Anesthetic Management of a Patient Undergoing Minimally Invasive Myocardial Revascularization Before Lung Transplantation

Cardiac surgery results in marked reductions in lung volumes and impairment of pulmonary mechanics, which may result in significant morbidity and even mortality in patients with limited pulmonary reserve [1]. Minimally invasive direct coronary artery bypass (MIDCAB) is being increasingly used to decrease morbidity and to lower the cost of cardiac surgery [2,3]. We present the first case report in the literature of a patient with end-stage lung disease who underwent a single-vessel MIDCAB graft in preparation for lung transplantation. The procedure was performed using video-assisted thoracoscopic surgery (VATS) and a limited anterior thoracotomy without cardiopulmonary bypass (CPB). Case Report The patient was a 59-yr-old man with significant two-vessel coronary artery disease (CAD) that was detected during evaluation for lung transplantation due to end-stage chronic obstructive pulmonary disease (COPD). Medical history included heavy smoking, pulmonary emphysema, and chronic essential hypertension. The chest radiograph showed severe bilateral hyperinflation and mild interstitial fibrosis. The electrocardiogram showed occasional premature supraventricular complexes. Pulmonary function studies revealed a severe obstructive pattern (Table 1). Baseline arterial blood gas analysis (ABG) results are shown in Table 2. An exercise study revealed a marked decrease in oxygen saturation to 85% at minimal work load. Coronary angiography showed 99% stenosis of the mid-left anterior descending artery (LAD), 90% stenosis of the first septal perforator, and 100% occlusion of the circumflex artery. Echocardiography revealed normal biventricular function and right ventricular hypertrophy. A radionuclide scan showed a left ventricular ejection fraction of 82% and a right ventricular ejection fraction of 54% (normal). The surgical plan was to perform single-vessel bypass grafting using the left internal mammary artery (LIMA) to the LAD artery via thoracoscopy and a small anterior thoracotomy without the use of CPB.Table 1: Pulmonary Function TestsTable 2: Arterial Blood Gas Values at Various Periods of SurgeryIn addition to standard monitors, a 20-gauge catheter was placed in the left radial artery and an oximetric pulmonary artery catheter was placed via the right internal jugular vein. The femoral arteries were preserved for possible femoral bypass and/or an intraaortic balloon pump if necessary. Baseline hemodynamic data obtained before the induction of anesthesia were: pulmonary artery pressure (PAP) 37/24 mm Hg, central venous pressure (CVP) 12 mm Hg, mixed venous oxygen saturation (SvO2) 79%, and cardiac output (CO) 6.0 L/min. General anesthesia was induced with fentanyl 30 [micro sign]g/kg, midazolam 5 mg, and isoflurane. Muscle relaxation was provided with vecuronium 0.1 mg/kg, ventilation was controlled using 100% oxygen, and the trachea was intubated with a 39-F left double-lumen tube (DLT), which was positioned using fiberoptic bronchoscopy. A multiplane transesophageal echocardiography probe, a urinary bladder catheter, and rectal and nasal temperature sensors were placed. Results of ABG analysis while ventilating both lungs with 100% oxygen are shown in Table 2. Transesophageal echocardiography examination showed right atrial dilation, right ventricular hypertrophy with a slightly dilated cavity, mild right ventricular dysfunction, and mild left ventricular hypertrophy with normal systolic function. The patient was then positioned in the right lateral decubitus position. One-lung ventilation (OLV) to the right lung was started at a rate of 12 breaths/min, tidal volume 8 mL/kg, with a resulting peak airway pressure of 44 cm H2 O. Arterial hypoxemia to a PaO2 of 55 mm Hg was treated with continuous positive airway pressure of 5 cm H2 O applied to the nondependent (left) lung (Table 2). The LIMA was harvested using VATS. A left anterior minithoracotomy incision was then made in the 6th intercostal space with resection of the 5th rib and division of pectoralis major and serratus anterior muscles. After starting an esmolol infusion of 300 [micro sign]g [center dot] kg-1 [center dot] min-1 to achieve a heart rate of 50-60 bpm, the CO decreased to 3.8 L/min, CVP increased to 20 mm Hg, PAP increased to 50/30 mm Hg, and SvO2 decreased to 52%. Two units of packed red blood cells were transfused to replace blood loss (600 mL). Although the hematocrit at that time was 30%, our goal was to maintain optimal oxygen carrying capacity during that period of decreased cardiac performance and tissue perfusion. Nitroglycerin 0.5-1.5 [micro sign]g [center dot] kg-1 [center dot] min-1 was used to lower the increased PAP and to protect against the impending period of myocardial ischemia. The LAD was then occluded and incised. Neither ST segment changes nor regional wall motion abnormalities (RWMA) were observed at that time. After the uneventful completion of the LIMA to LAD anastomosis, the esmolol infusion