Intravascular Catheters

For arterial pressure measurements, short, narrow catheters are recommended (20 gauge or smaller) because they have favorable dynamic response characteristics and are less thrombogenic than larger catheters.¹² Catheters made from Teflon are most widely used because they are softer and less thrombogenic, but they are prone to kinking. An artifact associated with intra-arterial catheters has been designated end-pressure artifact.¹³ When flowing blood comes to a sudden halt at the tip of the catheter, it is estimated that an added pressure of 2 to 10 mm Hg results. Conversely, clot formation on the catheter tip will overdamp the system and narrow the pulse pressure.

Coupling System

The coupling system usually consists of pressure tubing, stopcocks, and a continuous flushing device. This is the major source of distortion of arterial pressure tracings. Hunziker¹⁴ studied the damping coefficients and natural frequencies of various coupling systems. All systems were severely underdamped, and most led to systematic overestimation of the systolic arterial pressure.

Transducers

The function of transducers is to convert mechanical forces into electrical current or voltage. Over the years, this has been achieved by several different mechanisms, but today most transducers are of the resistance type. Pairs of resistors are incorporated into a circuit on the arms of a Wheatstone bridge type of electrical circuit. Most modern disposable transducers have a silicone diaphragm into which resistive elements have been etched. The manufacturers have adopted an output standard of 5 μV per volt excitation per 1 mm Hg so that, theoretically, any transducer can be used with any monitor.¹⁵ The dynamic response of bare transducers is usually in the 100- to 500-Hz range. Modern disposable transducers have eliminated many of the difficulties that used to require frequent recalibration because of drifting of the zero point. The major practical problem remaining with transducer systems is improper zeroing relative to the patient.

Analysis and Display Systems

Most modern equipment designed to analyze and display pressure information consists of a computerized system that handles several tasks. These include the acquisition and display of pressure signals; the derivation of numerical values for systolic, diastolic, and mean pressures; alarm functions; internal data storage; automated data transfer to an anesthesia information management system; trend displays; and printing functions. The algorithms used to analyze the pressure information and to provide numerical data vary among manufacturers. Venous pressures, as well as arterial pressures, to a lesser degree, are significantly affected by respiratory fluctuations.¹⁶ Most display systems average hemodynamic parameters over several cardiac cycles to minimize the effects of respiratory variability.

Flush Systems

The arterial catheter should be kept patent with a continuous infusion of normal saline solution (1 to 3 mL/hr). The infusion minimizes thrombus formation and helps prolong the usefulness of the catheter.¹⁷ Heparin is no longer routinely recommended as an additive to flush solutions because of the risk for heparin-induced thrombocytopenia in susceptible patients.

Characteristics of a Pressure Measurement System

The dynamic response of a pressure measurement system is characterized by its natural frequency and its damping.¹⁸ These concepts are best understood by snapping the end of a transducer-tubing assembly with a finger. The waveform on the monitor demonstrates rapid oscillations above and below the baseline (the natural frequency), which quickly decays to a straight line because of friction in the system (damping). The peaks and troughs of an arterial pressure waveform will be amplified if the transducer-tubing-catheter assembly has a natural frequency that lies close to the frequencies of the underlying sine waves of an arterial pressure waveform (typically < 20 Hz). This is commonly known as ringing or resonance of the system (Figure 14-2). For an arterial pressure monitoring system to remain accurate at greater heart rates (HRs), its natural frequency should, therefore, be higher, typically more than 24 Hz.¹⁶ In practical terms, longer transducer tubing reduces the natural frequency of the system and tends to amplify the height of the SBP (peak) and the depth of the DBP (trough) values.^17,18 Boutros and Albert¹⁹ demonstrated that, by changing the length of low-compliance (rigid) tubing from 6 inches to 5 feet, the natural frequency decreased from 34 to 7 Hz. As a result of the reduced natural frequency, the SBP measured with the longer tubing exceeded reference pressures by 17.3%.

