Historical Background
In 1927 Moniz at the University of Lisbon was the first to demonstrate the clinical utility of angiography by performing the first cerebral angiogram using sodium iodide. In 1929 dos Santos performed the first aortogram. Swick in 1928 reported the initial experience with water-soluble iodinated organic compounds as intravenous contrast agents for urography. By 1956 a less toxic, triiodinated, fully substituted benzene derivative, diatrizoic acid (Hypaque, iodine content 300 mgI/mL, 1550 mosm/kg H 2 O) was introduced, and in 1968 Almén began to develop lower-osmolar (400-800 mosm/kg H 2 O) nonionic compounds to limit hemodynamic alterations, which had been attributed to the high osmolality of prior ionic agents. Low-osmolar ionic compounds such as ioxaglate (Hexabrix, iodine content 320 mgI/mL, 580 mosm/kg H 2 O) and nonionic contrast media such as iohexol (Omnipaque, iodine content 350 mgI/mL, 884 mosm/kg H 2 O) and iopamidol (Isovue, iodine content 370 mgI/mL, 796 mosm/kg H 2 O) were introduced to the United States in the late 1980s. This was followed by the introduction of an iso-osmolar contrast agent, iodixanol (Visipaque, iodine content 320 mgI/mL, 290 mosm/kg H 2 O), with an osmolality similar to blood but with considerably increased viscosity.
Intravascular ultrasound (IVUS) supplements the two-dimensional (2D) and three-dimensional (3D) images obtained by angiography and computed tomography scanning with cross-sectional ultrasound images of the vessel and its wall. Early studies of intracardiac ultrasound and IVUS by Cieszynski in the 1950s, as well as by Eggleton and Carelton in the 1960s, led to the first report of IVUS applied as an alternative to transthoracic echocardiography in 1972. In the late 1980s Yock at Stanford University introduced the first IVUS catheter designed for clinical use, which was quickly adapted for use in coronary and peripheral circulation.
Sedation, Analgesia, and Anesthesia
Pain associated with percutaneous or limited surgical procedures for arterial access can be managed in the majority of patients with local infiltration of an anesthetic, such as 1% lidocaine. In most angiography suites or operating rooms, hemodynamic monitoring is readily available and procedural sedation can be administered by appropriately privileged nurses and physicians. Sedation improves patient tolerance of the procedure by reducing symptoms of anxiety and claustrophobia while decreasing the discomfort associated with manipulation of devices or balloon angioplasty. General recommendations include monitoring for arrhythmias with an electrocardiogram, as well as monitoring blood pressure, pulse, respiratory rate, oxygen saturation, and pain level. Sedation should be administered in accordance with the American Society of Anesthesia guidelines for nonanesthesiologists and the Joint Commission standards.
Sedation is usually achieved by a combination of a narcotic opioid and benzodiazepine. Shorter-acting drugs, such as fentanyl and midazolam (e.g., Versed), are preferred. Each drug is given as a slow intravenous injection, with typical initial dosing for fentanyl at 0.5 mcg/kg (e.g., 25 mcg) and for midazolam at 0.02 mg/kg (e.g., 1 mg). The initial dose and all subsequent doses should always be titrated slowly, administered over at least 2 minutes, and monitored over 2 minutes or longer to fully evaluate the sedative effect. Smaller, incremental doses are recommended for elderly patients and those with renal or hepatic failure. The initial dose of midazolam should not exceed 2.5 mg in a normal healthy adult. Oversedation may limit the patient’s ability to follow directions and may paradoxically produce a disinhibited, agitated state; it may also limit the physician’s ability to identify changes in a neurologic examination. Monitoring of vital signs and patient responsiveness to verbal or tactile stimulation is critical to recognizing oversedation from which the patient may exhibit depressed cardiac function and hypoxia that may progress to airway compromise and apnea. Oversedation and disinhibition are treated similarly, although disinhibition is related to only benzodiazepines. In both cases the procedure needs to be stopped to allow proper assessment of the patient, cessation of medication, and continuation of supportive care. Both opioids and benzodiazepines can be treated by administration of an opioid antagonist, such as naloxone hydrochloride (e.g., Narcan), or flumazenil (Romazicon), a benzodiazepine receptor antagonist. The intravenous dose of naloxone hydrochloride should be titrated according to the patient’s response at increments of 0.2 mg given intravenously at 2- to 3-minute intervals to the desired degree of reversal. Likewise, flumazenil is administered at 200 mcg every 1 to 2 minutes until the effect is seen, to a maximum of 1 mg in 10 minutes or 3 mg in 1 hour. Both medications are short-lived, and sedation or agitation may return.
