Advertisement

Arterial Line

  • James Bardes
  • Lydia LamEmail author
Chapter

Abstract

  • Arterial lines are indicated for continuous invasive blood pressure monitoring or in patients that require frequent arterial blood sampling. The invasive blood pressure measurement is more accurate than the noninvasive sphygmomanometric measurement, especially in the critically ill.

  • Consent should be obtained, if possible.

  • Complications include catheter dislodgement and bleeding, hematoma, thrombosis, false aneurysm, peripheral tissue ischemia and necrosis, and infection.
    • Although rare, the most serious complication is the development of ischemia and necrosis of the extremity, usually the fingers or toes. Extremity ischemia can occur due to embolization by a dislodged clot, or atheromatous debris, or due to fragmentation of the catheter.

    • Routine monitoring of perfusion to the distal extremity should be performed.

  • The radial artery is the most commonly accessed vessel followed by the femoral artery, in both adults and children.
    • Alternative sites of insertion include the ulnar, brachial, and the dorsalis pedis.

    • Caution should be used when accessing the ulnar artery, because this is the dominant artery to the hand in 95% of patients. In the presence of poor collateral flow, or an occlusion of the radial artery, the hand can become ischemic. The adequacy of the collateral circulation can easily be assessed by performing the Allen’s test (see radial artery catheter).

  • Arterial catheterization is contraindicated by lack of arterial pulse, inadequate collateral flow or circulation to an extremity, infection at the catheter site, and the presence of a synthetic vascular graft.

  • Use of ultrasound guidance improves cannulation rates, especially in patients with not easily palpable pulses.
    • A straight linear array probe is preferred for vascular imaging.

    • These probes produce higher frequencies (5–13 MHz), which provide better resolution for blood vessels.

    • Color Doppler can be used to confirm flow within the artery.

15.1 General Principles

  • Arterial lines are indicated for continuous invasive blood pressure monitoring or in patients that require frequent arterial blood sampling. The invasive blood pressure measurement is more accurate than the noninvasive sphygmomanometric measurement, especially in the critically ill.

  • Consent should be obtained, if possible.

  • Complications include catheter dislodgement and bleeding, hematoma, thrombosis, false aneurysm, peripheral tissue ischemia and necrosis, and infection.
    • Although rare, the most serious complication is the development of ischemia and necrosis of the extremity, usually the fingers or toes. Extremity ischemia can occur due to embolization by a dislodged clot or atheromatous debris or due to fragmentation of the catheter.

    • Routine monitoring of perfusion to the distal extremity should be performed.

  • The radial artery is the most commonly accessed vessel followed by the femoral artery, in both adults and children.
    • Alternative sites of insertion include the ulnar, brachial, and the dorsalis pedis.

    • Caution should be used when accessing the ulnar artery, because this is the dominant artery to the hand in 95% of patients. In the presence of poor collateral flow, or an occlusion of the radial artery, the hand can become ischemic. The adequacy of the collateral circulation can easily be assessed by performing the Allen’s test (see radial artery catheter).

  • Arterial catheterization is contraindicated by lack of arterial pulse, inadequate collateral flow or circulation to an extremity, infection at the catheter site, and the presence of a synthetic vascular graft.

  • Use of ultrasound guidance improves cannulation rates, especially in patients with not easily palpable pulses.
    • A straight linear array probe is preferred for vascular imaging.

    • These probes produce higher frequencies (5–13 MHz), which provide better resolution for blood vessels.

    • Color Doppler can be used to confirm flow within the artery (Fig. 15.1).

Fig. 15.1

Ultrasound of the radial artery (white arrow). Note the color Doppler in (b) identifies flow within the artery

15.2 Radial Artery Catheter

  • The Allen’s test should always be performed to confirm adequate collateral circulation to the hand (Fig. 15.2).
    • Elevate the hand for approximately 30 seconds.

    • Apply pressure over the radial and ulnar arteries simultaneously to occlude flow distally. The hand should appear pale.

    • Pressure is released from the ulnar artery. The skin color to the hand should return within a few seconds.

