The use of long- and short-term mechanical circulatory support in the form of ventricular assist device (VAD) has increased over the last decade. Although cardiothoracic anesthesiologists care for these patients during device placement, increasingly higher numbers of general anesthesiologists are involved in the management of VAD patients during noncardiac surgery and procedures. An understanding of devices, their indications, and complications is essential to the anesthesiologists caring for these patients. We review the anesthetic considerations for the implantation of these devices and concerns when caring for patients with durable and short-term devices already in place.
Ventricular assist devices
Indications for ventricular assist devices
Mechanical circulatory support (MCS) in the form of ventricular assist devices (VADs) can be used in cases of acute or chronic cardiopulmonary failure. Conditions where MCS is used include cardiomyopathies, postmyocardial infarction cardiogenic shock, myocarditis, postcardiotomy stunning, and primary graft failure following heart transplantation.
The Interagency Registry for Mechanical Circulatory Support (INTERMACS) is a collaboration between hospitals; industry; and the National Heart, Lung and Blood Institute that collects data on over 15,000 patients who have undergone long-term Federal Drug Administration (FDA)-approved continuous flow VAD placement. INTERMACS defines seven profiles for acute and chronic heart failure for MCS insertion, ranging from acute critical shock to stable New York Heart Association III heart failure, and timeline for insertion ( Table 1 ) .
| Risk level | Short hand | Description | Time frame for intervention |
|---|---|---|---|
| 1 | “Crash and burn” | Critical cardiogenic shock | Definitive intervention needed within hours. |
| 2 | “Sliding on inotropes” | Progressive decline on inotropic support | Definitive intervention needed within few days. |
| 3 | “Dependent stability” | Stable but inotrope dependent | Definitive intervention elective over a period of few weeks to few months. |
| 4 | “Frequent flyer” | Resting symptoms home on oral therapy | Definitive intervention elective over a period of few weeks to few months. |
| 5 | “House bound” | Exertion intolerant | Variable urgency, depends upon maintenance of nutrition, organ function, and activity. |
| 6 | “Walking wounded” | Exertion limited | Variable, depends upon maintenance of nutrition, organ function, and activity level. |
| 7 | “Place holder” | Advanced NYHA Class III symptoms | Transplantation or circulatory support may not be currently indicated. |
The use of MCS can be described in terms of bridge or destination therapy (DT). Bridge therapy includes bridge to recovery if the myocardium is expected to recover, a bridge to a bridge or bridge to a decision in cases where extracorporeal support is placed as a rescue or more time is needed to decide definitive therapy, a bridge to transplant or bridge to improve candidacy for transplantation, or DT . DT is permanent therapy for individuals who are not considered candidates for heart transplantation and is progressively increasing as a designation for VAD implantation, now accounting for 38% of implants in the most recent INTERMACS report .
Device classification
VADs can be categorized by the duration of intended support (short term or long term), pump flow type (pulsatile or continuous), engineering design (first, second, or third generation), which ventricle the device can support (left, right, or biventricular support), and FDA-approved indications. Table 2 outlines established and investigational devices that, in the experience of the authors and based on literature reviews , are currently being implanted in larger numbers. Only the most salient points about the design and function of these devices are noted in the table.
| Device | Location | Flow type | Duration of support | Maximum flow in liters per minute | FDA-approved indications |
|---|---|---|---|---|---|
| Thoratec HeartMate II | Subdiaphragmatic | Axial | Long term | 10 | BTT, DT |
| Thoratec HeartMate III | Intrapericardial | Centrifugal | Long term | Flow calculated based on power and speed, and may be inaccurate | Investigational |
| Jarvik 2000 | Intrapericardial | Axial | Long term | 7 | Investigational |
| HeartWare HVAD | Intrapericardial | Centrifugal | Long term | 10 | BTT |
| HeartWare MVAD | Intrapericardial | Axial/ Centrifugal | Long term | 7 | BTT |
| Reliant HeartAssist 5 | Subdiaphragmatic | Axial | Long term | 10 | Investigational |
| Thoratec CentriMag | Left atrium to aorta (LVAD) Right atrium to pulmonary artery (RVAD) | Centrifugal | Short term | 6 | 6 h (LVAD) 30 days (RVAD) |
| TandemHeart P | Femoral vein transseptally to LV | Centrifugal | Short term | 4.5 | 6 h but in practice used for up to 1 week |
| Impella P (2.5, 4.0/CP, 5.0) | Retrograde from femoral artery and across aortic valve | Axial | Short term | 2.5, 4.0, and 5.0, respectively | Cardiogenic shock: 2.5/CP: <4 days 5.0: <6 days High-risk PCI: ≤6 h |
Pulsatile VADs are first-generation and use volume displacement. First-generation Left ventricular assist devices (LVADs) are loud, large, and require placement in a subdiaphragmatic pocket. This pocket can be a nidus for infection and bleeding after implantation. Second-generation devices were developed addressing these issues, offering simpler, smaller, quieter designs that are associated with fewer cerebral vascular events and less device malfunction than pulsatile flow devices. Hence, first-generation devices are no longer in use .
