Chapter 10
Invasive Blood Gas Analysis and
Cardiovascular Monitoring
Indications
• Similar to that of an adult
• Acid base balance, ventilation, oxygenation status
• Oxyhemoglobin, intrapulmonary shunting
• Response changes to therapy
• Severity of diseases….
• Respiratory distress
• Baby on oxygen
• Shock
• Sepsis
• Suspected metabolic disorder
• Failure to thrive (weight loss or no wt gain)
Pain Control
Pain control during draw
• Infants most likely have higher pain sensitivity
• Groups older than 4 months anesthetic cream may be
used
• Premature newborns/neonates not intubated may use a
pacifier dipped in 24% sucrose, intubated may give as
drops on the tongue
Pain Control
• The synergistic effect of the combination of sucrose and
non-nutritive sucking has shown clinically effective and
safe in relieving the pain of simple procedures such as
venipuncture or heel stick in preterm and term infants, but
further research is needed on these interventions alone
and in combination with other behavioral interventions in
neonates.
Blood Gas Sampling
ABG sampling sites
• Brachial and femoral sites are avoided because
both feed large distal networks and neither has
collateral circulation
• Brachial sites are hard to palpate due to large fat
pad in arm, high risk in damaging nerve
• Femoral site puncture never done in neonates
due to proximity to vein, nerves and hip joint
• Preferred site for ABG in both neonatal and
pediatric populations is radial (easy to manipulate
wrist and collateral circulation)
ABG sampling sites
• Dorsalis pedis or posterior tibial artery considered if radial
artery shows poor collateral circulation
• Temporal artery provides an alternative site
ABG Sampling Sites
• Umbilical artery
catheter (UAC)
• Clots may form on the
end
• Remember, it is postductal blood so the
PaO2 may be lower
than pre-ductal PaO2
ABG Sampling Sites: Punctures
• Radial artery and
temporal artery
• Can be hard to hit
• Brachial should not
be used
• NEVER use the
femoral artery in an
infant!
ABG Sampling Sites: Capillary
• Easier to puncture
than radial or
temporal artery
• PO2 may not
correlate well to
PaO2
• Heel has to be
warmed prior to
puncture to
“arterialize” the site
Puncture Sites
Allen’s test
• Can be modified depending on age of child
• For patients who cannot follow order
• For foot (dorsalis pedis and posterior tibial arteries)
• a. Elevate infant’s hand.
• b. Occlude both radial and ulnar arteries at wrist.
• c. Massage palm toward wrist.
• d. Release occlusion of the ulnar artery only.
• e. Look for color to return to the hand in 6 seconds or less
indicating adequate collateral supply. Do not puncture radial
artery if color returns take more than 6 seconds.
• f. Document inadequate collateral circulation
Arterial Puncture Procedure
• Often more difficult and therefore less frequently done
• Requires more skill, time and patience
• On pediatrics, have two people, one to console the child
and one to puncture
• For neonates, may use a transillumination light to visulize
the artery
• May be performed in cases of low perfusion where a CBG
is not appropriate
Arterial Puncture Procedure
• Equipment required
• 1 ml preheparinzed tuberculin syringe
• 25 Gauge needle or 25 Gauge butterfly
• Gloves
• Alcohol wipes/ Iodine
• Gauze
• Needle cap
• Label
Arterial Puncture Procedure
• Position needle for arterial puncture against direction of
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blood flow.
Keep angle of entry shallow for superficial vessels:
a. 35 to 45 degrees for superficial artery, advance
slowly/gently. May insert through artery, may have to pull
back slowly if flash disappears. If resistance occurs
withdraw, most likely hitting bone
b. Palpate artery using index finger and middle finger of
the non dominate hand to stabilize artery
C. If using a butterfly only require enough to fill tubing,
otherwise roughly 0.4-0.6 ml is required for adequate
sampling. Get enough blood and run it quickly to avoid
having to do it again.