was discontinued, and the chest was closed. Hemodynamic status improved to CO 4.8 L/min, heart rate 80 bpm, CVP 10 mm Hg, PAP 33/12 mm Hg, and SvO2 76%. The DLT was changed to a single-lumen endotracheal tube without difficulty. The ABG analysis in the intensive care unit during mechanical ventilation with a tidal volume of 10 mL/kg, respiratory rate of 8 breaths/min, fraction inspired oxygen of 0.9, and positive end-expiratory pressure of 3 cm H2 O are shown in Table 2; the hematocrit was 35%. The patient was weaned from mechanical ventilation and the trachea was extubated 16 h after arrival in the cardiac intensive care unit. He was transferred to the postcardiac surgical unit on the first postoperative day (POD 1). The remainder of his hospital course was uneventful, and he was discharged home on POD 6 to await the availability of a donor lung. Discussion Changes in pulmonary mechanics and gas exchange are well recognized sequelae of thoracotomy and cardiac surgery that can result in significant postoperative pulmonary morbidity and mortality. An acute restrictive lung defect develops as a result of multiple factors, including lung trauma, atelectasis, pleural effusion, phrenic nerve dysfunction, decreased lung and chest wall compliance, respiratory muscle weakness, uncoordinated ribcage expansion, and postoperative pain [1]. The structural alterations of the chest wall that result from median sternotomy and excessive rib retraction are responsible for the persistence of the restrictive pulmonary impairment for several weeks postoperatively [4]. In addition, CPB could induce a spectrum of lung injury ranging from a relatively insignificant increase in extravascular lung water to a life-threatening postperfusion syndrome that is similar to the adult respiratory distress syndrome. Fortunately, recent advances in surgical and extracorporeal perfusion techniques have decreased the incidence of this syndrome to 1%-2% [5]. The forced expiratory volume in one second, forced vital capacity, and functional residual capacity are decreased by 30%-50% immediately after standard surgical coronary artery bypass grafting (CABG) and remain below baseline for six weeks [6]. Shapira et al. [7] demonstrated a 65% reduction of the peak expiratory flow rate immediately after extubation and a 35% reduction at the time of hospital discharge in patients who underwent median sternotomy. Rea et al. [8] demonstrated an immediate increase in the alveolar to arterial oxygen gradient that persisted for several weeks after cardiac surgery. The decrease in total pulmonary compliance results in an increase in the work of breathing and oxygen consumption by at least 20% in spontaneously breathing cardiac surgical patients [9]. Several clinical studies have indicated that harvesting of the LIMA has a deleterious effect on postoperative pulmonary function. A more pronounced restrictive ventilatory defect and greater reductions in PaO2, functional residual capacity, expiratory reserve volume, and peak expiratory flow rate were reported after LIMA compared with saphenous vein grafting [10]. Higgins et al.1 reported that the presence of COPD might be an important risk factor for the development of postoperative pulmonary complications, which is in agreement with earlier findings by Ratliff et al. [11] that pathologic changes in the lung after CPB were more severe in patients with abnormal preoperative lung function. Air trapping and intrinsic positive end-expiratory pressure increase after chest closure in patients with COPD [12]. The type of thoracic incision also seems to influence the degree of postoperative pulmonary impairment. Posterolateral thoracotomy, which is the standard approach for most pulmonary resections, is associated with more significant postoperative pain and reduction in pulmonary function than median sternotomy, which is the standard approach for cardiac surgery [13]. Changes in pulmonary function after minimally invasive myocardial revascularization have not been studied. Because our patient was considered to be at high risk of developing postoperative pulmonary complications, one of our main goals was to choose the surgical approach that would result in the smallest degree of reduction in lung function. (1) Higgins TL, Yared JP, Paranandi L, et al. Risk factors for respiratory complications after cardiac surgery [abstract]. Anesthesiology 1991;75:A258. Minimally invasive techniques for myocardial revascularization are being increasingly used in an effort to decrease the cost and morbidity of CABG [2,3]. The procedure may be performed via a ministernotomy or a minithoracotomy, with or without CPB, and with or without thoracoscopic assistance. MIDCAB refers to the performance of the procedure on the beating heart without the use of CPB. Fanning et al. [14] reported the performance of CABG without CPB in patients requiring reoperative myocardial revascularization with good results (3.4% mortality and 1.8% myocardial infarction rates). Graft occlusion rates were comparable to those after revascularization using