Preliminary report of localization of spinal cord blood supply by hydrogen during aortic operations

Our experience with 1000 recent thoracoabdominal aneurysm repairs, including endovascular stenting

OBJECTIVE

Managing patients with thoracoabdominal aneurysms is demanding yet fascinating, and requires a team effort. This invited talk presents lessons learned as our history with open and endovascular procedures evolved for 2578 descending and thoracoabdominal repairs over the past 20 years.

METHODS

Beginning in 1985 with an analysis of 596 traumatic aortic ruptures and the risk of spinal cord ischemia, the evolution of research and procedures for thoracoabdominal aneurysms progressed. The focus of these studies, medication trials, and procedure adjustments was on lowering the risk of spinal cord ischemia.

RESULTS

Between January 2002 and December 2021, 2578 aneurysm repairs were performed. The respective mortality rates were 6.8% and 4.0% for all patients treated. The permanent spinal cord ischemia rates were 1.3% for open descending thoracic aortas and 4.9% for open thoracoabdominal aneurysms. A detailed analysis of open and thoracoabdominal repairs showed better long-term outcomes with open repairs.

CONCLUSIONS

Through multiple randomized trials and innovations with procedures and techniques, the risk of death and spinal cord ischemia have been reduced. Long-term survival has also been improved. The pursuit of reducing the risks of descending and ascending thoracoabdominal repairs is a fascinating endeavor that has resulted in better patient outcomes. Nevertheless, this is a journey, and there will always be more room to achieve even better results.

Extent II Thoracoabdominal Aortic Aneurysm Repair: How I Do It

The primary risks associated with thoracoabdominal aortic aneurysm (TAAA) repair-namely operative death, paraplegia, and renal failure necessitating dialysis-are commonly related to the distal ischemia that occurs during aortic clamping and the disruption of vital branching arteries. Our technique for open TAAA repair has evolved over the course of 3 decades, from the unheparinized, simple "clamp-and-sew" approach learned directly from E. Stanley Crawford himself to a contemporary, multimodal strategy that uses an array of surgical adjuncts. Today, our approach to TAAA repair is largely standardized and based on the Crawford extents of TAAA repair, but we have maintained flexibility to explore new techniques and to adapt to the specific needs of patients. To protect the spinal cord, we routinely use mild passive hypothermia, cerebrospinal fluid drainage, left heart bypass, and reimplantation of crucial intercostal or lumbar arteries. The renal arteries are perfused with cold solution to protect the kidneys from ischemic damage, and the celiac axis and superior mesenteric artery are perfused with isothermic blood from the left heart bypass circuit, which minimizes the duration of abdominal-organ ischemia. The most extensive repair, Crawford extent II repair, typically replaces the aorta from just beyond the left subclavian artery to the aortic bifurcation; unsurprisingly, it commonly poses greater operative risk than do less extensive TAAA repairs (extent I, III, and IV). Subsequently, most surgical adjuncts used today were developed to ameliorate risk in extent II repair. Here, we provide a detailed description of our approach to open extent II TAAA repair.

In vivo NIRS monitoring in pig Spinal Cord tissues

Little is known about the processes occurring after Spinal Cord damage. Whether permanent or recoverable, those processes have not been precisely characterized because their mechanism is complex and information on the functioning of this organ are partial. This study demonstrates the feasibility of Spinal Cord activity monitoring using Near Infra-Red Spectroscopy in a pig animal model. This animal has been chosen because of its comparable size and its similarities with humans. In the first step, optical characterization of the Spinal Cord tissues was performed in different conditions using a spectrophotometer. Optical Density was evaluated between 3.5 and 6.5 in the [500; 950] nm range. Secondly, adapted light sources with custom probes were used to observe autonomic functions in the spine. Results on the measured haemodynamics at rest and under stimulation show in real time the impact of a global stimulus on a local section of the Spinal Cord. The photoplethysmogram signal of the Spinal Cord showed low AC-to-DC ratio (below to 1 %).

Anatomy of Spinal Cord Blood Supply in the Pig

BACKGROUND

In a species as popular in research as the pig, little information is available concerning the blood supply and vascular anatomy of the spinal cord and comparability to humans.

METHODS

To visualize vessels contributing to the blood supply of the spinal cord, x-ray digital subtraction angiography and vascular casting by injection of a polymerizing solution of methylmethacrylate were used.

