Repair of the descending thoracic aorta: impact of open distal anastomosis technique on spinal cord perfusion, neurological outcome and spinal cord histopathology.

OBJECTIVES: We investigated the impact of equilibrating distal aortic pressure with atmospheric pressure (open distal anastomosis) on spinal cord perfusion, neurological outcome and spinal cord histopathology in a rat model of descending thoracic aortic surgery. METHODS: Proximal thoracic aortic occlusion was obtained in Sprague-Dawley rats by inflating the balloon of a 2F Fogarty catheter introduced through the left femoral artery. Rats were separated into three groups: sham-operation (n = 5) without balloon inflation, control (n = 15) with inflation of the balloon, and open distal (n = 15) with inflation of the balloon combined with incision of the right femoral artery to allow free drainage of distal aortic blood. Balloon inflation was maintained for 15 min. Rectal temperature, arterial blood gases and pH, distal arterial blood pressure (DABP) and lumbar spinal cord blood flow (SCBFl) were recorded throughout the procedure. Neurobehavioral status was assessed daily using a 0-5 scale and rats were sacrificed after 48 h of reperfusion and their spinal cord harvested for histopathology and immunohistochemistry for microtubule-associated protein-2 (MAP-2). RESULTS: DABP and SCBFl values were lower during thoracic aortic occlusion in the open distal group, compared to the control group (P < 0.001). Paraplegia and mortality rates were dramatically increased in the open distal group (87.7 and 46.6%, respectively) compared to the control group (0 and 6.6%, respectively, (P < 0.001 and 0.02). Severe metabolic acidosis and bowel infarct were also more frequent in the open distal group (P < 0.001). Sham-operated and control rats had virtually normal spinal cords, whereas rats in the open distal group had severe ischemic injury throughout gray matter. CONCLUSIONS: Equilibrating distal arterial pressure with atmospheric pressure during thoracic aortic occlusion decreased spinal cord blood flow, increased mortality and worsened spinal cord injury in rats. These results suggest that the open distal anastomosis technique should be used with caution in patients undergoing repair of the descending thoracic or thoracoabdominal aorta.     

Assessment of spinal cord integrity during thoracoabdominal aortic aneurysm repair

BACKGROUND: Monitoring motor-evoked potentials (MEPs) is an accurate technique to assess spinal cord integrity during thoracoabdominal aortic aneurysm (TAAA) repair, guiding surgical strategies to prevent paraplegia. METHODS: In 210 consecutive patients with type I (n = 75), type II (n = 103), and type III (n = 32) TAAA surgical repair was performed using left heart bypass, cerebrospinal fluid drainage, and MEPs monitoring. RESULTS: Reliable MEPs were registered in all patients. The median total number of patent intercostal and lumbar arteries was five. After proximal aortic crossclamping, MEP decreased below 25% of base line in 72 patients (34%) indicating critical spinal cord ischemia, which could be corrected by increasing distal aortic pressure. By using sequential clamping it appeared that in 43% of type I and II cases spinal cord circulation was supplied between T5 and L1, and 57% between L1 and L5. In type II and III cases cord perfusion was dependent upon lower lumbar arteries in 16% and pelvic circulation in 8%, necessitating reattachment of these segmental arteries. In 9% of patients critical ischemic MEP changes occurred without visible arteries, requiring aortic endarterectomy and selective grafting. One patient suffered early paraplegia and 2 delayed, and 2 patients had temporary neurologic deficit (5 of 210; 2.4%). CONCLUSIONS: In patients with TAAA, blood supply to the spinal cord depends upon a highly variable collateral system. Monitoring MEPs is an accurate technique for detecting cord ischemia, guiding surgical tactics to reduce neurologic deficit (2.4%).     

