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Arterial puncture and cannulation in children

Arterial puncture and cannulation in children
Literature review current through: Jan 2024.
This topic last updated: Jan 04, 2024.

INTRODUCTION — The procedures for obtaining and handling arterial blood gas specimens in children are reviewed here. The technique for arterial blood sampling in adults and the interpretation of blood gas results and pulse oximetry are discussed separately. (See "Arterial blood gases", section on 'Arterial sampling' and "Measures of oxygenation and mechanisms of hypoxemia" and "Pulse oximetry" and "Simple and mixed acid-base disorders".)

ARTERIAL PUNCTURE

Indications, contraindications, and precautions — In children, indications for arterial puncture include:

Assess acid-base status and oxygenation

Correlate arterial with less invasive measurements (eg, venous blood gas or pulse oximetry)

Obtain a blood sample when venipuncture is unsuccessful.

Arterial puncture should not be performed at arterial sites with overlying skin infection. For puncture at the radial or posterior tibial artery sites, collateral circulation should

be assured prior to the procedure. If not present, another site should be chosen. (See "Arterial blood gases", section on 'Ensure collateral circulation' and 'Site selection and equipment' below.)

Arterial cannulation instead of puncture is advisable in critically ill patients for whom multiple arterial measurements or continuous arterial blood pressure monitoring will be required. (See 'Indications, contraindications, and precautions' below.)

Site selection and equipment — We suggest that children have arterial puncture performed at the distal radial arterial site (figure 1). The radial artery can be tested for collateral circulation using the modified Allen test (figure 2 and picture 1) and is easily accessed in most children [1,2]. Positioning and restraint of the upper extremity is also more easily accomplished in the uncooperative child. Finally, the risk of complications following arterial puncture at the radial site is low, especially compared with the femoral or brachial sites [2].

Testing for collateral blood flow with the Allen or modified Allen test is discussed in detail separately. (See "Arterial blood gases", section on 'Ensure collateral circulation'.)

Alternative sites include the posterior tibial (figure 3), the dorsalis pedis (figure 4), the brachial, and the femoral (figure 5) arteries. Of these, the dorsalis pedis can be tested for collateral circulation. (See 'Site selection and equipment' below and "Arterial blood gases", section on 'Ensure collateral circulation'.)

The femoral, and if absolutely necessary, the brachial arteries may be used for arterial puncture in children if other sites are not available, but they have less collateral arterial flow, are more difficult to access in the uncooperative patient, and especially in the coagulopathic patient, femoral arterial puncture can lead to retroperitoneal hematoma.

The following equipment should be assembled prior to the procedure [1]:

Antiseptic solution (eg, povidone-iodine solution) and sterile gauze, or prepackaged antiseptic wipes.

Gloves (sterile preferred).

A one inch butterfly needle with tubing or a prepackaged blood gas needle – The needle size for puncture is selected based upon the child's weight (table 1). Proper needle size is an important means of avoiding vessel thrombosis. If using a butterfly needle, the clinician will need to prepare a heparinized syringe by drawing up 1 mL of heparinized saline (1000 units heparin/1 mL), drawing back the plunger to coat the barrel, and then pushing it out through the butterfly needle and tubing. It is important to rapidly expel all of the heparin solution to avoid inaccurate measurement of pCO2.

Pain control — Whenever time permits, our approach to pain control during arterial puncture in children consists of application of topical anesthetic (eg, liposomal lidocaine or lidocaine-prilocaine) or subcutaneous or pressure injection of local anesthetic and use of the smallest gauge of needle that is appropriate for the child's weight (table 1). If lidocaine injection is used, then the clinician should wait for the lidocaine to infiltrate so that landmarks can be used. This approach is indirectly supported by trials in adults [3,4]. In one study in adults, a 23-gauge needle permitted more rapid arterial blood sampling than a 25-gauge needle but was not associated with greater reported pain [4]. Thus, 23-gauge needles are suggested for children who weigh >10 kg.

Technique — To obtain a single arterial blood gas specimen, perform the following steps [1]:

Ensure that the selected site has no signs of infection and, if applicable, adequate collateral circulation (radial and dorsalis pedis sites). (See "Arterial blood gases", section on 'Ensure collateral circulation'.)

