Medical Tests sexual Medicine

Arterial catheterization techniques for invasive monitoring

Arterial catheterization techniques for invasive monitoring

Authors
Gilles Clermont, MDCM, MSc
Arthur C Theodore, MD
Section Editors
John F Eidt, MD
Joseph L Mills, Sr, MD
Deputy Editor
Kathryn A Collins, MD, PhD, FACS

Disclosures

Last literature review version 19.3: Fri Sep 30 00:00:00 GMT 2011 | This topic last updated: Mon Jun 13 00:00:00 GMT 2011 (More)

INTRODUCTION — Arterial catheters (also called intra-arterial catheters or A-lines) are common in critically ill patients. They can be used to obtain arterial blood for laboratory testing, and for direct measurement of blood pressure and cardiac output. However, insertion of an arterial catheter is an invasive procedure and complications can occur.

This topic will review the indications, insertion techniques, and complications of arterial catheterization. The use of arterial catheters to monitor blood pressure is also reviewed. Percutaneous arterial puncture and arterial blood gases (ABGs) are discussed elsewhere. (See “Arterial blood gases”.)

INDICATIONS — Advantages of an indwelling arterial catheter include continuous access to arterial blood and the ability to continuously measure the blood pressure. As a result, arterial catheterization is indicated when:

  • Frequent blood gases are necessary, such as with acute respiratory failure.
  • The blood pressure must be monitored closely, such as during shock, major surgery, hypertensive emergency, or vasopressor therapy. This is particularly true if the blood pressure abnormality is acute or the blood pressure is labile.
  • Continuous monitoring of cardiac output and stroke volume are needed but it is impractical to place a pulmonary artery catheter [1].

For patients who do not have central venous access, arterial catheters can be used in lieu of venipuncture to obtain blood specimens.

INSERTION — The required equipment for arterial cannulation is listed in the table (table 1).

Site selection — Arterial catheters are placed under sterile conditions. The access site is prepared and draped with standard techniques. Full barrier precautions (including eye protection) should be used to minimize the risk of disease transmission associated with blood splatter, and reduce the potential for catheter site infection. (See “Overview of control measures to prevent surgical site infection”.)

The initial step in arterial catheterization is locating a palpable arterial pulse. Data do not support a particular site, but common sites include the radial, femoral, brachial, dorsalis pedis, or axillary arteries. In the pediatric population, the temporal and umbilical arteries can also be used. These sites are the same as those used for percutaneous needle puncture and anatomy landmarks are described in detail separately. (See “Arterial blood gases”, section on ‘Site selection’.)

Patients undergoing radial or dorsalis pedis arterial catheterization should have the collateral flow to the hand or foot assessed prior to the procedure to identify increased risk for an ischemic complication. Collateral flow to the radial artery can be evaluated by the Allen test or modified Allen test. The Allen test and modified Allen test are described in detail separately. (See “Arterial blood gases”, section on ‘Site selection’.)

Collateral flow to the dorsalis pedis artery can be evaluated in a similar manner by occluding the dorsalis pedis artery and compressing the nail bed of the great toe. Color should return rapidly to the nail bed when pressure on the toenail is released.

Ultrasound guidance — We suggest using ultrasound to identify and guide catheter placement for patients in whom vessel palpation is difficult (eg, small vessels, obesity). Either B-mode or color duplex imaging can be used to identify the vessel, although visualization of needle placement is better with B-mode imaging due to less artifact. An echogenic needle system improves visualization under ultrasound guidance.

The use of ultrasound was first described for arterial site salvage following failure of traditional methods; however, ultrasound is used more and more for initial arterial catheter placement [2-5]. A metaanalysis of four trials (adults and children) that included 152 patients undergoing arterial line placement guided by palpation and 159 with ultrasound-guided access found significant improvement in the rate of successful first attempt for the ultrasound-guided group compared with palpation (relative risk, 1.71; 95% CI 1.25-2.32) [6]. The benefit of ultrasound is the real-time visualization of the needle entering the vessel. When used only for mapping the vessel, no benefit is seen [7].

