What the Anesthesiologist Should Know before the Operative Procedure
Open thoracic surgery for aortic repair or replacement is performed for the treatment of aortic aneurysms and dissections. A thoracic aortic aneurysm has a localized vessel diameter 50% more than the normal value (adjusted for age and height), whereas an aortic dissection is the structural violation of one or more aortic vessel layers that results in extension of a tear or bleeding into an abnormal space.
The potential for aneurysm rupture or aortic dissection is of critical importance in deciding when to intervene, along with the location of the pathology and involvement of perfusion to other organs. Elective resection of an aortic aneurysm is performed usually when the aortic diameter of more than an absolute diameter of 5-5.5 cm is reached, since aneurysms > 6 cm are at a progressive increase in rupture, dissection or death. Average growth of an aneurysm is about 0.1 cm/year. The decision for surgery is dependent on patient characteristics (e.g., sex, age, height, body surface area) that have been used to develop indexed aneurysm size for prediction of surgical risk. Some centers support intervention on an ascending aortic aneurysm under 5 cm in diameter in the presence of a bicuspid aortic valve.
Evaluation of the vessel wall is performed using imaging modalities such as computerized tomography (CT), computerized tomography with angiography (CTA), magnetic resonance imaging (MRI), or transesophageal echocardiography (TEE). Aneurysms that involve all three layers of the vessel wall (intima, media, and adventitia) are known as true aneurysms, whereas pseudoaneurysms involve only the intima and/or media. Often, coronary angiography and echocardiography are performed to evaluate the aortic valve and root, and identify the need for concomitant cardiac procedures.
Aortic dissections may be classified using the Debakey or the Stanford classification. The Debakey classification divides these into three types: Type I, involving the ascending and descending aorta; Type II, which involves the ascending aorta only; and Type III, which involves the descending aorta distal to the origin of the left subclavian artery. More commonly, the Stanford classification is used: Stanford Type A involves the ascending aorta and/or arch, while Stanford type B extends distal to the arch-descending aorta transition.
Risk factors for developing acute aortic syndromes and dissection include long-standing hypertensive disease, family history of aneurysm, arteritis (e.g., giant cell, Takayasu), pregnancy, weightlifting, and cocaine use. Connective tissue disorders, such as Ehlers-Danlos and Marfan syndromes, may weaken the vessel wall and promote accelerated aneurysm formation. Other common comorbidities include cerebrovascular, cardiovascular disease renal disease, peripheral vascular disease and atherosclerosis, obesity, COPD, and diabetes, which increase surgical risk.
Several other conditions predispose patients for aneurysm formation. Patients with bicuspid aortic valves, or coarctation of the aorta may also develop ascending aortic aneurysms. Pathophysiology also includes direct trauma to the aorta, and inflammation or infection of the aortic wall.
1. What is the urgency of the surgery?
What is the risk of delay in order to obtain additional preoperative information?
Extensions of aortic dissection and aneurysm rupture are major complications in the absence of surgical intervention. If elective, the patient should be optimized for this major operation, and preoperative counselling is recommended. Repair of an aneurysm, dissection, or rupture should be performed expeditiously if life-threatening. Many referral centers have a diagnostic and treatment pathway for acute aortic dissection, as published in recent multidisciplinary guidelines by the AHA/ACC (See references).
For type A aortic dissections, surgical mortality is 15-30%, whereas non-operative mortality approximates 70%. Therefore, in the absence of multisystem organ failure, the benefit of surgery outweighs the risk.
Type B dissections, which extend distal to the aortic arch-descending aorta transition (DeBakey Type III), have lower non-operative mortality risks (30-50%), and operative versus medical management risks are fairly equal. Therefore, uncomplicated type B dissections may be observed for progression and may be surgically repaired in a non-emergent fashion or through an endovascular approach (see Thoracic Aortic Procedures: Endovascular Procedures). In 25% of patients with type B dissections, their course is complicated by a malperfusion syndrome or hemodynamic instability, which results in a high risk of early mortality.
Thoracic aortic surgery is an emergency when the aorta has ruptured or a vessel tear has occurred, compromising blood flow to vital organs or limbs. In such cases, where revascularization would improve end organ function, the benefit of surgery greatly outweighs the risk of waiting for further diagnostic studies. Transthoracic, transesophageal, or epiaortic echocardiography is of particular value in these situations because they provide real time information, and are easily performed perioperatively. Echocardiography can confirm the diagnosis and extent of the aneurysm, identifying concomitant cardiac problems (need for valve replacement, coronary revascularization), as well as other indicators of emergency (pericardial effusion or tamponade, pleural hemorrhage).
Coronary artery involvement is prevalent in 20% of patients presenting with type A aortic dissection, sometimes seen as wall motion abnormalities on TEE. Mortality rate increases by 1% to 2% per hour, following the onset of symptoms. Patients are immediately taken to the operating room.
Surgical treatment may be urgent if an aneurysm is at high risk for rupture or extension of dissection, but waiting for more definitive imaging such as a CTA or MRI of the entire aorta will improve the quality of the repair. Patients who are smokers, elderly, or who have other significant comorbidities may require more expeditious repair; however, the value of obtaining additional diagnostic information may significantly alter surgical management.
Given the extensive nature of open thoracic aortic surgery for aneurysm resection, an elective repair allows for identification of the extent of aneurysm, coexisting cardiac lesions, progression of vascular disease and optimization of medical comorbidities. Additional testing and extensive imaging assists surgical and aesthetic decision-making in terms of creating a perioperative plan, and proper allocation of needed resources (hybrid operating room, perfusion, cardiac anaesthesia, and neuromonitoring teams, availability of blood products, peripheral access for cardiopulmonary bypass, etc.).
