AD 2016 Q3

RESEARCH, EDUCATION & MEDICINE
FROM THE MEDICAL LINE
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facility available at the time of the call,
if necessary. Access to a hyperbaric
facility is always through an emergency
department, especially after normal
working hours. Even 24/7/365 chamber
facilities are not staffed after hours until
they’re notified of an emergency.
A common misconception is that all
diving emergencies require hyperbaric
treatment. For lung-expansion
injuries — including pulmonary
barotrauma, pneumothorax (collapsed
lung), and mediastinal emphysema
(air under the skin) — hyperbaric
treatment is contraindicated.
The DAN Emergency Hotline
is available 24 hours a day, 365 days a year, to both DAN members and
nonmembers. Call us at +1-919-684-9111 at the time of the emergency,
and we will provide you with the most current information for the most
appropriate chamber near you.
— Frances Smith, MS, EMT-P, DMT
STEPHEN FRINK
Q:
What is the current thinking regarding scuba diving and
freediving on the same day?
A:
Shallow, low-intensity freediving before scuba diving creates only mild
concern. The stress of repeated middle-ear equalization can make
subsequent efforts more difficult. Increasingly deep or aggressive
freediving requires progressively longer surface intervals before scuba diving.
For example, the decompression implications of a few relaxed breath-hold
dives in the 40- to 50-foot depth range prior to scuba diving are probably
very small with a 15- to 30-minute surface interval before commencing the
scuba dive. Deeper or more numerous breath-hold dives should be followed
by a longer surface interval that increases along with intensity, but we do not
have the data available to make specific recommendations.
Freediving after scuba diving is more of a concern; it requires
consideration of the existing inert gas load, the intensity of the exercise
during the freediving and the depth of the freediving. The goal is to reduce
bubble formation and the potential for migration of bubbles into the
systemic circulation.
Even shallow freediving after scuba diving is a problem because of the
diver’s inert gas load. The primary concern is not the additional gas loads
the freediving can produce but the pulmonary shunting that will occur with
exercise. Any bubbles present following a scuba dive can be driven across the
lung at a much higher rate because of physical activity. (Physical activity may
also increase the bubble load.)
It is reasonable to recommend that divers not mix meaningful freediving
and compressed-gas diving on the same day. I realize that the word
“meaningful” is vague, but it’s probably necessary given the wide range
of ability and activity possible. I would not worry about casual freediving
after a 30-minute scuba dive to a maximum depth of 40 feet because the
58 | SUMMER 2016