RESULTS

The pig has larger internal thoracic arteries and subscapular arteries than the human, providing extensive collateral flow to the lower body, which offers blood supply to the spinal cord through the collaterals. The pig has a fine-caliber vessel plexus providing blood to the neck area, from which flow will reach both the spinal cord and the base of the brain. The segmental thoracic and lumbar arteries are relatively small in pigs, and they almost all originate as a single branch from the aorta and divide after 3 to 4 mm. The segmental vessels show a clear diminution after 2 to 3 cm at the level of the vertebral bodies. Pigs show major differences in the anatomy of the aortic bifurcation compared with humans. The median sacral artery in pigs is a large-caliber vessel, of a size almost comparable to the common iliac artery, with an isolated single dorsal branch leading to the spinal cord.

CONCLUSIONS

Documenting the anatomic differences in spinal cord blood supply between pigs and humans will aid in the planning of future experimental studies and in determining the clinical relevance of such studies.

Paralysis after aortic surgery: In search of lost cord function

During the early 1980s, the rate of paralysis after aortic surgery was as high as 41% in patients for the most complex thoracoabdominal aortic operations. After comparing human and chacma baboon (papio ursinus) spinal cord vascular anatomy, an animal model was established to study the pathophysiology of aortic cross-clamping and the aetiology of the paralysis. Techniques, including motor evoked responses for monitoring spinal cord function, were developed that were tried in humans and later culminated in prospective and randomized studies. These established that the following were protective: combining cerebrospinal fluid with intrathecal papaverine; cooling systemically to moderate or profound hypothermia; minimizing intercostal ischaemia time; using a sequential segmental repair approach; re-attaching all patent and segmental intercostal arteries below T8 for descending thoracic aortic repair and from T6 to L2 for thoracoabdominal repairs; continuing cerebrospinal fluid drainage for at least two days and maintaining patients hypertensive after surgery. The net result has been that, in two of our recent series, the risk of permanent paralysis has been reduced to between 3.1% and 3.8%.

Complications of major aortic and lower extremity vascular surgery

Atheromatous disease and invasive intervention of the aortoiliac and distal arteries are common. Morbidity and mortality have been reduced through understanding and management of patient risk factors. Complications of this form of treatment affect all organ systems; mortality is most frequently caused by a cardiovascular complication (eg, myocardial infarction). Infection, leading to aortoenteric fistula is a dreaded complication, and paraplegia, though rare, is a devastating outcome. Multiorgan failure and death may result from a systemic inflammatory response syndrome. Vascular surgery for infrainguinal disease also has a significant cardiovascular complication rate. Resulting complications may affect all organs; loss of an extremity may occur. The first part of this article reviews perioperative and postoperative complications of open aortic repair and lower-extremity revascularization and addresses the issue of regional anesthesia for major vascular surgery. The second part reviews endovascular aortic repair (EVAR). EVAR is a new intervention that combines surgery and radiology. Complications of EVAR are similar to open repair, but early results suggest they may be less frequent. New technology leads to new complications; endoleaks, migration of the endoprosthesis, and surgical conversion are unique to EVAR. The benefits of EVAR may be less blood loss, shorter hospitalization, and less cardiovascular stress; the risks may be aneurysm recurrence, prolonged surveillance and repeated secondary procedures. The development of EVAR, the complications, and the anesthesia-related concerns of EVAR, including its use in management of acute abdominal aortic aneurysm are reviewed.

Prevention of postoperative paraplegia during thoracoabdominal aortic surgery1This article has been selected for the open discussion forum on the CTSNet Web site: http://www.ctsnet.org/discuss1

BACKGROUND

We present data showing the impact of sequential multisegmental aortic clamping accompanied by reimplantation of as many segmental arteries as possible on the prevention of postoperative paraplegia or paraparesis during thoracoabdominal aortic graft replacement.

METHODS

Since 1987 we have performed graft replacements in 51 individuals undergoing thoracoabdominal aortic surgery using the technique of normothermic partial bypass with sequential multisegmental aortic clamping. The procedure was performed emergently in 10 patients and electively in 41 patients. The patients ranged in age from 22 to 82 years (mean, 57.6 +/- 13.8 years). Indications for surgery included dissecting thoracoabdominal aortic aneurysm (n = 19) and nondissecting thoracoabdominal aortic aneurysm (n = 32). The extent of aneurysm was Crawford type I in 19 patients, type II in 7 patients, type III in 12 patients, and type IV in 13 patients. Along the entire extent of aneurysm to be replaced, we reimplanted as many of the patent segmental arteries as feasible.

