Arterial puncture and cannulation in children for pediatric emergency medicine and critical care

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 blood gas results with less invasive measurements (eg, venous blood gas, pulse oximetry, end-tidal CO2 monitoring or transcutaneous carbon dioxide monitoring)

●Obtain a blood sample when venipuncture is unsuccessful

Arterial puncture should not be performed at arterial sites with overlying skin infection. Providers should consider how puncture may impact distal perfusion and blood flow to the extremity and monitor for complications closely. (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 blood gases, frequent laboratory studies, or continuous arterial blood pressure monitoring will be required. (See 'Indications, contraindications, and precautions' below.)

Site selection and equipment — The distal radial artery is the usual site for arterial puncture in children (figure 1). The radial artery is superficial and can be easily accessed in most children [1,2]. Positioning and restraint of the upper extremity are 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 [2,3]. If both radial sites are unavailable or attempted without success, then alternative sites, in order of our preference, include the ulnar, posterior tibial (figure 2), dorsalis pedis (figure 3), brachial, and femoral (figure 4) arteries. (See 'Site selection' below.)

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

Ultrasound can establish flow through the ulnar and posterior tibial artery and ensure safe performance of radial or dorsalis pedis artery puncture, respectively. However, we reserve this assessment for pediatric patients at high risk for ischemia or thrombotic complications (eg, patients in shock).

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

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

●Gloves (sterile preferred).

●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), infiltration of local anesthetic, or deployment of a needle-free anesthetic delivery device 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 [4,5]. 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 [5]. Thus, 23-gauge needles are suggested for children who weigh >10 kg. (See "Clinical use of topical anesthetics in children" and "Subcutaneous infiltration of local anesthetics", section on 'Lidocaine'.)

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

●Select an appropriate site, ensuring no surrounding or overlying signs of infection. (See "Arterial blood gases", section on 'Ensure collateral circulation'.)

●Provide analgesia whenever time allows. (See 'Pain control' above.)

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

●If performing needle puncture by palpation, use one or two gloved index fingers of the nondominant hand to locate the most easily palpated portion of the artery; use of two fingers gives further sense of the route of the artery. Alternatively, the clinician may use ultrasound to identify the artery location statically as well as dynamically during arterial puncture. (See 'Ultrasound guidance' below.)

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 1)

•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; they should avoid grasping the extremity so tightly that the arterial pulse is diminished.

●Using an appropriately sized butterfly needle (table 1) or prepackaged blood gas syringe with needle, puncture the skin slightly distal to the point of maximal pulsation, 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. A needle angle that is too steep risks missing the flash of blood from the smaller artery in these patients.

Transillumination with an approved temperature-safe fiberoptic light source may assist in identifying the more superficial radial, posterior tibialis, or dorsalis pedis arteries in infants and small children (such as those <10 kg).

●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 these patients. If a butterfly needle is used, the proceduralist can have an assistant attach the hub to a standard blood gas or heparinized syringe after blood flow is obtained.

●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 analyze within 15 to 30 minutes. If analysis is expected to be delayed, then place the sample on ice. (See 'Specimen handling and analysis' below.)

●Hold pressure over the sampling site until complete hemostasis has been achieved after the procedure (typically a full five minutes).

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 – Indications for arterial cannulation in children include:

•Frequent arterial blood gases and other laboratory studies are necessary, such as for patients with acute respiratory failure.

•The blood pressure must be monitored directly and continuously, such as for patients with shock, severe traumatic brain injury, major surgery, hypertensive emergency, or in patients receiving vasopressor therapy. This is particularly true if the blood pressure abnormality is acute or the blood pressure is labile.

Although used in adults, most arterial pulse waveform analysis devices designed to estimate stroke volume and/or cardiac output from arterial line catheters are not validated in children. (See "Novel tools for hemodynamic monitoring in critically ill patients with shock", section on 'Arterial waveform-based devices'.)

●Contraindications – Indwelling arterial catheters should not be placed in arterial sites with overlying skin infection or abscess. Placement of a femoral artery catheter in the same side as a femoral central venous catheter may increase the risk of vascular compromise on that side and should be avoided when possible.

●Assessment of collateral flow – While the use of an Allen or modified Allen test has traditionally been incorporated into arterial cannulation, emerging data from adult patients undergoing radial artery access for coronary procedures have raised concerns about the specificity and sensitivity of the Allen/modified Allen test. While some organizations still recommend the use of the Allen test, others (including the American Heart Association) do not. Many experts do not routinely perform Allen testing. (See "Percutaneous arterial access techniques for diagnostic or interventional procedures", section on 'Assessment of hand circulation'.)

