Perioperative management of a patient with an axial-flow rotary ventricular assist device for laparoscopic ileo-colectomy.

The use of mechanical circulatory support devices as a bridge to transplant or destination therapy decreases mortality, improves quality of life, and functional status. The paucity of clinical data and the challenges faced by noncardiac anesthesiologists warrant us to present the perioperative care of a patient with a HeartMate II (Thoratec Corp. Pleasanton, CA, USA) left ventricular assist device (LVAD), who underwent a successful major laparoscopic abdominal surgery. Key issues highlighted are the limitations of oxygen saturation (SpO(2)) monitoring, accuracy of blood pressure (BP) measurement, and the potential usefulness of intraoperative transesophageal echocardiography (TEE). The hemodynamic changes, impact on the LVAD function during laparoscopic surgery, and the multidisciplinary approach are addressed.

Introduction

Heart failure is a major public health problem globally with significant morbidity and mortality despite maximal medical therapy. Ventricular assist devices (VAD) have been increasingly used in Asia, Europe, and the United States as a treatment modality for destination therapy or as a bridge to heart transplantation. The incidence of heart failure in India is estimated to be between 491,600 and 1.8 million.[1] The American Heart Association estimates that there are 4.6 million Americans with heart failure who could benefit from mechanical support.[2] There are reports of research to invent low-cost VAD device to meet the demands in India, which could be beneficial and a cost-effective replacement for heart transplants.[3] With increasing number of patients undergoing VAD implantation either as a bridge to transplant or as destination therapy, anesthesiologists will be faced with the task of providing care to these patients for various noncardiac surgical procedures. Case reports of patients with a VAD undergoing different types of noncardiac surgery have been reported.[24] However, none of these cases have reported the perioperative management for major abdominal laparoscopic surgery in a patient with a nonpulsatile rotary assist device. In addition to the interactions of impaired cardiac function and the nonpulsatile pump, the anesthesiologist is faced with the challenge of managing these hemodynamic changes secondary to the pneumoperitoneum and positioning of the patient.

A left ventricular assist device (LVAD) is placed to support the failing left ventricle. The LVAD (HeartMate II, Thoratec Corp. Pleasanton, CA, USA) is an axial flow, rotary pump connected in parallel to the native circulation. REMATCH trial showed a 52% survival at 1 year in patients with VAD compared to 25% in patients medically managed. At 2 years, there was a 23% survival in VAD group compared to 8% survival in medically treated group.[5] An increasing number of these patients may present for noncardiac surgical procedures, and it is important for anesthesiologists to be aware of management of these devices and address various intraoperative concerns including the use of intraoperative transesophageal echocardiography (TEE).

Case Report

The patient is a 56-year-old gentleman who had undergone an emergency coronary artery bypass graft (CABG) due to occluded coronary stents and severe left ventricular (LV) systolic dysfunction. An intraaortic balloon pump (IABP) was placed due to difficulties with weaning off cardiopulmonary bypass. Persistent hemodynamic deterioration with oxygenation issues resulted in the placement of an extracorporeal membrane oxygenation circuit (ECMO) and emergency transfer to our tertiary center.

After 2 weeks of intensive care at our institution and persistent LV systolic dysfunction despite ECMO support, LVAD was electively placed. In a LVAD, the inflow cannula is attached to the apex of the left atrium and the outflow cannula is attached to the ascending aorta. The postoperative period was prolonged and complicated by acute gastrointestinal (GI) bleeding and acute renal failure requiring continuous renal replacement therapy (CRRT). The patient was discharged to a rehabilitation facility with return of normal renal function, regular diet intake, and routine follow-up. However, he was followed up by the GI team for episodes of bleeding due to ischemic enterocolitis. Three months later, he was readmitted for an acute episode of GI bleeding and surgical intervention, i.e., laparoscopic ileo-colectomy was considered necessary to control bleeding and to maintain future anticoagulation requirements for LVAD. In addition, he was scheduled for debridement of a sacral pressure sore in the lateral position at the same time.

