Case diagnosis

1. Clinical diagnosis

• Sudden fall in ETCO₂
• Hypotension, tachycardia, fall in cardiac output
• Hypoxaemia and increased PaCO₂-dead space gradient
• Rise in pulmonary artery pressure, right-heart strain
• “Mill-wheel” murmur on precordial auscultation, a late sign
• Severe embolism: right ventricular outflow tract obstruction, cardiovascular collapse or cardiac arrest
• If PFO/right-to-left shunt is present: paradoxical air embolism causing stroke or coronary embolism.

2. Complications of the sitting posture

Major complications

1. Venous air embolism and paradoxical air embolism
2. Hypotension and reduced cerebral perfusion pressure
3. Pneumocephalus, including tension pneumocephalus
4. Quadriplegia/cervical spinal cord injury, especially with excessive neck flexion, extension, or rotation
5. Macroglossia and facial/airway oedema due to venous/lymphatic obstruction from neck flexion
6. Peripheral nerve injuries, including brachial plexus, ulnar, sciatic, and common peroneal injury
7. Pressure injuries at face, elbows, ischial regions, heels
8. Deep venous thrombosis/venous stasis in prolonged surgery
9. Rarely, tongue swelling causing postoperative airway obstruction.

3. Immediate steps in management

1. Call out suspected VAE and inform the surgeon immediately.
2. Prevent further air entry:
   • Surgeon floods the field with warm saline.
   • Pack with wet swabs.
   • Apply bone wax to diploic bone/skull edges.
   • Identify and occlude the venous entry site.
3. Stop nitrous oxide immediately.
4. Administer 100% oxygen and increase ventilation as required.
5. Aspirate air through the correctly positioned right-atrial/multiorifice central venous catheter, if present.
6. Give rapid IV fluid to increase CVP and venous pressure.
7. Treat hypotension with vasopressors/inotropes, for example phenylephrine or noradrenaline; use adrenaline if severe right ventricular failure/collapse.
8. Bilateral jugular venous compression may transiently increase cerebral venous pressure, reduce air entrainment, and help the surgeon identify the open vein.
9. If persistent instability, lower the head / head-down position and consider abandoning the sitting position.
10. In cardiac arrest: return supine as feasible and commence ACLS/CPR.

4. Definitive treatment

• Definitive treatment is surgical control of the air-entry site: saline flooding, wet packing, bone wax, and closure/ligation of the open venous sinus or emissary/diploic vein.
• Remove entrained air by aspiration through a right atrial central venous catheter when available.
• Continue 100% oxygen, haemodynamic support, and correct the position.
• In severe persistent cardiovascular collapse: supine positioning, resuscitation, and ICU care.
• If paradoxical air embolism with neurological or end-organ injury is suspected, consider urgent imaging and hyperbaric oxygen after stabilization.

5. How VAE can be minimized/prevented

Preoperative

• Assess suitability for sitting posture.
• Exclude patent foramen ovale/right-to-left shunt, preferably with contrast echocardiography or TEE where appropriate.
• Avoid sitting position in a patient with significant PFO or other contraindications when an alternative position is feasible.
• Discuss VAE risk and management plan with the surgical team.

Anaesthetic measures

• Avoid nitrous oxide.
• Ensure adequate hydration and maintain normovolaemia.
• Avoid excessive negative intrathoracic pressure and avoid spontaneous ventilation where inappropriate.
• Consider a multiorifice central venous catheter with its tip at the SVC-right atrial junction for potential aspiration.
• Use PEEP cautiously. It can increase venous pressure but may worsen right-to-left shunting if a PFO is present.
• Maintain adequate MAP measured/corrected at the level of the external auditory meatus to protect cerebral perfusion.

Surgical measures

• Meticulous haemostasis.
• Early bone wax application to exposed diploic veins and skull edges.
• Prompt identification and sealing of open venous sinuses/emissary veins.
• Keep the operative field moist with saline-soaked swabs when appropriate.
• Avoid excessive elevation of the operative site above the heart where possible.

6. Monitors for early detection of VAE

7. Name of manoeuvre used