Version May 2024
INTRODUCTION — Intra-arterial catheters (also called arterial cannulas or A-lines) are often inserted for invasive blood pressure (BP) monitoring and intravascular access for blood sampling in high-risk surgical and critically ill patients. This topic will review techniques, complications, advantages, and uses of intra-arterial catheterization, as well as sources of error that may occur during monitoring and interpretation of the arterial pressure waveform. Pulmonary artery catheterization is discussed separately. (See "Pulmonary artery catheterization: Indications, contraindications, and complications in adults" and "Pulmonary artery catheters: Insertion technique in adults" and "Pulmonary artery catheterization: Interpretation of hemodynamic values and waveforms in adults".)
USES — Advantages of an indwelling arterial catheter include continuous access to arterial blood and blood pressure (BP) values. Indications include the need for:
●Continuous monitoring of arterial BP – Intra-arterial BP monitoring is often employed during the intraoperative period when major surgery is planned, significant comorbidities are present, or difficult intravascular access is anticipated, and when patients are critically ill and require titrated vasoactive medications. (See "Basic patient monitoring during anesthesia", section on 'Invasive blood pressure monitoring'.)
●Identification of abnormal arterial waveform patterns – (See 'Interpretation of the arterial waveform tracing' below.)
●Evaluation of respirophasic variations in the arterial pressure waveform to predict fluid responsiveness – Visual estimates or manual calculations of systolic pressure variation (SPV) or pulse pressure variation (PPV) are possible (figure 1 and figure 2), or commercially available devices that provide automated calculation of SPV, PPV, or stroke volume variation (SVV) may be employed (table 1). (See "Intraoperative fluid management", section on 'Dynamic parameters to assess volume responsiveness' and "Novel tools for hemodynamic monitoring in critically ill patients with shock", section on 'Arterial pulse waveform analysis'.)
●Frequent blood sampling – Occasionally, an arterial catheter is placed for intermittent blood sampling for laboratory testing, including point-of-care tests such as arterial blood gases with pH, hemoglobin, electrolytes, glucose, lactate, and tests of hemostasis [1]. Intra-arterial access is particularly useful in patients who do not have intravascular access via a central venous catheter (CVC). (See "Arterial blood gases" and "Clinical use of coagulation tests", section on 'Point-of-care testing'.)
Routine arterial catheterization in the absence of a reasonable indication is not recommended since complications may occur (see 'Complications' below), and thrombosis or stenosis may render future cannulation of previously used arteries more difficult [2].
CONTRAINDICATIONS — There are several contraindications to arterial line placement, some of which are site-specific and other that are general. These contraindications are similar to those described for arterial blood gas sampling and are discussed separately. (See "Arterial blood gases", section on 'Indications and contraindications'.)
SITE SELECTION — The initial step in selection of a catheterization site is the location of a palpable arterial pulse. Common sites include peripheral arteries (radial [most common], brachial, or dorsalis pedis sites) and central arteries (femoral [most common] or axillary sites). The peripheral arteries are typically located more easily, and have a lower infection risk compared with central arterial sites. In most institutions, the radial, axillary, and femoral sites are most commonly accessed, while the brachial site is accessed only rarely for selected cardiac surgical or medically complex patients [3-5]. While frequently used in children, the dorsalis pedis site is often avoided in adult patients with diabetic complications or significant peripheral arterial disease of the lower extremities. Anatomical landmarks for these sites are described separately. (See "Arterial blood gases", section on 'Site selection'.)
●Checking for collateral flow – Prior to radial arterial catheterization, a check for collateral flow to the hand is performed to identify possible risks for an ischemic complication [6]. Variable blood supply to the deep and superficial palmar arches occasionally causes inadequate perfusion and ischemia following placement of an arterial catheter.
A physical examination that includes the Allen test or modified Allen test is often employed, although there is significant interobserver variability, and the test lacks predictive accuracy for subsequent hand ischemia [6-9]. Although the best method for assessing radial arterial patency and collateral competency is color Doppler ultrasonography, equipment is not always immediately available [10]. Alternative methods are being developed (eg, photoplethysmography) [11,12]. (See "Arterial blood gases", section on 'Ensure collateral circulation'.)
●Immobilization – If the radial artery is selected, the wrist is often immobilized on a padded arm board. At the brachial or femoral site, positioning to straighten the extremity is helpful for initial catheter insertion and maintenance of catheter integrity.
INSERTION TECHNIQUES — Arterial catheterization should be performed using standard sterile precautions. All equipment including equipment for monitoring and the ultrasonography device should be prepared and the transducer zeroed and ready for use. The equipment necessary is listed in the table (table 2).
