Chapter 57. Arterial Puncture and Cannulation

Arterial blood gas (ABG) sampling is an essential component of the care of many Emergency Department patients. It provides key information regarding a patient's oxygenation and acid-base status. Arterial cannulation allows for continuous and accurate blood pressure monitoring and frequent blood gas sampling in the care of the critically ill patient.

Knowledge of the arterial anatomy is a key factor in the success of arterial puncture and cannulation. It is important to recognize that nerves and veins are located in close proximity to the desired arteries in order to avoid complications. The anatomy and positioning for radial, brachial, femoral, and dorsalis pedis artery access is described below.

Radial Artery

The radial artery is the preferred site for arterial puncture and cannulation. One reason is the comparative ease of identifying the anatomical location of this artery. A second reason is the collateral nature of the arterial blood supply to the hand provided by the radial and ulnar arteries. The ulnar artery is not often used due to its smaller size. Terminal branches of these two arteries meet in the palm of the hand to form the deep and superficial palmar arterial arches (Figure 57-1).

The radial artery can be found just medial and proximal to the radial styloid process on the ventrolateral wrist (Figure 57-1). Dorsiflexing the wrist approximately 60° can aid in palpating the arterial pulse. Another notable landmark is the flexor carpi radialis tendon that runs immediately medial to the radial artery. The recommended point of needle or catheter insertion is at the proximal flexor crease of the wrist and directly above the radial artery pulse.

An Allen test should be performed to assess the adequacy of the collateral circulation to the hand prior to radial artery puncture or cannulation (Figure 57-2).1,2 Ask the patient to repeatedly close their hand tightly into a fist and open it, to force blood out of the fingers, while manually occluding the radial and ulnar arteries (Figure 57-2A). Continue this process for 1 minute. Ask the patient to open their hand. The fingers should be blanched and pale due to the occlusion of the arterial inflow. Release the finger occluding the ulnar artery. Measure the time it takes for blushing of the palm to occur. It is considered normal if it is <7 seconds, equivocal at 8 to 14 seconds, and abnormal if >14 seconds.1 Repeat the test, but this time release the radial artery compression to confirm arterial flow into the hand (Figure 57-2B). The purpose is to confirm arterial inflow from both the radial and ulnar arteries.

An alternative method of evaluating the collateral circulation involves the use of a pulse oximeter with a visual pulse waveform display.3 This is useful in the young, unconscious, or uncooperative patient. Place the pulse oximeter sensor on the patient's thumb. Observe the visual display to confirm a waveform is present. Occlude the radial artery and examine the waveform on the monitor. Either an ulnar dominant system or a radial dominant system with adequate collateral circulation is likely if the waveform remains unchanged during radial artery occlusion.3

The performance of an Allen test to confirm adequate collateral circulation to the hand is generally advocated before radial artery puncture or cannulation. There is concern that radial artery occlusion from an intraluminal clot or an external hematoma can result in hand ischemia if the ulnar artery cannot provide adequate collateral blood flow. Some authors have questioned the utility of performing an Allen test.1,2,4,38 The Allen test is subjective, often improperly performed, and has poor sensitivity and specificity to predict complications.39 The relative safety of radial artery cannulation without the Allen test has been demonstrated in a large case series of patients without major peripheral vascular disease.4 Although an abnormal Allen test may not preclude radial artery puncture or cannulation, it may indicate a greater need for caution and alert the Emergency Physician to potential problems after the procedure is performed.2 This can include arterial thrombosis, hand ischemia, and hand necrosis. Thus it is recommended, but not required, to cannulate another site if the Allen test is abnormal.