Arterial Puncture Procedure
• Contraindications are similar to adults as are hazards.
• Just remember that ABG’s are not done if a less invasive
means can achieve the same results; such as a CBG
Factors affecting arterial blood gas values
• Clotting – heparin is utilized to prevent clotting of the blood sample.
• The sample must be rotated/agitated to ensure adequate mixing of
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heparin and blood to prevent clotting.
Excessive heparin – changes the pH of the specimen.
Air contact – no air must come into contact with the blood sample. Air
contact can increase the PO2 and decrease the PCO2 since there is
usually more oxygen and less carbon dioxide in the air than in the
blood as measured by partial pressures.
Temperature – red cell metabolism must be minimal. The sample
must be placed immediately in ice slush to slow metabolism. Red
cells that are warm will continue to metabolize, giving off CO2 and
consuming O2, thus affecting the blood gas values.
Steady rate – the blood should be drawn when the patient is in an
equilibrated state, that is, when at least 20 minutes have elapse since
any change has occurred or been made that might affect the blood
gas
Significant changes are respiratory rate, tidal volume
, minute volume, Fi02, and suctioning before sampling time.
Capillary Blood Gas Samples
• Less blood required
• Less invasive
• Correlates best with pH and PaCO2
Capillary Blood Gas Samples
• Conditions of decreased venous return (right heart
failure) can lead to venous congestion and higher
capillary CO2 levels, increased cardiac output may
lead to decreased capillary CO2 levels
• CBG should be correlated with an initial ABG if
possible
• Accuracy of CBG affected by hypotension,
hypothermia, hypovolemia
• PcO2 values are not utilized and do not correlate
with arterial (unless patient has hypoxia), but may
be used to trend PaO2 values
Procedure for CBG
Procedure for CBG (cont.)
Procedure for CBG (cont.)
• Select puncture site and warm area for 5-10 minutes, use
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a heel warmer 42-45 C
Give a 12% to 24% sucrose solution pacifier 2 minutes
before procedure
Wash hands/gloves
Remove heel warmer, clean site with alcohol or iodine,
wipe dry with gauze, alcohol will hemolyze the blood
Immobolize the area by grasping the hand or foot and
stabilize the area by anchoring the hand or foot on a hard
surface, swaddle newborns/infants
Hold heel gently/firmly, wrap forefinger around infants
upper heel and ankle while holding the arch of the foot
with the thumb
Procedure for CBG (cont.)
• Position lancet and depress – depth around 1-2 mm, only
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puncture once without slicing
Ease thumb pressure after the lancet is removed
Wipe away the first drop of blood which may be
contaminated with intracellular, interstitial or lymphatic
fluids with a dry gauze
Apply moderate pressure to the heel or digit without
massaging or squeezing, until a free flowing drop of blood
appears
Squeezing or “milking” the sample may cause hemolysis
(more fragile RBC’s in neonates); also may cause brusing
and contamination
Procedure for CBG (cont.)
• Place tip of capillary into the droplet without touching the
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puncture wound
Hold the tube angled horizontally or slightly downward but
avoid getting air into tube.
Fill tube as much as possible to avoid air contamination
Do not scrap the skin, may contaminate the sample with
skin cells
If sample can not be analyzed immediately insert a metal
mixing “flea” into the capillary tube and seal it, mix the
sample by running a magnet gently back and forth (if
available) or simply roll in your fingers
Contraindications
• Need accurate assessment of oxygenation
• Neonates less than 24 hours old
• Decreased peripheral blood flow
• Polycythemia
• Avoid areas that are:
• Edematous
• Inflamed
• Infected
• Callused
Complications
• May not accurately reflect patient’s
condition
• Mismanagement
• Burns
• Infection
• Scarring/bruising
• Inflammatory changes
• Nerve damage
• Artery damage
• Bruising
• Hematoma
• Bleeding
Arterial Catheter
• Indications: Need for continuous
measurement,
• Sites
• Umbilical arteries
• Neonates
• Peripheral arteries
• Radial artery
• Posterior tibial
• Dorsalis pedis
Arterial Catheter (cont.)