Technique — Once a palpable arterial pulse has been identified, the planned catheterization site is sterilely prepped. For the radial artery, the wrist is immobilized on a padded armboard. Local analgesia should be considered because it appears to prevent pain without adversely impacting the success of the procedure in patients undergoing percutaneous needle puncture [8,9]. A skin nick (ie, dermatotomy) should be considered in patients with tough skin to prevent a skin plug from occluding the insertion needle and damage to the plastic component of the catheter. If a dermatotomy is performed, local analgesia is mandatory.

Catheter insertion can be performed using one of three different approaches: the separate-guidewire approach, the integral-guidewire approach, or the direct puncture approach. The catheter should be secured after its insertion, usually with one or two sutures or alternatively with a sutureless fixation device.

We suggest either guidewire approach, unless the operator has experience with and is more comfortable with the direct puncture approach. In addition, we advocate changing to a guidewire approach if difficulties are encountered with the direct puncture approach. In one trial, 69 critically ill patients were randomly assigned to have arterial catheters placed by the direct puncture, separate-guidewire, or integral-guidewire approach [10]. The direct puncture approach was less likely to be successful, took longer to perform, used more catheters, and required more punctures than the separate-guidewire or integral-guidewire approaches. Similarly, in a prospective cohort study of 138 patients, insertion was more often successful using a guidewire approach, rather than the direct puncture approach (82 versus 65 percent) [11]. In this study, greater success was achieved in male patients and those with a bounding arterial pulse.

Separate-guidewire — During the separate-guidewire approach, the nondominant hand gently palpates the artery, while the dominant hand manipulates the intravascular catheter (an outer catheter over a needle) (figure 1).

The intravascular catheter is inserted at a 30 to 45 degree angle and advanced slowly until pulsatile blood return is observed [12]. Once pulsatile blood return is observed, the intravascular catheter is advanced slightly, until the blood return ceases. This step acknowledges that initial blood return begins as soon as the needle enters the lumen, but before the outer catheter also enters the artery’s lumen. Advancing the intravascular catheter ensures that the outer catheter has advanced into the lumen.

The nondominant hand then stabilizes the intravascular catheter while the dominant hand removes the needle from the intravascular catheter.

  • If pulsatile blood return is observed after the needle is removed, a guidewire is advanced through the outer catheter.
  • If pulsatile blood is not observed after the needle is removed, the outer catheter is gently withdrawn until pulsatile blood return is obtained. A guidewire is then advanced through the outer catheter.

The guidewire is advanced until its distal end is well beyond the distal end of the outer catheter. Finally, the outer catheter is advanced into the artery over the guidewire and the guidewire is removed.

Integral-guidewire — The integral-guidewire approach is similar, except the guidewire is inseparable from the intravascular catheter (figure 1). The nondominant hand gently palpates the artery, while the dominant hand manipulates the needle-guidewire-catheter unit. The needle-guidewire-catheter unit is inserted at a 30 to 45 degree angle and advanced slowly until pulsatile blood return is obtained. The nondominant hand then stabilizes the unit, while the dominant hand advances the guidewire tab to push the wire into and through the needle and catheter. The catheter is advanced into the artery over the needle and guidewire. Finally, the needle-guidewire unit is removed.

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Direct puncture — For the direct puncture approach, the nondominant hand gently palpates the artery, while the dominant hand manipulates the intravascular needle/catheter. The intravascular needle/catheter is inserted at a 30 to 45 degree angle and advanced slowly until pulsatile blood return is obtained. The outer catheter is then advanced into the artery directly from the needle without the aid of a guidewire.

COMPLICATIONS — Significant complications of arterial catheterization are uncommon. Most complications can occur at any insertion site, although a few site-specific complications exist (table 2).

All sites — Complications of indwelling arterial catheters include local and systemic infection, bleeding, hematoma, bruising, pain, swelling, and iatrogenic blood loss. In addition, vascular complications can occur, such as blood vessel injury, thromboembolism, vasospasm, pseudoaneurysm, and arteriovenous fistula. Several of the vascular complications can cause distal ischemia or, if severe, necrosis.

