Blood Gas Sampling and Monitoring
CLINICAL GUIDELINES
Children who are physiologically compromised and/or those who need adjunctive oxygen therapy may require blood gas analysis and/or monitoring.
Blood gas analysis provides a direct method to assess oxygenation, acid-base balance, adequacy of ventilation, hypoxic states, and evaluation of the child’s response to therapy via blood sample collection.
Blood gas samples are obtained upon a healthcare prescriber order using aseptic technique and standard precautions.
Healthcare prescribers, respiratory care practitioners, and registered nurses (RNs) may collect blood gas samples after demonstrating competency by the selected route.
Blood gas samples may be obtained from arterial lines or puncture (arterial blood gas [ABG]), capillary puncture (CBG), or, if necessary, venous blood draw (VBG). Capillary sampling is a useful alternative to arterial sampling even in the presence of hypothermia and hypoperfusion, provided that hypertension is not present. CBG and VBG are not recommended for determining Po2 of arterial blood.
If a child is to receive frequent blood gas sampling, consider arterial line cannulation to reduce the child’s discomfort, vasospasm, hematoma, or neurovascular compromise.
Samples should be analyzed as soon as possible after collection to prevent errors caused by contamination of the sample by room air, metabolic changes in the sample, or improper mixing of samples before the measurements are taken.
Local anesthesia should be used for ABG sampling by arterial puncture in nonemergent situations (see Chapter 7).
Continuous hemodynamic monitoring of arterial pressures by arterial cannulation also provides for direct blood gas collection. Clearly label and monitor these lines to avoid inadvertent intravenous (IV) use and possible exsanguination from dislodgment (see Chapter 46).
Transcutaneous monitoring (TCO2M) measures skin surface Po2 and Pco2, providing estimates of arterial partial pressure (Pao2) and carbon dioxide (Paco2). This estimation allows for the monitoring of arterial oxygenation and/or ventilation and for evaluation of therapeutic interventions.
Transcutaneous blood gas monitoring can be performed by trained healthcare prescribers, respiratory care practitioners, and RNs.
Those patients with poor skin integrity or adhesive allergy may not tolerate this type of monitoring.
If the child is hemodynamically compromised, the TCO2M may not be an accurate measure.
ABG values should be compared with transcutaneous readings taken at the time of arterial sampling to validate the transcutaneous values. Factors that may increase the discrepancy between arterial and transcutaneous values include hyperoxemia, a hyperperfused state (e.g., shock, acidosis), improper electrode placement, use of vasoactive drugs, increased skinfold thickness, or tissue edema.
Manufacturer’s recommendations for maintenance, operation, and safety of transcutaneous monitoring equipment should be followed.
A basic understanding of normal ABG values is essential for accurate interpretation of blood gas results (Table 19-1).
EQUIPMENT
FOR CAPILLARY BLOOD GAS SAMPLING
Warm, moist cloth or commercially prepared warming pad
Nonsterile gloves
Skin antiseptic
Preheparinized glass capillary tube
Clay or wax sealant or cap
Sterile lancing device (1.5 mm in depth)
Adhesive bandage
Patient specimen label
Ice (sample must be on ice if analysis delayed >10 minutes)
TABLE 19-1 Pediatric Arterial Blood Gases
pH
Paco2 (mm Hg)
Pao2 (mm Hg)
HCO3 (mEq/L)
Causes of Imbalance
Normal Values
Preterm infant
7.11-7.36
27-40
55-85
21-28
Term infant
7.35-7.45
27-41
54-95
21-28
Child
7.35-7.45
35-45
80-100
21-28
Abnormal Values
Respiratory acidosis (acute alveolar hypoventilation)
<7.30
>50
WNL or <80
WNL
Chronic lung disease (chronic bronchitis, asthma), respiratory depression from drugs or anesthesia, pneumonia, respiratory distress
Respiratory alkalosis (acute alveolar hyperventilation)
