FRCA Notes

Anaesthesia for Parathyroidectomy

Resources

  • The paired pairs of parathyroid glands, embedded within the thyroid tissue, play a key role in calcium homeostasis
  • Surgery is usually indicated in primary or secondary hyperparathyroidism
  • Incidence 25 per 100,000

Aetiology

  • Single parathyroid adenoma (90%)
  • Multiple adenomas or parathyroid hyperplasia (10%)
  • Parathyroid carcinoma (1 - 2%)

  • May form part of a syndrome such as MEN1, MEN2A or Familial isolated hyperparathyroidism

Pathophysiology

  • Renal
    • Increased calcium resorption in the loop of Henle, DCT and collecting duct
    • Increased phosphate excretion in the PCT
    • Increased production of vitamin D3 (1,25-dihydroxycholecalciferol)

  • Gastrointestinal
    • Increased indirect calcium reabsorption

  • Bone
    • Increased osteoclast activity and calcium release
    • Inhibition of osteoblast activity

    → The net effect is hypercalcaemia and hypophosphataemia

Clinical features

Bones Moans i.e. neuropsychiatric Stones i.e. renal Groans i.e. GI Cardiovascular
Bone pain Depression (40%)/anxiety Renal stones Constipation Hypertension
Muscle weakness Cognitive dysfunction Polyuria Anorexia Tachycardia
Fatigue Confusion or psychosis Dehydration Nausea and vomiting Short QTc
Hyporeflexia Insomnia Pancreatitis (acute/chronic) ST segment changes

Investigations

  • U&E may demonstrate:
    • Raised calcium
    • Raised chloride
    • Low phosphate
    • Impaired renal function
  • Raised PTH
  • Raised ALP from bony turnover
  • Raised urinary calcium (or cAMP)

  • The imaging modality of choice is technetium-99m-sesatmibi scintigraphy; a nuclear medicine scan which will identify the hyper-functioning gland
  • It can facilitate minimally-invasive parathyroidectomy

Medical management

  1. Rehydration; may require several litres of crystalloid to replace deficit and dilute calcium

  2. Decrease skeletal release of calcium
    • Bisphosphonates e.g. pamidronate 60mg/500ml 0.9% NaCl over 4hrs
    • Calcitonin 3 - 4U/kg IV, followed by 4U/kg SC BD

  3. Other methods for reducing calcium
    • Phosphate 500ml of 0.1M solution over 6 - 8hrs
    • Furosemide diuresis e.g. 40mg IV every 4hrs
    • Haemodialysis

Secondary hyperparathyroidism

  • Secondary hyperparathyroidism is a compensatory parathyroid hypertrophy due to chronic hypocalcaemia
  • It is most commonly seen in patients with renal failure, although may also occur in osteomalacia/Rickett's and malabsorption syndromes
  • There is excessive bone reabsorption, typically demonstrated by radiological irregularities of the radial aspect of the middle phalanx of the index finger
  • There is usually:
    • Low-normal calcium levels → calcium and vitamin D supplements
    • Hyperphosphataemia → dietary phosphate restriction and phosphate binders
    • Increased PTH levels → may require surgical management in the 5 - 10% for whom medical management fails
    • Increased ALP levels

Tertiary hyperparathyroidism

  • There is development of autonomous, hyper-secreting parathyroid glands and hypercalcaemia
  • Typically occurs following chronic secondary hyperparathyroidism e.g. after renal transplant
  • Presents with hypercalcaemia and its associated symptoms (see primary hyperparathyroidism)

Perioperative considerations for parathyroidectomy


  • Standard anaesthetic pre-assessment should take place, including history/examination, investigations (see above) and optimisation (see below)

Surgical planning

  • Those with parathyroid adenoma(s) may have minimally invasive surgery if the glands have been identified with technetium-99m-sintamibi scintigraphy
    • May require bilateral neck dissections

  • Parathyroid carcinoma typically warrants en bloc dissection
  • Those with secondary hyperparathyroidism or parathyroid hyperplasia may need all four glands removed

Optimisation

  • Airway encroachment by tumours is rare

  • Calcium concentration
    • Levels >3mmol/L should be correct using saline/pamidronate
    • Levels <3mmol/L are generally acceptable for surgery

  • Maintain hydration and adequate urine output using peri-operative crystalloid therapy
    • This may necessitate either pre-admission for hydration, or reducing starvation time e.g. first on the list

  • Those with profound renal failure may need peri-operative dialysis and vitamin D supplementation

Anaesthetic technique

  • Minimally invasive parathyroidectomy for localised adenoma can be done under sedation + local anaesthetic e.g. infiltration, superficial cervical plexus block
  • More invasive surgery will require a GA (see below)

Monitoring

  • AAGBI as standard
    • Be cognisant that if methylene blue is used for gland localisation, doses >5mg/kg may interfere with saturations monitoring
  • An asleep arterial line may prove beneficial if repeated intra-operative sampling of PTH and calcium levels is desired, as it saves repeated venepuncture

Positioning

  • Supine + head-up tilt + neck extension by shoulder bolsters + head stabilisation on head ring
  • Eye protection is imperative due to proximity of surgical retractors
  • Careful positioning and intra-operative movement due to higher incidence of osteopaenia and risk of pathological fractures

General anaesthetic

  • No demonstrated superior choice of induction/maintenance drugs
  • A reinforced ETT or LMA is used
  • Patients with hypercalcaemia-induced somnolence may require lower doses of anaesthetic agents
  • Hypercalcaemia can augment neuromuscular blockade by causing muscle weakness, but conversely also antagonises NMBAs
    • Using a lower dose of NMBA titrated using quantitative neuromuscular monitoring is sensible
  • Increased incidence of cardiac arrythmias

Homeostasis

  • Warming devices are required as operating times can be unpredictable owing to:
    • Difficulty finding the glands
    • Protracted waiting for frozen section results

  • Antibiotic and VTE prophylaxis as standard

  • Analgesic requirements are fairly modest; simple analgesia, local anaesthetic and PRN opioids typically suffices
  • Check serum calcium at 6hrs and 24hrs

Hypocalcaemia

  • Patients may develop profound hypocalcaemia following parathyroidectomy
  • It is characterised by hyperexcitability, manifesting as:
    • Airway & breathing: laryngospasm
    • Cardiovascular: arrhythmias, negative inotropy/chronotropy, prolonged QTc/Torsades de pointes
    • Neurological: seizures, paraesthesia, carpopedal spasm, Chvostek's sign (cheek spasm), Trousseau's sign (carpal spasm with BP cuff)
  • Continued use of alfacalcidol reduces risk of post-operative hypocalcaemia

Others

  • Recurrent laryngeal nerve injury
  • Bleeding
  • Hypomagnesaemia due to 'hungry bone syndrome'