Patient Medications

Many medications may affect the patient’s catheterization risk (Table 8-3).

Table 8-3 Medications That May Impact Cardiac Catheterization Risk

Warfarin should be held for at least 72 hours before the procedure. The goal international normalized ratio (INR) should be achieving an INR of less than 1.5 before the procedure to reduce the bleeding risk. Understanding why the patient has been taking warfarin is important as he or she may require bridging therapy with heparin, particularly if a mechanical valve is involved.

Diuretics should generally not be taken the morning of the procedure. Dehydration may decrease renal flow and increase the risk of contrast nephropathy and hypotension.

Diabetic patients should not take any short-acting insulin on the morning of the procedure and decrease their long-acting insulin dose by half to help reduce the risk of hypoglycemia. Metformin poses a slight but very real risk of lactic acidosis. Because of this, Metformin should be held for at least 24 hours before the procedure and one should consider holding for 48 hours in those with renal insufficiency. This medication can be restarted 48 hours after the procedure if there is no evidence of decrement in renal function. Other oral diabetic medications may also need to be held.

Because of sedation during the procedure, it is difficult to monitor the diabetic patient for signs/symptoms of hypoglycemia or hyperglycemia. One should check blood sugar before initiation of the procedure and as needed throughout the case to minimize risk. If appropriate, the patient should have a dextrose or insulin infusion maintained during the periprocedure period in an attempt to avoid hypoglycemia or hyperglycemia.

Erectile dysfunction medications can also cause significant harm in the catheterization laboratory. When combined with nitrate therapy, there can be a precipitous drop in blood pressure that does not respond well to volume or vasopressor resuscitation. Therefore sildenafil (Viagra) and vardenafil (Levitra) should be held for a minimum of 24 hours before the procedure. Tadalafil (Cialis) has a half-life of 17.5 hours and must be held for 4 days before the procedure.

Radiographic Contrast Media

The use of iodinated contrast must always be considered a potential source of complications in patients undergoing catheterization. There are multiple contrast agents currently available, and differentiating between them requires knowledge of their characteristics (see Chapter 4) and recognition of their chemical and trade names. Low osmolar and nonionic contrast agents are associated with a lower incidence of bradycardia, hypotension, and myocardial ischemia developing in the patient, and these agents are now routinely used during cardiac catheterizations. Almost all cardiac catheterizations today are routinely performed with nonionic, low-osmolality agents.

Contrast-induced renal insufficiency represents the leading cause of in-hospital acute renal failure and is discussed in detail in Chapter 4. Several risk factors have been identified that are found in patients at higher likelihood of developing contrast-induced nephropathy (CIN) (Table 8-4). Unfortunately, many of these parameters are not changeable and therefore do not lend themselves as potential ways to avoid CIN. A risk score has been devised identify patients at higher risk for CIN and is shown in Figure 8-1. Prophylactic strategies to decrease the risk of CIN center around three strategies: maintaining adequate intravascular volume, limiting the amount of contrast delivered, and avoiding medications that could exacerbate renal dysfunction.

Table 8-4 Risk Factors for Development of Contrast-Induced Nephropathy

Figure 8-1 A risk score developed by Mehran et al to predict the likelihood of contrast-induced nephropathy (CIN) after percutaneous coronary intervention. Each risk factor listed is associated with a score. Adding up all of the points for any given patient then calculates the total risk score. On the right of the figure, the table depicts the estimated risk for CIN and dialysis.

(From Mehran R, Aymong ED, Nikolsky E., et al: JACC 44:1393-1399, 2004.)

There are many protocols that have been published that outline how to ensure adequate hydration. The most commonly cited formula uses 0.9% normal saline for 12 hours before and 12 hours after the procedure. Sodium bicarbonate for hydration also is commonly used (154 ml of 1000 mEq/L sodium bicarbonate to 846 ml of 5% dextrose with an initial intravenous (IV) bolus of 3 ml/kg per hour for 1 hour immediately before contrast followed by a rate of 1 ml/kg per hour during the contrast exposure and for 6 hours after the procedure). Data supporting the use of acetylcysteine (600 mg orally twice daily the day before and day of the procedure), although modest, suggest that it can be considered for patients at high risk of contrast nephropathy. Many other pharmacologic treatments (including furosemide, mannitol, dopamine, and fenoldopam) have not been shown to be effective or even have caused more harm and should not be used.

To minimize the chance of CIN, use the lowest amount of IV contrast necessary to perform the study. Whether the iso-osmolar or low-osmolar agents reduce CIN remains under study.

Medications such as angiotensin receptor blockers (ARBs), angiotensin-converting enzyme inhibitors (ACEi), and nonsteroidal antiinflammatory drugs (NSAIDs) should be discontinued for 1 to 2 days before a catheterization. Withholding them for 3 to 4 days following the procedure is also commonly done. However, it has never been shown that the use of ACEi or ARBs in the absence of renal artery stenosis truly increases the risk of renal insufficiency.

