---

{}

---

Patient Positioning in Anaesthesia

• Adequate positioning protects the airway and circulation, preserves organ perfusion, and prevents the “three Ps”: pressure, plexus, and perfusion injury.

Physiological Consequences

Position	Cardiovascular	Respiratory	Cerebral	Airway / GOJ
Supine	Baseline; aorto-caval compression in pregnancy/obesity	FRC ↓ ~ 0–15 %	Neutral ICP	Least reflux protection
Trendelenburg	↑ venous return → ↑ CVP, ↓ MAP if extreme; risk facial oedema	Cephalad diaphragm → FRC ↓ > 20 %	↑ ICP & IOP	GOJ barrier pressure ↓ (reflux)
Reverse Trendelenburg / Head-up	↓ venous return; MAP falls if hypovolaemic	FRC ↑ 10–20 %	↓ ICP	Improves reflux profile
Lithotomy	Autotransfusion ~300 mL when legs raised; reperfusion hypotension on lowering	FRC ↓ > 15 % with high lithotomy	Neutral	Hip flexion > 90° ↓ barrier pressure
Prone	↑ SVR; IVC compression if abdomen unsupported	FRC ↑; improved V/Q matching	↓ ICP if neck neutral / head level	Secure airway; tube kinking risk
Lateral decubitus	Stable CO; “down” arm venous congestion if axilla compressed	Dependent lung ↑ perfusion; ventilation favours non-dependent lung → V/Q mismatch	ICP unaffected	Dependent airway contamination risk
Sitting / beach-chair	Venous pooling → ↓ preload; risk VAE; BP at circle of Willis = MAP–(0.77 mm Hg cm⁻¹ × height)	FRC ↑	Marked ↓ CPP if MAP not corrected	Improved laryngoscopy

FRC = functional residual capacity; ICP = intracranial pressure; CPP = cerebral perfusion pressure; VAE = venous air embolism.

Pressure Point & Nerve-Injury Prevention

Common Nerves at Risk

Position	Nerves	Mechanism	Key Counter-measures
Supine	Ulnar; brachial plexus	Elbow flexion > 90°, shoulder abduction	Arm on board ≤ 90°, pad elbow
Lithotomy	Common peroneal; femoral; sciatic	Stirrup compression; hip flex > 120°	Boot-type stirrup, knees level with hips, limit time
Prone	Brachial plexus; lateral femoral cutaneous; occipital	Shoulder sag; pelvic bolsters	Chest rolls from clavicle → iliac crest; neutral neck
Lateral	Brachial plexus (axilla); radial	Axillary compression, arm-over-arm traction	Axillary roll distal to axilla, pillows between knees
Sitting	Sciatic; cervical plexus	Hip flexion; extreme neck flexion (“chin on chest”)	Pad ischial tuberosities; two-finger distance between chin & sternum

• General principles
  1. Head & neck: neutral alignment, avoid extreme rotation or flexion; secure ETT.
  2. Shoulders: < 90° abduction; support forearms and hands.
  3. Hips/knees: avoid flexion-extension extremes; pillow between legs in lateral.
  4. Pressure redistribution: visco-elastic gel pads or vacuum positioning; reposition long cases (> 4 h) where feasible
  5. Documentation: record position, pressure-relief devices, limb checks (ASA 2022 Advisory).

Peri-operative Visual Loss (POVL)

Incidence: 0.02 % after spine surgery; 75 % is posterior ischaemic optic neuropathy (ION).

Risk Factors

• Prone duration > 6 h, blood loss > 1 L, hypotension (MAP < 65 mm Hg), anaemia, obesity, male sex, Wilson frame, large crystalloids.

Prevention

• Head level with or higher than heart; reverse Trendelenburg 5–10°.
• Maintain MAP within 20 % baseline; avoid venous congestion (no direct eye pressure).
• Staged procedures if anticipated blood loss > 2 L/≥ 8 h.