Continuous flow devices are either second or third generation, as distinguished by the bearing design, which can be contact or noncontact. This determines the device support, movement, friction, and heat created. Second-generation devices employ contact-bearing design and axial pattern of blood flow .
Sometimes referred to as “bearing-less,” third-generation devices employ noncontact-bearing design, which utilizes magnetic and hydrodynamic levitation to suspend the device impeller and a centrifugal flow path of blood, with the exception of the Incor (Berlin Heart GmbH, Berlin, Germany), which employs axial blood flow design. Perceived benefits of centrifugal pumps include greater sensitivity of pressure–flow relationship, resulting in greater changes in pump flow for changes in pressure across the pump and increased reliability of estimated flow .
Anesthetic management of long-term device placement
Preoperative assessment
Preoperative evaluation of all organ systems should be performed. The extent of ischemia, valvular abnormalities, arrhythmias, and right heart function should be noted. Right heart catheterization data should be reviewed. Neurological deficits should be noted. Pulmonary function tests, if available, and chest radiography should be reviewed. Electrolyte abnormalities secondary to renal dysfunction and use of diuretics should be corrected preoperatively. Coagulation laboratories should be evaluated in light of intentional medical anticoagulation and hepatic dysfunction from congestive hepatopathy. Patients should be screened for absolute and relative contraindications to the intraoperative use of transesophageal echocardiography (TEE) .
Induction
Prior to induction of anesthesia, routine noninvasive monitoring and invasive arterial blood pressure monitoring should be established to allow for beat-to-beat blood pressure monitoring. External defibrillator pads should be placed on the patient. Slow induction of anesthesia should be performed with agents that are routinely used for inducing patients in heart failure.
Anesthetic considerations in heart failure predevice implantation
The heart failure patient will have alterations in neuroendocrine systems (renin–angiotensin–aldosterone system, natriuretic system, and sympathetic nervous system) and may be on agents to compensate for these alterations. Heart failure patients may present to the operating room grossly volume overloaded or adequately diuresed and perhaps hypovolemic. Trendelenburg position can be utilized for a gross assessment of volume responsiveness, keeping in mind that a failing heart may not tolerate an acute increase in preload.
Medical management including inotropic and hemodynamic support may already be initiated in patients with heart failure. Milrinone is often used in patients with nonischemic cardiomyopathy to improve systolic function, decrease afterload, and improve diuresis . Hypotension and arrhythmias can occur with milrinone . The anesthesiologist should continue this support in the operating room, monitor, and be prepared to increase or add additional agents as some patients may not be able to tolerate the decrease in systemic vascular resistance (SVR) that accompanies many anesthetic agents. Careful titration of anesthetic agents or consideration of use of anesthetic agents with greater hemodynamic stability is advised.
Patients with heart failure are on the plateau portion of the Frank-Starling preload-cardiac output curve and may not be able to mount an increase in stroke volume in response to increased preload. Therefore, if an increase in cardiac output is desired, consider increasing the heart rate. Increases in heart rate come at the cost of decreased time in diastole for ventricular relaxation, coronary perfusion, and ventricular filling. If high-dose opioid techniques are used, the resulting bradycardia may need to be counteracted by positive chronotropic medications to maintain cardiac output.
Patients may not tolerate further increase in pulmonary vascular resistance (PVR) that may accompany periods of hypoventilation. PVR may already be increased because of elevated pressures from a failing left heart, and further increase in PVR may cause acute or worsened right heart failure. Ventilation is therefore recommended throughout induction. Should aspiration be a concern, a modified rapid sequence with intermittent ventilation and cricoid pressure may be considered .
