1. Art and Diseño

EAB
Muestras de elección para su
analisis
Fases: Preanalítica
Analítica
Postanalitica
Errores preanaliticos
75% de los errores en un laboratorio
4 etapas:
1) Preparación del paciente
2) Toma de muestra
3) Manejo de la muestra
4) Conservación y transporte
Las cuatro principales causas de los
errores preanaliticos son
1) Anticoagulantes
2) Toma de muestra desde cateteres
3) Hemolisis
4) Conservacion
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Anticoagulante de elección: HEPARINA.
Origen: 1916, mastocitos y basofilos en
higado
Estructura: Mucopolisacárido (
glycosaminoglicanos), compuesto por
secuencias repetidas de disacáridos, no
ramificados y de extensión variable, con
una alta proporción de disacáridos
sulfatados.
PM: Variable, desde 3 a 30 KDa.
Mecanismo : Potencia la acción de la
Antitrombina III
La acción de la heparina
es tanto en vivo como in vitro.
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Anticoagulation
• Tipos de Heparina disponibles
-Liquid non-balanced heparin
-Dry non-balanced heparin
-Dry Ca2+-balanced heparin
-Dry electrolyte-balanced heparin
(Na+, K+, Ca2+)
-Dedicated blood gas syringes and
capillary tubes are coated with
heparin to prevent coagulation in
the sampler and inside the blood
gas analyzer
Other anticoagulants, e.g. citrate and
Why is there no alternative to
EDTA are both slightly acidic.
heparin when measuring blood
There is a risk of pH being falsely lowered
gases?
by this effect.
4
Unidades. UI/ml
Concentración usada para anticoagular 10 a 15 UI/ml sangre
ES SUFICIENTE?
3 PROBLEMAS: DILUCIÓN, ADICION,
QUELACION
Liquid heparin - dilution
• El uso de Heparina liquida
como anticoagulante causa
dilución de la muestra
• Esto afecta a la medición de
los parámetros en forma
significativa.
• Na+, cK+ and especially cCa2+
will bind to heparin and be
biased even further
• Co-oximetry : sus parametros
dados como fracciones no se
veran afectados, pero si la Hb
Total
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DILUCIÓN
ADICIÓN.
Cual es la composición de la solución de heparina?
CUAL ES EL “MEDIO INTERNO” DE LA HEPARINA
LIQUIDA ?
Concentración de las presentaciones comercial de
Heparina Sodica. ( 5000 UI/ml)
pH 6, 70 – 6,40
pCO2. < 4 mm HG
pO2. 160 mmHG
Na: 160 - 170 meq/l
Cl : 96 -100 meq/l
CUAL ES LA SOLUCION: HEPARINAS LITIO,
LIOFILIZADAS, ELECTROLITICAMENTE BALANCEADA
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QUELACION
• Always use electrolyte-
balanced heparin when
measuring electrolytes in
combination with blood gases
• Non-balanced heparin binds
positive ions such as Ca2+, K+
and Na+
• The binding effect and the
resulting inaccuracy of results
are especially significant for
cCa2+
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Union del Calcio Iónico
• La muestra tiene un
True value
1.15 mmol/L
Measured
value 1.08
mmol/L
verdadero valor de cCa2+ de
1.15 mmol/L
• Si uso 50 I.U. heparina
liofilizada no balanceada por
mL de plasma, obtengo un
valor 1.08 mmol/L
• El delta, de 0.07 mmol/L
corresponde al 50 % del
rango del valor de referencia
del cCa2+ (1.15 - 1.29
mmol/L)
Consequence of using non-balanced heparin:
The cCa2+ result is below the reference range.
There is a risk of misdiagnosing the patient.
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Electrolyte-balanced heparin
• Electrolyte balanced heparin
significantly reduces the
binding effect and the
resulting inaccuracy
• Electrolytes are added to the
heparin during
manufacturing, so that the
activity of the electrolytes in
the heparin is the same as in
normal plasma
11
Toma desde una via
• Las solucines de lavado
usadas en una via deben
removerse por completo
antes de tomar una muestra
• Se recomienda remover al
menos dos veces el espacio
muerto de la via
12
Inadequate removal of flush solutions
– an example
• Sample B and A are both a-line samples taken from the same
patient immediately after each other
• Before taking sample B only 1 mL of saline solution was removed the tubing, however, looked red
• Before taking sample A saline solution was removed as
recommended
Sample A
ctHb
cGlu
cK+
cNa+
cCa2+
cClpH
pCO2
pO2
6.2 mmol/L
9.6 mmol/L
3.8 mmol/L
130 mmol/L
1.00 mmol/L
101 mmol/L
7.271
50.5 mmHg / 6.7 kPa
116.7 mmHg / 15.56 kPa
Sample B
ctHb
cGlu
cK+
cNa+
cCa2+
cClpH
pCO2
pO2
4.6 mmol/L
6.9 mmol/L
2.5 mmol/L
137 mmol/L
0.61 mmol/L
113 mmol/L
7.275
35.9 mmHg / 4.8 kPa
129.3 mmHg / 17.2 kPa
Consequences of removing insufficient flush volume: All parameters are
diluted, except the saline components (Na+ and Cl-) which are increased.