If time allows, in conscious patients, place a topical anesthetic over the site or alternatively, infiltrate the skin with 1 percent buffered lidocaine. (See "Clinical use of topical anesthetics in children" and "Subcutaneous infiltration of local anesthetics", section on 'Lidocaine'.)

Use clean or sterile technique throughout the procedure. Sterile technique is necessary if blood cultures are being obtained.

Use the gloved index finger of the nondominant hand to locate the most easily palpated portion of the artery. Depending upon the chosen site, position the extremity to bring the artery closer to the surface:

Radial artery – Slightly extend the wrist beyond neutral until the maximum pulsation is palpated (picture 2)

Posterior tibialis – Dorsiflex the foot and evert the ankle

Dorsalis pedis – Plantarflex the foot with the ankle in neutral position

Have an assistant restrain the patient without grasping the extremity so tightly that the arterial pulse is diminished.

Using a small gauge butterfly needle (eg, 23 gauge) or prepackaged blood gas syringe with needle, puncture the skin at a 30 to 45 degree angle from horizontal and advance towards the arterial pulse until blood flow is obtained. The angle of entry for successful arterial puncture may be closer to 30 degrees rather than 45 degrees, especially in infants and young children. Too steep of a needle angle risks missing the flash of blood from the smaller artery in these patients. Transillumination with an approved fiberoptic light source may assist in identifying the more superficial radial, posterior tibialis, or dorsalis pedis arteries.

If a butterfly needle is used, attach the hub to a standard blood gas or heparinized syringe after blood flow is obtained.

Note that in young infants, the arterial blood flow may not appear pulsatile. Bright red blood that is easily withdrawn by syringe suggests an arterial sample in this circumstance.

Obtain a minimum of 0.3 mL of blood into a commercial 1 mL blood gas syringe or 3 mL syringe that contains a small amount of heparin. Remove any air bubbles, cap the syringe and place on ice for transport to the clinical laboratory and analysis within 15 minutes. (See 'Specimen handling and analysis' below.)

Hold pressure over the sampling site for a full five minutes after the procedure.

Complications — Arterial puncture may cause local hematoma, temporary arterial spasm, and transient pain [1]. Rarely, permanent arterial injury or, with femoral arterial puncture, injury to the developing femoral head can occur.

ARTERIAL CANNULATION

Indications, contraindications, and precautions — Indications for arterial cannulation in children include:

Frequent arterial blood gases are necessary, such as with acute respiratory failure.

The blood pressure must be monitored closely, such as during shock, major surgery, hypertensive emergency, or vasopressor therapy. This is particularly true if the blood pressure abnormality is acute, or the blood pressure is labile.

Continuous monitoring of cardiac output is necessary.

Depending upon the chosen site, the collateral flow to the artery should be assessed prior to cannulation using the modified Allen or Allen test (radial artery) or assessment of great toe perfusion after dorsalis pedis artery occlusion. Another site should be chosen in patients without collateral arterial blood flow. (See "Arterial blood gases", section on 'Ensure collateral circulation' and 'Site selection and equipment' below.)

Indwelling arterial catheters should not be placed in arterial sites with overlying skin infection or abscess.

Pain control and sedation — The approach to pain control for arterial cannulation consists of injection of local anesthetic as described above (See 'Pain control' above.)

Procedural sedation is commonly necessary to permit safe and successfully placement of an arterial catheter in children, especially at the femoral site. (See "Procedural sedation in children: Approach" and "Procedural sedation in children: Selection of medications", section on 'Moderately or severely painful procedures'.)

Site selection and equipment — We suggest that children have arterial cannulation performed at the distal radial site (figure 1). Relative to other sites, the radial artery has the following advantages:

Collateral flow can be readily assessed. (See "Arterial blood gases", section on 'Ensure collateral circulation'.)

Risk of ischemic complications is low, especially when compared with femoral artery cannulation [5]. (See 'Complications' below.)

Aseptic technique and line management is easier to maintain.

