Capillary Blood Gas Sampling for Neonatal and Pediatric Patients

Ramaz Mitaishvili, MD
  • Capillary sampling for blood gas analysis
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

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.

Capillary sampling may be performed by trained health care personnel in
  • Acute care hospitals,
  • Clinics,
  • Physician offices,
  • Extended care facilities,
  • Homes.

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, 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.


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 need for direct analysis of oxygenation;
  • when there is 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.


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 posterior medial aspect of heel may result in

tibial artery laceration

I. Pain

J. Bleeding

K. Inappropriate patient management may result from reliance on capillary

PO2 values.


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

  • Sample must be anticoagulated and obtained anaerobically with capillary tube filled completely and air bubbles expelled immediately.
  • 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.

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.

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 occur:

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).


A. Equipment:

Single puncture-preheparinized 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 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.

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 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.

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.

A. Those patients requiring frequent CBGs should be considered candidates for placement of an indwelling arterial access for blood gas sampling or  noninvasive monitoring techniques, to limit trauma associated with repeated punctures.

B. Repeated puncture of the foot/finger increases the risk of scarring or serious laceration. Care should be exercised to alternate the sampling site for patients requiring multiple punctures.


A. Universal Precautions as published by the Centers for Disease Control

and directives issued by the Department of Labor concerning occupational exposure to blood-borne pathogens must be followed during capillary  sampling.

B. Aseptic techniques should be employed due to the invasive nature of

this procedure. Punc-ture site should be cleaned with antiseptic solution.

C. Blood specimens, contaminated materials, and lancets must be disposed

of in appropriate containers.

D. Gloves should be worn by caregivers to protect against blood splashes

on sores or skin breaks.


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