Arterial catheterization is a procedure that is common to the intensive care settings and the operating room. It involves placement of a catheter into the lumen of an artery to provide at least a continuous display blood pressure with access to frequent arterial blood sampling. The discovery of the arterial waveform by insertion of a catheter into an artery dates to 1847 by the German Physiologist Carl Ludwig. More recently, the widely known Seldinger technique has been adopted by guiding catheter into a vessel over a wire previously inserted into the lumen or the artery. With knowledge of anatomy, various sites of insertion are available. However, practitioners must be mindful of indications and contraindications, proper preparation of equipment and personnel as well as the technique of insertion. As all invasive procedures, the placement of arterial catheters may present complications, with an advised operator who must be ready to intervene promptly to prevent unnecessary harm to the patient.
The arterial pulse may be palpated in the extremities and the neck. With the knowledge of the contour of these vessels, the operator may easily identify the location of the artery. The anatomy of every site of insertion must be analyzed to determine the landmarks, the depth, the relationship to adjacent anatomical structures, and the size of the artery. 
The radial artery is superficial in the thenar area of the wrist where the radial bone joins the metacarpal bones. There, the radial pulse is best felt slightly medial to the extensor tendons of the thumb. The radial artery is a preferred site of insertion.
The ulnar artery is opposite to the radial pulse in the volar aspect of the wrist at the joint of the ulnar bone to the metacarpal bones. The artery divides into 2 branches, both of which join a similar division of the radial artery to form a rich, collateral network known as the deep and superficial palmar arch. The ulnar artery is smaller and not as readily palpable as the radial artery. It is used less commonly but may be accessed situations where other options have been exhausted.
The axillary artery rises to the superficial area of the axilla in its course through the pectoralis minor muscle which is delineated best while the arm is in the abduction. The pulsation of this large vessel can be palpated slightly lateral to the belly of the pectoralis major muscle into the axilla. The axillary vein hugs the artery very closely flowing on the medial aspect of the later. Both vessels are enveloped by branches of the brachial plexus as they all branch into different structures of the arm. The access and maintenance of the axillary artery require abduction of the arm. It may be used when peripheral options have failed. The axillary artery is near the thoracic wall and provides a central pressure waveform as it is advanced further into the subclavian artery.
The brachial approach of placing arterial catheters is traditionally considered problematic and prone to complication because of the paucity of arterial collateral circulation. It should not be accessed for cannulation to avoid the risk of ischemic injury to distal part of the extremity.
The pulse of the dorsalis pedis artery is readily felt on the bony prominence of the navicular bone at the mid-dorsal aspect of the foot. The operator reaches the artery as if performing a venipuncture aiming directly at the pulsation. There is ample collateral circulation of this artery making it a preferred access site of the lower extremity.
The posterior tibial artery is the second major arterial supply to the food running posterior to the medial malleolus in a groove that is bordered by the Achilles tendon posteriorly. There is a higher potential for occlusion of this artery because of its smaller caliber as compared to the dorsalis pedis artery.
The femoral artery gives the largest arterial supply of the lower extremity. The pulsation of this major vessel is a well-known landmark in juxtaposition to the femoral vein. The location of this pulse divides the inner third of the inguinal ligament to the outer two-thirds. The femoral artery is the single trunk that perfuses the lower extremity as it divides into 4 major branches as it wraps around the structures of the thigh. There are no other major collateral vessels for the arterial supply of the lower extremity. Therefore, complete obstruction of the femoral artery leading to ischemia may have devastating consequences.
The superficial temporal artery rises from the external carotid artery from the neck toward the temporal aspect of the skull anterior to the earlobe.
The umbilical artery can be visualized only for a few days after birth, while the umbilical stump has not yet involuted. A clean section of the umbilical stump readily displays 2 arteries and one larger thin-walled vessel representing the umbilical vein. During the first week after birth, the umbilical arteries are accessible, joining the iliac arteries respectively and the aortic artery subsequently.
