Intraoperative management of VAD (ventricular assist device)
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Used in setting of heart failure, either as a bridge to transplant or as a destination therapy. Usually two types of continuous flow pumps: centrifugal and axial-flow. Centrifugal pumps more sensitive to preload and afterload. Patients frequently anticoagulated. More likely to encounter HeartMate 3 (centrifugal) or HeartWare HVAD.
Overview
Indications
Surgical procedure
Preoperative management
Clarify type of LVAD. Note baseline LVAD settings. Address anticoagulation, risks of bleeding versus thromboembolic complications. Assess RV function. Check for compatibility of LVAD with defibrillation/cautery. Physical exam focused on sequelae of heart failure. Baseline ECG, Echo, and labs. If applicable, manage pacemaker/AICD.
Intraoperative management
Recommend having staff familiar with LVAD (trained anesthesiologist, VAD nurse, cardiothoracic surgery team, cardiologist)
Switch patient to AC power to save battery. Bipolar cautery preferred. Consider placing external defibrillation pads. Maintain NSR.
For patients with pulmonary hypertension or mod-severe RV dysfunction undergoing higher risk surgeries with blood loss and fluid shifts, consider CVC or PAC. May want to have TEE available for unstable patients.
Monitor LVAD parameters with patient controller or device monitor; usually speed, power, flow, and pulsatility index (PI); speed and power are directly measured, while flow and PI are derived. PI ranges between 1-10, usually 3-6.
PI = 10 x (Qmax – Qmin)/Qaverage
Low PIs (with stable RPM, or hypotension (MAP < 60)):
High flows (power): decreased afterload (vasodilation):
- sepsis
- vasodilating agent (eg anesthetic agent)
Low flows (power): low LV preload; hypovolemic, cardiogenic, mechanical obstructive:
- pulmonary hypertension, arrythmia
- low CVP (hypovolemia, bleeding, reverse Trendelenburg)
- high CVP (consider PAC or echo for further workup): RV dysfunction; tamponade, pulmonary embolus, tension pneumothorax, auto-PEEP, abdominal compartment syndrome
High PIs:
low flow/power (increased afterload, decreased speed)
high flow/power (increased myocardial contractility from recovery, inotropes or exercise, or greater LV filling resulting in greater Frank-Starling increase of contractility)
Pulse oximetry may be unreliable in setting of decreased pulsatility. Can consider using cerebral oximetry (which doesn’t require a pulse). May need to obtain blood gas.
NIBP cuff successful 53% of time, with 41% of time only showing mean value. Doppler ultrasound may be a reliable method; study with HM II showing 94% success rate.
Intra-operative malignant arrhythmias occurring in 1.2% of patients. 0.1% reported intraoperative device failure.
With regards to cardiac arrest: while chest compressions may dislodge LVAD, overall compressions may be more beneficial.
Postoperative management
Standard PACU unless patient with ICU needs. Avoid hypoventilation and optimize oxygenation (prevent changes in PVR). Address anticoagulation when appropriate. Make sure that LVAD has appropriate power supply. Careful treatment of pain to prevent hypertension, but also need to avoid oversedation leading to hypercarbia or hypoxia.
Pathophysiology
Determinants of flow:
Pressure gradient across pump: inversely proportional to pump flow (amount of cardiac output support); gradient defined as difference between outlet and inlet pressures, which correlate with left ventricular and aortic pressures.
Afterload sensitivity: High MAP increases pressure gradient, thus decreasing flow. Hypotension may increase pump flows but can cause injury to organs if too low. Recommend keeping MAP between 70-90.
Preload dependence: increased LV preload increases LVEDP which decreased the pressure gradient and thus increases flow. Centrifugal LVADs are limited by the available volume in the LV. Adequate RV function is necessary, as well as maintaining normal pulmonary vascular resistance. A suction event (collapse of LV walls toward inflow conduit) can occur when the LVAD flow exceeds available preload; such an event may precipitate ventricular arrythmias.
Speed: RPMs (speed of pump) is proportional to flow. Upper limit of RPM may be limited by underlying LV function (as in most cases the desire is to maintain pulsatility, i.e. ejection out of aortic valve). Diminished pulsatility implicated in long-term sequelae such as arteriovenous malformations (some leading to GI bleeds), aortic valve thrombosis, aortic insufficiency.
Heartmate II patients with development of acquired type 2A von Willebrand disease (likely from shearing forces in LVAD).
Epidemiology
2021 study found that the inpatient utilization of LVADs was 0.93% (1690 out of 184,115) in CHF patients.
References
Roberts, S.M., Hovord, D.G., Kodavatiganti, R. et al. Ventricular assist devices and non-cardiac surgery. BMC Anesthesiol 15, 185 (2015). https://doi.org/10.1186/s12871-015-0157-y
Nicolosi AC, Pagel PS. Perioperative considerations in the patient with a left ventricular assist device. Anesthesiology. 2003 Feb;98(2):565-70. doi: 10.1097/00000542-200302000-00038. PMID: 12552217.
Chung M. Perioperative Management of the Patient With a Left Ventricular Assist Device for Noncardiac Surgery. Anesth Analg. 2018 Jun;126(6):1839-1850. doi: 10.1213/ANE.0000000000002669. PMID: 29200070.
Modi K, Pannu AK, Modi RJ, Shah SD, Bhandari R, Pereira KN, Kubra KT, Raval MR, Ajibawo T. Utilization of Left Ventricular Assist Device for Congestive Heart Failure: Inputs on Demographic and Hospital Characterization From Nationwide Inpatient Sample. Cureus. 2021 Jul 1;13(7):e16094. doi: 10.7759/cureus.16094. PMID: 34367750; PMCID: PMC8330485.
Manning, Michael. Anesthesia for noncardiac surgery in adults with a durable ventricular assist device. In: UpToDate, Post, TW (Ed), UpToDate, Waltham, MA, 2023.