Prior to surgery, in the intensive care unit (ICU), the patient was awake, alert, and spontaneously ventilating without any vasopressor or inotropy. All routine laboratory tests including coagulation tests were within normal limits. Due to ongoing bleeding, the patient was bridged with heparin, which was stopped preoperatively. Review of TEE findings performed during and after LVAD placement revealed severe LV systolic dysfunction and mild right ventricular (RV) dysfunction. The inflow and outflow cannulae of the LVAD were noted to be in good position with low flow velocities and laminar flow on pulse wave and color Doppler interrogation. No mention was made of any other significant findings. The anesthesia team, accompanied by a certified perfusionist, transported the monitored patient to the operating theatre (OT) directly from the ICU. The LVAD was functional on a battery unit while transporting and then placed back on its permanent power source on arrival in the OT.

Standard American Society of Anesthesiologist (ASA) monitors were placed. The HeartMate II displayed a flow of 5.1 l/min at a speed of 9800 rpm and the SpO2 was 98% on room air with a good pulsatile waveform possibly due to some return of ejection through the native aortic valve. A Doppler ultrasound was used to place the radial arterial catheter due to a weak radial pulse. A preexisting peripherally inserted central access catheter (PICC) was used for induction of anesthesia with etomidate 18 mg, fentanyl 100 mcg, and vecuronium 8 mg. Anaesthesia was maintained with isoflurane, fentanyl, and vecuronium with a fractional inspired oxygen concentration of 50%. Soon after induction, the waveforms on the arterial blood pressure (ABP) and pulse oximetry (SpO2) flattened. The ECG was noted to be in normal sinus rhythm. A TEE probe was placed for evaluation of intraoperative cardiac function. Initialfindings noted weregood systolic function of RV free wall, global severe LV dysfunction, mild mitral regurgitation (MR), mild tricuspid regurgitation (TR), and a continuously closed aortic valve. The inflow and outflow cannulae of the LVAD were unobstructed with low flow velocities on Doppler interrogation. An atrial septal defect (ASD) of approximately 7 mm size with bidirectional shunting was noted immediately after the placement of TEE probe during the laparascopic colectomy. We feel this was either unappreciated earlier or possibly a new finding, which was detected during our TEE exam for the noncardiac surgery. The central venous pressure (CVP) was measured as 10 cmH2O through the PICC catheter. Sinus rhythm was maintained and arterial blood gas analysis revealed pH 7.38, pCO2 39.8 mmHg, pO2 91 mmHg, bicarbonate 24 mEq/l, and SaO2 97% (SpO2 read 82% with no waveform). ABP was noted to read 65 mmHg (MAP). After establishment of pneumoperitoneum at pressures of 15 cm of H2O, laparascopic surgical access ports were placed and the patient was positioned in steep Trendelenburg position for good surgical access. Bilateral breath sounds were auscultated after positioning of the patient. The LVAD speed was maintained at 9800 rpm and the flow measured at 6.1 l/min. The flows subsequently decreased to 4.9 l/min. The TEE now revealed a right to left atrial level shunt and bowing of the intraventricular septum into the LV cavity and there was no opening of the aortic valve. TEE findings were conveyed to the surgeons and the Trendelenburg position was neutralized with reduction in right to left shunt. Enterectomy was completed in approximately 2 h and the patient was then positioned laterally for the sacral wound debridement. The LVAD speed was unchanged and flow in the lateral position was 6.6 l/min. TEEfindingsincluded a significant increase in TR, right to left atrial shunting, and RV distension. The entire procedure took approximately 4.5 h necessitating a fluid input of 2300 ml, with total urine output measured was 350 ml. All TEE findings were noted to return to baseline function (reduced right to left shunt at the atrial level) in supine position before recovery from anesthesia. The neuromuscular blockade was reversed and trachea extubated after the patient awakened in the OT. Patient was transported back with monitoring on a battery power source with a LVAD flow of 6.5 l/min at a speed 9800 rpm. The patient remained hemodynamically stable during the postoperative period with no major clinical issues. The patient recovered well after this surgery and came back for heart transplant a few months later and currently is doing well.

