Capillary Blood Gas Sampling for Neonatal and Pediatric Patients

August 19, 2008

In the critical care of neonates and pediatric patients, ensuring proper oxygenation and acid-base balance is paramount. This is where blood gas analysis comes into play, providing vital information for informed treatment decisions. While arterial blood gas (ABG) sampling is the gold standard, there are situations where obtaining an arterial sample may be impractical. Capillary blood gas (CBG) sampling emerges as a valuable alternative in such scenarios.

This review dives into Dr. Ramaz Mitaishvili’s guide, “Capillary Blood Gas Sampling for Neonatal and Pediatric Patients,” offering a clear understanding of this technique and its applications.

1. PROCEDURE:

Capillary sampling for blood gas analysis

2. DESCRIPTION:
Capillary blood gas (CBG) samples may be used in place of
samples from arterial punctures or indwelling arterial catheters to
estimate acid-base balance (pH) and adequacy of ventilation (PaCO2).
Capillary PO2 measurements are of little value in estimating arterial
oxygenation.

A puncture or small incision is made with a lancet or similar
device into the cutaneous layer of the skin at a highly vascularized area
(heel, finger, toe). (The lancet may be used freehand or as part of a device that limits puncture depth.) To accelerate blood flow and reduce the difference
between the arterial and venous gas pressures, the area is warmed prior to
the puncture. As the blood flows freely from the puncture site, the sample
is collected in a heparinized glass capillary tube.

3. SETTING:
Capillary sampling may be performed by trained healthcare personnel in

Acute care hospitals,
Clinics,
Physician offices,
Extended care facilities,
Homes.

4. INDICATIONS:
Capillary blood gas sampling is indicated when

Arterial blood gas analysis is indicated but arterial access is not available.
Noninvasive monitor readings are abnormal: transcutaneous values, end-tidal CO2, and pulse oximetry.
Assessment of initiation, administration, or change in therapeutic modalities (i.e., mechanical ventilation) is indicated.
A change in patient status is detected by history or physical assessment.
Monitoring the severity and progression of a documented disease process is desirable.

5. CONTRAINDICATIONS:

A. Capillary punctures should not be performed

at or through the following sites;
posterior curvature of the heel, as the device may puncture the bone;
the heel of a patient who has begun walking and has callus development;
the fingers of neonates (to avoid nerve damage);
previous puncture sites;
inflamed, swollen, or edematous tissues;
cyanotic or poorly perfused tissues;
localized areas of infection;
peripheral arteries.
on patients less than 24 hours old, due to poor peripheral perfusion;
when there is a need for direct analysis of oxygenation;
when there is a need for direct analysis of arterial blood;

B. Relative contraindications include

peripheral vasoconstriction;
polycythemia (due to shorter clotting times);
hypotension may be a relative contraindication.

6. HAZARDS/COMPLICATIONS:

A. Infection

Introduction of contagion at sampling site and consequent infection in patient, including calcaneus osteomyelitis and cellulitis
Inadvertent puncture or incision and consequent infection in sampler

B. Burns

C. Hematoma

D. Bone calcification

E. Nerve damage

F. Bruising

G. Scarring

H. Puncture of the posterior medial aspect of the heel may result in

tibial artery laceration

I. Pain

J. Bleeding

K. Inappropriate patient management may result from reliance on capillary

PO2 values.

7. LIMITATIONS OF METHOD/ VALIDATION OF RESULTS:

A. Limitations

Inadequate warming of the site prior to a puncture may result in capillary values that correlate poorly with arterial pH and PCO2 values.
Undue squeezing of the puncture site may result in venous and lymphatic contamination of the sample.
A second puncture may be needed to obtain an adequate amount of blood for analysis.
Variability in capillary PO2 values precludes using these samples for assessing oxygenation status.

B. Validation of results

The sample must be anticoagulated and obtained anaerobically with a capillary tube filled completely and air bubbles expelled immediately.
The sample should be immediately chilled or analyzed within 10-15 minutes if left at room temperature.
A respiratory assessment of the patient should be documented in the medical record at the time a capillary sample is performed
An arterial sample may be analyzed to compare with the capillary pH and PCO2 values.

8. ASSESSMENT OF NEED:
Capillary blood gas sampling is an intermittent procedure and should be performed when a documented need exists. Routine or standing orders for capillary puncture are not recommended. The following may assist the clinician in assessing the need for capillary blood gas sampling:

A. History and physical assessment;

B. Noninvasive respiratory monitoring values

Pulse oximetry;
Transcutaneous values;
End-tidal CO2 values;

C. Patient response to initiation, administration, or change in therapeutic modalities;

D. Lack of arterial access for blood gas sampling.

9. ASSESSMENT OF TEST QUALITY:
Sampling of capillary blood is useful for patient management only if the procedure is carried out according to an established quality assurance program. The validity of the test may be jeopardized if any of
the following occurs:

A. The sample is contaminated by air;

B. Clots prevent accurate analysis;

C. Quantity of sample is insufficient for analysis;

D. Analysis of sample is delayed (> 15 minutes for samples at

room temperature, or > 60 minutes for samples held at 4°C).

10. RESOURCES:

A. Equipment:

Single puncture-pre heparinized glass capillary (eg, Natelson) tubes, metal fleas, magnet, clay/wax sealant or caps, lancet to make incision < 2.5 mm in depth, gauze/cotton balls, ice, gloves, skin antiseptic, warm and moist cloth/diaper or commercially prepared warming pads (42°C), sharps container, labeling materials

B. Personnel:

Capillary sampling must be performed under the direction of a physician. Individuals who perform capillary sampling should have a background in mathematics and science and specific training in capillary blood sampling and related procedures. They must competently demonstrate capillary blood gas sampling and undergo periodic skills assessment of technique: implementation of Universal Precautions; success at obtaining a quality sample; preparation, storage, and transport of specimens; documentation; and post-sampling site care and/or complication rate.

11. MONITORING:
The following should be monitored and documented in the medical record as part of the capillary sampling procedure:

A. FIO2 or prescribed oxygen flow;

B. Oxygen administration device or ventilator settings;

C. Free flow of blood without the necessity for `milking’ the

foot or finger to obtain a sample;

D. Presence/absence of air or clot in the sample;

E. Patient temperature, respiratory rate, position, or level of

activity, and clinical appearance;

F. Ease or difficulty of obtaining sample;

G. Appearance of puncture site;

H. Complications or adverse reactions to the procedure;

I. Date, time, and sampling site;

J. Noninvasive monitoring values: transcutaneous O2 & CO2,

end-tidal CO2, and/or pulse oximetry;

K. Results of the blood gas analysis.

12. FREQUENCY:
The frequency of capillary sampling should depend upon the clinical status of the patient and the indications for performing the procedure, not upon a prescribed frequency.