Thrombosis — Thrombosis can be detected by Doppler ultrasound in up to 25 percent of patients who have an arterial catheter, although clinically significant thrombosis occurs in less than 1 percent of such patients [13,14]. Risk factors for thrombosis include [14-17]:

  • Increased duration of catheterization (ie, >72 hours) [15,17]
  • Larger catheters [14-16]
  • Smaller blood vessels [14-16]
  • Low flow states (eg, low cardiac output)
  • Peripheral artery disease
  • Vasospastic disorders (eg, Raynaud phenomenon) [14]

Numerous controlled trials have demonstrated the incidence of thrombosis can be reduced by flushing the arterial catheter with heparin, rather than normal saline [18-22]. This is best illustrated by a trial that randomly assigned 5139 patients to receive either a heparinized or non-heparinized flush for up to 72 hours [22]. Heparin increased the patency of the arterial catheters, as determined by evaluation of the backflow of arterial blood and the waveform achieved with the catheter.

Sodium citrate is an alternative flushing agent with catheter patency rates equivalent to heparin and, therefore, may be useful when heparin is contraindicated (ie, heparin-induced thrombocytopenia). A trial randomly assigned 40 critically ill patients to receive 1.4 % sodium citrate flush solution, or heparin flush solution for up to 96 hours [23]. There were no differences in arterial catheter patency assessed at 48 and 96 hours. However, these results should be applied with caution because of the small size of this trial.

Embolism — Extremity ischemia as a consequence of embolization is due to dislodgement of thrombus or atheromatous debris by the catheter. The nature of symptoms and signs depends upon the presence (or absence) of collateral channels and size of the debris that has embolized. Distal ischemia (ie, in the digits) is more typical of emboli related to indwelling arterial catheters (picture 1), unless the access site itself thromboses, in which case more proximal limb ischemia will occur. In addition, arterial catheters in proximity to the origin of the carotid artery (eg, axillary artery) can cause cerebral emboli.

Distal pulses should be monitored regularly in all patients who have an arterial catheter. Caution is advised during flushing of arterial catheters; high pressure flushing should be avoided to minimize the potential for retrograde embolization [24,25].

Infection — It is difficult to estimate the incidence of arterial catheter-related infection because studies used varying definitions and frequently included both arterial and venous catheters. We estimate that 10 to 20 percent of arterial catheters are complicated by local (eg, insertion site) infection, approximately 10 percent by colonization, and 0.4 to 5 percent by bacteremia or sepsis [26-31].

Small studies have not found a relationship between the anatomic site of arterial catheterization and the incidence of arterial catheter-related infection [26,29,32]. However, a prospective cohort study that compared femoral with radial arterial catheters in almost 2500 patients found that femoral artery catheters were associated with an increased incidence of both local infection (3.02 versus 0.75 infections per 1000 catheter-days) and bloodstream infection (1.92 versus 0.25 infections per 1000 catheter-days) [33]. The average duration of catheter insertion was longer for femoral artery catheters (5.9 versus 5.75 days); however, it is uncertain whether this contributed to the different infection rates since the duration of infected catheters from each site was not reported. No catheters were left in place longer than seven days. (See “Epidemiology and microbiology of intravascular catheter infections”.)

Several risk factors for arterial catheter-related infection have been identified, including poor aseptic technique during insertion, insertion by surgical cut-down, and increased duration of catheterization [27,28,30,34]. Most studies have demonstrated that infection due to arterial catheters is most common among arterial catheters used for four days or longer.

There is a paucity of data about prevention of arterial catheter-related infections. Thus, the following approach is extrapolated from studies that evaluated the prevention of catheter-related infection in patients with a central venous catheter or a pulmonary artery catheter (table 3). (See “Prevention of intravascular catheter-related infections”.)

  • Arterial catheters are not routinely changed to a new site [31,35]. Instead, we use vigilant clinical assessment of the insertion site and the patient to determine whether an arterial catheter needs to be replaced. One trial randomly assigned 160 critically ill patients with a central venous or pulmonary artery catheter to one of four groups: replacement with a new insertion every three days, replacement by exchange over a guidewire every three days, new insertion when clinically indicated, or replacement by exchange over a guidewire when clinically indicated [31]. There were no differences in the incidence of bloodstream infection among the four groups. New insertions were associated with more mechanical complications.
  • Disposable or reusable transducers are replaced at 96-hour intervals. The associated tubing, continuous flush device, and flush solutions are also replaced. This is based upon studies that evaluated the impact of changing intravenous fluid administration sets in patients with a central venous or pulmonary artery catheter. A meta-analysis of 15 controlled trials found no evidence that changing intravenous fluid administration sets more often than every 96 hours reduced the incidence of bloodstream infection [36]. The data were insufficient to determine whether changing administration sets less often than every 96 hours affected the incidence of infection.
  • The dressing is replaced when it becomes damp, loose, or soiled, or the arterial catheter is removed or replaced.
  • All catheters placed under emergency conditions (ie, catheters placed without the usual sterile precautions) are replaced as soon as the patient’s condition permits.