Invasive monitoring
Following the induction of anesthesia, central venous access should be established. Pulmonary artery catheters may be useful in the postoperative period to monitor both left and right heart pressures, cardiac output, and allow mixed venous saturation sampling. It is prudent to replace existing catheters with new catheters to minimize sources of infection during new device placement.
Antibiotic prophylaxis
Prior to surgical incision, prophylactic antibiotics should be administered. The choice of antibiotics will vary between institutions. Staphylococcus spp. and Pseudomonas spp. are the main bacteria implicated in VAD infections . Evidence supports the use of a beta-lactam first-generation cephalosporin and vancomycin in hospitals where methicillin-resistant Staphylococcus aureus rates are high. Some centers include fluoroquinolones for additional gram-positive coverage. Antifungal prophylaxis can be used in patients at risk of fungal infections or in patients where the closure of the chest following VAD insertion is temporarily deferred .
Autologous blood
Sequestration of autologous blood in patient-labeled citrate-phosphate-dextrose bags for reinfusion after cardiopulmonary bypass (CPB) can be considered if preoperative hematocrit is at an appropriate level. This process is similar to acute normovolemic hemodilution, which is used by some centers in cardiac surgery, without the infusion of crystalloid to maintain normovolemia. In the severely volume-overloaded heart failure patient, this approach may help resolve hypervolemia and re-establish euvolemia . Removal of autologous blood (500 ml–1 l) is usually well tolerated or may improve hemodynamics prebypass. Autologous blood can be kept at room temperature (22–25 °C) and periodically agitated to prevent platelet aggregation and preserve platelet function. Autologous blood should be re-infused into the patient within 4–8 h of removal. After 8 h, the blood should be stored at 1–6 °C for up to 24 h and re-infused. It is not recommended to store autologous blood longer because of the risk of infection. Although perceived benefits of improved volume state and possible reduction of allogenic red blood cell and blood factor transfusion, this practice has not been formally studied VAD populations.
Preimplantation TEE exam
A comprehensive perioperative TEE exam should be performed pre and post VAD insertion. Inspection for intracardiac shunts, specifically patent foramen ovale (PFO), should be performed because once the device is in place and left-sided heart pressures are reduced, right to left shunting can result in systemic delivery of hypoxic blood and paradoxical emboli. If identified, shunts may be closed at the time of device insertion. It may be challenging to identify a PFO in the setting of elevated left heart pressures. Saline contrast study with a ventilator-induced Valsalva maneuver is recommended. The examiner should assess thrombus in the cardiac chambers, particularly the left ventricular (LV) apex. Native and prosthetic valvular function should be assessed. Mitral stenosis is of particular concern as it may prevent LV and device filling. Aortic insufficiency (AI) will result in recirculation of flow through the device and decreased flow to the systemic circulation. Both a failing LV, with increased end-diastolic pressure, and decreased SVR under anesthesia may mask the severity of AI, resulting in higher degrees of AI once the device is activated. The aortic valve may be sutured closed should severe AI be present. The ascending aorta should be examined for significant calcification at the intended site of VAD outflow cannula placement. The right ventricle (RV) function and tricuspid regurgitation must be assessed as patients with borderline RV function are at a high risk of RV failure postimplantation . ( Table 3 ).
| Pre-implantation TEE exam | Post-implantation TEE exam |
|---|---|
| L eft ventricle size and systolic function | Left ventricle size |
| Right ventricle size and systolic function | Right ventricle size and systolic function |
| Evaluate for septal defects , including PFO | Evaluate for tricuspid regurgitation |
| Evaluate all chambers for thrombus | Re-evaluate for septal defects, including PFO |
| Evaluate aortic valve (is there greater than mild aortic insufficiency ?) | Evaluate aortic valve opening and aortic insufficiency |
| Evaluate mitral valve (is there greater than moderate mitral stenosis ?) | Evaluate inflow cannula position, color Doppler, and flow velocities |
| Evaluate the function of the tricuspid valve | Outflow cannula position, color flow Doppler, and flow velocities |
| Evaluate the aorta | Evaluate the aorta to exclude dissection |
| Document changes in pump speed during assessment |
Device implantation
Implantation of durable LVADs is most often performed utilizing median sternotomy and CPB. If no valvular, septal, or other anatomic abnormalities require repair, LVADs can usually be placed without arresting the heart. As technology has evolved and some devices have become smaller, experience has been gained with minimally invasive surgical approaches, avoiding sternotomy, utilizing peripheral CPB or avoiding CPB altogether. It is desirable to avoid sternotomy in patients with adhesions from previous surgery or in patients likely to have re-operations . Theoretical benefits of performing an implantation without CBP include less vasodilation, infection, coagulopathy, and RV failure after separation from bypass . Minimally invasive approaches capitalize on anastomosing the VAD outflow cannula to the innominate artery, the subclavian artery, or the descending aorta, through left or right clavicular incisions, left or bilateral anterior thoracotomies, or mini-sternotomy approaches . Pump pockets can be created through anterolateral thoracotomy, left lateral mini-thoracotomy, bilateral thoracotomy incisions, or left subcostal incision . If a minimally invasive strategy is employed, lung isolation may be required for surgical access .