• Direct measurement of BP (MAP)
• Waveform
• Patency of arterial line
• Quality of pulse pressure
• Calculation of MAP
Continuous Invasive Blood Gas
Monitoring
• Closed loop
• Frequent ABGs
• Low volume
UAC procedure
• Umbilical artery lines are entered for removal of blood for
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monitoring of laboratory work and arterial blood gases.
Umbilical arterial lines are entered for the administration
of intravenous fluids and medications.
Any time an arterial line is entered, sterile technique
should be maintained.
Care should be taken to prevent blood clots or air emboli
from entering the patient.
The umbilical artery line should be maintained as a closed
circuit to prevent the loss of blood or intravenous fluids.
UAC procedure
Contraindications
• Signs of complications (i.e.: leg blanching, discoloration,
decreased peripheral pulses, improper position of
catheter) indicating that infusion or withdrawal through the
catheter may cause or further decrease circulation to an
extremity.
• An infant with an already depleted blood volume.
UAC procedure
Equipment required
• 3 cc sterile dry syringe for clearing line
• 1 cc sterile syringe with dead space filled with 1000 units
per cc of heparin
• 1 cc syringe for drawing lab work
• 1 cc syringe of normal saline for flush (This syringe is
placed on the stopcock at the beginning of each shift).
Step
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Action
Verify Physician's Order and Patient identification. Evaluate infant for
feasibility of drawing ABG.
Assemble Equipment.
Wash hands. Wear gloves.
Check position of stopcock, making sure it is closed to the flush
syringe.
Remove flush syringe, cap and set aside.
Place 3 cc drying syringe on stopcock.
Turn stopcock off to intravenous fluids
Draw back 2-2½ cc of blood to clear line and obtain an
uncontaminated blood sample.
One-fourth turn stopcock off. Remove syringe, cap and set aside
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Place appropriate syringe on stopcock.
Turn stopcock off to intravenous fluids and draw blood sample
needed.
a. 0.3 cc for ABG in heparinized TB syringe (flush syringe with 1000u
Heparin leaving a tiny amount in dead space of syringe).
b. Appropriate amount for laboratory work in proper vacutainer tubes.
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Remove cap from the syringe of blood drawn earlier to clear the line.
Replace this into stopcock.
Step
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Action
One-fourth turn stopcock and remove sample syringe.
For ABG's prepare for transport -- Remove air bubbles and ice sample.
For laboratory -- Place in appropriate vacutainer and label.
Remove cap from the syringe of blood drawn earlier to clear the line. Replace
this into stopcock
Turn stopcock off to intravenous fluids, draw slightly back on syringe and flick
to remove air bubbles. Then slowly re-infuse blood. Observe line to make
sure no air or clots are infused.
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One-fourth turn stopcock OFF, remove syringe.
Remove cap from flushing syringe, place in stopcock.
Turn stopcock off to intravenous fluids, draw back slightly on syringe and flick
any air bubbles to top, using as little flush as possible to clear line of blood.
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Return stopcock off to flush syringe, leaving I.V. open.
Make sure all connections are tightly secure and that the stopcock is open to
intravenous infusions.
Make sure all connections are tightly secure and that the stopcock is open to
intravenous infusions.
Observe infant for any adverse reaction to the procedure.
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Wash hands.
Chart the amount of blood withdrawn, keeping a running total. The amount of
flush solution used will be added to the cumulative total of fluid intake.
UAC Care
• The umbilical arterial catheter should be maintained as a
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sterile infusion line. Good hand washing technique is
IMPERATIVE.
The arterial line should be observed at all times to
maintain a closed system to:
Prevent loss of blood
Prevent loss of I.V. fluids
Prevent air embolisms.
Maintain patency of line.