Air embolism — Air bubbles in the flush solution of an arterial catheter can embolize antegrade or retrograde and cause ischemic damage to end organs, such as the brain, spinal cord, heart, and skin. In a primate model, 2 mL of air injected into the radial artery with a standard pressurized infusion apparatus could result in clinically significant cerebral air emboli [37]. Such emboli are more likely in smaller patients or those sitting upright. (See “Air embolism”.)

It is important to realize that air introduced into the arterial circulation via an arterial catheter is more likely to have adverse sequelae than air introduced into the venous circulation via a venous catheter because venous air will travel to the pulmonary capillaries and be filtered out. An exception exists if an anatomic right to left shunt exists. In this situation, venous air can be equally problematic because the pulmonary capillaries can be bypassed with the air traveling directly from the venous to the arterial circulation. Though rare, venous air may not get filtered and may pass through the lung into the arterial circulation even in the absence of a septal defect. This phenomenon has been described as a complication of foam sclerotherapy during the treatment of venous disease [38]. (See “Liquid and foam sclerotherapy techniques for the treatment of lower extremity veins”, section on ‘Air microembolization’.)

Iatrogenic blood loss — Laboratory tests not only require withdrawal of the blood sample to be tested, but an additional 3 to 12 mL of blood can be wasted (ie, to avoid sample contamination with saline or heparin). Substantial blood loss can result if frequent testing is necessary [39,40]. Strategies to help minimize iatrogenic blood loss include:

  • Sampling from the port nearest to the catheter insertion, or using a closed blood draw system that allows re-infusion of unused blood [41].
  • Use of intraarterial blood gas monitoring if withdrawal of blood for ABGs is the major source of blood loss. This technique uses a fluorescent optode to measure arterial pH, PaCO2, and PaO2 measurements as needed without removing blood from the patient [42]. Fiberoptic continuous sensor systems (eg, Paratrend 7+®; Philips Medical Systems) are also available, which may offer an advantage if monitoring is needed over a prolonged period of time [43].
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Site-specific — Each arterial catheterization site is associated with a unique set of potential complications (table 2) [17,29,44,45]. As examples, radial artery insertion is associated with peripheral neuropathy, femoral artery insertion with retroperitoneal hematoma, axillary artery insertion with brachial plexopathy, and brachial artery insertion with injury to the median nerve.

Although many sites share the same possible complications (eg, bleeding), the frequency of these complications varies among the different insertion sites. As examples:

  • The most common complications associated with radial artery catheterization are occlusion (2 to 35 percent) and hematoma (up to 15 percent) [37,46,47]. Permanent injury rarely results from either complication.
  • The most common complication associated with femoral artery catheterization is hematoma (6 percent), which can be large and difficult to detect if extension to the retroperitoneum occurs [46].

BLOOD PRESSURE MONITORING — Direct measurement by an arterial catheter is the gold standard for measuring blood pressure, provided the pressure transducer is free of technical problems. The mean arterial pressure determined by direct measurement generally correlates well with sphygmomanometry in healthy patients. Sphygmomanometry is less accurate in the presence of calcified arteries, shock, cardiac arrhythmias, or increased systemic vascular resistance (eg, vasoconstrictor drugs) [48-50].

Similarly, noninvasive finger artery blood pressure monitoring correlates well with radial artery blood pressure monitoring in ambulatory patients, but should not be relied upon when hemodynamic instability is present [51-53].

Sources of error — Despite the superiority of direct blood pressure measurement, technical problems may introduce errors [54].

Dynamic response — Dynamic response is determined by two factors, the resonant frequency and the damping coefficient:

  • The resonant or natural frequency of the system is the frequency at which it oscillates when stimulated. Physiologic peripheral arterial waveforms have a fundamental frequency of 3 to 5 Hz, although some components may range up to 20 Hz [55]. Thus, the resonant frequency of the system used to monitor arterial pressure must be greater than 20 Hz to avoid ringing and systolic overshoot [56]
  • The damping coefficient is a measure of how quickly an oscillating system comes to rest [56]. A system with a high damping coefficient (eg, compliant tubing) absorbs mechanical energy well and causes a diminution in the transmitted waveform.