For cannulation of the radial or dorsalis pedis artery, it is reasonable to assess for collateral flow prior to cannulation using ultrasound (US) evaluation of collateral arteries or, for the radial artery, an Allen or modified Allen test. Direct testing of collateral flow for the radial or dorsalis pedis artery is described separately. (See "Arterial blood gases", section on 'Ensure collateral circulation'.)

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

Procedural sedation is commonly necessary to permit safe and successful 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 — The distal radial artery is the most common site for arterial cannulation in children (figure 1) [6,7]. The radial artery has the following advantages compared with other sites:

●The vessel is superficial and easy to identify by palpation and by ultrasonography.

●Risk of ischemic complications is low, especially when compared with femoral artery cannulation [7]. (See 'Complications' below.)

●Aseptic technique and line management is easier to maintain.

●In children with congenital heart disease, right radial artery (pre-ductal) measurements of blood gases more accurately reflect cerebral oxygenation and perfusion pressure.

Alternate arterial sites include the following [3,8]:

●Ulnar artery – The ulnar artery is located on the medial aspect of the wrist (figure 1). While more difficult to palpate, it is easily accessible with US guidance. In neonates, the ulnar artery may be of larger caliber than the radial and may be preferentially cannulated in some instances [9,10]. We recommend the use of US for ulnar artery cannulation given the proximity to the ulnar nerve, which may be easily damaged [2].

●Posterior tibial – The posterior tibial artery (figure 2) 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 5) [11].

●Dorsalis pedis – The dorsalis pedis artery (figure 3) 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.

●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 4). This site is used when peripheral arterial access on the wrist, arm, or foot is contraindicated or not achievable. Femoral artery cannulation is associated with the highest rate of complications among all sites, particularly in neonates [8]. Despite this, the femoral artery is still a reasonable site of access in critically ill children with emergency conditions. Femoral arterial cannulas should be discontinued when peripheral arterial access becomes available.

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 4). 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 and with US guidance, when available.

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]. It is a favored site by some pediatric anesthesiologists for intraoperative use when the radial or ulnar artery is unable to be cannulated, especially in children undergoing cardiac procedures. Good collateral flow to the arm occurs through the thyrocervical trunk and subscapular artery, which is advantageous compared with the femoral or brachial artery. The clinician should ensure puncture at the point of maximal impulse and with US guidance, when available, to reduce the risk of inadvertently damaging the terminal branch nerves of the brachial plexus (figure 6).

Equipment — The following equipment should be assembled prior to the procedure:

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

●Sterile gloves, eye protection, and surgical mask.

●Sterile drapes or operating room towels.

●Intravascular catheter or prepackaged arterial cannulation kit – The catheter size for puncture is selected based upon the child's weight (table 1).

●Guidewire (optional). A 0.18 inch guidewire is commonly used, widely available, and works in most 24-gauge and larger catheters. A 0.14 or 0.10 inch wire may be preferred by some operators for smaller catheters or neonatal patients. Prior to the procedure, test to ensure the guidewire selected will pass through the catheter and/or needle being utilized during the procedure.

●Stopcock.

●3 or 5 mL syringe filled with heparin or saline, which may be placed on the end of the arterial catheter after cannulation, prior to connection to tubing, while catheter is being secured.

●Pressure transducing device.

●Extension tubing flushed with heparinized (eg, 1 unit of heparin/mL) saline or, in patients for whom heparin is contraindicated, normal saline or 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) or other commercial securement devices.

●Transparent sterile adhesive dressing for the arterial catheter site.

●Arm board and tape.

●Ultrasound equipped with a small linear probe, sterile probe sleeve, and sterile sonic gel.

Techniques — Arterial cannulation can be accomplished via direct cannulation (with or without a guidewire) or via transfixion (through-and-through) utilizing a guidewire [12,13]. Transfixion may be the preferred technique of some operators, particularly in neonates in whom direct cannulation of the artery may be challenging. The steeper angle utilized in the transfixion technique reduces the risk of advancing a guidewire into the vessel intima, which may result in dissection. Ultrasound assistance, when available, can be used for either technique [14].

Site identification and preparation — Prepare the arterial cannulation site as follows:

●Ensure that the selected site has no signs of infection and consider assessment of collateral flow. (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 easily palpable.

