Emergency Physician Rode Kruis Ziekenhuis Beverwijk ROD 17012013 What will we discuss Warming up Aa gradient Arterial ID: 785014
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Slide1
Slide2Bloedgas Workshop
Laura Kater
Emergency
Physician
Rode Kruis Ziekenhuis, Beverwijk
ROD
17.01.2013
Slide3What will we discussWarming up
Aa gradient
Arterial
vs
venous
blood gas
Slide41kPa = 7.5 mmHg
Slide5Warming up
Slide635 yo femaleDyspneaFiO2 100%
ABG: pH 6.76
pCO2 72
Bic 10
BE -26.0
pO2 24 Sat 94
Slide731 yo maleDyspneaFiO2 100%ABG:
pH 6.72 pCO2 87
Bic 11
BE -28.7
pO2 301
Sat
97
Slide894 yo femaleDyspneaFiO2 4
ltr O2 = ongeveer 30%?
ABG:
pH 7.15
pCO2 55
Bic 19
BE -10.2
pO2 62 Sat 83
Slide9Aa
Gradient
Slide10Aa gradient = alveolar minus arterial
oxygen pressure
pAO2 – paO2
Slide11pAO2: calculationpaO2: measurement in arterial
blood gas
Slide12Why is this important?
Slide13pAO2pAO2 (mmHg) = 7x %O2 – paCO2 – 10So at room air
: 7x21 – 40 – 10 = 97 mmHg
Slide14Example65 yo, room air (FiO2 21%) ABG 7.44 / 29 / 88 / 19 / -3 / 95
%
pAO2 =
7x21 – 29 – 10 =
108
mmHg
paO2
in ABG = 88 mmHg
Difference = Aa gradient = 20 mmHg
Slide15Is that normal???
Slide16Aa gradientAa max = age / 3 + pAO2 / 5 – 23
Our pt
: 65
/ 3 + 108 / 5 – 23
=
21.67
+ 21.6 – 23 = 20.27Calculated gradient was 20.
Slide17Another one 61 yo, FiO2 30%
ABG 7.02 / 22 / 146 / 6 / -24 / 98%
pAO2
= 7x30 – 22 – 10 = 178
mmHg
paO2
= 146
Aa gradient = 32 Aa max for
this age: 61/3 + 178/5 – 23 = 20.3 + 35.6 – 23 = 32.9Conclusion: normal
Aa
gradient
Slide18En nu?30 yo, non rebreather (FiO2 +/-80%)
ABG: 7.40 / 40 / … / 25 / 0 / 100%What
pO2 do
you
expect
?
pAO2 = 7x80 – 40 – 10 = 510 mmHgMax Aa gradient =
30/3 + 510 / 5 – 23 = 10 + 102 – 23 = 89Expected paO2 in ABG is about 421 mmHg
Slide19Last…74 yo, room airABG: 7.42 / 39 / 62 / 25 / 1 / 90%pAO2
= 7x21 – 39 – 10 = 98 mmHg
paO2
=
62
Aa
gradient = 36Aa max = 74/3 + 98/5 – 23 = 24.7 + 19.6 – 23
= 21Aa gradient 15 mmHg to high = low paO2 Pulm.problem?, shunt / VQ mismatch?
Slide20Lifeinthefastlane.com
Slide21Arterial
or
Venous
Slide22Use
bloodgas
in
ED
acid-base
status
pH, bicarbonaatrespiratory functionpCO2, sometimes pO2
Slide23Why venous?Painful arterial
punction
Hematoma
after
art.punction
Easy to sample a
venous one when you’re already drawing blood for standard labs
Slide24BUTIs a venous bloodgas clinical
equivalent
to
arterial
?????
Slide25EMRAP
june
2008
summarizes
a few
publications
:
(www.emrap.org)
Slide26A few
publications
in:
Annals of EM april 1998
In diabetic ketoacidosis in adults the venous blood gas measurements accurately demonstrate the degree
of acidosis.
Mean
difference
between
arterial
and
venous
pH was 0.03 (range 0.0-0.11
)
Slide27EM Journal sept 2001
strong
correlation
between
arterial and venous pH, difference 0.4.
Slide28Journal
EM jan
2002
Very
good
agreement in pH
with
venous samples being -/-34 units lower than arterial samples. pCO2 on average 5.8 mmHg higher in venous
samples
Slide29Canadian Journal EM 2002
pH art
an
venous
difference
0.36
pCO2 6 mmHgHCO3- 1.5
Slide30Annals
of EM 2005
very
good
correlation
between arterial and venous pH and HCO3-
Slide31EM
Australasia
feb 2006
in
pts
with
DKA the
weighted average differences between arterial and venous
pH was 0.02
bic -1.88
Slide32For details look at the studies
Slide33Resus.meCliff Reid:
Slide34Professor
Anne-
Maree
Kelly,
June
2009
pH
- Close enough agreement for clinical purposes in DKA, isolated metabolic disease; more
work
needed
in shock, mixed
disease
Bicarbonate
-
Close
enough
agreement
for
clinical
purposes
in most cases; more
work
needed
in shock, mixed
disease
,
calculated
vs
measured
gap
pCO2 –
NOT
enough
agreement
for
clinical
purposes
;
potential
as a screening test
Base
excess
–
Insufficient
data
Slide35Lim
and
Kelly
Eur
J of EM 2010
Available evidence suggests that there is good agreement for pH and HCO3 values between arterial
and
pVBG
results
in
patients
with
COPD, but
not
for
pO2 or pCO2.
Widespread
clinical
use
is
limited
because
of the
lack
of
validation
studies on
clinical
outcomes
Slide36Questions
???
Slide37Slide38Take home
message
When
in
doubt
of a
pulmonary
problem causing hypoxia, use the Aa gradient to calculate if the oxygen you
give
your
patiënt
correlates
with
the paO2 in the ABG
Think
before
you
ask
for
an
ABG.
What
do
you
need
to
know
,
will
a
venous
blood
gas do?
When
in
need
of
an
ABG:
local
anesthesia
.
Slide39Thank
you
!