The damping coefficient and resonant frequency of a monitoring system can be assessed at the bedside by the rapid-flush test (figure 2). This test is performed by briefly opening and closing the valve in the continuous flush device, which produces a square wave on the monitor. The square wave is followed by ringing (ie, rapid variation around the baseline), and a return to baseline. No ringing is seen with an over-damped system and excessive ringing is seen with an under-damped system. Common causes of underdamping include connecting tubing with stopcocks, excessive tubing length, and patient factors (eg, tachycardia, high output states). A common cause of overdamping is air bubbles in the connecting tubing.

Transducer position — Transducer position can be checked (ie, zeroed) by turning the stopcock off to the patient and open to air, adjusting the height of the stopcock to align with the level of the heart (usually approximated with the mid-axillary line), and adjusting the monitor to display zero. This procedure should be repeated each time the patient’s position is changed, when significant changes in blood pressure are noted, and routinely every six to eight hours [57].

Calibration — Routine calibration of the monitor and transducer is no longer necessary because the current disposable transducers are standardized [58].

SUMMARY AND RECOMMENDATIONS

  • Arterial catheterization is indicated when blood pressure must be monitored on a moment-to-moment basis or frequent arterial blood gases (ABGs) are necessary. (See ‘Indications’ above.)
  • Direct measurement by an arterial catheter is the gold standard for measuring blood pressure. However, errors can be introduced by technical problems, such as an inappropriate dynamic response or faulty transducer position. (See ‘Blood pressure monitoring’ above.)
  • The initial step in arterial catheterization is locating a palpable arterial pulse overlying an accessible and suitable vessel. Common sites include the radial, femoral, brachial, dorsalis pedis, or axillary artery. In the pediatric population, the temporal and umbilical arteries can also be used. (See ‘Site selection’ above.)
  • For patients with vessels that are difficult to palpate, we suggest using ultrasound to identify and guide catheter placement (Grade 2B). The use of ultrasound is associated with fewer attempts, and therefore a quicker time to catheterization. (See ‘Ultrasound guidance’ above.)
  • Prior to catheterization of the radial or dorsalis pedis artery, we recommend establishing the adequacy of collateral flow to the hand or foot by physical examination, Doppler ultrasound, pulse oximetry or, for the radial artery, the modified Allen test (Grade 1C). (See ‘Site selection’ above.)
  • We recommend that arterial catheters be placed with full barrier precautions (including eye protection) to minimize the risk of disease transmission and reduce the potential for catheter site infection (Grade 2C).
  • We recommend administering local anesthesia prior to arterial catheterization (Grade 1B). Local anesthesia prevents pain without adversely impacting the success of the procedure. (See ‘Technique’ above.)
  • For most operators, we suggest using the separate-guidewire approach or the integral-guidewire approach, rather than the direct puncture approach (Grade 2B). The catheter should be secured after its insertion, usually with one or two sutures. (See ‘Technique’ above.)
  • For patients who do not have a contraindication to heparin (eg, heparin-induced thrombocytopenia), we recommend use of heparinized flush solution over non-heparinized flush solution (Grade 1B). For patients who have a contraindication to heparin, a 1.4% sodium citrate flush solution is an acceptable alternative. (See ‘Thrombosis’ above.)
  • We suggest that arterial catheters not be replaced routinely (Grade 2C). Instead, we use vigilant clinical assessment of the insertion site and the patient to determine whether an arterial catheter needs to be replaced. It is preferable not to leave femoral catheters in place for longer than five days and arterial catheters at other sites should not be left in place for more than seven days. (See ‘Infection’ above.)
  • We suggest that disposable or reusable transducers be replaced at 96-hour intervals (Grade 2C). We replace the associated tubing, continuous flush device, and flush solutions at the same time. (See ‘Infection’ above.)
  • Complications of indwelling arterial catheters include local and systemic infection, bleeding, hematoma, bruising, pain, swelling, and iatrogenic blood loss. In addition, vascular complications can occur, such as blood vessel injury, limb ischemia, thromboembolism, vasospasm, pseudoaneurysm, and arteriovenous fistula. (See ‘Complications’ above.)
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