Reappraisal of the role of motor and somatosensory evoked potentials during open distal aortic repair

ObjectiveIntraoperative motor and somatosensory evoked potentials have been applied to monitor spinal cord ischemia during repair. However, their predictive values remain controversial. The purpose of this study was to evaluate the impact of motor evoked potentials and somatosensory evoked potentials on spinal cord ischemia during open distal aortic repair.MethodsOur group began routine use of both somatosensory evoked potentials and motor evoked potentials at the end of 2004. This study used a historical cohort design, using risk factor and outcome data from our department's prospective registry. Univariate and multivariable statistics for risk-adjusted effects of motor evoked potentials and somatosensory evoked potentials on neurologic outcome and model discrimination were assessed with receiver operating characteristic curves.ResultsBoth somatosensory evoked potentials and motor evoked potentials were measured in 822 patients undergoing open distal aortic repair between December 2004 and December 2019. Both motor evoked potentials and somatosensory evoked potentials were intact for the duration of surgery in 348 patients (42%). Isolated motor evoked potential loss was observed in 283 patients (34%), isolated somatosensory evoked potential loss was observed in 18 patients (3%), and both motor evoked potential and somatosensory evoked potential loss were observed in 173 patients (21%). No spinal cord ischemia occurred in the 18 cases with isolated somatosensory evoked potential loss. When both signals were lost, signal loss happened in the order of motor evoked potentials and then somatosensory evoked potentials. Immediate spinal cord ischemia occurred in none of those without signal loss, 4 of 283 (1%) with isolated motor evoked potential loss, and 15 of 173 (9%) with motor evoked potential plus somatosensory evoked potential loss. Delayed spinal cord ischemia occurred in 12 of 348 patients (3%) with intact evoked potentials, 24 of 283 patients (8%) with isolated motor evoked potentials loss, and 27 of 173 patients (15%) with motor evoked potentials + somatosensory evoked potentials loss (P < .001). Motor evoked potentials and somatosensory evoked potentials loss were each independently associated with spinal cord ischemia. For immediate spinal cord ischemia, no return of motor evoked potential signals at the conclusion of the surgery had the highest odds ratio of 15.87, with a receiver operating characteristic area under the curve of 0.936, whereas motor evoked potential loss had the highest odds ratio of 3.72 with an area under the curve of 0.638 for delayed spinal cord ischemia.ConclusionsSomatosensory evoked potentials and motor evoked potentials are both important monitoring measures to predict and prevent spinal cord ischemia during and after open distal aortic repairs. Intraoperative motor evoked potential loss is a risk for immediate and delayed spinal cord ischemia after open distal aortic repair, and somatosensory evoked potential loss further adds predictive value to the motor evoked potential.     

Ischemic Preconditioning to Prevent Lethal Ischemic Spinal Cord Injury in a Swine Model

Objective: Paraplegia is a serious complication of thoracic and thoracoabdominal aortic operations and is the result of ischemic spinal cord injury induced by low perfusion pressure during cross-clamping of the aorta. Ischemic preconditioning (IPC) of the heart or brain with reversible sublethal ischemic injury induces resistance to subsequent lethal ischemia. The aim of this study is to investigate whether ischemic tolerance can be induced by IPC of the spinal cord in a swine model. Study Design: The animals were randomly divided into three groups: the sham group (n = 3), control group (n = 6) and IPC group (n = 8). In the sham group, we performed a left thoracotomy without any ischemic injury. In the IPC group, the swine received a reversible ischemic spinal cord injury by aortic clamping for 20 min, whereas in the control group, no aortic cross-clamping was performed. Forty-eight hours later, the animals in both the IPC and control groups underwent aortic clamping for 30 min. Neurological examination was done 24 h later, and then the animals were euthanized for histopathology and a malonedialdehyde spectrophotometry assay of the spinal cord tissue. Results: A statistically significant difference in neurological outcome was observed between the control and IPC groups at 24 h after ischemic injury. The incidence of paraplegia and severe paresis was 100% in the control group and 62.5% in the IPC group (p =. 028). Between control and IPC groups, there was no statistically significant difference in histopathology and only a borderline statistical difference in the malonedialdehyde assay of the ischemic spinal cord (p =. 0745). Conclusion: In this study, IPC induced protection against a 30-min ischemic insult of the spinal cord, although complete recovery was not achieved (standing up or walking). We expect that combining this IPC with other existing protective methods might lead to a synergistic effect, which warrants further investigation.     