In intensive care settings, various clinical situations require continuous monitoring of the arterial blood pressure in addition to a frequent sampling of arterial blood for the analysis of the partial pressure oxygen, carbon dioxide, and pH determination. This is particularly important when vasoactive medications are being administered and the minute to minute evaluations are necessary for the clinician to make decisions in the titration of these medications. The systolic, diastolic, and mean arterial blood pressure are readily displayed on the monitoring system using a transducer device that is attached to a non-compliant tubing system. On occasion, lifesaving procedures require the pressure of arterial blood flow to perfuse an extracorporeal circuit. A common practice is to insert an arterial catheter for continuous arterio-venous hemoperfusion, or dialysis. Other indications include cardiac catheterization and radiological interventional procedures, manual or automated exchange transfusions, plasmapheresis and extracorporeal membrane oxygenation. Some of these modalities require a surgical approach to the placement of arterial catheters.
Clinicians must proceed carefully to minimize the risk of serious complications that may occur with the presence and placement of an arterial catheter. Advance knowledge of contraindications to the placement of an arterial catheter can prevent such adverse events. Contraindications include peripheral or distal arterial vascular insufficiency, peripheral arterial vascular diseases (medium to small vessel arteritis), anatomical variants in which there may be a lack of collateral circulation (absence of the ulnar artery), infection at the site of insertion. Special consideration should be given in cases of coagulation disorders and situations of medical anticoagulation, burns and surgical interventions at the site of insertion.
Before the procedure, the gathering of equipment and infection control barrier bundle at the bedside is necessary. Commercially bundled kits are available to minimize the time required to search for the various gadgets. Additionally, these kits help with adherence to evidence-based essential steps to minimize the risk of catheter-related infection during the insertion. At a minimum, these include the appropriate-sized arterial catheter and the corresponding search needle that usually is available in an arterial catheter package that includes lidocaine, gauze tissue, sterile gloves, mask and gowns, and chlorhexidine solution for aseptic cleansing. The transducer, connecting tubing and monitor cable system must be available before the insertion of the catheter. The waveform obtained after connecting the arterial catheter ensures the successful placement in the lumen of the artery.
The placement of an arterial catheter requires at least one other helper in addition to the operator. This additional personnel will help with the non-sterile aspects of the procedure and the general circulating tasks. If the patient requires sedation during the procedure, another practitioner will administer and monitor that aspect of the procedure.
The placement of an arterial line requires careful planning to minimize the risk of complications for this invasive procedure. Before engaging in the insertion of the catheter, the intensive care team is encouraged to use a check-list often called a bundle to review the items that will be necessary during the insertion including the connectors and transducers for infusion. The team also performs a “time out” procedure in which everyone involved in the procedure stops to verify the identity of the patient and to confirm the site of insertion and make sure they have all the required equipment. The proper aseptic technique includes hand washing, wearing of sterile gloves, cleaning the area with chlorhexidine, and application of sterile covering of the site of insertion with a bio-occlusive tape allowing for a small opening for the proposed site of insertion. After that, the point of puncture may be determined by palpation, doppler auditory assistance, or ultrasound guidance.
Prior to the placement of the arterial catheter, the operator must have knowledge of the anatomical location of the arterial vessel. The direct palpation of the arterial pulse is evidence of finding the proper location for the procedure. Following the routine preparation, the operator may proceed with direct puncture of the artery with the chosen device. The angle of insertion will vary depending on the site of arterial insertion, and the degree of difficulty will also be determined by the depth of the artery in the subcutaneous tissue.
The Allen Test
This is a traditionally well-known procedure done prior to the insertion of a radial arterial catheter. The goal of this test is to provide assurance that the collateral ulnar arterial blood flow is sufficient to avoid distal ischemic injury. Both radial and ulnar pulses are occluded forcefully by manual palpation for 10 to 15 seconds or until blanching of the palm are noted. The ulnar arterial occlusion is released. If the blanching resolves quickly, the patency of the ulnar artery is enough to perfuse the hand in spite of a complete or partial occlusion of the radial artery.
Doppler Auditory Assistance
In addition to palpating the arterial pulse, an auditory doppler device can aid the operator in refining the point of entry for the access needle. This device may be particularly helpful in situations of low blood pressure when feeble pulsations make the arterial pulse localization difficult.
The use of ultrasound guidance during the procedure for radial, arterial-line placement has been associated with a high success rate. The number of attempts prior to the success of the procedure reduced significantly. We strongly suggest the addition of this modality for infants and small children because the repeated attempts may increase the complication and the rate of success was even higher in this age group. In addition, the measurement of the arterial internal diameter by sonography may inform the operator on the most appropriate catheter size. This measurement may be particularly important in pediatric patients because of the different artery caliber expected in neonates, small infants, and older children. Ultrasound-guided artery cannulation has now become the standard of care.
