Hyperventilation for Prehospital Treatment of Head Injury

Quoting from a letter I wrote March 14, 1992 regarding
training standards for EMT-paramedics, regarding whether
medics should be trained to hyperventilate all patients
with head injury and decreased level of consciousness:

                       Just last week, I attended a
presentation by the neurosurgeon who is head of the
Head Injury program at the University of Pittsburgh.
He presented very persuasive information on regional
blood flows and responsiveness to CO2 after head
injury.  Quoting from Head injuries: current principles
of triage and acute care (a manual for health care
professionals) by Donald W. Marion, M.D., Director,
Head Injury Research Center, University of Pittsburgh
School of Medicine:  "Hyperventilation has long been
considered a conerstone in the treatment of increased
ICP.  Although it remains the most rapid technique to
reduce pressure, recent evidence from direct cerebral
blood flow measurements suggest that the use of hyper-
ventilation therapy during the first 10-24 hours after
the injury may be deleterious to the damaged brain.
Most studies of the cerebral blood flow soon after head
injuries have found that the acutely damaged brain is
ischemic and has regions of critically low blood flow.
Because hyperventilation lowers ICP by further reducing
cerebral blood flow, the early post-traumatic use of
this therapy very possibly could worsen pre-existing
ischemia, thereby leading to infarction, or cause
ischemia in areas of the brain that previously had
normal blood flow.  We therefore caution against the
prophylactic application of hyperventilation and sug-
gest that its use be reserved for patients whose
elevated ICP is refractory to other forms of control.
We do not hyperventilate comatose head-injured patients
during the first 12-24 hours after injury because this
is the period during which they are most likely to have
cerebral ischemia."  He provides the following
references:  Bouma GJ, Muiaelarr JP, Choi SC, Newlon
PG, Young HF.  Cerebral circulation and metabolism
after severe traumatic brain injury: the elusive role
of ischemia.  J Neurosurg 1991;75:685-693.  Eisenberg
HM, Aldrich EF.  Management of head injury.
Neurosurgical Clinics of North America 1991;2:1-506.
    If this parallels what other head injury centers
are thinking, and it seems to, then hyperventilation
will soon be "out" as routine prehospital management
for head injury.  In view of this, we might want to
reword this section to suggest that hyperventilation be
applied only on medical command.  Similarly, head
elevation has been studied by neurosurgeons at several
head injury centers and found to do little if anything
to increase cerebral perfusion pressure; though the
intracranial pressure decreases with head elevation,
the cerebral blood pressure increases even more.  I'm
not asking you to take my word on this.  However, I am
asking that we carefully investigate and find out if
indeed hyperventilation and head elevation are, accord-
ing to the best scientific evidence at this time, worth
including as prehospital management.  It looks to me as
though we are merely perpetuating prehospital dogma
that is also well-established in the medical community
but perhaps erroneously.