Preanesthetic Assessment

Identification of the aortic diagnosis is paramount because its extent and physiologic consequences dictate both anesthetic management and surgical approach. Aortic diseases proximal to the left carotid artery typically are approached via a median sternotomy, whereas aortic diseases distal to this point usually are approached via a left thoracotomy or thoracoabdominal incision. Although an aortic diagnosis often is established in advance, at times a definitive diagnosis must be verified after operating room (OR) admission by direct review of diagnostic studies or by subsequent transesophageal echocardiography (TEE). In every case, a review of the operative plan with the surgical team facilitates thorough anesthetic preparation. Direct review of adequate aortic diagnostic imaging studies not only verifies the operative diagnosis but also determines the surgical possibilities. The anatomic details of an aortic disease permit the anesthesiologist to anticipate potential perioperative difficulties, including likely postoperative complications.

Anesthetic Management

Inherent in surgical procedure is the potential for massive bleeding and cardiovascular collapse. Therefore, it is essential to have immediate availability of packed red blood cells and clotting factors, large-bore vascular access, invasive blood pressure monitoring, and central venous access. Pulmonary artery catheterization assists in the management of cardiac dysfunction associated with CPB, DHCA, and PLHB. Intraoperative TEE is indicated in thoracic aortic procedures, including endovascular interventions, in which it assists in hemodynamic monitoring, procedural guidance, and endoleak detection A rationale exists for choosing to cannulate the left or right radial artery for intraarterial blood pressure monitoring. Right radial arterial pressure monitoring will often detect compromised flow into the brachiocephalic artery because of aortic cross-clamping too near its origin. Right radial arterial pressure monitoring also makes sense in procedures that require clamping of the left subclavian artery. Left radial arterial pressure monitoring is indicated when selective antegrade cerebral perfusion (ACP) is planned via the right axillary artery; however, a right-sided catheter may be preferred for ACP if direct brachiocephalic cannulation is used by the surgeon. At times, bilateral radial arterial pressure monitoring may be required. Femoral arterial pressure monitoring allows the assessment of distal aortic perfusion in procedures with PLHB.

Large-bore peripheral intravenous cannulation secures vascular access for rapid intravascular volume expansion. Rapid transfusion is desirable via an intravenous set with a fluid-warming device. Alternatively, large-bore central venous cannulation can be utilized for volume expansion. If a pulmonary artery catheter (PAC) is required, a second introducer sheath dedicated to volume expansion also can be placed in the same central vein. Central venous cannulation with ultrasound guidance often increases speed and safety, especially in emergencies. Both a urinary and a nasopharyngeal temperature probe are required for monitoring the absolute temperature of the periphery and core, as well as the rates of change during deliberate hypothermia and subsequent rewarming. The rectum is an alternative site for monitoring peripheral temperature, and the PAC can provide core temperature monitoring.

The induction of general anesthesia requires careful hemodynamic monitoring with anticipation of changes because of anesthetic drugs and tracheal intubation. Appropriate vasoactive drugs should be immediately available as required. Concomitant vasodilator infusions often are discontinued before anesthetic induction. Because etomidate does not attenuate sympathetic responses and has no direct effects on myocardial contractility, it may be preferred in the setting of hemodynamic instability. Thereafter, titration of a narcotic such as fentanyl and a benzodiazepine such as midazolam will provide maintenance of general anesthesia. In elective cases, anesthetic induction can proceed with routine intravenous hypnotics, followed by narcotic titration for attenuation of the hypertensive responses to tracheal intubation and skin incision. Antibiotic therapy optimally should be completed in most cases at least 30 minutes before skin incision to achieve adequate bactericidal tissue levels.

General anesthetic maintenance is typically with a balanced intravenous and inhalation anesthetic technique, and neuromuscular blockade is achieved by titration of a nondepolarizing muscle relaxant. Anesthetics can be reduced during moderate hypothermia and then discontinued during deep hypothermia. With concomitant electroencephalographic (EEG) and/or somatosensory-evoked potential (SSEP) monitoring, anesthetic signal interference is minimized with the avoidance of barbiturates, bolus propofol, and doses of inhaled anesthetic greater than 0.5 minimum alveolar concentration. Propofol infusion, narcotics, and neuromuscular blocking drugs do not interfere with SSEP monitoring. With intraoperative motor-evoked potential (MEP) monitoring, high-quality signals are obtained when the anesthetic technique comprises total intravenous anesthesia with propofol and a narcotic such as remifentanil without neuromuscular blockade.

