Diving for sharks Flashcards
Discuss pathophysiology of barotrauma - list change in volume at altitude and depth
Results when a diver is unable to equalize the pressure within air filled structures to the ambient pressure of the environement during ascent or descent. -Fractional changes in volume are greater near the surface and as such shallow water is th greatest risk for barotruama.
10mls at sea level
- 5ml at 10metres depth
- 3.3mls at 20 meters depth
- 11ml at 2000 feet
- 14mls at 10000 feet
Discuss disolvability of gas at pressure
Henry’s law states that the amount of any gas that dissolves in a liquid at a given temperature is directly proportional tot he partial pressure of that gas. Therefore at higher ambient pressures an increasing concentration of each componenet gas of inhaled air will dissolve in solution until a new steady state concentration is acheived.
The lenght of time the diver is rbeathing the gas at the icreased pressure and the inherent solubitility of the gas also govern the quantity of a particualr gas that dissolves- the dissolved gas remains in solution as long as the pressure is maintained
As the diver ascends howevere increasinlgy more of the dissolved gas comes out of solution. A rapid ascent may reduce the pressure at a rate higher than the body can accommodate and teh bubbles may accumulate and disrupt body tissue systems.
If the ascent is controlled the gas is carried to the lung vascular bed and is exhaled before it accumulates to form significantly larger or numebrous bubbles in the tissues.
Discuss features of a directed dive history
When was the first onset of symptoms
#what type of equipment was used
-compressed air, ixed gas, enriched air, rebreather
-what was the source of the gas
# did the dive approach or exceed decompression limits? was a dive computer used?
#what were the number, depth, bottom time, total time and surface intervals for all dives in the preceding 72 hours before symptoms (dive profile)
#
Discuss disorders related to descent
Middle ear barotrauma
- Most common complaint of scuba divers.
- The middle ear is an air filled space with solid bone walls excpet for the tympanic membrane with the eustachian tube as the only antomical passage
- As the diver decsned the water exterts increasing pressure against the intact tympanic membrnae.
- If diver does not use maenevers to maintain equal pressure the floppy medial third of the eustachian tube collapses making any further attempts at equalisation futile
- painful with associated tinnutis some patient develop transiet vertigo
- further descent with increasing pressure can cause the TM to rupture - this can lead to caloric stimulation inducing tanseitn nsytagmus and vertigo - can be life threatening due to disorientation
External ear barotrauma
- less common than MEBT
- normally external ear canal is filled with water on descent if any obstruction such as wax a pocket of air is trapped
- this causes -ve pressure to develop leading to pain and or haemorrhagess
Inner ear barotrauma
- Results in damage to the cohleovestibular apparatus.
A large -ve pressure gradient develops in the middle ear if the diver is unable to equalize the ear during descent.
-inward deflection of the TM is transmitted to the oval window of the cochlea through the ossicles. Movement of the oval window creates pressure on the endolymph which causes an outward distension of the round window into the middle ear.
-Sudden equilisation or valsava in the middle ear may rupture the round window leading to severe vertigo and ataxia.
Barosinusisite
- obstruction of the sinus ostia for any reason (mucous thickening, polyps) predisposes to sinus barotrauma the second most common complaint among divers.
- The most common symptoms are facial pain and epistaxis
Facial baratrauma
- as water pressure increases during descent a -ve pressure develops within the dive mask over the eys and nose which must be equalised by forced exhalation through the nose.
- When this is not adequatley perforemd the large -ve pressure gradient may lead to facial and conjunctival oedema, diffuse petehcial haemorrhage on the face and subconjunctival haemorrahge.
- very rarelyu optic nerve damage can result from severe facial barotrauma
Discuss disorders arising at depth
Nitrogen narcosis
- Results from the intoxicating effects of increased tissue nitrogen concentration at depth
- Symptoms include euphoria, false feeling of well being, confusion, loss of judgement or skill, disorientation, diminished motor contrrol,
- Symptoms typically beign to occur at approximately 100 feet and often profound at depths of 150 feet
- Higher risk with compressed air as such mixed gases are used for sport diving to depths more than 120 feet.
- At elevated pressure for extended period o2 can be toxic to the CNS or lungs
- o2 becomes toxic to the CNS when parital pressure exceeds 1.6 atmposphere - this is reached with compressed air at a depth of 218 FT much lower then recreational divers
- Pulmonary o2 toxicity can occur after 24 hours of expsoure to partial pressure of o2 in excess of 0.6 atmosphere - symptoms include burning sensation or pain on inspiration and coughing. Function generally returns to normal but pneumonitis and fibrosis are possible.
contaminated air
hypoxia
Discuss disorders associated with ascent
Alternobaric vertigo
- ABV resutls from an inability to equalise pressure within the middle ear during ascent.
- Active measures are needed to maintain equalisation on descent this is not generally the case for ascent as the pressure in the middle is higher the atmosphere.
- if any blockage a pressure gradient in the middle ear is formed if this reaches 60 cm H20 increased labyrinthine discharged produces nystagumus.
- clinicall leads to profound but transient sense of vertigo
- Serious GIT barotrauma is rare and resutls from the expansion of bowel gas in the small intestine and colon on ascent after diving.
- Risk factors include (consumption of carbnoated beverages, large meals or gas producing foods)
- Symptoms include eructation, flatulence, bloating crampy abdo pain.
pulmonary barotrauma
- Without continuously expiring on ascent the lungs of a diver who takes a full breat at 33 feet would expand to double thier volume by surfacing.
- the increase in pressure either forces bubbles across the alveolar capillary membrane or ruptures the alveola
- the greatest risk for pulmonary barotrauma occurs in less than 10 feet of water as this is the greatest change in pressure.