Sterile technique — The access site is prepared with standard techniques. For peripheral arterial access sites (ie, radial, brachial, dorsalis pedis), a chlorhexidine-alcohol skin antiseptic solution is applied to the access site and allowed to dry, and sterile gloves are worn. If a fenestrated drape is used, it should be positioned after the antiseptic solution is dry on the skin [2]. For central arterial access sites (ie, femoral, axillary), full barrier precautions including masks, caps, and eye protection can be used to reduce the potential for catheter site infection and minimize risk for disease transmission associated with blood splatter [2]. (See "Central venous access in adults: General principles", section on 'Aseptic technique'.)
Local anesthetic injection — We use local anesthesia at the site of insertion in conscious patients. Injection of local anesthetic does not adversely impact the success of the procedure and may reduce vasospasm [13]. In particular, local anesthesia is necessary in awake patients with tough skin if a small dermatotomy (ie, "skin nick") is made in order to prevent occlusion of the insertion needle with a skin plug and/or damage to the plastic catheter.
Use of ultrasound guidance — We often use ultrasonography to identify a patent arterial vessel and guide catheter placement [14-16].
A 2020 meta-analysis of randomized trials of ultrasound-guided catheter insertion (19 trials; 3229 patients) noted a higher incidence of first attempt success (risk ratio [RR] 1.39, 95% CI 1.21-1.59), fewer mean attempts (weighted mean difference [WMD] -0.80, 95% CI -1.35 to -0.25), shorter mean time to success (WMD -41.2, 95% CI -75.4 to -6.9), and reduced risk of hematoma (RR 0.40, 95% CI 0.22-0.72) with use of ultrasound compared with traditional palpation techniques [17]. Similarly, a 2018 meta-analysis of randomized trials (12 trials; 2,432 patients) also noted that use of ultrasound guidance was associated with higher first attempt success rate (RR 1.35, 95% CI 1.16-1.57) and decreased failure rate (RR 0.52, 95% CI 0.32-0.87) compared with digital palpation alone [16]. Other meta-analyses have noted similar results [17-19].
The presumed benefit of ultrasound is to allow visualization of the needle entering the vessel in real time. Efficacy has not been demonstrated in studies employing ultrasound to simply locate or map an arterial vessel without dynamic real-time visualization of needle placement [14,20]. Transverse (ie, short axis) and/or longitudinal (ie, long axis) views may be used to locate and cannulate the artery. In one trial in 164 patients undergoing radial artery catheterization, the first attempt success rate was higher with transverse axis views than with longitudinal axis views, but the overall incidence of failure to cannulate was similar [21]. A 2018 meta-analysis reported that the highest first attempt success rates were achieved by employing both long and short axis views with dynamic needle tip positioning (a technique that requires real-time ultrasonographic confirmation of the needle tip in the vessel prior to advancement of the catheter) [16]. Short axis visualization without dynamic needle tip positioning was associated with lower first attempt success rates that were similar to palpation techniques without ultrasound guidance. Although either B-mode or color duplex ultrasound imaging can be employed, visualization of the needle is typically better with B-mode imaging due to fewer artifacts. However, clinician preferences depend in part on the selected arterial site.
Notably, use of ultrasound may decrease risk of complications such as hematoma formation by identifying an evolving hematoma or presence of a pseudoaneurysm or arteriovenous fistula [22-24]. Also, ultrasound guidance may decrease risk of embolism since the operator can avoid catheter insertion at the site of an atheroma or calcified area along the arterial wall [25]. Furthermore, during axillary artery catheterization, ultrasonography may prevent injury to surrounding structures including the brachial plexus [25].
Use of a guidewire — We suggest using a guidewire during arterial catheter insertion, unless the operator is experienced and more comfortable with a direct puncture approach. Furthermore, we suggest changing to a guidewire approach if difficulties are encountered with the direct puncture approach. In one trial in 69 critically ill patients, the direct puncture approach was less likely to be successful, took longer to perform, used more catheters, and required more punctures compared with using a separate-guidewire or integral-guidewire approach [26]. Similarly, first attempt success rates were higher using a guidewire rather than the direct puncture approach in a prospective cohort study of 138 patients (82 versus 65 percent overall), particularly in 42 female patients (57 versus 14 percent) [27].
For all approaches to arterial catheterization, the operator's nondominant hand gently palpates the artery, while the dominant hand manipulates the intravascular catheter (an outer catheter over a needle). Specific approaches include:
●Separate-guidewire approach – During the separate-guidewire approach, the intravascular catheter with an inner needle is inserted at a 30 to 45 degree angle and advanced slowly until pulsatile blood return is observed (figure 3) [28]. The intravascular catheter is then advanced slightly, assuring that the catheter tip is now within the lumen, or 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.
