) Diagnosis of carbon monoxide poisoning is confirmed  by measurement of blood carboxyhemoglobin (COHb),  which should be performed in all patients in whom inhalation  injury is suspected.
Obstruction  of the upper airway: In burns to the face, assessment  of potential obstruction by edema of the upper airway  is more problematic and requires insight into burn wound  pathology. Evidence of burning within the buccal cavity  (e.g., blistering of the mucosal membrane), or symptoms  such as hoarseness or stridor suggest that airway obstruction  is imminent, warranting rapid intervention to secure  airway integrity. A limited superficial burn to the face, such  as a scald burn, is less likely to be problematic. Edema formation  in the head and neck may be insidious and obstruction  can become manifest within up to 24 h or longer post  burn. The clinical approach is discussed below.
Smoke  inhalation:
·        The presence of soot in the oral cavity is indicative  of smoke inhalation.
·        Signs and symptoms such as hoarseness,  wheeze, cough, tachypnea, and hypoxemia can be present  on admission or may develop within up to 48 h after exposure.  
·        The initial chest X-ray is often normal.
·        Diagnosis is generally  accepted as positive by the detection of soot in sputum  in combination with any of the above findings, or by the  observation on bronchoscopy of damaged mucosa below the  larynx [62].

Balance of benefits and harms
The technique for initial assessment (see Recommendation 1 above)  of the patient with suspected inhalation injury is a rapid, sensitive,  but non-specific approach to ensuring that patients with  potentially life-threatening injuries are identified. Subsequently  a more thoughtful and considerate approach to establishing  the diagnosis must be carried out because the supportive  treatment indicated by a diagnosis of inhalation injury  (i.e., endotracheal intubation and ventilatory support) not  only introduces the patient the risk of iatrogenic harm, but also  requires the expenditure of significant resources. 
Therefore,  the ideal screening tool for inhalation injury would not only  be highly sensitive (thus avoiding the loss of life due to missed  diagnosis) but also specific, avoiding intubation of patients  who do not need to be intubated. For example, singeing  of facial or nasal hair, hoarseness, and expectoration of  carbonaceous sputum are ‘‘sensitive’’ signs because they are present  in nearly all patients with inhalation injury, but they are  not ‘‘specific’’ because many patients with these signs do not  have clinically significant inhalation injury. There remains an  ongoing dilemma about which patients require early intubation  to prevent loss of airway after smoke inhalation.

Values and preferences
Fortunately, the diagnosis of CO poisoning can be made definitively  by the assay of COHb. However, there is not a universally accepted standard for the diagnosis of thermal injury  to the upper airway or of significant damage to the lower airways.  For example, even within resource-abundant settings, there  is variation among burn centers on the routine use of fiberoptic  bronchoscopy for the initial diagnosis of inhalation injury  [63].

The diagnosis of inhalation injury requires considerable skill and  experience. Furthermore, diagnosis implies the availability  of resources to respond to a positive diagnosis; inhalation injury  can only be managed in a well-equipped intensive care unit.  COHb measurements can be made with little additional cost  to the basic cost of an arterial blood gas analysis. However,  if the facility lacks the basic equipment to obtain and analyze  arterial blood gases, diagnosis will be made on clinical grounds  only. The advantage of proper diagnosis and timely treatment  of CO poisoning is the elimination of unnecessary deaths  and neuropsychological disability, which reduce the indirect  medical costs to the community. Similarly, there are significant  costs of providing fiberoptic bronchoscopy, which may  be ultimately defrayed in the reduction of unnecessary deaths  or prolonged hospital stay. However, even in resourcerich  settings, in the great majority of cases diagnosis is made primarily  on clinical appearances.

Treatment for suspected or confirmed carbon monoxide poisoning is administration  of high-flow supplemental oxygen for at least 6 h.