Figure 14-2 The fast-flush test demonstrates the harmonic characteristics of a pressure monitoring system (i.e., transducer, fluid-filled tubing, and intra-arterial catheter). In an optimally damped system (A), the pressure waveform returns to baseline after only one oscillation. In an underdamped system (B), the pressure waveform oscillates above and below the baseline several times. In an overdamped system (C), the pressure waveform returns to the baseline slowly with no oscillations.

(Adapted from Gibbs NC, Gardner RM: Dynamics of invasive pressure monitoring systems: Clinical and laboratory evaluation. Heart Lung 17:43, 1988.)

Damping is the tendency of factors such as friction, compliant (soft) tubing, and air bubbles to absorb energy and decrease the amplitude of peaks and troughs in the waveform. The optimal degree of damping is that which counterbalances the distorting effects of transducer-tubing systems with lower natural frequencies. This is difficult to achieve. The damping of a clinical pressure measurement system can be assessed by observing the response to a rapid high-pressure flush of the transducer-tubing-catheter system (see Figure 14-2). In a system with a low damping coefficient, a fast-flush test results in several oscillations above and below the baseline before the pressure becomes constant. In an adequately damped system, the baseline is reached after one oscillation, whereas in an overdamped system, the baseline is reached after a delay and without oscillations.^20–23

The formulas for calculating the natural frequency and damping coefficient are as follows:

where d = tubing diameter; L = tubing length; ρ = density of the fluid; V_d = transducer fluid volume displacement; and n = viscosity of the fluid.

Radial and Ulnar Arteries

The radial artery is the most commonly used artery for continuous BP monitoring because it is easy to cannulate with a short (20-gauge) catheter and readily accessible during surgery. The collateral circulation is usually adequate and easy to check. It is advisable to assess the adequacy of the collateral circulation and the absence of proximal obstructions before cannulating the radial artery for monitoring purposes.

The ulnar artery provides most blood flow to the hand in about 90% of patients.²⁸ The radial and ulnar arteries are connected by a palmar arch, which provides collateral flow to the hand in the event of radial artery occlusion. Palm²⁹ showed that if there is adequate ulnar collateral flow, circulatory perfusion pressure to the fingers is adequate after radial arterial catheterization. Some clinicians perform the Allen test before radial artery cannulation to assess the adequacy of collateral circulation to the hand.

The Allen test is performed by compressing the radial and ulnar arteries and exercising the hand until it is pale. The ulnar artery is then released (with the hand open loosely), and the time until the hand regains its normal color is noted.³⁰ With a normal collateral circulation, the color returns to the hand in about 5 seconds. If, however, the hand takes longer than 15 seconds to return to its normal color, cannulation of the radial artery on that side is controversial. The hand may remain pale if the fingers are hyperextended or widely spread apart, even in the presence of a normal collateral circulation.³¹ Variations on the Allen test include using a Doppler probe or pulse oximeter to document collateral flow.^32–34 If the Allen test demonstrates that the hand depends on the radial artery for adequate filling, and other cannulation sites are not available, the ulnar artery may be selected.³⁵

The predictive value of the Allen test has been challenged. In a large series of children in whom radial arterial catheterization was performed without preliminary Allen tests, there was an absence of complications.³⁶ Slogoff et al³⁷ cannulated the radial artery in 16 adult patients with poor ulnar collateral circulation (assessed using the Allen test) without any complications. An incidence of zero in a study sample of only 16 patients, however, does not guarantee that the true incidence of the complication is negligible. In contrast, Mangano and Hickey³⁸ reported a case of hand ischemia requiring amputation in a patient with a normal preoperative result for the Allen test. Thus, the predictive value of the Allen test is questionable. Alternatively, pulse oximetry or plethysmography can be used to assess patency of the collateral arteries of the hand. Barbeau et al³⁹ compared the modified Allen test with pulse oximetry and plethysmography in 1010 consecutive patients undergoing percutaneous radial artery cannulation for cardiac catheterization. Pulse oximetry and plethysmography were more sensitive than the Allen test for detecting inadequate collateral blood supply, and only 1.5% of patients were not suitable for radial artery cannulation.

