Anaesthesia for children with left ventricular assist devices undergoing non-cardiac surgery

Key points.

• •Children with ventricular assist devices (VADs) present a unique set of challenges for the anaesthetist.
• •Perioperative management requires a multidisciplinary team approach with essential input from the patient's VAD centre or VAD specialists.
• •A good understanding of VAD-supported physiology is required to ensure safe perioperative care.
• •Key goals of haemodynamic management include optimising preload, maintaining right ventricular function, managing systemic vascular resistance, and maintaining device function.
• •The choice of intraoperative monitoring must be considered carefully in patients with a VAD.

Learning objectives.

By reading this article, you should be able to:

• •Explain the principles of how a ventricular assist device supports a patient's physiology.
• •Outline the key perioperative considerations for children with ventricular assist devices.
• •Discuss the challenges of intraoperative monitoring associated with the presence of ventricular assist devices.

Ventricular assist devices (VADs) are mechanical devices used to support cardiac function in patients with refractory heart failure. Although heart transplantation is the definitive treatment, mortality is considerable in patients waiting for a suitable donor. Extracorporeal membrane oxygenation (ECMO) was until relatively recently the mainstay of mechanical support for children with severe heart failure awaiting transplantation, but this is only a short-term means of support because of its significant morbidity and mortality. VADs have been used as long-term support in adults for many years; with improved technology and reduced device size, the use of VADs in children needing long-term cardiac support has increased, and outcomes have become more favourable.¹ More children with end-stage heart failure are now being implanted with VADs, with devices remaining in situ for an increasing length of time. This has resulted in a growing pool of VAD-supported children who may require anaesthesia for non-cardiac procedures. Many of these children will remain as hospital inpatients in their specialist cardiac centre. However, with continuing improvements in the development of smaller implantable continuous flow VADs, increasing numbers of children are being discharged to their local communities and may present with acute medical or surgical conditions to non-specialist hospitals, where they may need clinical input from anaesthetists.

Children with VADs present a unique set of challenges for the anaesthetist. They may have significant comorbidities arising from their underlying heart disease and morbidity associated with the mechanical device and anticoagulation. Perioperative management requires an understanding of their unique VAD-supported physiology, and how best to optimise cardiovascular function. In many of these patients it can be problematic to achieve reliable monitoring. A team approach is essential to delivering safe anaesthesia to this population.

Ventricular assist devices

VADs assist or assume the role of the ventricle in moving blood through the heart. The left ventricle (LV) is the most frequently supported ventricle (LVAD) and is the focus of this article. Occasionally biventricular (BiVAD) support may be initiated.

The main indication for VAD implantation is to support patients awaiting heart transplantation, termed ‘bridge-to-transplant’. Less commonly, VADs may be implanted as a bridge to myocardial recovery, or as a ‘destination therapy’ (i.e. permanent device placement without planned heart transplantation). Dilated cardiomyopathy, congenital heart disease, and myocarditis are the most common causes of refractory heart failure in children requiring VAD support.2, 3

Devices

LVADs typically have three main components: an inflow cannula (usually implanted in the LV, occasionally in the left atrium), a mechanical pumping system (unloading the LV), and an outflow cannula (returning blood to the ascending aorta). Pumping systems vary with device and are the mechanism by which blood flow is generated, producing either pulsatile flow (PF-VAD) or continuous flow (CF-VAD).

Pulsatile flow

PF-VADs are the most common type of device used in children currently.³ The only VAD officially licenced for paediatric use, the Berlin Heart EXCOR^® (Berlin Heart GmbH, Berlin, Germany), is one such example (Fig. 1A).⁴ A pneumatically driven volume-displacement pump mimics the action of the ventricle and generates pulsatile flow, with power delivered by a large stationary driving unit (Fig. 1B). As these devices use an extracorporeal pump and drive system, internal components are reduced so less space is needed for implantation. This allows them to be used in children as small as 3 kg in weight.⁴ However, the bulky drive system reduces the patient's ability to move; this, combined with a continuous requirement for expert clinical input, means that children with such devices need to be managed as inpatients in a specialist VAD centre.

Fig 1.

(A) Berlin Heart VAD providing left ventricular support. The device pump sits outside of the body, connected to the left ventricle and aorta by two cannulae. (Courtesy of Berlin Heart, EXCOR® Paediatric.) (B) Berlin Heart Ikus drive unit. The drive unit provides pneumatic power to the pump. (Courtesy of Berlin Heart, EXCOR® Paediatric.)

