Off-bypass CABG is performed to avoid the complications associated with CPB and to minimize aortic manipulation. Proximal grafts are performed using either a partial aortic cross-clamp technique or a specifically designed proximal anastomotic device that precludes aortic clamping. Distal grafts are performed using one of several heart-stabilizing devices. Considerations for this procedure include the following:
Consider tailoring anesthetic management to allow possible early extubation after surgery (eg, fentanyl 5 to 10 μg/kg, volatile anesthetic followed by an infusion of propofol or dexmedetomidine).
Heparin is given to maintain ACT above 400 seconds. This allows the patient to be emergently initiated on CPB if necessary. Antifibrinolytic therapy is avoided. A small dose of protamine (50 to 100 mg) is given after the procedure.
Hemodynamic instability is common, particularly when the surgeon is performing the distal anastomoses. Grafts to vessels with less disease
tend to be associated with more instability than those to vessels that are occluded. Increasing MAP to optimize coronary perfusion is critical for the ischemic heart during creation of the distal anastomosis. If hemodynamically intolerable ischemia results, coronary shunting may be indicated. Occasionally, repositioning of the heart is required to permit augmented right-sided filling when hemodynamic instability is due to obstruction of right heart inflow.Volume requirements tend to be high. A full heart tends to tolerate physical manipulation better.
Ventricular dysrhythmias may be treated with an amiodarone 150-mg IV bolus and then followed with 1-mg/min infusion. Acid–base and electrolyte abnormalities should be corrected.
“Redo” cardiac surgery
Mediastinal structures, including the heart, major vessels, prior coronary bypass grafts, as well as the lungs may be adherent to the underside of the sternum. They can be lacerated during sternotomy. Usually, 2 to 4 units of blood must be in the OR before sternotomy begins. An additional 14 g IV catheter or a rapid infusion catheter should be placed to facilitate volume resuscitation. Because the patient may need to go on CPB emergently, heparin must be in a syringe ready to administer immediately. In emergency situations, venous return may be supplied from the pump suction line on the field (“sucker bypass”).
Insertion of a PA catheter equipped with pacing capability is prudent as epicardial pacing may not be possible during chest opening. Transcutaneous defibrillation pads should be applied to treat malignant arrhythmias.
Diffuse bleeding from dissection of scar tissue may occur after CPB. Amicar is useful in standard doses.
ECG monitoring is imperative because manipulation of atheromatous grafts may send emboli to the coronary circulation. Because myocardial protection is more challenging in patients with previous coronary grafts, postbypass myocardial dysfunction is more likely.
DHCA may be necessary for surgery on the distal ascending aorta or aortic arch (eg, for an aneurysm or aortic dissection). Circulatory arrest provides a bloodless field for distal aortic anastomosis. Hypothermia decreases the metabolic rate and minimizes the risk of cerebral and organ ischemia during circulatory arrest. Problems associated with DHCA include increased CBP time, coagulopathy, and neurologic and end-organ dysfunction. The risk of permanent neurologic injury after aortic arch surgery using DHCA is approximately 3% to 12%. Most patients tolerate 30 minutes of DHCA without significant neurologic dysfunction. Management issues include the following:
Cerebral protection during DHCA
Hypothermia. Systemic cooling to 18 °C produces electrical silence on the EEG in most patients. There is no outcome evidence to support topical cooling of the head in humans.
Antegrade cerebral perfusion (ACP) via the right axillary artery or retrograde cerebral perfusion (RCP) via the SVC cannula can be used to extend the duration of safe circulatory arrest. ACP is thought to be superior to RCP for cerebral protection and avoid deep hypothermia.
Glycemic control is important. Glucose metabolism is impaired under DHCA. Blood glucose concentration should be maintained below 180 mg/dL to avoid worsening neurologic injury.
Temperature monitoring. It is commonly preferred to use more than one site for core body temperature monitoring. Nasopharyngeal
temperature provides the closest assessment of brain temperature for adults.Acid–base management depends on whether α-stat or pH-stat is used (see Section IV.C.2). The pediatric literature generally recommends the use of pH-stat management during DHCA for both cerebral and myocardial protection.
Cardiac tamponade and constrictive pericarditis
Avoid decreases in myocardial contractility, peripheral vascular resistance, and heart rate. Pericardiocentesis prior to induction may be advisable in patients with tamponade unless the condition is secondary to aortic dissection.
An arterial catheter, a large-bore IV catheter should be inserted. A central venous catheter or PA catheter may be used if the patient can tolerate insertion.
Useful induction agents include etomidate and ketamine.
A method for backup atrial pacing (transesophageal or transvenous) should be available.
Patients should be prepped and draped for surgery prior to induction. In severe cases, awake intubation with maintenance of spontaneous ventilation should be considered.
