|
| |
Upper
airway obstruction
Gavin Joynt
Pathophysiology
- obstruction is likely to occur at sites of anatomic narrowing such as the
hypopharynx at the base of the tongue and the false and true vocal cords at the
laryngeal opening.
- sites of airway obstruction are referred to as supraglottic (above the true
cords), intraglottic (involving the true vocal cords) or infraglottic (below the
true cords and above the carina)
- can also be divided into intrathoracic and extrathoracic portions: behave
differently during inspiration and expiration. The intrathoracic airway dilates
during inspiration as it is exposed to outward force of negative intrapleural
pressure. Positive intrapleural pressure during expiration causes compression
and narrowing. The compliant extrathoracic airway, not exposed to intrapleural
pressure, collapses during inspiration and increases in diameter during
expiration.
Aetiology
Functional causes
- CNS depression
- Peripheral nervous system and neuromuscular abnormalities
- Recurrent laryngeal nerve interruption (postoperative, inflammatory,
tumour infiltration)),
- obstructive sleep apnoea
- laryngospasm
- myasthenia gravis
- Guillain-Barre polyneuritis
- hypocalcaemia (causing vocal cord spasm).
- tetanus
Mechanical causes
- Foreign body aspiration
- Infections
- Laryngeal oedema
- allergic
- hereditary angioedema
- Haemorrhage and haematoma
- post operative
- anticoagulation therapy
- coagulopathy
- Trauma
- Burns
- Neoplasm
- pharyngeal, laryngeal and tracheobronchial carcinoma
- vocal cord polyposis
- Congenital
- vascular rings
- laryngeal webs, laryngocoele
- Miscellaneous
- crico-arytenoid arthritis
- achalasia of the oesophagus
- hysterical stridor
- myxoedema
Clinical presentation
- may be complete or partial
- complete UAO: rapidly progressing series of events
- patient is unable to breathe, speak, or cough and may hold the throat
between the thumb and index finger (the universal choking sign)
- anxious and agitated. Vigorous attempts at respiration with intercostal
and supraclavicular retraction. Heart rate and blood pressure raised Patient
becomes rapidly cyanosed
- respiratory efforts diminish, loss of consciousness, bradycardia and
hypotension
- cardiac arrest
- death is inevitable if the obstruction is not relieved within 2-5 minutes
of the onset
- partial UAO: stable, or progressive deterioration
- signs and symptoms may be mild but as they worsen include coughing,
inspiratory stridor, crowing or noisy respiration, dysphonia, aphonia,
choking, drooling and gagging
- dyspnoea, feeble cough, respiratory distress and signs of hypoxaemia and
hypercarbia such as anxiety, confusion, lethargy and cyanosis may be present
as the obstruction worsens
- powerful inspiratory efforts against an obstruction may produce dermal
ecchymoses and subcutaneous emphysema. Partial airway obstruction that is
worsening should be aggressively managed and if rapidly progressing
immediate preparation for treatment as complete obstruction should be made
(see Figures 1 and 2)
In stable, non-progressing cases of partial obstruction specific diagnostic
evaluation may be undertaken provided the patient is strictly observed for any
signs of deterioration and facilities for skilled airway management are
immediately available.
Special investigations
Laryngoscopy and bronchoscopy
- indirect laryngoscopy in a stable, cooperative patient is useful in
diagnosing foreign bodies, retropharyngeal or laryngeal masses and other
glottic pathology. In skilled hands it is quick, simple and atraumatic.
- flexible fibreoptic bronchoscopy or laryngoscopy is useful for both
diagnosis and management of UAO. Advantages:
- ability to directly see upper airway anatomy and function and make an
accurate diagnosis
- can be performed in emergency department without moving patient and
risking complete obstruction in an inadequately staffed or poorly equipped
area
- spontaneously breathing, awake patient
- if care is taken is atraumatic and should not worsen obstruction
- definitive airway control can usually be achieved at conclusion of
examination by railroading an endotracheal tube into trachea
Disadvantages: need for a skilled operator, cooperative patient
- difficult in presence of blood and secretions
- direct laryngoscopy may be both diagnostic and therapeutic. Foreign
bodies, blood, vomitus, and secretions can be suctioned or removed with
forceps. Endotracheal intubation can be rapidly achieved under direct
vision. Disadvantages:
- necessity for good local analgesia (often difficult in the emergency
setting) or general anaesthesia with the resultant risk that spontaneous
breathing and airway control is completely lost
- traumatic procedure and may lead to worsened swelling, bleeding and
oedema.
Radiographic imaging
- AP and lateral plain neck radiographs are useful to detect radiopaque
foreign bodies, retropharyngeal
masses and epiglottitis. Lateral view
should be obtained during inspiration with the neck fully extended.)
