6.2 Hoarseness + Microlaryngoscopy Flashcards
You are asked to see a 70-year-old man with a hoarse voice who is
booked for an elective micro laryngoscopy and excision of vocal cord lesion.
What are the causes of a hoarse
voice?
- Vocal cord pathology—paralysis, nodules, etc.
- Extrinsic airway compression
- Nerve lesions
- Functional dysphonia
- Laryngeal papilloma
- Reflux laryngitis
- Laryngeal carcinoma
What is the nerve supply of the larynx?
Motor and sensory supply is by branches of the Vagus nerve.
Motor
* Recurrent laryngeal nerve supplies all muscles except cricothyroid.
- External laryngeal nerve supplies cricothyroid muscle.
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Sensory
* Recurrent laryngeal nerve:
sensation below vocal cords
- Internal laryngeal nerve:
sensation above the vocal cords
What are the effects of laryngeal nerve damage?
- Partial recurrent laryngeal nerve damage
The vocal cords are held in midline position as
abductors are more affected than adductors
(Semon’s law).
- Unilateral lesion may lead to hoarseness.
- Bilateral lesions can lead to complete airway obstruction.
_____________________________________________________
- Complete recurrent laryngeal nerve damage
The vocal cords are held midway
between the midline and abducted position.
- Unilateral lesion can lead to stridor.
- Bilateral lesions result in loss of voice and aspiration.
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- Superior laryngeal nerve damage
- Leads to a weak voice because of slack vocal cords.
What are the issues anaesthetising this patient?
Patient factors
* Likely to be a smoker
* Cardiovascular and respiratory comorbidities
Anaesthetic factors
* Difficult airway risk
* Need for airway that allows surgery with
possible use of jet ventilation and lasers during surgery
Surgical factors
* Shared airway
* Head end distant from anaesthetic machine
What special investigations would you like this patient to have?
- Flexible nasendoscopy to know vocal cord movement
- CT scan of neck
- Pulmonary function tests if indicated
Your airway assessment on the patient does not show the presence of a difficult airway.
What are the airway options in
this case?
Standard intravenous induction
with insertion of a micro laryngoscopy tube (MLT)
or
jet ventilation.
What are the features of a micro laryngoscopy tube?
It is longer than standard endotracheal tubes
of this diameter (usually a small diameter to aid surgery)
with a high-volume, low-pressure cuff.
This is the micro laryngoscopy picture of the vocal cord lesion that the
surgeon decides to excise with laser.
- Laryngeal carcinoma (more likely)
- Vocal cord nodules, polyps, or cysts
- Laryngeal papilloma
- Granuloma
What are the risks of laser surgery?
- Ocular damage
The nondivergent beam of laser light,
even when reflected, may be focused on the fovea
and cause irreversible blindness.
Co2 lasers will not penetrate farther than cornea.
Staff should wear goggles to protect them
from specific wavelength that is being generated.
- Explosions and fires
Instruments should have a matte finish to minimise reflection.
Special hazard associated with laser surgery to upper airway.
Surgical swabs and packs can also ignite and thus must be kept moistened with saline.
What precautions are suggested in laser surgery?
- Flexible metallic or metallic coated tubes
- Cuff inflation with saline instead of air
- Use of nonexplosive mixture of gases
- Limitation of LASER power and duration of bursts
- Avoidance of tracheal intubation (e.g. HFJV)
What are the pros and cons of jet ventilation?
Advantages
Advantages
* Improved surgical access
- Reduced peak airway pressure
- Reduced cardiovascular compromise
- Avoidance of endotracheal tube ignition if laser is used
What are the pros and cons of jet ventilation?
Disadvantages
- Barotrauma—
pneumothorax,
pneumomediastinum,
pneumopericardium,
pneumoperitoneum,
subcutaneous emphysema - Malposition—
gastric distension, rupture - Dysrhythmias
- Airway soiling during surgery
- Inhalational anaesthesia impossible
- Efficacy of gas exchange less predictable
What types of jet ventilation are available?
Low-frequency jet ventilation delivered via Sanders or Manujet
- High-frequency jet ventilation (HFJV)
What are the basic settings on a jet ventilator?
- Driving pressure (DP)
The DP is the operating pressure for the jet ventilation that may range
from 103–405 kPa.
‘Start low, go slow’ is the appropriate approach
for initiating jet ventilation.
In an adult, one can start with a DP of 150–200 kPa,
apply a few manual breaths, watching chest movement,
airway pressure, and expiratory Co2.
- Frequency of breaths (respiratory rate)
Automatic jet ventilators are capable of delivering jets at 1–10 Hz.
An initial rate of 100–150 breaths/min is commonly chosen.
It is then adjusted depending on the limits of other
interacting parameters and the adequacy of ventilation.
- Inspiratory to Expiratory (I:E) Ratio
.
A longer expiratory time is normally chosen with a
typical 1:E ratio of 1:3 for better emptying of the lungs
- Inspiratory to Expiratory (I:E) Ratio
- End Expiratory Pressure (EEP) Limit
Rate dependent gas trapping is due to inadequate time for full expiration
of gases and altered lung mechanics.
The EEP is an indicator of alveolar distension or the state of FRC.
The value for EEP limit on the ventilator is
set at a similar level to the PEEP during IPPV (5–10 cm of H2o).
What is the mechanism of gas exchange in HFJV?
- Pendelluft occurs
as a result of regional variation in airway resistance and
compliance causing some areas of the lung to fill
or empty more rapidly than others. - Convective streaming/Taylor dispersion
occurs as a result of the asymmetrical velocity profile
of the inspired gas front as it moves through
the bronchial tree.
Molecules in the central zones where axial velocities
are higher diffuse to lateral zones with lower axial velocities.
- Cardiogenic mixing
where beating heart enhances gas exchange through
agitation of surrounding lung tissue and molecular diffusion. - Bulk flow—partial contribution.