Cardiac transplantation
Anesthetic management of the donor
Basic management of donor patients and organs is discussed in Chapter 25: Anesthesia for Transplant Surgery.
Donor after cardiac death organ transplantation is an emerging technique with promising initial results that serves to increase the overall number of organ donations. In donor patients, after cardiac arrest has occurred and is deemed irreversible, both heart and lungs may be harvested and transported with various preservation techniques. Outcomes in transplant recipients of these organs have been comparable with recipients of organs from donor after brain death patients.
Anesthetic management of the recipient
The key to patient survival is minimizing the ischemic time of the donated heart. Consequently, expeditious preparation of the recipient and communication with the surgical team are essential.
Preoperative evaluation of the recipient should determine whether the patient has had previous chest surgery, has an elevated PVR (>6 Wood units, transpulmonary gradient >12 mm Hg), has pulmonary hypertension responsive to vasodilators, or is coagulopathic.
Invasive monitoring includes arterial and central lines. A PA catheter and TEE should be used. Internal cardiac defibrillator (ICD) should be turned off.
Precautions for a full stomach may be necessary during induction. If the patient is receiving inotropic infusions, consider increasing their doses before induction. If a ventricular assist device (VAD) is present, venous return must be maintained for the pump to maintain its flow rate.
Right heart failure and coagulopathy are common during the rewarming phase of bypass. Cellular blood products should be irradiated or leukocyte depleted to minimize foreign HLA antigen exposure. An inhaled pulmonary vasodilator, such as nitric oxide, is often empirically initiated to mitigate right heart strain.
The donor heart may be unresponsive to drugs whose actions are mediated by the recipient’s cholinergic nervous system (eg, atropine
and glycopyrrolate). Upon termination of CPB, the recipient’s heart rate should be maintained between 80 and 110 beats/min. This can be accomplished with epicardial pacing or pharmacologically with dopamine (2 to 10 μg/kg/min), epinephrine (0.01 to 01 μg/kg/min), or isoproterenol infusion (0.5 to 5 μg/min).Immunosuppressants and steroid will be necessary and are administered in consultation with the surgeon and transplant cardiologist.
Lung transplantation
Indications and surgical technique: Lung transplantation is performed for end-stage nonmalignant lung disease. Common indications are severe emphysema, α1-antitrypsin deficiency, cystic fibrosis, pulmonary fibrosis, and pulmonary hypertension. Specific operations include living-related lobar lung transplant (LRLLTx), single-lung transplant (SLTx), double-lung transplant (DLTx), sequential SLTx, and combined heart–lung transplantation. The patient’s position depends on the incision required for adequate surgical exposure (lateral decub/thoracotomy for SLTx and clamshell incision/supine for DLTx or LRLLTx). Patients will have undergone preoperative counseling, exercise and cardiac testing, and a conditioning program.
Anesthetic management of the recipient
Invasive monitoring with arterial line, central venous line, and PA catheter. A femoral arterial line and large bore femoral venous access are contemplated for patients who have a high likelihood of requiring extracorporeal membrane oxygenation (ECMO) or CPB. TEE is useful for assessing heart function and pulmonary blood flow after implantation.
Medications should be immediately available to treat bronchospasm, electrolyte disturbances, pulmonary hypertension, and right ventricular failure. Immunosuppressants, steroids, and antibiotics should also be administered. All blood products must be leukocyte depleted and transfused via a filter. Anticipation of a large transfusion requirement and maintenance of an ample supply of blood products are important. A total IV anesthetic is commonly administered.
Analgesia: Intraoperative cryoablation of intercostal nerves by the surgeon is increasingly common. Alternatively, a postoperative epidural catheter may be placed for pain management, unless the patient is already on ECMO or has other contraindications.
Induction with a technique that provides cardiovascular stability is appropriate. Most recipients are considered “full stomachs.”
Lung isolation is best achieved with a left-side DLT or less commonly large (>8 mm) single-lumen endotracheal tube with an endobronchial blocker. The DLT is exchanged for a single-lumen tube at the end of operation.
VA-ECMO or CPB is frequently used to facilitate cardiopulmonary stability during recipient lung explantation and donor lung implantation. ECMO is typically weaned off by case end but may be continued or reconfigured to V-V to manage refractory hypoxemia. Regardless of institutional preferences, CPB or ECMO should be available to initiate should refractory hypoxemia occur. Indications for full CPB include arterial oxygen saturation of less than 90% after clamping of the PA, low cardiac index of less than 2.0 L/min/m2 despite inotropic therapy, or a systolic blood pressure of less than 90 mm Hg.
Capnography may be misleading because of severe mismatching of ventilation to perfusion. Frequent measurements of ABG tensions
are warranted to assess ventilation. Worsening acidemia may also signal inadequate tissue perfusion from a variety of causes (hypovolemia, air trapping, and decreased cardiac output).Postoperative management
Pulmonary hypertension will cause increased hydrostatic pulmonary edema and worsening gas exchange and lung compliance. Serial ABGs are followed to document the function of the transplanted lung. The donor lungs should be ventilated at a low FiO2 (21% to 30%) using a pressure control mode to achieve peak inspiratory pressures <25 cm H2O.