Continuous flow

In adults PF-VADs have been almost entirely replaced by CF-VADs. These devices have an internalised rotator driven axial or centrifugal pump which, rather than replace the pumping function of the ventricle, unloads the ventricle and generates blood flow in a continuous non-pulsatile fashion.⁵ They are smaller and fully implantable within the thoracic cavity, with power supplied through an external driveline connected to a small portable controller unit. These more compact devices are suitable for children weighing more than 15 kg; the HeartWare^TM device (Fig. 2) is the most commonly implanted CF-VAD in children.³ Importantly they allow the possibility for children to be discharged from their specialist centre with the device in situ and managed at home or in a local hospital. With continued miniaturisation of CF-VADs, it is probable that they will be applicable in even smaller children, and likely that there will be an increasing number of children with CF-VADs who may present as an emergency to a non-specialist hospital.

Fig 2.

HeartWare VAD providing left ventricular support. The device pump sits inside the body attached directly to the left ventricle. A driveline cable connects the pump to an external controller. (Courtesy of Medtronic.)

LVAD-supported physiology

LVADs offload volume from the LV, reducing LV work, and deliver blood to the ascending aorta thus augmenting cardiac output, arterial BP, and perfusion. Pump speed is essentially fixed (set by specialist personnel under echocardiography guidance) and independent of environment. Cardiac output is therefore an interaction between pump function, underlying patient haemodynamics, and native cardiac function.

LVADs are preload-dependent with volume status and right ventricle (RV) function as important factors in maintaining preload to the LV, ensuring adequate filling of the device and subsequent cardiac output. RV dysfunction is not uncommon in LVAD-supported patients because of underlying cardiac disease. It is necessary to avoid increases in pulmonary vascular resistance (PVR) and consider the effects of positive pressure ventilation on venous return. Positive inotropic drugs, pulmonary vasodilators, or both may be required to maintain good RV function.⁶ Afterload also has a significant impact on LVAD function. Increases in systemic vascular resistance (SVR) directly impede forward flow, reducing peripheral perfusion and, because of increased stasis, may also increase the risk of device thrombus formation.⁶ Meticulous attention to this preload dependence and afterload sensitivity is key to managing haemodynamics in patients who have an LVAD.

Native LV function may continue to contribute to cardiac output. This can occur in the context of myocardial recovery or because of poor LVAD performance leading to inadequate offloading of the ventricle. Evidence of this may be a pulsatile invasive arterial waveform, increased flow pulsatility on the device control unit, or increased aortic valve opening observed on echocardiography.

Device variables

A microprocessing unit is integrated into the drive unit, and controls and manages the VAD system. A monitor displays system performance and permits adjustment of selected variables. Settings and functional variables differ and depend on the specific device. The device-specific user manual provides an essential reference with instructions for use, explanations of settings, and guidance of interpretation of measurements.4, 5 Devices are fitted with inbuilt alarms including warnings of high power, low flow, and suction conditions (e.g. caused by left ventricular collapse or inflow occlusion). Anaesthetists would not be expected to alter these pump settings without direct consultation with a VAD specialist.

Anticoagulation

VAD support necessitates long-term anticoagulation to reduce the risk of pump thrombosis. In the acute setting this is usually achieved using heparin, with warfarin and antiplatelet therapy (typically aspirin) started later. International normalised ratio (INR) targets are device-dependent (Berlin Heart device: target INR, 2.7–3.5; HeartWare™ device: target INR, 2.0–3.0).4, 5

Patients with a VAD may develop complex coagulopathies in the context of heart failure-induced liver dysfunction and associated shear stress from the device; an acquired form of von Willebrand syndrome may be associated with CF-VADs.⁶ Mechanical haemolysis and platelet dysfunction may be present.

Anaesthesia for non-cardiac surgery

Although heart transplantation is the most common surgery performed in VAD-supported patients, children may present for a variety of non-cardiac procedures. These may relate to complications associated with VAD therapy such as emergency neurosurgical procedures (e.g. management of intracranial haemorrhage), insertion of intravascular catheters, wound management (for device-associated infections), airway interventions (after long-term tracheal intubation), endoscopies (for gastrointestinal bleeding), and any other surgical presentations common in childhood.7, 8

All surgical procedures should ideally be performed at centres experienced in the management of VADs, and the expectation would be that these patients will be transferred urgently to their VAD centre. However, with increasing numbers of children being discharged home with CF-VADs, the initial management of some acute emergencies may be necessary in their local, non-specialist centre. Management must involve a multidisciplinary team, with early input from VAD specialists, cardiologist, and cardiac surgeons, in addition to the primary surgical and anaesthetic teams.

