Most interventional radiological (IR) procedures are safe and help patients immensely, but sometimes they are associated with complications. Some complications are inherent to the nature of a procedure, while others are not and are preventable by taking some precautions before, during, and after a procedure. Here, I offer general guidelines to physicians and patients on how to prepare for IR procedures.
There are specific preparations for individual procedures. These are usually explained to the patient at the interventional radiology clinic or in their room (if they are hospitalized); such explanation should be part of the process of obtaining an informed consent for a procedure. You may review them at this web site under “About IR procedures and tests”, or, visit www.sirweb.org/patients for more information.
Diet, medications, and hydration
Although many interventional radiological (IR) procedures are performed with only local anesthesia, a majority require conscious sedation for the patient’s comfort and alleviation of pain and anxiety. A few require more sophisticated anesthesia. Since the medications used to induce conscious sedation depress respiration and consciousness (and some directly stimulate the vomiting center in the brain stem), administering them to patients with full a stomach is risky since they may vomit and choke themselves during a procedure. It is important then that the stomach is empty when a patient receives conscious sedation. Generally, different meals clear the stomach at different rates, water and other liquids clearing the fastest, while fatty meals clear the slowest; carbohydrates and proteins lie in between, carbohydrates clearing quicker than proteins. Most meals will vacate the stomach by 8 hours. Herein lies the justification for having nothing by mouth after the midnight preceding the morning of a procedure, the assumption being that there would be ample time for the contents of the stomach consumed at midnight to vacate it before a procedure slated for 8:00 am or thereabout. Patients may, however, drink clear water until 2 hours before the start of a procedure; in fact they are encouraged to do so in some instances, when adequate hydration is necessary to prevent renal injury from iodinated radiocontrast.
Exposure to iodinated radiocontrasts (contrast agents) deserves special mention. Iodinated radiocontrasts are chemical agents rich in iodine that are given to patients either by mouth or intravenously to improve the visibility of normal and abnormal tissues in the body when x-rays pass through them. Since abnormal tissues have more blood vessels most of which abnormally ‘leak’ intravenously administered radiocontrast into the tissue interstices, delaying its washout, they stand out in recognition more than normal tissues, the so-called contrast enhancement. This is the reason intravenous contrast enhancement is encouraged in studying such disorders as tumors, infections, inflammations, radiation injuries, post-surgical changes, etc., – situations in which the examiner wishes to leverage or take advantage of the differences in the number and abnormalcy of blood vessels in diseased tissues to distinguish them from normal ones. Such use of radiocontrast is employed in IR in addition to its use in opacifying the lumens of blood vessels when working on them.
Iodinated radiocontrasts given by mouth, to a large degree, cause no harm, but those given intravenously can alter renal function in some patients. These include those older than 60 years; those with existing poor renal function; those who are dehydrated; those with multiple myeloma; and diabetics. People who belong to one or more of these groups are at increased risk of contrast-induced nephropathy, a state of diminished renal function following exposure to an iodinated radiocontrast. Their risk for this may be reduced by sufficient hydration with normal saline and the administration of such free-radical scavenger as acetyl cysteine (Mucomyst) before exposure to the radiocontrast. Of course, it is important to weigh the risks of such exposure against its potential merits before proceeding with a test or procedure; there are moments when doing nothing (masterly inactivity) is wiser and safer than taking an action. Adequate intravenous hydration of a patient before exposure to iodinated radiocontrast is second only to no exposure to it in the prevention of contrast-induced nephropathy.
Diabetic patients on metformin are a special case because the concurrent taking of the drug and the development of renal impairment can cause lactic acidosis. Lactic acid is one of the many products of metabolism excreted by the kidneys. When it exists in excess the condition is called lactic acidosis. Any form of renal impairment will reduce the excretion of metformin and lactic acid leading to type B (non-hypoxic) lactic acidosis. This condition, though rare, is reported to have a 50% mortality rate. Metformin is a biguanide oral hypoglycemic agent that works by increasing the movement of sugar into glucose-utilizing cells while suppressing the synthesis of sugar in the liver (gluconeogenesis). It is excreted by the kidneys and, like other biguanides, suppresses the action of pyruvate dehydrogenase as well as decrease the transport of mitochondrial reducing agents. These two actions accumulate pyruvic acid in the cell that is converted into lactic acid. Since contrast-induced nephropathy is associated with diminished renal function, diabetic patients (who are already at increased risk for contrast-induced nephropathy) taking metformin should switch to non-biguanide oral hypoglycemics or insulin starting on the day of radiocontrast exposure until their blood chemistry taken 48 hours to 72 hours after the exposure documents normal renal function.
Some complications of interventional radiological (IR) procedures like bleeding at an arterial puncture site, systemic or local skin infection, or acute or delayed thrombosis of a revascularized artery are preventable.
The process of re-establishing blood flow through an occluded artery can be complicated and challenging. It also traumatizes the arterial wall and may precipitate acute re-thrombosis or occlusion of the vessel during or shortly after the procedure. Not only does this jeopardize the interventionalist’s work, it also re-exposes a patient to the ordeal of repeating the intervention at enhanced risk of complications. For these reasons, interventional radiologists give oral Aspirin and clopidogrel (Plavix) (both of which are called antiplatelets because they prevent platelet aggregation) to their patients before starting arterial interventions and intravenous heparin (and sometimes other antiplatelets drugs) during the procedure to reduce the risk of acute thrombosis; patients continue oral clopidogrel for 3 to 6 months afterwards and Aspirin for life.
The commonest reason for bleeding at an arterial puncture site is uncontrolled hypertension, of course assuming a normal coagulation profile. Therefore, hypertensive patients are encouraged to take their morning dose of antihypertensive (s) before arriving for their procedure.
Diabetics on insulin should skip the morning dose of their short-acting insulin and take half their dose of the long-acting insulin; they should receive D5/0.45 normal saline infusion for maintenance therapy and have their blood sugar monitored before, during, and after the procedure. Importantly, their procedure should be done as early in the day as is possible to avoid hypoglycemic attacks.
Infections are known to complicate procedures done on certain parts of the body: the skin, the alimentary tract, and the genitourinary tract. They can also complicate interventions that devitalize tissues like embolizations. Sometimes, mere knowledge of the hazards of infection complicating a procedure on certain anatomic areas of the body, such as vertebroplasty, informs the decision for antibiotic coverage. In all these circumstances it is prudent to provide patients with prophylactic antibiotic coverage and the choice of the antibiotic is governed by the prevailing body flora of the area of the procedure and local microbiologic idiosyncrasies. There are now guidelines for this provided by the Centers for Medicare and Medicaid Services (CMS) in association with other recognized associations, and their use is mandatory. The reader is encouraged to visit www.cms.gov for more information on this.