Another infrequently used method of radial arterial catheterization involves percutaneous insertion of a long catheter to obtain a central aortic tracing of arterial pressure.⁴⁰ No complications were attributed to these catheters in a series of patients.⁴¹ The advantage of a central arterial tracing is the increased accuracy compared with radial arterial pressure in patients with low-flow states or after CPB.^42,43 Although reasons for the difference between central and peripheral measurements of BP are not entirely clear, after CPB, they were transiently present in 17% to 40% of patients in several studies.^11,44–46 Kanazawa et al⁴⁷ suggested that a decrease in the arterial elasticity is responsible for instances in which lower radial artery pressures (compared with aortic pressures) are observed after CPB. When the palpated central aortic pressure is high despite a low radial arterial BP value, the central aortic pressure also may be temporarily monitored using a needle attached to pressure tubing placed in the aorta by the surgeon until the problem resolves. Alternatively, a femoral arterial catheter may be inserted.

Chest wall retractors that are used during internal mammary artery dissection may impede radial arterial pressure monitoring in cardiothoracic procedures in some patients. The arm on the affected side may have diminished perfusion during extreme retraction of the chest wall. If the left internal mammary artery is used during myocardial revascularization, the right radial artery could be monitored to avoid this problem. Alternatively, a noninvasive BP cuff on the right side could be used to confirm the accuracy of the radial artery tracing during periods of chest wall retraction.

Monitoring of the radial artery distal to a brachial arterial cutdown site is not recommended. Acute thrombosis or residual stenosis of the brachial artery will lead to falsely low radial arterial pressure readings.¹⁹ Other considerations related to the choice of a radial arterial monitoring site include prior surgery of the hand, selection of the nondominant hand, and the preferences of the surgeons and anesthesiologists.

Brachial and Axillary Arteries

The brachial artery lies medial to the bicipital tendon in the antecubital fossa, in close proximity to the median nerve. Brachial artery pressure tracings resemble those in the femoral artery, with less systolic aug- mentation than radial artery tracings.⁴⁸ Brachial arterial pressures were found to more accurately reflect central aortic pressures than radial arterial pressures before and after CPB.⁴⁹ The complications from percutaneous brachial artery catheter monitoring are fewer than those after brachial artery cutdown for cardiac catheterization.⁵⁰ A few series of patients with perioperative brachial arterial monitoring have documented the relative safety of this technique.^11,42,50 Armstrong et al⁵¹ published data on 1326 patients with peripheral vascular disease undergoing angiography with percutaneous brachial artery access and found an overall complication rate of 1.28% with a greater risk for thrombosis in female patients. There is little or no collateral flow to the hand if brachial artery occlusion occurs, however. Most clinicians, therefore, choose other sites, if possible.

The axillary artery is normally cannulated by the Seldinger technique near the junction of the deltoid and pectoral muscles. This has been recommended for long-term catheterization in the intensive care unit (ICU) and in patients with peripheral vascular disease.^52,53 Because the tip of the 15- to 20-cm catheter may lie within the aortic arch, the use of the left axillary artery is recommended to minimize the risk for cerebral embolization during flushing. Lateral decubitus positioning or adduction of the arm occasionally results in kinking of axillary catheters with damping of the pressure waveform. Arterial pressures measured in the axillary artery (by radial artery cannulation with long catheters) more closely reflect central aortic BP than brachial arterial BP measurements.⁴⁵