Preoperative considerations

Preoperative assessment

A thorough preoperative assessment is required in all patients and medical conditions optimised where possible. Preoperative assessment should focus on the device, comorbidities, and baseline status. It has been suggested that patients with VADs undergoing non-cardiac surgery can be safely looked after by general anaesthetists in conjunction with a VAD specialist.⁸ We would suggest that for major non-cardiac surgery in children, such as craniotomy for intracranial bleeding, additional support is obtained from a cardiac-specialist anaesthetist.

Patients or their carers are typically well informed about their child's device as part of a comprehensive discharge process, and they will have been advised to travel with relevant documentation and spare equipment. Device information can be obtained from the nearest VAD centre or VAD manufacturer with 24-h contacts available. Inpatient information should be readily accessible with an allocated VAD specialist nurse and comprehensive notes. Baseline values should be established and discussed with the VAD specialist to be involved in the patient care.

The patient's underlying cardiac disease and native function of the supported LV, and unsupported right ventricle should be established. A review of other organs (hepatic, renal, or pulmonary) that may be affected by baseline heart failure, and any complications secondary to VAD implantation (e.g. infections, neurological insults) should be sought. Functional status will gives an indicator of VAD function and physiological reserve.

A medication review should be performed. In addition to anticoagulation and antiplatelet therapy, patients may be on diuretics, inotropes, and pulmonary vasodilators.

Preoperative investigations

Echocardiography is an invaluable tool for LVAD assessment, confirming cannula positions and assessing device performance. The end-diastolic interventricular septal position provides a valuable indicator of performance and should be reported as neutral, leftward-, or rightward-shifted. A leftward shift can occur in conditions of reduced LV preload, increased RV pressures, or secondary to excessive device pump speeds (resulting in excessive LV suction). A rightward shift suggests elevated LV volume which may be secondary to impaired unloading caused by inadequate LVAD speeds, pump dysfunction, or increased LV afterload.⁹ The amount and duration of any aortic valve opening is also key in functional assessment, with increases in duration occurring in the context of increased LV intrinsic function, LV overload, or poor device performance.⁹ Echocardiography also provides an important functional assessment of the native RV.

A baseline ECG should be obtained. LVAD function is independent of native heart rate, but abnormal sustained rhythms such as ventricular tachyarrhythmias can precipitate RV dysfunction and compromise left heart filling.⁸

Chest radiography can be used to evaluate gross positioning of inflow and outflow cannulae and the pump.

Laboratory investigations should include a full blood count and coagulation screen to assess any coagulopathy and haemolysis. Liver and renal function tests may assist the evaluation of any organ dysfunction. A ‘group and save’ or crossmatch will be determined by the planned procedure.

Managing anticoagulation therapy

The effects of multimodal anticoagulation must be considered and may need to be reduced, stopped, or reversed in some situations.

Temporary substitution of warfarin therapy with an intravenous heparin infusion enables greater control in the perioperative period if time allows. In the acute setting, fresh frozen plasma may be indicated to normalise INR. We do not advocate the use of prothrombin concentrate because of the risk of device thrombus. Vitamin K administration is generally avoided as it hinders rewarfarinisation after the procedure, but may be necessary for major surgeries. Platelet transfusion may be needed to mitigate the effects of antiplatelet therapy in the presence or risk of significant bleeding.

Anticoagulation management strategies must be made with input from the VAD team, surgeons, and haematology, weighing the risks of device thrombosis against the risks of significant operative bleeding. A re-initiation plan should be agreed to reduce the risk of thrombosis after the procedure.

Intraoperative considerations

Monitoring

Intraoperative monitoring can be challenging in LVAD-supported patients, as there may be difficulty in attaining Association of Anaesthetists of Great Britain and Ireland (AAGBI) minimum standards of monitoring.¹⁰

Patients with PF-VADs will usually have a detectable pulse resulting from the pulsatility generated by the device. However, those with CF-VADs will generally have an absent pulse because of continuous flow mechanics, with pulsatility present if being dependent on contribution from the native LV. In patients with CF-VADs, pulse oximetry and non-invasive BP monitoring, which rely on pulsatility and oscillations, respectively, will usually be unobtainable.

ECG

As noted above, LVAD function is independent of native heart rate, but it is important to monitor for rhythm disturbances that may compromise RV function.

Oxygenation

Given the likely unreliability or absence of pulse oximetry, particularly with CF-VADs, we would advocate the use of near-infrared spectroscopy (NIRS) intraoperatively, which provides a surrogate marker of tissue oxygenation non-reliant on pulsatile flow.