The potential for significant bleeding and rapid transfusion is always relevant in thoracic aortic procedures. Consequently, it is prudent to have fresh frozen plasma and platelets available for ongoing replacement during massive red blood cell transfusion. The time delay associated with standard laboratory testing severely limits the intraoperative relevance of these data to guide transfusion; however, viscoelastic tests are being used with greater frequency to determine coagulation needs. Strategies to decrease bleeding and transfusion in these procedures include timely preoperative cessation of anticoagulants and platelet blockers, antifibrinolytic therapy, intraoperative cell salvage, biologic glue, activated factor VII, and avoidance of perioperative hypertension. The antifibrinolytic lysine analogs, epsilon-aminocaproic acid or tranexamic acid, are the commonly utilized blood conservation agents in thoracic aortic surgery with and without DHCA. Recombinant activated factor VII is a synthetic agent that accelerates thrombin production leading to hemostasis, and it may be considered for the management of intractable nonsurgical bleeding after CPB that is unresponsive to routine therapy. Although this agent has demonstrated efficacy in complex aortic surgery, concerns for arterial thrombotic events remain, requiring further trials to investigate perioperative safety. Finally, the use of fibrinogen concentrates in the management of coagulopathy continue to be investigated in cardiac surgery, with recent evidence suggesting decreased intraoperative bleeding when fibrinogen concentrates are used as a first-line therapy for coagulopathy after major aortic surgery.

Postoperative Care

With the exception of some endovascular aortic procedures, patients often remain intubated and sedated at the completion of the operation, when they are transported directly from the OR to the intensive care unit (ICU). The continuation of care from the OR to the ICU should be seamless and protocol-based. In the absence of complications, early anesthetic emergence is preferable for early assessment of neurologic function. If delayed anesthetic emergence is indicated, then sedation and analgesia can be provided. The chest roentgenogram allows confirmation of endotracheal tube and intravascular catheter position, as well as the diagnosis of acute intrathoracic pathologies. Common early complications include hypothermia, coagulopathy, delirium, stroke, hemodynamic lability, respiratory failure, metabolic disturbances, and renal failure. Frequent clinical and laboratory assessment is essential to manage this dynamic postoperative recovery, including the safe conduct of tracheal extubation. Given the risks associated with hyperglycemia after cardiac surgery, management of blood glucose levels should be standardized, with more recent data to suggest more liberal control (glucose less than 180 mg/dL) is acceptable with good outcomes. Antibiotic prophylaxis is typically continued for 48 hours after surgery to minimize surgical infection risk.

Preanesthetic Assessment

Identification of the aortic diagnosis is paramount because its extent and physiologic consequences dictate both anesthetic management and surgical approach. Aortic diseases proximal to the left carotid artery typically are approached via a median sternotomy, whereas aortic diseases distal to this point usually are approached via a left thoracotomy or thoracoabdominal incision. Although an aortic diagnosis often is established in advance, at times a definitive diagnosis must be verified after operating room (OR) admission by direct review of diagnostic studies or by subsequent transesophageal echocardiography (TEE). In every case, a review of the operative plan with the surgical team facilitates thorough anesthetic preparation. Direct review of adequate aortic diagnostic imaging studies not only verifies the operative diagnosis but also determines the surgical possibilities. The anatomic details of an aortic disease permit the anesthesiologist to anticipate potential perioperative difficulties, including likely postoperative complications.

Anesthetic Management

Inherent in surgical procedure is the potential for massive bleeding and cardiovascular collapse. Therefore, it is essential to have immediate availability of packed red blood cells and clotting factors, large-bore vascular access, invasive blood pressure monitoring, and central venous access. Pulmonary artery catheterization assists in the management of cardiac dysfunction associated with CPB, DHCA, and PLHB. Intraoperative TEE is indicated in thoracic aortic procedures, including endovascular interventions, in which it assists in hemodynamic monitoring, procedural guidance, and endoleak detection A rationale exists for choosing to cannulate the left or right radial artery for intraarterial blood pressure monitoring. Right radial arterial pressure monitoring will often detect compromised flow into the brachiocephalic artery because of aortic cross-clamping too near its origin. Right radial arterial pressure monitoring also makes sense in procedures that require clamping of the left subclavian artery. Left radial arterial pressure monitoring is indicated when selective antegrade cerebral perfusion (ACP) is planned via the right axillary artery; however, a right-sided catheter may be preferred for ACP if direct brachiocephalic cannulation is used by the surgeon. At times, bilateral radial arterial pressure monitoring may be required. Femoral arterial pressure monitoring allows the assessment of distal aortic perfusion in procedures with PLHB.

