anaesthesia in thyroid disease

1

anaesthesia in thyroid disease
www.anaesthesia.co.in anaesthesia.co.in_at_gmail.c
om
2
ANATOMY

• 2 lateral lobes connected by an isthmus, lie at
  the level C5-C7
• Very vascular organ
• Surrounded by a sheath from pretracheal layer of
  deep fascia
• Closely attached to thyroid cartilage to upper
  end of trachea thus moves on swallowing
• Embryologically originates from base of tongue
  descends to middle of neck

3

• Blood supply
• I) superior thyroid artery
• ii) inferior thyroid artery
• iii) thyroidea ima

4

• Normal function of thyroid gland directed to
  secretion of T3 T4
• Insufficient hormone secretion hypothyroidism
  /myxedema
• Excessive secretion hyperthyroidism
• Hormone action-
• - influence the growth maturation of
  tissues
• - cell respiration total energy
• expenditure
• - turnover of essentially all
  substrates,
• vitamins, hormones

5
PHYSIOLOGY

• Recommended daily intake 140ug
• The synthesis depends on
• I) quantities of iodine ii) normal iodine
  metabolism in the gland iii) synthesis of
  thyroglobullin
• Dietary iodine absorbed by GIT converted to
  iodide ion actively transported into thyroid
  gland
• Once inside iodide is oxidized back to iodine,
  which is bound to tyrosine
• End results triiodothyronine (T3) thyroxine
  (T4)

6

• T4 released more than T3, but T3 is more potent
  lt protein-bound
• Most T3 is formed peripherally from partial
  deiodination of T4
• In plasma, gt90 of T4 T3 is bound to
  hormone-binding proteins
• Only free hormone available for tissue action

7
PHYSIOLOGY OF HYPOTHALAMIC-PITUITARY-THYROID AXIS

• 1- TRH released in hypothalamus stimulates TSH
  release from pituitary
• 2- TSH stimulates TSH receptor in the thyroid, to
  ?synthesis both T4, T3 stored hormone ?
  increased plasma levels of T4 T3
• 3- ? serum levels of T3 T4 conversion of T4
  to T3
• 4- T3 T4 will enter cells bind to nuclear
  receptors promote ? metabolic celular activity

8
Hypothalamus
TRH
Pituitary
TSH
Thyroid
T3
Tri-iodothyronine
T4
Thyroxine
Peripheral Tissues
Physiological Effects
9

• Patients with thyroid disease can present for
• i) surgery to the thyroid gland
• ii) Surgery to pituitary gland
• iii) Any incidental surgery

10
Problems in anaesthesia.

• Airway
• - tracheal compression/ deviation difficult
  intubation
• - Infiltration by thyroid gland tumour
• Tracheomalacia
• 2) Endocrine status
• hyperthyroidism thyroid crisis
• Hypothyroidism - ?sensitivity to anaesthetic
  agents with delayed recovery poor tolerance to
  blood loss other stresses

11

• 3) Surgery
• head neck surgery with ? accessibility to
  airway
• Injury to recurrent laryngeal nerve
• Venous air embolism
• Hypocalcaemia
• Haematoma
• hypothyroidism

12
HYPERTHYROIDISM

• Causes
• - Graves disease, toxic multinodular goitre,
  thyroiditis, pituitary tumours, functioning
  thyroid adenomas, overdosage of thyroid
  replacement hormone
• Clinical manifestations
• - weight loss, heat intolerance, muscle
  weakness,
• diarrhea, hyperactive reflexes,
  nervousness,fine tremor, exophthalmos, sinus
  tachycardia, atrial
• fibrillation, CCF
• Diagnosis- abnormal TFT

13

• Medical Tx
• PTU, methimazole (inhibit hormone synthesis)
• Potassium, sodium iodide (Prevent hormone
  release)
• Propranolol (Mask signs of adrenergic
  overactivity)
• Radioactive iodine
• 2) Surgery

14
Anaesthetic Considerations

• PREOPERATIVE
• Postpone all elective cases till patient is
  rendered
• euthyroid with medical tx
• Airway
• Determine ease of intubation
• Compression Sx- hoarseness of voice, stridor,
  dysphagia
• Cervical x-ray tracheal deviation / compression