This approach allows the operator to gain access of the arterial lumen with the help of a guidewire. After localization of the pulse by palpation, doppler or ultrasound guidance, the vessel is punctured with an introducer needle. Once the pulsatile blood flow is detected, the guidewire is quickly inserted into the hub of the needle to gain access to the artery. Once sufficiently advanced, the introducer needle is removed. The opposite end of the guidewire is threaded into the sharp or distal end of the arterial catheter, sliding it until it is completely flush with the skin. The guidewire is removed inspecting for complete integrity of the tip. The Seldinger technique is particularly useful for the access of central vessels that run deeper into the extremity.
Catheter Over the Needle
The traditional insertion of typical of inserting a peripheral venous catheter can also be used to access peripheral arteries that run more superficial and readily palpable. After localization, the artery is directly punctured with the catheter-over-the-needle device at the proper angle. Once arterial blood flow is detected, the operator slides the catheter over the needle in a forward motion before removing the needle.
Securing the Arterial Catheter
After the successful placement of the catheter and the connection of the transducer apparatus, the procedure team now engages in the process of securing the catheter to prevent accidental dislodgement, exposure to infection and to minimize excessive motion of adjacent joint that may interfere with the accurate monitoring. This procedure is also useful to increase the longevity of the catheter, avoiding a repeat procedure. Transparent adhesive dressings are preferred for direct visualization of the insertion site. If the wrist is the site of choice, the hand is kept slightly extended with a soft roll fixated between the dorsum of the wrist and a rigid board where the hand and forearm will be fixated. The connection tubing takes a loop around the thumb and is secured a second time to the forearm. To obtain an accurate reading of the blood pressure, the monitoring device must be set to "zero" while the transducer hub is leveled at the height of the atrium.
The placement of an arterial catheter for a small pediatric patient can be daunting. Operators are often challenged with a blood vessel with a caliber of 2 to 3 millimeters in diameter. Therefore, the likelihood of complications must be entertained. The rate of complications has not been well reported for pediatric patients. In contrast, the overall rate of arterial catheter complication in adult patients has been reported to be in the range of 10% to 13%. The largest retrospective analysis of more than 10,000 patients reported similar complication rate (10.3%) in pediatric patients. Among the various complications, catheter-related infection and inflammation were the most common (61.8%). Other others include mechanical complications (14.1%), embolic or thrombotic events (7.5%), amputation for ischemic injury (0.6%). Femoral artery catheter placement has been associated with a higher risk of thrombosis as compared to the radial approach. A higher complication rate is associated with critically ill patients, cardiac surgery, bone marrow transplantation and dialysis. A young age (1 to 4 months), late catheter placement during the hospital course, and systemic infections are additional risk factors for these complications.
The placement of arterial catheters is often necessary for the management of critically ill patients. Procedures common to the intensive care unit and the operating room rely on the access to the arterial vessels. However, multiple complications including catheter-related infections, loss of distal blood flow, and the availability of other modalities for hemodynamic monitoring have decreased the frequency of arterial catheter placement in the intensive care unit. The placement of arterial catheters should not be considered routine in the management of critically ill pediatric patients.
Blood draws from the arterial lines should preferably have some initial blood wasted (usually 1-3 ml depending on the age of the patient and circulating blood volume) to prevent lab errors secondary to fluid being infused through the catheter to keep it patent. It is vital to ensure that for catheter patency there is always fluid being infused through the catheter at 1-3 ml/hour, with or without a pressurized bag system. The infusate fluids that are commonly used are normal saline or normal saline with 1-2 units/ml of heparin. Based on RCT's use of a heparinized solution has not been shown to reduce the risk of catheter thrombosis. 
There have been previous reports of hyperglycemia because of infusion of glucose-containing fluids through the arterial lines, limb ischemia, skin/tissue necrosis due to accidental infusion of medications through the arterial catheter. To avoid this the arterial line should be clearly labeled and the infusing fluids should be thoroughly checked by 2 nurses to prevent any errors.
The perfusion distal to the catheter needs to be monitored ongoingly by bedside nurses and the catheter should be removed if any concerns for ongoing impairment in perfusion arise.
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