RESULTS

Five patients died during hospitalization, for an in-hospital mortality rate of 9.8%. The number of aortic clampings per patient ranged from one to five (median, three). A total of 124 segmental arteries were reimplanted in 44 (86.3%) of 51 patients. Of the 124 arteries, 90 (72.6%) were distributed between T9 and L2. Postoperative paraplegia or paraparesis did not develop in any of the patients.

CONCLUSIONS

Our results demonstrate that extensive reimplantation of segmental arteries using sequential multisegmental aortic clamping, accompanied by adequate intraoperative distal aortic perfusion, is effective in preventing spinal cord ischemia.

Ischemic spinal cord syndrome after transthoracic esophagectomy: two cases of a rare neurologic complication

Anterior spinal artery syndrome (ASAS) is a rare complication after surgery of the thoracic or abdominal aorta. The sulco commissuralis syndrome represents a partial or incomplete ASAS. We report two cases of ischemic spinal cord syndromes after transthoracic esophagectomy. This represents a prevalence of this syndrome of 0.2% in more than 1000 consecutive esophagectomies performed at our institution. Patient 1 developed an ASAS on the first day after esophagectomy. Patient 2 showed the pathognomonic clinical signs associated with sulco commissuralis syndrome after an asymptomatic window. In both patients, the extent of the neurologic symptoms initially improved but then remained unchanged for the rest of the follow-up of 9 and 12 months. Although the prognosis of neurologic syndromes resulting from spinal cord infarction is poor, preoperative tests to identify patients at risk appear not to be justified because of the very low incidence of these syndromes after esophagectomy and the poor sensitivity and specificity of currently available diagnostic modalities. However, the possibility of ischemic spinal cord syndrome should be kept in mind when patients present with neurologic symptoms after esophagectomy.

Acute thoracoabdominal aortic dissection presenting as painless, transient paralysis of the lower extremities: a case report

Acute dissection of the aorta can be one of the most dramatic of cardiovascular emergencies. Its symptoms can occur abruptly and progress rapidly. Prompt recognition and appropriate intervention is crucial. However, not all aortic dissections present with classic symptoms of abrupt chest, back, or abdominal pain, and the diagnosis may be missed. A 63-year-old woman presented with transient loss of lower extremity motor and sensory function as the only symptom of an acute thoracoabdominal aortic dissection. Aortic dissection presenting as a transient neurologic syndrome is quite unusual. The sudden onset of weakness and parasthesia can result from the interruption of blood flow to the spinal cord. These symptoms of acute spinal cord ischemia, suggestive of a serious cardiovascular event, must be recognized and thoroughly investigated.

A new method of intrathecal PO2, PCO2, and pH measurements for continuous monitoring of spinal cord ischemia during thoracic aortic clamping in pigs

BACKGROUND

Impaired spinal cord circulation during thoracic aortic clamping may result in paraplegia. Reliable and fast responding methods for intraoperative monitoring are needed to facilitate the evaluation of protective measures and efficiency of revascularization.

METHODS

In 11 pigs, a multiparameter PO2, PCO2, and pH sensor (Paratrend 7, Biomedical Sensors Ltd, United Kingdom) was introduced into the intrathecal space for continuous monitoring of cerebrospinal fluid (CSF) oxygenation during thoracic aortic cross-clamping (AXC) distal to the left subclavian artery. A laser-Doppler probe was inserted into the epidural space for simultaneous measurements of spinal cord flux. Registrations were made before and 30 minutes after clamping and 30 and 60 minutes after declamping. The same measuring points were used for systemic hemodynamic and metabolic data acquisition.

RESULTS

The mean CSF PO2 readings of 41 mm Hg (5.5 kPa) at baseline decreased within 3 minutes to 5 mm Hg (0.7 kPa) during AXC (P < .01). Spinal cord flux measurement responded immediately in the same way to AXC. Both methods indicated normalization of circulation during declamping. Significant (P < .01) changes were also observed in the CSF metabolic parameters PCO2 and pH.

CONCLUSIONS

In this experimental model of spinal ischemia by AXC, online monitoring of intrathecal PO2, PCO2, and pH showed significant changes and correlated well with epidural laser-Doppler flowmetry (P < .01).

Influence of segmental spinal cord perfusion on intrathecal oxygen tension during experimental thoracic aortic crossclamping

PURPOSE

The purpose of this study was to evaluate the possibility of identifying alterations in blood supply to the spinal cord during thoracic aortic crossclamping.