Discussion

LVAD have formed an integral part of end-stage heart failure management as well as acute pump failure/postcardiotomy shock. The medical management of heart failure includes diuresis, afterload reduction, and ionotropic support. Cardiac resynchronization therapy (CRT) has been found to be useful after failed medical management therapy. CRT improves the dysynchrony between the ventricles.[6] When less invasive therapies fail, there are various assist devices currently available to support either left, right or both ventricles.

The LVAD device may be one of either volume–displacement (pulsatile), axial-flow, or centrifugal pump. The HeartMate II [Figures 1 and 2] is an axial flow rotary pump, which draws blood from the LV apex and returns it to the ascending aorta and produces a nonpulsatile flow. A rotor assembly inside the pump contains a magnet and is rotated by the electromotive force to propel the blood from the LV to the ascending aorta. The primary operating mode is fixed speed control. In a fixed speed mode, the device operates at a constant speed, which may be varied manually by qualified personnel. The system can be powered utilizing portable batteries or with an isolated power base unit (PBU). There is a rechargeable battery inside the PBU, which can provide 30 min of backup power to the LVAD in case of AC power failure. The display on the screen shows pump flow, pump speed, pulse index, and pump power [Figure 3]. The amount of power provided to the motor is between 0 and 25.5 watts. The pulsatility index (PI) is measurement of the flow pulse through the pump. This is affected by native LV function and pump speed. The HeartMate II displays a flow based upon pump power consumption and pump rotational speed. The HeartMate II LVAD is comprised of the HeartMate II LVAD, system controller, power base unit, system monitor, and rechargeable batteries.

Figure 1

Schematic diagram of HeartMate II displaying the pump controller system. (Reproduced with permission from Thoratec Corporation, Pleasanton, CA, USA)

Figure 2

Split view of HeartMate II pump along with inflow and outflow cannulae. (Reproduced with permission from Thoratec Corporation, Pleasanton, CA, USA)

Figure 3

HeartMate II display screen

The pumping mechanism of LVAD depends on both preload and afterload.[78] Pulsatile LVADs pump the delivered volume and therefore inadequate filling may lead to inadequate flow.[4] In nonpulsatile devices, flow is a function of the pressure difference between the inlet and outlet of the pump and pump speed. Maintaining preload and systemic vascular resistance (SVR) is very important to maintain flow. The HeartMate II is preload dependant and afterload sensitive.[2]

Patients with HeartMate II LVAD have the device placed inside the chest cavity unlike pulsatile LVADs, which were placed in the preperitoneal part of the abdominal cavity.

The need for rapid sequence induction in patient with HeartMate II is not mandatory unless there is a high risk for aspiration. We have not come across complications related to aspiration of gastric contents in patients with LVAD. Aspiration precautions should be taken as one does with any patient coming for anesthesia and surgery.