    • If color does not return to the hand within a few seconds, the ulnar artery does have sufficient flow to fully perfuse the hand. In this case, it is unsafe to place a radial arterial line.

  • The patient’s arm and wrist should be extended with the palmar surface visible. A small towel may be rolled and placed under the wrist to achieve correct positioning. However, overextension of the wrist may make the artery more difficult to palpate (Fig. 15.3).

  • Puncture sites should be over the radial pulse, as distal as possible, about 1 cm proximal to the radial styloid process.

Fig. 15.2

Allen’s test. (a) Pressure is applied to the radial and ulnar arteries simultaneously until the hand appears pale. (b) After releasing the pressure on the ulnar artery, the color returns to the hand. This demonstrates adequate flow from the ulnar artery to the hand; a radial arterial line can safely be placed

Fig. 15.3

Positioning for radial arterial line placement. Note the slight extension of the wrist with a small towel underneath

15.3 Brachial Artery Catheter

  • The patient should be supine and the arm extended (Fig. 15.4).

  • The artery can be palpated, or identified with ultrasound, proximal to the antecubital fossa and between the heads of the biceps and triceps.

  • Care should be taken when selecting the brachial artery for cannulation; the median nerve travels adjacent to the vessel and may be injured.

Fig. 15.4

Positioning for a brachial arterial line. The solid line represents the space between the heads of the biceps and triceps

15.4 Femoral Artery Catheter

  • Patients should be placed supine with slight external rotation of the selected hip if possible.

  • The key anatomic landmark for the femoral artery is the inguinal ligament, which extends from the anterior superior iliac spine to the pubic tubercle. The external landmark for the femoral artery is the middle of the inguinal ligament. The puncture site should be about 2–3 cm below the middle of the inguinal ligament (Fig. 15.5).

  • Within the femoral triangle, the artery is lateral to the femoral vein and medial to the femoral nerve.
    • The anatomy of the femoral triangle can be remembered by the mnemonic VAN from medial to lateral (vein, artery, nerve).

Fig. 15.5

(a, b) Landmarks for femoral artery catheter placement

15.5 Dorsalis Pedis Artery Catheter

  • The patient should be supine with a slight extension of the ankle joint.

  • The dorsalis pedis can be palpated lateral to the extensor hallucis longus tendon on the dorsal surface of the foot (Fig. 15.6).

  • Adequacy of the collateral flow to the foot can be assessed by occlusion of the dorsalis pedis artery and compression of the nail bed of the big toe for a few seconds. The color of the nail bed should return to normal as soon as the pressure is released.

Fig. 15.6

Positioning for dorsal pedis placement, dashed line indicates the extensor hallucis longus tendon

15.6 Equipment

  • Ultrasound machine, if ultrasonic guidance will be used.

  • Arterial line kits are commercially available. Most kits include an 18 g Seldinger needle, a guidewire, in some cases a dilator, and a catheter (Fig. 15.7).

  • There are several commercial devices that include self-contained guidewires and allow performance of a modified Seldinger technique (Fig. 15.8).

  • The operator should don full universal sterile precautions.

  • Chlorhexidine prep, sterile towels, drapes, gauze, and sterile ultrasound covers should be available.

Fig. 15.7

Equipment needed for an arterial line placement. (A) Seldinger needle, (B) syringe, (C) dilator, (D) guidewire, (E) femoral catheter, (F) radial catheter

Fig. 15.8

Device with self-contained guidewire. Note the arrow identifying the extended guidewire in Fig. B

15.7 Procedure

  • The artery is palpated or identified with ultrasound.

  • Chlorhexidine antiseptic should be applied widely and then sterile drapes placed.

  • Local anesthetic should be injected over the cannulation site with a 27 g needle. About 1 milliliter of 1% plain lidocaine is recommended.
    • Too much local anesthetic can obscure the vessel either to palpation, or the image if using ultrasound.

  • The arterial catheter can be placed by direct insertion or by a Seldinger technique.

15.8 Direct Insertion Technique (Catheter over a Needle)

  • This is the preferred technique for radial artery or dorsalis pedis artery cannulation.