Brachial Artery

The brachial artery courses along the medial side of the antecubital fossa just lateral to the median nerve (Figure 57-3). The brachial artery divides at approximately the level of the neck of the radius to become the ulnar and radial arteries. In the antecubital fossa, the brachial artery is located lateral to the medial epicondyle of the humerus and medial to the biceps brachii muscle. The brachial artery is more easily identified when the elbow is fully extended. In order to locate the artery, start by palpating the medial epicondyle of the humerus. Move laterally until the medial edge of the biceps muscle is palpated. The brachial artery pulse should be palpable just medial to the biceps muscle. The arterial pulsation is most easily identified at the level of the proximal flexor crease of the antecubital fossa. The preferred location for puncture or cannulation of the brachial artery is in, or just proximal to, the antecubital fossa and directly above the brachial artery pulse. If the artery is to be cannulated, the arm should remain in extension while the cannula is in place.

Femoral Artery

The bony anatomic landmarks used to identify the femoral artery are the anterior superior iliac spine and the tubercle of the pubic symphysis. The artery lies approximately midway between these two points after it courses under the inguinal ligament to enter the thigh (Figure 57-4). The femoral nerve and vein are found running in parallel and adjacent to the artery. The vein lies just medial to the artery and the nerve just lateral. The femoral artery is larger than other arteries commonly cannulated and lies significantly deeper than the radial or brachial arteries. This makes it necessary to use a longer cannula and, depending on the patient's body habitus, may require a longer needle for a simple arterial puncture to be successful. Extension and slight abduction of the hip maximizes access to the femoral triangle, improves the ability to palpate the artery, and provides a maximal work area for the procedure.

Dorsalis Pedis Artery

The dorsalis pedis artery is a continuation of the anterior tibial artery on the dorsal surface of the foot. Puncture and cannulation of the dorsalis pedis artery is a good second choice if the radial artery is unsuccessfully cannulated or unavailable. The pulse is often easily palpable between the first and second metatarsal due to its superficial location. Its distal location does not interfere with other resuscitative efforts and is convenient for the patient. The risk of foot ischemia is minimal due to the abundant collateral circulation to the foot and ankle. There are no significant structures to injure adjacent to the dorsalis pedis artery. This artery can be absent in some people or have significant variability in its anatomic location. It may be difficult to identify the pulse in the hypotensive patient.

Alternative Arterial Sites

There are several alternative sites that are occasionally used for arterial puncture and cannulation. These include the superficial temporal artery, the axillary artery, and the ulnar artery. The superficial temporal artery is often used in neonates and young infants in the intensive care unit. Cannulation of this artery is rarely performed in the Emergency Department because of its location and the ability to maintain access.

The axillary artery is a continuation of the subclavian artery after the first rib. The axillary artery crosses the teres major tendon to enter the arm as the brachial artery. The axillary artery can be deep to the skin surface. The advantages of this artery include the ease of locating a the palpable pulse, even in the hypotensive patient. An accurate blood pressure, devoid of the effects of vasoconstriction, can be obtained. Unfortunately, the disadvantages of cannulating the axillary artery are significant. The axilla is poorly accessible. The patient's arm must be abducted, externally rotated, and immobilized during and after the procedure. The course of the artery changes with arm position. The artery is contained within the axillary sheath along with the axillary vein and brachial plexus. There is a significant risk of nerve injury if the needle penetrates the brachial plexus. The risk of an arterial embolus is higher in central arteries when compared to peripheral arteries.

The ulnar artery, along with the radial artery, is one of the terminal branches of the brachial artery. It is superficial at the wrist and the pulse is easily palpable. The ulnar artery is significantly smaller in most people when compared to the radial artery, making the procedure more technically difficult. An ulnar artery may be absent or extremely small in some patients. The ulnar artery lies adjacent to the ulnar nerve. This increases the possibility of nerve injury if the needle penetrates the ulnar nerve. It can be difficult to identify the artery in the patient with anasarca, obesity, peripheral edema, or peripheral vascular disease.