Compartment & Crush Injuries

• Well-leg compartment syndrome after lithotomy (> 5 h)–monitor calf firmness, pain on awakening; measure intracompartmental pressure if suspected.
• Rhabdomyolysis in obese patients prone/lateral–keep abdomen free, periodic table tilt

Airway, Lines & Equipment Considerations

Position	Specific issues	Solutions
Prone	ETT dislodgement, circuit tension	Reinforced tube; bite block; two-person turn
Lateral	Dependent ETT kink, neck lines	Loop circuits over arm-board; secure CVC with transparent dressing
Sitting	VAE via venous sinuses	Pre-cordial Doppler or TOE; irrigate field; aspirate via multi-orifice RA catheter

Returning to Supine (“Reversal”)

• Re-check haemodynamics; expect ↓ CVP & ↑ MAP on tilting head-down patients back.
• Ventilate with 100 % O₂ for 5 min – decreased FRC positions risk desaturation.
• Confirm cuff pressures, line patency, pupils (ION check).

Checklist for Safe Positioning

1. Plan–discuss with surgeon, anticipate duration & special frames.
2. Protect–pad bony prominences; secure eyes & airway.
3. Peruse–final 360° check before drapes.
4. Pressures–measure arterial line at external auditory meatus if head elevated.
5. Periodic reassessment–limbs visible? BP/SpO₂ symmetric?
6. Post-operative review–document and examine limbs, eyesight, pressure areas

Repositioning Checklist

• A. Airway
  • Endotracheal tube/LMA: Patent and in correct position
• B. Breathing
  • Ventilation: Pulmonary compliance satisfactory
  • Auscultation: Both axillae
  • Monitoring: SaO₂, Capnograph trace and shape
• C. Circulation
  • Monitoring: HR/BP/ECG still functioning and readings stable
  • Intravascular lines: All still in situ, patent, and accessible
• D. Disability/Neurology
  • Eyes: Closed and protected
  • Neurovascular: Padded vulnerable areas and avoidance of excessive passive stretch
• E. Exposure
  • All cables, catheters, and electrodes: Checked and removed from the patient/operating table interface
  • Access: Maintain access for review of at-risk areas if possible

Position-related Peripheral Nerve Injury

• Incidence & medicolegal impact
  • Overall peri-operative peripheral neuropathy (PPNI) ≈ 0.03 % across all surgeries 15 % of ASA Closed-Claim cases involve nerve injury, with the ulnar nerve (≈ 1⁄3), brachial plexus (≈ ¼) and lumbosacral roots most common.
  • Updated ASA 2022 Advisory stresses frequent checks, ≤ 90° joint angles and generous padding

Upper-limb Nerves at risk

Nerve (roots)	Vulnerable sites / mechanisms	Clinical picture	Prevention pearls*
Ulnar (C8–T1)	Medial epicondyle compression; elbow flex > 90°	Numb 4th–5th digits, weak interossei → claw hand	Forearm supinated/neutral; elbow < 90°, pad cubital tunnel
Brachial plexus (C5–T1)	Shoulder abduction > 90°, head turned away; sternal retractors; axillary roll mis-placement	“Waiter’s tip” (upper), “claw hand” (lower) ± paraesthesia	Abduction ≤ 90°, neutral neck, axillary roll below axilla
Radial (C5–T1)	Spiral groove pressure (BP cuff, table edge)	Wrist-drop, dorsal hand numbness	Pad distal arm; cycle cuff opposite arm
Median (C5–T1)	Elbow hyper-extension, carpal tunnel compression	Thenar weakness, palmar/thumb-index paraesthesia	Elbow < extension limit; neutral wrist
Axillary (C5–6)	Shoulder dislocation / traction	Deltoid paralysis, “regimental badge” numbness	Sling arm in gutter board; avoid extreme external rotation
Musculocutaneous (C5–7)	Anterior shoulder traction	Weak elbow flexion, lateral forearm numbness	As for axillary; support forearm

Lower-limb Nerves at risk

Nerve (roots)	High-risk positions	Clinical picture	Prevention pearls*
Sciatic (L4–S3)	Lithotomy, high-flex hip > 120°, IM injections	Foot-drop, sensory loss below knee (except medial leg)	Raise legs together; flex hips < 90°, use well-padded boots
Femoral (L2–4)	Retractor on pelvic brim, lithotomy extreme abduction	Weak hip flex / knee extension, ↓ patellar reflex	Thigh abduction < 45°, minimise self-retaining retractors
Common peroneal (L4–S2)	Fibular head compression (lateral, stirrup)	Foot-drop, dorsum-foot paraesthesia	Pad lateral fibula; pillow between knees; knees slightly flexed
Saphenous (L3–4)	Medial tibial condyle compression	Medial leg/foot numbness	Padding as above

• In addition to normothermia, normotension and periodic limb checks.

