Diving medicine Flashcards
Scuba Diving
Self-Contained Underwater Breathing Apparatus
Buoyancy control device (BCD)
Diving cylinders
Regulator mechanism to control gas pressure
submersible pressure gauges
open circuit used more commonly (exhausts exhaled air to environment)
Free Diving
Breath-holding activities
Physiological adaptationg - reduced HR, blood flow and volume redistributed (via reflex vasoconstriction), body cooling
risk of hypoxic blackout and drowning
Competitive apnoea
A discipline where you attempt to achieve great depths (using weights, weighted sled or guide rope) for longer times or distances, with a single breath.
11 disciplines involved
Ideal Gas Law (Hyperbaric medicine)
PV = nRT
P = absolute pressure V = volume n = no. of moles R = universal gas constant T = temperature
Associated laws to gas law (3)
- Boyle’s law: P 1/α V
- Gay-Lussac’s law: P α T
- Charle’s law: V α T
In diving, when the T gets colder, the P in the cylinder may drop (GL) and the V of the air in the lunges or BCD jacket drops (Charle). As the P increases in deeper diving, the volume of air in the lungs or BCD jacket drops (Boyle).
Dalton’s and Henry’s Laws
- Dalton’s: The total pressure of a mixture of gases exerted is equal to the sum of the individual gases, as if they occupied the total volume alone.
- Henry’s: The amount of any gas that will dissolve in a liquid at a given temperature is a function of the partial pressure of the gas in contact with the liquid and its solubility coefficient.
Gas pressure increases as depth increases; Partial pressures of N2 and O2 in breathing air increase. For every 33ft of depth, pressure increases by 1bar. According to Henry’s law, more gas will dissolve into the blood and body tissue, as depth increases.
Nitrogen Narcosis and blood bubbles
With continuing descent more N2 is released into the blood stream and gradually dissolves into the lipid part of the tissue.
Every 50ft of depth is equivalent to 1 alcoholic drink; at >150ft the divers experience altered thinking, reasoning, memory loss, calculation errors, increased response time.
Bubbles are formed in the blood and tissue when the diver ascends very quickly, causing the N2 to turn back to its gas form. This is due to lagging between the release of N2 in the blood stream.
Tissue => local issues
Blood => embolisation
Decompression Sickness Type 1
Bubble forms in the blood and tissue causing local probs
Pain (the bends; 70-85%) in a joint/tendon area
- most commonly at shoulder
- initially mild and gradually worsens - mistaken for pulled muscle
- dull, deep, throbbing, toothache-like
Pruritus (the skin bends)
- itching or burning + skin rash
- papular-like skin rash or, mottling or marbling of skin
Oedema
- non-pitting, painless
- uncommon
Anorexia or excessive fatigue
Decompression Sickness Type 2
Discomfort on inspiration, burning, sub-sternal
Non-productive cough
- paroxysmal
- severe respiratory distress in 2% (potentially fatal)
Hypovolemic shock
Low back pain (30%)
- sudden onset within minutes to 24hrs; can be delayed to 36hrs esp if diver has been to high altitudes 24hrs prior
- may progress to more severe neurological Sx e.g. paralysis, paresis, loss of sphincter tone
Predisposing DCS factors
Diving - inadequate decompression, failure to take safety stops, rapid ascent, failure to reduce accumulated N2 (i.e. surface intervals), going to higher altitudes too soon post diving (12-24hrs)
Individual - obesity, fatigue, age, dehydration, poor physical condition, prior MSK injury, smoking
Environmental - cold weather (vasoconstriction), heavy work (vaccumn effect => tendon gas pockets), poor buoyancy/ rough sea conditions, heated diving suit (dehydration)
Arterial Gas Embolisation (AGE)
Pulmonary over-pressurisation causing large gas emboli to enter pulmonary vein and subsequently systemic circulation
continues to expand as ascending pressure is reduced => increases severity
Sx within 10-20mins of resurfacing and depend on location of embolisation
Coronary = MI or dysrrhythmias
Cerebral = stroke or seizures
Clinical features start sudden or gradually
begin with dizziness, headache and profound anxiousness
more severe symptoms=> unresponsiveness, shock, seizures
neurologic Sx vary and can result to death
General Acute Management of diving problems
If shock => resus Do not delay HBO therapy 100% O2 administered do not put pt in trendelenburg position consider IV fluids transport to nearest ED and hyperbaric facility try and keep all diving gear with pt
In-water recompression not safe
Oxygen Toxicity
Harmful effects of breathing molecular oxygen at elevated partial pressures
Sx - disorientation, seizures, breathing problems, vision changes, death
Patho
- collapse of alveoli => hypoxia
- destruction of membrane => chemical toxicity and haemolysis
- hepatic and renal damage
- neural toxicity
Ear Barotrauma
MEBT = most common (10-30%), due to insufficient equilibration of the middle ear
EEBT = during ascend if high pressure air is trapped in external auditory canal either by tight fitting equipment or ear was
IEBT = less common, can lead to varying degrees of conductory or sensorineural hearing loss, vertigo, auditory hypersensitivity
Lung Barotrauma
Caused by breath-holding ascend
Trapped gas in the lungs expands as ambient pressure decreased
causes lungs to over-expand and rupture unless breathes out