2. Preoperative evaluation
Patients with aortic disease also often have uncontrolled hypertension, cardiopulmonary disease and smoking history, renal disease, diabetes, and other systemic risk factors for aneurysm. These conditions should be assessed and optimized if possible for an elective procedure.
When preparing an anesthetic plan, although all open approaches to dissection and aneurysm will involve cardiopulmonary bypass, the planned surgical approach is of utmost importance to the anesthesia team’s understanding of patient positioning, access and invasive monitoring choices, and anesthetic drug choice. For example, a decision for axillary cannulation may eliminate the radial artery as a site for systemic pressure monitoring; coronary revascularization may require saphenous vein harvest; a thoracotomy approach to a descending aneurysm may warrant one-lung ventilation.
Understanding where cannulas for cardiopulmonary bypass will be placed is a key question; in the case of aortic dissection, differentiation of the true and false lumens using ultrasound, TEE or fluoroscopy may be required to identify placement of lines and cannulas in the true lumen, so special equipment may be needed. Other important issues to clarify with the surgical team include 1) ability to cross-clamp the aorta and where cross-clamps will be placed; 2) need for concomitant cardiac procedures; 3) plans for deep hypothermic circulatory arrest (DHCA; if debranching of the arch vessels, or cross-clamping of the aorta is impossible); 4) if selective perfusion will be provided to certain body parts during the procedure to limit ischemic time (head vessels, viscera, renal arteries); and 5) risk of bleeding.
Concomitant cardiac conditions should be evaluated as part of the perioperative risk assessment and identifying medical and surgical treatments. The aortic valve, coronary arteries, aortic root, and all aspects of the aorta (ascending, arch, and descending) must be evaluated. Aortic valve pathology, which is commonly encountered in patients with aortic disease, influences medication choice for induction and maintenance of anesthesia. For example, hemodynamic goals for aortic stenosis (low heart rate, maintained afterload) differ from aortic insufficiency (high heart rate, low afterload), cardiac tamponade (high heart rate, high afterload), and reducing aneurysmal wall stress (low heart rate, low afterload); at times these goals conflict and an overarching hemodynamic goal must be identified.
The presence of end organ dysfunction (renal, hepatic) should be considered when choosing anesthetic agents, as dysfunction or failure may prolong metabolism and delay subsequent neurologic exams. Inhaled and intravenous anesthetics, and neuromuscular blockade, in particular, may adversely affect the ability to perform additional neuromonitoring (neurologic exam, EEG, motor evoked potential, and somatosensory evoked potentials). If such approaches are planned, medications should be reviewed carefully prior to proceeding.
Elective surgery may be delayed if the risk of operating exceeds the benefit, or a concomitant condition can be optimized, particularly in patients who have had a recent myocardial infarction, stroke, or renal failure. These patients have a greater chance of perioperative mortality than their previously healthy counterparts, and delaying surgery may identify whether recovery is possible.
3. What are the implications of co-existing disease on perioperative care?
In addition to consultation provided by an experienced cardiovascular surgeon, an anesthesiologist experienced in cardiovascular surgery should be consulted or involved in the care of these patients. The operation generally requires the use of cardiopulmonary bypass, invasive hemodynamic and invasive cardiac output monitoring (pulmonary artery catheter and/or TEE). In experienced hands, TEE in particular can dramatically affect the choice of operation, guide management, and influence outcome of the operation.
Optimization of comorbidities and early detection of cerebrovascular or cardiac compromise can alter the shared hemodynamic goals set at the beginning of the case, and may prompt early interventions by the surgical and anesthesia teams.
Regarding perioperative imaging, a diagnostic MRI of the thoracic aorta and its branches, or CT angiography with contrast of the entire aorta is considered the gold standard for identifying and characterizing aortic aneurysms and dissections. TEE is more sensitive than CT and aortography; however, it should be noted that image dropout/attenuation artifact encountered at the level of the left bronchus or trachea may obscure visualization. Image measurements may also be affected by oblique imaging of the aorta, which can occur in all the modalities mentioned. Choice of imaging modality is dependent on institutional capability and immediate availability.
A carotid ultrasound, CTA, or MRI of the cranial vessels may yield additional valuable information, such as carotid stenosis, subclavian artery/vertebro-basilar stenosis, or, sometimes, an incomplete circle of Willis. These conditions may influence choice of retrograde and/or antegrade cerebral perfusion, and may require additional debranching procedures for the cerebral vessels.
Perioperative risk reduction strategies
Cardiovascular risk (see also “Cardiovascular system”)
Heart rate and blood pressure should be carefully controlled in these patients to reduce the risk of aneurysm extension or rupture. Tachycardia and afterload increases may increase the shear forces and direct wall stress on the aneurysm, and their reduction should be targeted if possible. However, patients with chronic atheromatous disease and hypertension have less compliant arterial vasculature and may not respond as expected with vasodilator medication. Blood pressure should be primarily with a medical strategy that also reduces heart rate, with a heart rate goal of 60 bpm or less, and 130-140/80-90 mm Hg per AHA guidelines. After heart rate control is obtained, vasodilators can be initiated; vasodilator therapy should not be initiated first to avoid associated reflex tachycardia. In the patient with acute aortic disease, or during the perioperative period where significant lability in blood pressure is anticipated and immediate control is desired, intravenous medications that are quickly metabolized are excellent in achieving the above goals and are easily titrated during the anesthetic (e.g., esmolol, clevidipine, nitroglycerine, nitroprusside). If symptomatic, pain control is also key in meeting the above hemodynamic goals.