Paraplegia after surgery for aneurysm of the descending thoracic aorta

Postoperative paraplegia caused by ischemic injury of the spinal cord is the most disabling complication of thoracoabdominal surgery, particularly when repair of the descending thoracic aorta is involved. We describe the case of a 59-year-old man who underwent emergency surgery for placement of a Dacron prosthesis to repair a ruptured descending thoracic aorta aneurysm, using an aortic cross-clamping technique plus aortic-femoral partial bypass with normothermia and an ischemic time of 165 minutes. The early postoperative course included complete spinal syndrome with motor and sensory loss below T5, with consequent respiratory insufficiency of neuromuscular origin. The result was a difficult postoperative course including prolonged mechanical ventilation and recurrent respiratory infections. Possible causes include prolonged time of ischemia, inadequate monitoring of distal aortic pressure and inappropriate surgical technique related to the absence of angiographic data on spinal vascularization. We conclude that ischemic time should be kept to under 30 minutes whenever possible. In cases of prolonged ischemia, bypass techniques with outflow to the distal aortic segment are more effective whenever mean blood pressure at this point rises to 60 mmHg or more. Vasodilator use should be reserved for cases of severe arterial hypertension and left ventricular failure and/or life-threatening increases in aortic wall stress even if not leading to dangerous decreases in distal aortic pressure. Finally, angiographic study to obtain anatomical details of spinal blood flow is advisable.     

Strategies to prevent neurologic deficit based on motor-evoked potentials in type I and II thoracoabdominal aortic aneurysm repair

Purpose: Motor-evoked potentials (MEPs) were monitored during thoracoabdominal aortic aneurysm (TAAA) repair to assess spinal cord ischemia and evaluate the subsequent protective strategies to prevent neurologic deficit. Methods: Between January 1996 and December 1997, 52 consecutive patients with type I (n = 24) and type II (n = 28) TAAA underwent surgery (mean patient age, 60 years; range, 21–78 years). The surgical protocol included left heart bypass, cerebrospinal fluid drainage, and monitoring transcranial myogenic MEPs. When spinal cord ischemia was detected, distal aortic pressure and mean arterial pressure were increased. By means of sequential crossclamping, MEPs were used to identify critical intercostal or lumbar arteries. Results: Reproducible MEPs could be recorded in all patients, and spinal cord ischemia was detected within 2 minutes. During distal aortic perfusion, 14 patients (27%) showed rapid decrease in the amplitude of MEPs to less than 25% of baseline, indicating spinal cord ischemia, which could be corrected by increasing distal aortic pressure. The mean distal aortic pressure to maintain adequate cord perfusion was 66 mm Hg; however, it varied among individuals between 48 and 110 mm Hg. In 24 patients (46%), MEPs disappeared after segmental clamping and returned after reattachment of intercostal arteries. In 9 patients (17%), MEPs disappeared completely, but no intercostal arteries were found. After aortic endarterectomy, 6 or 8 mm Dacron grafts were anastomosed to intercostal arteries, and MEPs returned after reperfusion. Using this aggressive surgical approach based on MEPs, no early or late paraplegia occurred in this series. Conclusion: Monitoring of MEPs is an effective technique to assess spinal cord ischemia. Operative strategies based on MEPs prevented neurologic deficits in patients treated for type I and II TAAA. (J Vasc Surg 1999;29:48-59.)     