- Can results in 4 conditions
1) pneumothorax
2) pneumomediastinum
3) subcut emphysema
4) alveolar haemorrhage - risk factors include (panic, rapid ascent, running out of air, difficulty in regulating buoyancy), patient with restrictive or obstructive lung disease are at particular risk - asthma 2x
- Athmatic patients should
- –have a thorough history and physical prior to dive
- –should be well controlled and ahve normal spiro
- –Complete bronchial provocation challenge prior to diving
- –Should not dive if needed rescue medication in the past 48 hours
- Results when air bubbles are forced across the alveolar capillary membrane, escape into the pulmonary venous circulation and proceed through the left atrium and ventricle into the arterial circulation.
- Coronary and cerebral arteries are associated with most serious consequences
- Coronary AGE - MI, dysrythmias or cardiac arrest
- Bubbles to the middle and anterior circulation can cause stroke like symptoms
- any diver breathing compressed air at any depth who surfaces unconscious or who loses consciousness within 10 minutes should be assumed to be suffering from AGE
pulmonary oedema
Discuss decompression sickness
Spectrum of disease resulting from the formation of small bubbles of nitrogen gas in the blood and tisseus on ascent.
DCS typically is manifested within hours after surfacing
-40% occur withi 1 hour
60% occur within 3 hours
80% occur wihtin 8 hours
Type 1 effects the MSK, skin and lymph system
- variable and periarticular pain in the arms and legs - elbow and shoulder are most commonly effected
- the placement of a blood pressure cuff inflated to 150-200 mmhg on an affected joinnt produces relieve and confirms the diagnosis
- Skin marbling known as cutis marmorata resutls from venous stasis. It may begin as severe pruiritis and progress to erythematous rash and then skin mottling.
- limb oedema due to lymph obstruction.
Type 2 involves any other organ system
- CNS is particularly susceptible to DCS due to its high lipid content
- Spinal cord especially the upper lumbar area is more often involved than cerebral tissues
- Symptoms of spinal DCS include (limb weakness or paralysis, parethesias, numbness and low back and abdomianl pain) Symptoms often start as distal prickly sensation that advances proximally followed by progressive sensory or motor loss. Bladder symptoms, faecal incontinence and priapism may occur. -Unlike trauma symptoms can be patchy and unequally distributed
- Inner ear DCS have similar symptoms to IEBT include nausea and severe vertigo and hearin loss.
- Pulmonary DCS - progressive dyspnoea cough and chest pain - cyanosis and hypoxia progressing to resp arrest can be seen
Type 1 and 2 and the differentiation between DCS and AGE is no longer used. Instead they are categorised by four components
1) acute vs chronic
2) evolution of sympotms ( sponta, resolving, static, progressive or relapsing)
3) body system involved
4) any signs of barotrauma
Discuss risk fractors for decompression sickness
Demographics and co-morbidities
- age
- obesity
Dive
- Length and depth of dive
- cold ambient temperatures after divign
- diving at high altitude
- flying after diving
- rapid ascent
- repetitive dives (off gassing continues after the diver has surfaced)
Other
- fatigue
- heavy exertion
- dehydration
- fever
Co-morbidities
-PFO
Discuss first aid of dive injuries in general
Patient with stable vital signs and suspected dive injury should be given 100% o2 - 100% 02 at normal atmospheric pressure can improve otucomes and should be provided until the patient can be definitively treated
Treatment with 100% o2 replacese inert gases in the lungs with 02. By establishment of a large gradient from the tissues to the alveoli removal of inert gases is enchanced and bubble size is reduced. In addition o2 treats tissue hypoxia caused by gas bubbles
List dive disorderds that require recompression therapy
AGE
DCS 1 and 2
contaminated air
Discuss management of conditions that require recompressive therapy
The goals of recompression therapy are
1) to reduce the mechanical obstruction of air bubbles
2) to facilitate the washout of nitrogen by increasing the tissue blood nitrogen gradient
3) to increase o2 delivery to ischaemic tissue
Hyperbaic therapy for AGE should be administered as soon as possible with significnat improvement in morbidity and mortality with sooner recompression.
Recompression for DCS is also time sensitive with best outcomes with sooner recompression – treatment for DCS can be started as late as 10-14 days after exposure with some benefit
C: Dehydration worsens DCS and hydration to maintain urine output of 0.5ml/kg is needed – caution should be taken if pulmonary DCS is suscpeted as ppulmonary oedema will worsen this stage
Ground transport is preferred to flight as a decrease in atmospheric pressure allows microbubbles to expand.
Adjuncts
- NSAID - tenoxicam reduces number of dives required
- Anticoagulatns should not be used routinely in the treatment of DCS the exception is in divers with lower extremity paralysis caused by neurological DCS or AGE. LMWH 30mg BD may be used in patient with inability to walk to prevent VTE
- Lignocaine may be neuroproctive in AGE patients with neurolgoical symptoms given as a bolus of 1mg/kg floowed by infusion of 2-4mgmin
- Cardiac dysrythmias may be refractory until recompression- defib is contraindicated in compressed environement
- Urinary retention is common in spinal DCS paitents – ETT and catheter balloons should be filled with water not air if recompression is to be undertaken
Discuss relative contraindications for helicopter retrieval
- DGI/AGE - diving realted bubble problems due to boyels law and expansion
- intracranial/intraspinal iar
- other air if not decompressed (pneumo/ bowel obstruction)
- Cardiac arrest
- Aggressive combative patient (unless adeqauted sedated and restrained)