As with any patient after cardiac surgery, the aortic surgery patient carries a risk of post-operative atrial fibrillation, of which beta-blockers serve as first line medical prevention.
Neurologic risk (see also “Neurologic System”)
Some institutions recommend the routine use of preoperative steroids to mitigate inflammatory mediators and cell damage that can occur during this major operation. However, the literature is inconclusive regarding the neuroprotective benefit, and, in some cases, the use of steroids may predispose patients to more harm than benefit, especially in the setting of profound hyperglycemia. There has been evidence to support use of steroids for spinal cord protection. If steroids are selected, methylprednisolone (1000 mg) is typically administered preoperatively; hyperglycemia (glucose target <200) is treated using an insulin infusion.
If deep hypothermic circulatory arrest is needed, standardization of medical therapies for neuroprotection during DHCA is lacking. Hypothermia, selective cerebral perfusion, and short cerebral ischemic times have been associated with improved outcomes; the use of barbiturates, propofol, and isoflurane can cause burst suppression, but these have not been associated with clinical neuroprotective effects. Etomidate, lidocaine, and magnesium are also commonly used during DHCA, but again, none have been associated with a neuroprotective benefit.
In addition to the above risks, these patients also carry significant risks of cardiopulmonary and renal complications, as well as risks of hemorrhage and coagulopathy.
b. Cardiovascular system
Acute myocardial infarction, pericardial tamponade, and coronary dissection may occur in patients with thoracic aortic aneurysms or aortic dissection. Pericardial tamponade or pleural hemorrhage are also emergency indicators. Right ventricular outflow compression or SVC syndrome may also be present from mass effect and may be seen in patients with large aneurysms. If these findings are present, urgent or emergent repair is indicated.
Baseline coronary artery disease or cardiac dysfunction – goals of management
Patients with aneurysmal disease typically carry many risk factors for coronary artery disease and myocardial infarction. For elective procedures, a preoperative electrocardiogram and transthoracic echocardiogram can be useful in identifying baseline rhythm, any active ischemic changes, baseline ventricular function, and wall motion abnormalities. Although the procedure and the patient are high risk, an exercise stress test may be considered for patients in whom functional capacity is unknown and the results will change management, but this may pose an unnecessary risk if the patient is symptomatic or has a hypertensive response to exercise. If desired, a pharmacologic stress test poses less risk of a hypertensive response. For elective procedures, a left heart catheterization can be performed to identify coronary lesions that may need to be repaired. If ST segment elevation is present on EKG, suggestive of active ischemia, this should be treated as a primary cardiac event without delay for definitive aortic imaging.
In patients with chronic coronary ischemia or a history of coronary artery revascularization, obtaining further information about previous therapeutic interventions is useful. For example, a patient who has had coronary artery bypass grafting (CABG) may have an internal mammary artery graft, making surgical exposure challenging during a redo-sternotomy.
A patient with a history of profound congestive heart failure may require judicious fluid resuscitation and cautious inotropic support. In either case, the goal is the same – avoid increased myocardial oxygen demand or ischemia, and maintain sinus rhythm if possible.
Chronic obstructive pulmonary disease (COPD) is common in patients with vascular disease, secondary to a history of long-standing smoking. Other pulmonary manifestations of thoracic aortic aneurysms may include hoarseness due to recurrent laryngeal nerve compression and direct bronchial or tracheal stenosis, secondary to compression by the aorta. Fistulae between the aorta and pulmonary artery have also been reported.
Aside from chest X-ray, which should be performed on all low or intermediate risk patients, patients with significant pulmonary disease or obstructive pulmonary disease may undergo pulmonary function testing for prediction of risk and response to bronchodilators, especially if lung isolation is planned. Baseline arterial blood gases are particularly useful in patients with significant pulmonary disease or concern for malperfusion, to identify and treat ongoing acidosis or electrolyte abnormality, and set appropriate targets for extubation.
In the setting of acute aortic syndromes or malperfusion, these patients should be provided with supplemental oxygen to promote better oxygenation, while avoiding respiratory depression. If the patient has already decompensated or is at risk for loss of airway, the airway must be secured with an endotracheal tube.
Renal disease is not uncommon for patients having aortic disease, as they have many comorbidities that predispose them to renal insufficiency; these include uncontrolled hypertension, diabetes, atheromatous disease, age and embolic atheroma.
Renal insufficiency maybe present in these patients due to poor perfusion secondary to the aneurysm (atheromatous or thrombotic emboli, mass effect on distal vessels, etc.), type A aortic dissection extension to the renal arteries, as well as coexisting disease intrinsic to the kidney and its vasculature.
The degree of involvement of thoracic aortic aneurysms and renal arteries can be described by using the Crawford Aneurysm Classification system and may alter the manner in which the operation is performed; such as a staged approach to repair the ascending and arch first, followed by descending aorta repair as a separate operation.
Ensuring adequate cardiac output, optimizing fluid status, and avoiding renal-toxic medications are the mainstay of treating oliguria and avoiding renal injury. For patients who have extensive renal insufficiency or failure, hemodialysis may be considered preoperatively.