METHODS

In 17 pigs, a multiparameter PO(2), PCO(2,) and pH sensor was introduced into the intrathecal space for continuous monitoring of cerebrospinal fluid (CSF) oxygenation during aortic crossclamping. An epidural laser Doppler probe was used to measure spinal cord flux. After insertion of an aortic shunt from the left subclavian to the left iliac artery and interruption of the right subclavian and lumbar arteries (L2-L5), the thoracic aorta just distal to the left subclavian artery was clamped for 60 minutes. By placement of the distal aortic crossclamping below the level of L1 in group A (n = 9 animals), perfusion of only the abdominal visceral arteries was maintained. In group B (n = 8 animals), the distal aortic crossclamping was above the level of T12, and thus some spinal cord perfusion was maintained through the aortic shunt.

RESULTS

The significant decrease in CSF PO(2) was observed within 3 minutes after the placement of the proximal aortic crossclamping and was normalized in all animals after establishment of the shunt flow. In group A, distal aortic crossclamping caused a decrease in CSF PO(2) with at least 50% of the preclamping values within 3 minutes. The mean CSF PO(2) of 2.99 +/- 0.70 kPa at 60 minutes of distal aortic crossclamping in group B was significantly higher than in group A (0.11 +/- 0.11 kPa; P <. 001). In group A, PCO(2) measurements showed no significant changes in 3 minutes after distal aortic crossclamping but revealed significantly higher values at 30 and 60 minutes compared with group B. Spinal cord flux values showed similar changes as CSF PO(2) during the whole experiment in both groups.

CONCLUSION

In this experimental model of aortic crossclamping, continuous CSF oxygen tension monitoring allows rapid detection of alterations in spinal cord circulation.

Preliminary report on prediction of spinal cord ischemia in endovascular stent graft repair of thoracic aortic aneurysm by retrievable stent graft

OBJECTIVE

To predict spinal cord ischemia after endovascular stent graft repair of descending thoracic aortic aneurysms, temporary interruption of the intercostal arteries (including the aneurysm) was performed by placement of a novel retrievable stent graft (Retriever) in the aorta under evoked spinal cord potential monitoring.

METHODS

From February 1995 to October 1997, endovascular stent graft repair of descending thoracic aortic aneurysms was performed in 49 patients after informed consent was obtained. In 16 patients with aneurysms located in the middle and distal segment of the descending aorta, the Retriever was placed temporarily before stent graft deployment. The Retriever consisted of two units of self-expanding zigzag stents connected in tandem with stainless steel struts. Each strut was collected in a bundle fixed to a pushing rod, and the stent framework was lined with an expanded polytetrafluoroethylene sheet. The Retriever was delivered beyond the aneurysm through a sheath and was retracted into the sheath 20 minutes later. A stent graft for permanent use was deployed in patients whose predeployment test results with the Retriever were favorable. Evoked spinal cord potential was monitored throughout placement of the Retriever and stent grafting until the next day.

RESULTS

The Retriever was placed in 17 aneurysms in 16 patients. There were no changes in amplitude or latency of evoked spinal cord potential records obtained before or during Retriever placement. After withdrawal of the Retriever, all aneurysms were excluded from circulation immediately after permanent stent grafting. There were no changes in evoked spinal cord potential, nor were neurologic deficits seen after stent graft deployment in any patient.

CONCLUSIONS

These results suggest that predeployment testing with the Retriever under evoked spinal cord potential monitoring is promising as a predictor of spinal cord ischemia in candidates for stent graft repair of thoracic aortic aneurysms.

Intraoperative adjuncts of spinal cord protection

Immediate neurological deficits as a complication of aortic surgery occur as the direct result of hypoxia, related to the acute deprivation of spinal cord blood supply inflicted by prolonged aortic cross-clamping (AXC). The etiology of spinal cord ischemia constitutes a series of progressive interdependent events which include proximal hypertension, increase in cerebrospinal fluid pressure, perioperative hypotension, inadequate perfusion to critical intercostal or lumbar vessels, extent of aortic pathology and duration of AXC. Several intraoperative interventions and strategies, which address the multifactorial nature of cord injury, are presented by the authors. Of critical importance is the role of adequate distal aortic perfusion, with either left atrium-femoral artery (LA-FA) bypass or arterial-arterial passive shunts, to control both central hypertension, through proximal unloading, and hypotension distal to AXC. Equally crucial is the increase in CSF pressure, secondary to proximal hypertension, which acts antagonistically to distal aortic pressure in regulating spinal cord perfusion pressure (SCPP). Cerebrospinal fluid drainage (CSFD) reduces CSF pressure to offset SCPP to favor cord perfusion. Pharmacological agents, such as papaverine and steroids in combination with CSFD, produce a synergistic benefit of extending the time interval of safe AXC. Encouraging results have also been realized with circulatory arrest and profound hypothermia which reduce oxygen demand of neural tissues and extend the safe duration of AXC interval. The use of distal bypass is most effective with CSFD as an integral component of a multimodality approach, which also incorporates the intraoperative monitoring of somatosensory evoked potentials (SSEP), to detect the onset of spinal cord ischemia and assess the adequacy of distal aortic perfusion and disposition of critical segmental vessels.

