abg interpretation 3rd year final

8/9/2019 ABG Interpretation 3rd Year Final

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Arterial Blood GasesAn Introduction to Interpretation


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Aim

To provide an introduction to arterial bloodgas analysis


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Outcomes

Recognise the common indications forperforming an ABG

Be able to explain how it is performed

List the normal values pertinent to ABGinterpretation

orrectly identify abnormalities in gasexchange

orrectly identify acid!base disturbances


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Outcomes







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"hat is it# $Blood test that is performed using blood from an

artery%

&sed to evaluate gas exchange and acid!base status

Radial ' (emoral ' Brachial


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"hen#

Acute respiratory distress

To evaluate the e)ectiveness of arespiratory intervention

To analyse the acid!base status of a patient

To obtain blood for for routine $venous% tests

A*+ RITI ALL+ &*",LL -ATI,*T


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.ow is it performed#


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Things to note//

lear ,xplanation

Rule out contra!indications

Allen%s test

Gentle aspiration

(irm compression


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Outcomes



List the normal values pertinent toABG interpretation




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*ormal 0alues

p. 1/23 4 1/53 -aO6 78/8 4 72/2 9:-a; -a O6 5/5 4 > ! >? 9mmol;

B@ !> ! >


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Rule of thumb

The PaO2 should be around ! lessthan the percentage of inspired

ox"gen# (or example 4 A >2 year old asthmatic on

of 73D This isrubbish and is an example of defective

oxygenation/


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Outcomes




$orrectl" identif" abnormalities in gasexchange



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7 ! Gas ,xchange

ells use O6 to ma:e energy and produceO6 as waste/

Blood supplies O6 to the cells and removesunwanted O6/

The lungs enrich the blood with O6 and clear

the blood of unwanted O6 This ta:es place by di)usion across the

alveolar!capillary membrane


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Gas ,xchange

ABGs help assess the e)ectiveness of gasexchange by measuring the partial

pressures of O6 and O6 in arterial blood9-aO6 and -a O6;


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*ormal 0alues

p. 1/23 4 1/53 -aO6 78/8 4 72/2 9:-a; Pa$O% & ' (# )*Pa+ . O2= >> ! >? 9mmol;

B@ !> ! >


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O> ,limination

Ei)usion of O6 from the blood to thealveoli is very eFcient/

The limiting factor when it comes to O6elimination is how fast we can $blow o)% the

O6 in our alveoli

The -a O6 is determined by,-.T/LAT/O.


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ontrol of 0entilation

0entilation iscontrolled by the

respiratory centrein the brainstem

This area containsreceptors sensitive

to O6 /


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.+-O@I ERI0,

ome patients havechronically high -a O6levels 9e/g severe O-E;

The respiratory centrebecomes insensitive to

O6 and they aredependent on -aO6/

This means that low -aO6levels becomes the mainstimulus for 0entilation/


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"hy is it important to be

aware that some patientsrely upon low O> tostimulate respiration#


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.+-O@I ERI0,

upplemental oxygencan remove the hypoxicdrive and ventilationcan become suppressedleading to a dangerousrise in -a O6/

-atients with chronic

hypercapnia need toreceive oxygen in acontrolled manner withABG monitoring#


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*ormal 0alues

p. 1/23 4 1/53 PaO% !#! ' 0#0 )*Pa+ -a O6 5/5 4 > ! >? 9mmol;

B@ !> ! >


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Oxygen

The ma ority of O> is bound to .b

The amount of O> in the blood depends ontwo :ey factors

oncentration of .b aturation 9 aO>;

The -aO> is the driving force for saturationD


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O@+.A,HOGLOBI*EI O IATIO* &R0,


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"hat in uences the-aO>##

+ Alveolar ,entilation 4 Impairedventilation causes -aO> to fall and -a O> to

rise 2+ $oncentration of O2 in inspired air

)1iO2+

0+ atching of ventilation withperfusion ),34+


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0JK Hismatch

*ot all blood owing through the lungsmeets with well!ventilated alveoli and not

all ventilated alveoli are perfused with blood4 especially in the presence of lung disease

-rovided overall alveolar ventilation ismaintained ,34 mismatch causes a

decrease in PaO% and aO6 but .OT anincrease in Pa$O%#


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Gas ,xchangeummary

A low -aO> and normal -a O> is normallycaused by 0JK mismatch

Treatment is aimed at trying to achieveadeMuate -aO> and aO> withsupplemental oxygen while treating theunderlying cause

T5P- R-6P 1A/L7R- 4 PaO2 8 9 withnormal or low Pa$O2


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auses of Type 7Respiratory (ailure

-neumonia

-,

-neumothorax

Acute Asthma

Lung (ibrosis ARE


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auses of Type >Respiratory (ailure

O-E

,xhaustion

yphoscoliosis

*euromuscular Eisorders

OpiateJBenPodiaPepine Toxicity

.ead in ury

leep apnoea


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Acid Base tatus

p: ;#0< ' ;#&< -aO6 78/8 4 72/2 9:-a; -a O6 5/5 4 29 )mmol+

B@ !> ! >


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Acid Base Balance

orrect acid!base balance is important forcellular processes to occur eFciently /

In day to day functioning the body ischallenged by the inta:e and production ofacids more than bases

. ions must be removedJbu)ered tomaintain normal p.


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Acid Base Balance

The lungs excrete the vast ma ority of theacid in the form of O6

The :idneys are responsible for excretingmetabolic acids/ They secrete . ions andreabsorb . O2!/


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Acid Base Balance

The Lungs and idneys wor: together tomaintain a very tight control on p./

If one system is not wor:ing properlyleading to a change in blood p. the other$O P-.6AT-6 /

Respiratory compensation happens overminutes to hours renal compensation ta:esdays to develop/


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.ow are the lungs and:idneys lin:ed#

:%!?$O%@:%$O @: ?:$O C


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,xample 4 HetabolicAcidosis

Eiabetic Acidosis

.68 O6Q.6 O Q .S . O

.68 O6Q.6 O Q .S . O


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Bringing it alltogetherU

.ave a system for interpretationD


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Algorithm for ABGinterpretation

+ .ow is the patient# "hat do you predict#

2+ -aO> 4 Is the patient hypoxaemic#

0+ p. 4 Is the patient acidaemic or al:alaemic#

&+ -a O> 4 what has happened to the -a O>#9is the abnormality wholly or partially due to a

defect in the respiratory system#; 3; . O2! J B, 4 what is the metabolic e)ect#


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,xample ase 7

>7 year old female who fell of a horseadmitted with reduced consciousness andrespiratory rate of < bpm/

p. 1/>

-aO> 1/3

-a O> ?/8. O2! >1

B, >


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,xample ase >

A >V year old man has ta:en a suspectedoverdose of antifreePe in an attempt to endhis life/ The patient is still conscious and isbrought to AW, by his partner/

p. 1/>

-aO> 7V/8

-a O> >/2. O2! 77

B, !78


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*ow some more casesUUU

abg interpretation 3rd year final

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