Heparinization and antifibrinolytic agents for device insertion will vary depending on whether CBP is used. When CPB is not used, partial heparinization for device placement can be employed, with a goal activated clotting time of 250 s to prevent thrombosis during clamping of access vessels.
To place the LVAD inflow cannula or device, the surgeons locate the LV apex by palpation. The midesophageal 4- or 2-chamber view can be used for TEE confirmation during minimally invasive approaches. When the inflow cannula is inserted, the patient should be placed in the Trendelenburg position to prevent air entrainment, and rapid ventricular pacing through epicardial leads to 180 beats/min can be used to decompress the LV. Hypotension and ventricular fibrillation can persist after rapid pacing and may need to be treated. The outflow graft can be placed through a side-binding clamp on the target vessel. The echocardiographer should ensure that the heart is free of air as the surgeon completes the de-airing process of the device with progressive clamping of the device from inflow to outflow . Air usually collects along the atrial or ventricular septum, along the LV apex, and in the pulmonary veins, but the aorta and the inflow and outflow grafts should be checked for air .
To initiate the device, revolutions per minute (rpm) are increased gradually, while myocardial function, hemodynamics, and echocardiographic parameters (discussed below) are followed closely. If RV failure is expected to occur, the device can be initiated while on CPB to support the RV. To allow full flow through the device, CPB must be fully weaned. Temporary hemodynamic support may be required in the form of bolus vasopressor or inotrope agents to allow for this transition.
Postimplantation assessment of RV function
Careful attention should be placed on assessing the RV function during weaning, which includes TEE (See Table 3 ) and hemodynamic monitoring as well as visual inspection in the surgical field. The function of the RV is dependent on preload, afterload, and contractility, all of which can be altered by device placement. With initiation of the device, RV preload will be increased and afterload may be reduced or remain the same. A dysfunctional RV may not be able to compensate for these changes and failure may occur. The interventricular septum may bow to the left, impairing the septal contribution to RV contractility requiring the RV free wall to compensate in function, which can result in RV exhaustion . The function of an already incompetent tricuspid valve can be worsened if the tricuspid annulus dilates with increase in preload or if the septal leaflet of the tricuspid valve becomes tethered by changes in interventricular septal architecture post LVAD implantation . Despite mixed outcomes, a severely incompetent tricuspid valve can be augmented with a ring or replaced .
The RV can be supported with inotrope infusions such as milrinone, afterload reduction in the form inhaled pulmonary dilators such as nitric oxide or iloprost (a synthetic PGI 2 analog), and preload optimization. To minimize PVR, hypoxia, hypercarbia and acidosis should be avoided . An RV may be able to compensate for a brief period of time in the operating room after device insertion and fail several hours later in the intensive care unit (ICU). If supportive measures do not improve RV function, ECMO or a RV assist device may be inserted .
Postimplantation coagulopathy
Once the device is in place and the patient has been separated from CPB, protamine is given to reverse the effects of heparin. Transfusion of fresh frozen plasma, cryoprecipitate, and platelets may be needed to reverse coagulopathy. Bearing in mind the risk of thrombotic complications, the safe use of prothrombin complex concentrate, which can replace clotting factors in a smaller volume than FFP, has been reported . Thromboelastography or rotational thromboelastometry can be used for real-time assessment of coagulation deficits.