Management of segmental intercostal and lumbar arteries during descending and thoracoabdominal aneurysm repairs

The etiology of spinal cord injury after descending or thoracoabdominal operation is multifactorial. There are three major events that may cause the injury. This review addresses the second, namely the operative management of the segmental intercostal and lumbar arteries. However, failure to address any of the etiological events may result in injury, and thus a multimodal approach is required to prevent spinal cord injury.

Measurement of spinal cord blood flow by an inhalation method and intraarterial injection of hydrogen gas

PURPOSE

This study was performed to determine spinal cord blood flow using the H2 clearance method.

METHODS

In 12 dogs we measured blood flow determined by hydrogen clearance techniques (BF) in both gray and white matter by spinal cord puncture, and compared the results with BF measured by a catheter inserted intrathecally to avoid spinal cord injury. We studied direct intraarterial and intravenous injection of hydrogen in addition to the inhalation method because hydrogen is an explosive gas.

RESULTS

BF measured intrathecally with catheters adherent to either the ventral or the dorsal funiculus did not differ significantly from that of the gray matter. BF measured with a catheter inserted into the epidural space was about one fourth of the BF measured intrathecally. Values measured by the intraarterial injection method did not differ significantly from those obtained by the inhalation method.

CONCLUSIONS

BF measured with a catheter inserted intrathecally reflects blood flow in the gray matter of the spinal cord. Using intraarterial injection of H2, BF was safety and accurately measured while avoiding the risk of explosion.

Intraoperative identification of spinal cord blood supply during repairs of descending aorta and thoracoabdominal aorta

OBJECTIVE

The aim was to intraoperatively identify the spinal cord blood supply and shorten the aortic crossclamp time.

METHODS

A platinum electrode was placed intrathecally by lumbar puncture alongside the spinal cord. After the aorta was crossclamped, hydrogen in a saline solution was injected into the aorta and, if it was shown that the segment supplied the spinal cord and there were multiple arteries, then these were individually injected. The repair was performed by a sequential segmental method as described previously.

RESULTS

Postoperatively, highly selective angiography was used to confirm that reattached intercostal arteries supplied the spinal cord. The technique was accurate in all patients. Five spinal cord perfusion patterns were noted: (1) direct, (2) collateral, (3) no direct supply from segment tested, (4) from atriofemoral bypass, and (5) occluded reattached intercostals. When no response was obtained or no further testing was required (n = 8), testing time was 4.2 minutes and crossclamp time 41.9 minutes. When multiple segmental arteries required further testing, the mean testing time was 10.4 minutes and crossclamp time 58.5 minutes, including reattachment of intercostal vessels (p = not significant).

CONCLUSION

Preliminary findings indicate that this method is a safe research technique, can detect radicular arteries, and may reduce the time for aortic crossclamping if no vessels are identified as supplying the spinal cord.

The risk of ischemic spinal cord injury in patients undergoing graft replacement for thoracoabdominal aortic aneurysms

PURPOSE

We developed a monitoring system to detect spinal cord ischemia during aortic cross-clamping (AXC). This system was used to prospectively determine in which patients ischemia occurs, in which patients reimplantation of intercostal arteries is unnecessary or mandatory, and when reperfusion of intercostal arteries (ICAs) is urgent.

METHODS

Two hundred sixty patients underwent thoracoabdominal aortic aneurysm (TAA) repair with simple AXC. In 167 patients, two electrocatheters were placed before the onset of anaesthesia at level L1/L2 (stimulation) and level T5/T6 (recording) within the epidural space. During surgery, spinal cord function was monitored by recording spinal somatosensory evoked potentials (sSSEP). According to the extent of aortic replacement, most patients were expected to have a high risk of paraplegia.