Classification & Prognosis

Seddon / Sunderland grade	Pathology	Recovery
I Neurapraxia	Focal demyelination	Days–12 wks
II Axonotmesis (axon)	Axon loss, intact endoneurium	1 mm d⁻¹ (months)
III–IV Axonotmesis	Endoneurial/perineurial disruption	Often incomplete
V Neurotmesis	Complete transection	Requires surgery

• 50 % of PPNI resolve inside 12 months; early neuro-referral improves outcome

Immediate Management Algorithm

1. Suspect PPNI if new pain/weakness/paraesthesia > block duration (≈ 48 h).
2. Review notes, positioning, BP cuffs, tourniquet use.
3. Examine & document neuro-deficit.
4. Mild/improving sensory symptoms → reassure & review @ 4 weeks.
5. Motor loss / progressive deficit → urgent surgical & anaesthetic review, rule-out haematoma; arrange MRI ± EMG/NCS within 3–7 days; consider fasciotomy/decompression.
6. Persistent symptoms (@ 4 weeks) → neurophysiology; start physio, analgesia.

Links

• Robotic surgery
• Prone ventilation
• Gynaecological Surgery
• Urology
• Posterior fossa surgery
• Spine surgery
• Shoulder surgery
• Awake craniotomy

---

Past Exam Questions

Anaesthetic Considerations for Brainstem Glioma Excision in the Sitting Position

A 20-year-old male is booked for excision of a brainstem glioma. The surgeon wants to operate in the sitting position.
a) List 6 anaesthetic concerns in patients undergoing surgery in the sitting position. (3)
b) Intra-operatively, the patient suddenly develops cardiovascular instability. What is the differential diagnosis and your management in each instance? (6)
c) Name 2 neurophysiology monitors that may alert you to critical cerebral or brainstem ischaemia intra-operatively. (1)

---

References:

1. Butterworth J, Mackey D, Wasnick J. Morgan and Mikhail’s Clinical Anesthesiology, 7th Edition. 7th edition. New York: McGraw Hill Medical; 2022.
2. Patient Positioning During Anaesthesia. Dr. Jennifer Hartley. Anaesthetic Registrar, The Canberra Hospital, Australia(https://resources.wfsahq.org/atotw/patient-positioning-during-anaesthesia/)
3. American Society of Anesthesiologists. Practice Advisory for the Prevention of Perioperative Peripheral Neuropathies: 2022 Update. Anesthesiology. 2022;136:31-49.
4. Lee LA, et al. Postoperative visual loss after spine surgery: a systematic review. Anesth Analg. 2023;136:1123-1132.
5. Hodges JT, et al. Physiological changes and complications in the prone position. BJA Educ. 2024;24:135-142.
6. Kwee MM, et al. Compartment syndrome following prolonged lithotomy: meta-analysis of 103 cases. Acta Anaesthesiol Scand. 2023;67:818-827.
7. Tighe PJ, et al. Intraoperative nerve injury: risk factors and medicolegal trends. Anesthesiology. 2021;135:963-976.
8. National Audit Project 5. Accidental awareness and patient positioning complications 2019–2024. Royal College of Anaesthetists; 2024.
9. FRCA Mind Maps. (2024). Retrieved June 5, 2024, from https://www.frcamindmaps.org/
10. Anesthesia Considerations. (2024). Retrieved June 5, 2024, from https://www.anesthesiaconsiderations.com/

Summaries:
Video from GasNovice.com
Positioning
Peri-operative nerve injuries

---

---

Copyright
© 2025 Francois Uys. All Rights Reserved.

id: “744025e1-808b-4f58-8f39-6c4f5e822c02”