Ann Thorac Surg 2000;70:44-47
© 2000 The Society of Thoracic Surgeons
Original articles: Cardiovascular
Selective intercostal arterial perfusion during thoracoabdominal aortic aneurysm surgery
Taijiro Sueda, MDa,
Satoru Morita, MDa,
Kenji Okada, MDa,
Kazumasa Orihashi, MDa,
Hiroo Shikata, MDa,
Yuichiro Matsuura, MDa
a First Department of Surgery, Hiroshima University School of Medicine, Hiroshima, Japan
Address reprint requests to Dr Sueda, First Department of Surgery, Hiroshima University, School of Medicine, 1-2-3 Kasumi, Minami-ku, Hiroshima, 734, Japan
e-mail: sueda{at}mcai.med.hirosjima-u.ac.jp
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Abstract
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Background. This clinical study evaluated changes in motor evoked potentials (MEP) elicited by direct cerebral cortical stimulation and evoked spinal cord potentials (ESCPs) elicited by direct spinal cord stimulation during selective intercostal arterial perfusion for thoracoabdominal aortic aneurysm (TAAA) repair. We also determined the efficacy of this perfusion method for prevention of paraplegia.
Methods. Two kinds of ESCPs and MEPs were monitored during the prosthetic replacement step for TAAA surgeries. We performed selective intercostal arterial perfusion from the T7 intercostal artery to the L1 intercostal artery through a small piece of Dacron graft while monitoring spinal cord potentials in five cases of TAAA.
Results. The MEP amplitude decreased after clamping the aorta but quickly recovered after selective perfusion of intercostal arteries. Other spinal cord potentials did not change during the reconstruction of intercostal arteries. Postoperative paraplegia or parapalesis did not occur in any of the patients.
Conclusions. Monitoring of MEPs during selective intercostal arterial perfusion was a useful adjunct to prevent postoperative paraplegia in TAAA surgery.
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Introduction
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Improvements in operative techniques and perioperative management have reduced the overall mortality and morbidity associated with thoracoabdominal aortic aneurysm (TAAA) repair, but the incidence of spinal cord injury remains substantial [1, 2]. Evoked spinal cord potentials (ESCPs) or somatosensory evoked cortical potentials reflect the function of the sensory nervous system and the function of the white matter of the spinal cord [3, 4]. However, ischemic changes in the motor nerve cannot be recorded by this type of monitoring. We therefore measured motor evoked potentials (MEPs) elicited by direct transcranial stimulation of the cerebral cortex during thoracoabdominal aortic aneurysm (TAAA) surgery. In addition, we also performed selective intercostal perfusion for prevention of spinal cord damage. This article describes a novel method of selective intercostal arterial perfusion for spinal cord protection during TAAA repair using MEP monitoring.
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Patients and methods
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A flexible, bipolar, platinum catheter electrode (UKG-100-2PM, Unique Medical, Tokyo, Japan) was introduced into the dorsal epidural space through a 17-gauge Tuohy needle at the cervical cord levels (C5 and C6) for stimulation in the measurement of descending ESCPs. A catheter tube with five unipolar electrodes (UKG-100-5PM), Unique Medical, Tokyo, Japan) was placed at the lumbar enlargement (T12-L1) on the day before surgery as a stimulating electrode for measurement of all spinal cord potentials. We then recorded sensory-evoked potentials using two types of ESCPs, descending ESCPs at the lumbar enlargement after cervical spinal cord stimulation, and segmental ESCPs at the lumbar enlargement elicited by left superficial peroneal nerve stimulation delivered by a surface electrode (Vitrode S-200, Nihon Koden, Tokyo, Japan).
After general anesthesia was induced by a high dose of fentanyl, two flexible bipolar platinum catheter electrodes were inserted into the supracranial space and placed into the cranial bone on the dura mater of both motor cortices through needle puncture. Direct transcranial electrical stimulation of the cerebral motor cortices was then performed, and MEPs and ESCPs were recorded at the lumbar enlargement (Fig 1). Stimulation and recording were conducted using a Nicolet Viking IV stimulator (Nihon Coden, Tokyo, Japan). All action potentials were recorded by the one of five electrodes at the lumbar enlargement, which recorded the largest amplitude detected along the spine.
