FRCA Notes


Park Bench and Lateral Positioning


  • Has superseded the sitting position for neurosurgery owing to less risk of air entrainment
  • It is used most often for posterior fossa surgery

Position

  • Patient log rolled into lateral position
  • Head is held by pins in a Mayfield frame
    • In order to access the base of skull/posterior fossa, the head is tilted to towards the lower shoulders
    • This curves the C-spine down from the shoulders
  • Upper arm is pulled towards feet, and secured
  • An axillary roll or chest pad is placed under the chest wall, below the axilla
  • Patient is secured by padded supports, strapping and/or beanbag mattress

Nerve injury

  • The major pressure points are:
    • Upper limb: shoulder
    • Torso: chest wall
    • Abdomen: iliac crests
    • Dependent lower limb

  • Excessive gap between skull base and shoulder may put excessive tension on the brachial plexus
  • Nerve pressure and other stretch injuries can occur
  • Subclavian artery obstruction may cause thoracic outlet syndrome
  • Eye protection is required although rigid eye shields should be avoided as they can damage the supra-orbital trigeminal nerve

  • Facial and corneal oedema may occur
    • Especially lingual oedema due to EJV obstruction on dependent side
  • Saliva from the mouth may damage surrounding skin so appropriate skin protection or anti-sialagogues should be used

Position

  • Positioned such that a 90° angle between patient's back and operating table
  • Head supported such that the C-spine is in a neutral position
  • Legs:
    • Lower leg flexed to stabilise the torso against tilt
    • Upper leg extended
    • Pillow between legs
  • A pad/roll may be placed just below the axilla to reduce pressure on the down-shoulder, but must check radial pulse on dependent arm as axillary artery may be compressed

Considerations

  • The major pressure points are on the dependent side:
    • Head: ear
    • Upper limb: shoulder, olecranon process
    • Torso: acromial processes, ribs
    • Abdomen: iliac crests, greater trochanter, medial/lateral condyles
    • Lower limb: medial/lateral malleoli

Risks

  • Displacement of endotracheal tube, including DLT
  • V/Q mismatch

  • Brachial plexus injury
    • Compression of the brachial plexus can occur between the torso and humeral head
    • May also be stretched if the head, C-spine and T-spine are not kept in neutral alignment
    • If upper arm ABducted and there is excessive plexus stretch

  • Radial nerve palsy (non-dependent limb)
    • From excessive arm ABduction (especially if >90°)
    • From mid-humeral compression of the nerve

  • Common peroneal nerve palsy (dependent limb)
    • Compression between fibular head and operating table

  • Saphenous nerve palsy (dependent and non-dependent limb)
    • Compression at the knees

  • Ear injury on the dependent side e.g. due to folding
  • Optic neuropathy or corneal abrasion in the dependent eye from pressure against the pillow
  • Pressure injury to bony prominences e.g. iliac crest