While stabilizing the intravascular catheter with the nondominant hand, the dominant hand removes the needle from the intravascular catheter. If pulsatile blood return is observed after the needle is removed, the separate-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, and only then is the guidewire advanced through the outer catheter. Then the guidewire is advanced further, until its distal end is well beyond the distal end of the outer catheter. Finally, the outer catheter is advanced over the guidewire into the artery, then the guidewire is removed.
●Integral-guidewire – The most common approach uses an integral-guidewire that is inseparable from the prepackaged intravascular catheter (figure 3). This approach is similar to that for a separate guidewire. While the nondominant hand gently palpates the artery, the dominant hand manipulates the catheter, inserting it at a 30 to 45 degree angle and advancing it slowly until pulsatile blood return is obtained. Then the angle of the needle-guidewire-catheter unit is decreased, so that the needle-guidewire-catheter unit is more parallel to the skin. If blood flow is still observed, the guidewire tab is advanced with the dominant hand pushing the wire into and through the needle and catheter. However, if decreasing the angle of the needle-guidewire-catheter unit results in loss of blood return, the unit is advanced slowly until blood flow is observed again. Then the catheter is advanced into the artery over the needle and guidewire, and the needle-guidewire component of the unit is removed.
●Direct puncture – For the direct puncture approach, while the nondominant hand gently palpates the artery, the intravascular needle-catheter unit is inserted by the dominant hand at a 30 to 45 degree angle and advanced slowly until pulsatile blood return is obtained. Then the angle of the needle-catheter unit is decreased, so that the needle-catheter unit is more parallel to the skin. The needle-catheter unit is then slowly advanced another millimeter or two, assuring that blood return continues and that not only the inner needle tip, but also the catheter tip is now within the arterial lumen. The outer catheter is then advanced into the artery directly from the needle without the aid of a guidewire, and the needle is removed.
When using the direct puncture technique, it is important to recognize that the needle tip extends beyond the catheter tip by approximately 1 to 2 mm. When puncturing the artery with the needle-catheter unit, the initial, "flash," of arterial blood comes from the leading needle tip, and if the needle-catheter unit is not advanced slightly into the arterial lumen, the catheter tip may remain outside of the vessel wall. Attempts to advance the catheter tip will then be unsuccessful, because the catheter will displace the vessel wall rather than enter the vessel lumen.
Similarly, when advancing the needle-catheter unit at a shallow angle to assure that the catheter is intraluminal, blood return may cease. Again, since the leading tip is the needle rather than the catheter, the needle alone should be slowly withdrawn. Often, the catheter tip will still be in the arterial lumen, blood return now resumes, and the catheter may be advanced into the artery. Alternatively, the catheter may also need to be withdrawn slightly if along with the needle, the catheter tip has also penetrated the back wall of the artery and there is no blood return. Slight catheter withdrawal will then restore blood return as the catheter re-enters the arterial lumen. The catheter is then advanced within the artery.
Catheter stabilization — All equipment should be prepared in advance, including syringes with flush solution and the tubing that will be connected to the arterial catheter. Once the catheter is advanced into the artery, the needle is removed. The artery should be compressed proximal to the catheter to prevent bleeding after removing the needle and during connection of the pre-flushed arterial tubing. Finally, the catheter should be secured via sutures or with a transparent adhesive dressing.
MONITORING BLOOD PRESSURE — Direct continuous measurement with an intra-arterial catheter is the gold standard for determining arterial blood pressure (BP). The mean arterial pressure (MAP) determined by direct measurement generally correlates well with pressures from manual sphygmomanometry and automated non-invasive BP cuffs in healthy adults. (See "Basic patient monitoring during anesthesia", section on 'Noninvasive blood pressure monitoring'.)
However, in one trial conducted in 152 patients undergoing major noncardiac surgery, continuous arterial catheter-based monitoring detected hypotension <65 mmHg more often than monitoring with oscillometric-based monitoring with a BP cuff (odds ratio [OR 1.78, 95% CI 1.18-2.70) [29]. Furthermore, non-invasive cuff pressure measurements are less accurate in patients with shock, cardiac arrhythmias, severely increased systemic vascular resistance (SVR; eg, due to administration of vasoconstrictor drugs) [30], severely decreased SVR (eg, distributive shock) [31,32]. Non-invasive BP measurements appear to show the greatest discrepancies at the extremes of BP values compared with invasive measurements, such that actual BP is overestimated during severe hypotension and underestimated during severe hypertension [33]. Newer developments in technology (eg, noninvasive hydraulic coupling of brachial artery pulsation using an upper arm BP cuff or continuous BP monitoring with a finger cuff) may improve accuracy and precision of noninvasive BP monitoring [34,35]. Such developments may be particularly important when establishing intra-arterial access is challenging (eg, patients with obesity, children) [35,36].