Central Venous Catheters
• Sites vary with patient age and
condition
• Measures
• Right atrial pressure
• Mixed venous blood
gases/saturations
• CVP
• Volume status
Pulmonary Artery Catheters
• Less frequently used with children
Pulmonary Artery Catheters
Cardiac Output
Noninvasive Measurement of Cardiac
Output
• Fick equation
• Rebreathing CO2
• Pulse oximetry
• Perfusion Index
Normal values of arterial O2 tension
• Oxygen tension in term neonates is 50-70 mm of Hg and
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in children 70-100 mm of Hg.
PaO2 monitoring has recognized shortcoming.
Validity of values are optimal when blood gas samples are
obtained from indwelling catheters under quiet, resting
conditions. In a crying neonate due to pain of
percutaneous puncture values obtained may not reflect
steady state conditions.
paO2 values vary considerably throughout the day in sick
neonates.
Intermittent sampling produces only a limited view of a
single point in time.
Normal values of arterial O2 tension
• Transcutaneous (TcPO2) monitors are useful for judging
trends in oxygenation during management of acute lung
disease. These monitors measure skin surface pO2 (not
paO2), which under proper conditions is closely correlated
with arterial pO2
• The TcPO2 sensor combines a miniature blood gas
electrode with a servo controlled probe. The sensor is
applied to the skin in a way that excludes any effects of
environmental air on values measured. The technique
depends on heating the skin at the sensor site to 43.5C to
44C.
Normal values of arterial O2 tension
• Correlation is poor and TcPO2 may underestimate paO2
• Such conditions include circulatory insufficiency,
inadequate electrode temperature, improper calibration
and lack of user expertise, patient age greater than 10
weeks (skin thickness factor), and use of vasodilator
agents.
• Maturation and thickening of skin with increasing
postnatal age limits the use of transcutaneous monitoring
to neonates.
• All of these artifacts of measurement result in
underestimation of arterial pO2
• Under usual circumstances TcPO2 should be in the 40 to
80 mm Hg range.
Normal values of arterial O2 tension
• There is a time lag between measured TcPO2
• and paO2 values. As a result, oxygen concentration
• should not be continuously raised and lowered in attempts
to “chase” fluctuating TcPO2
ABG Values: ELBW/Premature <28 wk
• pH: >7.20
• PaCO2: 45-55
• Depends on pH
• PaO2: 45-65
• HCO3: 15-18
ABG Values: 28-40 wk GA
• pH: 7.25 – 7.45
• PaCO2: 45-55
• PaO2: 50-70
• HCO3: 18-20
ABG Values Term infant to toddler (up to
2)
• pH: 7.30-7.40
• PaCO2: 30-40
• PaO2: 80-100
• HCO3: 20-22
ABG Values Child to adult
• Normal ranges for all
categories
Metabolic Acidosis
• Diarrhea
• Lactic Acidosis (sepsis,
• Small bowel. Biliary or
hypoxia, cold stress)
• Ketoacidosis (starvation,
DM)
• Toxins (salicylate,
poisoning, methanol,
ethylene)
• Inborn errors of
metabolism
pancreatic tube or fistula
drainage
• Hyperalimentation
• Ingestion of chloride
compounds
• Renal tubular acidosis
• Renal failure
• Carbonic anhydrase
deficiency
Metabolic Alkalosis
• Vomiting
• Hypokalemia
• NG suctioning
• Hypocholermia
• Congenital chloride-
• Chewing tobacco
wasting diarrhea
• Dehydration
• Drugs (diuretics,
steroids, Sodium
Bicarb)
• Cushings syndrome
• Bartters syndrome
• Massive blood
transfusion
• Cystic fibrosis
Bartter syndrome
• Bartter syndrome is a rare inherited defect in the thick
ascending limb of the loop of Henle. It is characterized by
hypokalemia, alkalosis, and normal to low blood pressure.