Blood pressure

A manual BP cuff with Doppler can be used to measure BP in patients with CF-VADs, but this is rarely feasible in the operating room. In the presence of some pulsatility, automated non-invasive BP measurement may provide a mean arterial pressure (MAP) and be sufficient for minor procedures with limited anticipated haemodynamic disturbance. Where there is the possibility of unstable perioperative haemodynamics, invasive arterial monitoring is advocated. This will provide a reliable MAP with the added advantage of the availability of arterial blood gas sampling.8, 11 Ultrasound will be helpful in arterial line placement in the absence of a pulse.

Capnography

Monitoring of end-tidal carbon dioxide by waveform capnography provides an essential indicator of adequacy of ventilation, and as a surrogate monitor of cardiac output may facilitate early detection of impaired device function or volume status.

Central venous monitoring

Central venous access will be necessary in patients undergoing major surgery where significant fluid shifts are expected and in high-risk patients where inotropic drugs to support the RV may be required.

Transoesophageal echocardiography

Transoesophageal echocardiography (TOE) may be selectively used in high-risk patients to provide critical information on volume status, RV function, and VAD function, and allow informed perioperative adjustments to VAD setting to be made if required.6, 11

Depth of anaesthesia

Because cardiac output is maintained by the LVAD, normal haemodynamic responses to pain and awareness will be diminished. Bispectral index monitoring, although not validated in children, may be of value in assessing depth of anaesthesia.6, 8

Goals of anaesthesia

Key haemodynamic goals include: (i) optimising preload; (ii) maintaining RV function; (iii) managing SVR; and (iv) maintaining VAD function.

Optimising preload

The aim should be to maintain adequate volume status without overloading the RV. Prolonged preoperative fasting and dehydration should be avoided. Perioperative fluid losses should be closely monitored and actively replaced. Acute volume expansion may be required, but caution should be exercised to not precipitate RV failure in susceptible patients. Externalised PF-VADs have the advantage of providing a visual indicator of filling status by observing the device membrane and chamber. A wrinkled membrane during filling suggests an underfilled patient, whereas incomplete chamber emptying may indicate volume overload.

Maintaining RV function

RV function is important for LVAD filling. The negative inotropic effects of some anaesthetic drugs need to be considered, and these drugs need to be used cautiously. Increases in PVR should be avoided (i.e. avoiding hypoxia, hypercarbia, circulatory overload, lung hyperinflation, and acidosis).¹¹ Pulmonary vasodilators may be required in established right heart failure with increased PVR. Although LVAD function is independent of heart rhythm, arrhythmias can impair the unassisted RV and should be treated promptly. Inotropic augmentation of RV function may sometimes be required.

Managing SVR

As cardiac output is fixed, there is limited potential for compensatory changes in SVR. Increases in SVR and afterload impede forward flow and should be avoided. It is important to ensure an adequate depth of anaesthesia during surgical stimulation. If the patient is volume overloaded, diuretic therapy may be indicated. Precipitous decreases in SVR may also be harmful, reducing coronary perfusion. Vasopressors and fluids may be required and used judiciously to limit decreases in SVR associated with anaesthesia or sepsis.

Maintain VAD function

VAD function must be monitored during surgery by a dedicated person, ideally a VAD specialist or perfusionist if available. Any changes to baseline function should be communicated to the wider team to allow haemodynamic function to be optimised continuously. Reduced VAD flow can often be treated with a fluid challenge in the first instance. If associated with an increase in CVP, inotropic support of the RV or pulmonary vasodilators should be considered. On rare occasions, perioperative adjustments to baseline VAD settings are required.

Induction of anaesthesia

VADs provides a reliable cardiac output, which typically results in increased stability during induction of anaesthesia.6, 8 Intravenous or volatile anaesthetics are generally well tolerated, with the VAD compensating for their negative inotropic effects. Reductions in SVR, however, cannot be compensated for, and fluids or vasopressor therapy may be required. High-risk patients with poor preoperative RV function require a more cautious induction of anaesthesia, with means to support the RV as necessary.

Airway and ventilation

Airway management and ventilation should be determined by factors related to the procedure and the patient. Spontaneous ventilation may be beneficial in maintaining venous return to the heart, but intermittent positive pressure ventilation (IPPV) may provide a greater degree of control, particularly for patients at risk of pulmonary hypertension. If IPPV is used, a ventilation strategy to minimise intrathoracic pressure should be used.

Maintenance of anaesthesia

Maintenance of anaesthesia with either a volatile agent or total intravenous anaesthesia is acceptable. Anticoagulant therapy and potential coagulopathies generally preclude central neuroaxial anaesthesia.