Interpretation of the arterial waveform tracing — The arterial waveform results from ejection of blood from the left ventricle into the aorta during systole, followed by peripheral runoff during diastole [37]. The normal arterial waveform is shown in the figure (figure 4). Unusual radial arterial pressure waveforms may occur due to pathology in the ascending aorta or aortic valve (eg, aortic dissection, aortic valve replacement) [38,39], or with decreases in systemic BP or systemic vascular resistance. Examples of abnormal arterial waveforms that are associated with clinical pathology include pulsus alternans in left ventricular failure, pulsus paradoxus in cardiac tamponade, pulsus bisferiens or water hammer pulse in aortic regurgitation, or an anacrotic pulse, pulsus parvus or pulsus tardus in aortic stenosis. These and other examples are described in detail in a separate topic. (See "Examination of the arterial pulse".)
The systolic upstroke represents the systolic ventricular ejection. The peak systolic pressure is followed by a rapid decrease in pressure as ventricular contraction ends (ie, the systolic decline). The dicrotic notch (ie, the incisura) represents the closure of the aortic valve, which indicates the start of diastole. The pressure throughout diastole is the primary determinant of left ventricular blood flow. The lowest pressure at the end of the diastolic cycle occurs immediately before the next arterial upstroke.
In addition to providing absolute numerical data for peak systolic and nadir diastolic BP values, other useful hemodynamic information that can be derived from the arterial pressure waveform include:
●Mean arterial pressure
•MAP is the mean pressure averaged over several cardiac cycles at the measurement site. It represents the area under the curve during a single beat. Most monitors average this number electronically over a period of time.
•MAP may be estimated mathematically as the sum of diastolic BP plus one-third of the pulse pressure, although this formula is valid only at a heart rate of approximately 60 beats per minute [40].
●Pulse pressure
•Pulse pressure is the difference between systolic and diastolic pressures. Generally, elevated pulse pressure indicates age-associated vascular stiffness, particularly in hypertensive older patients [41]. Decreases in a patient's pulse pressure relative to baseline are typically caused by hypovolemia, decreases in stroke volume (SV), or increases in systemic vascular resistance (SVR). Increases in a patient's pulse pressure relative to baseline are caused by increases in SV and/or decreases in SVR (eg, during exercise).
•Pulse pressure variation (PPV) may be used to assess intravascular volume status. (See "Intraoperative fluid management", section on 'Dynamic parameters to assess volume responsiveness' and "Basic patient monitoring during anesthesia", section on 'Other monitors of circulation'.)
●Additional systolic and diastolic pressure parameters
•The slope of the systolic upstroke is generally related to left ventricular contractility, although other hemodynamic variables affect this relationship [42]. For example, this slope becomes steeper as the waveform is measured further from the aorta [43]. (See 'Site of arterial catheterization' below.)
•The slope of the diastolic decline in pressure (ie, diastolic runoff) varies with resistance in the arterial tree. If stroke volume is constant, diastolic runoff decreases sharply if SVR is low (eg, vasodilator therapy, septic shock), but is more gradual if SVR is high (eg, vasoconstrictor therapy, severe heart failure).
Factors affecting measurement of blood pressure — Despite the superiority of direct intra-arterial BP measurement compared with noninvasive techniques, misinterpretation of data or technical problems may introduce errors [44].
Site of arterial catheterization — Arterial pressure waveforms change as the pressure wave moves from the aorta to the periphery. Peripheral arterial waveforms have a higher systolic BP, steeper systolic upstroke, lower diastolic BP, lower and later dicrotic notch, and wider pulse pressure compared with measurements obtained at the aortic root [43,45]. For example, the systolic BP in the radial artery can be 10 to 35 mmHg higher than the systolic BP in the aorta, while measurements of diastolic pressure and MAP are less affected in a peripheral site [46,47]. These changes are the result of the decreased diameter of peripheral blood vessels, their elasticity, and wave reflections off the peripheral vessel branch points and walls [48].
Transducer level — The pressure transducer should be leveled to a point that corresponds with the level of the heart, aiming for 5 cm behind the sternum in a supine patient (picture 1) [49,50], which best approximates the location of the aortic root in an adult. Alternatively, the mid-axillary line is used as an appropriate reference level, particularly when direct arterial pressure is simultaneously being monitored along with pulmonary arterial or central venous pressures [51-53]. In either right or left lateral decubitus position, the transducer should be leveled at the mid-sternum (see "Patient positioning for surgery and anesthesia in adults", section on 'Lateral decubitus'). In some cases (eg, the sitting position), the anesthesiologist may decide to level the transducer with the external auditory meatus to reflect the pressure at the Circle of Willis and therefore brain perfusion pressure. (See "Patient positioning for surgery and anesthesia in adults", section on 'Physiologic effects of sitting position'.)
