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Bloedgas Workshop. Laura Kater Emergency Physician Rode Kruis Ziekenhuis, Beverwijk ROD 17.01.2013. What will we discuss. Warming up Aa gradient Arterial vs venous blood gas. 1kPa = 7.5 mmHg. Warming up. 35 yo female D yspnea FiO2 100%

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bloedgas workshop

Bloedgas Workshop

Laura Kater

EmergencyPhysician Rode Kruis Ziekenhuis, Beverwijk

ROD 17.01.2013

what will we discuss
Whatwill we discuss
  • Warming up
  • Aa gradient
  • Arterialvsvenousblood gas
slide6

35 yo female

  • Dyspnea
  • FiO2 100%
  • ABG: pH 6.76

pCO2 72

Bic 10

BE -26.0

pO2 24

Sat 94

slide7

31 yo male

  • Dyspnea
  • FiO2 100%
  • ABG: pH 6.72

pCO2 87

Bic 11

BE -28.7

pO2 301

Sat 97

slide8

94 yo female

  • Dyspnea
  • FiO2 4 ltr O2 = ongeveer 30%?
  • ABG: pH 7.15

pCO2 55

Bic 19

BE -10.2

pO2 62

Sat 83

slide9
Aa

Gradient

slide10

Aa gradient =

alveolarminusarterialoxygenpressure

pAO2 – paO2

slide11

pAO2: calculation

paO2: measurementin arterialblood gas

slide13
pAO2

pAO2 (mmHg) = 7x %O2 – paCO2 – 10

So at room air: 7x21 – 40 – 10 = 97 mmHg

example
Example
  • 65 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
aa gradient
Aa gradient

Aa max = age/ 3 + pAO2 / 5 – 23

Ourpt: 65 / 3 + 108 / 5 – 23 =

21.67 + 21.6 – 23 = 20.27

Calculated gradient was 20.

another one
Anotherone

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 forthisage:

61/3 + 178/5 – 23 =

20.3 + 35.6 – 23 = 32.9

Conclusion: normalAa gradient

en nu
En nu?

30 yo, non rebreather (FiO2 +/-80%)

ABG: 7.40 / 40 / … / 25 / 0 / 100%

What pO2 do youexpect?

pAO2 = 7x80 – 40 – 10 = 510 mmHg

Max Aa gradient = 30/3 + 510 / 5 – 23

= 10 + 102 – 23 = 89

ExpectedpaO2 in ABG is about421 mmHg

slide19
Last…

74 yo, room air

ABG: 7.42 / 39 / 62 / 25 / 1 / 90%

pAO2 = 7x21 – 39 – 10 = 98 mmHg

paO2 =62

Aa gradient = 36

Aa max = 74/3 + 98/5 – 23 =

24.7 + 19.6 – 23 = 21

Aa gradient 15 mmHgto high = low paO2

Pulm.problem?, shunt / VQ mismatch?

use bloodgas in ed
Usebloodgasin ED
  • acid-base status

pH, bicarbonaat

  • respiratoryfunction

pCO2, sometimes pO2

why venous
Whyvenous?
  • Painfularterialpunction
  • Hematomaafterart.punction
  • Easy to sample a venousonewhenyou’realreadydrawingbloodfor standard labs
slide24
BUT

Is avenousbloodgasclinical

equivalent toarterial?????

a few publications in
A few publicationsin:

Annalsof EM april 1998

In diabeticketoacidosis in adults the venousblood gas measurementsaccuratelydemonstrate the degree of acidosis. Meandifferencebetweenarterialandvenous pH was 0.03 (range 0.0-0.11)

slide27

EM Journal sept 2001

strong correlationbetweenarterialandvenous

pH, difference 0.4.

slide28

Journal EM jan 2002

Verygood agreement in pH withvenous samples being -/-34 units lowerthanarterial samples.

pCO2 on average 5.8 mmHghigher in venous samples

slide29

Canadian Journal EM 2002

pH art anvenousdifference 0.36

pCO2 6 mmHg

HCO3- 1.5

slide30

Annals of EM 2005

verygoodcorrelationbetweenarterialand

venous pH and HCO3-

slide31

EM Australasia feb 2006

in ptswith DKA the weightedaveragedifferencesbetweenarterialandvenous

pH was 0.02

bic -1.88

slide33

Resus.me

Cliff Reid:

professor anne maree kelly june 2009
Professor Anne-MareeKelly, June 2009
        • pH - Close enough agreement forclinicalpurposes in DKA, isolatedmetabolicdisease; more workneeded in shock, mixed disease
  • Bicarbonate- Close enough agreement forclinicalpurposes in most cases; more workneeded in shock, mixed disease, calculatedvsmeasured gap
  • pCO2 – NOT enough agreement forclinicalpurposes; potential as a screening test
  • Base excess – Insufficient data
lim and kelly
Limand Kelly

Eur J of EM 2010

Availableevidencesuggeststhatthere is good agreement for pH and HCO3 valuesbetweenarterialandpVBGresults in patientswith COPD, but notfor pO2 or pCO2. Widespreadclinicaluse is limitedbecause of the lack of validation studies on clinicaloutcomes

take home message
Take home message
  • When in doubt of a pulmonaryproblemcausinghypoxia, use the Aa gradient tocalculateif the oxygenyougiveyour patiënt correlateswith the paO2 in the ABG
  • Thinkbeforeyouaskforan ABG. What do youneedtoknow, will a venousblood gas do?
  • When in need of an ABG: localanesthesia.