The principal indications for arterial blood sampling include the determination of the blood carbon dioxide (CO2) content, oxygen (O2) content, and acid–base status.5,6 The need for ABG sampling for determination of oxygenation has decreased substantially with the advent of pulse oximetry. Pulse oximetry may poorly reflect true oxygenation in the setting of severe hypoxia or severe hypotension. Therefore, ABG analysis persists as the true measure of arterial oxygenation.7 End-tidal CO2 (ETCO2) monitoring has decreased the utilization of ABG samples for CO2 measurement. In patients who have large dead space ventilation or low cardiac output, ETCO2 measurements may grossly underestimate the true CO2 contents of the blood.8

Arterial blood gas samples are useful for accurate pH monitoring of patients with shock, obstructive lung disease, and other pulmonary disorders. Possibly the most important indication for ABG sampling in the critically ill patient is the determination of the patient's acid–base status. Venous sampling may occasionally suffice for monitoring the pH in a few illnesses such as diabetic ketoacidosis.9 The measurement of venous blood pH is much less reliable as a surrogate for arterial pH in patients with shock and other critical illnesses.10 Arterial blood samples are still used for the measurement of carboxyhemoglobin and methemoglobin level. One study found that venous and arterial co-oximetry carboxyhemoglobin values are closely correlated and may be used to screen a patient thought to have been exposed to carbon monoxide.11

The three principal indications for arterial catheter placement are the need for continuous monitoring of arterial blood pressure, the need for frequent ABG sampling, and the need for frequent blood sampling for laboratory analysis in the critically ill patient. Cycled oscillometric blood pressure measurement may be insufficient to gauge rapid hemodynamic changes in critically ill hypertensive or hypotensive patients. Continuous blood pressure monitoring facilitates titration of rapid-acting vasodilators and vasopressors. The accuracy of auscultated or oscillometric blood pressure readings under conditions of severe shock or malperfusion are suspected.1,2 Centrally measured aortic pressure is the true gold standard.1,2 However, given the impracticality of measurement of aortic pressure, peripheral arterial pressure measured with an intraarterial catheter connected to a pressure transducer is the next best gauge.

Contraindications to arterial puncture and catheter placement relate primarily to abnormalities at the insertion sites. Avoid skin and arteries that are already compromised by trauma, burns, infection, severe dermatitis, severe peripheral vascular disease, or previous surgery in the area.1,5 Puncture or cannulation of synthetic vascular grafts is also relatively contraindicated. Do not puncture where the artery “should be” if the arterial pulsation cannot be palpated. Attempts at cannulation of nonpalpable arteries are generally fruitless and sometimes hazardous. Arterial puncture or catheterization is relatively contraindicated in patients with bleeding diatheses and those who have received, or may receive, thrombolytic therapy.

Arterial Puncture for Single ABG Sample

• Povidone iodine or chlorhexidine solution
• Dorsal wrist extensor splint or small rolled up towel
• 1% lidocaine, 1 mL in a tuberculin syringe
• 5 mL syringe for blood collection with cap retained
• Prepackaged blood gas syringe with lyophilized heparin pellet
• 20 to 22 gauge needle for arterial puncture
• 1 to 2 mL of heparin (1000 U/mL)
• Gauze pads
• Adhesive tape
• Specimen collection bag or cup with 2 to 3 inches (in) of ice

Arterial (Brachial, Radial, Dorsalis Pedis) Cannulation

• Povidone iodine or chlorhexidine solution
• Dorsal wrist extensor splint or small rolled up towel
• 1% lidocaine, 1 mL in a tuberculin syringe
• 4 × 4 gauze squares
• Adhesive tape
• Nylon suture, 3-0 or 4-0 and needle drivers
• 20 or 22 gauge, 1¾ in polyurethane angiocatheter or catheter-over-the-needle
• 0.45 mm diameter, 5¼ in spring wire guide compatible with above catheter

Femoral Artery Cannulation

• Povidone iodine or chlorhexidine solution
• 1% lidocaine, 3 mL in a syringe armed with a 25 gauge needle
• 4 × 4 gauze squares
• #11 scalpel blade
• Nylon suture, 3-0 or 4-0 and needle drivers
• Femoral artery needle, approximately 18 gauge, 2 7/8 in.
• 4 French single lumen catheter, at least 15 cm in length
• 30 cm guidewire compatible with above needle and catheter