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Fig 1. Schema of the spinal cord monitoring. An electrode was introduced into the dorsal epidural space at C5 and C6, and a catheter tube with five unipolar electrodes was placed at the level of the lumbar enlargement. The former electrode was used as a stimulating electrode for measuring descending evoked spinal cord potentials and the latter was used as a recording electrode for measuring all spinal cord potentials. Segmental evoked spinal cord potentials elicited by left peroneal nerve stimulation were also recorded. Two electrodes were inserted into the supracranial space. Both motor cortices were electrically stimulated and motor evoked potentials were recorded.
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The aneurysmectomy was performed through a left thoracotomy using a paramedial retroperitoneal approach. The proximal aorta was initially clamped and anastomosed to the tube prosthesis. After systemic heparinization (2 mg/kg), a femorofemoral partial cardiopulmonary bypass was created using a long venous cannula inserted through the right femoral vein into the inferior vena cavae and an arterial cannula through the right femoral artery. Mean pump flow was maintained at 2,200 to 3,000 mL/min and body temperature at 32°C measured rectally. The aortic cross-clamp was then moved distally and placed above the diaphragm. We then observed the changes in both ESCP and MEP amplitudes for 10 minutes. If there was significant decrease in amplitude, the aortic cross-clamp was released and reperfused for 10 minutes. After the aorta was clamped again, the aneurysm was opened and several intercostal arteries were reconstructed. Five to seven pairs of intercostal arteries were generally involved in the posterior wall of the aneurysm. Intercostal arteries were typically reconstructed from the seventh to the 10th pair of intercostal artery using a small piece of Dacron prosthesis (diameter, 10 mm), and immediately perfused with blood at 40 to 100 mL/min and a constant perfusion pressure of 100 mm Hg for each pair. The distal clamp was then moved distally to below the level of the renal arteries and the aneurysmectomy was extended peripherally. If MEP amplitude did not recover sufficiently, we continued reconstruction from the 11th pair of intercostal arteries to the L1 lumbar arteries and reperfused these intercostal arteries in the same manner. After completing selective intercostal arterial perfusion, individual Dacron grafts to intercostal arteries were anastomosed to the tube graft used to reconstruct the descending aorta (Fig 2). Distal reconstruction of the aneurysm was then quickly performed, with visceral arterial reconstruction using the branched grafts under visceral arterial perfusion (150 mL/min for each visceral artery).
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Fig 2. Schema of selective intercostal arterial perfusion. Intercostal arteries were reconstructed from the ninth pair of intercostal arteries to L1 pair of lumbar arteries using a small piece of Dacron prosthesis (diameter, 10 mm), and immediately perfused with blood at 40 to 100 mL/min and a constant perfusion pressure of 100 mm Hg for each pair. After completing selective intercostal arterial perfusion, individual Dacron grafts to intercostal arteries were anastomosed to the tube graft used to reconstruct the descending aorta.
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Five cases with thoracoabdominal aortic aneurysm were operated on using this monitoring protocol in combination with selective intercostal arterial perfusion. Three of these were cases of atherosclerotic aneurysm and two were cases of dissecting aneurysm (Stanford type B). During reconstruction of these intercostal arteries, MEPs, ESCPs, and S-ESCPs were monitored to detect any diminution of amplitude because of spinal cord ischemia and to monitor recovery of each potentials after reconstruction of the appropriate spinal cord arteries. Our institutional review board approved the monitoring and perfusion protocol beforehand. Informed consent was obtained from the patients before implementation.