Femoral Artery

The femoral artery may be cannulated for monitoring purposes and typically provides a more reliable central arterial pressure after discontinuation of CPB. Scheer et al⁵⁴ have reviewed the literature on peripheral artery cannulation for hemodynamic monitoring, including 3899 femoral artery cannulations. Temporary occlusion was found in 10 patients (1.45%), whereas serious ischemic complications requiring extremity amputation were reported in 3 patients (0.18%). Other complications that were summarized from the published data were pseudoaneurysm formation (0.3%), sepsis (0.44%), local infection (0.78%), bleeding (1.58%), and hematoma (6.1%). Based on the reviewed literature, they concluded that using the femoral artery for hemodynamic monitoring purposes was safer than radial artery cannulation. Older literature stated that the femoral area was intrinsically dirty, and that catheter sepsis and mortality were significantly increased compared with other monitoring sites. This could not be confirmed in the more recent literature.^55,56

In patients undergoing thoracic aortic surgery, distal aortic perfusion (using partial CPB, left-heart bypass, or a heparinized shunt) may be performed during aortic cross-clamping to preserve spinal cord and visceral organ blood flow. In these situations, it is useful to measure the distal aortic pressure at the femoral artery or a branch vessel (i.e., dorsalis pedis or posterior tibial artery) to optimize the distal perfusion pressure (see Chapter 21). In repairs of aortic coarctation, simultaneous femoral and radial arterial monitoring may help determine the adequacy of the surgical repair by documenting the pressure gradient after the repair. It is necessary to consult with the surgeon before cannulating the femoral vessels because these vessels may be used for extracorporeal perfusion or placement of an intra-aortic balloon pump during the surgical procedure.

Dorsalis Pedis and Posterior Tibial Arteries

The two main arteries to the foot are the dorsalis pedis artery and the posterior tibial artery, which form an arterial arch on the foot that is similar to the one formed by the radial and ulnar arteries in the hand. The dorsalis pedis or posterior tibial arteries are reasonable alternatives to radial arterial catheterization. The SBP is usually 10 to 20 mm Hg greater in the dorsalis pedis artery than in the radial or brachial arteries, whereas the diastolic pressure is 15 to 20 mm Hg lower (see Figure 14-1).⁵⁷ The dorsalis pedis is a relatively small artery that may be cannulated when other sites are not available, but the vessel may not be palpable or present in 5% to 12% of patients.⁵⁸ The incidence rate of failed cannulation is up to 20%, and the incidence rate of thrombotic occlusion is about 8%, because of the small size of the artery.⁵⁹ A modified Allen test may be performed by blanching the great toe during compression of the dorsalis pedis and posterior tibial arteries, and then releasing the pressure over the posterior tibial artery. These vessels should not be used in patients with severe peripheral vascular disease from diabetes mellitus or other causes.

Local Infection

Placement of an arterial catheter through infected tissues is likely to result in catheter sepsis. If signs of infection develop at an existing arterial cannulation site, the catheter must be removed. A separate cannulation site should be found. Strict aseptic technique is necessary during the insertion and maintenance of arterial cannulas.

Coagulopathy

Coagulopathy is a relative contraindication because it may result in hematoma formation during arterial cannulation. It is more difficult to apply direct arterial pressure with failed attempts or when the catheter is removed when using more central cannulation sites. In anticoagulated patients, it is therefore recommended that more peripheral arterial cannulation sites be considered when this form of monitoring is required.

Proximal Obstruction

Anatomic factors may lead to intra-arterial pressure readings that markedly underestimate the central aortic pressure. The thoracic outlet syndrome and congenital anomalies of the aortic arch vessels will obstruct flow to the upper extremities. Aortic coarctation will diminish flow to the lower extremities. Arterial pressure distal to a previous arterial cutdown or cannulation site may be lower than the central aortic pressure because of arterial stenosis at the site of the prior intervention.

Raynaud Syndrome and Buerger Disease

Radial and brachial arterial cannulations are contraindicated in patients with a history of Raynaud syndrome or Buerger disease (i.e., thromboangiitis obliterans). This is especially important in the perioperative setting because hypothermia of the hand is the main trigger for vasospastic attacks in Raynaud syndrome.⁶⁰ It is recommended that large arteries, such as the femoral or axillary, be used for intra-arterial monitoring if indicated in patients with either of these diseases.