15

• ii) Cardiovascular system
• heart rate rhythm ( lt85 bpm ), atrial
  fibrillation
• Heart failure
• Ischemic heart disease
• iii) Endocrine status
• palpitations, tachycardia (awake sleeping
  pulse)
• Bruit over thyroid gland
• Problems with CVS instability thyroid storm
• Latest thyroid function test

16

• iv) Current treatment
• continue medication serve on morning of surgery
• v) Indirect laryngoscopy
• ENT review on vocal cord function as a baseline
  finding
• Premedication
• no premedication in pt with airway obstruction
• Pt adequately sedated to prevent anxiety
  apprehension ( BDZ / narcotic premedication )
• Emergency surgery esmolol infusion
• (50-150ug/kg/min)

17

• B) INTRAOPERATIVE
• Anaesthetic options
• A- No difficulty anticipated
• - usual iv induction intubation
  (fentanyl, STP, non-depolarizing
• muscle relaxant
• B- possible difficulty in intubation
• - iv induction, test ventilation when pt
  is unconscious, intubation
• - suxamethonium
• C- definite intubation problem / evidence of
  airway obstruction
• - awake fibreoptic intubation
• - inhalational induction
• - choice of ETT- armoured ETT (lt risk of
  kinking)
• important measures
• - closely monitor pts CVS function
  body
• temperature
• - eyes protection
• - to raise head of operating table 15-20
  degrees to aid
• venous drainage (although ?risk of
  venous air
• embolims)

18

• choice of anaesthetic agents
• - induction agent thiopentone
• - muscle relaxant atracurium,
  vecuronium
• - volatile agent isoflurane
• - narcotic analgesics fentanyl,
  morphine
• - anaesthetic technique balanced
  anaesthesia with N2O-O2-isoflurane-muscle
  relaxant-narcotic analgesics --- IPPV
• No controlled study has demonstrated clinical
  advantages of any anaesthetic drug over another
  Miller
• University of California (1968-1982)- all
  anaesthetic agents techniques have been
  employed without adverse effects being even
  remotely attributable to agent / technique

19

• Precautions
• avoid ketamine, pancuronium, indirect-acting
  adrenergic agonists other drugs that stimulate
  the sympathetic nervous system
• Prone to exaggerated hypotensive response on
  induction
• Achieve adequate anaesthetic depth before
  laryngoscopy / any surgical stimulation
• Administer neuromuscular blocking agent
  cautiously ( thyrotoxicosis a/w ?incidence of MG
  myopathies )
• Hyperthyroidism does not ? anaesthetic
  requirements

20

• Reversal
• uncomplicated cases reverse extubate as usual

21

• C) POSTOPERATIVE
• Possible problems
• Thyroid crisis / storm
• decompensated hyperthyroidism with excessive
  release of thyroid hormone
• Onset intraoperative / 6-24 hours after surgery
• Sn Sx- hyperpyrexia, tachycardia or atrial
  fibrillation, hypotension, vomiting, dehydration,
  tachypnoea, acute abdominal pain simulating an
  acute abdomen, agitation, psychosis
• May mimic malignant hyperthermia

22

• Precipitants
• infection, surgery, poorly prepared thyroid
  surgery, diabetic ketosis, radioiodine therapy in
  a poorly prepared pt, MI

23

• management A) supportive
• B) medical Tx
• 1- investigate for precipitants FBC, BUSE,
  blood glucose, FT4, FT3
• 2) hyperthyroidism
• i- inhibition of thyroid hormone formation
• - PTU 900-1200mg/day orally / NG in 3-4
  divided doses
• OR
• - carbimazole 60-120mg/day 3-4 divided doses
  orally / NG

24

• ii) Inhibition of thyroid hormone release
• sodium iodide IV 1gm/24hr slow infusion
• or
• oral potassium iodide 100mg 6hrly
• Given 1hr after 1st dose PTU/carbimazole
• 3) Steroids - iv dexamethasone 2mg 6hrly
• inhibits thyroid hormone release peripheral
  conversion

25

• 4) Receptor blockade ( in the absence of HF)
• Iv propranolol 1-2mg slowly 4-6hrly / oral
  propranolol 40-80mg 6hrly
• 5) Cardiac failure
• - diuretics, digoxin, O2 -propranolol if d/t
  uncontrolled AF with good LV function
• 5) Hyperpyrexia
• fans, tepid sponge, PCM
• 6) Dehydration
• IVD, CVP
• 7) Anticoagulation
• heparin infusion in AF
• Other pt s/c heparin 5000U 2-3x dly
• 8) Severe agitation chlorpromazine 150mg 8hrly
  PO / 25mg 8hrly IM
• 9) Exchange transfusion / PD/HD
• If pt fails to improve within 24-48hrs

