Assessment and Management Of Airway Burns

The term “inhalational injury” has been used to describe the aspiration of toxic products of combustion, but also more generally any pulmonary insult associated with a burn injury. Patients with cutaneous burns are two to three times more likely to die if they also have lower airway burns. Death may be a direct result of lung injury but is usually due to the systemic consequences of such injury. It may be impossible to distinguish lung injury caused at the time of the burn directly to the lungs by a burn from injury due to the systemic consequences of the burn. Inhalation injury, age, and burn size are the three most commonly cited predictive factors for prolonged ventilator dependence, hospital stay, and death in burn patients. The injuries can generally be divided into three classes:
- thermal injury (restricted to upper airway structures except in cases of blast injury or steam inhalation),
- local chemical irritation throughout the respiratory tract, and
- systemic toxicity (eg, inhalation of toxins such as carbon monoxide or cyanide).

In the clinical setting, diagnosis of inhalation injury is usually a subjective decision based on a combination of history and physical exam, and confirmed by diagnostic studies (eg, fiberoptic bronchoscopy).
History includes -
mechanism of exposure, (eg, flame, electricity, blast injury, steam, or hot liquid)
quality of inhaled irritants (eg, house fire, industrial toxins), and
duration of exposure eg, trapped in an enclosed space or
conditions that limit avoidance behavior such as intoxication, loss of consciousness, or physical disability).

Physical exam can provide
an estimate of the intensity of exposure and includes findings such as
evidence of exposure of the respiratory tract to extreme heat (facial burns or singed facial or nasal hair),
soot deposited on the face or carbonaceous sputum,or
early manifestations of respiratory compromise such as airway obstruction by edema or parenchymal damage.

Defining diagnostic criteria for inhalation injuries is made difficult by the extreme heterogeneity of clinical presentation as evaluated therefore, diagnosis is with a high index of suspicion of airway burns in patients with one or more of the warning signs.

Warning signs of airway burns - Suspect airway burn if:
• Burns occurred in an enclosed space
• Stridor, hoarseness, or cough
• Burns to face, lips, mouth, pharynx, or nasal mucosa - Singed nasal hairs; red, tender oral membranes; or obvious intraoral or pharyngeal burns indicate likely airway burn.
• Soot in sputum, nose, or mouth
• Dyspnoea, decreased level of consciousness, or confusion
• Hypoxaemia (low SpO2 or PaO2) or increased carbon monoxide levels (>2%)
Onset of symptoms may be delayed

Mechanisms of pulmonary insult after lower airway burns
• Mucosal inflammation • Ciliary paralysis
• Mucosal burn • Reduced surfactant
• Bronchorrhoea • Obstruction by debris
• Bronchospasm • Systemic inflammatory response

The pathophysiology of airway burns is highly variable, depending on the environment of the burn and the incomplete products of combustion. The clinical manifestations are often delayed for the first few hours but are usually apparent by 24 hours. Airway debris—including secretions, mucosal slough, and smoke residue—can seriously compromise pulmonary function.

Management of Airway burns—key clinical points
• Restricting fluids increases mortality
• If in doubt, intubate
• Give 100% oxygen until carbon monoxide toxicity excluded
• Ventilatory strategies to avoid lung injury (low volume or pressure)
• Aggressive airway toilet
• Early surgical debridement of wounds
• Early enteral feeding

There is no specific treatment for airway burns other than ensuring adequate oxygenation and minimising iatrogenic lung insult. Prophylactic corticosteroids or antibiotics have no role in treatment. Studies on Beta 2 agonists, Nebulized Heparin,Tocopherol, Inhaled NO are also inconclusive or lack sufficient data.

Control of the airway, by endotracheal intubation, is essential before transporting any patient with suspected airway burn. Rapid fluid administration, with inevitable formation of oedema, may lead to life threatening airway compromise if control of the airway is delayed. Endotracheal intubation before oedema formation is far safer and simpler. Oxygen (100%) should be given until the risk of carbon monoxide toxicity has been excluded, since high concentrations of oxygen will clear carbon monoxide from the body more rapidly than atmospheric concentrations. Importantly, carbon monoxide toxicity may result in a falsely elevated pulse oximetry saturation.