Acute rejection may manifest as decreasing pulmonary compliance with worsening arterial oxygenation.
Many patients will remain intubated until the transplanted lung begins to function well, and symptoms of reperfusion edema and acute rejection are controlled. The trachea is extubated only when the patient is hemodynamically stable and breathing comfortably, which is sometimes possible in the OR.
Observe for signs of toxicity from the immunosuppressive regimen, including acute renal failure.
Repeated bronchoscopies and biopsies of the transplanted lung are necessary after surgery and are often managed under local anesthesia with IV sedation.
Mechanical circulatory support (MCS) may be classified as extracorporeal, percutaneously inserted, or implantable. Patients with decompensated heart failure (biventricular, LV, or RV injury) in cardiogenic shock (CS) may benefit from ECMO or temporary extracorporeal and/or percutaneously inserted VADs to support myocardial recovery before a durable implantable VAD may be appropriate.
Extracorporeal devices
Extracorporeal centrifugal pumps (eg, CentriMag, TandemHeart) may be implanted surgically to support univentricular function via surgical implantation to the LA or LV and aorta, or RA or RV to PA. At MGH, these devices have been supplanted by VA-ECMO and percutaneously inserted microaxial flow pumps (eg, Impella 5.5).
ECMO is an alternative form of extracorporeal life support to VADs. ECMO is indicated for the short-term management of severe but reversible CS or respiratory failure that is refractory to conventional treatment. It is an option for treatment of severe postcardiotomy ventricular dysfunction with or without hypoxemia. It consists of an external pump that pushes venous blood through a membrane allowing gas exchange before returning the blood to the circulation via a warmer.
Venous drainage usually occurs from the internal jugular (IJ) vein or femoral vein. Blood is returned either to an artery (venoarterial [VA] ECMO) or a central vein (venovenous [VV] ECMO).
Venoarterial (VA) ECMO bypasses the patient’s heart and lungs with diversion of complete or partial flow through the ECMO circuit, providing both respiratory and hemodynamic support. It can be used for refractory postcardiotomy CS. The same cannulation setup during CPB can be used for ECMO. If considered subsequently, ECMO can be established from the femoral artery and vein. A condition called differential hypoxemia can occur in VA ECMO when a proportion of venous blood in a patient with some return of cardiac function is pumped into the diseased lungs, with subsequent ejection of hypoxic blood to the coronaries and
great vessels. This may be revealed by a difference in oxygenation from sampling of left-sided and right-sided arterial lines.Venovenous (VV) ECMO provides gas exchange support in patients with good left cardiac function. Venous cannulae are usually placed in the right femoral vein for drainage and right IJ for infusion. A dual-lumen cannula (Avalon or Protek Duo) can be inserted into the IJ vein. The cannula drains blood from IVC and SVC or RA returns oxygenated blood into RA or PA.
Aggressive medical support is required to optimize the results of ECMO and facilitate weaning. Interventions may include the use of pulmonary vasodilators for pulmonary hypertension, lung-protective ventilation strategies; optimization of preload to provide pulmonary perfusion; and the use of renal replacement therapy. To avoid thrombus formation in the ECMO circuit, heparin is administered to maintain the ACT at 1.5 to 2.0 times normal.
Percutaneously inserted devices
Impella are percutaneously inserted microaxial VADs. The contemporary model Impella 5.5 provides up to 6.2 L/min of flow and is an approved therapy for patients with LV failure, CS, and high-risk patients undergoing percutaneous intervention. It may be placed via retrograde approach across the aortic valve using femoral or axillary artery access.
The ProtekDuo is a dual-lumen device inserted percutaneously via the right IJ vein to the right heart to provide RV MCS when used in conjunction with an extracorporeal centrifugal pump. Inflow ports are positioned in the RA and outflow ports in the main PA. While not actively used at MGH, the ProtekDuo is a valid alternative strategy for MCS in RV failure.
The IABP is normally placed in the cardiac catheterization lab under sedation. It provides circulatory assistance for the failing or ischemic heart. Inflation of the intra-aortic balloon early in diastole augments aortic diastolic pressure and thus coronary perfusion. The effect is most beneficial for the LV which receives most of its blood supply during diastole. Deflation of the balloon during isovolumic contraction reduces the impedance to LV ejection, thereby reducing myocardial oxygen consumption. IABPs have fallen out of favor due to questionable mortality benefit and supplanted by Impella and VA-ECMO MCS strategies.
Implantable devices (eg, Heartmate III).
These devices are used as a bridge to cardiac transplantation or destination therapy.