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

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

Direct method — Although US guidance is recommended, the technique for arterial cannulation by the direct method may also be used if US guidance is not available [12,13]:

●Identify and prepare the cannulation site. (See 'Site identification and preparation' above.)

●Advance the IV catheter (table 1) at a 30- to 45-degree angle until arterial blood is obtained.

●Advance the catheter off the needle and into the artery. The technique depends upon whether a guidewire is used:

•Direct access with a guidewire – Once blood return is observed, insert the guidewire through the catheter into the artery or deploy the integrated guidewire (if using a prepackaged arterial cannulation kit). The guidewire should easily advance without any resistance. Subsequently advance the catheter over the guidewire, being sure to have control of the guidewire at all times during the procedure to avoid inadvertent migration of the wire into the patient.

We suggest that, when equipment and expertise are available, children undergoing arterial cannulation without US guidance have the procedure performed using a guidewire. In addition, we advocate use of a guidewire if direct cannulation without a guidewire proves challenging or if US visualization is poor. 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].

•Direct access without a guidewire – Once blood return is observed, lower the angle of the IV catheter and needle and advance an additional 3 to 4 mm to ensure the catheter has entered the vessel. If using US guidance, visualize the needle in the middle of the artery as it is advanced. Stabilize the catheter with the nondominant hand and advance the catheter 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. Ensure adequate blood return and ensure all bubbles have been removed from the tubing, 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 waveform directly analyzed on the monitor. Alternatively, use simple manometry with saline flushed tubing (figure 7).

●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 2).

Transfixion (through-and-through) method with guidewire — The transfixion (through-and-through) technique for placement of an arterial cannula requires use of a guidewire; use of US guidance is also suggested. (See 'Ultrasound guidance' below.)

The method is as follows [12-14,16]:

●Identify and prepare the cannulation site. (See 'Site identification and preparation' above.)

●Advance an intravascular catheter (table 1) at a steep (approximately 45-degree) angle until blood is obtained.

●Once blood return is observed, advance the needle at the same 45-degree angle an additional 5 to 7 mm. Stabilize the catheter with the nondominant hand and remove the needle completely.

●Slowly withdraw the catheter until brisk blood flow is obtained (blood flow may not be pulsatile, particularly in neonates).

●Advance a guidewire through the catheter. There should be no resistance if the catheter is positioned in the true lumen of the artery.

●Advance the catheter over the guidewire, maintaining control of the guidewire at all times to avoid migration of the wire into the patient.

●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 waveform 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 2).

Ultrasound guidance — For children undergoing arterial cannulation, we suggest US guidance whenever equipment and expertise are available. Use of US for arterial cannulation decreases the number of attempts and increases procedural success with a lower risk of complications [17-20].

Ultrasound guidance can be applied to either the direct cannulation technique (with or without a guidewire) or the transfixion (through-and-through) technique [21]. The fundamental principles of US guided arterial access share many commonalities with venous access, outlined separately. (See "Basic principles of ultrasound-guided venous access".)

Ultrasound techniques:

●Short-axis approach – The US probe is positioned perpendicular to the radial artery, demonstrating a pulsatile dark (hypoechoic) circular structure that is cannulated "out-of-plane" of the image. The probe is held such that the tip of the needle is visualized during the procedure, requiring the operator to move the probe more proximally as the needle is advanced. A properly calibrated center-line marking or the use of acoustic shadowing created by sterile external material attached to the probe further improves first-pass success rate for experienced practitioners [17].

●Long-axis approach – The US probe is positioned longitudinal to the radial artery such that both the vessel and the needle/catheter are continuously imaged "in plane" during the procedure.

The use of US guidance for pediatric arterial cannulation is supported by clinical trials and meta-analyses [20]. In a meta-analysis of eight trials including 708 children who were randomly assigned to have the procedure performed with or without US guidance (in most trials, palpation alone was used as the control; one trial used auditory Doppler guidance), the first-attempt success rate was higher in the US group (49 versus 24 percent; relative risk [RR] 2.01, 95% CI 1.64-2.46) as was the overall success rate (80 versus 61 percent; RR 1.32, 95% CI 1.10-1.59) [20]. The mean number of attempts was lower in the ultrasound group (1.1 versus 2.1 attempts per procedure). In addition, fewer patients in the US group developed hematomas at the puncture site (6 versus 22 percent; RR 0.14-0.47). Most of the trials in the meta-analysis (seven of eight) involved infants and children undergoing arterial catheterization in the operating room in preparation for cardiac surgery. All eight trials were unblinded.