Regardless of the level chosen for the transducer, it should be recognized that transducer position is a critical determinant of all directly monitored intravascular pressures. If the position of the patient relative to the transducer is changed, the level of the transducer should also be adjusted to avoid erroneous BP readings [54]. The hydrostatic pressure difference between various vertical locations of the transducer is easily calculated (10 cm water height = 7.4 mmHg), and subsequent transducer height adjustments will always produce these exact differences in measured pressures (see below, transducer calibration).
In addition to assuring the appropriate transducer level, the transducer must also be, "zeroed," prior to monitoring. To do this, the stopcock adjacent to the transducer is turned off to the patient, then opened to air to be exposed to ambient atmospheric pressure. The bedside monitor pressure zero button is then selected, which assigns atmospheric pressure to be zero. The stopcock is then closed to air and adjusted to the height that will best align it with the level of the heart as described above. Note that the pressure transducer need not be re-zeroed when transducer height is adjusted slightly to align it appropriately with the patient. However, the transducer must always be zeroed before monitoring begins, whenever the electronic pressure monitoring cable is disconnected, and when BP accuracy is in question [55].
Over-damping or under-damping of the pressure tracing — The arterial catheter, noncompliant tubing, and three-way stopcocks used for invasive monitoring each change the degree of damping of the pressure waveform between the artery and the transducer that measures it [56]. Thus, unnecessary length of tubing and extra stopcocks should be avoided. Also, the arterial pressure waveform may become damped by air bubbles or clot in the arterial catheter, causing a characteristic (though sometimes subtle) change in the waveform, with a decrease in the displayed systolic pressure, and a falsely narrowed pulse pressure. However, MAP often remains accurate in these circumstances. Removal of air or flushing the catheter often resolves such overdamping. If a clot on the catheter tip is suspected, then the catheter should be replaced.
Whether the degree of damping (ie, dynamic response) in a monitoring system is appropriate can be assessed at the bedside by the rapid-flush test (figure 5) [57,58]. This test is performed by briefly opening and closing the valve in the continuous flush device (rapid flushing), which produces a square wave on the monitor. The square wave is followed by, "ringing" (rapid oscillations in pressure), then a return to baseline. Over- or under-damping may be present:
●Over-damping – No ringing is observed after a rapid flush of an over-damped system. Common causes of over-damping include air bubbles or clots in the connecting tubing, loose connections, kinks, or arterial spasm (figure 6).
●Under-damping – Excess ringing is observed after a rapid flush in an under-damped system (figure 7). Common causes of under-damping include excessive tubing length, tubing connected with stopcocks, and patient factors such as tachycardia, high cardiac output, or hypothermia. In general, most arterial pressure monitoring systems in clinical use are slightly under-damped, resulting in systolic pressure, "overshoot," that is commonly observed [56,59].
Calibration — Routine calibration of the monitor and transducer is no longer necessary since modern disposable transducers are standardized [60]. However, if a calibration error is suspected, it is easy to perform a simple test at the bedside by creating a "water column" of standard height with the saline-filled monitoring tubing. For example, a 30 cm height should display a pressure of approximately 22 mmHg [61].
MONITORING INTRAVASCULAR VOLUME STATUS
Interpretation of respiratory variation — Arterial waveform analysis can be used to determine fluid responsiveness. Variations in the waveform that occur during respiration (eg, pulse pressure variation [PPV] or systolic blood pressure variation [SPV], stroke volume variation [SVV]) can be observed or measured to assess responses to fluid challenges (figure 1 and figure 2) [62-66]. Each of the dynamic indices based on respiratory variation has advantages and disadvantages, with limitations in sensitivity and specificity (table 1) [62,67-69]. Although hemodynamic indices of respiratory variation can be computed (manually or automatically), visual estimation may be adequate to guide fluid therapy. (See "Intraoperative fluid management", section on 'Respiratory variations in arterial pressure waveform' and "Novel tools for hemodynamic monitoring in critically ill patients with shock", section on 'Volume tolerance and fluid responsiveness'.)
Cardiac output measurement — Although the gold standard for cardiac output measurements is use of thermodilution techniques with a pulmonary artery catheter (PAC), the risks of central venous catheterization and introduction and maintenance of a PAC have led to development of alternative methods such as arterial waveform-based devices, lithium dilution-based devices, and thermodilution-based devices [62,70]. Information regarding the accuracy and utility of these technologies is discussed elsewhere. (See "Novel tools for hemodynamic monitoring in critically ill patients with shock", section on 'Arterial pulse waveform analysis'.)
COMPLICATIONS — Clinically significant complications of arterial catheterization are uncommon. Most complications can occur at any insertion site, although a few are site-specific (table 3). Proper site selection, sterile technique, and ultrasound guidance during catheterization minimize complications.