In the acute setting, if the thoracic aortic aneurysm or dissection involves the descending aorta, gut ischemia and malperfusion may be encountered, and may cause a significant lactic acidosis. Compromise of this system is important in weighing the decision to take the patient to surgery, particularly if work on the ascending aorta and arch is also required; revascularization of the gut would likely be performed after these procedures and the ischemic injury, bacteremia and severe metabolic acidosis may significantly increase the morbidity and mortality associated with surgery on the ascending arch and aortic arch.
A preoperative neurologic examination for baseline function is important in light of the significant risk of neurologic injury to the central nervous system, approaching 5-25% in ascending and total arch procedures. Immediately postoperatively, early and frequent neurologic examinations are important for detection of these complications and potential intervention. The etiology is attributed to embolic phenomenon resulting in cerebral ischemia or temporary neurologic dysfunction (TND). TND is associated with DHCA duration or longer intervals of interruption of antegrade cerebral perfusion. Risk of spinal cord injury may exist when the aneurysm or dissection also involves the proximal descending thoracic to the infrarenal abdominal aorta.
Patients with aortic disease also commonly suffer cerebrovascular disease or carotid disease. If time permits, high-risk patients should have carotid ultrasound, and/or the brain and cerebral vessels should be imaged to assess collateral blood flow in the brain and risk of ischemic insult. If a patient has recent or ongoing cerebral ischemia, he or she is at higher risk for extension of ischemic injury or conversion to hemorraghic stroke in the perioperative period and a serious discussion regarding risk should occur.
Acute neurologic changes such as stroke must be evaluated immediately and carefully. Anticoagulation in the setting of a hemorrhagic stroke would be contraindicated and may exclude the patient from an operation. An embolic stroke may be the result of atheromatous emboli from the diseased aorta or from mechanical manipulation. Last, the stroke may be caused by ischemia due to reduced blood flow or thrombosis of the carotid artery from the extension of a dissection, or low cardiac output state due to intrathoracic hemorrhage, aneurysm rupture, or heart failure.
In patients with acute aortic disease, early identification of neurologic changes and rapid intervention is key in preventing the evolution of an ischemic stroke, particularly in the case of aortic dissection.
On the other hand, chronic neurologic disease or history of repeated strokes may require further risk stratification. A thorough history must be obtained and careful documentation of signs, symptoms, and deficits must be made preoperatively to effectively evaluate postoperative neurologic status.
Patients who receive aortic surgery frequently show initial recovery of postoperative neurocognitive decline; however, this may progressively worsen years after the initial operation. It is important that the patient’s family/caregivers are aware so that early intervention can occur should symptoms develop.
As with all coexisting disease, the risks and benefits of proceeding with an open thoracic aortic operation must be discussed at length with the patient and family due to the potential for significant neurologic morbidity and mortality. Ensure adequate perfusion and oxygen delivery to cerebral tissue monitored by cerebral oximetry and/or EEG monitoring.
The most common endocrine derangement includes hyper- or hypoglycemia, depending on any history of diabetes, steroid administration, or ongoing stress response. Insulin infusion may be administered perioperatively for moderate glycemic control (blood glucose 127-179 g/dL).
In the emergency setting, aggressive treatment of acidosis and rescuscitation in the setting of bleeding is imperative in the acute operative period. The presence of lactic acidosis preoperatively may signal the presence of malperfusion due to low cardiac output, bleeding, or visceral ischemia; as the patient is revascularized on bypass this acidosis will escalate and should resolve over the initial 12-24 hours post surgery. A non-gap acidosis may be attributed to severe renal disease or acute renal failure in this setting.
g. Additional systems/conditions which may be of concern in a patient undergoing this procedure and are relevant for the anesthetic plan (e.g., musculoskeletal in orthopedic procedures, hematologic in a cancer patient)
Bleeding is a major complication of this procedure, which is related to the use of cardiopulmonary bypass and heparinization, degree of tissue manipulation and extent of dissection, use of deep hypothermic circulatory arrest, use of foreign graft material, and profound inflammatory response. Therefore, it is prudent to obtain baseline values for platelets, hematocrit, prothrombin time, partial thromboplastin time, and fibrinogen. Certain institutions may also have the capability to obtain a thromboelastogram, but this test is not routinely performed pre-procedure unless significant bleeding has occurred.
The potential for blood transfusion should be discussed with the patient, a type and crossmatch performed, and the blood bank should be notified and prepared to handle the increased demand. For patients who also have antibodies to blood products, close communication with the blood bank in advance of the surgery to prepare sufficient product is critical. For all arch and hemi-arch cases, a baseline fibrinogen value is useful for comparison with intraoperative fibrinogen value (drawn at 28-30ºC while rewarming) in order to appropriately make decisions regarding the use of fresh frozen plasma or cryoprecipitate.
The use of perioperative antifibrinolytics (tranexamic acid or aminocaproic acid) is recommended for the surgical event, and can mitigate fibrinolysis due to cardiopulmonary bypass. Factor concentrates, such as prothrombin complex concentrates and activated factor VII, can be useful in the setting of managing hemorrhage post-heparin reversal, can reduce the amount of total blood products used, and can be considered if available. Their use must be weighed against the risk of thrombosis and cost.
4. What are the patient's medications and how should they be managed in the perioperative period?
See “Cardiovascular System” for recommendations on managing blood pressure and heart rate according to AHA guidelines.
h. Are there medications commonly seen in patients undergoing this procedure and for which should there be greater concern?
Medications that stimulate the adrenergic system should be avoided if possible due to the potential for aneurysm rupture or extension. Beta-blockers should not be withheld because of the potential for rebound tachycardia and hypertension, and should be administered prior to vasodilators to avoid reflex tachycardia. Heart rate should be controlled to decrease shearing forces on the aneurysm or vessel wall.