In children with congenital heart disease, right radial artery measurements of blood gases more accurately reflect cerebral oxygenation and perfusion pressure.

The radial artery is also the preferred site for perioperative and intensive care cannulation in children, accounting for 68 to 82 percent of all intraarterial catheters in two large observational studies [5,6]. The radial artery is palpable between the distal radius and the tendon of the flexor carpi radialis and usually can be more easily accessed with the wrist extended. The modified Allen test should be used to demonstrate collateral flow through the superficial palmar arch prior to cannulation (figure 2 and picture 1).

Alternate arterial sites include the following:

Posterior tibial – The posterior tibial artery (figure 3) is palpable just posterior to the medial malleolus and is preferred to the femoral site in neonates and young infants. Cannulation of the artery may be facilitated by holding the foot in comfortable dorsiflexion with eversion of the ankle. The most accessible area is a point between the medial malleolus and the calcaneus tendon (figure 6) [7].

Dorsalis pedis – The dorsalis pedis artery (figure 4) is located lateral to the extensor hallucis longus tendon and has collateral flow from the lateral plantar artery through an arch system similar to that in the hand. It is preferable to the femoral site in neonates and young infants. Collateral flow should be checked by occluding the dorsalis pedis artery, compressing the nail bed of the great toe, and confirming a rapid return of color when pressure on the toe is released.

Femoral – The femoral artery site is located midway between the symphysis pubis and superior iliac spine and approximately 2 cm below the inguinal ligament (figure 5). This site is used when peripheral arterial access on the wrist or foot is not achievable. The patient’s hip should be flexed and externally rotated and a towel roll placed to improve the approach to the femoral artery prior to the procedure (figure 5). The femoral artery can be palpated just below the midpoint of the inguinal ligament. The needle should be inserted just below the inguinal ligament, at a 90-degree angle toward the pulsation. Arterial catheterization via the femoral route may lead to thrombosis and distal embolization to the foot and must be accompanied by close monitoring of distal pulses. (See 'Arterial obstruction (vasospasm)' below and 'Arterial thrombosis and embolism' below.)

Brachial – The brachial artery can be accessed at the point of maximal pulsation just above the antecubital fossa on the medial aspect of the arm. The author’s approach is to avoid this site for arterial cannulation because of limited collateral flow to the distal arm, especially in neonates and young infants [1]. However, if absolutely necessary, this site can be used. As an example, no serious complications or permanent damage was reported in a large perioperative series of neonates and young children undergoing surgery for congenital heart defects, and complications were not more frequent than in children undergoing radial artery cannulation despite duration of insertion of several days [6]. Of note, these patients needed assessment of preductal arterial oxygenation. Thus, cannulation of an artery in the right upper extremity was essential.

Axillary – The axillary artery is a continuation of the subclavian artery and is palpable medial to the pectoralis muscle high up in the axilla when the arm is abducted to 90 degrees and the dorsum of the hand flat on the stretcher near the ipsilateral ear or placed under the head [1]. This site may be used in older children with poor perfusion when cannulation of other sites is unsuccessful. It is typically avoided in neonates and young infants. Good collateral flow to the arm occurs through the thyrocervical trunk and subscapular artery. Thus, the risk of ischemic complications to the arm is low. The clinician should ensure puncture at the point of maximal impulse to reduce the risk of inadvertently damaging the terminal branch nerves of the brachial plexus (figure 7).

The following equipment should be assembled prior to the procedure:

Antiseptic solution (eg, povidone-iodine solution) and sterile gauze, or prepackaged antiseptic wipes.

Sterile gloves, eye protection, and surgical mask.

Sterile drapes.

Intravascular catheter or prepackaged arterial cannulation kit – The catheter size for puncture is selected based upon the child's weight (table 1). The use of a separate or integral guidewire is suggested. (See 'Guidewire method' below.)

Stopcock.

Pressure transducing device.

Extension tubing flushed with heparinized (eg, 2 units of heparin/mL) saline or, in patients for whom heparin is contraindicated, 1.4 percent sodium citrate solution and connected to a continuous pump system to increase duration of catheter patency and decrease ischemic complications of arterial thrombosis [2]. (See 'Complications' below.)