  • This technique requires either a needle with angiocatheter or a device used for the modified Seldinger technique.

  • The artery is palpated with the non-dominant hand, while the dominant hand inserts the intravascular needle/catheter, at an angle of 30–45°, until pulsatile blood is obtained (Fig. 15.9). The catheter is then advanced into the artery, and the inner needle is removed (Fig. 15.10).

Fig. 15.9

Direct insertion of a dorsalis pedis arterial line. (a) The vessel is accessed at a 30–45° angle (b) until bright-red blood returns

Fig. 15.10

Direct insertion of a dorsalis pedis arterial line. After accessing the vessel the catheter is advanced over the needle into the vessel

15.9 Seldinger Technique (Catheter over Guidewire)

  • This is the preferred method for femoral or brachial artery cannulation.

  • An 18 g needle is used to access the vessel at a 45° angle until a flash of bright-red blood is seen in the needle hub (Fig. 15.11).

  • After a flash of bright-red blood is seen, the needle should be lowered to an angle closer to 20–30°. It is important to hold the needle very steadily in position; otherwise, the tip may leave the artery.

  • A guidewire is then advanced into the artery, and the needle is removed over the wire (Fig. 15.12).

  • If a dilator is used it should only be used to dilate the soft tissue. These are commonly used with femoral catheters.

  • A small skin incision is made at the site of the needle entry, to facilitate the insertion of the catheter through the skin and avoid kinking of the catheter during its advancement (Fig. 15.13).

  • The catheter is advanced over the guidewire into the artery. A gentle twisting motion may help the catheter pass through the tissue. The guidewire is then removed, and bright-red pulsatile blood should be visualized.

  • The catheter should pass smoothly over the guidewire. If resistance is met, the operator should reassess correct placement of the guidewire (Fig. 15.14).

Fig. 15.11

Seldinger technique to place a brachial arterial line. (a) A linear ultrasound probe can be used to identify the vessel. (b) An 18 g needle is used to access the vessel at a 45° angle until a flash of bright-red blood is seen in the needle hub; in this case the artery is identified by palpation

Fig. 15.12

Seldinger technique to place a brachial arterial line. A guidewire is advanced into the artery and the needle removed over the wire

Fig. 15.13

Seldinger technique to place a brachial arterial line. A small skin incision is made at the site of the needle skin entry

Fig. 15.14

Seldinger technique to place a brachial arterial line. (a) A catheter is advanced over the guidewire (b) and the guidewire removed

15.10 Modified Seldinger

  • This technique is performed with devices that have built-in guidewires.

  • The artery is punctured in a similar fashion to the Seldinger technique (Fig. 15.15).

  • Once a flash of blood returns, the angle is again lowered to 20–30°. The built-in guidewire is then advanced fully (Figs. 15.16 and 15.17).

  • The catheter can then be advanced over the wire (Fig. 15.18).

  • Lastly the wire and needle assembly are removed together.

Fig. 15.15

Modified Seldinger technique, inserting a radial arterial line. The artery is punctured in a similar fashion to the Seldinger technique

Fig. 15.16

Modified Seldinger technique, inserting a radial arterial line. Once a flash of blood returns, the angle is lowered to 20–30°

Fig. 15.17

Modified Seldinger technique, inserting a radial arterial line. The internal guidewire is advanced

  • Once in place, the catheter is connected to a pressurized bag of normal saline connected to a pressure transducer.

  • The arterial line should be sutured in place and a sterile dressing applied.

Fig. 15.18

Modified Seldinger technique, inserting a radial arterial line. The guidewire and needle assembly are removed

15.11 Blood Pressure Monitoring

  • Blood pressure is monitored by measuring the pressure wave transmitted by the arterial pulse, through a fluid-filled tube, connected to a pressure transducer.

  • The tubing that connects the catheter to the pressure transducer is not normal IV tubing. Normal IV tubing is too compliant and will not allow accurate measurements. The tubing should be non-compliant to allow proper transducing of the pressure wave. The tubing should be less than 1.2 m (4 ft) for the most accurate reading. Longer tubing may make the blood pressure appear elevated.

