Anesthetic Management for Abdominal Aortic Aneurysm Repair




INTRODUCTION



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CASE DISCUSSION


A 72-year-old, 96-kg, 179-cm male is scheduled for a transperineal repair of a 6-cm suprarenal abdominal aortic aneurysm repair. His past medical history is significant for coronary artery disease, hypertension, gastroesophageal reflux, smoking, and chronic obstructive pulmonary disease. His current medical management includes metoprolol, losartan, atorvastatin, and omeprazole. He has not taken any medications this morning. His ­current vital signs are: pulse 95/min, blood pressure 165/96 mm Hg, oxygen saturation 92%, and respiratory rate 19/min.





PREMEDICATION



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  • Anxiolytic: Intravenous midazolam



  • β blocker: Intravenous metoprolol, esmolol infusion, or propranolol



  • Antihypertensive: Intravenous labetalol, hydralazine, or nicardipine



  • Statin: Oral atorvastatin, simvastatin, pravastatin, or fluvastatin



  • Thoracic epidural: Preoperative placement




Sample Dosing Regimen





  • Anxiolytic: Intravenous midazolam 1 to 2 mg, 15 to 30 minutes prior to induction



  • a blocker: Consider slowly titrating intravenous metoprolol 1 to 10 mg (0.1 mg/kg) to a heart rate of < 65 beats/min, 30 minutes prior to induction.



  • Antihypertensive: Consider intravenous labetalol 5 to 50 mg titrated to blood pressure within 20% above baseline blood pressure if not achieved with anxiolysis 10 minutes prior to induction.



  • Statin: Oral atorvastatin 20 to 40 mg, 30 minutes prior to induction



  • Thoracic epidural: Placement of an epidural catheter in the T10–11 interspace 30 minutes preoperatively, with administration of 3 mL of 1.5% lidocaine with 1:200,000 epinephrine as a test dose




Clinical Pharmacology



Anxiolysis prior to major vascular surgery can have the additional benefit of reducing adrenergic tone. Anxiolysis may be sufficient to return this patient’s heart rate and blood pressure to baseline. Midazolam is frequently chosen due to its rapid onset, but the slower offset of midazolam can be a source of sedation into the postoperative period. Prolonged sedation is of more concern in the elderly and those with preexisting cognitive dysfunction.



β Blockers should not be acutely discontinued, because this can result in rebound tachycardia, hypertension, and angina. Evidence supports the continuation of chronic β-blocker therapy.1 Initiation of perioperative β blockade has been questioned based on the PeriOperative Ischemic Evaluation (POISE) trial. The POISE trial demonstrated that perioperative β blockade decreased the incidence of myocardial infarction but increased overall mortality and stroke.2 There are several limitations to the POISE trial; the 2 major limitations are (1) the fixed high dose of metoprolol (100 mg) and (2) the revised cardiac risk index (RCRI) of 1 or 2 in most of the patients (Table 32–1). Therefore, there may still be overall benefit in patients with high cardiac risk (RCRI ≥ 3).




Table 32–1Revised cardiac risk index (rcri) predictors of perioperative cardiac risk.3



The Dutch Echocardiographic Cardiac Risk Evaluation Applying Stress Echocardiography (DECREASE) IV trial demonstrated significant reduction in cardiac mortality and myocardial infarction using bisoprolol 2.5 mg.4 In contrast to the POISE trial, β blockade was initiated a month prior to the procedure, and β blockade was titrated to a heart rate of 50 to 70 beats/min in the DECREASE IV trial. Comparing the results of the DECREASE IV and POISE trials, β blockade is likely still of benefit in most patients presenting for abdominal aortic repair when initiated at least 1 month in advance, titrated to heart rate of 60 to 70 beats/min; hypotension is avoided. Table 32–2 summarizes the recommendations for perioperative β blockade.




Table 32–2Recommendations for perioperative β blockade.



It is extremely important that statins are continued in the perioperative period. Observational data suggest a significant increase in the risk of adverse cardiac events with acute perioperative cessation of statins. Unfortunately, there is no intravenous statin, and most patients are not fed for several days after open abdominal aortic aneurysm repair. Administration via nasogastric tube during this fasting period to avoid discontinuation of statins in the perioperative period has been shown to prevent the increase in cardiac events.5 Statins have benefit in excess of their lipid-lowering effect, including plaque stabilization, anti-inflammation, and reduction of thrombogenesis. There is good evidence supporting initiation of statin therapy in patients undergoing major vascular surgery.6 Ideally, statin therapy should be initiated at least 30 days prior to the operation and continued for at least 30 days afterward. When initiating therapy, the extended-release formulation of fluvastatin is the best choice. The increase in adverse cardiac events is less after the cessation of extended release fluvastatin when compared to shorter acting statins.7 In urgent cases, there may still be benefit in acute initiation of therapy, and there is unlikely to be any harm. Table 32–3 summarizes the recommendations for perioperative statin therapy.




Table 32–3Recommendations for perioperative statin therapy.