Large-bore peripheral intravenous cannulation secures vascular access for rapid intravascular volume expansion. Rapid transfusion is desirable via an intravenous set with a fluid-warming device. Alternatively, large-bore central venous cannulation can be utilized for volume expansion. If a pulmonary artery catheter (PAC) is required, a second introducer sheath dedicated to volume expansion also can be placed in the same central vein. Central venous cannulation with ultrasound guidance often increases speed and safety, especially in emergencies. Both a urinary and a nasopharyngeal temperature probe are required for monitoring the absolute temperature of the periphery and core, as well as the rates of change during deliberate hypothermia and subsequent rewarming. The rectum is an alternative site for monitoring peripheral temperature, and the PAC can provide core temperature monitoring.

The induction of general anesthesia requires careful hemodynamic monitoring with anticipation of changes because of anesthetic drugs and tracheal intubation. Appropriate vasoactive drugs should be immediately available as required. Concomitant vasodilator infusions often are discontinued before anesthetic induction. Because etomidate does not attenuate sympathetic responses and has no direct effects on myocardial contractility, it may be preferred in the setting of hemodynamic instability. Thereafter, titration of a narcotic such as fentanyl and a benzodiazepine such as midazolam will provide maintenance of general anesthesia. In elective cases, anesthetic induction can proceed with routine intravenous hypnotics, followed by narcotic titration for attenuation of the hypertensive responses to tracheal intubation and skin incision. Antibiotic therapy optimally should be completed in most cases at least 30 minutes before skin incision to achieve adequate bactericidal tissue levels.

General anesthetic maintenance is typically with a balanced intravenous and inhalation anesthetic technique, and neuromuscular blockade is achieved by titration of a nondepolarizing muscle relaxant. Anesthetics can be reduced during moderate hypothermia and then discontinued during deep hypothermia. With concomitant electroencephalographic (EEG) and/or somatosensory-evoked potential (SSEP) monitoring, anesthetic signal interference is minimized with the avoidance of barbiturates, bolus propofol, and doses of inhaled anesthetic greater than 0.5 minimum alveolar concentration. Propofol infusion, narcotics, and neuromuscular blocking drugs do not interfere with SSEP monitoring. With intraoperative motor-evoked potential (MEP) monitoring, high-quality signals are obtained when the anesthetic technique comprises total intravenous anesthesia with propofol and a narcotic such as remifentanil without neuromuscular blockade.

The potential for significant bleeding and rapid transfusion is always relevant in thoracic aortic procedures. Consequently, it is prudent to have fresh frozen plasma and platelets available for ongoing replacement during massive red blood cell transfusion. The time delay associated with standard laboratory testing severely limits the intraoperative relevance of these data to guide transfusion; however, viscoelastic tests are being used with greater frequency to determine coagulation needs. Strategies to decrease bleeding and transfusion in these procedures include timely preoperative cessation of anticoagulants and platelet blockers, antifibrinolytic therapy, intraoperative cell salvage, biologic glue, activated factor VII, and avoidance of perioperative hypertension. The antifibrinolytic lysine analogs, epsilon-aminocaproic acid or tranexamic acid, are the commonly utilized blood conservation agents in thoracic aortic surgery with and without DHCA. Recombinant activated factor VII is a synthetic agent that accelerates thrombin production leading to hemostasis, and it may be considered for the management of intractable nonsurgical bleeding after CPB that is unresponsive to routine therapy. Although this agent has demonstrated efficacy in complex aortic surgery, concerns for arterial thrombotic events remain, requiring further trials to investigate perioperative safety. Finally, the use of fibrinogen concentrates in the management of coagulopathy continue to be investigated in cardiac surgery, with recent evidence suggesting decreased intraoperative bleeding when fibrinogen concentrates are used as a first-line therapy for coagulopathy after major aortic surgery.

Postoperative Care

With the exception of some endovascular aortic procedures, patients often remain intubated and sedated at the completion of the operation, when they are transported directly from the OR to the intensive care unit (ICU). The continuation of care from the OR to the ICU should be seamless and protocol-based. In the absence of complications, early anesthetic emergence is preferable for early assessment of neurologic function. If delayed anesthetic emergence is indicated, then sedation and analgesia can be provided. The chest roentgenogram allows confirmation of endotracheal tube and intravascular catheter position, as well as the diagnosis of acute intrathoracic pathologies. Common early complications include hypothermia, coagulopathy, delirium, stroke, hemodynamic lability, respiratory failure, metabolic disturbances, and renal failure. Frequent clinical and laboratory assessment is essential to manage this dynamic postoperative recovery, including the safe conduct of tracheal extubation. Given the risks associated with hyperglycemia after cardiac surgery, management of blood glucose levels should be standardized, with more recent data to suggest more liberal control (glucose less than 180 mg/dL) is acceptable with good outcomes. Antibiotic prophylaxis is typically continued for 48 hours after surgery to minimize surgical infection risk.