Sympathetic responses should be blunted when possible and anticipated with intubation, sternotomy and manipulation of the aorta; using intravenous beta blockers or vasodilators that are easily titrated with a short drug effect are ideal for the immediate perioperative period or emergency situation.
i. What should be recommended with regard to continuation of medications taken chronically?
Administration of long-acting beta-blockers prior to surgery is preferred; short-acting agents may be used in the acute setting for ease of titration. For an elective procedure, one month of beta-blockade is traditionally preferred, followed by an additional month of postoperative treatment with a gradual reduction in dose.
A 50% to 90% reduction in perioperative mortality has been observed in vascular surgery patients who received beta-blockers perioperatively. However, increasing evidence suggests that, although chronic beta-blockade may be effective in Marfan patients, it may be of limited use in aortic aneurysm patients due to the potential for decreasing elasticity of the aortic wall. Nevertheless, because the benefit outweighs the risk, beta-blockers are still used to decrease the “shear forces” that result from each cardiac cycle.
Because beta-blockade may have negative consequences for patients with a history of obstructive pulmonary disease, sound clinical judgment should be used in balancing beta-1 blocking agents with beta-2 agonists. Conversely, one could forgo beta-blockers in this population and use alternatives, such as calcium channel blockers to achieve rate control.
For acute obstructive pulmonary symptoms, extremely high doses of bronchodilators, such as albuterol or epinephrine, should be avoided due to systemic absorption and risk of beta agonism. Ipratropium bromide or steroids may be better options, although the onset of bronchodilation may take longer. If the patient meets criteria for intubation, it should be performed expeditiously with adequate anesthetic depth prior to any airway manipulation, due to the risk of aneurysm rupture or worsening of an aortic dissection.
Diuretics should be discontinued unless the patient is in the rare condition of volume overload, which may occur with congestive heart failure or when large volume of crystalloids are administered for resuscitation.
Medications for epilepsy should be continued in the perioperative period.
Clopidogrel should be held in preparation for surgery. If antiplatelet therapy is necessary, then convert to short-acting infusions anticoagulants, such as Integrilin or abciximab is useful. Anticoagulation with heparin may also be an option.
Provide anxiolytics cautiously and in a monitored setting due to the potential for apnea, hypercarbia, and cardiopulmonary collapse in the absence of adequate support, especially in the setting of evolving neurologic changes in the acute setting. However, avoid withholding anxiolytics for patients who are on chronic therapy or are considerably anxious.
Pain control is also desirable to reduce heart rate and blood pressure, while avoiding the respiratory depression from narcotics. Adjunct medications, such as acetaminophen and lidocaine (patches, or infusion for inpatients) are reasonable alternatives if patients are highly likely to experience side effects from narcotics.
j. How to modify care for patients with known allergies
k. Latex allergy – If the patient has a sensitivity to latex (eg. rash from gloves, underwear, etc.) versus anaphylactic reaction, prepare the operating room with latex-free products.
Although devices and equipment in the OR are generally latex-free, it is prudent to screen the patient preoperatively for history of latex allergies.
l. Does the patient have any antibiotic allergies – Common antibiotic allergies and alternative antibiotics
See the Surgical Care Improvement Project (SCIP) recommendations section.
m. Does the patient have a history of allergy to anesthesia?
If the patient has a family history of malignant hyperthermia or a positive caffeine halothane contracture test, a total IV anesthetic (TIVA) approach should be used, along with an ICU ventilator or properly cleared OR ventilator to avoid triggering agents.
A TIVA approach with avoidance of muscle relaxants may be desirable for monitoring of motor evoked or somatosensory evoked potentials, while low dose inhaled anesthetics may be preferable for EEG monitoring. For verified allergic reactions to specific anesthetic drugs or agents, an alternative class of drug with similar therapeutic profile should be used to ensure the lowest risk for an undesired response.
5. What laboratory tests should be obtained, and has everything been reviewed?
Complete blood count, complete metabolic panel, albumin level, coagulation panel (PT, PTT, INR, fibrinogen), and type and crossmatch should be obtained. A baseline activated clotting time, and or heparin level and arterial blood gas should be obtained upon the patient’s arrival in the room.
Definitive aortic imaging (MRI, CTA, or TEE) should be obtained. A chest X-ray is indicated in intermediate or low risk (elective) patients, as well as a baseline EKG. Finally a TEE, or TTE if previously obtained, would be useful, although a TEE is performed intraoperatively for these cases.
Intraoperative Management: What are the options for anesthetic management and how to determine the best technique?
Open thoracic aortic surgery is performed under general anesthesia. In addition to the usual risks of a general anesthetic, these patients are at higher risk for hemodynamic instability and blood pressure lability, as well as perioperative myocardial infarction, stroke, renal injury, and death. These rates vary by patient comorbidities, institutional experience and volume. Comparisons of outcomes in high volume, experienced centers vs small centers are difficult.
In addition to standard ASA monitoring equipment, the patient should receive bilateral arterial lines when arch procedures or antegrade cerebral perfusion is planned. A femoral arterial line may be needed for monitoring of the lower body systemic pressures if work on the thoracoabdominal aorta is planned. At least one arterial line should be placed prior to induction. If the aneurysm is limited to the proximal aorta without arch involvement, a single radial arterial line will be sufficient.
