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Periprocedural Patient Evaluation

Randall C. Edgell and Justin Sweeney

Informed consent is a critical preprocedural task in today’s medico-legal environment. This involves a detailed discussion between the neurointerventionist or designated physician and either the patient, the patient’s family, and/or the person holding the patient’s power of attorney regarding the disease process and the proposed treatment (Table 9.1).

Neurointerventional procedures carry the specific risks of anesthesia, stroke, kidney damage, bleeding, contrast allergy, vessel injury, and infection;¹ these are discussed in more detail in the sections below.

Cardiac Disease

Atherosclerosis

Atherosclerosis develops as oxygen free radicals oxidize low-density lipoproteins (LDLs) that in turn damage the intima, or inner lining of the arterial walls. This leads to a chronic inflammatory response involving macrophage accumulation and smooth muscle hyperplasia, with subsequent cholesterol and calcium deposition (Table 9.2).

Because atherosclerosis of the coronary and cerebral arteries is usually concomitant, it is important to obtain an appropriate preoperative work-up from a multidisciplinary point of view, and to incorporate this information in the context of perioperative management² (Table 9.3).

Difficulties with Anesthesia

Cardiac disease can often complicate cardiovascular and respiratory management for both the neurointerventionist and the anesthesiologist. A comprehensive pre-operative work-up to define the extent of both cerebral and cardiac atherosclerotic disease is an imperative first step in this process. This allows both the interventional and anesthesia teams to stratify the risks involved in the procedure, particularly those with severe cardiac disease, and plan accordingly.

Postoperative myocardial infarction is a serious concern for patients with cardiac disease. It most commonly occurs 48 hours following anesthesia. Greater than 90% are silent, but symptoms may include chest pain, shortness of breath, and a fluttering sensation in the chest. Close monitoring with serial ECGs, telemetry and cardiac enzymes in high-risk patients is recommended.

Table 9.1 Components of Informed Consent

Table 9.2 Major Risk Factors for Atherosclerosis

Table 9.3 Preoperative Considerations for the Patient with Severe Cardiac Disease15

Abbreviations: CHF, congestive heart failure; MAC, monitored anesthesia care.

Careful monitoring of respiratory status includes oxygen saturation (pulse ox monitoring), breath rate, and volume status. Aspiration, mucus obstruction, medication-induced bronchospasm, and sedation- or analgesic-induced respiratory depression are important causes of respiratory compromise in any patient undergoing anesthesia (Table 9.4).

Table 9.4 Important Factors Compromising Respiratory Status

Atherosclerosis is a systemic disease affecting the length of the vascular tree and often presenting challenges to vascular access. Vascular access is frequently obtained through a transfemoral route with navigation of wires and catheters in the aorta; peripheral vascular disease (PVD) is often severe along this route and can be focal, circumferential, or run the length of the approach. This can lead to unsuccessful access or complications, such as dissection, distal thromboemboli, and vessel occlusion requiring further treatment (see Chapter 7).

Peripheral Vascular Injury

Dissection or thromboembolism leading to a distal vessel occlusion and an ischemic leg most often presents early after a procedure; however, delayed occlusion is possible. Serial evaluation of any attempted vascular access points with pulse, temperature, pain, and ankle-brachial indexes (ABIs), if necessary, is an important step in recognizing problems. If distal occlusion is suspected or discovered, anticoagulation with intravenous heparin is critical in these patients to prevent continued organization and propagation of the clot. Vascular surgery consultation for open repair or revascularization may be necessary in severe cases.

Stroke Risk

Patients with PVD undergoing routine diagnostic angiography have an increased risk of stroke of 1–2%, as compared with disease-free counterparts.² The more severe the disease, the more prevalent atherosclerotic plaques, which increases the risk of catheter-related complications, including stroke. Furthermore, catheters, wires, stents, and coils all have the possibility to form clot on and around them, potentially leading to thromboemboli. The judicious use of wires and roadmap technology, while minimizing catheter contact with the vessel walls, usually decreases this risk.

Renal Disease

Contrast-induced nephropathy (CIN) is one of the most common iatrogenic causes of kidney injury. In most cases, it causes a benign and often transient form of acute renal failure, which is defined as having at least a 0.5 mg/dL or a 25% increase in the baseline serum level of creatinine. However, in patients with preexisting renal insufficiency with or without concomitant diabetes, it may be more severe and eventually require dialysis. The pathogenesis of this condition is complex and not completely understood; the available literature suggests direct free radical tubular injury and/or a hemodynamic imbalance leading to medullary ischemia as possible etiologies.3 Patients with baseline creatinine concentrations above 1.5 mg/dL have an approximately 40% chance of developing CIN.⁴ Preoperative screening for these risk factors is an important first step in prevention (Table 9.5).