Allergic reactions to contrast are discussed in Chapter 1. It is worth remembering that these reactions are characterized as “anaphylactoid” in that they do not require previous exposure to contrast (and thus circulating IgE) to exist but do occur as a result of mast cell degranulation. A patient with a history of multiple food and drug allergies and, of course, those that have had previous reactions to contrast are especially at high risk. The perception that patients having a seafood or shellfish allergy also are at higher risk has never been shown to be true and should not be used as criteria to administer prophylaxis for contrast reactions.

Prophylaxis for patients who are at risk for reactions to contrast media should include prednisone and diphenhydramine. Figure 8-2 depicts treatment algorithms for mild and severe reactions.

Figure 8-2 Treatment paradigm to guide prophylaxis against contrast-induced allergic reactions.

(From Klein LW, Sheldon MW, Brinker J, et al: Cathet Cardiovasc Intervent 74:731, 2009, fig 1c.)

{Fig. 8-3}

Figure 8-3 Treatment protocols used when allergic reactions to contrast are encountered. A, For mild allergic reactions. B, For severe reactions.

(From Klein LW, Sheldon MW, Brinker J, et al: Cathet Cardiovasc Intervent 74:731, 2009, fig 1a and b.)

Thrombocytopenia

Thrombocytopenia (low platelet count) is a troublesome finding on the preprocedural laboratory work. If thrombocytopenia is medication related, that medication should be stopped. A more difficult scenario is the patient with end-stage liver disease who has significant splenic sequestration of platelets. The platelet count is often less than 50,000. There is debate as to whether transfusing platelets before the procedure is helpful because transfused platelets are rapidly consumed and are not available to aid in clotting. Platelet transfusions, if done, should occur during the procedure and not before. For patients at high risk of bleeding, one should consider radial artery access. Of course, the nonaccess site bleeding risks remain the same.

Systemic Hypertension

Poorly controlled hypertension increases the risk throughout the procedure. In addition to the increased risk of cerebrovascular accident and respiratory insufficiency from the hypertension alone, elevated blood pressure increases the risk of vascular access complications. Closure devices are relatively contraindicated in patients with significant hypertension. Attempts should be made to lower the blood pressure safely before sheath removal. Hydralazine (50 mg PO) can acutely lower blood pressure after procedures to aid in sheath removal. It is important to continue hemodynamic monitoring of the patient postcatheterization because hypertensive-related complications can be detected early with continued reassessment of the patient’s status.

Other Comorbidities

Other comorbidities the patient may have should be stabilized before the patient is sent to the catheterization suite, if possible. Anemia and bleeding tendencies should be identified and the etiologies known before undergoing the procedure. This is especially true for those patients who require PCI and may be on multiple anticoagulant and antiplatelet agents.

Patients with decompensated congestive heart failure in whom catheterization can be delayed should be diuresed to help aid the comfort of the procedure for them.

Chronic obstructive pulmonary disease is another illness often coexisting with cardiovascular disease and patients who are experiencing acute exacerbations of the problem should have their procedure postponed if possible. Another underdiagnosed problem in medicine is obstructive sleep apnea. These patients often become hypoxic with sedation and should have their non-invasive ventilation (CPAP) or BiPAP) devices with them during the procedure to minimize the risk of worsening their baseline respiratory insufficiency.

Vascular Complications

Causes of peripheral arterial complications should be identified early. If a large dissection or thrombotic occlusion occurs, a vascular surgeon should be consulted immediately or, alternatively, access can be obtained in the contralateral femoral artery and the dissection may be treated percutaneously (i.e., stenting).

Enlarging hematomas should be given prompt attention because they may result in neurovascular compromise to the leg. Direct pressure usually is sufficient to obtain hemostasis, but sometimes patients need to be brought back to the laboratory. To tamponade the bleeding site, a balloon may be inflated in the area of the femoral artery where contrast is leaking from the vessel. In some cases, the placement of a covered stent to ensure hemostasis of the artery is necessary. A vascular surgeon typically will be able to identify the defect in the artery and achieve hemostasis in the operating room.

Arterial thromboembolism to other areas, such as the brain, may not be immediately treatable but requires close observation or prolonged heparin, depending on neurologic findings. Occipital blindness, a rare event that is caused by hyperosmolarity of the contrast agent, is usually transient and requires no definitive treatment except for hydration and maintenance of blood pressure. Steroids have also been used to treat this condition.

An air embolus to the central nervous system may cause the patient to show features of acute stroke such as agitation, confusion, or aphasia. A small air embolus usually resolves and does not often result in permanent damage. Although hyperbaric oxygen chambers have been used successfully for treatment, these are not widely available.

Hypotension may occur before, during, and after cardiac catheterization from a variety of conditions. Before cardiac catheterization, hypotension may be caused by hypovolemia induced by fasting before the procedure (water intake should be allowed) or diuretics.

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