Vascular access in the form of a free-flowing peripheral IV (preferably large bore) and a central line (preferably a 9 Fr double lumen introducer and/or 8 Fr double lumen catheter) should be placed in the right internal jugular under ultrasound. For emergent cases, using a vascular ultrasound to place the central venous line can also be useful for identifying an intimal tear that may extend into the carotid arteries.
The rationale for inserting a right-sided central line is that the brachiocephalic vein on the left may be injured during exposure of a thoracic aortic aneurysm due to its distorted location, leading to loss of central vascular access. In cases where the ascending aortic/arch aneurysm is particularly large, superior vena cava syndrome may be encountered; if this occurs, femoral venous lines will need to be placed for vascular access.
The central line is usually placed prior to or after induction of anesthesia, depending on the stability of the patient, adequacy of peripheral access, and need for central access for monitoring and drug administration during induction.
The goal of the anesthetic induction is to blunt the adrenergic response to stimulus from intubation; otherwise, aortic dissection may worsen or rupture may occur. The usual target for systolic blood pressure is 100 to 110 mm Hg, with a heart rate of 60 to 80 bpm. For best results, short-acting drugs are used to achieve this range; these patients frequently have labile blood pressures.
When adequately anesthetized, intubation is performed with a standard endotracheal tube for a sternotomy approach to the aneurysm. If a thoracotomy approach is planned, either a standard endotracheal tube with a bronchial blocker or (preferably) a double-lumen endotracheal tube may be used for lung isolation. Thoracic aortic aneurysms may sometimes impinge on the bronchus or trachea, causing tracheal deviation or difficult endotracheal tube advancement. Therefore, it may be wise to avoid large endotracheal tubes.
TEE is valuable in evaluating thoracic aortic aneurysms and in that the experienced clinician can visualize the aortic valve, root, and all aspects of the aorta directly and monitor ventricular function in real-time, and share concerns with the surgical team. The placement and image acquisition in the setting of a large aneurysm may be challenging if the aneurysm compresses or shifts the esophagus and cardiac structures. An alternative invasive strategy for cardiac output and pulmonary pressure monitoring is the pulmonary artery catheter. This may provide valuable information about cardiac output and systemic vascular resistance determination, and would allow for continuous monitoring postoperatively in the intensive care unit.
a. Regional anesthesia
During arch/hemiarch thoracic aneurysm operations, sternotomy approaches are usually preferred. Parasternal blocks and paravertebral/epidural catheter approaches have been described but due to concerns of coagulopathy and systemic anticoagulation, is not routinely performed.
b. General anesthesia with EEG monitoring
If EEG monitoring is required, consider a total intravenous anesthetic (TIVA) or using a maximum of 0.5 MAC of inhaled agent in addition to TIVA; there is no contraindication to muscle relaxant for EEG monitoring. Otherwise, inhalational anesthetics can be used with intermittent intravenous maintenance drugs (fentanyl, NMDBs). Bolus medications of anesthetic, such as propofol, benzodiazepines, barbiturates, etomidate, or other hypnotics should be discussed with the surgical and neuromonitoring teams prior to administration, as these can cause burst suppression. For early extubation, pharmacologic agents with rapid drug onset and metabolism are preferred.
6. What is the author's preferred method of anesthesia technique and why?
The repair of aortic dissection or proximal aortic aneurysm involves a median sternotomy because it allows superior access to the aorta. When peripheral access for cannulation is chosen, a small incision is also usually made at the right upper chest to access the right axillary artery for cardiopulmonary bypass (CPB; discussed below). It is important to communicate with the surgeon preoperatively regarding the approach, as it may affect the positions of critical lines and monitors.
Operations on the proximal aorta and aortic arch employ CPB. Procedures on the aortic arch requiring debranching of the head vessels, or if cross clamp of the aorta is impossible, hypothermic circulatory arrest will be performed. This allows better visualization and control of the fragile aorta. To minimize neurologic injury, deep hypothermic circulatory arrest, use of selective antegrade (ACP) or retrograde cerebral perfusion (RCP) have been shown to be beneficial in experienced centers. Institutional experience is important in selection of these techniques.
Thought to be somewhat superior to RCP, ACP can be delivered at near systemic pressures either by hand-held techniques, or by flowing through the right axillary, subclavian, or innominate artery (hemispheric). The left common carotid artery may also be perfused (bihemispheric). Pressures are typically measured via the radial arterial line on the right, and flows are adjusted to achieve a pressure of 40-70 mm Hg. RCP is performed by cannulating the superior vena cava, with occlusion or snaring of the inferior vena cava, with flows 300-500 mL/min to achieve a perfusion pressure of 25-35 mm Hg. This can be monitored by transducing venous pressure of the SVC using the most proximal port on the central venous line, and allows for more homogenous cooling of the brain, and helps in flushing embolic debris (bubbles, solid particles, metabolites) from the arterial system.
If the entire aortic arch is involved, then a staged operation is performed, in which a synthetic graft is used to replace the arch and a trifurcating synthetic limb is connected individually to the arch vessels. The distal end of the graft is connected at a later date, using an endovascular approach (“Hybrid approach”). For high-risk patients with total arch or arch and descending disease, an alternative to this strategy is the arch transposition procedure, in which an off pump brachiocephalic transposition is performed followed by endovascular exclusion.
A major potential complication of aortic surgery involving the proximal thoracic aorta is spinal cord ischemia, which can result from the interruption of blood flow associated with clamping and repair of the aorta. This danger is more pronounced in descending thoracic aortic surgery; left-heart bypass is used to preserve spinal cord perfusion pressure because there is a significant increase in the risk for paraplegia when cross-clamp time exceeds 30 minutes. Another adjunct technique to decrease the likelihood of paraplegia is the use of a lumbar drain (discussed in Endovascular Aortic Operations).