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BURBUJAS
• Una vez tomada la muestra,
se debe remover lo mas
rapido posible toda burbuja
de aire de la jeringa, sobre
todo:
-Antes de mezclar la jeringa con la
heparina
-Antes de refrigerar la muestra
• Aun las burbujas mas chicas
deben ser eliminadas.
• Se estima que cualqueir
burbuja de mas del 1% del
volumen de la muestra
tomadas, puede influir de
manera importante en el
resultado
14
Effect of air bubbles - an example
• Sample A and B were taken from the same patient immediately
after each other
• Sample A without air bubbles was analyzed immediately after
collection
• 100 µL air was added to sample B (1 mL). It was stored cold
(0-4 °C) for 30 minutes and mixed for 3 minutes before sample
analysis
Sample A
pO2
71.0 mmHg / 9.5 kPa
Sample B
pO2
88.3 mmHg / 11.8 kPa
(air bubble pO2150 mmHg / 20
kPa)
Consequence of air in sample: pO2 is positively biased due
to the air bubble. In this situation, the biased patient result
is within normal ranges for pO2 (83-108 mmHg or 11.114.4 kPa)
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Hemolysis
• Hemolysis may lead to
cCa2+ (c)= 1 µmol/L
cK+(c) = 145 mmol/L
significantly increased plasma
cK+ values due to the large
difference in the K+
concentration inside and outside
the blood
• Extensive hemolysis may also
result in a significant fall in
cCa2+
• Hemolysis may, for instance,
occur due to
- Too narrow needle diameter
cCa2+(P)
= 1.2 mmol/L
cK+(P) = 4 mmol/L
- Vigorous rubbing or squeezing of the
skin during capillary sampling
- Vigorous mixing of the sample
- Cooling down the sample below 0 °C
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HEMOLISIS
Hemolysis - an example
• Sample A and B were taken from the same patient immediately
after each other
• Sample A was analyzed immediately after collection
• Sample B was stored on ice for 25 minutes and mixed
for 5 minutes before sample analysis
Sample A
cK+
mmol/L
cCa2+
mmol/L
3.3
1.08
Sample B
cK+
43.6
mmol/L
cCa2+
0.33 mmol/L
• Extensive hemolysis as the above will often be
detected
• A smaller degree of hemolysis and the resulting
inaccuracy may often not be detected
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Inadequate mixing of sample before analysis
• How fast does a whole-blood
sample sediment?
- Within 30 minutes?
- Within 10 minutes?
• There is no universal answer
• Sedimentation time is
individual and depends on age
and immunological condition
• A fully sedimented sample is
easy to detect, but can you
spot a sample that is only 5 %
sedimented?
Consequence of inadequate mixing before
analysis: ctHb will be biased, but the actual
bias will depend on which portion of the sample
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Inadequate mixing of sample before analysis
• If the sample is visibly
sedimented, it needs mixing
for several minutes. Follow
the mixing procedures of your
unit.
• The cell stacks are most
effectively disturbed when the
syringe is rotated through
two axes, i.e.
-Rolling it between the hands AND
-Inverting it vertically
20
Insufficient mixing with heparin
• Insufficient mixing can cause
coagulation of the blood
- Inside the syringe and inside the
blood gas analyzer
• A coagulated blood sample is
not homogenous and the
results are not reliable
• It is recommended to mix the
blood sample in two
dimensions
- Roll it between your palms AND
- invert it vertically
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Conservacion. Recomendaciones
General storage recommendation
Medir la muestra inmediatamente
Si la conservacion es inevitable:
Analizar la muestra dentro de los 30
minutos
Para muestras con valores altos de
pO2, Leucocitos o plaquetas:
Medir dentro de los primeros 5
minutos
Para estudios especiales: ( shunt)
Analyze within 5 minutes
Si se esta seguro que la muestra se
va a demorar mas de 30 minutos,
es recomendable sacar con jeringa
de vidrio y conservar en agua(/
hielo
• El tiempo de transporte y
conservacion debe ser el
minimo posible
-Volatile nature of gases
-El metabolismo en la sangre
continua
• Para mediciones de GLU/LAC,
saber que mas de 30 minutos
de demora puede conducir a
valores no reales
• No conservar muestras en
frio si estan sacadas en
jeringas de plastico
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Continued cellular metabolism in the sample
pO2
Disminuye
( Por consumo)
pCO2
Aumenta
Se sigue produciendo
pH
Disminuye:
Por aumento de la CO2 y la glycolisis
cCa2+
Aumenta
El medio acido creciente lo libera de las
proteinas
cGlu
Disminuye
cLac
Aumenta:
Por la glicólisis
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Slowing down the metabolism
pO2
• Blood gas samples in glass
Time
0-4 C
25 C
samplers can be cooled
• Storing the sample at a lower
temperature (0-4 °C) will slow
down the metabolism by at
least a factor of 10 [NCCLS]
• Cool samples in an ice
slurry or other suitable coolant
• Never store the samples
directly on ice as this causes
hemolysis of the blood cells
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MUCHAS GRACIAS
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