Download - Basic Blood Gas Interpretation

Basic Blood Gas Interpretation

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Values Measured

• PaO2 – amount of oxygen in the arterial blood

• SaO2 – percent saturation of the hemoglobin as

measured by a CO-oximeter

Values Measured

• SpO2 – percent saturation of the hemoglobin as

measured by a pulse oximeter

• Hb – amount of hemoglobin present

Values Measured

• Hct (Hematocrit) – percent of the blood that is

composed of cells

• pH – concentration of hydrogen ions (H+) in the

arterial blood

Values Measured

• PaCO2 – amount of carbon dioxide in the arterial

blood

• HCO3ˉ – amount of bicarbonate in the arterial blood

Values Measured

• B.E. (base excess/base deficit) – the total of all

buffering systems in the arterial blood

• CO – amount of carbon monoxide present in the

arterial blood

Determination of Oxygenation

• Normal Values– PaO2

• 80 – 100 mmHg

– Mild hypoxemia • 60 – 79 mmHg

– Moderate hypoxemia • 40 – 59 mmHg

– Severe hypoxemia • < 40 mmHg

– SaO2 • 93% – 97%

• 88-92% COPD/lung disease

– Hb • Males: 13.5 – 16.5 g/dl• Females: 12 – 15 g/dl

– Hct • Males: 42 – 54%• Females: 38 – 47%

Determination of Oxygenation

• Normal Values– CaO2

• Males: 17.1 – 21.7 ml/dl• Females: 14.9 – 19.7 ml/dl

– COHb • <3%

Method of Determining Oxygenation

• Evaluate the PaO2

– 80 – 100 mmHg: normal oxygenation

– > 100 mmHg: hyperoxygenation

– 60 – 79 mmHg: mild hypoxemia


• Evaluate the PaO2

– 40 – 59 mmHg: moderate hypoxemia

– < 40 mmHg: severe hypoxemia


• Evaluate the SaO2

– > 93%: normal oxygenation

– < 93%: may be hypoxemic; examine the hemoglobin


• Evaluate the Hb

– 12 – 16 g/dl: normal

– < 12 g/dl: anemic

– > 16 g/dl: polycythemic


• Evaluate the CaO2

– 17 – 20 ml/dl: normal

– 15 – 17 ml/dl: mild hypoxia

– 12 – 14.9 ml/dl: moderate hypoxia

– < 12 ml/dl: severe hypoxia


• Other factors in oxygenation

– Abnormal forms of hemoglobin:

• Detectable by CO-oximeter, not pulse oximeter

Estimate PaO2

• Predicated PaO2 based on age= Estimated value of what there PaO2 might be

• • PaO2= 110 – half the person’s age• example: 20 year old. 110 – 10= PaO2 100• • (PaO2 of 60 will equal approximately 90% saturation based

on the oxyhemoglobin curve)

Determination of Acid Base Balance

• pH is equal to the –log of the hydrogen ion

– pH = – Log [H+]


• Henderson-Hasselbalch equation

– pH = pK + Log HCO3 H2CO3

– pH = pK + Log HCO3 (Renal) Paco2 x0.03 (Lungs)


• pH measures the blood’s acidity or alkalinity

– Must always be determined first when assessing

acid- base balance


• PaCO2 is our stimulus to breathe

– A high PaCO2 indicates that not enough carbon dioxide is

being exhaled

– A low PaCO2 indicates that too much carbon dioxide is

being eliminated


• Evaluate base excess or bicarbonate (metabolic

parameter)

– Is it acidic or alkaline

– 22- 26 mEq/L is normal

– > 26 Indicates metabolic alkalosis

– < 22 Indicates metabolic acidosis


• Bicarbonate is the base or buffer that “neutralizes”

hydrogen ions (HCO3)

• Bicarbonate is made in the red blood cells, liver,

and kidney


• When bicarbonate levels are elevated, an excess

of alkalinity exists in the metabolic systems

• When bicarbonate levels are low, an excess of

acidity exists in the metabolic systems


• If the pH is not normal, identify whether it is acidic

or alkaline


• Identify whether the PaCO2 or bicarbonate

disturbance (acidosis or alkalosis) matches The pH

change (acidosis or alkalosis)

– This is the “cause” of the problem and represents where

treatment should be directed. (e.g. if pH is acidic, PaCO2

is alkaline and bicarbonate is acidic, the problem is a

metabolic acidosis)


