Cardiopulmonary Bypass in a Patient with Moyamoya Disease

Abstract

Moyamoya disease (MMD) is a progressive cerebrovascular occlusive disease of the internal carotid arteries and anterior and middle cerebral arteries that affects children and young adults. Affected patients are pathophysiologically analogous to patients with bilateral internal carotid artery stenosis who are at very high risk of neurologic complications during cardiac surgery. Patients with MMD have not previously been reported to undergo cardiac surgery and cardiopulmonary bypass (CPB). We report a case of a patient with MMD and an atrial septal defect (ASD) who underwent general anesthesia for attempted device closure of an ASD followed by uneventful surgical closure with CPB. Case Report A 9-yr-old girl with MMD, a large secundun ASD, symptomatic with dyspnea on exertion, and asthma was referred to our institution. The ASD, which was large and without surrounding anchoring septum, was unsuitable for device closure, and surgical closure was proposed. MMD was diagnosed angiographically when, at age 4 yr, she became symptomatic with seizures, vascular headaches, nausea and vomiting, and transient ischemic attacks. Her symptoms were controlled with verapamil and carbamazepine. She now has migraines but has been free of seizures and transient ischemic attacks for 3 yr. Preoperative electroencephalogram (EEG) failed to show buildup or rebuildup with 4 min of hyperventilation. Recent magnetic resonance imaging angiography demonstrated supraclinoid bilateral internal carotid artery total occlusion without areas of cerebral infarction, and the basilar artery was patent. Her medications included beclomethasone, albuterol, and cromolyn for asthma and methylphenidate for attention deficit disorder. We performed an uneventful 3-h general anesthetic for attempted device closure with thiopental, lidocaine, halothane, and vecuronium, with continuous EEG and invasive blood pressure monitoring 10 weeks prior to surgical closure. After discussion with her neurologist and other experts in MMD, the decision was made to proceed with surgical closure of the ASD without prophylactic cerebral revascularization in light of her minimum neurologic symptoms at the time. Prophylactic nimodipine was begun 15 h prior to surgery (30 mg per os every 4 h) with close monitoring of arterial blood pressure for possible hypotensive response. The anxious child was premedicated with diphenhydramine, cimetidine, and midazolam. Prednisone was used for asthma prophylaxis. Intravenous (IV) induction of anesthesia with etomidate, vecuronium, and fentanyl was performed. Anesthesia was maintained with sevoflurane up to 1.5%, nitrous oxide up to 50% [discontinued upon sternotomy and for cerebral blood flow (CBF) measurements], IV fentanyl, and preservative-free morphine 1.7 mg via caudal epidural injection. Continuous monitoring included electrocardiogram, systemic arterial pressure, capnography, pulse oximetry, central venous pressure, and jugular bulb oximetry (SJVO2) (4 French oxymetric catheter; Abbott, Mountain View, CA). Values of all monitored modalities were maintained within 15% of baseline. Prior to anesthetic induction, EEG electrodes were placed according to 10-20 system using a 16-channel anterior-posterior bipolar montage. Real-time EEG monitoring was performed during induction and anesthesia emergence as well as shortly prior to, during, and shortly after CPB. Burst suppression was achieved with thiopental 16 mg/kg prior to the onset of CPB. Perfusion pressure was maintained within 10% of baseline with phenylephrine infusion. While on CPB, blood gas parameters were continuously monitored with in-line arterial and venous monitors (Sorin CDI, Irving, CA). During CPB, normocapnea, pH stat management, pO2 of 200-300 mm Hg, SVO2 >or=to70%, and pump flow index >3 L [centered dot] min-1 [centered dot] m-2 were maintained while the nasopharyngeal temperature was allowed to drift to 34 degrees C. Primary closure of the ASD was performed during electrical fibrillation for 10 min, with total bypass time of 17 minutes. Return of EEG slow activity was noted after 8 min of CPB while fast activity returned after 13 min. The SJVO2 had a postinduction value of 50%. It progressively increased with adjustment of the ventilatory setting (Figure 1). SJVO2 increases were noted with the increase of PaCO2 from 37 to 50 mm Hg, with the increase of inspired of O2 from 21% to 70% and, ultimately, with induction of burst suppression prior to CPB. During CPB, SJVO2 decreased from 80% to 58% at the end of nonpulsatile bypass, despite the maintenance of perfusion pressure and high bypass flow rate.Figure 1: Continuous intraoperative jugular bulb oximetry. Jugular bulb saturation (SJVO2) was monitored continuously intraoperatively. Initial SJVO2 at 52% was increased by an increase of FIO2 from 21% to 70%. Adjustment of ventilatory setting to avoid hypocapnea (PaCO2 37 mm Hg) resulted in an overshoot of PaCO (2) to 50 mm Hg and a further increase of SJVO2. Subsequent hemodynamic effects of surgical dissection and cannulation decreased SJVO2 to 60%, which returned to 78% with induction of electroencephalograph-documented burst suppression. SJVO (2) decreased to a nadir of 58% with nonpulsatile cardiopulmonary bypass; upon return of ejection and pulsatility, SJVO2 returned to 70%-80%. The patient's awakening resulted in a steady drop of SJVO2 to 60%.Global CBF was measured by the Kety-Schmidt technique [1] using N (2) O (10%-15% inspired fraction) at baseline after induction of general anesthesia and again 40 min after discontinuing CPB (Table 1). CBF under anesthesia was measured with nitrous oxide at 60 mL [centered dot] 100 g-1 [centered dot] min-1 prior to CPB and 45 mL [centered dot] 100 g-1 [centered dot] min-1 after CPB. Cerebral metabolic rate for oxygen (CMRO2) was calculated at 1.6 mL O2 [centered dot] 100 g-1 [centered