Postimplantation intraoperative TEE
The echocardiographer should examine blood flow at the inflow and outflow cannulas using spectral and color Doppler to verify laminar low velocity flow (flow should be <2.0 m/s, ideally <1.5 m/s). Examination of the aorta for dissection at the site of cannulation is imperative. Aortic valve function, frequency of opening, and insufficiency should be assessed. It is possible that AI can be unmasked after the device decompresses the LV, creating a pressure gradient favorable to reveal AI . Adequate decompression of the LV and septal wall position should be noted. A midline septum indicates optimal device and myocardial function. A septum shifted to the left could be a sign of excessive LV decompression due to high device speed or RV failure leading to incomplete filling of the LV. Septal shift to the right signifies incomplete LV emptying, which may be due to inflow cannula obstruction or inadequate device function. RV function should be examined . TEE should again verify the absence of intracardiac shunts and thrombus (See Table 3 ).
Postdevice implantation
Transportation of patients with devices to and from the operating room requires multiple team members. Pulse oximetry, ECG, arterial pressure monitoring, and backup power supply should be available on transport. Care should be taken to prevent device dislodgement if there are any external components (peripherally inserted RV support, ECMO, or as in the case with short-term devices).
Patients with newly implanted LVADs should be transferred to an ICU intubated and sedated. Once hemodynamic, pulmonary, and coagulation parameters have stabilized, sedation can be weaned and patients extubated. ICU length of stays can be shorter in patients with well-functioning RVs and those who did not require CPB for VAD implantation.
Understanding VAD parameters
Speed, power, flow, and pulsatility are parameters that vary between devices. Though every patient’s clinical situation must be evaluated individually, key VAD concepts help the anesthesiologist to understand acute events. Echocardiography can be invaluable in the diagnosis of device dysfunction .
Pump speed is the revolutions per minute of the impeller and is a parameter that is set. At low pump speeds, there is a low flow state and an increased risk of thrombosis. At high pump speeds, suction events may occur (see below). Power is directly measured as the watts needed to drive the pump at a set speed. There is a direct relationship between power and flow. An increase or decrease in one results in a proportional change in the other. Sustained elevations in power can be observed when device thrombosis develops. Low power can be because of occlusion of either the device inflow or outflow or low device preload.
Device flow does not equal cardiac output as it does not consider any native output of the ventricles or any regurgitant flow. Flow in two commonly inserted devices, HeartMate II and HeartWare, is preload and afterload dependent. Low flows may be due to low LV preload to the device (hypovolemia, bleeding, RV dysfunction, tamponade, arrhythmias, or a suction event). Typically, high flow may be the result of sepsis or vasodilation, or it may be erroneously high if there is a device thrombosis. Increases in SVR increase the pressure differential across the HeartMate II or HeartWare pumps and, consequently, decrease flow.
Pulsatility or pulsatility index (PI) is a unitless measure that reflects the stroke volume added by the native ventricle to flow through the device. PI depends on ventricular preload, myocardial function, afterload, and device output. PI can increase with high preload, recovery of myocardial function, and increased afterload and can decrease with inadequate LV preload and increased device output. PI for HeartMate II ideally should be 4.0–6.0 and serves as an indirect indicator of ventricular volume. For HeartWare, pulsatility is visually assessed by the peaks and nadirs of the flow waveforms on the display.
A “suction event” occurs when a portion of the LV myocardium contacts and obstructs VAD inflow, resulting in decreased flow, and is associated with low pulsatility. The LVAD pump will detect a sudden decrease in flow and alarm. Echocardiographic evaluation during a suction event will reveal decreased LV chamber size. Depending on the cause and severity, it may show right-to-left interventricular septal shift, inflow cannula abutting the endocardium and with off-axis appearance or increased inflow peak velocity if partial obstruction is present . Because of the negative pressure gradient created between the LV and the left atrium, the mitral valve leaflets may be in a fixed open position . Suction events can result from high pumps speeds reducing LV chamber dimensions and presenting increased preload to a tenuous RV. After device implantation, a suction event that occurs despite low pump flows may represent a failing RV that is unable to pump preload forward to the LV . Treatment would be decreasing pump speed, supporting a failing RV, or addressing the primary reason for decreased preload to the device.