standard CPB techniques. Robinson et al. [15] described the use of VATS for the dissection of the LIMA pedicle in patients undergoing minimally invasive myocardial revascularization. The grafting of the LIMA to the proximal LAD or right coronary artery was completed via a two- to three-inch left anterior parasternal incision using CPB and hypothermic ventricular fibrillation without aortic cross-clamping. VATS permits the complete dissection of the LIMA up to the subclavian region, allowing for anastomosis without tension or distortion. In addition, complete hemostasis can be better achieved by the direct inspection of the LIMA bed on the posterior surface of the sternum [16]. To the best of our knowledge, this is the first case report describing the concomitant use of VATS (to dissect the LIMA) and MIDCAB (without CPB) in a patient with end-stage pulmonary disease. Major advantages of not using CPB include the avoidance of bypass-related coagulopathy, as well as central nervous system, renal, and pulmonary dysfunction [17]. Our patient was undergoing a single-vessel primary revascularization, and our primary goal was to avoid CPB-induced pulmonary dysfunction. Two articles discussed some of the anesthetic considerations in patients undergoing minimally invasive myocardial revascularization [18,19]. OLV is required during VATS and minithoracotomy to facilitate exposure. Lung separation can be achieved using a DLT or a bronchial blocker. In our patient, hypoxemia during OLV was easily treated with continuous positive airway pressure. The moderate increase in PaCO2 to 60 mm Hg was not aggressively treated to avoid barotrauma (permissive hypercapnia). The increase in PAP, presumably resulting from respiratory acidosis, was treated with a nitroglycerin infusion. The infusion of esmolol was shown to delay the onset of RWMA during coronary occlusion in patients undergoing balloon angioplasty [20], and intraoperative ischemia in patients undergoing CABG [21]. We used an esmolol infusion to decrease the heart rate to 50-60 bpm to protect against myocardial ischemia and also to facilitate the technical completion of the distal coronary anastomosis. In patients with COPD, the use of beta-blockers could potentially induce bronchospasm and increase air trapping. Esmolol has relative beta1-adrenergic selectivity, and despite the relatively high infusion rates used in our patient, we did not encounter any bronchospasm or decrease in systemic arterial oxygenation related to its use. The administration of adenosine to produce transient asystole has been described, but its use has also been associated with bronchospasm [22]. The recent development of special surgical instruments that provide mechanical epicardial stabilization of the target coronary artery could obviate the need for pharmacologic slowing of the heart [23]. We did not use ischemic preconditioning, which consists of several five-minute periods of coronary occlusion separated by a few minutes of reperfusion [19]. The clamping of the LAD in our patient did not result in any new RWMA, further increase in PAP, or in new electrocardiographic changes consistent with myocardial ischemia. Reperfusion arrhythmias are common, and some advocate the prophylactic use of lidocaine 1 mg/kg before removal of the mammary clip [18]. CPB standby was available at all times during the surgical procedure and would have been immediately instituted if OLV was not tolerated or if severe hemodynamic instability resulted from cardiac manipulation, myocardial ischemia, or esmolol-induced myocardial dysfunction. Postoperative analgesia is an important component of managing the patient with a thoracic incision. Intercostal nerve blocks supplemented with opioids and ketorolac have been used successfully in patients undergoing minimally invasive CABG [18,19]. A thoracic epidural catheter can provide excellent analgesia and improvement in postoperative pulmonary function in patients undergoing thoracotomies. However, because of the potential for needing to use CPB with full heparinization (especially during our early experience with MIDCAB), we did not insert an epidural catheter before the induction of anesthesia. The patient had adequate pain control with parenteral opioids. He was easily weaned from mechanical ventilation and the trachea was extubated on POD 1. Early extubation (within four hours) and short hospital stays (less than three days) are possible in most patients undergoing MIDCAB [18,19]. However, because of the severity of his lung disease, we did not consider our patient to be a good candidate for fast-tracking or early extubation. In summary, we described the first case report of a patient with end-stage lung disease who underwent MIDCAB performed using thoracoscopic assistance in preparation for lung transplantation. Prospective studies are needed to compare the outcome of patients with poor pulmonary function after median sternotomy and CABG using CPB, with that of similar patients undergoing minimally invasive myocardial revascularization with or without CPB.