The benefit of US-guided arterial cannulation may be especially pronounced in infants and young children and when performed by trained and experienced providers. However, US guidance may also facilitate learning of the procedure as well. For 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 associated with shorter procedure time (average time 8 versus 17 minutes, respectively) and number of attempts (average number 3 versus 7, respectively) [18].

Complications — Complications of arterial cannulation in children are rare but can include (in descending order of frequency) 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 [22,23]. The risk of arterial obstruction is increased with younger patient age and longer duration of cannulation [24]. 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% 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 [25-27]. 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 [2,6,28]. 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 can lead to significant morbidity. (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 [2,28,29]. 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 longer 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 intra-arterial access.

Arterial thrombosis and embolism — Remove the arterial catheter and promptly consult a vascular surgeon in patients with [2]:

●Signs of focal compromised distal circulation (eg, decreased or absent pulse, blanched or mottled skin, delayed capillary refill, cold distal extremity)

and

●Arterial thrombosis or embolism on imaging (eg, Doppler US, angiography, magnetic resonance imaging)

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 [2,7,29-31]. Arterial thrombosis is common with radial artery catheters, but embolic complications (eg, skin necrosis, permanently compromised circulation, amputation) are rare (<1 percent) [7,29].

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 [8,31].

Embolization of thrombi from smaller arteries (radial, dorsalis pedis) may cause digital emboli with distal discoloration, skin necrosis, and, rarely, amputation [2]. Emboli from the femoral artery may also produce distal limb ischemia and lead to injury or amputation [31]. Pulses distal to these sites should be monitored regularly. In addition, arrest of the growth plate resulting in skeletal deformity in adolescence has been reported after arterial cannulation of the femoral, brachial, and radial arteries in infancy [23]. Patient-related factors (eg, shock, peripheral vascular disease, Raynaud phenomenon, systemic vasoconstrictor therapy) may also increase the risk of embolic complications [2,32].

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

●When possible, perform arterial cannulation in the distal radial or ulnar sites. (See 'Site selection' above.)

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

●To increase the success rate on the first attempt and avoid excess trauma during arterial cannulation, use US guidance and, in patients undergoing cannulation by the transfixion method, a guidewire. (See 'Ultrasound guidance' above and 'Transfixion (through-and-through) method with guidewire' above.)

●Provide a continuous flush with heparinized saline (eg, 1 to 2 units heparin/mL at 3 mL of flush solution per hour) [2,33]. 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 [34].

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). Careful attention should be paid to the pressure utilized when flushing catheters to avoid cerebral embolism [2,35].

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 through a vented filter cap 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 rapidly analyzed to reduce oxygen consumption by leukocyte metabolism. In settings in which more than 15 to 30 minutes pass between sample collection and analysis, the sample should be placed on ice. 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 is usually 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 does 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 are highly accurate, with the most accurate value being the mean arterial pressure, which is minimally affected by over- or under-dampening. In non-shock states, the systolic blood pressure measured via the arterial line is frequently increased due to the alteration in pulse contour as the pressure wave moves more 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 intra-arterial blood gas monitors have been used successfully in infants and children [36-39]. 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 [40]. 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 [38].

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 – Skin infection at the procedure site is the primary contraindication to arterial puncture or cannulation. (See 'Indications, contraindications, and precautions' above.):

●Arterial puncture – The distal radial artery is the usual site for arterial puncture (figure 1). Alternative sites include the ulnar, posterior tibial (figure 2), dorsalis pedis (figure 3), femoral (figure 4), or brachial 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 infiltration of local anesthetic; in addition, use the smallest gauge needle that is appropriate for the child's weight or a needleless delivery system. (See 'Pain control' above.)

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

●Arterial cannulation – The distal radial artery is also the usual site for arterial cannulation (figure 1). Alternative sites include the ulnar, femoral, posterior tibial, and dorsalis pedis arteries. 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' 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 suggest ultrasound (US) guidance whenever equipment and expertise are available (Grade 2B). Use of US for arterial cannulation decreases the number of attempts and increases procedural success with a lower risk of complications. (See 'Ultrasound guidance' above.)

The proceduralist may use either the direct or transfixion (through-and-through) method. The transfixion method requires use of a guidewire (figure 8); the direct method may be performed with or without a guidewire. (See 'Transfixion (through-and-through) method with guidewire' 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