Outcome of thoracoabdominal aortic operations using deep hypothermia and distal exsanguination

BACKGROUND: Operation of the descending and thoracoabdominal aorta may be affected by a significant perioperative morbidity, mainly because of ischemic damage of the spinal cord and malperfusion of the abdominal organs. METHODS: A comparative analysis was performed on two consecutive series of patients operated between 1982 and 1998. Group 1 consisted of 90 patients operated with moderate hypothermic left heart bypass. Group 2 included 38 patients operated using deep hypothermic cardiopulmonary bypass and a period of circulatory arrest while performing the proximal anastomosis and distal exsanguination during confection of the distal anastomosis. RESULTS: Main demographic factors and causes of the aortic disease were similar in both groups. Early mortality was significantly higher in the group of patients with aortic cross-clamping (15 of 90, 16%) than in those operated with circulatory arrest (2 of 38, 5.2%), p < 0.001. Paraplegia occurred in 8 patients in the group operated with mild hypothermia (8.8%) but in only 1 patient (2.6%) when deep hypothermia had been used. CONCLUSIONS: In our experience, deep hypothermia combined with distal exsanguination significantly improved the early postoperative outcome after operation of the descending and thoracoabdominal aorta. This technique allowed easy confection of proximal and distal anastomoses, and the duration of the operation was not prolonged significantly through this approach.     

Open stent-grafting for aortic arch aneurysm is associated with increased risk of paraplegia

BACKGROUND: Open surgery using the endovascular stent-graft is a novel technique that lessens the invasiveness of surgery for the aortic arch. However, the outcome of this procedure remains uncertain. METHODS: Between November 1996 and July 2000, a total of 19 patients underwent open surgery using an endovascular stent-graft for thoracic aortic aneurysms. There were 15 men (78.9%) and 4 women (21.1%). Patient age ranged from 29 to 82 years (mean 69.3 years, median 74 years). Atherosclerotic thoracic aortic aneurysms were present in 17 patients (89.4%) and aortic dissection in 2 patients (10.5%). RESULTS: Two patients (10.5%) died in the hospital and 4 patients (21.1%) presented with paraplegia postoperatively. Among the 4 patients with postoperative paraplegia, 1 case was complicated with intraoperative aortic dissection. The other 3 patients with paraplegia had spinal cord ischemic time of more than 60 minutes and intraoperative body weight gain of more than 4 kg. Of these 3 patients, hemodynamic instability after cardiopulmonary bypass was observed in 1 patient and cholesterin embolus in the anterior spinal artery was found at autopsy in another. On univariate analysis, age greater than 75 years was the only risk factor associated with paraplegia (p < 0.05). Autopsy findings for the 2 patients showed that the Adamkiewicz arteries were not blocked by the stent-graft in either patient. CONCLUSIONS: Intraoperative aortic dissection, embolization of the intercostal arteries, long ischemic time of the spinal cord, and excessive weight gain during operation may have been associated with the high incidence of paraplegia after open surgery using the endovascular stent-graft.     

Spinal cord monitoring: somatosensory- and motor-evoked potentials.

Monitoring myogenic motor EPs after transcranial electrical stimulation is effective in detecting spinal cord ischemia. During thoracoabdominal aortic aneurysm surgery, this technique is sufficiently rapid to allow timely interventions aimed at correcting ischemic conditions and preserving spinal cord blood flow. If strategies are applied to protect the spinal cord during thoracoabdominal aortic aneurysm repair (e.g., distal bypass, cerebrospinal fluid drainage, reattachment of segmental arteries), motor EP monitoring should be included in this protocol to improve neurologic outcome further. Although SSEPs provide information regarding the adequacy of spinal cord blood flow, monitoring SSEPs during thoracoabdominal aortic aneurysm repair has serious limitations. The response time is too slow to be of practical use. SSEPs also do not provide information regarding anterior horn motor function and supply, whereas the motor neurons in the anterior horn are most likely to sustain ischemic injury.     