Ultrasound Guidance

• Ultrasound machine
• 5 to 10 MHz linear array ultrasound probe
• Sterile ultrasound gel
• Sterile ultrasound probe cover

If a syringe that has not been designed specifically for ABG sampling is used, and it has not been pretreated with heparin or does not contain a lyophilized heparin pellet, it is necessary to prepare the syringe using heparin solution. Draw up 1 to 2 mL of heparin solution into the syringe and then expel the heparin, leaving only the heparin remaining in the dead space of the syringe and the needle. This amount of heparin is sufficient to prevent clotting of the sample.5 It is important to remove all but the necessary amount of heparin as excess heparin has been found to falsely lower the PCO2 measurement and may elevate the PO2 measurement.37

Commercially produced, prepackaged kits are available for arterial puncture and arterial cannulation. These kits are complete and contain all the required equipment. Also available are individually packaged heparinized ABG syringes and arterial line catheters in various sizes.

The catheter size used for the procedure will vary by patient age and the artery chosen to cannulate. In neonates and infants, use a 22 or 24 gauge catheter for the radial or dorsalis pedis arteries and an 18 or 20 gauge for the femoral artery. In children up to 8 to 10 years of age, use a 22 gauge catheter for the radial or dorsalis pedis arteries and a 16 to 20 gauge for the femoral artery. In a larger child, adolescent, or adult, use a 20 or 22 gauge catheter for the radial or dorsalis pedis arteries and a 14 to 20 gauge for the femoral artery.

Explain the procedure, its risks, and benefits to the patient and/or their representative. Obtain an informed consent unless the procedure is being performed emergently or the patient is unable to give consent. Identify by palpation the arterial pulse at the intended skin puncture site. Clean the skin of any dirt and debris. Cleanse the skin with chlorhexidine or povidone iodine solution and allow it to dry.

Studies that examined the use of topical anesthetic agents have not shown a benefit that outweighs the delay required to perform the procedure.12 The use of an injectable local anesthetic agent, however, may greatly aid in the process of arterial puncture or cannulation and significantly reduces patient discomfort.13 Infiltrate 1 mL of local anesthetic solution subcutaneously over the brachial, dorsalis pedis, or radial arteries. Infiltrate 2 to 5 mL of local anesthetic solution subcutaneously and into the subcutaneous tissues over the femoral artery. Aspirate before infiltrating the local anesthetic solution to prevent inadvertent intravascular injection.

Descriptions of the anatomy for arterial puncture or cannulation sites are described in detail earlier in this chapter. The preferred site for the initial attempt at arterial puncture or cannulation is the radial artery.1 Begin distally where the pulse is most palpable near the proximal wrist flexor crease. If the first attempt at needle or catheter introduction is unsuccessful, and the pulse is still palpable, reattempt the procedure more proximally along this same artery. The radial artery on the contralateral wrist is also a satisfactory second site for attempted access. Other acceptable second-attempt sites of access include the femoral, dorsalis pedis, and brachial arteries. An attempt at ipsilateral ulnar artery catheterization is not advisable as both limbs of the hand's circulation may be compromised. The discussion below focuses on puncture or cannulation of the radial and femoral arteries as over 90% of arterial punctures or cannulations occur at these sites.1 The use of other sites generally follows the techniques described below for the radial artery with the exception of the regional anatomic differences. Other useable sites include the dorsalis pedis, brachial, posterior tibial, and superficial temporal arteries.

Arterial Puncture for a Single Sample

Position the patient to maximize exposure of the skin surface overlying the chosen artery. For the radial artery, this is best accomplished by dorsiflexing the wrist and supporting this position with a small towel rolled up under the dorsal wrist surface (Figure 57-5). For brachial and femoral artery puncture, ensure that the elbow or hip is extended fully. These positions provide maximum exposure and working area for the procedure. Locate the chosen artery, prep the overlying skin, and infiltrate local anesthetic solution subcutaneously.