Surgical Considerations

Several surgical maneuvers may interfere with intra-arterial monitoring. During mediastinoscopy, the scope intermittently compresses the innominate artery against the manubrium. In this situation, accurate systemic arterial pressure monitoring may be affected if a right-sided upper extremity arterial cannula is used. Regardless of which side is chosen for arterial cannulation, a pulse oximeter probe should be placed on the opposite hand. In case a left-sided arterial catheter is chosen, accurate systemic pressure readings can be monitored and compression of the innominate artery detected by a diminished pulse oximetry signal. Depending on the surgeon’s and/or anesthesiologist’s preference, this setup can be reversed.

The lateral decubitus position may compromise flow to the downward arm if an axillary roll is not properly positioned. In this situation, the damping may be prolonged. Nevertheless, during descending thoracic aortic aneurysm repairs, the right radial, brachial, or axillary artery should be monitored because the left subclavian artery may be occluded during various phases of the procedure.

Direct Cannulation

Proper technique is helpful in obtaining a high degree of success in arterial catheterization. The wrist is often placed in a dorsiflexed position on an armboard over a pack of gauze and immobilized in a supinated position. Overextension of the wrist should be avoided because this flattens and decreases the cross-sectional area of the radial artery⁶¹ and may cause median nerve damage by stretching the nerve over the wrist. A 20-gauge or smaller, 3- to 5-cm, nontapered Teflon catheter over needle is used to make the puncture. If a syringe is used, the plunger may be removed to allow free flow of blood to detect when the artery has been punctured. The angle between the needle and the skin should be shallow (£30 degrees), and the needle should be advanced parallel to the course of the artery. When the artery is entered, the angle between the needle and skin is reduced to 10 degrees, the needle is advanced another 1 to 2 mm to ensure that the tip of the catheter also lies within the lumen of the vessel, and the outer catheter is then threaded off the needle while watching that blood continues to flow out of the needle hub (Figure 14-3).

Figure 14-3 The direct-cannulation technique for the radial artery.

A, The wrist is dorsiflexed over a towel or a small pack of gauze and loosely taped to a stable surface such as an armboard. B, The artery is directly cannulated at a 30- to 40-degree angle to the plane of the wrist. Arterial blood flows steadily into the “flashback” chamber. C, The catheter-over-needle assembly is lowered until the angle is approximately 10 degrees to the plane of the wrist. The entire assembly is advanced another 1 to 2 mm, until the tip of the catheter lies within the lumen of the artery. The catheter is then advanced into the artery completely while the needle is held motionless.

(From Lake CL: Cardiovascular anesthesia. New York: Springer-Verlag, 1985, p 54.)

Transfixation

If blood ceases flowing while the needle is being advanced, the needle has penetrated the back wall of the vessel. In this technique, the artery has been transfixed by passage of the catheter-over-needle assembly “through-and-through” the artery. The needle is then completely withdrawn. As the catheter is slowly withdrawn, pulsatile blood flow emerges from the catheter when its tip is within the lumen of the artery. The catheter is then slowly advanced into the artery. A guidewire may be helpful at this point if the catheter does not advance easily into the artery. Alternatively, the catheter-over-needle assembly may be withdrawn slowly as one unit until flow of blood has returned. As soon as this occurs, the needle and catheter are most likely in the lumen of the artery and the catheter may be gently threaded off the needle into the artery.

Seldinger Technique

The artery is localized with a needle, and a guidewire is passed through the needle into the artery. A catheter is then passed over the guidewire into the artery. Alternatively, a catheter-over-needle assembly may be inserted in the artery in a through-and-through fashion, the needle withdrawn, and the wire passed through the catheter after pulsatile flow is encountered. It is important when using this technique to avoid withdrawal of guidewires through needles to prevent shearing of the wire and embolization. Mangar et al⁶² showed that when using the direct or modified Seldinger technique compared with a direct-cannulation method, the success rate of arterial catheter placement increased from 62% to 82%.