All sites — Complications of indwelling arterial catheters include bruising, pain, swelling, hematoma or bleeding at the insertion site, damage to adjacent structures, local or systemic infection, and iatrogenic blood loss due to sampling. In addition, specific vascular complications include vasospasm, thromboembolism, dissection, pseudoaneurysm, or arteriovenous fistula formation. These vascular complications may cause local or distal ischemia that can progress to necrosis in rare instances.
Vasospasm — Vasospasm is a common complication following arterial catheterization, occurring in 57 percent of patients in one study, and is typically an initial sign in arteries that develop thrombosis [71] (see 'Thrombosis' below). Vasospasm is identified by pain in the extremity, decrease in arterial blood pressure (BP), severe damping of the arterial waveform, loss of the arterial pulse or significant decrease in the oximetry plethysmogram signal quality index distal to the arterial cannulation site [72]. Risk factors may include female sex, diabetes mellitus, and/or the ratio of catheter size to radial artery size [73].
We do not employ intra-arterial injection of any agent to reduce the incidence of vasospasm. Studies to decrease vasospasm risk have included intra-arterial injection of heparin, nitroglycerin, nitroprusside, verapamil, and phentolamine, as well as administration of systemic sedative agents [74-77]. Systemic sedatives can decrease sympathetic output to the predominantly alpha-1 receptors of the distal arteries, which may decrease the risk of vasospasm. However, results in these studies were not consistent, and most were conducted in patients undergoing percutaneous coronary interventions with a large catheter-to-radial artery size ratio.
Thrombosis — Arterial thrombosis can be suspected in patients with decreased distal pulses, dampened or lost arterial waveform, or cyanotic digits. In rare cases, gangrene may occur [78]. 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 [79,80]. Risk factors for thrombosis include [80-83]:
●Increased duration of catheterization (ie, >72 hours)
●Larger catheters
●Smaller blood vessels
●Low flow states (eg, low cardiac output)
●Peripheral artery disease
●Vasospastic disorders (eg, Raynaud phenomenon)
We do not routinely use heparin or sodium citrate to maintain patency of intra-arterial catheters but rather use saline for flushing and maintenance of catheter patency. A 2014 meta-analysis noted no significant differences in catheter patency or functionality in individual studies with or without use of heparinized solution flushed with continuous pressure at a heparin dose of 1 to 2 international units/mL (seven trials; 505 patients) [84]. As an alternative to heparin flushing, sodium citrate is used by some centers to maintain catheter patency when heparin is contraindicated (ie, heparin-induced thrombocytopenia). However, in one small randomized trial in 40 critically ill patients, no differences in catheter patency were noted for flush solution containing either sodium citrate 1.4% or heparin 4 international units/mL [85].
Particulate embolism — Extremity ischemia as a consequence of embolization may occur if intra-arterial catheter insertion or manipulation causes dislodgement or fragmentation of thrombus or atheromatous debris. 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 with an arterial catheter for early detection of embolization. Caution is advised during flushing of the catheter (ie, manual catheter flushing performed gently with the lowest pressure needed). Prolonged high pressure flushing using the system flush valve should be avoided to minimize the potential for retrograde embolization of particulate matter or air [86,87]. (See 'Air embolism' below.)
Signs and symptoms of ischemia due to embolization depend on the presence (or absence) of collateral circulation and the size of the embolized particles. Distal embolization and ischemia (ie, in the digits) is more typical for an indwelling arterial catheter. However, proximal limb ischemia may occur if the access site itself thromboses.
Air embolism — Air bubbles in the flush solution of an arterial catheter monitoring system can embolize antegrade or retrograde and may cause ischemic damage to the brain, spinal cord, heart, or skin. In a primate model, 2 mL of air injected into the radial artery with a standard pressurized infusion apparatus results in clinically significant cerebral air emboli [88]. Such emboli are more likely in patients who are small in size or sitting upright. (See "Air embolism", section on 'Etiology'.)
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 via intravenous catheters because venous air will travel to the pulmonary capillaries and not pass to the left side of the heart. (See "Air embolism", section on 'Arterial air embolism'.)
Accidental intra-arterial injection of medications — Unintentional intra-arterial injection of a medication may lead to limb or other end-organ ischemia or damage. The mechanism of injury may be related to cytotoxicity of the agent itself or to obstruction of blood flow caused by formation of drug crystals, hemolysis and platelet aggregation due to vessel intima damage, or profound vasoconstriction and subsequent thrombosis (eg, due to norepinephrine injection) [89,90]. Specific adverse reactions caused by various agents after intra-arterial injection are shown in the table (table 4).