Thoracic epidural analgesia using a combination of local anesthetics and opiates is the standard practice for aortic aneurysm repairs at many institutions. A Cochrane systematic review demonstrated a reduction in pain, postoperative intubation, cardiac complications, gastric complications, and renal complications when comparing thoracic epidural analgesia with systemic opioid analgesia.8 No overall reduction in postoperative mortality has been demonstrated. Epidural placement appears to be safe in the setting of intraoperative heparinization, especially if heparinization occurs at least 1 hour after placement. In the event of a bloody tap, it is typical to proceed with surgery, but this should be communicated to the surgical team. There is no evidence to support cancellation of surgery based on a bloody or traumatic neuraxial procedure.9 Patients presenting for vascular surgery are often on chronic anticoagulants and antiplatelet medications. Some of these therapies significantly increase the risk of epidural hematoma and contraindicate epidural placement, as discussed in Chapter 16.




INDUCTION



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  • Analgesic: intravenous fentanyl, sufentanil, morphine, or hydromorphone



  • Local anesthetic: Intravenous lidocaine



  • Sedative–hypnotic: Intravenous propofol, etomidate, or ketamine



  • Muscle relaxant: Intravenous succinylcholine, rocuronium, vecuronium, or cisatracurium



  • Hemodynamic agent: Consider intravenous esmolol, intravenous nitroglycerin, or intravenous labetalol.




Sample Dosing Regimen





  • Analgesic: Intravenous fentanyl 2 to 3 mcg/kg 5 minutes prior to induction



  • Local anesthetic: Intravenous lidocaine 1 mg/kg 15 seconds prior to propofol



  • Sedative–hypnotic: Intravenous propofol titrated to loss of consciousness, approximately 1 mg/kg at induction



  • Muscle relaxant: Intravenous succinylcholine 1.5 mg/kg administered immediately after propofol



  • Hemodynamic agent: Consider intravenous esmolol 1 to 2 mg/kg 2 minutes prior to intubation if blood pressure and heart rate remain poorly controlled.




Clinical Pharmacology



Propofol is an ideal induction agent for the patient in this case. Propofol minimizes airway responses to intubation to a greater extent than other induction agents,10 which is beneficial in this smoker. Elderly patients require lower doses of propofol, especially when paired with opioids.11 Propofol can cause excessive decreases in blood pressure and cardiac output, especially in patients with decreased intravascular volume or reduced cardiac function. Lidocaine is often given just prior to propofol administration to reduce the risk of pain with injection. Mixing lidocaine with propofol in a single syringe should be avoided based on experimental data that demonstrates droplet formation, which theoretically could lead to pulmonary embolism.12



There is a large gap in the anesthetic requirements to ensure unconsciousness and the requirements to prevent a significant adrenergic surge. Dosing induction agents to achieve the latter goal can result in persistently elevated drug levels and prolonged hypotension, especially once an inhaled anesthetic is added. The addition of esmolol can be used to bridge this gap in anesthetic requirements, and esmolol’s effects dissipate very rapidly, minimizing the risk of prolonged hypotension. Esmolol is a extremely short-acting β1-selective adrenergic antagonist with rapid onset within 60 seconds and a short duration of action of 10 to 20 minutes.13 Nitroglycerin and lidocaine are also advocated to help decrease the adrenergic response to laryngoscopy, but when compared with esmolol, neither of these is very effective.14,15 Esmolol has been shown to reduce propofol requirements by as much as 20%.16 If prolonged airway manipulation or awake intubation is anticipated, a bolus of 0.5 mg/kg followed by an infusion of 50 to 300 mcg/kg/min can be used.



Labetalol has also been shown to be useful in preventing hypertension and tachycardia associated with laryngoscopy. Labetalol is a selective α1– and nonselective β-adrenergic antagonist with a 1:7 α/β ratio in the intravenous formulation.17 Labetalol 0.5 mg/kg was shown to be superior to low-dose esmolol (0.25 mg/kg) in controlling heart rate, blood pressure, and rate pressure product during laryngoscopy and intubation.18 Labetalol should be administered 5 minutes prior to laryngoscopy in order to utilize peak drug effect. Labetalol’s 2- to 4-hour duration of action may be beneficial in reducing postoperative hypertension but may also be detrimental during cross-clamp release or significant blood loss.




MAINTENANCE OF ANESTHESIA



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  • Sedative–hypnotics: Sevoflurane, desflurane, isoflurane, nitrous oxide, or propofol infusion



  • Analgesics: Fentanyl, sufentanil, alfentanil, remifentanil, morphine sulfate, or hydromorphone



  • Muscle relaxants: Rocuronium, vecuronium, or cisatracurium



  • Antiemetics: Ondansetron, dolasetron, metoclopramide, dexamethasone, or droperidol as needed


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Dec 30, 2018 | Posted by in ANESTHESIA | Comments Off on Anesthetic Management for Abdominal Aortic Aneurysm Repair
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