The monitor of the CentriMag displays the pump speed and flow that is directly measured from a flow probe on the cannula. Flow in the CentriMag is affected by pump speed, differential pressure across the pump, afterload, and preload. Inadequate preload, excessive pump speed, or return of ventricular activity reducing preload to the device will result in “chattering,” which is a low-frequency jerking movement of the cannulas. Chattering can usually be treated by correcting hypovolemia or decreasing pump speed. The pulmonary or systemic arterial tracing pulsatility can be used to determine if RV or LV function is improving, respectively.
Following device insertion
The life expectancy of patients with continuous flow devices has improved over the last 5 years with 1- and 2-year life expectancy now being 80% and 70%, respectively . Causes of mortality in the first few months after device implantation are multisystem organ failure, neurologic injury, and right heart failure. The causes of late mortality include multisystem organ failure, neurologic injury, and infection .
Neurologic injury in VAD patients is a concern. A prospective study of 402 LVAD patients (HeartMate II and HeartWare) demonstrated a stroke rate of approximately 17%, with equal prevalence of ischemic and hemorrhagic strokes. Modifiable risk factors identified were tobacco use, pump thrombosis, pump infection, bacteremia, and hypertension . The ENDURANCE and MOMENTUM 3 trials did not reveal a statistically significant difference in stroke rates between LVAD types . Post hoc analysis of the ENDURANCE trial data suggested that MAP greater than 90 mmHg in the HeartWare population was associated with more hemorrhagic strokes .
Right heart failure can occur in 10%–50% of LVAD recipients . RV failure in LVAD population is defined by INTERMACS as CVP greater than 18 mmHg with a cardiac index less than 2.0 l/min/m 2 without increased left heart filling pressure or a patient requiring an RVAD, inotropic agents, or nitric oxide for more than 14 days post LVAD implantation . Models using clinical, hemodynamic, and echocardiographic markers have been developed to predict which patients are at risk of early and late onset RV failure post LVAD implantation . One such model is the CRITT score, which assigns a point to the following five variables: ‘C’ – CVP >15 mmHg, ‘R’ – severe RV dysfunction, ‘I’ – preoperative mechanical ventilation/intubation, ‘T’ – severe TR, and ‘T’ – tachycardia (>100 bpm). In the CRITT score study, 93% of patients with a score of 0 or 1 did not require RVAD support, but 80% of patients with a score 4 or 5 required RVAD in addition to LVAD support . Patients who require unplanned RVAD insertion have higher mortality, postoperative complications, renal failure, and recurrent RV failure .
LVAD patients require anticoagulation to prevent thrombosis, which may require device exchange and is a significant cause of morbidity in long-term support. Thrombosis risk results from factors associated with the pump itself (sheer stress, blood surface contact, heat, device malposition, and platelet activation) and from underlying patient pathology (current thrombus, atrial fibrillation, hypercoagulability, surgical inflammatory state, and Virchow’s triad). Risk factors associated with pump thrombosis in HeartMate II patients are female sex, White race, younger age, increased BMI, CHA2DS2-VASc score of >3, increased creatinine, LVEF >20%, higher LDH at 1-month postimplantation, history of treatment nonadherence, and RV failure . Recent efforts to decrease the morbidity in HeartMate II patients have centered around preventing pump thrombosis by adhering to the guidelines suggested by the PREVENT investigators: optimizing anticoagulation (warfarin and antiplatelet), positioning of inflow and outflow cannulas, and appropriate VAD flow >9000 rpm . The MOMENTUM 3 trial found HeartMate II axial flow devices had a statistically significant greater rate of suspected or confirmed pump thrombosis leading to device replacement or urgent transplant (10.1%) than the HeartMate III group, which had no cases of pump thrombosis during the trial . Risk factors associated with pump thrombosis in the HeartWare population are MAP >90 mmHg, ASA dose <81 mg, INR <2, and INTERMACS >3 .