Discontinuation of nephrotoxic medications 48 hours prior to angiography can help reduce the rate of CIN. Patients with glomerular filtration rates (GFRs) less than 60 mL/min may benefit from further preventative measures to reduce renal injury, such as preoperative hydration and bicarbonate or Mucomyst intravenous administration.

Prophylaxis

The most commonly used regimens for CIN prophylaxis include hydration with intravenous bicarbonate, saline, and/or the use of N-acetylcysteine (Table 9.6). These are discussed in more detail below. The effects of ascorbic acid, calcium channel blockers, dopamine, fenoldopam, furosemide, mannitol, and theophylline have also been studied; however, no clear benefit bears out in the literature.

Table 9.5 Risk Factors for Developing Contrast-Induced Nephropathy4

Table 9.6 CIN Prophylaxis

The primary prophylaxis for CIN is hydration. However, caution should be exhibited in patients with preexisting renal impairment, as overzealous fluid administration can lead to pulmonary edema and respiratory compromise. There continues to be controversy in the literature regarding which type of hydration, i.e., sodium chloride or sodium bicarbonate, is more effective. Bicarbonate is a safe, readily available agent that alkalizes the tubular urine and is thought to attenuate free radical formation, thus preventing renal tubular injury. A randomized, controlled single-blinded study of 353 well-matched patients with baseline creatinine levels of 1.5 mg/dL and GFR of 48 mL/min found a rate of CIN of ~14% in both those pre-treated with 0.9% saline and those pretreated with 150 mEq/L of sodium bicarbonate.5 They concluded that there was no extra benefit in using sodium bicarbonate.

Mucomyst

The use of Mucomyst (N-acetylcysteine [NAC]) has been validated by recent studies.^6,7 The exact mechanism of nephroprotection provided by NAC is unclear, but it has been proposed to be a vasodilator via nitric-oxide pathways, a free radical scavenger by increasing available glutathione, which is effective in the prevention of apoptosis. The typical regimen given is 600 mg PO twice daily for 24 hours prior to the procedure and for 48 hours after the procedure. There is also evidence of a dose-dependent effect in patients without preexisting renal impairment whereby using a higher dosage protocol of 1200 mg may further reduce the risk of CIN.⁶ A recent review of available studies by Stenstrom et al⁷ found that the use of NAC is safe and inexpensive and will prove to be beneficial in prophylactic prevention of CIN.

The Diabetic Patient

Patients with diabetes and preexisting diabetic nephropathy provide unique challenges to the interventional team. Other common, coexisting comorbities frequently include HTN, hyperlipemia, and hypercholesterolemia, all major risk factors for the development of atherosclerosis and pathology requiring angiography. These patients often have a reduced GFR and are taking medications, such as ACE inhibitors that may predispose them to CIN. Diabetes has been found to be an independent risk factor for CIN and preventative measures should be taken to reduce renal insult.

Glucophage (Metformin)

Glucophage is an oral antihyperglycemic agent used in type 2 diabetics to reduce gluconeogenesis in the liver, glucose uptake in the intestines, peripheral glucose intolerance, and LDL levels in the blood. It is not metabolized by the liver, but is excreted primarily by the kidneys. Its most serious side effect is a rare condition called metformin-associated lactic acidosis (MALA), which can develop when exposed patients taking this medication undergo contrast angiography. Contrast media may reduce renal tubular excretion of metformin, leading to enhanced anaerobic metabolism. The incidence of MALA is 1 in 33,000/yr and has a mortality of 50%. Patients with preexisting kidney and liver disease, congestive heart failure, excessive alcohol use, or dehydration are at highest risk. Metformin should be discontinued 24 hours prior to the procedure and for 48 hours thereafter. It may be restarted when baseline creatinine levels are reached. Symptoms of lactic acidosis include irregular heartbeat, dizziness, fatigue, abdominal and muscle pain, and shortness of breath (Table 9.7

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Endovascular Complications Radiation Physics and Safety Spinal Arteriovenous Malformations Endovascular Techniques for Aneurysm Therapy, Arteriovenous Malformation Treatment, and Carotid Artery Stent Placement Extracranial Arterial Occlusive Disease Introduction to Endovascular Equipment

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