- CT: in stable patients the integrity of the thyroid, cricoid and arytenoid
cartilages as well as the status of the airway lumen can be assessed
- MRI has been used to image the upper airway but use in obstruction is
unproved
Gas flow measurement
- flow volume measurement reveals characteristic patterns corresponding to
different types and position of pathologic lesions
Management
- reverse hypoxia:100% O2 or as close as possible
- no single correct approach to the management
- in difficult situations technique in which the physician has greatest skill
and experience is usually the most appropriate
General measures
- equipment: good suction, a choice of laryngoscopes, blades and endotracheal
tubes, fibreoptic bronchoscope or laryngoscope, emergency drugs and equipment
necessary for a surgical airway (cricothyroidotomy set, tracheostomy tray and
pre-prepared circuit for trans tracheal jet ventilation).
- IV access as soon as practicable.
- continuous monitoring and observation with the most skilled personnel.
- transport of patient before airway is secured should be carefully considered
as it is difficult to provide safe conditions either during transport or in
radiology suites
Principles of airway management techniques
Airway manoeuvres
- try simple manoeuvres to open airway. Jaw thrust (triple airway manoeuver)
is used when other methods have failed.
- oropharyngeal airway or nasopharyngeal airway may be useful in the
unconscious patient.
- if the patient is not immediately intubated the coma position (semi-prone,
slightly head down) should be used.
Endotracheal intubation
- direct laryngoscopy and tracheal intubation is method of choice for the
unconscious, apnoeic patient
- awake fiberoptic intubation. Following are important in setting of acute UAO:
- procedure should be clearly explained to reduce anxiety and improve
cooperation.
- good local anaesthesia is important.
- phenylephrine (1-2%) or cocaine (2ml of 5% solution) decrease nasal
bleeding
- suction catheters (oro or nasopharyngeal) may improve success rates
- suction port can be used to insufflate 100% oxygen. Also keeps the
bronchoscope tip free of secretions.(25)
- blind nasotracheal intubation is becoming a less attractive option in UAO.
- retrograde tracheal intubation over a j-tip guidewire: less invasive
alternative to cricothyroidotomy and transtracheal jet ventilation. Airway
can be secured within five minutes. Can be achieved with minimal neck
movement and is useful where fibreoptic bronchoscopy is not available, or
difficult because of retropharyngeal secretions and blood. Relatively safe,
simple and requires minimal operator skill
Surgical Airway
- indicated when endotracheal intubation is not possible, or an unstable
cervical spine is threatened by available airway techniques.
- percutanous transtracheal jet ventilation using a large bore intravenous
catheter inserted through the cricothyroid membrane
- quick, simple, relatively safe, effective technique in situation where
patient cannot be intubated or ventilated
- quicker than cricothyroidotomy or tracheostomy
- ventilation through an intravenous cannula with a standard bag valve
resuscitator or anaesthesia circuit will be less than adequate
- jet ventilation system and gas source of appropriate pressure (60 lbs/in2)
should be immediately available
- expiratory gases must be able to escape via the glottis and in cases of
complete UAO the technique should be used with caution.
- appropriate chest movement must be carefully observed during expiration
- consequence of expiratory obstruction is severe and potentially fatal
barotrauma.
- cricothyroidotomy
- reliable, safe, relatively easy way of providing an emergency airway
- method of choice if complete UAO exists and expiration is unlikely to be
possible via the glottis.
- minimum internal diameter tube to allow adequate gas exchange (using
supplemental O2): spontaneous breathing 3mm; ventilation with a bag valve
resuscitator 2.5mm
- diameter of the cricothyroid space is 9mm by 30mm and therefore a size 8.5
outer diameter tube should avoid complications such as laryngeal fracture
and vocal cord damage. #4 Shiley tracheostomy tube has an internal diameter
of 5mm and an outer diameter of 8.5mm and is therefore ideal. A standard
6-6.5 endotracheal tube could also be used.
- commercially available percutanous tracheostomy sets (Cook) that meet
above requirements are available.
- complications (eg subglottic stenosis, thyroid fracture, haemorrhage and
pneumothorax) uncommon.
- emergency tracheostomy rarely required. Formal surgical tracheostomy under
local anaesthesia may be a prudent approach under some controlled conditions
Common clinical conditions
Extrinsic airway compression
- commonly due to haemorrhage, infections and tumours. Haematomas should be
considered following trauma, neck surgery, central venous catheterization, as
a complication of anticoagulation therapy and in patients with abnormal
bleeding tendency.
