Hyperbaric Medicine

What physics principle do Hyperbaric chambers rely on?

Henry’s Law - the amount of a gas dissolved in a liquid is directly proportional to the partial pressure of that gas above the liquid.

When chamber pressure increases, Henry's Law dictates that far more oxygen molecules are forced directly into solution within the blood plasma itself

What is the difference between a monoplace and a multiplace hyperbaric chamber

• Monoplace chamber - Single person chamber

• Multiplace chamber - several people can be in a chamber

What is a significant hazard that must be mitigated in a hyperbaric chamber?

Potential of flame/sparks since there is so much oxygen in the chamber

What is so special about the floor of a hyperbaric chamber room"?

Floor is engineered with copper wiring to prevent any sort of static electricity buildup

What is a dive table?

Depth vs time at depth graph of the atmospheric pressure and changes during a treatment of hyperbaric chamber therapy. Different conditions have different tables

How does a hyperbaric chamber work

Chamber is sealed, and excess amounts of oxygen are pumped into the chamber, equaling up to ~3-3.5 atm’s. More oxygen to oxygenate tissues and the body

What are some of the physiologic effects of being in an increaed oxygen environment?

• Anti-inflammatory and immune modulating effects

• Bacteriostatic/cidal effects - bacteria do not survive at >1atm.

• Synergy with pharmacokinetics and certain drugs

• Can bypass circulatory system to an extent to oxygenate tissues

Mechanism + Relevance of hyperoxia effect of HBOT

Increased plasma dissolved oxygen (up to 20X) - improves oxygen delivery to ischemic/hypoxic tissues (esp. grafts + reconstructions)

Mechanism + Relevance of neovascularization effect of HBOT

Increased O₂ stimulates angiogenesis - supports wound healing especially in chronic ulcers and radiation injury

Mechanism + Relevance of enhanced leukocyte function effect of HBOT

Hyperoxic conditions Improves neutrophil oxidative killing = aids in infection control in hypoxic/infected wounds

Mechanism + Relevance of antibacterial effects of HBOT

Direct bacteriostatic/bactericidal effects on anaerobes; enhances antibiotics - important in necrotizing infections and refractory osteomyolitis

Mechanism + Relevance of reduced edema effect of HBOT

Allows vasoconstriction without compromised oxygen delivery - decreases tissue swelling in crush injuries + compartment syndromes

Mechanism + Relevance of modulation of inflammation effect of HBOT

Downregulates pro-inflammatory cytokines, reduces oxidative stress - benficial in autoimmune/inflammatory conditions

Mechanism + Relevance of fibroblast + collagen stimulation effect of HBOT

Hyperoxic conditions promotes ECM formation - supports granulation tissue formation and epithelializations

Mechanism + Relevance of osteogenesis and bone healing effect of HBOT

Enhances osteoblast activity and bone turnover - relevant for osteoradionecrosis, non-union fractures

Mechanism + Relevance of reduction of gas bubbles in HBOT

Boyle’s Law: increased pressure reduces volume of gas bubbles - core mechanism in decrompression sickness and air embolism

What are the indications for hyperbaric oxygen therapy

• Acute thermal burn injury

• Air/gas embolism

• Arterial insufficiency

• CO poisoning

• Clostridial myositis and myonecrosis (gas gangrene)

• Compromised grafts and flaps

• Crush injury, compartment syndrome, and other acute traumatic ischemias

• Decompression sickness

• Delayed radiation injury (soft tissue + bony necrosis)

• Idiopathic sudden sensorineural hearing loss

• Intracranial abscess

• Necrotizing soft tissue infection

• Osteomyelitis (refractory)

• Severe anemia

What is carbon monoxide

Colorless, odorless gas formed from incomplete combustion

Why is it dangerous to not have a CO monitor in your house

CO is colorless and odorless, and has a similar vapor density to O2, so it can move through dry walls and buildings

Target of toxicity of CO

Multi-organ toxicity, especially CNS and Heart

What is CO delayed neurologic sequelae

known complication of CO toxicity - happens due to tissue ischemia and edema happening in brain = concussion-like symptoms that are long term and debilitating

CO causes functional asphyxia and is a direct cellular toxin. What does this mean?

CO starves cells of oxygen, and obstructs oxidative phosphorylation + the electron transport chain. Shifts body over to anaerobic metabolism

What are some relevant lab tests to look at Carbon monoxide in patints

Carboxyhemoglobin (HbCO0

CO-oximetry devices (sensors that measure CO in blood like a pulse ox)

Novel tests such as total carbon monoxide (TCO)

What % of carboxyhemoglobin is used to decide who needs CO poisoning acute treatment

25% or above

What are some non-poisoning conditions that lead to an increased HbCO?

Infants - fetal hemoglobin causes lab interference = increased

Smoking: smokers have elevated CoHB

Effect of CO on hemoglobin

CO binds to hemoglobin with 200-250X affinity compared to O2. COHb cannot transport oxygen efficiently

Does COHb track with symptom severity

NO. Different levels can have varying symptoms between people

Effect of carboxyhemoglobin on the body

• Causes functional anemia

• Left shift of oxyhemoglobin curve = impaired release

• Mitochondrial toxicity via ETC inhibition

• Neuroinflammatory and oxidative stress pathways increased

Symptoms seen at 10-20% HBCo

Headache, mild symptoms

Symptoms seen at 20-40% HBCo

Confusion, ataxia, syncope (fainting)

Symptoms seen at >50% HBCo

Coma, high mortality

How does hyperbaric therapy improve CO poisoning in terms of half life?

CoHB half life is 4-6 hours in room air, and 60-90 mins in 100% O2

CoHb half life is 20 mins in hyperbaric O2, so we can remove CO from blood significantly faster

What is Total Blood CO (TBCO) testing

Emerging biomarker testing total blood Carbon monoxide using GC-MS (instead of derivative testing like HBCo). TBCO is more stable, but still research stage

Symptoms/manifestations of Delayed neurologic sequalae from CO poisoning

Cognitive issues such as: memory loss, concentration problems, disorientation

Motor problems: Parkinsonism and gait disturbances

Psychiatric symptoms: Anxiety, depression

Non-CO lab tests that are relevant to carbon monoxide patient workup

Look at lab results that display organ toxicity

• Troponin for cardiotoxicity (increased)

• Lactate for muscle breakdown (increased due to switch to anerobic metabolism)

• ECG

Key treatment of CO poisoning

1. Evacuate toxic atmosphere

2. ABCs (airway, breathing, circulation)

3. Consider use of normobaric oxygen vs HBOT

4. Steroids - decrease inflammation and tissue edema

5. Supportive care

What CO poisoning symptom is usually an indication that they should use hyperbatic oxygen therapy

Neurologic symptoms such as syncope - can indicate a potential case of DNS in the future