The use of anesthesiologist-directed sedation, spinal anesthesia, or general anesthesia may be dictated by the complexity and length of the procedure and the necessity for an associated surgical procedure. Other relative indications for the involvement of an anesthesiologist include the need for deep sedation in a patient with a difficult airway; cardiopulmonary, renal, or hepatic comorbidities (American Society of Anesthesiologists level > 2); or a high anxiety level. As an example, general anesthesia is usually required in hybrid cases that involve both an endovascular and an open surgical procedure when concerns exist over the patient’s ability to maintain an airway or when deployment of a thoracic endograft may require cardiac overdrive pacing or medical asystole with adenosine. Spinal anesthesia provides complete analgesia of the lower abdomen, groin, and legs, which can allow a hybrid procedure in a patient with severe chronic obstructive pulmonary disease. Likewise, complex catheter-based procedures that are better tolerated under general anesthesia or monitored anesthesia care (MAC) include recanalization of an occluded superior vena cava or removal of a malpositioned inferior vena cava filter. The extended duration of such procedures and requirement for a large sheath in the neck increase patient anxiety and discomfort despite optimal sedation and local pain control. In general, MAC should also be considered for interventions lasting more than 2 hours and for patients with low tolerance such as those with movement disorders or chronic back pain.
Fluoroscopic Principles
The performance of endovascular procedures requires a thorough understanding of image acquisition, contrast injection techniques, radiation safety, and ultrasound-guided puncture.
Image Acquisition
Digital angiography is required for optimal diagnosis and therapy using 2D imaging. In selective circumstances, rotational angiography with 3D image reconstruction is used. Digital subtraction angiography (DSA) removes background structures with computer-based subtraction to create a high-fidelity image with lower amounts of iodinated contrast material. In the usual acquisition sequence the mask image is obtained, contrast is injected, and the computer subtracts the opacified vessels from the native mask image. Postprocessing can improve image quality in the presence of slight motion artifact, but patient movement should be avoided having the patient hold his or her breath or using other maneuvers. Road mapping is a term that refers to use of an image selected from DSA that is overlaid on the monitor during live fluoroscopy to limit the number of angiographic runs and facilitate vessel access during interventions. Intravenous DSA is now used infrequently for angiography with the advent of low-profile, high-flow, multihole flush arterial catheters.
Contrast Injection Techniques
Despite the convenience of manual contrast injection, use of a power injector allows precise selection of the rate, total volume, maximum pressure, and rate of rise or time to peak flow of administered contrast. In general, the rate and total volume of contrast administered are increased when imaging larger vessels. Some general guidelines can be found in Table 2-1 . Whereas flush multihole catheters can accommodate higher delivery pressures and are often rated up to 1200 psi, end-hole catheters require lower pressures. General settings for pressure are 900 psi for a flush catheter and 300 to 500 psi for an end-hole catheter. Likewise, reducing the maximum injection pressure to 100 to 200 psi, as well as the rate of rise, should be considered when a catheter could be easily dislodged from the orifice of a vessel. Power injection also allows all personnel to move away from the x-ray source, thus decreasing radiation exposure.
| Type of Catheter | Pressure (psi) | Rate of Rise (sec) | Rate (mL/sec) | Total Volume (mL) | |
|---|---|---|---|---|---|
| Aortic arch | Flush | 900-1200 | 0.1 | 15 | 30 |
| Carotid | End hole | 300 | 0.7 | 3-5 | 6-10 |
| Subclavian/brachial segments ∗ | End hole | 300 | 0.7 | 3-5 | 6-10 † |
| Abdominal aorta | Flush | 900 | 0.1 | 15 | 30 |
| Superior mesenteric/celiac artery | End hole | 200 | 1.0 | 3 | 6-20 † |
| Renal | End hole | 200 | 1.0 | 3 | 6 |
| Pelvic vessels | Flush | 900 | 0.1 | 10 | 20 |
| Infrainguinal segments ∗ | End hole | 300 | 0.7 | 3-5 | 6-10 |
∗ Contrast rate and volume increase with distal extremity imaging and increasing vessel disease.