Reidentify the pulse by palpation with the nondominant hand (Figure 57-6A). Grasp the heparinized syringe with the dominant hand. Withdraw the plunger of the syringe so that 1 to 3 mL of air space is available in the syringe. This will allow for easier assessment of arterial blood return. Insert the needle at a 30° to 45° angle to the skin and just above the arterial pulse (Figure 57-5). Advance the needle through the skin until blood enters the syringe (Figure 57-6B). The blood flow will generally fill the syringe without necessitating the withdrawal of the plunger in a patient with a brisk pulse. If no blood return occurs, slowly withdraw the needle and watch for blood flow into the syringe. If it is necessary to redirect the needle, it is imperative to first withdraw the needle until the tip is just below the skin surface before changing the angle in order to avoid lacerating the artery or adjacent structures. To minimize the possibility of error due to the presence of heparin, it is necessary to collect at least 1 mL of blood in a prepackaged syringe or 3 mL of blood if preparing your own syringe with heparin.5

Withdraw the needle after the arterial sample has been collected. Apply pressure to the puncture site for 3 to 5 minutes followed by a bandage or gauze dressing. Carefully remove the needle from the syringe if not using a safety needle. Evacuate any air from the syringe and apply a cap on the syringe. Place the syringe on ice for immediate transportation to the laboratory. Recheck the skin puncture site in 5 to 10 minutes to assess for the formation of a hematoma and/or vascular compromise to the distal extremity.

Radial Artery Cannulation: Catheter‐over‐the-Needle-Technique

The most basic method is direct introduction of the catheter-over-the-needle in a manner similar to that of inserting an intravenous catheter (Figures 57-5 & 57-7). This method is as effective as the more specialized wire-guided-catheter technique, except in situations where the pulse is weak, the pulse is absent, or in the hands of more experienced operators.14,15 Clean, prep, and identify the radial artery as described previously. Insert the catheter-over-the-needle at a 30° to 45° angle to the skin and directly over the arterial pulse (Figures 57-5 & 57-7A). Advance the catheter-over-the-needle into the artery (Figure 57-7A). Bright red blood in the hub of the needle indicates that the tip of the needle is within the artery. Advance the catheter-over-the-needle another 1 to 2 mm to ensure that the catheter tip is completely within the arterial lumen. Securely hold the hub of the needle. Advance the catheter over the needle until its hub is against the skin (Figure 57-7B). Remove the needle and confirm pulsatile arterial flow from the hub of the catheter. Free-flowing, pulsatile blood confirms proper catheter placement within the artery. Apply a stopcock or intravenous extension tubing to the hub of the catheter. Secure the catheter to the skin. Apply a dressing to the skin puncture site.

Radial Artery Cannulation: Seldinger-Type, Single Arterial Wall Puncture

The second technique for arterial cannulation is a Seldinger-type technique (catheter-over-the-wire) utilizing one of a number of prepackaged commercially available kits. A commercially available one-piece catheter-over-the-needle kit is very popular (Figure 57-8). As noted previously, these wire-guided catheters have not been shown to increase successful cannulation or reduce the number of attempts except in situations where a weak or absent pulse is present, or with more experienced Physicians.14,15 One study noted that the guidewire can be useful in salvaging an arterial line when a catheter-over-the-needle cannot be effectively advanced.

Open the package, remove the unit, and remove the protective cover over the needle. Advance and retract the guidewire to confirm it moves smoothly and does not get caught on the needle. Retract the guidewire as far back as possible. Identify the arterial pulse with the nondominant hand. Insert the catheter-over-the-needle through the skin and into the artery using a slow and continuous forward motion (Figure 57-8A). A flash of blood in the hub of the needle confirms successful entry through the arterial wall and into the vessel lumen. Stabilize the catheter-over-the-needle.

Advance the guidewire through the needle by pushing the actuating lever as far as possible toward the needle (Figure 57-8B). Immediately stop if resistance is encountered while advancing the guidewire. The guidewire may be within the artery wall or through the artery wall and into the perivascular tissue. Do not try to force the guidewire into the vessel. Do not retract the guidewire. Withdraw the entire unit and apply pressure to the puncture site to prevent a hematoma. Obtain a new kit and repeat the procedure.