TEE is useful in assessing the hemodynamic changes to laparoscopy and patient positioning. In general, measurement of blood pressure should include either arterial cannulation or auscultation. If significant hemodynamic changes are anticipated ABP monitoring is recommended. ABP monitoring is not always needed as the pump flow displayed in LVAD should help guide monitoring fluid management. If there is a fall in displayed flow rate from baseline, fluid bolus or challenge is the first line of management. RV overload should be avoided and iontropes should be used if there is no response to fluid challenge. The LVAD supports only the LV and RV dysfunction can lead to reduced flow to the pump. Pulmonary artery catheterization can be useful in patients with nonpulsatile circulation especially if there is concern of pulmonary hypertension. Central venous pressure (CVP) is useful for monitoring fluid balance in surgery involving major fluid shifts. Maintaining sinus rhythm is important in patient with univentricular assist device as arrhythmia can impair function of the unsupported ventricle. LVAD function is dependent on preload and this makes patient positioning a significant determinant for LVAD output.[9] Placement of an arterial cannula is difficult due to nonpulsatile circulation and a Doppler probe is useful. Although we did not use it in this case, cerebral oximetry is worth considering as a useful non-invasive monitoring tool in patients with nonpulsatile circulation. We recommend recording baseline saturations prior to induction of anesthesia and aim to maintain the same. If there is a significant change, we recommend increasing the inspired oxygen concentration and if there is an associated drop in flow rate, we follow the same approach as mentioned above. Clinical assessment of hemodynamics under anesthesia is challenging due to the limitations of accurate BP monitoring capabilities. The challenging part of our case was managing hemodynamic changes due to alterations in patient positioning and initiation of pneumoperitoneum. In response to initiation of pneumoperitoneum during laparoscopy, an increase in SVR, mean arterial pressure (MAP) and cardiac filling pressures can be seen.[10] These hemodynamic changes are exacerbated in patients with severe preexisting cardiac disease.[11] With the initiation of pneumoperitoneum and Trendelenburg position the shunt direction in our patient at the atrial level changed from predominantly left to right (noted at baseline) to right to left. The RV increased in size and the intraventricular septum bowed into the LV cavity with increased TR. Simultaneously, the LVAD flows increased briefly from 5.1 l/min to 6.1 l/min without any alterations in the LVAD speed settings. This may have been due to the transient increase in the preload to the RV due to steep head down position and subsequently followed by the increase in intrathoracic pressures with positioning and pneumoperitoneum, which lead to decreased the venous return and eventually the LVAD flows[9] and MAP. The intracardiac shunt would have been undiagnosed without the aid of TEE monitoring in light of unreliable SpO2 monitoring. Understanding and communicating these findings to the surgical team resulted in neutralizing the patient position and eventually improvement of TEE findings (reversal of the right to left atrial shunt, decrease in RV size and improvement in LV cavity size) and MAP. Without the aid of real-time TEE monitoring, a clinical diagnosis of the right to left intracardiac shunt would not have been possible. Although one could have clinically guessed, it would have been very difficult to substantiate the possible diagnosis.

In view of the potential hemodynamic changes, we electively opted to place an intraoperative TEE probe and an arterial cannula for BP monitoring. The initial presence of a pulsatile waveform on the pulse oximetry was due to ventricular ejection. The loss of waveform pulsatility in the arterial pressure and the pulse oximetry may have been due to myocardial depression or reduced preload which would reduce LV ejection and arterial pulsatility. Reverse Trendelenburg, lateral decubitus positioning, fluid loss, and drug-induced venodilatation have been associated with decrease flow through the LVAD.[8912]

The HeartMate II LVAD is associated with an extremely low thromboembolic risk and can be managed with less stringent requirements for anticoagulation.[13] After device implantation the recommendation is to maintain a combination of aspirin, dipyridamole, and/warfarin. Warfarin should be stopped and the patient bridged with heparin perioperatively. In addition to the effects of anticoagulation, there can be a qualitative and quantitative abnormality of von Willebrand factor (VWF). This acquired von Willebrand (AVWD) disease secondary to the LVAD has been shown to cause nonsurgical bleeding.[14] The risk of bleeding is greater than risk of thromboembolism in patients with HeartMate II and less stringent anticoagulation regime is acceptable.[15]

Hemodynamic compromise in patients with HeartMate II devices coming for noncardiac surgery can be accurately diagnosed with TEE and appropriate interventions can be instituted quickly. TEE with appropriate interpretation facilitates safe perioperative management of these patients. Furthermore, a team approach with good communication involving the anesthesia, surgery, and perfusion teams is paramount to the successful management of these critically ill patients