Colin Beard talks us through what hyperbaric oxygen can and can’t be useful for.
What is hyperbaric oxygen therapy?
- > 0.21 atmospheres = hyperoxic
- > 1 atmosphere = hyperbaric
- > 3 atmospheres = harmful as the toxicity outweighs any benefit
Air or gas embolism can be treated by increasing pressure. If ‘depth’ greater than 3 atmospheres is required, the fraction of oxygen can be reduced, and pressures of up to 6 atmospheres can be used to compress a bubble reducing the symptoms of the embolism.
Colin outlines the pathophysiology
What can HBOT be used for?
Colin outlines many indications, but NHS England will only fund treatment for air/gas embolism and decompression injury (with severe neurological injury)
Necrotising soft tissue infections (NSTI)
Most infections are mixed aerobes and anaerobes. Patients are often complicated by co-morbidities such as diabetes.
The HBOT treatment profile includes 3x episodes in 24 hours, and given the multi-system complications of NSTI, this can be difficult to implement safely.
AVOID trial – supplemental O2 vs normoxia – demonstrated harm from too much oxygen. This leads to the Goldilocks principle: not too much, not too little, it needs to be just right.
Neurotoxicity was first described in 1878! Similarly, pulmonary toxicity was described in 1899.
Ischaemic repercussion injury – interruption and subsequent restoration of oxygen – often causes further acute injury. This is often seen during organ transplant, for example. “We have an awful long way to go to fully understand what oxygen does”
It’s difficult to deliver hyperbaric oxygen. Multiple chambers have increased pressure but the oxygen is delivered local to the patient only. All the equipment must be “chamber safe”, in the same way we prepare for MRI scans. The risk of fire is significant. All machines must be electrical brush-contact free (spark risk) and without oils as lubricants! Machines and monitors must be able to compensate for gas density changes – perhaps that FRCA revision does get used in some areas of clinical care!? And what if there is a cardiac arrest in the chamber whilst pressurised and hyperbaric? Defibrillation is too high risk! Colin recalls a story of this happening, leading to an emergency “surfacing” so that CPR and defibrillation could be safely delivered, but with the consequence that the attending clinician became unwell with decompression sickness!!