4.0 or 5.0 nonabsorbable suture (table 2) to secure catheter to the skin.

Topical antibiotic ointment.

Transparent sterile adhesive dressing for the arterial catheter site.

Arm board and tape.

Techniques — Arterial cannulation can be accomplished using a separate guidewire (Seldinger technique), an integral guidewire, or direct cannulation with an intravenous catheter. Ultrasound (US) assistance, when available, may result in a higher success rate for cannulation, depending upon the clinician’s experience.

Ultrasound guidance — We recommend that, when equipment and expertise are available, children undergoing arterial cannulation have the procedure facilitated using US guidance. Use of US for arterial cannulation decreases the number of attempts and increases procedural success [8-11].

Potential techniques include [12]:

Short-axis approach – US transverse to the radial artery identifies the vessel as a pulsatile hypoechoic structure that is cannulated "out-of-plane" of the image. Acoustic shadowing created by linear material attached to the probe further improves first-pass success rate for experienced practitioners using this technique [8].

Long-axis approach – US longitudinal to the radial artery images both the vessel and the needle/catheter tip so that cannulation is directly imaged "in plane."

Dynamic needle positioning – US transverse to the radial artery is shifted proximally up the wrist during the procedure so that the vessel and cannula are constantly visualized until cannulation is achieved.

This recommendation is supported by a metaanalysis of four trials (404 children) that reported a significant benefit of US guidance for arterial cannulation compared with artery palpation or Doppler auditory assistance techniques with an increase in first-pass success rate from 209 to 409 per 1000 patients and a decrease in hematoma formation from 153 to 31 per 1000 patients based upon moderate quality of evidence [13]. The benefit of US-guided arterial cannulation may be especially pronounced in infants and young children and when performed by an experienced practitioner.

US guidance also appears useful to aid arterial cannulation by trainees. As an example, in one prospective observational study of 45 trainees, not included in the above meta-analyses, use of US guidance instead of a landmark method was also associated with significantly shorter procedure time (average time 8 versus 17 minutes, respectively) and number of attempts (average number 3 versus 7, respectively) [9].

Although not widely available and potentially expensive, the use of smart glasses during arterial cannulation under US guidance shows promise for enhancing performance. For example, in a randomized trial of 116 children younger than two years old undergoing elective major surgery that required radial artery cannulation, first-attempt success rate was higher when smart glasses were used compared with traditional US guidance (88 versus 72 percent, respectively), and hematoma formation was lower (3 versus 21 percent) [14]. However, further study of this technology is needed to confirm its benefit in a broader pediatric population, including older children, and to assess cost-effectiveness.

Guidewire method — We suggest that, when equipment and expertise are available, children undergoing arterial cannulation have the procedure performed using a guidewire. In addition, we advocate changing to a guidewire approach if difficulties are encountered with the direct puncture approach. In an unblinded trial of 100 children undergoing radial artery cannulation, use of a guidewire was associated with significantly fewer cannulation attempts, shorter procedure time, a higher rate of success, and more frequent ability to perform satisfactory blood pressure monitoring [15].

The technique for placement of an arterial cannula using a separate or integral guidewire is as follows [1]:

Ensure that the selected site has no signs of infection and, if applicable, adequate collateral circulation (radial and dorsalis pedis sites). (See "Arterial blood gases", section on 'Ensure collateral circulation'.)

If time allows, place a topical anesthetic over the site or alternatively, infiltrate the skin with 1 percent buffered lidocaine. (See "Clinical use of topical anesthetics in children" and "Subcutaneous infiltration of local anesthetics", section on 'Lidocaine'.)

For radial artery cannulation, secure the hand and distal forearm to a padded armboard with tape and extend the wrist so that a maximal radial pulse is felt.

Sterilely prepare the puncture site and maintain sterile technique throughout the procedure. (See 'Site selection and equipment' above.)

Identify the cannulation site using US guidance (recommended) or, if US is not available, palpation. (See 'Ultrasound guidance' above.)

