Patient positioning

Goals:

• Facilitate surgical access
• Facilitate anaesthesia
• Reduce risk of injury to anaesthetised patient

Complications

• Peripheral nerve injuries
  • Likely multifactorial, and can occur despite optimal positioning, but we should be active in preventing them
    • Pre-op
      • Identify at-risk patients
      • Correct positioning
      • Attention to body alignment
      • Padding/gel pads over bony prominences
      • Arm abduction <90 degrees
    • Intra-op
      • Reduce tourniquet duration
      • Minimise retractors
      • Avoid hypotension/hypothermia
  • Risk factors
    • Obese or cachectic patients
    • Diabetics
    • Smokers
    • Surgery lasting >4 hours
  • Stretch, compression, generalised ischaemia, metabolic derangement and surgical section
  • Ulnar neuropathy - most common, but might not be related to positioning. Seems to occur without apparent cause in some patients.
  • Brachial plexus - most common in cardiothoracic procedures requiring median sternotomies. Avoid excessive neck rotation in the supine patient.
  • Lower limb - most common is peroneal nerve in lithotomy, especially with long surgery and thin patients. Also obturator, lateral femoral cutaneous, and sciatic.
  • Classification
    • Seddon's classification
    • Neuropraxia (Sunderland 1) - damaged myelin with intact axon
    • Axonotmesis (Sunderland 2-4) - axonal disruption, but with intact endoneurium and other supportive connecting tissue
    • Neurotmesis (Sunderland 5) - nerve is completely severed
  • Management
    • Assess with history and examination, and early neurology involvement
    • EMG and NCS can be done, but should be done after two weeks, to allow the process of demyelination to complete and an accurate picture of injury to be gained
  • Prognosis
    • Mostly reach full recovery with 6-12 weeks

Supine

• Physiological changes:
  • Lung volume reduced
  • Higher cardiac output due to increased venous return from legs
  • Central redistribution of blood - beware in CCF
  • Regurgitation
• Setup:
  • Arms strapped out on boards or wrapped at sides
  • Protect calcaneus: pillow under knees or gel pads behind ankles
• Vulnerable:
  • Occiput, scapulae, olecranon, thoracic vertebrae, sacrum, coccyx, and calcaneum
• Injuries:
  • Ulnar nerve - can be compressed at olecranon
  • Radial nerve - can be compressed between edge of table and humerus, especially if arm is abducted beyond 90 degrees
  • Brachial plexus - stretch, especially with abduction >90 degrees

Lithotomy/Lloyd Davies

• Lloyd-Davies - lesser degree of hip and knee flexion, with some Trendelenburg - allows longer operating than lithotomy
• Setup
  • Move patient down so GT is level with the bottom table break (I think)
  • Top of stirrup at ASIS
  • Aim the back of the boot, toe and knee to opposing shoulder
  • Top of the boot level with knee
  • One or two-hourly leg checks - correct leg alignment with no internal rotation, no pressure on legs, SCDS are working
  • Ideally, maximum of four hours in this position
• Physiological changes:
  • Similar to supine
• Injuries:
  • Lower limb nerve injuries
    • Hip flexion stretches sciatic and obturator nerves, and compresses femoral nerve under inguinal ligament
    • Common peroneal nerve - compressed against fibular head
    • Saphenous nerve can be injured at medial tibial condyle

Trendelenburg (head down)

• Physiological changes:
  • Abdominal viscera can severely impair diaphragm movement
  • Increased CVP
  • Increased intracranial pressure
  • Passive regurgitation increased

Reverse Trendelenburg

• Physiological changes:
  • Venous pooling - hypotension
• Injuries
  • Venous air embolism

Lateral

• Dependent lung is relatively underventilated and overperfused whereas the non-dependent lung is overventilated and underperfused
• Setup
  • Lower leg flexed and upper leg straight
  • Protect common peroneal and saphenous nerves by placing padding between the legs
  • Both arms slightly flexed
• Injuries:
  • Common peroneal nerve can be compressed between table and fibular head

Prone

• Improved oxygenation
• Increased abdominal pressure, reducing venous return and cardiac output
• Can create space for diaphragmatic excursion using chest and pelvis supports
• Can be harder to drive breathing with reduced chest compliance
• Setup
  • Anaesthetic induction on trolley, then log-roll onto table
  • Can use Gillespie pillow or Doig frame and head supports
  • Turn head to one side on a pillow, ensuring no pressure behind the ear
• Injuries:
  • Eye injuries - corneal abrasions, ischaemic optic neuropathy, central retinal artery thrombosis
  • Bruising of chest wall/hips, including breasts
  • Lateral cutaneous nerve of the thigh - 90% resolve in 3/12
  • Male genitalia can be twisted