Airway burns are associated with a substantially increased requirement for fluid resuscitation. Reducing the fluid volume administered, to avoid fluid accumulation in the lung, results in a worse outcome. Invasive monitoring may be required to guide fluid administration, especially with failure to respond to increasing volumes of fluid. Fluid administration should not be guided by calculated fluid requirements alone.Adequate oxygen delivery to all the tissues of the body is essential to prevent multi-organ failure.

Aggressive airway toilet is essential. Early surgical debridement, enteral feeding, mobilisation of the patient, and early extubation are desirable. Antibiotics should be reserved for established infections and guided by regular microbiological surveillance.

Several ventilatory strategies have been proposed to improve outcome following airway burns. Adequate systemic oxygenation and minimising further alveolar injury is the primary clinical objective. Prolonging survival will permit spontaneous lung recovery.

Critical Care/Medical Sites of Interest

Hi everyone, I am trying to collect and make list of all useful websites in CRITICAL CARE. Here is the beginning and if you know some, please share for benefit of all.

Critical Care Medicine
http://www.ccmtutorials.com
http://www.aic.cuhk.edu.hk/web8/index.htm
http://www.lhsc.on.ca/Health_Professionals/CCTC/edubriefs/index.htm
http://www.uihealthcare.com/vh/
http://cim.ucdavis.edu/
http://www.thoracic.org/sections/clinical-information/critical-care/index.html
http://www.anzics.com.au/
http://www.lhsc.on.ca/programs/critcare/pge/
http://www.dicm.co.uk/papers.htm - Great UK based website, primarily for those doing the UK DICM but a treasure trove of evidence for any intensivist

Evidence Based Medicine
http://www.ebmny.org/">http://www.ebmny.org/">http://www.ebmny.org/
http://www.cche.net/usersguides/ebm.asp
http://www.cebm.utoronto.ca/
http://www.cebm.net/

Anesthesia
http://www.virtual-anaesthesia-textbook.com/vat/main.shtml

Acid Base
Acid Base Tutorial - http://www.acid-base.com/
Acid Base Physiology - http://www.anaesthesiamcq.com/AcidBaseBook/ABindex.php

Mechanical Ventilation
http://www.ccmtutorials.com/rs/mv/index.htm">http://www.ccmtutorials.com/rs/mv/index.htm">http://www.ccmtutorials.com/rs/mv/index.htm
http://www.aic.cuhk.edu.hk/web8/mech%20vent%20intro.htm

Sepsis
http://www.sepsisforum.org/">http://www.sepsisforum.org/">http://www.sepsisforum.org/
http://www.elililly.com/
http://www.ardsfoundation.com/
http://ssc.sccm.org/
http://www.ardsnet.org/

Radiology
http://www.learningradiology.com/
http://www.anatomyatlases.org/

Chest XRay
http://www.meddean.luc.edu/lumen/MedEd/medicine/pulmonar/cxr/cxr.htm
http://www.meddean.luc.edu/lumen/MedEd/medicine/pulmonar/cxr/atlas/cxratlas_f.htm
http://www.learningradiology.com/lectures/facultylectures/BASIC%20CXR-mod-Adam_files/v3_document.htm
http://www.usfca.edu/fac-staff/ritter/chestxra.htm

Trauma
http://www.trauma.org/

Pupil assessment
http://cim.ucdavis.edu/EyeRelease/Interface/TopFrame.htm

Delirium
http://www.icudelirium.org/delirium/CAM-ICUTraining.html

Anatomy
http://www.pbs.org/wnet/brain/3d/
http://www.meddean.luc.edu/lumen/MedEd/GrossAnatomy/anatomy.htm
http://msjensen.cehd.umn.edu/webanatomy/
http://www.imaios.com/en/e-Anatomy

IABP
http://www.aic.cuhk.edu.hk/web8/IABP%20pressure%20waveforms.htm

ECHO
http://www.criticalecho.com (By Kishore CMC Vellore)

Brain Herniation
http://rad.usuhs.mil/rad/herniation

Assessment for extubation

Despite advances in mechanical ventilation and respiratory support, the science of determining if the patient is ready for extubation is still very imprecise. A lot depends on the clinician’s threshold for reduction in ventilatory support, than does the modes of ventilatory wean.