If using a separate guidewire, proceed as follows (figure 8) [16]:

Ensure that the guidewire passes easily through the needle of the intravascular catheter. The clinician can assess this without damage to the guidewire if it is passed in a retrograde fashion through the needle.

Using an 18 or 19 gauge needle, make a skin nick just distal to the cannulation site to prevent dermal plugging of the intravascular catheter when it is advanced through the skin.

Insert the intravascular catheter (table 1) and needle at a 30 to 45 degree angle slowly until pulsatile blood return is observed.

Once pulsatile blood return is observed, lower the angle of the intravascular catheter and needle and advance them together to ensure that the catheter itself enters the vessel lumen.

Stabilize the intravascular catheter with the nondominant hand and remove the needle from the intravascular catheter.

If pulsatile blood return occurs after the needle is removed, advance the guidewire through the catheter. If pulsatile blood return does not occur, gently withdraw the catheter until pulsatile blood return is obtained and then advance the guidewire. If properly positioned within the arterial lumen, the guidewire should move with little to no resistance.

Advance the guidewire while maintaining the distal end well beyond the distal end of the catheter and then advance the intravascular catheter over the guidewire, into the artery, and up to the hub. Proceed with steps following discussion of the integral guidewire system.

If using an integral guidewire system, proceed as follows (figure 8):

Using an 18 or 19 gauge needle, make a skin nick just distal to the cannulation site to prevent dermal plugging of the intravascular catheter when it is advanced through the skin.

Insert the integral guidewire system (table 1) at a 30 to 45 degree angle slowly until pulsatile blood return is observed.

Stabilize the needle-catheter-guidewire unit with the nondominant hand while advancing the guidewire tab to push the guidewire into the artery.

Advance the outer catheter over the guidewire, into the artery, and up to the hub.

Once, the catheter is advanced to the hub, attach flushed extension tubing, a stopcock, and syringe to the hub and gently flush the catheter.

If it is not clear whether an artery or vein has been cannulated, a small disposable direct pressure transducer, if available, can be applied to the flushed extension tubing and the wave form directly analyzed on the monitor.

Secure the catheter with nonabsorbable suture (table 2) and a transparent, clear adhesive dressing.

Attach the syringe to a pump to provide continuous flushing at a low infusion rate (picture 3).

Direct method — Although US guidance is recommended, the technique for arterial cannulation by the direct method may be used if US guidance is not available:

Prepare and locate the arterial site as described above. (See 'Guidewire method' above.)

Using an 18 or 19 gauge needle, make a skin nick just distal to the cannulation site to prevent dermal plugging of the intravascular catheter when it is advanced through the skin.

Advance an intravascular catheter (table 1) at a 30 to 45 degree angle until pulsatile blood is obtained.

Once blood return is observed, lower the angle of the intravascular catheter and needle and advance it over the needle. Stabilize the catheter with the nondominant hand and advance the catheter into the artery and up to the hub.

Alternatively, advance the needle and catheter until blood flow stops, remove the needle, and gently withdraw the catheter until pulsatile blood flow resumes and slowly advance the catheter into the arterial lumen [17].

Once, the catheter is advanced to the hub, attach flushed extension tubing, a stopcock, and syringe to the hub and gently flush the catheter.

If it is not clear whether an artery or vein has been cannulated, a small disposable direct pressure transducer, if available, can be applied to the flushed extension tubing and the wave form directly analyzed on the monitor.

Secure the catheter with nonabsorbable suture (table 2) and a transparent, clear adhesive dressing.

Attach the syringe to a pump to provide continuous flushing at a low infusion rate (picture 3).

Complications — Complications of arterial cannulation in children in descending order of frequency include arterial obstruction, hematoma formation, infection, arterial thrombosis, arterial embolism, and iatrogenic blood loss. Rare complications include air embolism, pseudoaneurysm and arteriovenous fistula.

Arterial obstruction (vasospasm) — Transient arterial obstruction has been reported in up to 37 percent of femoral and 54 percent of radial artery cannulations [18,19]. The risk of arterial obstruction is increased with younger patient age and longer duration of cannulation [20]. Transient arterial obstruction may cause dampening of the arterial waveform, blanching, pain, induration, and rarely skin necrosis. However, cutaneous signs of arterial obstruction are often not present.