• Seen between 24 and 30 weeks of gestation with
polyhydramnios
• After birth, the infant is seen with polyuria, and polydipsia
Life-threatening dehydration may result if the infant does
not receive adequate fluids. About 85% of infants dispose
of excess amounts of calcium in the urine (hypercalciuria)
and kidneys which may lead to kidney stones. In rare
occasions, the infant may progress to renal failure.
Cushings syndrome
• Associated with prolonged exposure to inappropriately
high levels of the hormone cortisol. This can be caused by
taking glucocorticoid drugs, or diseases that result in
excess cortisol, adrenocorticotropic hormone
• pituitary-dependent cause of Cushing's syndrome: a
tumor (adenoma) in the pituitary gland produces large
amounts of ACTH, causing the adrenal glands to produce
elevated levels of cortisol. It is the most common noniatrogenic cause of Cushing's syndrome, responsible for
70% of cases excluding glucocorticoid related cases
• Symptoms include rapid weight gain, particularly of the
trunk and face with sparing of the limbs (central obesity).
A common sign is the growth of fat pads along the collar
bone and on the back of the neck (buffalo hump) and a
round face often referred to as a "moon face."
CAPILLARY GASES USE
THE SAME VALUES
EXCEPT FOR PO2
Capillary PO2: 35-50
Capillary %sat: 75-85%
Why lower PO2 values Are acceptable in
the neonate
• O2 dissociation curve is shifted to the left so affinity is
increased – hemoglobin saturates at a lower PaO2
• Presence of HBF
• Decreased 2,3-DPG
• Neonate not considered hypoxemic until PaO2 is less
than 50!
Cyanosis
• Classic definition: 5 grams% of unsaturated hemoglobin
• Infant may not show signs of cyanosis until PaO2 < 40
(%sat between 75-85%)
Effects of Hypoxia
• Decreased tissue
oxygenation
• Lactic acidosis
• Hypoglycemia
• Increased PVR and
PAP
• May allow shunting
across ductus arteriosus
or foramen ovale
• Decreased surfactant
• Worsening of hypoxemia
• Decreased
thermogenesis
• Cold stress/hypothermia
• Brain & CNS damage
HYPEROXIA: PAO2 >
100
Hyperoxia may damage the neonate’s eyes
and/or lungs
Retinopathy of Prematurity (ROP)
• Hyperoxia causes vasospasm and ischemia in
retinal arterioles
• Ischemia and compensatory vasodilation and
proliferation causes retinal edema which may
lead to detachment and blindness
• ROP incidence increases with these three
factors:
• Prematurity, hyperoxia (it’s the PaO2, not the FIO2),
and the duration of O2
• Vitamin A and/or E may help prevent it
O2 Toxicity in the Lungs
Here it is the FIO2 which causes high PAO2
This causes the following pathological changes:
• Decreased alveolar volume, ie decreased FRC
(why?)
• Increased surface tension due to decreased
surfactant
• Inflammatory exudate and hyaline membrane
formation
• Sloughing of alveolar epithelium
• Fibrosis
Management of O2 Therapy
• Keep PaO2 between 50-70!
• For hypoxemia on 21%, start FIO2 between 25-35%
• Use guideline that 1% change in FIO2 will maximally
change PAO2 by 7 mmhg
• Avoid Flip-Flop phenomenon
• Changing FIO2 by more than 5-10% at one time may
cause sudden deterioration
• The longer the infant is on O2, the more prone he is to
Flip-Flop
• It is not unusual to limit changes in FIO2 to 1-2%!
O2 THERAPY DEVICES
Nasal Cannula
• Should be used with a
blender
• One or both prongs may
be removed
• Special flowmeters allow
flows of less than 1 LPM
to be used
• Vapotherm– high
humidity and flow
through cannula, e.g. 5-6
LPM
Hoods
• Best to use a blender
to flood the hood with
a precise FIO2
• Flow needs to be 5-7
LPM to flush out CO2
• Noise inside hood
may be damaging to
infants hearing
•Note: A heated, humidified flow of 10-12 LPM may be
used in isolette