>7.50
<30
WNL
WNL
Anxiety, fear, pain, improperly adjusted ventilator (overventilation), salicylate toxicity, fever, hyperventilation, hypoxia, tetany, head trauma, gram-negative septicemia
Metabolic acidosis
<7.30
WNL
WNL
<21
Severe diarrhea, kidney failure, diabetic ketoacidosis, shock, burns, malnutrition, ingestion of salicylates
Metabolic alkalosis
>7.50
WNL
WNL
>28
Loss of HCO3 by intestines, severe vomiting, cystic fibrosis, gastric suctioning, severe diarrhea, renal failure, diuretics
Respiratory acidosis with metabolic compensation (chronic alveolar hypoventilation)
WNL
>50
WNL or <80
>28
Kidneys try to retain more HCO3 by increasing retention
Respiratory alkalosis with metabolic compensation (chronic alveolar hyperventilation)
WNL
<30
WNL
<22
Kidneys try to reduce HCO3 by increasing excretion
Metabolic acidosis with respiratory compensation
WNL
<30
WNL
<22
Lungs try to reduce Paco2 by increasing ventilation
Metabolic alkalosis with respiratory compensation
WNL
>50
WNL
>28
Lungs try to increase Paco2 slightly by hypoventilation
Paco2, arterial carbon dioxide; Pao2, arterial oxygen pressure; HCO3, bicarbonate; WNL, within normal limits.
Gauze or cotton balls
Sharps and biohazard disposal container
Biohazard bag for transporting the specimen to the laboratory
FOR ARTERIAL BLOOD GAS SAMPLING BY ARTERIAL PUNCTURE
Preheparinized 1-mL syringe with cap
25-g needle or 25-g butterfly needle
Nonsterile gloves
Antiseptic wipes
Gauze or cotton balls
Patient specimen label
Ice (sample must be on ice if analysis delayed >10 minutes)
Adhesive bandage
Patient specimen label
Biohazard bag for transporting the specimen
Sharps and biohazard disposal container
Anesthetic for nonemergent sampling:
Topical agents (see Chapter 7)
Local anesthetic (injectable buffered lidocaine, 1% without epinephrine)
Ice pack for puncture site (if needed)
FOR BLOOD GAS SAMPLING BY INDWELLING HEPARINIZED ARTERIAL OR DEEP VENOUS CATHETER
FOR TRANSCUTANEOUS BLOOD GAS MONITORING
Transcutaneous monitor
Adhesive electrode rings
Transcutaneous sensor contact gel
Calibration gases and calibrator
CHILD AND FAMILY ASSESSMENT AND PREPARATION
Assess child and child’s medical record for:
History of circulatory impairment (i.e., presence of cardiac or vascular grafts). Puncture of vessels or grafts may cause hematoma and decreased circulation
Prolonged clotting times or bleeding disorders that may affect clotting times
Impaired gas exchange related to underlying disease processes or for impaired breathing and note oxygen therapy and whether child requires continuous ventilatory assistance
Factors that may influence blood gas measurements (i.e., anxiety, suctioning, child’s position, temperature, oxygen therapy, metabolic rate)
Allergies to local anesthetics (e.g., lidocaine) or latex; implement latex precautions if necessary
Explain the procedure, as appropriate, to both the child and the family. Provide the opportunity to ask questions and alleviate fears.
Explain to the child and family that a lancet or needle will be used to puncture the child’s skin and gain access to the blood that is needed for this procedure. A topical anesthetic may be administered with arterial punctures before the procedure to minimize the pain of this needle stick. Explain that the blood withdrawn will be used to look at the amount of oxygen in the child’s blood. After the procedure, a Band-Aid or small dressing will be placed on the site.
Encourage a family member to remain with the child during the procedure. Discuss with the family member comfort measures (e.g., swaddling, skin-to-skin contact, breastfeeding, use of sucrose pacifiers, sweet tasting solutions) and distraction techniques (e.g., audio-visual, music) that they can use with their child. Select measures to employ and initiate use of these measures before beginning the procedure (see Chapter 7).
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