Asian Cardiovasc Thorac Ann 2006;14:338-340
© 2006 Asia Publishing EXchange Ltd
An Alternative for Descending Thoracic Aortic Aneurysm Repair
Kenji Okada, MD,
Taijiro Sueda, MD,
Kazumasa Orihashi, MD,
Nobuhiro Tanaka, MD1,
Kazuyoshi Nakanishi, MD1,
Mitsuo Ochi, MD1
Department of Cardiovascular Surgery
1 Department of Orthopedic Surgery, Hiroshima University Hospital, Hiroshima, Japan
For reprint information contact: Kenji Okada, MD Tel: 81 82 257 5216 Fax: 81 82 257 5219 Email: kokada{at}hiroshima-u.ac.jp, Department of Cardiovascular Surgery, Hiroshima University Hospital, 1-2-3 Kasumi, Minami-ku, Hiroshima 734-8551, Japan.
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ABSTRACT
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A simple technique termed "clamp test and spinal cord-plegia" for descending thoracic aortic aneurysm surgery is described. The clamp test is a passive method of creating ischemic conditions, whereas spinal cord-plegia is an active method of decreasing metabolism. This technique is a practical test that double-checks for critical feeding arteries and seems to have an excellent spinal cord-preserving effect.
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INTRODUCTION
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Despite the introduction of various strategies to protect the spinal cord during descending thoracic aortic aneurysm (TAA) and thoracoabdominal aortic aneurysm repair, paraplegia remains a distinct possibility. Recent studies have described the use of motor-evoked potential (MEP) monitoring for the prevention of spinal cord disturbance, but this did not improve neurological outcome.1–2 The strategies for maintaining adequate spinal cord perfusion during aortic replacement include segmental aortic crossclamping combined with distal aortic perfusion, cerebrospinal fluid drainage, and re-implantation of the segmental arteries. However, these methods are not effective when critical segmental arteries originate between the aortic crossclamps. A period of spinal cord ischemia cannot be avoided when the feeding arteries of the spinal cord are located within the excluded aortic segment and the collateral circulation is insufficient. Therefore, it would be advantageous to selectively perfuse the segmental arteries during graft inclusion, and re-implant them to protect the spinal cord.3 If the artery is not an actual feeding artery, then the procedure would serve only to prolong the crossclamp time, which increases the risk of paraplegia. Therefore, it is very important to identify a critical vessel intraoperatively. The MEP can help to identify critical segmental arteries and also confirm successful re-implantation and adequate distal aortic perfusion during TAA repair.
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TECHNIQUE
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A simple technique termed the "clamp test and spinal cord-plegia" was investigated. This technique was developed because under normothermic conditions, the MEP amplitude decreases when spinal cord ischemia occurs. Also, the MEP wave disappears when the rectal temperature drops. It is believed that at 28°C there is considerable protection against neuronal damage after transient episodes of ischemia, because ischemia-induced release of excitotoxic neurotransmitter is decreased and the metabolic rate is slower.4 The clamp test is performed by clamping both sides of the aneurysm for 5 minutes with MEP monitoring. If any critical feeding arteries are present in the aneurysm, then spinal cord ischemia will occur and the MEP will change. If the MEP changes, then all the lumbar arteries should be reconstructed immediately after the aneurysm is opened. If there are no changes in the MEP, then all of the lumbar arteries should be sacrificed immediately after the aneurysm is opened. The spinal cord-plegia procedure is performed after both sides of the aneurysm have been clamped. Cold blood is perfused into the aneurysm. If critical arteries are present, the spinal cord will be cooled, the MEP will change, and the metabolism slowed, i.e., spinal cord-plegia. No change in the MEP means that any arteries present are actually too tiny to cool down the spinal cord, and thus are not feeding or critical arteries.
