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Query: UMLS:C0022116 (ischemia)
 91,303 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The primary etiologic factor in the production of pressure sores is considered to be pressure-induced ischemia with the threshold being 35mmHg for 2 hours. However, clinical evidence indicates that skin can withstand normothermic ischemia of 8 to 12 hours without necrosis. A detailed review of the literature indicates that previous experimental models are few in number and limited in clinical relevance. Therefore, a continuously monitored computer-controlled electromechanical pressure applicator was designed to produce pressure sores over the greater femoral trochanter of normal and paraplegic swine. Examination of the pressure site at 1 week revealed 3 groups of lesions: 1) muscle damage only, 2) muscle and deep dermis damage, and 3) full-thickness damage extending from bone to skin. A critical pressure-duration curve for the production of pressure sores is presented for normal swine. Muscle damage occurred at high pressure-short duration (500mmHg, 4 hours), whereas skin destruction required high pressure-long duration (800mmHg, 8 hours). On analysis, muscle is more sensitive than skin to the effects of pressure, and the initial pathologic changes occur in muscle. Skin breakdown did not occur with a pressure of 200mmHg for 15 hours, thus contradicting previous statements that pressure exceeding 35mmHg for 2 hours would cause ischemia with subsequent tissue necrosis resulting in a pressure sore. We hypothesis that normal tissue is far more resistant to pressure-induced ischemia that previously considered, and that the pressure-duration threshold for the production of pressure sores is lowered dramatically following changes in the soft tissue coverage due to paraplegia, infection, or repeated trauma.
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PMID:Etiologic factors in pressure sores: an experimental model. 730 43

Operative therapy is generally advocated for the management of chronic traumatic pseudoaneurysms of the aorta. A potential complication of both thoracic and abdominal aortic aneurysmectomies is paraplegia secondary to infarction or ischemia of the spinal cord. The present report describes a patient with a traumatic aneurysm of the lower thoracic aorta immediately adjacent to the origin of the anterior spinal artery, both delineated angiographically. In this particular situation, it was elected to follow the patient because the aneurysm was asymptomatic, small, and chronic, and because the risk of spinal cord injury associated with aneurysmectomy was estimated to be high. Serial computerized tomography (CT) scanning was used as a means of measuring the exact aneurysm size. Operation will be recommended if the aneurysm produces symptoms or enlarges, as demonstrated by CT scans.
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PMID:Traumatic pseudoaneurysm of the thoracic aorta in close proximity to the anterior spinal artery: a therapeutic dilemma. 735 87

The purpose of this study was to determine the spinal cord metabolic state for 24 hours after compression trauma to the feline spinal cord. Cats were anesthetized with pentobarbital and injured by placing a 190-gm weight on the spinal cord for 5 minutes. Biochemical analysis of the injured segment revealed a significant depletion in the levels of adenosine triphosphate (ATP), phosphocreatine (P-creatine), and total adenylates for the entire 24-hour recovery period. Glucose levels initially declined, but by 1 hour had normalized, and at 8 and 24 hours were significantly supranormal. The lactate/pyruvate ratio and tissue lactate concentrations increased four and five and half times, respectively, for the first 4 hours after injury. Between 8 and 24 hours, lactate levels remained elevated, whereas the lactate/pyruvate ratio declined to contol levels as the result of a significant rise in the tissue pyruvate concentration. This sequence of metabolic changes suggested that metabolism was probably not homogeneous throughout the injured segment, and that tissue metabolic rate was depressed for the initial 4 hours after trauma then increased in metabolically active tissue for the remainder of the 24-hour recovery period. This model of spinal cord trauma results in a severe, prolonged ischemia and metabolic injury to the affected tissue. Whether these metabolic changes results from or cause the tissue damage and irreversible paraplegia associated with this type of spinal cord injury remains to be determined.
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PMID:Spinal cord energy metabolism following compression trauma to the feline spinal cord. 742 Jan 53

Encouraged by reports on the safety of simple aortic cross-clamping for resection of descending aortic aneurysm, we began utilizing this technique more liberally in 1976. This study was undertaken to examine the results of operation in 36 patients, equally divided into two distinct groups. In Group 1, either extracorporeal circulation or indwelling temporary shunts were employed during the period of aortic occlusion. In Group 2, simple aortic cross-clamping was utilized to manage the lesion. No adjuncts were used to avoid ischemia in the latter group. The only 2 early deaths and two instances of paraplegia occurred in Group 1. In general, there were fewer complications in Group 2, with approximately two-thirds of the patients experiencing an uneventful postoperative course. These differences are considered important since the two groups were similar in respect to the extent and nature of the lesions and other factors contributing to operative risk.
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PMID:Descending aortic aneurysmectomy without adjuncts to avoid ischemia. 742 12