Bleeding complications are often the result of supratherapeutic anticoagulation, mechanical or enzymatic coagulation factor deficits or dysfunctions, mucosal bleeding, and arteriovenous malformations (AVM) . Patients with continuous flow VADs are at risk of an acquired form of Type 2A von Willebrand disease: a qualitative defect with inability to form the large von Willebrand factor (VWF) multimers required for clot formation . Sheer stress from the mechanical device likely results in VWF unfolding, which leaves the large multimers open to proteolytic cleaving . Although it has been observed that patients with centrifugal flow VADs (designed to have less sheer stress on blood) have preservation of large VWF multimers as compared to axial continuous flow devices, the MOMENTUM 3 trial did not find a statistically significant difference in bleeding complications between HeartMate II and HeartMate III patients, both maintained on antiplatelet and warfarin regimens . Lower PI is associated with a greater risk of nonsurgical bleeding (gastrointestinal, epistaxis, genitourinary, and intracranial), supporting the notion that the absence of or a decrease in pulsatility may lead to the formation of AVMs by way of dilation of mucosal veins and relaxation of arterial smooth muscle .
Infection is a cause of readmission for LVAD patients. A younger, more active LVAD patient may be at a higher risk of driveline infection . Sterile dressing changes at driveline sites are an important mainstay of VAD care. The treatment for infections can be medical and/or surgical depending on the extent of the infection (superficial or deep driveline infections, and pump pocket infections) .
Anesthetic management of patients with existing LVAD undergoing noncardiac surgery
LVAD patients may present for noncardiac surgery (NCS) or, with increasing frequency, for procedures outside the operating room (endoscopy, cystoscopy suites, interventional radiology, and catheterization laboratory) . Institutions are reporting a trend toward providing anesthetic care to these patients by noncardiac-trained anesthesiologists . Stone et al. reported that 88% of LVAD patients presenting for NCS had anesthetic care provided by noncardiac anesthesiologists. Aiding in this trend is the availability of LVAD nurses or technicians familiar with the patient and device, who can assist the anesthesiology team in connecting the patient to the external console so that device parameters (speed, power, pump flow, and PI) can be monitored throughout NCS procedures . When preparing patients with LVAD for NCS, it is important to evaluate patients with a multidisciplinary approach including heart failure cardiologists to optimize their clinical condition, hematologists to guide perioperative coagulation management, and intensivists for postoperative care, if indicated. Cardiac surgical resources and postoperative recovery units or ICUs experienced in LVAD care should be available .
Standard ASA monitors are sufficient for LVAD patients having nonmajor NCS . A noninvasive blood pressure cuff often provides adequate mean pressure readings in patients with continuous flow devices. However, in LVAD patients requiring general anesthesia, invasive blood pressure monitoring may be more reliable than oscillometric measurements, especially if rapid or marked changes in preload or afterload are expected . Central venous access is indicated if vasopressors are expected to be required. In the series reported by Degnan et al., of 74 NCS procedures performed on 31 LVAD patients, 88% did not require vasopressor doses, and only one patient who was on an inotropic infusion preoperatively had the inotrope continued intraoperatively . It should be noted, however, that 65% of these NCS procedures were upper and lower endoscopies, and 81% of the procedures were performed under MAC anesthesia . Stone reported similar vasopressor use in his reported series of 241 patients from 2003 to 2013, with vasopressor or inotrope bolus use in 24%, infusion use in 22%, and both bolus and infusion in only 7.5% of cases, all described as either “major” cases or having significant comorbidities . TEE or TTE can be used to assess right heart function. Cerebral oximetry can be used in lieu of pulse oximetry should lack of pulsatility preclude pulse oximetry measurement .
It is usually not necessary to alter the device settings in otherwise stable patients, provided that hemodynamics and volume status are maintained throughout the case. Hemodynamic derangements and resulting VAD parameter changes are described above. In general, if a patient with a VAD becomes hypotensive, the VAD flows should be checked. If the flows are high, vasodilation due to medications or infection are most common and should be suspected. If hypotension occurs with low flows, the differential diagnosis includes RV failure, cannula obstruction, tamponade, hypovolemia, arrhythmia, and suction event. Therefore, the clinical scenario, filling pressures, ECG, and echocardiogram can aid in the diagnosis and selection of focused treatment maneuvers.
Decisions regarding anticoagulation management for NCS should be made in conjunction with the surgeon, heart failure cardiologist, and hematologist . Consideration should be given to the patient’s history of thrombotic events and the nature of the procedure. Anticoagulation reversal may be considered in urgent surgery where anticoagulation has not been held, or in neurosurgery or ophthalmologic surgery . Blood product transfusion is according to usual expectations of surgical blood loss and coagulation status.
Patients having minimally invasive procedures can usually recover in postanesthesia care units, but hospitals should have ICU availability in case higher levels of care are required.
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