Prevention of spinal cord injury after cross-clamping of the thoracic aorta

Paraplegia has been a devastating and unpredictable complication following surgical procedures involving temporary occlusion of the thoracic aorta. This study was undertaken to determine the effect of the pressure gradient between the aortic pressure distal to the occluding aortic clamp and cerebrospinal fluid pressure, defined as “Relative spinal cord perfusion pressure” (RSPP) on the development of the ischemic spinal cord injury. In twelve mongrel dogs, the thoracic aorta just distal to the left subclavian artery was cross-clamped. Somatosensory evoked potentials (SEP) were generated by peripheral stimulation of the bilateral peroneal nerves. After complete loss of SEP was evident, six dogs, Group 1, were subjected to occlusion of the descending thoracic aorta for a period of 20 minutes with maintenance of 0 mmHg of RSPP, by an injection of normal saline into the subarachnoid space. Six other dogs, Group 2, likewise underwent 40 minutes of aortic occlusion, keeping the RSPP at 15 mmHg by withdrawal ofcerebrospinal fluid. All the dogs in Group 1 developed paraplegia, whereas all the dogs in Group 2 demonstrated complete postoperative recovery without any neurological sequelae. Thus, RSPP is a most important factor in the development of the ischemic spinal cord injury during the temporary thoracic aortic occlusion.     

Transcranial motor-evoked potentials monitoring can detect spinal cord ischemia more rapidly than spinal cord-evoked potentials monitoring during aortic occlusion in rats

In this study, we evaluated the efficacy of transcranial motor-evoked potentials (tc-MEPs), compared with segmental spinal cord-evoked potentials (SCEPs), for detecting spinal cord ischemia (SCI) and assessed the relationship between neurological outcome and tc-MEPs or SCEPs in the rat aortic occlusion model. In the rats, SCI was induced by aortic occlusion for 10 min with a balloon catheter. At first, tc-MEPs (Group A: n = 6) or segmental SCEPs (Group B: n = 6) was recorded during SCI. Second, in using the quantal bioassay for the relationship between an interval of aortic occlusion and the probability of positive response in tc-MEPs or segmental SCEPs, the P50_MEP and P50_SCEP which represent the interval of aortic occlusion associated with 50% probability of assessment of ischemic spinal cord dysfunction by tc-MEP and SCEP were analyzed. The amplitude of tc-MEPs decreased significantly at 30 s and disappeared completely at 2 min after aortic occlusion. In Group B, it took about 6 min after aortic occlusion to diminish SCEP signal amplitude by approximately 50%. P50_MEP obtained in the quantal analysis was 0.3 ± 0.1 min. P50_SCEP was calculated as 6.2 ± 0.5 min that was significantly (P < 0.01) longer than P50_MEP. Our data indicated that tc-MEP monitoring could detect the onset of SCI so rapidly in comparison with segmental SCEP monitoring, which could provide therapeutic windows in a surgical approach that includes spinal cord protection.     

Spinal cord stimulation evoked potentials during thoracoabdominal aortic aneurysm surgery.

Although monitoring of somatosensory evoked potentials elicited from stimulation of lower extremity peripheral nerves has been suggested as a method for assessing neural function during thoracoabdominal aortic aneurysm surgery, this technique has been reported to yield a large number of false positives. It was believed that direct stimulation of the spinal cord would eliminate some of the problems associated with peripheral evoked potentials. The present study compared in 18 patients the use of scalp recorded evoked potential following stimulation of either the posterior tibial nerve via percutaneous needles or the spinal cord via an epidural electrode previously placed fluoroscopically. In 10 patients in whom distal bypass or shunt was not used, peripheral evoked potentials totally disappeared within 5-30 min of aortic clamping. Spinal cord stimulation evoked potentials disappeared permanently in 2 patients shortly after aortic cross-clamping; 1 died shortly after the procedure, and the other awoke densely paraplegic and died the next day. When distal perfusion was maintained by shunt or bypass, the disappearance of both peripheral and spinal evoked potentials accurately predicted the neurologic outcome of 1 paralyzed patient. Loss of spinal cord stimulation evoked potentials was found to be correlated with adverse neurologic outcome. Over the period of aortic clamping a gradual decrease in mean amplitude (50% at 45 min [P less than 0.05]) and a 20% increase in mean latency time were observed. Maintenance of adequate distal perfusion may permit the use of peripheral evoked potentials in the assessment of spinal cord ischemia during aortic cross-clamping.(ABSTRACT TRUNCATED AT 250 WORDS)     