Recent studies have suggested that oxygen-derived free radicals play an important role in ischemia-reperfusion injury of the spinal cord. In other organ systems, reperfusion injury has been reduced by limiting the availability of oxygen in the reperfusion phase. The purpose of this study was to test the effect of normovolemic hemodilution and gradual reperfusion on spinal cord function after aortic cross-clamping in 84 New Zealand White rabbits. All animals underwent 21 min of infrarenal aortic cross-clamping in the conscious state by means of a previously placed aortic occlusion device and were randomized to four groups. Group 1 animals were hemodiluted to a mean (s.e.m.) hematocrit of 28(2)% by extracting 25% of the effective blood volume and reinfusing the plasma component after centrifugation concurrently with a volume of normal saline three times that of the discarded red cells. Group 2 animals (controls) were bled similarly but both plasma and red cells were reinfused, resulting in a mean (s.e.m.) hematocrit of 38(2)%. In the next two groups, distal aortic flow was recorded via an implantable Doppler device. After cross-clamping, flow was returned gradually over 45 min in animals of group 3, and abruptly in group 4. Animals were observed for 5 days and neurologic function was graded by an independent observer. Paraplegia at 5 h after clamping occurred in 75% of animals in group 1 versus 32% in group 2 (P < 0.05), and in 33% of group 3 versus 28% in group 4 (not significant). Of those animals showing initial neurologic recovery, delayed-onset paraplegia was seen in 100% in group 1 versus 87% in group 4 (not significant), and in 50% of group 3 versus 92% of group 4 (P < 0.03).(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Ischemia-reperfusion injury of the spinal cord: the influence of normovolemic hemodilution and gradual reperfusion. 758 94

Aortic replacement for thoraco-abdominal aneurysms remains a major challenge in vascular surgery. Related symptoms, maximal diameter > 6 cm, progression, aneurysm sac containing none or excentric thrombi and uncontrollable hypertension are factors in favour of surgery, if the general condition of the patient allows the operation. Patients with aneurysms < 5 cm maximal diameter, tube-size aneurysms, heavy calcification of the aortic wall, concentric thrombi within the aneurysmal sac and significant cardiopulmonary risks should be treated conservatively. Patients in good general condition with aneurysms around 5 cm maximal diameter should be controlled by computed tomography in 6 to 12 months intervals and in the case of progression surgery can be recommended despite missing symptoms. Crawford developed the 'graft-inclusion-technique', which combines the 'ingraft'-technique with reattachment of renal, visceral and segmental arteries. The 'clamp and repair' principle is used in patients with sufficient cardiac function. Otherwise shunt or left sided heart bypass are used to reduce cardiac afterload. According to the literature local cooling (flush perfusion), cytoprotective drugs and numerous methods to maintain or ameliorate distal aortic perfusion during clamping ischemia have been used in patients successfully for prevention of ischemic spinal complications. In physiological settings these methods may prove valuable, but under pathophysiological conditions of TAAA-repair one must doubt the efficacy, because the individual risk is difficult to assess. In our hands flush perfusion and cooling of the kidneys proved to be helpful. In animal experiments we have shown prolongation of ischemia tolerance time using eicosanoides to protect the kidneys and the spinal cord. If shunt or left-sided heart bypass can protect the spinal cord during clamping, is unknown, because the risk of paraplegia in the individual patient can be known only, if the function of the spinal cord is monitored. We have developed a spinal neuromonitoring system and found, that only one third of all TAAA-patients is at high risk to develop paraplegia during aortic clamping. The surgeon is guided by continuous recording of spinal evoked somatosensory potentials and can adapt the operative technique by early reimplantation and eventually subsequent separate reimplantation of segmental arteries supplying blood to the spinal cord, in order to reduce spinal ischemia time. Our results in 260 TAAA-patients are presented. In a high-risk population of patients with aneurysms type I-III (Crawford's classification) it was possible, to reduce the paraplegia rate from 7 to 3.5%, the risk of paraparesis from 15 to 6%, while the operative mortality was only reduced from 19 to 10%.
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PMID:[Surgical treatment of thoraco-abdominal aneurysm. Indications and results]. 758 56

We report 3 cases of dorsal ischemic myelopathy indicative of aneurysm of the abdominal aorta. In 2 cases the aneurysm was dissecting and in all patients medullary symptoms were preceded by sudden lumbar or abdominal pain. Neurological symptoms were slightly different in each case. One patient experienced 3 episodes of acute paraparesis and rapid regression evoking transitory medullary ischemic accidents (intermittent medullary claudication). Another patient suffered progressive asymmetric paraparesis which first stabilized and later improved partially after surgical treatment of the aneurysm. The third suffered acute paraplegia related to irreversible ischemia of the anterior 2/3 of the medulla. The great variety of clinical manifestations of spinal cord ischemia related to aneurysms of the descending aorta can be explained by the topography of the aneurysm, pecularities of medullary vascularization and, especially, by the diversity of etiopathogenetic mechanisms that give rise to ischemia. We conclude that in the face of symptoms suggesting dorsal ischemic myelopathy, the possibility that an aneurysm of the abdominal aorta may be the cause must be considered, whether or not pain has been experienced prior to signs of medullary involvement.
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PMID:[Spinal cord ischemia indicating aneurysm of the abdominal aorta. Report of three cases]. 761 38