Once advanced, the guidewire is successfully within the arterial lumen. Firmly grasp the clear hub of the needle and advance the catheter over the guidewire and into the artery (Figure 57-8C). A rotating motion of the catheter is often helpful to advance it if difficulty is encountered. Securely hold the catheter at the level of the skin. While firmly holding the catheter hub, remove the guidewire, needle, and feed tube assembly as a unit. Free-flowing, pulsatile blood confirms proper catheter placement within the artery. Apply a stopcock or intravenous extension tubing to the hub of the catheter. Secure the catheter by suturing it to the skin or by using commercially available devices that do not require suturing. Apply a dressing to the skin puncture site.

A commercially available Seldinger-type catheter-over-the-needle kit is an alternative to the one-piece unit (Figure 57-9). Open the package and review the equipment it contains. Place the finder needle on the syringe. Withdraw the plunger 1 cm to break the bead of the syringe. Identify the arterial pulse by palpation with the nondominant hand. Insert the needle through the skin and into the artery using a slow and continuous forward motion (Figure 57-9A). A flash of blood in the syringe confirms the successful entry through the arterial wall and into the vessel lumen. Firmly hold and stabilize the needle. Remove the syringe. Advance the guidewire through the needle (Figure 57-9B). The guidewire should advance without resistance. Immediately stop if resistance is encountered while advancing the guidewire. The guidewire may be within the artery wall or through the artery wall and into the perivascular tissue. Do not try to force the guidewire into the vessel. Do not retract the guidewire. Withdraw the entire unit and apply pressure to the puncture site to prevent a hematoma. Obtain a new kit and repeat the procedure.

After the guidewire is inserted, withdraw the needle while leaving the guidewire in place (Figure 57-9C). Do not re-advance the needle as it can shear off the guidewire. Make a 3 mm puncture wound next to the skin puncture site of the guidewire using a #11 scalpel blade to facilitate inserting the catheter (Figure 57-9D). Thread the catheter over the guidewire. Advance the catheter over the guidewire until the hub of the catheter is against the skin (Figure 57-9E). A rotating motion of the catheter is often helpful to advance it if difficulty is encountered. Securely hold the catheter at the level of the skin. Remove the guidewire while firmly holding the catheter hub against the skin. Free-flowing, pulsatile blood confirms proper catheter placement within the artery. Apply a stopcock or intravenous extension tubing to the hub of the catheter. Secure the catheter by suturing it to the skin. Apply a dressing to the site.

Radial Artery Cannulation: Seldinger-Type, Double Arterial Wall Puncture

While localization and needle puncture of the artery are identical in all three techniques, commonly encountered difficulties include threading of the catheter with the first technique and threading of the guidewire into the vessel lumen with the second technique.16 If the needle orifice is merely at the vessel edge, blood may enter and rise up through the needle. However, when trying to advance the catheter, it may get hung up outside the lumen with the catheter-over-the-needle technique.17 The guidewire may not easily pass or may dissect into the vessel wall creating a false lumen when using the Seldinger-type single arterial wall puncture technique. Since pulsatile flow is more easily confirmed prior to the passage of the guidewire, this third technique in which both walls of the radial artery are punctured may offer an advantage in passing the guidewire and catheter into the arterial lumen.

It is imperative that the Emergency Physician assumes a position out of the trajectory line of the catheter to avoid being sprayed with blood when using this technique. This method is also a Seldinger-type technique that utilizes a guidewire separate from the catheter-over-the-needle. Locate the arterial pulse and insert the catheter-over-the-needle into the artery. Immediately advance the catheter-over-the-needle through the posterior wall as confirmed by no blood exiting the needle hub. Withdraw the needle while leaving the catheter in place through the artery. Flatten the angle of the catheter to the skin to less than 30°. Hold the tip of the guidewire poised at the hub of the catheter. Slowly withdraw the catheter with the nondominant hand. Promptly insert the guidewire through the catheter and into the artery when pulsatile blood flow is noted from the hub of the catheter. Advance the catheter over the guidewire and into the lumen of the artery. Withdraw the guidewire and apply a stopcock or intravenous extension tubing. Secure the catheter and apply a bandage or dressing.

