Temperature measurement of adult patients on CPB
Effect of pharmacological intervention on core temp
|
|
Cardiac Indexes with hypothermia |
|
|
|
Temperature
(°C) |
Cardiac
index [l/min/m2] |
|
|
34—37 |
2.4 |
|
|
30—34 |
2.0 |
|
|
25—30 |
1.8 |
|
|
20—25 |
1.5 |
|
|
<18 |
1 |
1.
Effects
of hypothermia on biochemical reactions
a)
Q10
» 2
i)
For
each 10° drop in temperature, the rate of metabolic rate or O2
consumption is roughly halved
2.
Hypothermia
permits the use of lower blood flows
a)
Reduced
blood trauma
b)
Permitting
longer safe CPB
i)
Emergency
pump shut off
c)
Reduced
blood return to heart
i)
Reduced
non coronary collateral flow
ii)
Drier
operative field
d)
Cooler
heart
e)
Reduced
myocardial ischaemia
f)
·
Note
that the high blood flow to the upper body will cause preferential changes to
temperature here ie may have warm head but lower body is inadequately rewarmed
1.
CORE temperature
a)
Monitors
the well perfused organs
2.
SHELL [peripheral]
temperature
a)
Monitors
poorly perfused muscle-fat tissues
3.
Nasopharyngeal
a)
Good
estimate of brain temperature [roughly equivalent to core]
b)
May
be influenced by aortic temp?
c)
Adequacy
of rewarming at 37°C
4.
Oesophageal
a)
Estimate
of myocardial temperature
b)
Affected
by cold slush etc in mediastinum
c)
Must
be positioned below tracheal bifurcation
d)
Adequacy
of rewarming at 35°C
5.
Mixed
venous
a)
Measure
of average body temperature
6.
Tympanic
a)
Good
estimate of brain temperature
b)
Not
affected by major vessel temperatures
c)
Danger
of penetrating ear drum
d)
Adequacy
of rewarming at 37°C
7.
Rectal
a)
Shell
temperature
b)
Adequacy
of rewarming at 35°C
8.
Toe
a)
Indication
of peripheral temperature
b)
Adequacy
of rewarming at 30°C
c)
Use
in paediatrics
d)
A
widening gap between core &
peripheral temp indicates vasoconstriction
9.
Myocardial
a)
Needle
inserted into interventricular septum
b)
Should
be < 15°C during cold cardioplegia
1.
During Cooling
a)
Target
is brain (organ most likely to receive most benefit from hypothermic
protection)
b)
Nasopharyngeal,
oesophageal and tympanic membrane give good estimates of brain temperature
c)
Mixed
venous blood temperature gives average body temperature
d)
Reduction
to 28°C during routine CPB:
i)
Reduced
gradient between cooled heart & surroundings
ii)
Can
reduce flow rate, reducing collateral return to heart while still meeting the
metabolic needs of the organs
iii)
Safe
arrest of 10-12 minutes if required
2.
During Rewarming
a)
Target
is a normothermic patient at end of CPB
b)
Both
temperature & time dependent
c)
Rebound
hypothermia (afterdrop) following CPB due to deficit in heat return; may be
tackled by vasodilators to promote a more uniform rewarming
d)
Concerns
of too rapid rewarming
i)
GME
ii)
vasoconstriction
to brain with increased brain metabolism
e)
Concerns
of excessive temperature
i)
>
42°C associated with blood damage
ii)
Monitor
via oxygenator outlet blood temperature
·
Often
have a deficit in heat return during rewarming leading to ‘afterdrop’ in temperature
following termination of CPB
·
Rewarming
is associated with large gradients between shell and core temperatures due to
distribution of warm blood to well perfused core organs and reduced flow to
peripheral organs due to vasoconstriction
·
Use
of vasodilators during CPB rewarming promotes a more uniform rewarming thereby
reducing incidence of afterdrop and hastening rewarming