Considerations STEP 3
Although, for obvious reasons, no comparative clinical studies are  available, the recommendation is based on well-established  principles of pharmacology and physiology. Carbon monoxide  is a colorless, odorless gas that is produced by the incomplete  combustion of hydrocarbon fuels. CO diffuses rapidly  and competitively binds with hemoglobin, displacing oxygen,  which results in hypoxemia. The affinity of CO for hemoglobin  is approximately 200 times that of oxygen. In addition,  CO binds to cytochromes, interfering with cellular oxygen  utilization. Hypoxemia caused by CO poisoning is not detected  by pulse oximetry or by partial pressure of oxygen (pO2) measurements. The  COHb binding is stable, with a half-life of up to 4 hour in a person  breathing air. Increasing the arterial pO2 accelerates CO displacement  from the hemoglobin molecule; administration of  100% oxygen shortens the half-life of COHb to 40–60 min [64]. Therefore,  patients suspected of having CO poisoning should immediately  be given oxygen, preferably via a non-rebreathing mask,  at a rate of 8–15 L/min, depending on mask design. Treatment  should be maintained for at least 6 h, or longer if symptoms  persist. The indication for intubation and mechanical  ventilation is dictated by the level of consciousness.
Hyperbaric  oxygen: From theoretical considerations, one would  conclude treatment by hyperbaric oxygen would further  accelerate elimination of CO, but practical difficulties of  monitoring and providing ongoing vital care preclude this mode  of treatment in most instances. A systematic review of hyperbaric  oxygen treatment found insufficient evidence to recommend  its use [65].
Hydrogen  cyanide (HCN) is released by the combustion of nitrogen-containing  compounds, which are present in plastics,  fabrics and paper. Cyanide interferes with intracellular oxygenation,  principally by inhibition of cytochrome oxidases. There  is substantial evidence that hydrogen cyanide is commonly  inhaled by fire victims [66] and may contribute to  morbidity and mortality. The half-life of cyanide in man is approximately  one hour [66]. Presenting signs and symptoms are  similar to those of CO poisoning. Empirical treatment involves  administration of high-flow oxygen. Specific antidotes  are advocated, especially hydroxocobalamin, which binds  to cyanide and is relatively non-toxic; but administration  must be immediate for any effect to be useful [67].

Balance of benefits and harms
The use of increased levels of inspired oxygen content to reduce  the amount of CO bound to Hb is therapy that is presumed  to be effective at reducing morbidity and mortality from  CO poisoning is a presumption that is not supported by randomized,  clinical trials, yet is so theoretically sound that it defies  challenge. Similarly, the early effects of the inhalation of  smoke on the trachea-bronchial tree result in hypoxia, which  again is treated by the administration of oxygen. While there  is evidence that the prolonged administration of oxygen at  inspired concentrations above 40% may cause parenchymal damage,  the use of oxygen as an initial treatment of fire victims  is logical and potentially life-saving.

Values and preferences
The use of supplemental oxygen in patients extricated from structure  fires or exposed to smoke is dependent on provision of  this simple therapy throughout pre-hospital and basic hospital  systems throughout RLS. The lack of randomized, prospective  clinical trials to support this recommendation is likely  to remain because it would be unethical to perform a trial in  which supplemental oxygen administration would be withheld.

Pre-hospital care systems are either poorly developed or nonexistent  in RLS, yet provision of supplemental oxygen can be found  in many basic hospitals and some clinics. In resourceabundant  settings, established pre-hospital care systems routinely  provide supplemental oxygen therapy. Where supplemental  oxygen is a treatment available for administration,  the other critical step is providing health care providers with  necessary education so that appropriate patients will be selected  for support. The cost of education for this particular modality  can be bundled with the other educational activities proposed  in these recommendations.

Treatment of upper airway burns secondary to smoke inhalation  includes observation and monitoring. Patients with upper  airway burns should be nursed in the semi-upright position with moderate elevation of the head and trunk. Endotracheal intubation  or tracheostomy is indicated if airway patency is threatened.