Cannulation of the aorta for CPB may be accomplished through various routes. For proximal aortic operations, the arterial cannula may be placed in the ascending aorta, the transverse arch, or the femoral artery, with the cross-clamp proximal to the brachiocephalic artery. For axillary cannulation, a polyester graft is anastomosed to the right axillary artery. This offers the benefit of improved visualization and less manipulation of the aorta. Peripheral arterial and venous cannulation is performed before sternotomy, to quickly go on CPB should the aneurysm or other vascular structures be inadvertently entered.
Stages of surgery
Upon entering the operating suite, all members of the operative team should participate in a preoperative briefing, during which the patient is verified, the surgical plan is discussed, and special equipment or requirements are identified. Any critical concerns should be addressed at this time. Typed and crossmatched blood should be in the room and checked as early as possible, at minimum before sternotomy. A method of delivering large volumes of blood quickly should be identified and readily available (rapid infuser, pressure bags, large bore or central access).
During the pre-bypass period, the anesthesiologist takes great care to ensure depth of anesthesia, control blood pressure by providing analgesics and vasoactive drugs, and transiently lowers the systolic blood pressure for sternotomy. A complete perioperative TEE examination should be performed, with clear evaluation and measurement of the aortic valve, root, and all aspects of the aorta. Biventricular function should also be quantified, with attention to wall motion abnormalities. If a dissection is present, the TEE may be used to identify the location of the intimal tear, extension of the dissection, and identify the presence of aortic hematoma. Identification of the true and false lumens, and further assistance with placement of peripheral cannulas in the true lumen, can be exceptionally helpful to the surgical team. Comorbid conditions associated with dissection can also be easily identified on TEE, and include pericardial effusion and tamponade, as well as pleural hemorrhage.
TEE guidance during aortic cannula testing is also useful in assuring proper placement in the true lumen. The anesthesiologist should watch the aorta using echocardiography to determine which the lumen is expanding as the perfusionist increases flow through the aortic cannula. If the false lumen were accidentally cannulated, hypotension may worsen, the aortic line pressure may rise sharply, and the false lumen may expand while being visualized on TEE. Communication is key during this critical time.
After CPB is successfully started, the surgeon will begin the repair, applying clamps to isolate the aneurysm. He or she will communicate with the perfusionist to change aortic flow rates in order to reduce chances of injury. The surgeon will ask the perfusionist to cool the patient. If deep hypothermic circulatory arrest is planned, prior to initiating circulatory arrest, assuring stable and adequate anesthetic depth is vital, and good communication with the neuromonitoring team regarding EEG signals is imperative. The goal is to decrease CMRO2 maximally by cooling the patient to achieve isoelectric EEG silence.
Circulatory arrest begins when the surgeon asks the perfusionist to stop the CPB machine. The systemic arterial pressure should fall to 0 mm Hg, and you may be asked to monitor ACP or RCP pressures if used. Drug infusions should be paused and only restarted when circulation is resumed. As the surgeon completes the critical portion of the repair and exploration of the aorta, the CPB machine support is gradually increased back to calculated cardiac index.
Gradual rewarming is the next phase, which will take place after the surgeon is satisfied that the repair is proceeding as planned. During the rewarming phase, dissolved gases in the blood may coalesce as bubbles. Therefore, warming should be done gradually, and usually takes longer than the time it takes to cool the patient (roughly twice the time). Forced air-warming and water-assisted thermal pads placed preoperatively can also help. Achieving normal temperature is critically important in avoiding cardiac arrhythmia and coagulopathy.
Laboratory values, such as platelet count, hemoglobin, fibrinogen, and a thromboelastogram are obtained at 28ºC to 30ºC while on CPB in order to administer an appropriate amount of fresh frozen plasma while on pump and to effectively treat coagulopathy following culmination and separation of CPB. It should be noted that cryoprecipitate is more effective in treating hypofibrinogenemia but does expose the patient to multiple blood donors. Checking on the availability of prothrombin complex concentrates or activated factors, if needed post-protamine, is prudent.
After the repair is complete, the patient is weaned off CPB with a typical goal of mean systemic arterial pressures of 60 to 70 mm Hg. Careful assessment of the aorta, aortic valve, mitral valve and ventricles should occur post-bypass using TEE, prior to the administration of protamine. Platelets, FFP, cryoprecipitate, and factor concentrates should be administered if clinically significant bleeding has occurred and therapies can be targeted based on laboratory values. Assuming hemostasis is achieved and the planned operation is a success, the operative site(s) are closed and the patient is taken to the ICU, intubated, and sedated. A report is provided to the ICU team, along with a follow-up plan.
How to assist the surgeon and optimize patient care
The importance of blood pressure control is paramount. Hypertension has significant negative consequences, which are not limited to further aortic dissection or aneurysm rupture. On the other end of the spectrum, hypotension can lead to profound ischemia. The surgical team should communicate with the anesthesiologist when the aortic cross-clamp is being placed or removed, as this causes significant hemodynamic changes due to direct mechanical effects on afterload, as well as the return of ischemic blood after the cross-clamp is removed.
At minimum, the blood pressure should be lowered prior to sternotomy to decrease aneurysm size temporarily. It should also be lowered before aortic cannulation to decrease the risk for rupture or dissection of the aneurysm. Needless to say, this therapy must be balanced with perfusion pressure to the brain and coronary arteries, which may be compromised.
