FRCA Notes

Pituitary Surgery

The curriculum asks for knowledge of 'the anaesthetic implications of pituitary disease including endocrine effects and trans-sphenoidal surgery'.

In an SAQ from March 2018 on trans-sphenoidal hypophysectomy (49% pass rate), examiners felt there wasn't enough specific information on anaesthetic management.

Resources

  • Patients requiring pituitary surgery may have endocrine dysfunction as a result of their pituitary disease, such as prolactinoma, acromegaly or Cushing's disease
  • The majority of pituitary adenomas are resected via the trans-sphenoidal (extra-cranial) approach
  • Sub-labial approaches via the upper lip may sometimes be used
  • Transcranial resection is reserved for:
    • Large tumours
    • Tumours with little or no intra-sellar component
    • Previous failed trans-sphenoidal approach

  • Benefits of the trans-sphenoidal approach include:
    • Minimal surgical trauma
    • Reduced blood loss
    • Direct access to the gland
    • Avoidance of the generic hazards of craniotomy

  • Potential issues:
    • Supra-sellar extension: may require lumbar drain insertion and administration of 10ml aliquots of saline to promote prolapse of the supra-sellar component into the surgical field
    • Cavernous sinus erosion: risks carotid artery involvement and/or intra-operative puncture, which can cause rapid, signifnicat haemorrhage though usually responds to packing and controlled hypotension
    • Mass effect: more common in non-secretory macroadenomas, and may cause visual field defects or impaired CSF drainage → hydrocephalus → raised ICP

Perioperative management of the patient undergoing pituitary surgery


  • History, examination, investigations and MDT discussion should elucidate:
    • Standard features pertinent to the anaesthetist
    • Nature and degree of endocrine dysfunction
    • Size, site and degree of extension of the tumour
    • Planned surgical approach

  • Other pre-operative investigations will be different depending on the precise aetiology of the pituitary disease or its endocrine sequelae

Monitoring and access

  • AAGBI as standard
  • Arterial line
  • Wide-bore IV access, especially if concerns about carotid artery involvement

Positioning

  • For the trans-sphenoidal approach the patient is supine with the head tilted up ± slightly towards the surgeon
  • This leads to limited intra-operative access

Airway

  • There may be a difficult airway e.g. in acromegaly or Cushing's disease
  • An armoured ETT is used
    • Secured on the side opposite to the surgeon's approach
    • Must be carefully secured, but still facilitate surgical access to nose (trans-sphenoidal) or upper lip (sub-labial)
    • There is limited intra-operative access due to the presence of surgeons, microscopes/endoscopes and portable imaging arms
    • ± oropharyngeal/throat pack

  • Preparation of the nasal mucosa with vasoconstricting agents is required, although there may be exaggerated hypertensive response in those with Cushing's disease
  • Eye protection is key, from both cleaning solutions and inadvertent pressure by surgical assistants

Anaesthetic technique

  • No robust superiority of inhalational or IV anaesthesia although TIVA may improve surgical operating conditions (avoids nasal mucosa vasodilation)
  • Peripheral nerve monitor-guided NMBA should be used and maintained
  • Short-acting analgesics are preferred to balance:
    • Periods of intense surgical stimulation e.g. trans-sphenoidal access, breaching of the sphenoid bone
    • The need for rapid emergence at the end without clouding neurological assessment or causing an obtunded airway

  • Antibiotics are routinely required as endonasal route never truly sterile
  • IV hydrocortisone may be administered during induction, as per endocrine advice
  • Intra-operative paracetamol and titrated doses of opioids can be used for analgesia
  • Intra-operative mechanical VTE prophylaxis is important as patients are at higher risk of VTE

Pituitary descent

  • Supra-sellar extension of the tumour may make surgical access difficult
  • Descent of the pituitary can be achieved by
    1. Controlled hypercapnoea: increases CBF and thus ICP, pushing gland down into the sella turcica
    2. Injection of 10ml aliquots of saline into a lumbar drain: increases CSF pressure and thus ICP, pushing gland down into the sella turcica

Emergence

  • Removal of throat pack and careful suction

  • BVM ventilation cannot be safely applied in the presence of trans-nasal surgery, as there is risk of (tension) pneumocephalus
  • Post-operative CPAP or HFNO is equally contraindicated
  • As such, spontaneous respiration should be established prior to extubation

  • Rapid, smooth wake-up is preferable
  • Establish presence of laryngeal and pharyngeal reflexes prior to transfer to recovery

  • Typically managed in an HDU environment due to risk of post-operative airway obstruction
  • Slight head-up posture and adequate analgesia can reduce risk of post-operative haemorrhage or CSF leak
  • Ensure throat pack removed, although nasal packs often left in situ post-operatively

Endocrine dysfunction

  • Diabetes inspidus (rare)
    • Usually self-resolving but may require desmopressin
    • Suspect if UO >250ml/hr for 4hrs + hypernatremia
    • Managed with ddAVP
    • The hypothalamus does, however, continue to secrete ADH which merely bypasses the posterior pituitary

  • Panhypopituitarism
  • Adrenocortical deficiency
  • Altered glucose homeostasis
  • There may be a cessation of both TSH and ACTH release
    • This leads to atrophy of thyroid and adrenal glands
    • Typically hydrocortisone is prescribed in the short-term pending thorough endocrine assessment

  • Pituitary apoplexy
    • Acute haemorrhagic infarction of the pituitary gland, leading to acute failure of anterior lobe function
    • Presents as severe headache, nausea and vomiting, visual field defects and cranial nerve palsies
    • Management is with IV hydrocortisone, fluid and consideration of urgent trans-sphenoidal decompression

Neurosurgical complications

  • CSF leak / rhinorrhoea ± risk of post-operative meningitis (1%)
  • Vascular injury: internal carotid artery within the cavernous sinus
  • Cranial nerve injury, particularly CN II-VI
  • Nasal septum perforation (deliberate nasal septum fracture is required for a trans-sphenoidal, trans-nasal approach)
  • Anosmia from cribriform plate injury
  • Post-operative sinusitis

Other

  • SIADH and CSW can occur but are even rarer than DI; hyponatraemia is often due to iatrogenic fluid use or over-administration of ddAVP