RESULTS

In group A (59 patients), sSSEP remained normal throughout surgery, and in 54 of these patients ICAs were not reattached outside the proximal aortic anastomosis. In the other five patients ICAs were reimplanted separately because of possible anatomic relation to spinal cord blood supply. No patient in group A had postoperative neurologic deficit. In group B (54 patients) sSSEP remained normal until 15 minutes after AXC but were impaired thereafter. Nineteen patients had early reimplantation of ICAs. Of the 19, three had paraparesis and two had paraplegia. Neurologic deficit developed in the patients without early reimplantation of ICAs. In four patients separate reimplantation of ICAs was performed late in the procedure because of incomplete sSSEP recovery. Subsequently, the sSSEP returned to normal and only one of the four patients had mild paraparesis. The total rate of neurologic deficits in this group was 13% (paraplegia, 3.5%; paraparesis, 9.5%). All 54 patients in group C showed rapid loss of sSSEP within 15 minutes of AXC. In 28 patients ICAs were reimplanted only within the proximal anastomosis. Twenty-one of these patients showed prompt signal recovery after blood-flow release into the reimplanted ICAs, and none had neurologic deficit. Seven patients had no or very late and incomplete sSSEP recovery. Of the seven, three had paraplegia and four had paraparesis. In 26 patients ICAs were reimplanted separately to the proximal anastomosis. This was done early during the procedure in 17 patients, of whom 13 had full recovery of sSSEP and normal neurologic status. Four patients had incomplete or no recurrence of sSSEP, followed by paraplegia in one and paraparesis in three. In nine patients ICAs were reimplanted after the aortic replacement had been completed because of sSSEP recovery was not satisfactory. In all patients in this subgroup sSSEP returned to normal. Six patients had a normal neurologic status and three had mild paraparesis. The total neurologic complication rate in group C was 26% (paraplegia, 7.5%; paraparesis, 18.5%).

CONCLUSION

The risk of ischemic spinal cord injury during replacement for TAA can be assessed continuously by monitoring the sSSEP directly from the spinal cord. Patients without sSSEP changes during aortic reconstruction do not require ICA reattachment and will not have neurologic deficit. Patients who lose sSSEP after AXC are at risk for paraplegia. Patients with impairment or loss of sSSEP >15 minutes after AXC have some collateral vessels, and must have ICAs reimplanted only if sSSEP do not return within normal recovery time after blood-flow release into the proximal anastomosis. Loss of sSSEP within 15 minutes of AXC shows poor collateralization and mandates early restoration of spinal cord blood supply. If the surgeon can achieve the return of sSSEP to normal by subsequent separate reimplantation of ICAS, paraplegia will not occur and paraparesis will be rare and mild. Spinal cord monitoring is a valuable guide to detect whether the spinal cord is at risk and to take measures against par

A new technique using somatosensory evoked potential guidance during descending and thoracoabdominal aortic repairs

Recent work in our laboratory has demonstrated the effectiveness of somatosensory evoked potentials (SEPs) in identifying the critical intercostal arteries (CICAs) for preserving spinal cord integrity during simulated aortic aneurysm repairs in the pig. Further studies have also demonstrated increased preservation of neurological function during prolonged aortic clamping if CICAs are perfused until ligation or clipping, as opposed to transaortic identification of back-bleeding intercostals and their subsequent ligation. We have developed a technique of repair of descending thoracic and thoracoabdominal aortic aneurysms and dissections that uses these principles. Since January 1993, 26 patients have undergone repair of their aortas using this new technique and SEP directed intercostal artery ablation. There were 22 (85%) long-term survivors among 10 thoracoabdominal and 16 descending aortic repairs. All patients with uncorrected abnormal SEP recordings developed paralysis; one patient who required reimplantation of an intercostal artery island into the aortic graft had normal neurological function postoperatively. Paraplegia was seen in only one of the surviving patients, but this patient had normal intra- and postoperative SEPs (4% false negative). Our experience suggests that SEP-guided obliteration of intercostal arteries while maintaining perfusion may be a useful approach to the surgical repair of descending and thoracoabdominal aortic disease.

Influence of segmental arteries, extent, and atriofemoral bypass on postoperative paraplegia after thoracoabdominal aortic operations

PURPOSE

The purpose of this article was to study the influence of either reattachment or oversewing of patient segmental intercostal or lumbar arteries, extent of aneurysm, and atriofemoral bypass on the incidence of postoperative paraplegia/paraparesis in patients at high risk with type I or II thoracoabdominal aneurysms.