  • The transducer must be “leveled” at the patients’ bedside and aligned with the aortic root; externally this means alignment with midaxillary line in the 4th intercostal space. If the transducer is higher than this, the blood pressure will appear lower, and alternatively if the transducer is lower, the blood pressure will appear elevated. Leveling will need to be adjusted whenever the patients positioning is adjusted in bed.

  • The transducer is “zeroed” prior to measuring blood pressures. This exposes the transducer to atmospheric pressures and sets that point as zero. If not properly zeroed, the reported blood pressure will be significantly elevated.

  • Waveform (Fig. 15.19)
    • The normal waveform shape may vary depending on the caliber of the cannulated artery. However, the MAP remains the same throughout the arterial tree.

    • Over-damping of the catheter and the tubing system results in a muted waveform, which underestimates the systolic pressure and overestimates the diastolic pressure. The mean arterial pressure remains the same. The pressure waveform appears flattened. This may be caused by air bubbles or blood clots in the system, the tube kinking, loose connections, or vasospasm.

    • Under-damping leads to falsely elevated systolic pressures and lower diastolic pressures. The mean arterial pressure remains the same. The waveform has a steep systolic upstroke, a narrowed systolic peak, and rapid diastolic run off. This can be caused by hypothermia, tachycardia and arrhythmias, and in patients with severe atherosclerosis.

    • Some damping effect is normal and preferred in the pressure waves. A good measure of the damping effect is the square wave test (fast flush test) (Fig. 15.20).
      • Begin by flushing the arterial line. The wave will appear as a square. Then watch for the oscillations that occur when the flush is stopped.

      • A properly damped arterial line will have 2–3 oscillations immediately after the square wave disappears. The tracing will then return to a normal arterial waveform. A distinct dicrotic notch should be present.

      • An overdamped waveform will have only one oscillation after the square wave, and the dicrotic notch will disappear.

    • Under-damped lines will have multiple oscillations after the square wave, and multiple notches can be seen in the waveform.

    • Understanding the damping effect is important to the provider when making clinical decisions about blood pressure management or when setting blood pressure goals.

Fig. 15.19

Illustrations demonstrating damping effects on arterial waveforms

  • Troubleshooting should follow a systematic check of the transducing system.
    • Ensure all cables are securely connected.

    • The system can be re-zeroed and then the arterial tubing flushed.

    • The patient’s hand position should also be checked. Excessive extension or flexion can kink the catheter causing the waveform to be severely dampened.

Fig. 15.20

Illustration of the square loop test

15.12 Tips/Pitfalls

  • After several attempts at cannulation, the artery will spasm, making catheter placement difficult. A short time should be allowed to pass before attempting placement again.

  • Occasionally after advancing the catheter, no blood flow will be present after the guidewire is removed. It is possible that the practitioner has advanced the catheter through the posterior wall of the vessel inadvertently. The transfixation technique can then be applied.
    • The catheter is slowly retracted until blood flows freely from the end of the catheter.

    • A guidewire can then be advanced through the catheter into the vessels. The catheter is then advanced over the guidewire.

    • The guidewire can then be removed.

  • If there is resistance during insertion of the guidewire, rotate the needle gently and try advancing the guidewire again. No force should be used.

  • Inspect the extremity on a frequent basis for any signs of peripheral ischemia. If there are any signs of ischemia, remove the catheter immediately

  • Remove the catheter as soon as possible to reduce complications.

  • After catheter removal direct pressure should be held for 5–10 min, longer if the patient is coagulopathic. After removal, the catheter should always be inspected to ensure it is intact. The puncture site and pulse should be evaluated in about 15–20 minutes for hematoma or extremity ischemia.

Copyright information

© Springer International Publishing AG, part of Springer Nature 2018

Authors and Affiliations

  1. 1.Division of Trauma, Emergency Surgery and Surgical Critical CareUniversity of Southern CaliforniaLos AngelesUSA

Personalised recommendations