This double-puncture technique for cannulation theoretically may be associated with greater vascular damage. The technique should be reserved for instances in which the prior two arterial cannulation techniques have been unsuccessful. However, in an analysis of the complications associated with various techniques of peripheral artery cannulation, investigators found no difference in complications when using this technique.18

Femoral Artery Cannulation

The femoral artery may be cannulated if the radial artery is inaccessible or attempts at cannulation are unsuccessful. A longer catheter, catheter-over-the-needle, and needle is required as the femoral artery is not superficial. Slightly abduct the patient's leg and identify the femoral artery pulse. Prep, drape, and anesthetize the skin and subcutaneous tissues. Maintain the fingers of the nondominant hand on the arterial pulse. Insert the needle or the catheter-over-the-needle at a 45° angle to the skin with the needle bevel pointing superiorly. The remainder of the technique is as described previously.

Dorsalis Pedis Artery Cannulation

The procedure for cannulation of the dorsalis pedis artery is the same as that described for the radial artery. Clean, prep, and plantar flex the foot. Do not plantar flex the foot more than 45° as this can stretch and occlude the artery. The needle angle of entry should be less than that used for the radial artery due to the superficial location of the artery. Insert it at 20° to 30° to the skin rather than 30° to 45°.

Ultrasound-Guided Arterial Cannulation

Ultrasound can be used to guide arterial puncture or cannulation. It can be a rescue method if the palpation technique fails. It can also be used initially to decrease the number of puncture attempts, to decrease the amount of time spent gaining access, and to potentially decrease complications such as hematomas and arterial laceration.19,20 Most studies have focused on radial artery cannulation, but the technique for alternative sites is the same.

Clean and prep the skin over the artery. Apply a sterile probe cover or a sterile glove over the linear array ultrasound probe. Orient the probe marker on the side of the probe so it matches that on the screen. Identify the artery. It will appear as a round, thick-walled, and pulsatile vessel that is not easily compressible (Figure 57-10A). Move the probe proximally and distally over the artery to approximate its course, which is sometimes not perfectly parallel to the long axis of the extremity. Once the vessel has been identified, center it on the screen. The center of the probe is now directly over the vessel and can act as a guide to skin puncture. Hold the probe with the nondominant hand or have an assistant hold the probe. Insert the catheter 1 to 2 cm distal to the probe. When the needle is into the subcutaneous tissue, rock it in and out very slightly to create movement that is apparent on the screen. This will help to identify the location of the needle in relation to the artery. Slowly advance the needle. The needle itself may or may not be apparent, but motion through the tissue can be used to infer the site of the needle tip.

When the needle reaches the artery, it will dimple the wall of the artery. Advance the needle slowly while watching for the flash of blood in the needle hub. Once the flash is seen, ultrasound can be used to confirm placement of the needle and/or catheter within the artery (Figure 57-10B). Proceed from this point with either the catheter-over-the-needle or the Seldinger-type technique to complete the procedure.

A cutdown technique may be performed to cannulate an artery. It is primarily used for the brachial or radial arteries but may be used to access other peripheral arteries. This technique is rarely required with the availability of ultrasound to locate an artery The technique is briefly described here. Please refer to Chapter 54 for more complete details.

Clean, prep, anesthetize, and drape the skin overlying the chosen artery. Make a 1.5 to 2.0 cm transverse skin incision centered over the artery. Do not cut into the subcutaneous tissue so that blood vessels, nerves, and tendons are not transected. Spread the subcutaneous tissues parallel to the artery with a mosquito hemostat. Expose 1.0 cm of the length of the artery. Pass a silk suture under the proximal end of the exposed artery. Insert a catheter-over-the-needle through the skin just distal to the incision and advance it into the incision. Elevate the suture to control the artery and occlude distal blood flow. Advance the catheter-over-the-needle into the artery. Release the suture and advance the catheter into the artery. The remainder of the procedure is as described previously. Apply pressure over the incision site for 5 to 10 minutes to prevent the formation of a hematoma or seroma.