Intrathecal papaverine for the prevention of paraplegia after operation on the thoracic or thoracoabdominal aorta

Eleven patients undergoing operation on the descending or thoracoabdominal aorta were administered papaverine intrathecally in an attempt to protect the spinal cord from ischemic damage. Concurrently, 19 patients, also undergoing operation on the thoracic or thoracoabdominal aorta, were operated on with a variety of conventional techniques, including distal aortic perfusion, but were not given intrathecal papaverine. No signs of early neurologic injury developed in any of the patients in the intrathecal papaverine group, although delayed paraparesis developed in one of the patients (9%; 70% confidence limits = 1% to 28%). On the other hand, eight of 19 patients undergoing operation with conventional techniques had either lower extremity paraparesis or paraplegia postoperatively (42%; 70% confidence limits = 29% to 57%; p = 0.058). Intrathecal papaverine appeared to provide spinal cord protection during thoracic aortic operations, particularly during prolonged periods of aortic cross-clamping. Papaverine was not associated with increased risk and may be superior to other conventionally used modalities. We conclude that continued evaluation of this technique is justified.     

Aortic arch replacement for degenerative aneurysms: advances during the last decade

During the last decade, treatment paradigm for degenerative aortic arch aneurysms has been changed by a better understanding of the pathophysiology of brain complication and introduction of endovascular technologies. To avoid neurocognitive dysfunction, safe duration of deep hypothermic circulatory arrest is now considered <25 min, and retrograde cerebral perfusion became less frequently used. Selective cerebral perfusion (SCP) is not associated with neurocognitive decline unless profound hypothermia (<20 °C) is used, which may suggest profound hypothermic SCP is not advantageous but may be detrimental. Attempts have been made to use mild to moderate hypothermia during SCP, and safe duration of distal circulatory arrest seems <60 min at 28 °C to avoid ischemic spinal cord injury. Three-vessel perfusion seems advantageous to provide adequate brain and spinal cord protection. To avoid aortogenic brain atheroembolism in the high risk patients, we previously proposed the “isolation” technique, where SCP is established before systemic perfusion. This technique has subsequently been modified to use both axillary and left carotid arteries for systemic arterial return, so that aortogenic emboli may not enter the brain circulation. In the TEVAR (thoracic endovascular aortic repair) era, hybrid operations such as the frozen elephant trunk or TEVAR completion after the elephant trunk are increasingly performed for extensive or distal arch aneurysms. It should be noted, however, that the frozen elephant trunk operation for extensive aneurysms carries an increased risk of paraplegia, and for distal arch aneurysms its outcome is not better than that after the standard open repair in Japan.     

Prevention of spinal cord ischemia in surgery of choraco-abdominal aneurysms The Bio Medicus pump, the recording of somatosensory evoked potentials and the impact on surgical strategy

Over a 15-month period 14 consecutive patients underwent surgery for extensive thoracoabdominal aneurysms with a nonheparinized centrifugally pumped (Bio Medicus) bypass and somatosensory evoked potential (SEP) recording. Six patients had a femorofemoral and eight patients a left atrial-common femoral artery bypass. The study aimed to assess the contribution of this approach to the prevention of spinal cord ischemia and the impact of the approach on surgical strategy. All patients survived operation; the 30-day and hospital mortality was 21% (three patients). Two patients became paraplegic. No major cardiac and renal complications occurred. Distal aortic perfusion allowed staged cross-clamping of the aorta in five (35.7%) patients, resulting in a significant reduction in mean spinal cross-clamp time: 23.4 min versus a calculated time of 47.2 min in the same patients if distal aortic perfusion had not been used (p ≤ 0.002). In one patient surgical strategy was adjusted during cross-clamping in order to reattach a critical intercostal artery. SEP-derived information confirmed the appropriateness of the surgical strategy in all cases. Whether the spinal cord was protected by this perfusion remained unproven. No bypass-related complications occurred. Distal aortic perfusion and concomitant SEP monitoring offer an improvement of surgical strategy and safer surgery.     

