General Principles of Sedation, Angiography, and Intravascular Ultrasound

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.