Anesthetic Considerations for Cardiopulmonary Bypass and Deep Hypothermic Circulatory Arrest During Pulmonary Thromboendarterectomy in a Patient with Severe Chronic Thromboembolic Pulmonary Hypertension

Abstract

Introduction: Anesthesia for pulmonary endarterectomy (PEA) has always proven to be challenging. With PEA being the treatment of choice for chronic thromboembolic pulmonary hypertension (CTEPH) and a rising number of such surgeries performed, it is imperative that anesthesiologists are well equipped to manage patients for surgeries and their potential complications. Case Description: A 40-year-old female with group 4 pulmonary hypertension secondary to CTEPH presented for pulmonary thromboendarterectomy. She has a past medical history of multiple pulmonary embolisms (PEs) and was diagnosed with CTEPH in November of 2021, insulin-dependent diabetes mellitus, (Hemoglobin A1C 10.6), morbid obesity (Body mass index of 48.6) hypertension, gastroesophageal reflux disease, and uncontrolled obstructive sleep apnea. Computed tomography (CT) angiogram of the thorax showed a large amount of clot burden including the right distal main pulmonary artery and in all right lower lobe pulmonary arteries, chronic clots in the left lower lobe, and a dilated main pulmonary artery (figure 1). She had previously completed six months of warfarin with therapeutic international normalized ratios (INRs). Transthoracic echocardiography showed evidence of a severely dilated right ventricular (RV), and RV strain with contrast reflux into the Inferior vena cava and hepatic vein. Further workup for the surgery included Left and right heart catheterizations and Lower extremity venous and arterial doppler which yielded no coronary artery disease, elevated pulmonary artery (PA) pressures, normal perfusion, and no deep venous thrombosis respectfully. Pulmonary Angiogram (figure 2) showed evidence of patent vasculature but sequelae of CTEPH, and a nuclear medicine lung single-photon emission computerized tomography (SPECT) (figure 3) visualized areas of perfusion defects. Her pulmonary functions test (PFT) values were as follows: Forced vital capacity (FVC) 49% predicted, forced expiratory volume in the 1st second (FEV1) 46% predicted, and diffusing capacity for carbon monoxide (DLCO) 72% predicted. Intraoperatively, a left radial arterial line and left subclavian central line were performed awake. Once lines and appropriate monitors were placed, induction anesthesia and subsequent endotracheal intubation were performed. Post-induction, a pulmonary artery catheter was placed in the patient’s right internal jugular vein which yielded a PA pressure of 127/44 mmHg (figure 4). Intraoperative transesophageal echocardiography was performed during preintervention, and the results are as follows in figure 5. The patient tolerated the intraoperative course as well as multiple sessions of cardiopulmonary bypass (CBP) and deep hypothermic circulatory arrest (DHCA) as outlined in figure 6; the total bypass time being 5 hours and 4 minutes. postintervention TEE showed vast improvement in cardiovascular hemodynamics with a near normal right ventricular ejection fraction (figure 5). The patient remained intubated and was transferred safely to the surgical intensive care unit. Her postoperative course was uneventful. Discussion: The success of PEA surgery is largely contingent on a multidisciplinary team-based approach. The patient population generally has a degree of RV failure, and the goal of surgery is to ameliorate RV compromise as much as possible. CBP and DHCA have specific requirements regarding cooling and cerebral protection/oxygen monitoring. Post bypass, anesthesiologists also have to be prepared to deal with potential complications such as residual pulmonary hypertension, RV failure, reperfusion pulmonary edema, and pulmonary hemorrhage [1]. Special consideration is paid to patients with high baseline central venous pressure (CVP) or right atrial (RA) pressures for more aggressive diuresis preoperatively to lower the RA pressures in the hope of lowering the risk of subdural hemorrhages (SDH), and avoidance of all sedatives due to their potential for respiratory depression with subsequent hypercarbia and acidosis leading to increased pulmonary vascular