† Use larger volumes to fill distal and/or venous vasculature.
Radiation Exposure and Safety
Increasing complexity of endovascular cases has increased fluoroscopy times, with an attendant risk of radiation injury leading to increased lifetime cancer risk, cataracts, bone marrow suppression, and sterility, as well as local injury progressing from dermatitis to a full-thickness dermal ulcer or cancer. Increased awareness has led to consensus statements regarding best practices and an initiative by the U.S. Food and Drug Administration in 2010 focused on modifying fluoroscopy use and reducing radiation scatter and exposure consistent with as low as reasonably achievable (ALARA) radiation exposure guidelines ( Box 2-1 ). In general, fluoroscopy should be avoided unless acquiring an image or actively performing a task that requires visualization. For example, fluoroscopy should not be performed during a catheter exchange.
Ensure that all medical personnel are wearing leaded aprons, thyroid shields, and leaded glasses.
Modifications to image acquisition technique:
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Minimize the number of angiographic runs.
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Use DSA.
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Decrease the frame rate during routine pulsed fluoroscopy.
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Minimize fluoroscopy.
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Use road map or fluorofade and reference imaging.
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Increase kilovolt and lower milliampere settings.
Reduce radiation scatter and exposure:
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Use leaded shields.
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Move the table far from the radiation source and closer to the image intensifier.
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Remove all metal objects from the field of view.
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Use collimation to confine x-rays to the area of interest.
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Use filters.
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Avoid routine magnification or extreme angulation.
Other measures:
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Use information from other imaging studies such as computed tomography angiography or magnetic resonance angiography to improve preprocedural planning.
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Monitor fluoroscopy times and consider staging long, complex endovascular procedures.
Several techniques can also be used to minimize scatter and exposure. Because the radiation source is below the table and the image intensifier is above the patient, raising the table height and bringing the image intensifier as close to the patient as feasible provides a larger field of view and decreases x-ray scatter. Most modern imaging systems use an automatic dose rate control that modulates the radiation dose for denser objects to allow x-ray penetration and image sharpness. Thus removing metal objects such as clamps from the field of view avoids an automatic increase in radiation dose. In addition, use of collimators to confine the x-rays and focus on the anatomic area of interest reduces radiation exposure to the patient and minimizes scatter. Filters decrease scatter and improve image clarity. Minimizing radiation exposure can also be achieved by minimizing magnification and angulation of the radiation source.
Reducing radiation exposure can be achieved by use of leaded shielding and fluoroscopy table skirts, as well as personal protection equipment, including circumferential leaded aprons, thyroid shields, and lead-containing eyeglasses. Dosimeters should also be worn by personnel to monitor their exposure levels. The maximum allowable whole-body exposure to medical personnel from all sources is 5 rem/yr.
Principles of Ultrasound-Guided Arterial Puncture
Ultrasound-guided arterial puncture (UGAP) should be used routinely, because it reduces access site–related complications both for routine procedures and for those procedures in which large sheaths are used ( 
). Device requirements for UGAP include a portable ultrasound device with a 5- to 10-MHz probe that allows both B-mode and color flow imaging. Access is usually obtained by using a micropuncture set with a microneedle, short 0.018-inch guidewire, and microsheath of normal flexibility—or stiffened, should access be required through significantly scarred regions.
Ultrasound imaging of the common femoral, superficial femoral, and profunda femoris arteries, as well as the adjacent femoral vein, documents the location, patency, and extent of calcification ( Fig. 2-1 ). A typical radiographic landmark for common femoral artery puncture is the middle third of the femoral head. To maximize the transverse diameter of the vessel, the puncture is performed while holding the ultrasound probe in one hand and the needle in the other. It is often necessary to adjust the positioning of the ultrasound to optimize images of the needle tip entering the anterior wall of the vessel. After a single anterior wall puncture, arterial flow is noted at the hub of the needle, allowing wire passage and placement of a microsheath. The microdilator is removed, allowing placement of a 0.035-inch wire. The standard Seldinger technique allows placement of a regular, short, or long interventional sheath.