- haematomas following surgery should be immediately managed by suture removal
and haematoma evacuation in an attempt to relieve the obstruction. If this
fails an artificial airway should be immediately secured
- in patients with coagulation abnormalities intubation is preferred over a
surgical airway due to potential complications of bleeding. Most do not
require surgical intervention and resolve spontaneously with conservative
therapy - discontinuation of anticoagulants, vitamin K, fresh frozen plasma
and coagulation factors. Use of prophylactic antibiotics is controversial
Retropharyngeal abscesses causing partial UAO
- best managed by awake drainage under local anaesthesia
- gentle fibreoptic examination and intubation, or direct laryngoscopy and
intubation in lateral, head down position is favoured by some. Risks are
related to inadvertent rupture of abscess with subsequent soiling and
obstruction of airway.
Ludwig's angina
- mixed infection of floor of mouth.
- inflammatory mass develops in space between tongue and the muscles and
fascia of anterior neck
- supraglottic airway is compressed and becomes narrowed
- direct laryngoscopy is difficult as the tongue cannot be anteriorly
displaced
- awake fibreoptic bronchoscopy or a surgical airway are management options
Intrinsic airway compression
Inhalational injury
- UAO from progressive supraglottic oedema which usually develops within 24
hours of injury
- risk factors for severe oedema: increased size of cutaneous burns
(>30-45%), rapid, vigorous intravenous fluid administration and evidence of
facial and neck burns
- patients in these categories should be intubated early and even
prophylactically unless careful follow up, preferably with fibreoptic
bronchoscopy and lung function testing, can be undertaken.
- patients with stridor, hoarseness, or hypoxaemia should be immediately
intubated by an appropriate method
Allergic manifestations
- may be localized or part of a systemic anaphylactic reaction
- in acute allergic laryngeal oedema, angioedema of the lips and supraglottis,
glottis, and infraglottis results in airway obstruction
- systemic reaction consists of a variable combination of urticaria (79%),
bronchospasm (70%), shock, cardiovascular collapse and abdominal pain
- common causative agents are Hymenoptera stings, shellfish ingestion and
drugs
- angiotensin converting enzyme inhibitor therapy related angioedema is
becoming more common as the number of patients receiving this therapy
increases
- treatment consists of immediately ensuring an adequate airway and
administration of oxygen, intravenous fluids, epinephrine, antihistamines and
steroids:
|
Oxygen |
100% |
|
Intravenous fluid replacement |
|
|
Epinephrine (1:10 000) or
Epinephrine (1:1000) |
0.2-0.5 ml IV
0.3 ml SC |
|
Diphenhydramine |
50 mg IV/IM |
|
Methylprednislone or
Hydrocortisone |
125 mg IV
200 mg IV |
|
Aminophylline |
5.6 mg/kg over 30 min |
- as it is likely to recur, the exact nature of the event and agent or drugs
responsible should always be thoroughly investigated and communicated to the
patient prior to discharge
Hereditary angioedema (Quincke's disease)
- rare, inherited disorder of the complement system caused by either
functionless or low levels of C1 esterase inhibitor
- clinical manifestation is the occurrence of angioedema involving the deeper
layers of skin and subcutaneous tissue in various locations, particularly the
upper airway
- precipitating causes include stress, pregnancy, physical exertion and
especially localized trauma such as surgery (dental or maxillofacial) and
laryngoscopy
- management consists of establishing a secure airway and the infusion of
fresh frozen plasma to replace the missing esterase inhibitor or
administration of inhibitor
- poor response to epinephrine, antihistamines, and steroids can be expected
- danazol, anti-fibrinolytic agents(tranexamic acid) and fresh frozen plasma
(2-4 units) can be used prophylactically if time permits
Complications
- post obstruction pulmonary oedema occurs in as many as 11% .
- appears to be related to the markedly elevated intrathoracic pressure
caused by forced inspiration against a closed upper airway, resulting in
transudation of fluid from pulmonary capillaries to the interstitium
- in addition to the decreased interstitial pressure, increased venous
return to the right heart may increase pulmonary blood flow, further
worsening oedema
- hypoxia and the "hyperadrenergic state" may also affect
capillary hydrostatic pressure
- usually occurs within minutes after the relief of the obstruction but may
be delayed up to 2.5 hours
- management consists of supportive care and includes maintenance of airway
patency, oxygen, diuretics, morphine, fluid restriction, CPAP. Ventilation
with PEEP may be necessary in severe cases. Pulmonary capillary wedge
pressure is usually normal and pulmonary artery flotation catheterization
should be reserved only for complicated cases with severe underlying disease
Summary
Failure to treat acute UAO aggressively is associated with a worse outcome
than over treatment. It is essential to have a plan of management which includes
alternative approaches should the initial method fail. Emergency physicians
should be proficient in all types of airway management, including the techniques
required to secure a surgical airway. Difficult clinical problems may not
present with a clear " best approach". In this situation management
should be by those techniques in which the attending team has the greatest
skills and experience.
© Gavin Joynt 1996
|
