Chapter 10Chapter 10

Invasive Blood Gas Analysis and Invasive Blood Gas Analysis and Cardiovascular MonitoringCardiovascular 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 post-

ductal 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

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

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

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

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

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

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 Action1 Verify Physician's Order and Patient identification. Evaluate infant for

feasibility of drawing ABG.2 Assemble Equipment.3 Wash hands. Wear gloves.4 Check position of stopcock, making sure it is closed to the flush

syringe.5 Remove flush syringe, cap and set aside.6 Place 3 cc drying syringe on stopcock.7 Turn stopcock off to intravenous fluids8 Draw back 2-2½ cc of blood to clear line and obtain an

uncontaminated blood sample.9 One-fourth turn stopcock off. Remove syringe, cap and set aside

10 Place appropriate syringe on stopcock.11 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.

12 Remove cap from the syringe of blood drawn earlier to clear the line. Replace this into stopcock.

Step Action13 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.

14 Remove cap from the syringe of blood drawn earlier to clear the line. Replace this into stopcock

15 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.

16 One-fourth turn stopcock OFF, remove syringe.17 Remove cap from flushing syringe, place in stopcock.18 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.

19 Return stopcock off to flush syringe, leaving I.V. open.20 Make sure all connections are tightly secure and that the stopcock is open to

intravenous infusions.21 Make sure all connections are tightly secure and that the stopcock is open to

intravenous infusions.22 Observe infant for any adverse reaction to the procedure.

23 Wash hands.24 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

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

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• Small bowel. Biliary or pancreatic tube or fistula drainage

• Hyperalimentation• Ingestion of chloride compounds

• Renal tubular acidosis• Renal failure• Carbonic anhydrase deficiency

• Lactic Acidosis (sepsis, hypoxia, cold stress)

• Ketoacidosis (starvation, DM)

• Toxins (salicylate, poisoning, methanol, ethylene)

• Inborn errors of metabolism

Metabolic Alkalosis

• Vomiting• NG suctioning• Congenital chloride-wasting diarrhea

• Dehydration• Drugs (diuretics, steroids, Sodium Bicarb)

• Cushings syndrome• Bartters syndrome

• Hypokalemia• Hypocholermia• Chewing tobacco• 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 non-iatrogenic 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 PO2Capillary 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 > 100Hyperoxia 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 PAO2This 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