Dissection, pseudoaneurysm, arteriovenous fistula — Arterial dissection, pseudoaneurysm, and arteriovenous fistula formation are uncommon complications of arterial cannulation. Dissection occurs in approximately 1 percent of patients undergoing radial artery catheterization for coronary angiography [91]. Prompt identification by strict monitoring of the arterial waveform is important since acute dissection may lead to arterial occlusion and distal ischemia.
Pseudoaneurysm formation is a very rare complication of arterial cannulation, occurring with an incidence of <0.1 percent after radial artery access for coronary angiography [92]. It presents as a pulsatile mass and typically occurring after local site bleeding and/or hematoma formation. Such damage to the arterial wall is associated with multiple cannulation attempts, larger sheath size, anticoagulation, and catheter infection [93]. This can be an early or late complication.
Very rarely, an arteriovenous fistula may develop after arterial catheterization [94].
Local or systemic infection — Compared with central venous catheters (CVCs), it is generally accepted that the risk of infection is lower with arterial catheters. Most arterial catheter-related infections develop due to local (eg, insertion site) infection, approximately 10 percent by colonization, and only rarely due to bacteremia or sepsis [95-102].
The overall incidence of infection is difficult to estimate due to variable definitions for infection among studies, and inclusion of both arterial and venous catheters in many studies. A 2013 meta-analysis that included 49 studies and nearly 31,000 arterial catheters noted an incidence of 3.4 arterial catheter-related bloodstream infections per 1000 catheters, with 0.96 infections per 1000 catheter days [102]. A higher incidence of infections was noted for the femoral arterial site (1.5 per 100 catheters) compared with the radial site (0.3 per 100 catheters). However, another 2020 meta-analysis of 2256 femoral and 4117 radial catheters reported similar rates of catheter-related blood stream infections (0.4 versus 0.5 percent) and major catheter-related infections (0.7 versus 0.8 percent) despite a slightly higher rate of colonization in femoral catheters compared with radial catheters (8.6 versus 6.4 percent) [103]. (See "Intravascular catheter-related infection: Epidemiology, pathogenesis, and microbiology".)
Risk factors for catheter-related infection include poor aseptic technique during insertion, insertion by surgical cut-down, and longer duration of use (≥4 days) [2,96,97,99,104]. Preventive measures are based on studies of prevention of catheter-related infection in patients with a CVC or a pulmonary artery catheter (PAC) (table 5).
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 may be wasted (ie, to avoid sample contamination with saline or heparin). Substantial blood loss can result if frequent testing is necessary [105,106]. 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 [107].
●Use of intra-arterial blood gas monitoring if withdrawal of blood for blood gases is the major reason for blood sampling. This technique uses a fluorescent optode to measure arterial pH, partial pressure of arterial carbon dioxide (PaCO2), and partial pressure of arterial oxygen (PaO2) measurements as needed without removing blood from the patient [108]. Fiberoptic continuous sensor systems are also available, and may be advantageous if a prolonged period monitoring is anticipated [109].
Site-specific complications — Each arterial catheterization site is associated with a unique set of potential complications (table 3) [82,98,110,111]. 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). Permanent injury rarely results from either complication [112].
●A 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 [112]. (See "Access-related complications of percutaneous access for diagnostic or interventional procedures".)
MAINTENANCE OF AN INDWELLING ARTERIAL CATHETER — We employ the following measures to maintain intra-arterial catheter integrity and prevent local or systemic infection (see 'Local or systemic infection' above):
●Arterial catheters are not routinely changed to a new site after any interval [2,113]. Instead, vigilant clinical assessment of the insertion site and of the patient is employed to determine whether an arterial catheter should be replaced. However, any catheter inserted under emergency conditions (ie, placed without standard sterile precautions) should be replaced as soon as is feasible. Arterial catheters should be discontinued when their use is not critical to patient care. It is preferable not to leave femoral catheters in place for longer than five days due to a higher risk of infection, and not longer than seven days for other sites.
●Disposable or reusable transducers are replaced at 96-hour intervals. The associated tubing, continuous flush device, and flush solutions are also replaced [2].
●The catheter site dressing is replaced when it becomes damp, loose, or soiled, and when the arterial catheter is removed or replaced.
●Antimicrobial prophylaxis is used in selected settings. (See "Antimicrobial prophylaxis for prevention of surgical site infection in adults".)
REMOVAL OF AN ARTERIAL CATHETER — Before removing any arterial catheter, international normalized ratio, partial thromboplastin time, and platelet counts should be checked and administration of medications that affect coagulation and platelet function noted. If any of these are abnormal, or if the patient is on antiplatelet therapy, extended compression times will be needed. Unlike venous catheter removal, it is not necessary to maintain a Trendelenburg position to avoid air embolism, although the supine position is preferred in patients with a femoral catheter so that adequate pressure can be maintained after removal.