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Results
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These procedures were performed on 3 patients with atherosclerotic thoracoabdominal aneurysms (two with Crawford type I, 1 with Crawford type II) and two with type B dissecting aneurysms (two with Crawford type II). There were no complications associated with the spinal cord monitorings either during or after surgery. Patent intercostal arteries from the seventh intercostal artery to the first lumbar artery were principally reconstructed, whereas small and occlusive intercostal arteries were sacrificed (Table 1). The mean number of pairs of intercostal arteries and the mean selective intercostal perfusion time were 3.3 pairs and 69 minutes, respectively. The mean partial femorofemoral bypass time and the total operative time was 182 minutes and 428 minutes, respectively (Table 2). The MEPs were most sensitive for detection of spinal cord ischemia and were most responsive to recovery from ischemia during selective intercostal arterial perfusion. If there were critical intercostal arteries in the clamping area of the aneurysm, MEP amplitude decreased to approximately 50% of preoperative values within 20 minutes after clamping of the thoracoabdominal aorta. It took between 8 and 12 minutes to reconstruct a pair of intercostal arteries. Once the critical intercostal arteries were reconstructed and perfused, MEP amplitude recovered quickly. Amplitudes of ESCPs and S-ESCPs were less responsive to spinal cord ischemia, and ESCP amplitude did not change during the reconstruction of the intercostal arteries (Fig 3). Reconstruction of three to four pairs of intercostal arteries was usually sufficient to achieve full recovery of MEP amplitude. Full recovery of MEP amplitude was obtained by reconstructing three or four pairs of intercostal arteries (usually T7, 9, and 11). Once these intercostal arteries were reconstructed and perfused, MEP amplitude recovered to the preoperative value in all patients, and none of the patients suffered from postoperative spinal neurological deficits (Table 2).
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Fig 3. Changes in evoked spinal cord potentials during selective intercostal perfusion. During reconstruction of the intercostal arteries, the motor evoked potential was most sensitive to spinal cord ischemia. Motor evoked potential amplitude decreased to 30% of the preoperative value during reconstruction of critical spinal cord arteries and quickly recovered after selective intercostal arterial perfusion to T11 spinal cord artery (see case 2 in Table 1).
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Comment
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Among the three spinal cord potentials, the thoracic descending ESCP is specific for dorsal spinal cord ischemia, but is not sensitive to motor neuronal damage because it measures conductive potentials in the dorsal and dorsolateral funiculi [4]. We have previously reported the superior sensitivity of MEP in predicting approximately 90% prevalence of spinal cord damage in an animal model [5]. Monitoring of MEP proved to be valuable in the assessment of spinal cord damage in this study. The MEP amplitude began to decrease 10 minutes after aortic clamping, and disappeared 40 minutes after aortic clamping in our previous subject [6]. In this study, MEP amplitude decreased to approximately 50% of the preoperative value within 20 min after clamping the thoracic aorta. Our previous animal experiments [5] showed a slight degeneration of the spinal cortex when MEP amplitude decreased below 50% of the control value. A reduction in MEP amplitude was an indicator of irreversible damage of the spinal cortex. We surmise that the ischemic tolerance of the spinal cord may be less than 40 minutes and it is preferable to reconstruct critical spinal cord arteries within 30 minutes. We used segmental aortic clamping during reconstruction of the intercostal arteries and ischemic time during reconstruction of a pair of intercostal arteries was less than 10 minutes. Therefore, reconstruction of critical spinal cord arteries can be accomplished safely. Decrease in MEP amplitude during surgery suggests that there is a critical spinal cord artery in the aortic clamping area and rapid reconstruction of intercostal arteries is necessary. If MEP amplitude recovers to the preoperative value while reconstructing intercostal arteries, it is not necessary to reconstruct more intercostal arteries. Although this procedure is complicated and requires more experience, we believe that selective intercostal perfusion under MEP monitoring is a safe and effective method for prevention of spinal cord damage during TAAA surgery.
In conclusion, MEP amplitude decreased after clamping the aorta but quickly recovered after selective perfusion of intercostal arteries. Other spinal cord potentials did not change during reconstruction of the intercostal arteries. Selective intercostal arterial perfusion under MEP monitoring was a useful adjunct to prevent postoperative paraplegia in TAAA surgery.
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References
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Accepted for publication January 18, 2000.
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Abstract
Introduction
