Dysbarism Made Easy....

I always found it hard to remember all the different types of dysbarism, so I compiled some notes to use for revision purposes, that break it down and simplify it.

There are 2 subtypes of dysbarism:

 1. Barotrauma

• Localized
• POPs  (Pulmonary over-pressurisation syndrome)
• AGE (Air Gas Embolus)

2. Dissolved Gas Problem

• Nitrogen Narcosis

• Decompression Sickness

These are both due to gas volume changes with pressure.

Boyles Law

V = 1 / P

• Changes in volume are greatest near the surface of the water

• It is advisable to never hold breath when ascending.

Henry’s Law

• The amount of gas that dissolves into the tissues is proportional to the partial pressure of that gas in the lungs.

• The greater the pressure, the more gas there is in you. 

Barotrauma

Barotitis Media

• Eustacean tubes are blocked

• Can’t equalise pressure across tympanic membrane
  

• May rupture ear drum if dive is not stopped

Barotitis externa

• External auditory canal becomes oedematous 

Ascent Barotrauma (Rapid Ascent)

• Pulmonary over-pressurisation syndrome (POPS)

• Focal rupture of alveoli
  

• Results in pneumomediastinum, occasionaly pneumothorax
  

• Symptoms can be delayed for several hours
  

• Observation (pneumothorax may require decompression)
  

Dysbaric Air Embolism (Air Gas Embolism AGE)

• Severe form of POPs

• Major cause of diver death (drowning most common)
  

• Air bubbles forced into pulmonary veins, then go to arteries.
  

• Symptoms occur within 10 minutes of surfacing
  

Clinical Features

• Arrest

• Focal neuro deficit
  

• Altered mental status
  

• If unconscious within 10 minutes of surfacing, assume AGE.
  

 Management

• IV Fluids

• O2

• Hyperbaric Therapy

Dissolved Gas Problems

Nitrogen Narcosis

• Nitrogen gas at increased partial pressures acts like a general anaesthetic

• Generally only occurs in deep dives (> 120 feet)
  

• Clinical features similar to alcohol intoxication
  

• Management - ascend. 
  

Decompression Sickness (DCS)

Accumulated nitrogen in tissues during long dives is not water soluble, and comes out of solution when surfacing rapidly

Increased risk with

• Long, deep dives

• Cold
  

• Fatigue
  

• Dehydration
  

Symptoms typically develop between 1-6 hours after a dive, but can be delayed for days

Type 1 The Bends

• Affects muscles, skin, lymphatics

• Localised pain (esp shoulders, and elbows)
  

• Skin rash, cutis marmorata
  

Type 2 (most severe)

• Neuro symptoms - involving lower thoracic / lumbar / sacral spinal cord

• Paraplegia, paresis, bladder dysfunction
  

DCS Management

• Recompression - hyperbaric asap

• Oxygen

• IV fluids