Meticulous care must be taken when transferring the patient, to prevent any disruption to the VAD or circuitry. Once in the operating theatre, battery power should be switched to AC mains power. If an externalised VAD is present such as the Berlin Heart device, the use of clear drapes is beneficial to allow direct visual observation of device function during the procedure. The VAD computer display should be visible at all times.

Perioperative patient positioning and surgical requirements are important to consider. As in any patients, pneumoperitoneum and positional changes (such as reverse Trendelenburg) may impair venous return and increase afterload. Air insufflation or position changes should be adopted gradually to ensure VAD function is not being compromised.⁸ Extreme positions should be avoided.⁶

Emergence and tracheal extubation

Ideally, tracheal extubation should be performed as soon as appropriate criteria are met, reducing the negative effects of IPPV on pulmonary circulation and RV function. Neuromuscular blockade should be fully reversed and adequate respiratory effort verified to avoid postoperative hypoventilation and associated hypercapnia.

Other considerations

Antibiotics

At present there is no formal guidance relating to the presence of VADs and need for endocarditis prophylaxis. Antibiotic prophylaxis should therefore be directed by surgical requirements. Given the presence of an implanted device, meticulous aseptic techniques should be used when inserting and accessing invasive lines.

Electrical safety

Defibrillation pads should be applied or readily available in case of arrhythmia requiring electrical cardioversion. Bipolar diathermy is preferable to monopolar diathermy, with any grounding pad placed well away from the device to limit electromagnetic interference.⁶

Postoperative considerations

Recovery after anaesthesia

Close monitoring should continue in the immediate postoperative period, and patients may be best managed on a high dependency or intensive care unit if indicated. Recovery after anaesthesia is usually uneventful.

Analgesia

Adequate analgesia should be administered during and after surgery to prevent unwanted increases in SVR associated with pain.

Anticoagulation

Anticoagulation should be reviewed and resumed (usually with heparin bridging) as soon as the postoperative risk of bleeding is deemed acceptable.

Perioperative deterioration

Device failure/troubleshooting

Modern VADs are generally very reliable and well maintained. Device compromise, for example secondary to acute thrombosis or mechanical failure, is fortunately a rare event. Management of the compromised VAD is complex and beyond the remit of this article. In such an event a multidisciplinary approach is required with VAD specialist direction and may require involvement of cardiac surgeons. Twenty-four hour VAD support is available from manufacturers and VAD centres. Rescue TOE may provide useful guidance. Any native cardiac function should be supported whilst acute problems are addressed.

Advanced life support

The American Heart Association has released a recent scientific statement on cardiopulmonary resuscitation in patients with VADs.¹² In the event of circulatory arrest paediatric advanced life support protocols should be followed. Diagnosis of circulatory arrest, given a potentially absent pulse in the normally functioning CF-VAD patient, must include other parameters such as absence of detectable BP, absent respiratory effort, and loss of consciousness. A device check should be performed to check function and ensure that the driveline or tubing is not kinked or dislodged, and is connected to a power source. Medication administration and defibrillation should be performed as per Advanced Paediatric Life Support (APLS) protocols. The benefits of external chest compressions in patients with VADs has been much debated, with concerns about device dislodgement and myocardial trauma. Recent guidance from the ASA advocates chest compressions in children with both PF-VADs and CF-VADs when indicated.¹²

Summary

The number of children in whom a VAD can be used continues to increase as new miniaturised devices become available. Hence, VAD support is likely to play an increasingly prominent role in the management of end-stage heart failure in children. Anaesthetists may increasingly encounter children with a VAD as they present for non-cardiac procedures. Where possible patients should be transferred to a centre in looking after children with VADs. An understanding of VAD-supported physiology and key perioperative considerations, in conjunction with a robust multidisciplinary team approach, is essential for the safe perioperative care of children with a VAD.

Declaration of interest

The authors declare that they have no conflicts of interest.

MCQs

The associated MCQs (to support CME/CPD activity) will be accessible at www.bjaed.org/cme/home by subscribers to BJA Education.

Biographies

Natalie Forshaw FRCA is a consultant anaesthetist at Great Ormond Street Hospital for Children NHS Foundation Trust, who has a special interest in paediatric cardiothoracic anaesthesia.

Ian James FRCA is a consultant anaesthetist and past director of paediatric intensive care at Great Ormond Street Hospital for Children NHS Foundation Trust, with a special interest in paediatric cardiothoracic anaesthesia.

Matrix codes: 1A01, 1A03, 2A07, 2D02, 3D00, 3G00