Doppler-Assisted Technique

The artery is localized using a Doppler flow probe. The direction of insertion of the percutaneous catheter is guided by the acoustic Doppler signal.^63,64 This may be especially useful in small children and infants. In adults, this may be helpful when palpation of the artery is difficult, such as in obese patients requiring femoral arterial cannulation. With the more widespread availability of two-dimensional and color-Doppler ultrasonic devices, the acoustic Doppler-assisted method is used much less frequently.

Two-Dimensional Ultrasound-Assisted Method

The Doppler-assisted techniques have been supplanted in clinical practice by two-dimensional (2D) ultrasonic methods. Levin et al⁶⁵ randomized patients in a prospective study to ultrasound-guided (UG) radial artery cannulation versus a classic palpation technique. The use of ultrasound (US) resulted in a greater success rate on the first attempt, and fewer subsequent attempts were required to place the arterial catheter. The overall time for catheter placement was not significantly different between the two groups (trend for shorter overall time in UG group). In a similar study, Shiver et al⁶⁶ randomized patients in the emergency department to UG versus traditional palpation technique radial artery catheter placement. Patients in the UG group required a significantly shorter time (107 vs. 314 seconds; P = 0.0004), fewer placement attempts (1.2 vs. 2.2; P = 0.001), and fewer sites required for successful arterial catheter placement. The use of US in guiding arterial catheter placement is easy to learn when proper training in this technique is provided. There is, however, a significant learning curve, and studies reporting on the success rate of UG arterial cannulation compared with a traditional palpation technique have to be interpreted accordingly. Ganesh et al,⁶⁷ for example, did not find a significant difference in the time and attempts required in a pediatric patient population randomized to palpation versus UG radial artery catheter placement. None of the designated operators, however, had significant experience with this technique, with 19 of 20 pediatric subspecialty trainees and/or fully trained consultant anesthesiologists reporting experience with fewer than 5 cases. Figure 14-4 shows a proper full-sterile setup for UG arterial cannulation. Figure 14-5 demonstrates the “triangulation” technique typically applied with UG venous or arterial cannulation, or both. The US imaging plane and the needle plane can be viewed as the two sides of a triangle that should meet/intersect at the depth of the structure (e.g., radial artery) for which cannulation is attempted. The experienced operator will change the angle between the two planes (US and needle) and the distance (needle insertion site vs. imaging plane) depending on the depth of the structure. The US plane has to be adjusted further from needle entry through the skin to the perforation of the vessel to follow the needle tip in the transverse approach (vessel viewed in short axis). Figures 14-6 and 14-7 show typical US images obtained during short-axis (transverse) cannulation. Note the anatomic variation with a large (A1) radial artery next to a smaller size artery (A2) positioned laterally.

Figure 14-4 Demonstration of aseptic technique for ultrasonic guidance of radial artery cannulation.

Figure 14-5 Demonstration of the “triangulation” technique typically applied with ultrasound-guided venous and/or arterial cannulation in the transverse imaging approach. The echo imaging plane and the needle plane can be viewed as the two sides of a triangle that should meet/intersect at the depth of the structure (e.g., radial artery [red line]) for which cannulation is attempted. The experienced operator will change the angle (α) between the two planes (ultrasound and needle) and the distance (needle insertion site vs. imaging plane) depending on the depth of the structure. The echo plane has to be further adjusted from needle entry through the skin to the perforation of the vessel to follow the needle tip in the transverse approach (vessel viewed in short axis). A greater angle is used (echo plane angled toward the skin [1]) to visualize the needle tip after it penetrates the skin, and then a more perpendicular angle relative to the skin is applied to see the needle tip entering the vessel lumen (2).

Figure 14-6 A typical ultrasound image with color Doppler during short-axis (transverse) cannulation. Note the anatomic variation with a large (A1) radial artery next to a smaller size artery (A2) positioned laterally.

Figure 14-7 A typical ultrasound image during short-axis (transverse) cannulation.