These devices are designed for LV support only. They consist of an inflow cannula, a pump, and an outflow cannula. The inflow cannula is inserted into the LV apex while the outflow cannula is inserted into the ascending aorta. A driveline is tunneled through the skin to connect the implanted pump to the external console. CPB is always necessary for placement.
The HeartMate III is an electrically driven centrifugal flow pump. A rechargeable power source fits into a holster and allows the patient to leave the hospital. The HeartMate III is the only durable VAD currently implanted at MGH.
Anesthetic considerations for MCS insertion
Patients will have marginal cardiac function. Extreme care is required during induction to minimize decreases in contractility and preload.
Large-bore IV access is recommended and antifibrinolytics merit consideration depending on the type of support.
If the patient is receiving the device as a bridge to transplantation, transfuse with leukocyte-depleted cellular blood products to minimize human leukocyte antigen exposure.
Transesophageal echocardiography (TEE) and/or fluoroscopy is required to assess the position and flow of the cannula in addition to facilitating air removal. It also evaluates the position of the interventricular septum to guide the pump output and evaluate ventricular functions and volume status.
Patients receiving an LVAD frequently require RV support. Inotropes, inhaled prostaglandin or nitric oxide, and occasionally an RVAD are required.
The flow of the device depends largely on the volume in the ventricle. Decreased venous return or hypovolemia will be signaled by a decreased pumping rate which is typically improved with volume repletion. Vasopressors such as norepinephrine and vasopressin are typically needed to ameliorate vasodilation. Patients with an LVAD are preload dependent and afterload sensitive.
Subsequent to placement of temporary MCS, continual assessment of native cardiopulmonary function is essential. If the heart and lungs do not recover within the expected timeframe (1 to 2 weeks), the decision should be made to convert to long-term support such as a durable VAD or transplant. A discussion of the goals of care is important if the disease process is believed to be nonreversible.
Transcatheter aortic valve replacement (TAVR) is conducted for patients who are not surgical candidates for aortic replacement. An expanding bioprosthetic valve is placed over the native aortic valve. The procedure may be carried out using a transfemoral arterial or open transapical approach. The procedure is typically carried out in a hybrid OR or cardiac catheterization laboratory.
Anesthetic management
General anesthesia is not usually required unless TEE is needed for proper positioning of the new valve. The procedure can be well tolerated under monitored anesthesia care or conscious sedation if fluoroscopy and TTE are used for valve deployment and evaluation.
Rapid ventricular pacing is required to minimize cardiac motion during valve deployment. A temporary transvenous pacing lead is inserted into the right ventricle. A pacing rate of 140 to 200 beats/min frequently results in 1:1 ventricular capture and sufficiently lowers the pulse pressure and cardiac output. The rapid pacing periods must be minimized to avoid hemodynamic instability, especially in patients with depressed LV function and CAD.
Echocardiography is particularly useful to assess adequate placement and function of the valve. It is crucial to ensure accurate positioning of the valve with echocardiography and fluoroscopy prior to deployment to avoid embolization of the valve or a large perivalvular leaks. Transthoracic echocardiogram or TEE can assess stability, location, and function of the valve as well as the degree of perivalvular leak.
Complications include tamponade, cerebral vascular accident, aortic rupture or dissection, AI, conversion to emergent surgical aortic valve replacement, myocardial infarction, suboptimal valve deployment, and AV block.
Transcatheter MV replacement (TMVR) and repair (TMVRep) are effective for native primary and secondary MR in patients who are not suitable surgical
candidates. TMVR is also approved to treat MS with annular calcification or as valve-in-vale management of failed surgical bioprosthesis or ring. TMVRep may include leaflet, chordal, or annuloplasty repairs that are performed via trans-septal approach. TMVR is an evolving procedure with multiple devices available and more commonly performed via trans-septal approach than transapical approach which requires minithoracotomy.General endotracheal anesthesia with TEE and fluoroscopic guidance is frequently required for the procedure. However, these procedures are increasingly done under sedation and local anesthesia.
A radial arterial line is placed prior to induction and large bore access is obtained in case of complications necessitating rapid transfusion.
Right heart catheterization or PA catheter placement is often performed to monitor right- and left-sided hemodynamics before and after the procedure. For TMVR, placement of a transvenous pacing wire may facilitate rapid ventricular pacing for valve deployment.
Echocardiographic guidance is crucial for the trans-septal puncture and device positioning, as well as to assess severity of MR or MS pre- and postintervention.
Brief periods of apnea may be required to allow precise placement of the device.
Vasoactive agents and inotropes may be required to raise the blood pressure to adequately assess the severity of residual MR.
Complications include arrhythmias (especially atrial fibrillation), worsening MR, tamponade, device embolization, device entrapment in the chordal apparatus, or acute chordal rupture that may necessitate emergent open surgical repair.