METHODS

Data were prospectively collected on 99 patients undergoing type I or II thoracoabdominal aneurysm repairs, including exact extent of repair and whether atriofemoral bypass ws used. Patency of intercostal arteries from T3 to T12 and lumbar arteries from L1 to L4 were checked by intraoperative inspection. If the arteries were patent, note was taken of whether they were reattached to the new aortic prosthesis. Postoperative neurologic motor function was graded daily for the first 5 days, and the worst score in the first 30 postoperative days (POD) was used for analysis.

RESULTS

Ninety-five of 99 (96%) patients were 30-day survivors. By POD 30, 31 of 98 (32%) patients had had a neurologic deficit. There was no difference in the incidence of deficits according to whether lumbar or intercostal arteries were reattached, ignoring the effect of patency of the arteries. Of greater importance, however, was whether patent segmental arteries were oversewn at specific levels. Thus, for patients who had one or more arteries at T11, T12, or L1 oversewn (often because they could not be reattached), a deficit developed in 11 of 23 (48%) patients versus 20 of 75 (27%) patients who did not have patent arteries or had all patient arteries reattached (p = 0.05, odds ratio = 2.5). More specifically, if all arteries at this level were oversewn, a neurologic deficit developed in 63% of patients versus 23% if all their arteries were reattached (p = 0.01). Reattachment of patent arteries at individual levels from T7 to L4 showed a trend toward a lower risk of deficits but did not reach statistical significance. On multivariate analysis, atriofemoral bypass was associated with a lower risk of paralysis (p = 0.068), and significantly so when controlled for age (p = 0.0329, odds ratio 0.287). Subgrouping of extent type I thoracoabdominal aneurysms resulted in an incidence of paralysis of 14% (3/22) for subgroup A and 23% (5 of 22) for subgroup B compared with 43% (23 of 55) for type II thoracoabdominal aneurysms (type I [8 of 44 18%], versus type II [p = 0.0097]).

CONCLUSION

Patients with no or few patent segmental arteries in the aortic segment being replaced have a lower risk of neurologic deficits, compared with those with patent arteries. Every effort should be made to reattach all arteries at T11, T12, and L1 and, when possible within the constraints of technical feasibility and time, also those from T7 to L4. Preoperative angiography or intraoperative hydrogen testing may better identify the arteries that need to be reattached. When feasible, atriofemoral bypass appears to be protective, particularly when sequential clamping and segmental repairs can be performed.

Prevention of paraplegia during thoracic aortic cross-clamping: importance of patent internal mammary arteries

PURPOSE

Unexplained anatomic and physiologic factors account for the unacceptably high rate of paraplegia/paresis after thoracoabdominal aortic reconstruction. We assessed the neurologic significance of patent internal mammary arteries (IMAs) in a novel rat model of aortic clamping in which the aortic origins of the intercostal arteries (ICAs) were occluded.

METHODS

Twenty anesthetized, intubated, and halothane-ventilated adult male rats had catheters placed in the carotid and femoral arteries. ICAs arising from the aorta were divided at their origins through a left thoracotomy. IMAs were either divided (IMA-OUT, n = 10) or left intact (IMA-IN, n = 10). Proximal and distal descending aortic clamps were placed for 7 minutes. A neurologic deficit score (NDS) was assigned at 1, 4, 18, 24, and 48 hours by use of an established scoring system.

RESULTS

The mean IMA-IN NDS was statistically better than the mean IMA-OUT NDS at 1, 4, 18, and 24 hours with p = 0.0005, 0.0014, 0.0098, and 0.0151, respectively. Moreover, the mortality rate in the IMA-OUT group was statistically greater than in the IMA-IN group (p = 0.0036).

CONCLUSION

In this model, patent IMAs prevent paraplegia when the ICAs are occluded at their aortic origin and the aorta is clamped for 7 minutes.