Considerations step 4
Although evidence supporting this recommendation is weak, the  management of upper airway burns with respect to airway patency  is a clinical necessity. As edema formation continues for  many hours, continuous monitoring and frequent assessment  are essential.
Moderate  elevation of the head of the bed allows gravity to help  reduce airway edema by facilitating venous and lymphatic  drainage, and is therefore a sensible, critical standard  practice. The patient should be given oxygen by mask  to maintain adequate arterial oxygen saturation. Suction  should be used to keep the airway clear of debris and  secretions.
To  protect the airway, the presence of burns inside the oral cavity  and the occurrence of stridor are strong indications for immediate  intubation. Other signs for concern include tachypnea,  hoarseness and the use of accessory respiratory muscles.
Children  are at greater risk of obstruction, as are patients whose  burns include circumferential burns to the neck. Other early  signs and symptoms of respiratory dysfunction may be more  suggestive of smoke inhalation. These signs include a ‘‘brassy’’  cough, wheezing and breathlessness. Arterial oxygen desaturation  despite oxygen therapy by mask is an important marker  of respiratory compromise.
In  many cases of upper airway burns, it is prudent to observe  and hold off on immediate intervention. On the other hand,  failure to intervene presents a risk of airway obstruction later  as edema develops. If delayed, laryngoscopy and intubation  may be hazardous, due to the presence of pharyngeal  edema. The clinical decision to intubate in order to  protect the airway depends on the availability of technical expertise  and facilities and, above all, on the clinical insight of the  physician in charge. The decision is often facilitated by the presence  or absence of significant smoke inhalation, which requires  mechanical ventilation to maintain adequate gas exchange.
No  evidence supports the use of tracheostomy in burn patients.  In a recent survey of American burn centers, tracheostomies  were most frequently performed at 2 weeks, but  most respondents agreed that early tracheostomy was indicated  under certain circumstances [68]. Indications cited included  predicted need for prolonged mechanical ventilation, burns  of head and neck, and failure to wean. The conventional surgical  procedure was preferred to the percutaneous method, especially  in the presence of neck burns. In all cases requiring intubation,  meticulous hygiene of the oropharynx and trachea are  mandatory to prevent the occurrence of ventilatorassociated  pneumonia (VAP).

Balance of benefits and harms
This recommendation describes the best practice of care for patients  with inhalation injury. Although not supported by prospective,  randomized, clinical trials, this recommendation summarizes  the consensus of experienced burn clinicians, both  nurses and doctors. As such, this practice of care may be effective  at reducing, but not eliminating the complications associated  with inhalation injury. However, intubation and ventilation  may cause harm. Apart from the obvious risks of accidental  extubation and mechanical obstruction, there is growing  awareness of the risks of mechanical ventilation itself (see  Recommendation 5), patients require increased administration  of sedatives and analgesics and are no longer able to maintain  homeostasis. Intensive care facilities are then essential  for the provision of appropriate fluids and nutrition.

Values and preferences
Consistent with support for the recommendations above, education  is key to instituting this recommendation into consistent  clinical practice. However, barriers to ensuring permanent  implementation of these care plans include large volumes  of patients, shortage of human resources, and the absence  of clinical standards for intensive care.

The resources required for optimal clinical care plans for patients  with inhalation injury are high. The provision of intensive  care requires investment in human resources, education  and facilities and therefore represents a considerable  financial commitment. The ability to provide optimal care for  patients with inhalation injury is therefore dependent on the  availability of expensive intensive care facilities and clinical  expertise.

In those patients requiring ventilatory support, lung protective strategies  should be employed. Prophylactic antibiotics and corticosteroids  are not indicated for the treatment of smoke inhalation  injury.