dot] min-1 at baseline and 1.7 mL O (2) [centered dot] 100 g-1 [centered dot] min-1 after CPB Equation 1 where CaO2 is arterial oxygen concentration and CJVO2 is mixed jugular venous oxygen content.Table 1: Cerebral Blood Flow Before and After Cardiopulmonary Bypass Cerebral vascular resistance (CVR) was measured at 1.2 mm Hg [centered dot] 100 g-1 [centered dot] mL-1 [centered dot] min-1 at baseline and 1.7 mm Hg [centered dot] 100 g-1 [centered dot] mL-1 [centered dot] min-1 after CPB Equation 2 where CPP is cerebral perfusion pressure, MAP is mean arterial pressure, and PjV is jugular bulb pressure. This patient had an uneventful emergence from anesthesia and was tracheally extubated 2 h postoperatively. Detailed neurologic examination during the first 2 days postoperatively revealed no deficit. At 2 mo postoperatively, the mother reported that the patient had returned to her usual activity, functional level, and personality. Discussion Bilateral internal carotid artery occlusion in MMD, by virtue of both large and small vessel involvement, probably places patients in an analogous or pathophysiologically higher risk state than patients with bilateral atherosclerotic cerebrovascular disease, who are, by some reports, at 10- to 15-fold increased risk of major neurologic complications than other patients [2]. MMD is seen predominantly in children. Affected children show an unusual net-like appearance of small vessel neovascularization in cerebral angiograms. Usual pathological findings are stenosis or occlusion of the terminal portions of the internal carotid arteries and proximal portions of the anterior and middle cerebral arteries. These changes are due to laminated fibrocellular thickening of the intima. Subsequent neovascularization of small or medium-sized muscular arteries may result in hemodynamic implications different from atherosclerotic cerebrovascular disease of the adult patient. Most reports of perioperative management of noncardiac surgery in patients with MMD has centered around the high risk of ischemic infarctions and hemorrhagic sequelae of this progressive disease and strategies for their prevention [3,4]. The risks of hypocapnic cerebral vasoconstriction, hypercapnic cerebral steal, and increased oxygen extraction in areas of diminished CBF are well recognized [5]. CPB poses additional challenges to perioperative management with its risk of decreased CPP due to the variability in perfusion pressure at the initial stages of CPB and nonpulsatile flow. In the setting of deep hypothermia or moderate- to low-flow CPB, pulsatile flow has been shown, although with some controversy, to decrease hyperemia and cerebral edema [6]. In the setting of global ischemia, resumption of pulsatile flow improves CMRO2 and CMR for glucose compared with nonpulsatile flow [7]. CVR increases with duration of CPB; however, CMRO2 is maintained [8]. CMRO2 in our patient at 1.6-1.7 mL O2 [centered dot] 100 g-1 [centered dot] min-1 under general anesthesia is consistent with reported values of mean basal cerebral metabolic rates of 1.1-2.0 mL [centered dot] 100 g-1 [centered dot] min-1[9]. In this setting of major intracranial vessel occlusion and small muscular artery neovascularization, the changes in CVR and CBF during CPB have not been investigated in previous human or animal models. Our measurement of CBF and SJVO2 provides a global assessment of CBF/CMRO2 coupling in the setting of MMD and CPB; however, these are poor markers of regional cerebral hypoperfusion or ischemia. The CBF measured in this patient diminished from 60 mL [centered dot] 100 g-1 [centered dot] min-1 to 45 mL [centered dot] 100 g-1 [centered dot] min-1 after CPB without hemodynamic differences as measured by arterial pressure, heart rate, and oxygen saturation, despite a small CPP increase and relative anemia after CPB. The initial CBF of 60 mL [centered dot] 100 g-1 [centered dot] min-1, although confounded by the state of general anesthesia and mild hypercarbia, ought to be reassuring knowledge for anesthetic management in patients with MMD. The decrease in CBF after CPB possibly results from increased CVR [8]. Our preliminary studies in other patients have shown a consistent decrease in SJVO2 with the onset of CPB as well as the presence of a second nadir in SJVO2 toward the end of CPB despite maintenance of CPP. In addition to maintenance of narrow ranges for physiologic parameters of MAP, arterial saturation, PaCO2, and PaO2, we used two strategies of cerebral protection during periods of high risk. Thiopental was used to minimize the cerebral metabolic rate, and its effectiveness was monitored with burst suppression and SJVO2. Michenfelder [9] had shown, in the setting of CPB, that thiopental decreases CMRO2 to 58% of baseline by suppression of cortical neuronal function as evidenced by EEG. Thiopental may also vasoconstrict normal vessels and shunt blood flow toward ischemic areas [10]. Thiopental is thus protective in the settings of focal ischemia or anoxia not severe enough to abolish function, probably through the combination of these two mechanisms [10,11]. Nimodipine was used based on empiric improvement of this patient's initial symptoms with verapamil, as well as its neuroprotective and cerebrovasodilating properties [12]. Nimodipine has been reported to decrease stroke size in regional ischemia by improving perfusion to penumbra [13] and to ameliorate global ischemia by decreasing postischemic hypoperfusion [14]. This flow enhancement by nimodipine tends to redistribute blood flow to areas of low flow (Robin Hood steal) and could potentially benefit the cerebrovascular system in the setting of MMD [14]. Nimodipine for coronary artery bypass graft surgery resulted in increased bleeding in one study [15]; however, bleeding had not been our concern in this case of ASD repair due to short CPB time. 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