7.3 Thyroidectomy + Thyrotoxicosis

Question 1

a) Which investigations are specifically indicated in the preoperative assessment of a patient presenting
for thyroidectomy for treated thyrotoxicosis? (5 marks)

Answer 1

Blood tests:
» Thyroid function tests: confirm that the patient is euthyroid.

> > Full blood count: carbimazole and propylthiouracil can cause agranulocytosis. Check haemoglobin is adequate.

> > Two group and save samples: potential for blood loss.

> > Calcium: check preoperatively as level may drop postoperatively due to loss of parathyroid glands.

ECG:
» Should show normal rate if euthyroid. May be bradycardic if ongoing beta blocker use.

Fibreoptic nasendoscopy:
» If concerns about likely ease of visualisation of larynx at laryngoscopy.

CXR or lateral thoracic inlet film:
» May indicate tracheal deviation or narrowing.

CT:
» Assess for retrosternal extension
of goitre, tracheal compression.

Question 2

b) What particular issues must the anaesthetist consider during the induction, maintenance and
extubation phases of anaesthesia for a euthyroid patient having a total thyroidectomy? (11 marks)

Answer 2

Induction:

1. Tracheal compression
   » Possibility of deterioration in tracheal compression on lying flat if large goitre (although this should have been elicited by preoperative questioning and investigations).
   Head-up tilt for induction.
   Consider need for smaller-diameter endotracheal tube.
2. PreO2
   » Possibility of slower than usual intubation,
   if difficult, and, therefore, hypoxia.
   Pre-oxygenation required;
   consider use of high-flow nasal oxygen.
3. Difficult?
   » Choice of airway management is determined by preoperative investigations and discussion with the surgeon: straightforward intubation, asleep or awake fibreoptic intubation, awake tracheostomy.
   Full difficult airway kit should be ready.
4. Shared
   » Shared airway: armoured tube.
5. CICO
   » If ‘can’t intubate, can’t ventilate’ (CICO) situation is encountered due to goitre size, obstruction is likely below the level of a cricothyroidotomy:
   ENT surgeon ready for rigid bronchoscopy.

Question 3

maintenance anaesthesia for a euthyroid patient having a total thyroidectomy?

Answer 3

Unlikely but thyroid storm still possible
beta blockers to hand

shared airway - tube securely fastened - aware of rising airway pressures

chance for bleeding wide bore iv access group + x 2

remifentanil infusion - stimulating

temperature control and GDFT

Maintenance:
» Shared airway surgery, patient’s head distant to anaesthetist:
• Padding of eyes (extra care if exophthalmos).

• Secure taping of tube.

• Be alert to airway dislodgement or tube compression.

• Head-up tilt to improve venous drainage but not so as to impair arterial supply.

• Extensions on fluid administration set.

• Long breathing circuit for anaesthetic machine.

> > Drugs:
• Maintenance via intravenous or inhalational route.

• Remifentanil useful to minimise need for further muscle relaxant and to achieve a degree of hypotension that will improve surgical field.

• Vasopressor, e.g. phenylephrine, may be useful to achieve normotension towards the end of surgery to test haemostasis.

• High risk of nausea and vomiting: give antiemetics. Dexamethasone has added effect of reducing airway oedema.

• Plan for postoperative analgesia: important for blood pressure control postoperatively. Intravenous morphine towards end of surgery, regular paracetamol, NSAIDs if not contraindicated, oral morphine for breakthrough pain usually sufficient in addition to local anaesthetic
plus adrenaline infiltration by surgeon. Superficial cervical plexus blocks may also be used.

> > Thromboembolic prophylaxis: leg compression devices indicated due to surgery duration.

> > Warming mattress/forced air warmer and warmed fluids indicated due to surgery duration.

Question 4

Extubation anaesthesia for a euthyroid patient having a total thyroidectomy

Answer 4

Extubation:
» Assessment by surgeon for tracheomalacia (fibreoptic scope through tube, tube can be retracted to allow visualisation) or recurrent laryngeal
nerve palsy (visualisation of vocal cords with laryngoscopy) if concerns.

Extubation can be deferred if such complications have occurred.

> > Risk of failure of haemostasis: aim for smooth extubation, can continue remifentanil infusion if used, ensure analgesia sufficient, sitting up.

> > Risk of laryngeal oedema increases the risk of problems at extubation: dexamethasone given intraoperatively, then manage extubation
in standard manner, ensuring patient sitting up, fully awake, fully reversed
(assess train-of-four, appropriate dosing of neostigmine with glycopyrrolate, consideration of sugammadex use if high risk).

Question 5

c) Describe the specific postoperative problems that may be associated with this operation. (4 marks)

Answer 5

1. > > Failure of haemostasis:
   causing airway compression, necessitating
   removal of clips on ward or urgent return to theatre.
2. > > Tracheomalacia:
   not detected prior to end of surgery, causing airway
   obstruction necessitating immediate reintubation. Rare.

3.» Recurrent laryngeal nerve palsy:
can be difficult to detect on direct
visualisation prior to extubation.
Uni/bilateral may cause stridor, difficulty
breathing.
Unilateral may cause hoarse voice, difficulty phonating.

4. > > Laryngeal oedema:
   increased likelihood after
   complex surgery or difficult
   airway management.
5. > > Hypocalcaemia: .
   due to trauma to or removal of parathyroid glands.
6. > > Pneumothorax:
   if retrosternal dissection has
   been necessary due to goitre size.