Considerations STEP 5
In the past 15 years evidence has accumulated from studies in the  intensive care unit (ICU) that positive pressure mechanical ventilation  is associated with lung injury (ventilator-associated  lung injury, VALI) and acute respiratory distress syndrome (ARDS).  It is suggested that damage to small airways and alveoli  is caused by the mechanical forces transmitted by cyclical  positive inflating pressures [69]. Various studies show improved  survival using low tidal volumes in patients with ARDS  [70]. For this reason, lung protective strategies, maintaining  plateau pressures below 31 cm H2O and tidal volumes below  7 mL/kg, are being increasingly adopted in the ICU setting  [71].
Efforts  to apply protective ventilation strategies to burn patients  have been problematic [72]. The effect of smoke inhalation  on VALI is unknown and thoracic compliance may be  affected by burns to the thorax and abdomen. Above all, the hypermetabolic  response to burn markedly increases the demand  for respiratory gas exchange. A recent survey in North American  burn centers found a wide variation of ventilator practices,  with reported difficulties in adhering to low tidal  volume strategies, suggesting that burn patients on ventilators may comprise a unique subpopulation [68]. At the present  time, while conventional ICU ventilation guidelines may  not be pertinent, it nevertheless seems prudent to assume  that VALI also occurs in burn patients. Therefore, the use  of the lowest possible inflation pressures and tidal volumes,  compatible with respiratory demands, is suggested for  the mechanical ventilation of burn patients. At the same time,  it is acknowledged that the optimal approach to mechanical  ventilation in burn patients has yet to be established.
Ventilator-associated  pneumonia is common and potentially  fatal [73]. Scrupulous hygiene around the head and neck area,  including the oropharynx, and regular clearing of the airways  under sterile conditions are essential. Measures that help  to reduce ventilation requirements include nursing in a semi-upright  position and escharotomies as appropriate for burns  to the trunk, both of which increase total lung compliance.  Empirically, maintenance of optimal fluid balance  and other aspects of general burn care, such as nutrition, effective  wound coverage and pain control, all reduce the hypermetabolic  response, which decreases the respiratory demand.
Corticosteroids  are not recommended for the initial treatment  of inhalation injury [74]. Humidification of inspired gases  helps prevent mucus retention. Mucolytic agents such as  acetylcysteine and bronchodilator therapy may be useful adjuncts.  Antibiotics have no effect on inhalation injury until infection  supervenes, when the choice of antibiotics should be based  if possible on the antibiograms of the causative microorganisms.
In  conclusion, inhalation injury is a potentially lifethreatening  condition which can lead to respiratory failure from  a number of mechanisms. Recognition of inhalation injury  and the subsequent monitoring of vital signs are essential.  Initial treatment comprises the administration of oxygen  in high concentration. A conservative approach is advocated  if clinically appropriate, but intubation and mechanical  ventilation may be life-saving. Respiratory support  is not a cure, and all measures to promote body homeostasis  and wound healing should be aggressively pursued.

Balance of benefits and harms
This recommendation is supported by the scientific literature and  by expert clinical opinion. Clinical practice that is consistent  with this recommendation results in improved outcomes,  including fewer complications and reduced mortality.  Additionally, this topic is a field in which there are many  promising research endeavors currently underway, many  of which should help guide improvements in future care.

Values and preferences
Endotracheal intubation and mechanical ventilatory support are  now more common in RLS, but optimal ventilation requires  continuous monitoring and frequent adjustments, posing  additional strains on limited resources. Again, education  will play a key role in ensuring that these principles will  be employed in the care of patients with inhalation injury.

Dissemination of these clinical recommendations is an ongoing  responsibility of national, regional and international burn  care associations. However, there is an equal responsibility  of health care facilities and practitioners to guarantee that  management of inhalation injury is an ongoing priority for  continuing medical education activities. Thus, as in Recommendation  4 above, there is a considerable logistical challenge  to provide the support of hospital administrators and  government health officials, as well as the commitment of health  care professionals to acquiring and maintaining standards  of care in this field.
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