• If the pH is not 7.40 but within the normal range

(7.35 - 7.45), the disturbance is fully compensated

• If both the respiratory and metabolic parameters

match the pH, the problem is a combined

disturbance


• A change in the opposite direction (acidosis or

alkalosis) by the parameter (PaCO2 or bicarbonate)

that does not match the pH is an attempt to restore

the pH (referred to as partial compensation)

Evaluation of Compensation

pH Normal

PaCO2 NormalHCO3 Normal

Normal Acid-Base Balance

PaCO2 ElevatedHCO3 Elevated

Fully Compensated Respiratory Acidemia or

Fully Compensated Metabolic Alkalemia

PaCO2 DecreasedHCO3 Decreased

Fully Compensated

Respiratory Alkalemia of Fully

Compensated Metabolic Acidemia

Arterial Punctures

• Indications1

– Need to evaluate ventilation, acid-base balance, and

oxygenation of blood

– Assess the patient’s response to therapy

– Monitor and assess the severity and progression of a

disease process1 Excerpt from the AARC Clinical Practice Guideline for Sampling for Arterial Blood Gas Analysis

Arterial Punctures

• Contraindications1

– Negative Allen test

– Presence of a surgical shunt proximal to the sample site

http://www.youtube.com/watch?v=HRcVVGBb9fg

1 Excerpt from the AARC Clinical Practice Guideline for Sampling for Arterial Blood Gas Analysis

http://www.youtube.com/watch?v=HRcVVGBb9fg

Dialysis shunt

Arterial Punctures


– Presence of a lesion at the sample site

– Coagulopathy or medium to high dose anticoagulation

therapy (relative contraindication)


Hematoma

Arterial Punctures

• Hazards and complications1

– Arteriospasm

– Air or clotted blood emboli

– Hematoma


Arterial Punctures


– Hemorrhage

– Pain

– Arterial occlusion


Arterial Punctures


– Trauma to the vessel

– Vasovagal response

– Patient or sample contamination

– Anaphylaxis (if local anesthetic used, Xylocain)


Arterial Punctures

• Assessment of need for arterial sample1

– Initiation, change, or discontinuation of therapy (oxygen

or ventilatory support)

– History and physical indicators


Arterial Punctures

• Assessment of need for arterial sample1

– Presence of other abnormal diagnostic tests or findings

– Baseline study for pulmonary rehabilitation program


Arterial Punctures

• Frequency of monitoring1

– Dependent upon clinical status of the patient and

presence of indications

– If frequent monitoring required, use alternating sites or

indwelling arterial catheter


Arterial Punctures

• Allen Test

– Performed to determine presence of adequate collateral

circulation in the hand

– Cannot be used with uncooperative or unconscious

patients

Arterial Punctures

• Allen Test

– Procedure

• Have patient clench hand into a tight fist

• Apply pressure to occlude flow through the radial and ulnar

arteries

• Open hand; observe to ensure that the palm and fingers are

blanched

Arterial Punctures

• Allen Test

– Procedure

• Remove pressure from the ulnar artery

• Observe time necessary for flushing of hand

• Test is negative for collateral circulation if flushing does not

occur within 20 seconds; an alternative site is chosen

The Modified Allen Test

The modified Allen test. A, The hand is clenched into a tight fist and pressure is applied to the radial and ulnar arteries. B, The hand is opened (but not fully extended); the palm and fingers are blanched. C, Removal of pressure on the ulnar artery should result in flushing of the entire hand.

Which Artery to Choose?

• The radial artery is superficial, has collaterals and is easily compressed. It should almost always be the first choice.

• Other arteries (femoral, dorsalis pedis, brachial) can be used in emergencies.

Preparing to perform the Procedure:

• Make sure you and the patient are comfortable.• Assess the patency of the radial and ulnar arteries.

Procedure For Obtaining an Arterial Sample (Radius)

• Confirm the order in the patient’s chart

• Note any contraindications and notify physician if

any exist

Procedure For Obtaining an

Arterial Sample (Radius)

• Ensure that patient is in a steady state (no changes

in oxygen status for at least twenty minutes)

• Obtain and assemble necessary equipment



• Wash hands, don protective equipment, explain

the procedure to the patient

• Position the patient correctly



• Perform an Allen test and confirm collateral

circulation

• Cleanse the site with 70% isopropyl alcohol or

other antiseptic



• Inject local anesthetic, if hospital protocol

• Heparinize the syringe, if not already heparinized



• Palpate and secure the artery

• Insert the needle, bevel up, at a 45° angle through

the skin until blood pulsates into the syringe



• Withdraw the needle when sufficient sample is

obtained

• Apply firm pressure to the puncture site using a

gauze pad



• Maintain pressure for a minimum of five minutes,

longer if patient is on anticoagulant therapy

• Expel any air bubbles from the syringe



• Mix the sample and label it

• Place the sample in an icy slush (only if a delay in

running the sample is expected)