Spinal oxygenation, blood supply localization, cooling, and function with aortic clamping

Similar to other methods of organ preservation, "spinoplegia" may protect the spinal cord from the effects of oxygen desaturation during aortic cross-clamping. In porcine experiments, spinal cord O2 saturation was studied during intraoperative localization of the blood supply to the spinal cord using hydrogen; division of arteries not supplying the spinal cord; aortic cross-clamping for 60 minutes; and 60 minutes after unclamping. In 5 animals, 120 mL of cold saline solution with lidocaine (100 mg/dL) was infused into the aorta during aortic cross-clamping. During sequential localization, O2 saturation dropped by 40.02% (standard deviation, 20.16%) for T-14 artery testing versus a decrease of 17.27% (standard deviation, 11.88%; p = 0.0075) for L-5 artery segment testing in the control animals and returned to baseline thereafter. During aortic cross-clamping maximal O2 desaturation was 5% of baseline (15.7%; p less than 0.0001), which improved slightly by 30 minutes after clamping (48% of baseline +/- 37.37%; p = 0.048 versus maximum) and then returned to baseline (97.1% of baseline +/- 41%) with unclamping; 5 minutes later, hyperoxygenation occurred with a progressive decline thereafter (68% of baseline +/- 29.3%; p = 0.025, 45 minutes after unclamping versus baseline). The decrease in spinal motor evoked potentials was significantly less (p less than 0.02) in the treated group. Intraoperative hydrogen testing in 8 patients was demonstrated to be safe. It accurately localized reattached arteries, and O2 saturation of the spinal cord fell by 56% (standard deviation, 29%; p = 0.0025) with aortic cross-clamping. We conclude that spinal cord ischemia occurs with aortic cross-clamping in both animals and humans.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of exsanguination and sodium nitroprusside on compliance of the spinal canal during aortic occlusion

To evaluate the effects of sodium nitroprusside (SNP) and partial exsanguination (EXS) on systemic hemodynamics and cerebrospinal fluid dynamics, we monitored proximal and distal blood pressure (BP), cerebrospinal fluid pressure (CSFP), spinal cord perfusion pressure (SCPP), and compliance of the spinal canal (CSC) in 10 mongrel dogs during aortic cross-clamping of the descending thoracic aorta. CSC was measured by serial injections of 2 ml of saline solution into the cisterna cerebellomedullaris via a percutaneously placed catheter with simultaneous measurements of CSFP. Data were acquired at baseline (BL), during aortic cross-clamping with proximal hypertension (AXC), and after control of proximal hypertension with EXS and SNP. During the cross-clamp interval, mean proximal aortic pressure (PxBP) rose from 114 +/- 6 to 150 +/- 3 mm Hg (P less than 0.001), whereas mean blood pressure decreased to 88 +/- 5 and 82 +/- 4 mm Hg during the SNP and EXS intervals, respectively (P less than 0.05 vs BL). EXS and SNP were equally effective in controlling PxBP (82 +/- 4 vs 88 +/- 5 mm Hg, P greater than 0.05). Mean distal aortic pressure (DsBP) decreased from systemic values to 21.5 +/- 1.9 mm Hg during AXC, and to 12.4 +/- 1.0 and to 8 +/- 0.8 mm Hg during EXS and SNP, respectively (P less than 0.05 AXC vs EXS and SNP). SNP lowered DsBP significantly more than EXS, 8 +/- 0.8 vs 12.4 +/- 1.0 mm Hg (P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of preservation or perfusion of intraoperatively identified spinal cord blood supply on spinal motor evoked potentials and paraplegia after aortic surgery

Permanent ligation of arteries supplying blood to the spinal cord in operations for aortic aneurysm can lead to spinal cord ischemia, which can result in either paraparesis or paraplegia. This report describes a rapid method of intraoperative identification of those arteries that supply the spinal cord by use of an intrathecal platinum electrode to detect hydrogen in solution that has been injected into the aortic ostia. Preservation or perfusion of those identified arteries supplying the spinal cord may decrease the rate of postoperative neurologic complications. Of 28 porcine experiments with postoperative observation for 24 hours, there were 3 initial pilot experiments in which saline saturated with hydrogen was injected into the temporarily cross-clamped aorta. Twenty animals were then randomized to (1) preservation of only the vessels sequentially identified to supply blood to the spinal cord from T-13 to L-5 (n = 10); (2) division of the vessels supplying the spinal cord (n = 10). A further five animals underwent perfusion experiments wherein the identified cord arteries were perfused by a shunt, the other nonsupply arteries were divided, and the aorta was kept clamped for 45 minutes. Spinal motor evoked potentials were elicited with an intrathecal electrode and were highly sensitive for paralysis. Paralysis occurred in 0/3 pilot (p less than 0.013 vs division); 8/10 division; 1/10 preservation (p less than 0.0017 vs division); and perfusion 1/5 (p less than 0.025 vs division). Results of a pilot study in eight humans shows that the technique can be used to rapidly identify segmental arteries supplying the spinal cord, to determine if distal perfusion is supplying the spinal cord with blood flow, and if reattached segmental arteries are patent.