Patients who can be extubated safely can be divided into three phases-
1. Freedom from the primary problem that prompted mechanical ventilation
2. Identifying whether the patient will sustain spontaneous respiration and ventilation and also when the patient is failing the assessment
3. What to look for immediately before extubation.

These assessments are multifaceted and usually include the overall patient condition, hemodynamic stability, neurological and muscular status and adequacy of gas exchange.

Commonly used clinical parameters that predict successful weaning from
mechanical ventilation.

Parameter with Desired value
Respiratory rate Less than 30-38 breaths/minute
Tidal volume 4-6 mL/kg
Minute ventilation 10-15 L/minute
Negative inspiratory force -20 to –30 cm H2O
Maximal inspiratory pressure (MIP) -15 to –30 cm H2O
Mouth occlusion pressure 100 msec after the
onset of inspiratory effort (P0.1) divided by MIP 0.3
Rapid shallow breathing index (RSBI)
(respiratory rate divided by tidal volume) 60-105
Rapid shallow breathing index rate
[(RSBI2 – RSBI1)/RSBI1] x 100 Less than 20%
CROP score (an index including compliance,
rate, oxygenation and pressure) 13
PaO2/FiO2 ratio >150-200
Despite high sensitivity, however, these parameters lack specificity.

All the patients who are deemed fit for extubation should undergo some means of assessment to see if they will tolerate extubation. It is routine to perform Spontaneous breathing trial (SBT), by means of – CPAP of 5 cm of H2O, T –Piece trial, or Pressure support of 7 cm of H2O. Once the patient is on SBT we should watch for indicators of failure, which are –

1. Inadequate gas exchange
Arterial oxygenation saturation (SaO2) <85% - 90% PaO2 <50 – 60 mmHg pH < 7.32 Increase in PaCO2 >10 mmHg

2. Unstable ventilatory/respiratory pattern
Respiratory rate >30 – 35 breaths/minute
Respiratory rate change over 50%

3. Hemodynamic instability
Heart rate >120 – 140 beats/minute
Heart rate change greater than 20%
Systolic blood pressure >180 mmHg or <90 mmHg Blood pressure change greater than 20% Vasopressors required 4. Change in mental status
Agitation
Anxiety
Somnolence
Coma

5. Signs of increased work of breathing
Nasal flaring
Paradoxical breathing movements
Use of accessory respiratory muscles

6. Onset of worsening discomfort ± diaphoresis

Another parameter that is widely used is the Rapid shallow breathing index (RSBI), from which we can calculate the RSBI rate which is the measure of change of RSBI over time, and may offer more predictive value .A RSBI rate of less than 20% is 90 % sensitive and 100% specific for predicting weaning success .It has a positive predictive value of 100% and negative predictive value of over 81 %.

Finally, once it is confirmed that patient can sustain spontaneous breathing , we can extubate the patient provided—
1 .Presence of a patent airway –assessed with “Cuff leak test”( dividing expiratory volume by inspiratory volume and multiplying with 100)
2. Patients’ ability to consistently protect the airway and clear secretions –assessed by the presence of adequate cough and gag reflex.
3. Mental status compatible with maintenance of airway and secretion clearance.
4. Absence of any other reasons for potential post-extubation failure—
- severe pain
- presence of apnea
- poorly controlled seizures
- risk of massive upper GI bleeding.

Thanks to Dr Harjit Mahay for contributing this wonderful article.