When transient arterial obstruction occurs, warming of the arterial site with a hot pack or administration of 0.5 mg/kg of intravenous lidocaine may be beneficial [2].

Topical nitroglycerin ointment may also be useful if these methods fail. For example, in four neonates with radial artery catheters, application of a thin film of 2 percent nitroglycerin ointment to the wrist, palm, and fingers in a dose of 4 mm/kg was associated with rapid improvement of hand color and perfusion [21-23]. Although transient decrease in blood pressure was described, no patient had serious hypotension.

Hematoma — Hematoma formation occurs in 4 to 14 percent of arterial cannulations [2,6,24]. Hematoma formation may be a risk factor for hand ischemia in patients with radial artery catheters [2]. In most patients, hematomas resolve without specific interventions. However, unrecognized retroperitoneal hematomas after femoral artery cannulation have been described in adults and can result in significant blood loss. (See "Intra-arterial catheterization for invasive monitoring: Indications, insertion techniques, and interpretation", section on 'Site-specific complications'.)

Infection — Infections occur in 1 to 7 percent of children with indwelling arterial catheters that have been in place for prolonged periods [2,24,25]. Although debated, radial artery cannulation may be associated with a lower risk of infection than the femoral site [2]. The risk of infection is increased with younger age and increased duration of cannulation.

Meticulous attention to sterile technique during arterial cannulation and when drawing blood from the arterial line is important for reducing infection [2]. Limiting the duration of arterial cannulation as a means to reduce infection risk is also appropriate, especially in high-risk patients (eg, immunocompromised patients). However, the risk of infection from an indwelling arterial catheter is low, and routine removal and replacement is not indicated if the patient’s clinical condition requires ongoing intraarterial access.

Arterial thrombosis and embolism — In patients with signs of compromised distal circulation (eg, decreased or absent pulse, blanched or mottled skin, delayed capillary refill, cold distal extremity) and evidence of arterial thrombosis or embolism on imaging (eg, Doppler US, angiography, magnetic resonance imaging), arterial catheter removal and prompt consultation with a vascular surgeon is imperative [2].

Arterial thrombosis is described in up to 23 percent of children with indwelling arterial catheters and occurs more frequently in younger patients and those cannulated with larger catheters [2,5,25-27]. Arterial thrombosis is common with radial artery catheters but embolic complications (eg, skin necrosis, permanently compromised circulation, amputation) are rare (<1 percent) [5,25]. By contrast, the risk of ischemic complications of thrombosis after femoral artery cannulation in children is approximately 13 percent although this higher risk is in part due to the need to use the femoral artery instead of the radial artery in children with poor perfusion and thus, a higher risk for thrombosis [27].

Embolization of thrombi from smaller arteries (radial, dorsalis pedis) may cause digital emboli with distal discoloration, skin necrosis, and, rarely, amputation [2]. Emboli from larger vessels (femoral, brachial, axillary) may also produce distal limb ischemia and lead to amputation [27]. Pulses distal to these sites should be monitored regularly. In addition, arrest of the growth plate resulting in skeletal deformity in adolescence is reported rarely after arterial cannulation of the femoral, brachial, and radial arteries in infancy [19]. Patient related factors (eg, shock, peripheral vascular disease, Raynaud phenomenon, systemic vasoconstrictor therapy) may also increase the risk of embolic complications [2,28].

The following measures may reduce the risk of arterial thrombosis or embolism:

When possible, perform arterial cannulation in the distal radial site. (See 'Site selection and equipment' above.)

Ensure adequate collateral circulation with the modified Allen or Allen test prior to radial artery cannulation.

Use the proper catheter size based upon the child's weight (table 1).

Avoid excess trauma during arterial cannulation by using US guidance and a guidewire method to increase success rate on the first attempt. (See 'Ultrasound guidance' above and 'Guidewire method' above.)