Paraplegia or paraparesis caused by temporary cross-clamping of the aorta is a devastating sequela in patients after surgery of the thoracoabdominal aorta. No effective clinical method is available to protect the spinal cord from ischemic reperfusion injury. A small animal (rat) model of spinal cord ischemia is established to better understand the pathophysiological events and to evaluate potential treatments. Eighty-one male Sprague-Dawley rats weighing 300 g to 350 g were used for model development (45) and treatment evaluation (36). The heparinized and anesthetized rat was supported by a respirator following tracheostomy. The thoracic aorta was cannulated via the left carotid artery for post-clamping intra-aortic treatment solution administration. After thoracotomy, the aorta was freed and temporarily clamped just distal to the left subclavian artery and just proximal to the diaphragm for different time intervals: 0, 5, 10, 15, 20, 25, 30, 35, and 40 minutes (five animals per group). The motor function of the lower extremities postoperatively showed consistent impairment after 30 minutes clamping (5/5 rats were paralyzed), and this time interval was used for treatment evaluation. For each treatment, six animals per group were used, and direct local intra-aortic infusion of physiologic solution (2 mL) at different temperatures with or without buffer substances was given immediately after double cross-clamp to protect the ischemic spinal cord. Arterial blood (2 mL) was infused in the control group. The data indicate that the addition of HCO3-(20 mM) to the hypothermic (15 degrees C) solution offered complete protection of the spinal cord from ischemic injury.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Third place winner of the Conrad Jobst Award in the gold medal paper competition. Prevention of spinal cord dysfunction in a new model of spinal cord ischemia. 783 75

Paraplegia as a consequence of spinal cord ischemia associated with procedures on the thoracic and thoracoabdominal aorta has been linked to the interaction of proximal hypertension with elevated cerebrospinal fluid pressure (CSFP) during aortic cross-clamping (AXC). CSFP reduction via cerebrospinal fluid (CSF) drainage is thought to significantly prolong the cord's tolerance to AXC. Likewise, partial exsanguination is reported to effectively reduce ischemic injury by controlling proximal hypertension. To evaluate the individual and collective efficacy of both techniques, 18 mongrel dogs (25 to 35 kg), divided into three equal groups, underwent a fourth interspace left thoracotomy AXC. Baseline proximal arterial blood pressure (PABP), distal arterial blood pressure (DABP), and CSFP were established and monitored at 5-minute intervals during 120 minutes of AXC, and for 30 minutes thereafter. Group I animals were partially exsanguinated prior to AXC to maintain PABP at a mean of 115 to 120 mmHg. Group II animals had sufficient (16 +/- 5 cc) CSF withdrawn to maintain a DABP-CSFP gradient, i.e., spinal cord perfusion pressure (SCPP) of 20 mmHg. Group III animals were treated with both CSF drainage and partial exsanguination in the same manner as groups I and II, respectively. Perioperative somatosensory evoked potential (SEP) monitoring evaluated cord function. Postoperative neurological outcome was assessed with Tarlov's criteria. SEPs degenerated approximately 22 minutes following AXC for groups II and III. In contrast, group I exhibited rapid (10 +/- 7 min) SEP loss. All five surviving group I animals displayed paralysis 48 hours postoperatively.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Effect of cerebrospinal fluid drainage and/or partial exsanguination on tolerance to prolonged aortic cross-clamping. 784 43

Forty-three patients undergoing repair of a thoracoabdominal aortic aneurysm were monitored to evaluate spinal cord ischemia, as evidenced by somatosensory evoked potentials (SEPs). All patients were operated on using left heart bypass. In 34 patients (80%), staged clamping was used. Except for cerebrospinal fluid (CSF) drainage in 15 patients (35%), no other protective measures to preserve spinal cord function were used. The overall incidence of immediate onset paraplegia was 7%, and of immediate onset paraparesis was 5%; neither was limited only to those patients in whom potentials were lost. In 18 patients (42%), no change in the evoked potentials occurred; one of these patients (5%) awoke paraplegic after operation, and two others had a delayed onset paraplegia. In 13 patients (30%), evoked potentials were lost despite adequate perfusion; in 12 of them, potentials returned gradually, with one immediate paraplegia (8%), and in one potentials did not return at all, with subsequent immediate paraplegia (100%). In 12 patients (28%), evoked potentials decreased without being lost completely, and then recovered; in this group there were no immediate paraplegias. No relationship could be demonstrated between the extinction time, the recovery time, or the duration of loss of evoked potentials with postoperative neurological outcome. Intraoperative monitoring of SEPs is a good indicator of spinal cord ischemia, although we found a 5% incidence of false negatives. SEP monitoring offers an improvement in surgical strategy, and allows safer operations for thoracoabdominal aneurysms.
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PMID:Somatosensory evoked potentials during exclusion and reperfusion of critical aortic segments in thoracoabdominal aortic aneurysm surgery. 784 50


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