Aseptic technique is used during removal of arterial catheters, and care must be taken to avoid splashing blood. After hand washing, nonsterile gloves, a protective gown, and face mask with shield should be donned for any arterial catheter removal regardless of catheter location. The catheter should be flushed prior to removal, or alternatively, blood can be drawn back into the catheter to prepare it for removal.
To remove the catheter, clean the catheter site with chlorhexidine, place a 4x4 dressing and apply pressure overlying the arterial puncture site, then slowly pull the catheter out maintaining pressure at both the artery and skin puncture sites. Generally, pressure should be held for five minutes over the radial artery and for ten minutes over the femoral artery.
In addition to the cannulation site, the optimal duration for pressure application depends on the catheter size, with longer compression times for larger diameter devices or sheaths. For patients with known coagulopathy, compression times should be increased to ten minutes over the radial artery and 15 to 20 minutes over the femoral artery. If oozing continues, the artery should be compressed for five additional minutes and rechecked. Once bleeding has stopped, a dressing can be placed.
After removal, the catheter should be inspected to ensure that it is intact. If the catheter is fragmented, pressure should be applied above the site of catheter entry into the skin. Since embolization of catheter fragments can occlude the distal extremity circulation, urgent surgical referral should be obtained. (See 'Particulate embolism' above.)
After removal from a femoral puncture site, the hip should remain without flexion for up to two hours following removal. The pulse at the puncture site and pulses distal to it should be rechecked in 15 minutes for signs of hematoma or extremity ischemia.
SUMMARY AND RECOMMENDATIONS
●Uses – Indwelling arterial catheters are used for continuous monitoring of systemic blood pressure (BP), evaluation of respirophasic variations in the arterial pressure waveform to determine intravascular volume status, and intermittent blood sampling for laboratory testing. (See 'Uses' above.)
●Site selection – A catheterization site is selected by locating a palpable arterial pulse in a peripheral (radial, brachial, dorsalis pedis) or central (eg, femoral, axillary) arterial site. (See 'Site selection' above.)
●Techniques
•Sterile technique – Standard sterile techniques are always employed for peripheral arterial catheters including masks, sterile gloves, and drape. For insertion of central arterial catheters, full barrier precautions require the addition of caps and eye protection. Necessary equipment is listed in the table (table 2). (See 'Sterile technique' above.)
•Local anesthetic use – In conscious patients, we use local anesthesia to avoid pain (particularly if a skin incision is needed). (See 'Local anesthetic injection' above.)
•Ultrasound use – We routinely use ultrasonography to identify a patent arterial vessel and guide catheter placement.
•Guidewire use – A guidewire is typically used (figure 3), particularly if difficulties with the direct puncture approach are encountered. (See 'Use of a guidewire' above.)
●Monitoring considerations
•Blood pressure – Despite the superiority of direct intra-arterial BP measurement compared with noninvasive techniques, factors such as the site of arterial cannulation, transducer level, or damping of the pressure tracing may cause misinterpretation of the arterial pressure waveform or introduce errors (figure 4 and figure 8). (See 'Monitoring blood pressure' above.)
•Intravascular volume status – Arterial waveform analysis can be used to determine fluid responsiveness. Variations in the waveform that occur during respiration (eg, pulse pressure variation [PPV] or systolic blood pressure variation [SPV], stroke volume variation [SVV]) can be observed or measured to assess responses to fluid challenges (figure 1 and figure 2 and table 1). (See "Intraoperative fluid management", section on 'Respiratory variations in arterial pressure waveform' and "Novel tools for hemodynamic monitoring in critically ill patients with shock", section on 'Volume tolerance and fluid responsiveness'.)
●Complications – Complications of indwelling arterial catheters include vasospasm, thrombosis, particulate or air embolism, accidental intra-arterial injection of medications, dissection or pseudoaneurysm formation, iatrogenic blood loss, and local or systemic infection (table 3 and table 4 and table 5). (See 'Complications' above.)
●Maintenance – We suggest that arterial catheters not be replaced routinely (Grade 2C). Instead, we use vigilant clinical assessment of the insertion site and of the patient to determine the need to remove or replace an arterial catheter. It is preferable not to leave femoral catheters in place for longer than five days and arterial catheters at other sites for more than seven days. Arterial catheters should be discontinued when their use is not critical to patient care. We replace disposable or reusable transducers, associated tubing, and flush solutions at 96-hour intervals. (See 'Maintenance of an indwelling arterial catheter' above.)
●Removal – Aseptic technique is used during removal of arterial catheters. Optimal duration for pressure application depends on the cannulation site, catheter size, and whether the patient has coagulopathy. (See 'Removal of an arterial catheter' above.)
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