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DISCUSSION
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Up to now, the fact that the MEP wave disappeared under hypothermic conditions was considered a disadvantage of MEP monitoring; however, spinal cord-plegia is able to turn this phenomenon into an advantage. The technique was employed in a 66-year-old man who had been diagnosed with a TAA. Two-year follow-up computed tomography revealed that the aneurysm was gradually increasing in size, so he was admitted to our hospital for surgical repair. He had no history of hypertension, diabetes mellitus, atherosclerosis or spinal cord damage, but he had undergone total arch replacement by the elephant-trunk procedure for aortic arch aneurysm 3 years earlier, and abdominal aortic aneurysm repair 6 years earlier. Computed tomography revealed a fusiform 5.9 cm TAA extending from the midportion of the descending thoracic aorta to near the diaphragm (Figure 1A
). Conventional TAA repair was performed while monitoring for spinal cord ischemia with MEP. One day preoperatively, a spiral drainage tube and the electrodes for MEP monitoring were inserted. The monitoring method has been described previously.5–6 The TAA repair was carried out through the left thoracic cavity. The aneurysm arose 15 cm distal to the left subclavian artery and extended 8 cm proximal to the celiac artery. Both proximal and distal sides of the TAA were exposed, and tapes were put around the vessels. Under cardiopulmonary bypass with right femoral venous and arterial cannulation, the perfusate was cooled to produce a rectal temperature of 34°C. The aneurysm was long enough to clamp and sew the upper and lower parts separately. Initially, a clamp test for the upper part of the aneurysm was performed (Figure 1B). The proximal side and the mid portion of the aneurysm were clamped, and no procedures were performed during the next 5 min in order to observe the MEP. No changes were seen on MEP monitoring (Figure 2), and the two clamps were detached. After 5 min, the clamps were replaced in the same position, and spinal cord-plegia was performed. Via a 14G elastic cannula inserted into the upper part of the aneurysm, 300 mL of cold blood at 4°C was infused at a rate of 200 mL·min–1. During this period, no changes in MEP were noted so it was concluded that all lumbar arterial influx into the aneurysmal section would be stopped when the aneurysm was resected. The aneurysm was opened anteriorly, and 5 intercostal arteries (both of the thoracic 5 and 6, and the left side of thoracic 7) were seen feeding into it. The arteries were sacrificed immediately after opening the upper part of the aneurysm. A side-to-side proximal anastomosis was created with a reinforcing felt strip and a 24 mm Hemashield conduit of collagen-impregnated woven velour (Meadox Medicals, Inc., Oakland, CA, USA). Another clamp was placed on the lower side of the aneurysm (Figure 1C), and the tests were performed again. This time, the amplitude of the MEP began to decrease (Figure 3). It was concluded that all lumbar arterial influx into this part of the aneurysm should be re-implanted. The lower part was opened, and 4 intercostal arteries (both of the thoracic 9 and 10) were observed feeding into it. The arteries were reconstructed using 8 mm Hemashield conduit immediately after opening the lower part of the aneurysm. A side-to-side distal anastomosis was created by the same method. The cardiopulmonary bypass time and duration of aortic crossclamping were 174 min and 152 min, respectively. The intraoperative cerebrospinal fluid drainage was 80 mL. The postoperative course was uneventful and the patient underwent extubation on the 1st postoperative day. No neurological complications such as cerebral infarction, paraplegia, or paraparesis were observed.
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Figure 1. (A) Preoperative computed tomography showing the descending aortic aneurysm; (B) The clamp test on the upper part of the aneurysm. (C) The clamp test on the lower part of the aneurysm.
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Figure 2. Records of motor-evoked potential in the upper part of the aneurysm. Motor-evoked potential did not change during clamping, spinal cord-plegia (SCP), or after opening the aneurysm.
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Figure 3. Records of motor-evoked potential in the lower part of the aneurysm. Motor-evoked potential changed during clamping, spinal cord-plegia (SCP), and after opening the aneurysm. When all intercostal arteries were reconstructed and reperfusion started, the motor-evoked potential started to increase.
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In this patient, the MEP did not change during the test in the upper part of the aneurysm, although it did change in the lower part. When all intercostal arteries were reconstructed, the MEP stopped decreasing and started to increase a little. The clamp test is a passive method for creating ischemic conditions, whereas spinal cord-plegia is an active method for decreasing metabolism. The combined "clamp test and spinal cord-plegia" is a practical test that double-checks for critical feeding arteries and seems to have an excellent spinal cord-preserving effect. This method will be useful in the detection of critical segmental arteries and help to decrease the aortic crossclamp duration.
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REFERENCES
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- Allen BT, Davis CG, Osborne D, Karl I. Spinal cord ischemia and reperfusion metabolism: the effect of hypothermia. J Vasc Surg 1994;19:332–40.[Medline]
- Okada K, Sueda T, Shikata H, Orihashi K, Morita S, Hirai S, et al. Evoked spinal cord potential monitoring reveals peroneal nerve ischemia during thoracoabdominal repair: a case report. Ann Thorac Cardiovasc Surg 1999;5:350–2.[Medline]
- Sueda T, Morita S, Okada K, Orihashi K, Shikata H, Matsuura Y. Selective intercostal arterial perfusion during thoracoabdominal aortic aneurysm surgery. Ann Thorac Surg 2000;70:44–7.[Abstract/Free Full Text]
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ABSTRACT
INTRODUCTION
