RESUMEN
The acute interruption of blood supply to the spinal cord during thoracic and thoracoabdominal aortic reconstructions, if unabated, inevitably causes neurological injury secondary to regional hypoxia. Techniques that address the multifactorial nature of spinal cord ischemic injury have evolved to preserve neuromotor function. However, the overall incongruity of the spinal cord's vascular anatomy makes it virtually impossible to predict, with any degree of certainty, the duration of aortic cross-clamping (AXC) that can safely be endured. The sensitivity of evoked potential monitoring to the disruption of spinal cord perfusion has led to the emergence of this modality as an effective tool at the surgeon's disposal for the intraoperative assessment of distal aortic perfusion and cord viability during proximal AXC. Somatosensory evoked potentials (SSEP) provide invaluable diagnostic data as to the status of cord function, through the continuous appraisal of signal amplitude and latency. A latency increase, as small as 10% of the pre-AXC value, is linked to a reduction of spinal cord perfusion pressure and thereby associated with a high incidence of neurological impairment. Four discrete types of SSEP responses have been identified to represent differing surgical scenarios during AXC. The Type I response (deterioration of SSEP within 3 to 5 minutes) is indicative of a failure to maintain a distal pressure of at least 60 mm Hg, whereas a Type II signifies adequate distal aortic perfusion. Sudden loss of signal as witnessed in a Type III SSEP implies compromised critical intercostal vessels and indicates their expeditious reimplantation. A gradual (30 to 50 minutes) SSEP "fadeout" corresponds to marginal distal perfusion, suggesting the presence of extensive pathology. Intraoperative evoked potential monitoring, in conjunction with distal aortic perfusion, permits rapid identification and correction of compromised spinal cord blood flow, permitting repair of aortic lesions without the added liability of time constraints.
Asunto(s)
Potenciales Evocados Somatosensoriales , Complicaciones Intraoperatorias/diagnóstico , Isquemia/diagnóstico , Monitoreo Intraoperatorio/métodos , Procedimientos de Cirugía Plástica , Médula Espinal/irrigación sanguínea , Aneurisma de la Aorta Abdominal/cirugía , Aneurisma de la Aorta Torácica/cirugía , Humanos , Complicaciones Intraoperatorias/prevención & control , Isquemia/prevención & control , Sensibilidad y EspecificidadRESUMEN
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.
Asunto(s)
Aneurisma de la Aorta Abdominal/cirugía , Aneurisma de la Aorta Torácica/cirugía , Complicaciones Intraoperatorias/prevención & control , Isquemia/prevención & control , Médula Espinal/irrigación sanguínea , Potenciales Evocados Somatosensoriales , Humanos , Cuidados Intraoperatorios , Monitoreo Intraoperatorio , Paraplejía/prevención & controlRESUMEN
Surgical repair of traumatic lesions or aneurysmectomy of the descending thoracic aorta necessitates the interruption of distal aortic blood flow, a situation which invariably promotes proximal hypertension accompanied by a precipitous increase in cerebrospinal fluid pressure and distal hypoperfusion. All are significant determinants of postoperative paraplegia. The institution of aortic bypass, distal to cross-clamping, by either implantation of an extraluminal passive shunt or deployment of left atrial to femoral artery (LA-FA) cannulation with a centrifugal pump, is the most widespread modality to afford a means of proximal decompression and provide distal perfusion. Passive shunt techniques do not consistently provide optimal bypass efficiency, due to inherent limitations of device design and the inability to accurately monitor and control flow. The LA-FA bypass technique is superior to passive shunts in effecting proximal unloading by allowing for precise adjustment of blood flow to equilibrate proximal and distal aortic pressures. The concomitant use of cerebrospinal fluid drainage with LA-FA bypass can effectively reduce the incidence of postoperative paraplegia. Intraoperative monitoring of evoked potentials as a sensitive indicator of spinal cord ischemia should be considered an integral component of preserving cord function. The use of cerebrospinal fluid drainage and evoked potential monitoring in conjunction with LA-FA bypass is therefore highly advisable.
Asunto(s)
Aneurisma de la Aorta Torácica/cirugía , Arteria Femoral , Complicaciones Intraoperatorias/prevención & control , Isquemia/prevención & control , Médula Espinal/irrigación sanguínea , Aorta Torácica/lesiones , Circulación Extracorporea , Atrios Cardíacos , Humanos , Cuidados Intraoperatorios/métodos , Paraplejía/prevención & controlRESUMEN
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)
Asunto(s)
Aorta/cirugía , Líquido Cefalorraquídeo , Drenaje , Isquemia/prevención & control , Médula Espinal/irrigación sanguínea , Animales , Aorta/fisiología , Presión Sanguínea , Presión del Líquido Cefalorraquídeo , Constricción , Perros , Potenciales Evocados Somatosensoriales , Complicaciones Intraoperatorias/prevención & controlRESUMEN
Internal mammary artery (IMA) bypass grafting to the anterior descending coronary artery was performed in 2,100 patients between January 1978 and July 1986. The average number of additional saphenous vein grafts (SVGs) per patient was 1.8. During the same period, 1,753 patients underwent coronary artery bypass grafting using an SVG (average number of grafts per patient, 3.2). The average patient age was similar: 62.3 years for IMA grafts and 64.7 years for SVGs. Men constituted two thirds of each group. Left ventricular function was impaired (ejection fraction less than 45%) in 1,071 (51%) of IMA grafts and 847 (48.3%) of SVGs. Other aggregate risk factors, ie, elevated blood pressure, diabetes mellitus, previous myocardial infarction, and congestive heart failure, were similar in each group. Operative results and postoperative mortality of the IMA and SVG patients were comparable. However, the long-term probability of cumulative survival and occlusion-free survival were significantly greater and the probability of recurrent angina and reoperative coronary artery bypass grafting were significantly less in IMA graft patients (p less than 0.015). The relative risk of occlusion in an SVG was 4 to 5 times greater than that of the IMA graft. These data indicate that a patent IMA graft to the anterior descending coronary artery protects against recurrent angina and death from cardiac-related causes, and that the IMA should be the conduit of choice.
Asunto(s)
Angina de Pecho/cirugía , Anastomosis Interna Mamario-Coronaria , Adulto , Anciano , Angina de Pecho/mortalidad , Cateterismo Cardíaco , Puente de Arteria Coronaria/efectos adversos , Puente de Arteria Coronaria/mortalidad , Estudios de Evaluación como Asunto , Femenino , Estudios de Seguimiento , Oclusión de Injerto Vascular/epidemiología , Humanos , Anastomosis Interna Mamario-Coronaria/efectos adversos , Anastomosis Interna Mamario-Coronaria/mortalidad , Masculino , Persona de Mediana Edad , Recurrencia , Reoperación , Vena Safena/trasplante , Volumen SistólicoRESUMEN
This experiment evaluated the influence of blood on the weld strength of laser-assisted microvascular anastomoses (LAMA). Rat femoral arteries were anastomosed end-to-end by either direct laser welding (group I) or by a blood-bonded technique (group II) whereby fresh blood was applied to the vessel edges before laser exposure. Bursting strength was measured at 0, 1, and 24 hours and at 3 and 7 days by infusing methylene blue into the vessel while pressure was monitored. The results showed significantly increased bursting strength in group II compared with group I at 0 hour and 7 days (P less than 0.05). There was a significant increase in bursting strength in group I from 0 hour to 1 hour (P less than 0.05). It is concluded that blood-bonding enhances the early bursting strength of LAMAs and may facilitate arterial wall healing.