Provide a continuous flush with heparinized saline (eg, 1 to 2 units heparin/mL at 3 mL of flush solution per hour) [2,29]. Although this practice is common and supported by studies in adults, evidence is lacking in children. (See "Intra-arterial catheterization for invasive monitoring: Indications, insertion techniques, and interpretation", section on 'Thrombosis'.)

Iatrogenic blood loss — For every blood sample obtained from a traditional arterial line set-up, up to 2 to 4 mL of blood, depending upon the infusion tubing length, has to be first removed to clear the line of flush solution. Closed system blood conserving devices can limit the loss of this diluted discard by permitting the blood and flush solution to be drawn into a reservoir distal to the sampling point. Once the undiluted sample is collected, the blood and flush solution in the reservoir can then be reinfused [30].

Continuous intra-arterial blood gas monitors do provide accurate measures in children and infants and can decrease the amount of blood sampling but typically require placement of a femoral artery catheter in children. (See 'Blood gas monitors' below.)

Air embolism — Although rare, cerebral air embolism can occur after intermittent flushing of radial and axillary artery catheters (particularly those catheters placed on the right side) [2].

SPECIMEN HANDLING AND ANALYSIS — The results of arterial blood gases are affected by the following (see "Arterial blood gases", section on 'Sources of error'):

Type of syringe – Both plastic and glass syringes are available for blood glass collection. Gas diffusion through plastic syringes may introduce errors in blood gas analysis. However, studies vary regarding the magnitude of error. As a general rule, the error is not significant if the sample is analyzed within 15 minutes. Placement of the specimen on ice also reduces this error.

Air bubbles – Air bubbles that occupy more than 1 to 2 percent of the blood volume in the syringe may introduce error, leading to an artificially high arterial PO2 and an underestimation of the true arterial pCO2. The error can be decreased by gentle removal of bubbles without agitation and by rapid sample analysis.

Heparin use – Heparin is added to the syringe as an anticoagulant. The change in pH that results from the addition of acidic heparin is small. However, the dilutional effect of the heparin solution can produce significant reductions in the pCO2, depending directly upon the amount of heparin solution relative to the amount of blood. Thus, the amount of heparin solution should be kept to a minimum, and no less than 2 mL of blood should be obtained.

The blood gas sample should be placed on ice during transport, primarily to reduce oxygen consumption by leukocyte metabolism. Oxygen consumption is most pronounced in patients with profound leukocytosis. Rapid cooling of specimens obtained from these patients is necessary to avoid factitious hypoxemia. This error also can be reduced by rapid specimen analysis. (See "Arterial blood gases", section on 'Transport and analysis'.)

Analysis of arterial blood samples usually is performed using automated blood gas analyzers. Rigorous quality control with standardized testing materials is essential to assure the accuracy of results. (See "Arterial blood gases", section on 'Transport and analysis'.)

Arterial blood gas analyzers operate at 37ºC, which may differ from the body temperature of the patient from whom the blood sample was taken. Although the total content of carbon dioxide and oxygen in the blood do not change, the pH, pCO2, and PO2 of a blood sample all vary with temperature in a predictable way because gas tensions and hydrogen ion concentration decline with temperature (table 3). (See "Arterial blood gases", section on 'Transport and analysis'.)

Modern automated blood gas analyzers are capable of reporting values at either 37ºC (the temperature at which the values are measured by the machine) or at the patient's temperature. Whether values of pH, pCO2, and PO2 should be "corrected" to the patient's actual body temperature remains controversial, and "corrected" blood gas values should be interpreted with this in mind. Because of this uncertainty, most clinicians recommend using uncorrected values to guide therapy, recognizing that these results correspond to the arterial blood gas values that would have been present if the patient's temperature were 37ºC. (See "Arterial blood gases", section on 'Transport and analysis'.)

BLOOD PRESSURE INTERPRETATION — Blood pressure measurements obtained directly from an arterial catheter usually are higher (by 5 to 20 mmHg) than those measured by sphygmomanometry. In non-shock states, this increase results from the alteration in pulse contour as the pressure wave moves peripherally. The ascending portion of the wave becomes steeper, and the systolic reading becomes higher. However, the diastolic measurement usually is lower, leading to an unchanged mean arterial pressure. In shock states with a high systemic vascular resistance, the generated Korotkoff sounds may be inaudible by conventional sphygmomanometry, leading to erroneously low measurements.