If a longitudinal (“in-plane”) approach is chosen (i.e., the vessel viewed in its long axis), the needle tip can be followed more easily as it is advanced; however, structures adjacent to the US plane (lateral to the vessel) cannot be viewed simultaneously. For this reason, most practitioners prefer the transverse approach. Figure 14-8 shows the arterial catheter entering the radial artery using the longitudinal (in-plane) approach. Aseptic technique, including sterile sheaths, should always be used during UG of intra-arterial catheter placement to prevent catheter-related infections. A high-frequency linear array ultrasonic transducer (8 to 12 MHz) is optimal for UG arterial catheter placement because higher frequencies are needed for high-resolution imaging of the near field. Box 14-4 summarizes potential benefits and concerns related to UG arterial catheter placement.

Figure 14-8 A catheter entering the radial artery using the longitudinal (in-plane) approach.

Surgical Cutdown

An incision is made in the skin overlying the artery, and the surrounding tissues are dissected away from the arterial wall. Proximal and distal ligatures are passed around the artery to control blood loss but are not tied down. Under direct vision, the artery is cannulated with a catheter-over-needle assembly. Alternatively, a small incision is made in the arterial wall to facilitate passage of the catheter.

Infection

One potential complication that is common to all forms of invasive monitoring is infection from indwelling catheters. Indwelling percutaneous catheters can become infected because of insertion through an infected skin site, poor aseptic technique during insertion or maintenance, sepsis with seeding of the catheter, and prolonged duration of cannulation with colonization by skin flora. Historically, factors that were associated with catheter infection included nondisposable transducer domes, dextrose flush solutions, contaminated blood gas syringes, and duration of insertion.^68–71 In contrast with central venous catheterization, published data on vascular catheter infections did not find that full sterile barriers during arterial catheter placement reduced the risk for infection.^72,73 Nevertheless, these data do not exempt the practitioner from using strict aseptic technique. Guidelines for the prevention of intravascular catheter-related infections have been published by the Hospital Infection Control Practices Advisory Committee and the Centers for Disease Control and Prevention.⁷⁴

It is still common practice to remove percutaneous catheters when vascular catheter infection is suspected. This concept has been challenged, and a watchful waiting strategy has been advocated until a catheter-related bloodstream infection has been confirmed instead of immediate removal of the catheter.⁷⁵ Whenever infection at the cannulation site or a catheter-related bloodstream infection is confirmed, the catheter should be removed. The catheter is a foreign body that cannot be sterilized with antibiotic therapy. Lymphangitic streaks or cellulitis may occur as a result of catheter infection. These problems require systemic antibiotic therapy.⁷⁶

Hemorrhage

The use of an intra-arterial catheter carries the potential risk for major blood loss or exsanguination if the catheter or tubing assembly becomes disconnected. The use of Luer-Lok (instead of tapered) connections and monitors with low-pressure alarms should decrease the risk for this complication.⁷⁷ Stopcocks are an additional source of occult hemorrhage because of the potential for loose connections or inadvertent changes in the position of the control lever that would open the system to the atmosphere.

Thrombosis and Distal Ischemia

Thrombosis of the radial artery after cannulation has been extensively studied. Temporary arterial occlusion is the most commonly reported complication after radial artery cannulation.⁵⁴ Factors that correlate with an increased incidence of thrombosis include prolonged duration of cannulation,⁷⁸ larger catheters,⁷⁹ and smaller radial artery size (i.e., a greater proportion of the artery is occupied by the catheter).⁸⁰ The incidence of thrombosis is not affected by the technique of cannulation⁸¹ but is reduced with aspirin pretreatment.⁸²

The association between radial artery thrombosis and ischemia of the hand is less certain. An abnormal result for Allen test was not associated with hand complications after radial artery cannulation.³⁷ Despite the widespread use of radial artery cannulation, hand complications are rarely reported. Temporary occlusion after arterial cannulation is usually benign. Nevertheless, serious ischemic complications have been reported that required the amputation of a digit or extremity.^83–85 In the experience of Slogoff et al,³⁷

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