resistance (PVR) [1]. A 7 Fr swan sheath should be placed in the right internal jugular vein if possible.; head-down position during the insertion of all lines should be avoided if possible [2]. A transesophageal echocardiography (TEE) probe should be inserted postinduction and a PA catheter can then be placed under TEE guidance, The pulmonary artery (PA) catheter is docked but not floated [1]. Continuous cardiac output (CO) monitoring should be executed. The PA catheter can be wedged at baseline to obtain the PA wedge pressure (PAWP) [1]. In addition, bispectral index (BIS) and near infra-red spectroscopy are utilized for cerebral monitoring and cerebral oximetry during periods of DHCA [4]. Esophageal and bladder temperature probes are inserted to ensure even cooling and warming [5]. Controlled ventilation is maintained with care to avoid hypoxia, hypercarbia, and acidosis which will further increase PVR [1]. Dopamine is started at 5 mcg/kg/min, titrated, and continued for the duration of the surgery till transfer to the Intensive Care Unit (ICU). Maintenance of adequate systemic vascular resistance (SVR) is important as it determines the RV perfusion pressures. Boluses of phenylephrine can be administered for rapid titration of SVR [3]. CO measurements are taken before the initiation of CBP. These measurements are repeated after patients are weaned off CBP. Heparin of 4 IU/kg is given to the patient to achieve an activated clotting time (ACT) of >400 s. The bypass pump is primed as per normal to other procedures with the only change being that the priming solution is replaced by albumin 5% instead of crystalloids or gelafundin [1]. Propofol is infused for maintenance of anesthesia at the start of CBP, titrated as per BIS monitoring [1]. Patients with CTEPH and chronic hypoxemia are usually polycythemic. At the initiation of CBP, one to two autologous units of blood is obtained depending on the starting hemoglobin (Hb) concentration and size of the patient, targeting a Hemoglobin of 7–9 g/dL during bypass. The hemodilution of blood with autologous donation leads to decreased blood viscosity which aids with tissue oxygen delivery and promotes uniform cooling in preparation for DHCA [4]. Carbon dioxide is also given at low flow during bypass to promote cerebral vasodilatation and increase cerebral oxygenation before DHCA [5]. Patients are cooled gradually to a core temperature of 20°C or 18° C before circulatory arrest is initiated. DHCA is continued for a maximum of 20 min if cooled to 20°C, 25 min if cooled to 18°C, or when cerebral oximetry drops below 40%. Bypass is then resumed for 10 min before another round of DCHA is performed as required [4]. Rewarming is achieved gradually to ensure uniformity. Esophageal temperatures should not exceed 37°C and the gradient between esophageal and bladder temperatures should not exceed 5° at any point. Atrial-ventricular pacing is usually commenced at a rate of 80–90 beats/min if required to maintain CO. The aim is to wean off bypass with the patient relatively underfilled: CVP half of pre-bypass values [5]. Additional inotropic support may be started if required. The post-bypass CO measurements are recorded again. Should the MAP be borderline when coming off bypass, CO should be guided by cerebral oximetry as a surrogate marker instead of MAP, aiming for levels obtained when on full flow on bypass [3]. Once the patient is hemodynamically stable, protamine is administered to achieve pre-bypass values. A target Hb of 10 g/dL is desired, and respiratory rate is adjusted to achieve normocapnia [2]. Patients are transferred to the intensive care unit (ICU) with the ICU ventilator. Care is taken to avoid disconnecting the endotracheal tube from the ventilator to maintain PEEP as these patients are prone to reperfusion lung injury. Dopamine infusion is typically continued overnight to maintain CO and perfusion pressures at appropriate levels [3]. Pacing is continued from OR if needed. Patients are kept intubated overnight for lung protection with the aim of extubating after 24 hours. Fluids are kept at a minimum to maintain “dry lungs”, with the aim of a negative 1–1.5 L fluid balance by the first postoperative day [1]. References:

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