BLOOD GAS MONITORS — Continuous intraarterial blood gas monitors have been used successfully in infants and children [31-34]. Such monitors use fiberoptic and fluorescent dye technology for determination of PO2, pCO2, and pH through either an indwelling, continuous monitoring catheter or an external, intermittent sensor supplied with arterial blood through a tubing loop [35].

Although reliable blood gas measurements can be obtained, the size of the monitors and the associated dampening of blood pressure waveforms frequently encountered at the radial arterial site typically limit their use to femoral artery catheters [33].

SUMMARY AND RECOMMENDATIONS

Indications – Indications for arterial puncture or cannulation in children include (see 'Indications, contraindications, and precautions' above):

Arterial puncture – To assess acid-base status and oxygenation, to correlate arterial values with less invasive measurements (eg, venous blood gas or pulse oximetry), or to obtain a blood sample when venipuncture is unsuccessful.

Arterial cannulation – To provide multiple arterial blood gas measurements or continuous arterial blood pressure monitoring in critically ill children or those undergoing major surgery.

Contraindications and precautions – Contraindications to arterial puncture or cannulation include (see 'Indications, contraindications, and precautions' above):

Skin infection at the procedure site.

For the radial or posterior tibial artery, deficient distal collateral arterial flow which requires choosing another site for puncture or cannulation. (See "Arterial blood gases", section on 'Ensure collateral circulation' and 'Site selection and equipment' above.)

Arterial puncture – For arterial puncture in children, we suggest use of the distal radial arterial site (figure 1) (Grade 2C). Alternative sites include the posterior tibial (figure 3), the dorsalis pedis (figure 4), the brachial, or the femoral (figure 5) arteries. Select the appropriate needle size for puncture using the child's weight (table 1). If using a butterfly needle, heparinize the butterfly tubing and syringe. (See 'Site selection and equipment' above.)

Pain control consists of topical anesthetic (eg, liposomal lidocaine or lidocaine-prilocaine) when time permits or subcutaneous injection of local anesthetic; in addition, use the smallest gauge needle that is appropriate for the child's weight. (See 'Pain control' above.)

The step-by-step technique for arterial puncture technique is described above. (See 'Technique' above and 'Complications' above.)

Arterial cannulation – For arterial cannulation in children, we suggest use of the distal radial site once collateral circulation is assured (figure 1) (Grade 2C). Primary alternative sites include the femoral, posterior tibial, and dorsalis pedis arteries. Of these, the dorsalis pedis can be tested for collateral circulation. We avoid the brachial artery, especially in neonates and young infants. Select the appropriate catheter size using the child's weight (table 1). (See 'Site selection and equipment' above.)

For awake children, in addition to local anesthetic at the site, sedation to manage pain and to limit movement enhances safe performance of the procedure, especially during femoral arterial line placement. (See 'Pain control' above.)

For arterial cannulation in children, we recommend ultrasound (US) guidance when equipment and expertise are available (Grade 1B) (see 'Ultrasound guidance' above). We also suggest use of a guidewire (figure 8) rather than the direct method (Grade 2B). (See 'Guidewire method' above.)

Prevention of complications – Serious complications during and after arterial cannulation include infection and arterial thrombosis with embolism:

Risk of infection is decreased by (see 'Infection' above):

-Use of the radial arterial site

-Careful sterile technique during placement and subsequent catheter manipulation

-Limiting the duration of arterial cannulation whenever possible

Risk of arterial thrombosis with embolism is decreased by (see 'Arterial thrombosis and embolism' above):

-Use of the radial arterial site after ensuring collateral blood flow,

-Placing the appropriately sized catheter using the child’s weight

-Performing the procedure under US guidance to ensure higher first attempt success which avoids excess trauma during cannulation

-Continuous flushing of the catheter after placement with heparinized (eg, 2 units heparin/mL) saline

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Topic 6327 Version 25.0

References

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