Aneurysms of the descending thoracic aorta: Three hundred sixty-six consecutive cases resected without paraplegia

Purpose: The aim of this study was to present a 20-year experience with a single method of passive distal perfusion during descending thoracic aortic aneurysm resection.Method: Aortic repair with a Dacron graft interposition was performed for 366 consecutive aneurysms located between the left subclavian artery and the crux of the diaphragm. The extent of aorta resected in 335 patients (91.5%) represented one third or less of the aortic length. A 9 mm Gott shunt was cannulated proximally into the ascending aorta (235 cases), the aortic arch (60 cases), the descending aorta (68 cases), or the left ventricle (3 cases) and inserted distally into the descending aorta (232 cases), the femoral artery (127 cases), or the abdominal aorta (7 cases). Shunt flows were recorded in 91 cases and varied from 1100 ml to 4900 ml/min, (mean 2526 ml/min). Distal pressure during shunting was measured in 62 patients. It varied from 15 to 120 mm Hg (mean 64.5 mm Hg). The aortic cross-clamp time varied from 8 to 124 minutes (mean 30 minutes).Results: The hospital death rate was 12% overall and 9.9% (35/351) if ruptured aneurysms are excluded. Among 359 operating room survivors, neither immediate nor delayed ischemic spinal cord deficit occurred. Transient renal dysfunction occurred in nine patients (2.4%) and kidney failure in one (0.2%). Five deaths (1.3%) were shunt related.Conclusion: Distal perfusion with the 9 mm Gott shunt has proven to be an effective method to preserve spinal cord function. The limited extent of aorta resected and the brief aortic cross-clamp time may also be interactive factors of protection. (J VASC SURG 1995;21:385-91.)     

Prevention and detection of spinal cord injury during thoracic and thoracoabdominal aortic repairs

BACKGROUND: Spinal cord injury is a most dreaded and unpredictable complication. In this study, based on our experimental results in dogs and early clinical results, we reviewed the incidence of paraplegia and the detection of spinal cord injury. METHODS: Eighty-two patients who underwent elective surgical repair of the descending thoracic and thoracoabdominal aorta over 17 years were subjects for this study. Sixty-two patients were male and 20 were female. Their mean age was 61.6 years (range, 17 to 81 years). Monitoring somatosensory evoked potentials (SEP) and measurement of mean distal aortic pressure and cerebrospinal fluid pressure were performed perioperatively. RESULTS: Sixty patients had no ischemic change in SEP. In 17 patients with significant ischemic changes of SEP, SEP recovered by increasing spinal cord perfusion pressure to more than 40 mm Hg. Two patients with complete loss of SEP experienced paraplegia. One patient had delayed paraplegia. CONCLUSIONS: These results strongly suggest that SEP, mean distal aortic pressure, cerebrospinal fluid pressure should be monitored during aortic cross-clamping. Maintaining spinal cord perfusion pressure at more than 40 mm Hg by increasing mean distal aortic pressure or withdrawal of cerebrospinal fluid is valuable for preventing paraplegia.     

