14. Thyroid Flashcards
Surgical indications
- thyroid malignancy,
- goitres that produce
3 obstructive symptoms and/or are retrosternal;
- hyperthyroidism resistant to medical management;
- Cosmetic and anxiety related reasons.
Hypo - main respond to eltroxin, sx rare
Hyperthyroidism result from
Causes
results from excess circulating T3 and T4.
- Grave’s disease: An autoimmune condition
associated with eye signs and pretibial myxoedema
IgG - Thyroid secreting adenomas
- Toxic Multinodular Goitre. More common in women
- Other causes that may or may not be associated with goitre include:
EG AMIO, post irradiation thyroiditis
Hypothyroidism
May be from intrinsic thyroid disease or failure of the hypothalamo-pituitary axis.
Those associated with goitre include:
- Hashimoto’s thyroiditis
This is the commonest cause of hypothyroidism and although initially may cause gland enlargement will later lead to thyroid atrophy due
- Iodine deficiency. A lack of iodine leads to thyroid hormone depletion, Thyroid Stimulating
Hormone (TSH) stimulation and gland hypertrophy.
ANAESTHETIC CONSIDERATIONS
History
It is fundamental to ensure that patients are clinically and chemically euthyroid prior to embarking on
elective thyroid surgery
History
This should be focused on establishing
1. if the patient is clinically euthyroid
other systemic disease,
cardiorespiratory compromise and associated endocrine or automimmue disorders should also be
sought.
For example, medullary thyroid cancer associated with phaeochromocytoma.
- assessing for airway compromise
a pathological nature, position and size of the goitre
b large goitre that has been present for some
time may be associated with tracheomalacia postoperatively.
Symptoms of dysphagia, positional
breathlessness with a difficulty lying flat, change in voice or stridor may alert the anaesthetist to
possible difficulties with airway compromise on induction
Exam
goitre
fixed hard nodule suggests malignancy with possible tethering to surrounding structures and limited
movement
inability to feel the bottom of the goitre may indicate retrosternal spread
Trachea
HYPERTHYROIDISM
General
Weight loss, Malaise, Muscle weakness, Heat intolerance, Cachexia, Palmar erythma, Proximal muscle wasting, Pretibial myxoedema (Graves disease)
Central nervous system
Irritability, Anxiety,
Hyperkinesis, Tremor
Cardiovascular Palpitations, Angina, Breathlessness, Hypertension, Cardiac failure, Tachycardia, Tachyarrhythmias, Atrial fibrillation, Vasodilatation
Gastrointestinal Increased appetite,
Vomiting, Diarrhoea
Genitourinary Oligomenorrhoea,
Loss of libido
Eye (Graves disease only) Blurred / double vision, Exophthalmos, Lid lag, Conjunctival oedema
HYPOTHYROIDISM
Malaise, Cold intolerance, Myalgia, Arthralgia, Dry, coarse skin. ‘Peaches & Cream complexion’, Loss of eyebrows, Hypothermia, Carpal tunnel syndrome, Myotonia
Poor memory, Depression, Psychosis, Mental slowness, Dementia, Poverty of movement, Ataxia, Slow relaxing reflexes Deafness
Hypertension, Bradycardia,
Heart failure, Oedema
Pericardial & pleural effusions,
Anaemia, Cool peripheries
Constipation,
Obesity
Menorrhagia,
Loss of libido
Investigations
Routine blood tests include Full Blood Count (FBC), electrolytes, thyroid function and corrected
calcium levels.
euthyroid prior to surgery to avoid complications
of a thyroid storm or myxoedema coma in the perioperative period.
A CXR may be useful to assess the size of goitre and detect any tracheal compression or deviation.
- If there are any concerns regarding airway compromise, a CT scan is performed to determine the
extent and location of tracheal narrowing or detect tracheal invasion. - Nasendoscopy is often performed preoperatively by ENT to document vocal cord function.
Rx
Propanolol
Oral: 40-80mg TDS (May need higher dose as metabolism increased)
IV: 0.5mg titrated to effect
Controls sympathetic effects of thyrotoxic crisis.
Blocks peripheral conversion of T4 to T3
Negative inotropy & chronotropy. Bronchospasm Poor peripheral circulation. CNS effects
Rx Carbimazole
Initial:15-40mg daily
Maintenance: 5-15mg daily
Takes 6-8 weeks to work
Prodrug rapidly converted to methimazole.