• Dispose of any waste material in the appropriate

container

• Document the procedure

Arterial Puncture

http://www.youtube.com/watch?v=KbszTXeg71g

http://www.youtube.com/watch?v=KbszTXeg71g

The Kit

Air bubbles

• Gas equilibration between ambient air (pO2 ~ 150, pCO2~0) and arterial blood.

• pO2 will begin to rise, pCO2 will fall• Effect is a function of duration of exposure and

surface area of air bubble.• Effect is amplified by pneumatic tube transport.

Transport

• After specimen collected and air bubble removed, gently mix and invert syringe.

• Because the wbcs are metabolically active, they will consume oxygen.

• Plastic syringes are gas permeable.• Key: Minimize time from sample acquisition to analysis.

Transport

• Placing the AGB on ice may help minimize changes, depending on the type of syringe, pO2 and white blood cell count.

• Its probably not as important if the specimen is delivered immediately.

Pre-Analysis Errors

• Presence of air in the sample

– Recognized by presence of bubbles or froth,

inconsistent PaCO2

– Allows diffusion of CO2 into the air, lowering the PaCO2

– As the CO2 diffuses, pH is raised

Pre-Analysis Errors

• Presence of air in the sample

– In low PaO2 states, O2 diffuses into the blood, raising the

PaO2

– In high PaO2 states, O2 diffuses out of the blood,

lowering the PaO2

Pre-Analysis Errors

• Venous admixture

– Recognized by failure of syringe to fill by pulsations,

inconsistent PaO2

– Higher PaCO2 than expected

Pre-Analysis Errors

• Venous admixture

– Lower pH than expected

– Lower PaO2 than expected (may be significantly lower)

Pre-Analysis Errors

• Metabolic effects

– Caused by excessive time lag between sampling and

analysis or improper storage of sample

– Increase in PaCO2 as cellular metabolism continues

– Decrease in pH secondary to increase in PaCO2

– Decrease in PaO2 as cells use up oxygen

Pre-Analysis Errors

• Excessive anticoagulant in syringe

– Caused by allowing excessive heparin to remain in

syringe (dead space only should have heparin)

– Lowers PaCO2

– Raises pH

Pre-Analysis Errors

• Excessive anticoagulant in syringe

– Raises low PaO2

– Lowers high PaO2

Capillary Sampling

• Used as an alternative to arterial sampling in

infants and small children.

• Sample may approximate pH and PaCO2 values;

PaO2 value is generally inaccurate

Capillary Sampling

• Indications2

– ABG analysis is indicated, but access is not possible

– Assessment of initiation, administration, or change in

therapy is indicated

– Change in patient status is detected

2 Excerpt from the AARC Clinical Practice Guideline for Capillary Blood Gas Sampling for Neonatal and Pediatric Patients

Capillary Sampling

• Indications2

– Monitoring severity or progression of disease is

desirable

– Noninvasive monitor readings are abnormal


Capillary Sampling


– Capillary punctures should not be performed at or

through:

• The posterior curvature of the heel (Bone Damage)

• Fingers of neonates (nerve damage)


Capillary Sampling



through:

• Heel of an infant who has begun walking

• Previous puncture sites


Capillary Sampling



through:

• Inflamed, swollen, or edematous tissue

• Localized areas of infection

• Cyanotic or poorly perfused areas2 Excerpt from the AARC Clinical Practice Guideline for Capillary Blood Gas Sampling for Neonatal and

Pediatric Patients

Capillary Sampling


– Contraindicated:

• In patients less than twenty-four hours of age

• When there is a need for direct analysis of oxygenation

• When there is a need for direct analysis of arterial blood


Capillary Sampling


– Relatively contraindicated:

• When peripheral vasoconstriction is present

• In the hypotensive patient

• In polycythemia


Capillary Sampling

• Precautions and/or complications2

– Contamination and infection of the patient

– Inappropriate management through use of capillary

rather than arterial samples


Capillary Sampling


– Burns

– Bone calcification

– Bruising


Capillary Sampling


– Pain

– Hematoma

– Nerve damage


Capillary Sampling


– Scarring

– Bleeding

– Tibial artery laceration


Capillary Sampling

• Assessment of need2

– Should be performed only when a documented need

exists and arterial access is unavailable or

contraindicated


Capillary Sampling

• Assessment of need2

– When initiation, administration, or change in therapy

occurs

– When noninvasive monitoring and assessment indicates

a change in condition has occurred


Procedure for Obtaining a Capillary Sample

• Verify the order and the need for a capillary sample

• Note any complications and notify the physician if

any exist


• Ensure that patient is in a steady state (no changes

in oxygen status for at least twenty minutes)

• Wash hands and don protective equipment


• Select the site

• Warm the site up to 42° C For ten minutes using a

compress, heat lamp or commercial hot pack


• Cleanse the skin with an antiseptic solution

• Puncture the skin (less than 2.5 mm) with a lancet


• Wipe away the first drop of blood and observe free

flow (do not squeeze)

• Fill the sample tube from the middle of the drop

until it is full


• Place the flea in the tube and seal the ends

• Tape sterile cotton or a bandage over the puncture

site


• Mix the sample by moving the magnet back and

forth along the tube

• Place the sample in an icy slush


• Dispose of waste materials properly

• Document the procedure

Capillary Tubes

Neonatal Puncture Site

Capillary Sampling

Finger Stick Heel Stick

Capillary Blood Gas

• http://www.youtube.com/watch?v=7DPhP22KRbc&feature=related

• http://www.youtube.com/watch?v=N5Id1kOQzv4

Capillary Blood Gas

http://www.youtube.com/watch?v=7DPhP22KRbc&feature=related

http://www.youtube.com/watch?v=7DPhP22KRbc&feature=related

http://www.youtube.com/watch?v=N5Id1kOQzv4

• http://www.youtube.com/watch?v=pTjhMylgje0&feature=related

Cord Gas

http://www.youtube.com/watch?v=pTjhMylgje0&feature=related

http://www.youtube.com/watch?v=pTjhMylgje0&feature=related

Arterial Lines

• The arterial line with transducers is usually used to obtain accurate blood pressure readings every few seconds. This is especially important in monitoring the hemodynamic status of a critical patient. With an arterial line, the immediate effects of medication can be seen. Both systolic, diastolic and mean pressures can be monitored immediately. This is especially important when pressors such as Nipride, dopamine or Levophed are being used.

• Another advantage of using an arterial line is that frequent blood samples can be obtained.

Indications

This system consists of• arterial line connected by saline filled non-compressible

tubing to apressure transducer. This converts the pressure waveform into an electrical signal which is displayed on the bedside monitor

• pressurized saline for flushing

A-line monitoring

• Sources of error• failure of any one of the components in system• transducer position

– pressure displayed is pressure relative to position of transducer– in order to reflect blood pressure accurately transducer should be at level of heart.

Over-reading will occur if transducer too low and under-reading if transducer too high– transducer must be zeroed to atmospheric pressure

• damping. Important to have appropriate amount of damping in the system. Inadequate damping will result in excessive resonance in the system and an overestimate of systolic pressure and an underestimate of diastolic pressure. The opposite occurs with overdamping. In both cases the mean arterial pressure is the most accurate. An underdamped trace is often characterized by a high initial spike in the waveform.

A-Line Monitoring

A-line Monitoring

• distal ischemia• arterial thrombosis• embolism. • infection• hemorrhage

– disconnection– around line

• accidental drug injection• damage to artery eg aneurysm

A-line Complications

• http://www.wonderhowto.com/how-to-draw-blood-from-arterial-line-343135/

Drawing Blood from an A-line

http://www.wonderhowto.com/how-to-draw-blood-from-arterial-line-343135/

http://www.wonderhowto.com/how-to-draw-blood-from-arterial-line-343135/

• 1. Prepare a 500 ml bag of normal saline. Most institutions no longer use a heparinized bag. Spike the bag with the transducer administration set. Remove all air from the tubing and transducer set. Pay particular attention to the transducer part of the Tubing and the flush port. The smallest air bubble must be removed to insure transducer accuracy. The easiest way to do this is to pressurize the bag up to 300 mm Hg, then invert the bag, and fast flush it to remove all air from the bag.

• 2. Pressurize the pressure bag to 300 mm Hg. The purpose of this is to provide backpressure to prevent blood from contaminating the transducer.

• 3. With the transducer connected to the monitor, select arterial monitor, and perform a transducer check by fast flushing the line. As you do this, you should see a change in the waveform. This is called a square wave test.

