Cerebral Arterial Gas Embolism

Objectives
Diagnosis
Criteria for HBO therapy
Work-up considerations
Treatment
Suggested treatment threshold
ICD 10 codes
Level of evidence

Objectives

To overcome intravascular obstruction by reducing bubble size, where gas remains. To hyper-oxygenate areas with decreased cerebral blood flow. To reduce cerebral oedema. To attenuate ischemia-reperfusion injury.

Diagnosis

• Acute onset neurological event, following either:
  • A reduction in ambient pressure (decompression-induced)
  • Invasive diagnostic or therapeutic procedures (iatrogenically-induced)
  • Subsequent to a diagnosis of venous air embolism (paradoxical embolisation)
• While the diagnosis is relatively straightforward in decompression-related cases, a high index of suspicion is necessary in order to diagnose iatrogenically-induced injury. This is particularly true where the introduction of intravascular gas is not witnessed.

Criteria for HBO therapy

Acute neurological event immediately following decompression. Acute onset neurological event during or shortly after invasive diagnostic or therapeutic procedure, or traumatic/penetrating injuries (particularly to the head and neck). In case of decompression-induced CAGE, onset may be delayed up to 4 hours in the presence of an atrial septal defect or pulmonary shunt.

Work-up considerations

• Continue administration of 100% oxygen via non-rebreather mask or naso/endo-tracheal tube for up to 16 hours if re-compression is anticipated.
• If dive related: Complete dive history, including staged decompression and repetitive diving profiles.
• Past medical history.
• Physical examination including, but not limited to, full neurological examination.
• Special examinations: Exclude pneumothorax before re-compression; chest x-ray mandatory if lung over-expansion is suspected. CT scan in iatrogenically-induced cases to exclude other causes.
• DO NOT DELAY TREATMENT AWAITING SCAN.
• Other special examinations as required.
• Signed informed consent for HBOT as appropriate.

Treatment

1. Intravenous fluid resuscitation. Avoid dextrose containing solutions.
2. Urine output monitoring. Exclude urinary retention; catheterise if necessary. Maintain at least 1-2 mL/kg/hr.
3. Consider IVI Lignocaine. Dosage & duration: 1mg/ kg; followed by 1mg per minute for 24 hours under monitoring.
4. DVT prophylaxis critical for paralysed divers. Sedation and ventilation as required.
5. Monitor vital signs.
6. Prompt HBO with compression to:
   1. USNTT6 or equivalent
   2. Consider extensions at 2.8 ATA and/or 1.9 ATA where indicated.
   3. Consider deeper tables where indicated and technically feasible
7. In case of central nervous system oxygen toxicity, interrupt oxygen breathing and allow 15 minutes of air breathing after reaction has entirely subsided. Resume treatment schedule at point of interruption.
8. Retreat after 4 - 8 hours if residual symptoms remain:
   1. Major symptoms: Consider 1 – 2 further USNTT6.
   2. Minor symptoms: HBO at 2.0-2.4 ATA for 90 minutes daily.
9. Refer patients with residual symptoms for rehabilitation.
10. Risk assessment for return to diving, as indicated
11. Consider PFO screening.

Suggested treatment threshold

Stop treatment if no functional improvement after 2 consecutive treatments.

ICD 10 codes

Level of evidence

• Level C.
• All authorities consider it unethical to subject this indication to a randomised controlled trial with a non-treatment control group.