Prevents synthesis of T3 and T4 by blocking oxidation of iodide to iodine and inhibiting thyroid peroxidase
Rashes, arthralgia, pruritis, myopathy. Bone marrow suppression Agranulocytosis (0.1%) Crosses placenta: foetal hypothyroidism
Optimisation
Elective work should be postponed until the patient is euthyroid.
On the day of surgery, usual antithyroid medications should be administered
except for Carbimazole as it increases the vascularity
of the gland.
Benzodiazepines may be administered for anxiolysis but should be avoided if there is any airway concern
emergency surgery, it may not be possible to render those patients with uncontrolled thyroid disease
euthyroid. In these circumstances, hyperthyroid patients should have immediate control of symptoms
with beta blockade
emergency surgery, it may not be possible to render those patients with uncontrolled thyroid disease
euthyroid. In these circumstances, hyperthyroid patients should have immediate control of symptoms
with beta blockade
superficial cervical plexus block,
the patient should be positioned with their head
extended to the opposite side,
the midpoint of the posterior border of SCM visualised.
15-20mls of local anaesthetic (e.g. lidocaine and/or bupivacaine with adrenaline) is injected in a superficial wheal deep to the first fascial layer in caudad and cephalad directions along the posterior border of SCM
(Figure 1).
For thyroidectomy, bilateral blocks should be performed. A midline field block can be
achieved by a subcutaneous injection from the thyroid cartilage to the suprasternal notch. This is a
useful addition to prevent the pain from surgical retractors on the medial aspect of the neck.
GA
If concern over airway - AFOI
Or Could consider awake trach by surgeons
Positioning
- head up titlt for venous drainage
- secure tube tie - wont have access
- adequate eye tape and padding * exophthalmus
Analgesia - surgeon will often infiltrate LA with adrenaline
bl cervical plexus block option
reg paracetamol / nsaid + opiod
Antiemitics - increased risk ponv
End surgeons may request Valsalva - haemostasis
vis vocal cords if concern over RLNI
Postoperative Considerations
- Haemorrhage
Postoperative bleeding can cause compression and rapid airway obstruction. Signs of swelling or
haematoma formation that is compromising the patient’s airway should be immediately decompressed
by removal of surgical clips. Clip removers should be kept by the patient’s bedside. If there is time to
return to theatre, reintubation should be performed early. - Laryngeal oedema
This is an uncommon cause of postoperative respiratory obstruction. It can occur as a result of
traumatic tracheal intubation or in those who develop a haematoma that can cause obstruction to
venous drainage. It can usually be managed with steroids and humidified oxygen - Recurrent Laryngeal Nerve (RLN) Palsy
Trauma to the recurrent laryngeal nerve can be caused by ischaemia, traction, entrapment or transection
of the nerve during surgery and may be unilateral or bilateral. Unilateral vocal cord palsy will present
with respiratory difficulty, hoarse voice or difficulty in phonation whilst bilateral palsy will result in
complete adduction of the cords and stridor. Bilateral RLN palsy requires immediate reintubation and
the patient may subsequently need a tracheostomy. - Hypocalcaemia
Unintended trauma to the parathyroid glands may result in temporary hypocalcaemia. Permanent
hypocalcaemia is rare. Signs of hypocalcaemia may include confusion, twitching and tetany. This can
be elicited in Trousseau’s (carpopedal spasm precipitated by cuff inflation) or Chvostek’s sign (facial
twitch on tapping parotid gland) Calcium replacement should be instituted immediately as
hypocalcaemia can precipitate layngospasm, cardiac irritability, QT prolongation and subsequent
arrhythmias
5.tracheomalacia
The possibility of tracheomalacia should be considered in those patients who have had sustained
tracheal compression by large goitres or tumours. A cuff leak test just prior to extubation is reassuring
but equipment should be available for immediate reintubation if it occurs.
- Thyroid Storm
Characterised by hyperpyrexia, tachycardia, altered consciousness and hypotension this is a medical
emergency. Although less commonly seen now as patients are rendered euthyroid prior to surgery it
can still occur in patients with hyperthyroidism when they sustain a stress response such as surgery or
infection. Management is supportive with active cooling, hydration, beta blockers and antithyroid
drugs. Dantrolene 1mg/kg has also been successfully used in the treatment of thyroid storm
