Decompression Illness

Question 1

Describes physics behind evolved gases from decompression

Answer 1

Henry’s Law = at a k temp, the solubility of gas into a fluid is directly proportional to the partial pressure of that gas above the fluid. There is about IL of N2 in tissue

As the altitude increases, ambient pressure decrease, therefore PN2 decreases, creating a large pressure differential between the tissue and the ambient environment. This in turn supersaturated the tissue, and with the pressure differential the N2 leaves the tissue as bubbles. Once bubbles are formed, acc to Boyle’s law, the volume increases with increasing altitude.

Haldane’s Theory: if ascent rate does not allow the PP of inert gases in the tissues to exceed more than 2:1 then bubbles won’t form in those tissues.

Question 2

What is the pathophysiology of DCI?

Answer 2

With rapid ascent, ambient pressures of N2 decrease. Relative to thE PP of N2 in the air, the blood becomes supersaturated with N2 and cause bubbles to be formed in the blood down a larger pressure gradient.
Haldane’s supersaturation hypothesis 2:1

Question 3

What are the clinical manifestations of DCI?

Answer 3

Bends - bubbles in MSK - pain at joints
creeps - bubbles in skin - petechial rash
Chokes - bubbles in Q to lungs - dry persistent cough
4. Staggers- bubbles in the NS -
5 CAGE - bubble emboli in cerebral BV&raquo_space; TIA/ stroke like sx

Question 4

What are the predisposing/precipitating fx if DCI?

Answer 4

Altitude and duration of flight
Rate of ascent
Oxygenation on aircraft

Personal
Previous DCI, MHx, medications, age, female, poor conditioning, L to R shunt

Question 5

What is the mx of DCI?

Answer 5

1. ABCDE & lie pt supine
2. 100%O2 for 2 hours
3. IV fluids
4. Call AVMED/SUMU/Hyperbaric dept/ED
5. TMUFF for at least 24 h

Question 6

List the preventative strategies for Hypobaric decompression illness

Answer 6

Sortie limits - altitude and time of exposure
Preoxygenation
Pressure suits

Individual - fly only when healthy, minimise repetition exposure, stay fit

Question 7

List risk factors of DCI

Answer 7

Dosage:
Altitude > 18kft
Time

Rate of ascent

No preoxygenation

Individual - PFO, age and fitness, previous DCI, individual susceptibility

Sortie: recent exposure to HB environment, repetitive exposure, altitude, cold

Post sortie: exercise, rewarding

Question 8

What hx points to be taken if concerned about DCI?

Answer 8

Signs/sx/evolution
Time of onset of sx
MHx/medications/risk fx
72 hour hx
Sortie hx - has/O2 system/ preoxygenation/peak cabin altitude reached/duration of flight/
Action taken on the plane and response

Question 9

What examination to carry out if concerned about DCI?

Answer 9

Systems review

Neurological exam - include MMSE and Sharpened Rhombegs

Question 10

List management of DCS

Answer 10

In-flight: descend > 100%O2 > keep warm > minimise activity > PAN > AVMO review

DHM 2:7:9

Lie supine > 100%O2 for 2 hours > IV fluids > analgesia > observe 4 hours > review 24h > TMUFF 72h min ; may or may not need recompression