
4612. flow considerations in regional cerebral hypothermia
it is suggested that low flows are dangerous
and may cause anoxia either directly
or by interfering with cooling.  sixty dogs
have been subjected to local cerebral
hypothermia by the method of femoral to
carotid cooling of arterial blood with per-
fusion at a predetermined pressure rather
than predetermined flow rate.  the cir-
cuit is described and its advantages for
clinical use mentioned together with its in-
accuracies as a method of scientific investigation.
these are chiefly concerned
with maintenance of systemic blood pressure
which may require the injection of
pressor agents.  evidence for reduction in flow
at low temperatures is discussed
and evidence presented that this is not only due
to increase in viscosity but that
there is an active spasm, manifested by
'rewarming humps' which occur in the
cooling graphs.  mean carotid flow rates
were determined by a revolution counter
attached to a pump of fixed stroke volume,
the output of which was linked to the per-
fusion pressure and thus determined by the resistance.
the place of added co2
is discussed particularly in relation to the fall
in partial pressure which accompa-
nies the cooling of the blood.  the addition of 5% co2
did not increase total carotid
flows.  halothane had been used as an anesthetic
because of its sympatholytic ac-
tion.  it has increased flows by 37% and
abolished 'rewarming humps'.  rheomacro-
dex used as a priming fluid instead of blood
produced increased flow averaging 75%
but did not abolish spasm.  it is suggested that
cooling faster than 1 c. per minute
is not intrinsically dangerous if spasm is prevented
and high flow maintained by the methods described.