26

• 2) Airway obstruction
• Possible causes
• - neck haematoma with tracheal
• compression
• - recurrent laryngeal nerve palsy
• - tracheomalacia
• - incomplete reversal
• - central depression

27

• 3) Tetany
• clinical manifestations circumoral tingling,
  paraesthesia, laryngeal spasm, ()ve Chvostek
  Trousseau signs
• May result from respiratory alkalosis, d/t
• - over-ventilation in immediate
• postoperative period
• - hypocalcemia from
• hypoparathyroidism
• Mx
• calcium estimation
• Slow injection of 10 calcium gluconate 10 mls IV

28
HYPOTHYROIDISM

• Causes
• autoimmune disease, thyroidectomy, radioactive
  iodine, antithyroid medications, iodine
  deficiency, failure of hypothalamic-pituitary
  axis
• Clinical manifestations
• weight gain, cold intolerance, muscle fatigue,
  lethargy, constipation, hypoactive reflexes,
  depression, dull facial expression,
• ?HR, stroke volume, CO
• Pleural, abdominal, pericardial effusion
• Dx low free T4 level

29

• Tx
• oral replacement therapy with a thyroid hormone
  preparation

30

• Myxedema Coma
• results from extreme hypothyroidism
• Precipitated by infection, surgery, trauma
• C/f - most pts are female, elderly
• - impaired mentation
• - hypoventilation
• - hypothermia
• - hypotension
• - bradycardia
• - comatose
• - hyporeflexia
• - hyponatremia

31

• Management
• i) FT3, FT4, TSH, FBC,
• ii) Should start on clinical grounds
• iii) Thyroid hormone replacement
• - T4- iv 200 mcg bolus, daily dose
• 100mcg till pt can take orally
• - T3- iv/oral 10-20mcg bd till T4
• can be given orally
• iv)steroids- iv hydrocortisone 100mg stat,
  50-100mg tds

32

• v) ventilation assisted ventilation if RF
• vi) hypothermia
• do not warm rapidly (gt1C/hr) CVS collapse
• Blankets close temperature monitoring
• vii) Hypotension
• viii) Hyponatremia
• caused by dilution redistribution
• Fluid restriction
• ix) Tx of precipitating factors
• Full recovery replacement thyroxine dose
  titrated once / 2-3 weeks to maintain euthyroid
  state

33

• A) PREOPERATIVE
• Severe hypothyroidism ( T4 lt1mg/dL)
• Elective case to correct first
• Emergency case to treat with thyroid hormone
  prior to surgery
• Mild moderate- no absolute C/I

34

• i- Airway
• ii- CVS
• Iii- endocrine status
• - coarse dry skin, slow mentation, cold
• intolerance,
• - ?CO, hyporeflexia, hypoglycaemia
• Increased sensitivity towards anaesthetic agents
  central depressants
• Hypotension cardiac arrest following induction
• Delayed recovery from GA

35

• Premedication
• Do not require much, prone to drug-induced
  respiratory depression
• Histamine H2 antagonists metoclopramide d/t
  slowed gastric emptying times

36

• B- INTRAOPERATIVE
• - gt susceptible to hypotensive effect of
  anaesthetic agents
• - ? CO
• - blunted baroreceptor reflexes
• - ? intravascular volume
• induction agent of choice ketamine
• - does not ? MAC
• Potential problems
• - hypoglycemia, anemia, hypoNa
• - difficult intubation d/t large
  tongue
• - hypothermia d/t low BMR

37

• C) POSTOPERATIVE
• delayed recovery hypothermia, respiratory
  depression, slowed drug biotransformation
• Should remain intubated till awake close to
  normothermic
• Postoperative pain relief nonopiod (ketorolac)

38

• References
• i- Maged S. Mikhail clinical anaesthesiology,
  Lange 2002
• ii- Parveen Kumar clinical medicine, W.B
  Saunders,1998
• iii- Lee Choon Yee manual of anaesthesia
• iv- Braunwald Harrisons principles of internal
  medicine, 1998
• V- Soo Hua Huat Handbook of medical emergencies

www.anaesthesia.co.in anaesthesia.co.in_at_gmail.c
om