Apply direct pressure for 3 to 5 minutes to the skin puncture site after an arterial puncture or removal of an arterial catheter. Apply direct pressure for 10 minutes or more if the patient has a bleeding diathesis or has received thrombolytic therapy. Apply a bandage or gauze dressing to the skin puncture site. Reassess the skin puncture site in 15 minutes for continued bleeding or hematoma formation.

An arterial catheter must be secured to the skin to prevent inadvertent dislodgement, hematoma formation, and exsanguination. Sew the hub of the catheter to the skin using 3-0 or 4-0 nylon sutures. Apply a protective dressing over the site. A splinting device should be used to secure the limb in the desired position for optimal monitoring if the catheter is in the wrist, arm, or foot. Monitor the site regularly to assess for signs of bleeding, infection, hematoma, arterial thrombosis, or catheter dislodgement. It is also important to assess the extremity distal to the catheter for evidence of ischemia. Replace the dressing regularly in accordance with your institutional guidelines.

Flush the arterial catheter with sterile saline solution. In the past, heparinized saline was the standard arterial line flush solution. The use of heparinized saline has not been shown to improve functionality, prevent thrombotic complications, or increase the duration of catheter patency when compared to saline.40 The use of heparin risks an adverse reaction or heparin-induced thrombocytopenia.

Arterial puncture and catheterization are generally safe procedures with an incidence of clinically significant complications under 5%.1 The primary complications of arterial catheterization are infection, bleeding, arterial injury, and thrombosis.2,21–30 While secondary bacteremia and septic emboli may occur, infection is usually limited to the site of catheterization. The risk of catheter site infection is linearly related to the length of time the catheter is in place.2 The infection rate is similar for both femoral and radial artery sites.2,23,31–33 Nerve injury from direct puncture of the nerve has been reported in connection with arterial puncture or cannulation.34 Multiple cases of neuropathy have occurred as a result of a hematoma formation and subsequent nerve compression.35 In order to minimize hematoma formation after arterial puncture or arterial catheter removal, apply at least 3 minutes of direct pressure to radial, brachial, and dorsalis pedis puncture sites and 5 to 10 minutes of pressure to the femoral site.34,36 Although small hematomas are common after arterial puncture, major bleeding is unusual and generally occurs only in the concealed retroperitoneum after femoral artery puncture or cannulation. Angiographically demonstrable thrombosis is common (25% to 40%) after prolonged arterial catheterization.2 This rarely results in clinically significant morbidity. Secondary limb ischemia and necrosis requiring amputation occur in less than 1:2000 arterial catheterizations.2 Other rare complications include the formation of a pseudoaneurysm or arteriovenous fistula.

The complications associated with an arterial catheter can be limited. Only insert an arterial catheter if it is truly needed. Always insert it using strict aseptic technique. Remove the catheter as soon as it is determined it is no longer required to assist in the management of the patient. Frequently check the skin puncture site for signs of bleeding, a hematoma, and infection. Frequently assess the distal extremity for signs of perfusion. Remove the catheter at the first sign of a complication. Place the catheter in the patients' nondominant hand, if known, to limit the impact of any complications.

Arterial puncture and cannulation are quick, safe, and simple to perform. Arterial blood sampling may aid in determining the ventilator and acid–base status of critically ill patients. An arterial catheter is appropriate in patients who need continuous monitoring of arterial blood pressure or frequent ABGs. Arterial puncture and cannulation should be avoided in skin areas with evidence of burn, trauma, infection, severe dermatitis, or severe peripheral vascular disease. Palpation of the arterial pulse and correct anatomical positioning are necessary before these procedures are attempted. It is necessary to monitor the cannulated site for signs of bleeding, hematoma, thrombosis, or infection. After an arterial puncture or removal of an arterial catheter, it is necessary to apply direct pressure to the skin puncture site to prevent the formation of a hematoma.