• http://www.youtube.com/watch?v=F1s08XoKdYY

A-line Placement

http://www.youtube.com/watch?v=F1s08XoKdYY

A-line Placement

• 4. Zero the transducer and monitor by placing the transducer at the phlebostatic axis of the patient. Close the line off to patient and open to air. Press zero on the monitor. To monitor pressure, close the port off to an air and open to patient.

• 5. At this point the patient catheter is ready to be connected. Connect the catheter and fast flush to clear the catheter of blood.

• 6. You should now see an arterial waveform on the monitor with arterial blood pressure and mean should be on the monitor screen. Check for good waveform

MORE ABG PRACTICE

Can You Interpret this Blood Gas?

Blood Gas Drawn on Room Air

• pH 7.39

• PaCO2 42 mmHg

• HCO3 23 mEq/L

• PaO2 97 mmHg



• pH 7.39

• PaCO2 42

mmHg

• HCO3 23 mEq/L

• PaO2 97 mmHg

• Normal acid-base balance with normal oxygenation



• pH 7.32

• PaCO2 49

mmHg

• HCO3 26 mEq/L

• PaO2 60mmHg



• pH 7.32

• PaCO2 49

mmHg

• HCO3 26 mEq/L

• PaO2 60mmHg

• Uncompensated or acute respiratory acidemia with mild hypoxemia



• pH 7.31

• PaCO2 60

mmHg

• HCO3 29 mEq/L

• PaO2 58 mmHg



• pH 7.31

• PaCO2 60

mmHg

• HCO3 29 mEq/L

• PaO2 58 mmHg

• Partially compensated respiratory acidemia with moderate hypoxemia



• pH 7.50

• PaCO2 60

mmHg

• HCO3 19 mEq/L

• PaO2 60 mmHg



• pH 7.50

• PaCO2 60

mmHg

• HCO3 19 mEq/L

• PaO2 60 mmHg

• Lab error



• pH 7.35

• PaCO2 63

mmHg

• HCO3 33 mEq/L

• PaO2 60 mmHg



• pH 7.35

• PaCO2 63

mmHg

• HCO3 33 mEq/L

• PaO2 60 mmHg

• Compensated respiratory acidemia with mild hypoxemia



• pH 7.28

• PaCO2 28

mmHg

• HCO3 8 mEq/L

• PaO2 104 mmHg



• pH 7.28

• PaCO2 28

mmHg

• HCO3 8 mEq/L

• PaO2 104 mmHg

• Partially compensated metabolic acidemia with hyperoxygenation



• pH 7.36

• PaCO2 24

mmHg

• HCO3 18 mEq/L

• PaO2 109 mmHg



• pH 7.36

• PaCO2 24

mmHg

• HCO3 18 mEq/L

• PaO2 109 mmHg

• Fully compensated metabolic acidemia with hyperoxygenation



• pH 7.45

• PaCO2 48

mmHg

• HCO3 33 mEq/L

• PaO2 79 mmHg



• pH 7.45

• PaCO2 48

mmHg

• HCO3 33 mEq/L

• PaO2 79 mmHg

• Fully compensated metabolic alkalemia with mild hypoxemia



• pH 7.30

• PaCO2 30

mmHg

• HCO3 35 mEq/L

• PaO2 81 mmHg



• pH 7.30

• PaCO2 30

mmHg

• HCO3 35 mEq/L

• PaO2 81 mmHg

• Lab error



• pH 7.49

• PaCO2 47

mmHg

• HCO3 35 mEq/L

• PaO2 81 mmHg



• pH 7.49

• PaCO2 47

mmHg

• HCO3 35 mEq/L

• PaO2 81 mmHg

• Partially compensated metabolic alkalemia with normal oxygenation



• pH 7.24

• PaCO2 77

mmHg

• HCO3 7 mEq/L

• PaO2 28 mmHg



• pH 7.24

• PaCO2 77

mmHg

• HCO3 7 mEq/L

• PaO2 28 mmHg

• Combined acidemia with severe hypoxemia



• pH 7.36

• PaCO2 45

mmHg

• HCO3 25 mEq/L

• PaO2 108 mmHg



• pH 7.36

• PaCO2 45

mmHg

• HCO3 25 mEq/L

• PaO2 108 mmHg

• Lab error

– ( PaCO2 and PaO2 cannot

total more than 140 on

room air)

Download - Basic Blood Gas Interpretation

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