Lastly, the perioperative TEE findings should be reviewed both before and after the procedure, as these critical pieces of information impact the surgical decision to proceed with concomitant valve, CABG, and extent of the aorta that is diseased. TEE also allows real time guidance of cannula and line placement, and allows for assessment of the valve repair or replacement, valvular function, and biventricular function post-bypass, when additional intervention is feasible.
First generation and second generation cephalosporins are the most studied and most frequently given for the prevention of surgical site infections (SSIs) in cardiac procedures. Since cardiopulmonary bypass is frequently used for these procedures and significantly alters the volume of distribution and bioavailability of medications, many centers recommend a single bolus dose prior to incision, with an infusion through the case or repeat dosing post-bypass to increase the tissue concentrations of these medications until the chest is closed.
Vancomycin is not recommended for routine use due to the limited evidence of efficacy and concerns for increased microbial resistance, and there is no evidence to support its use in institutions with a high prevalence of methicillin resistant staphylococcus aureus (MRSA). Vancomycin is recommended for patients colonized with MRSA, and is often considered for patients with diabetes, immunosuppression, or prolonged hospitalization.
The accepted alternative for patients with penicillin allergies is vancomycin or clindamycin, with addition of aminoglycoside, aztreonam, or fluoroquinolone for gram-negative coverage.
All antibiotics should be redosed according to institutional recommendations and renal function.
An acceptable quantity of packed red cells is 4-8 units in a specialized cooler with ice. An equal amount of fresh frozen plasma should also be available in the room. The blood bank should have an adequate supply of products available should additional units be needed. After heparin reversal post-bypass, the clinician must not forget to recheck the ACT values frequently and administer additional protamine as necessary, along with keeping the patient warm to avoid further coagulopathy. It is useful to have platelets, cryoprecipitate, factor VIIa, and other factor concentrates ready after separation from bypass as well. Packed red blood cells should also be transfused to maintain adequate hemoglobin and blood viscosity.
Myocardial ischemia should be monitored postoperatively with EKG, and cardiac output values obtained from either TEE or a PA catheter.
Ventilator-associated pneumonia and atelectasis should be avoided by early extubation, incentive spirometry, and ambulation.
Patients who receive CABG surgery may have a substantially increased risk of postoperative cognitive decline. Because ascending aortic and aortic arch operations with DHCA are even more invasive, antegrade selective cerebral perfusion (discussed earlier) is an approach that may reduce the risk of permanent neuronal injury. Nevertheless, a thorough postoperative neurologic exam should be performed and compared with baseline. If there is evidence for stroke, neurology consultation may be useful.
Renal dysfunction is common after aortic surgery. Adequate urine output (>0.5 mL/kg/hr) should be maintained by optimizing perfusion, fluid status, or administration of diuretics. If kidney injury is severe, a nephrologist should be consulted for possible dialysis.
b. If the patient is intubated, are there any special criteria for extubation?
The patient is taken intubated and sedated to the ICU. For extubation, the patient should meet standard criteria and should not have a planned/possible return to the operating room within 24 hours.
c. Postoperative management
Postoperative analgesia management strategy
ICU care postoperatively is always required for these patients. Unless an emergency, this operation should not occur unless a bed in the ICU is available. Careful postoperative monitoring, early extubation, and ambulation are the mainstay of reducing postoperative morbidity and mortality.
Post-sternotomy, narcotics and non opioid adjuncts (acetaminophen, dexmetomidine, lidocaine, ketamine, gabapentin, etc. once taking oral medications) have been the mainstay of postoperative pain management, although there have been small studies describing single shot parasternal injections for postoperative pain control. Neuraxial and paravertebral blocks have been described for postoperative pain control for both sternotomy and thoracotomy. If regional and neuraxial anesthesia are selected, ASRA guidelines for cessation of anticoagulants should be followed, with consideration of the risk of systemic heparinization and coagulopathy, as well as hemodynamic consequences.
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- What the Anesthesiologist Should Know before the Operative Procedure
- 1. What is the urgency of the surgery?
- What is the risk of delay in order to obtain additional preoperative information?
- 2. Preoperative evaluation
- 3. What are the implications of co-existing disease on perioperative care?
- b. Cardiovascular system
- c. Pulmonary
- d. Renal-GI:
- e. Neurologic:
- f. Endocrine:
- g. Additional systems/conditions which may be of concern in a patient undergoing this procedure and are relevant for the anesthetic plan (e.g., musculoskeletal in orthopedic procedures, hematologic in a cancer patient)
- 4. What are the patient's medications and how should they be managed in the perioperative period?
- h. Are there medications commonly seen in patients undergoing this procedure and for which should there be greater concern?
- i. What should be recommended with regard to continuation of medications taken chronically?
- j. How to modify care for patients with known allergies
- k. Latex allergy - If the patient has a sensitivity to latex (eg. rash from gloves, underwear, etc.) versus anaphylactic reaction, prepare the operating room with latex-free products.
- l. Does the patient have any antibiotic allergies - Common antibiotic allergies and alternative antibiotics
- m. Does the patient have a history of allergy to anesthesia?
- 5. What laboratory tests should be obtained, and has everything been reviewed?
- Intraoperative Management: What are the options for anesthetic management and how to determine the best technique?
- 6. What is the author's preferred method of anesthesia technique and why?
- b. If the patient is intubated, are there any special criteria for extubation?
- c. Postoperative management