Thoracoabdominal aneurysm surgery and the risk of paraplegia: contemporary practice and future directions

Thoracoabdominal aneurysm surgery is associated with a high incidence of morbidity and mortality. Spinal cord ischemia and the risks of paraparesis or paraplegia remain devastating complications. The mechanisms of spinal cord injury involve both acute ischemic injury and delayed reperfusion injury. Blood flow to the spinal cord frequently arises in the segment of the aorta requiring aortic cross clamping. As such, there is an obligate period of blood flow disruption. Multiple strategies have evolved to reduce the ischemic interval and to provide adjunct interventions to reduce the impact of the ischemia. Despite a multidisciplinary approach, a spinal cord ischemia is present in approximately 4 to 16% of patients, depending on the type of aneurysm and other comorbid diseases. Cerebral spinal fluid drainage, distal perfusion techniques, intercostal artery anastomosis, hypothermia techniques, and mechanisms of ischemic preconditioning are interventions employed to reduce the risk of paraplegia after thoracal-abdominal aortic surgery. Surgeons, anesthesiologists, and perfusionist are intimately involved in the decision making as to which interventions will be employed in a given case. Although these adjuncts have been evaluated in multiple animal and human protocols, the efficacy of each intervention when looked at in isolation remains difficult to determine fully. This is attributable, in part, to the complex mechanisms of the patient injury, the inherint risks of the surgical procedure, and the confounding effects of comorbid disease states. Nonetheless, clinicians must have comprehensive understanding of these various interventions and their application. This review serves as an overview of these various interventions with special emphasis on outcome data.     

Single-clamp technique for aneurysms of the descending thoracic aorta: report of 132 consecutive cases.

OBJECTIVE: To determine the efficacy of a single-clamp technique in preventing spinal cord ischemia during repair of aneurysms of the descending thoracic aorta. PATIENTS AND METHODS: From January 1989 to May 1999, 132 consecutive patients (91 men and 41 women, aged 31-86 years), with aneurysms of the descending thoracic aorta underwent repair using a single-clamp technique and temporary partial distal exsanguination. The diseased aortic segment was replaced with a Dacron graft. Blood was re-infused from an auto-transfusion device, and the segmental vessels were over-sewn but not implanted into the graft. RESULTS: The average aortic cross-clamp time was 26.4 min (range, 11-67 min) for the overall group and 37.4 min for patients who had spinal cord complications. An average of 2066 ml of blood was auto-transfused (range, 450-6100 ml). During the first 30 postoperative days, 17 patients (12.9 %) died. Eleven patients (8.3%) had spinal cord dysfunction, six patients (4.5%) had lower-extremity paraparesis, and five patients (3.8%) had paraplegia. Nine patients (6.8%) had renal failure necessitating hemodialysis. Other complications included bleeding in 15 cases (11.4%), respiratory failure in 12 cases (9.1%), wound-related sequelae in five cases (3.8%), distal embolism in five cases (3.8%), and bowel ischemia in two cases (1.5%). CONCLUSION: The single-clamp technique yielded an acceptable complication rate, and the mortality was comparable to that seen after the use of more complex methods. For satisfactory results, the cross-clamp time should not exceed 30 min.     

Direct measurements of oxygen tension on the spinal cord surface of pigs after occlusion of the descending aorta

Spinal cord injury is the most dreaded complication of operative procedures on the descending aorta. Our previous experimental study on pigs indicated that an increase in the cerebrospinal fluid pressure after aortic cross-clamping did not influence the occurrence of spinal cord injury. We therefore concluded that the cause of spinal cord injury after aortic cross-clamping is due to primary oxygen deficiency in the spinal cord distal to the occlusion site, especially in the area supplied by the artery of Adamkiewicz. The aim of the present study is to examine the primary ischemic cause of spinal cord injury after aortic cross-clamping by directly measuring the oxygen tension on the spinal cord surface in pigs. During the occlusion phase, oxygen tension decreased significantly distal to the clamping site and especially in the areas supplied by the artery of Adamkiewicz both after occlusion of the high thoracic (Group I) and the lumbar aorta (Group II). The marked decrease in oxygen tension proves that hypoxia is the primary reason for spinal cord injury. The presence of a "steal phenomenon" should be discussed.