Regional blood flow during cross-clamping of the thoracic aorta and infusion of sodium nitroprusside

Merits of and Technical Tips for Supra-Mesenteric Aortic Cross Clamping

Supra-celiac aortic cross clamping is often utilized during aortic reconstruction for aneurysmal/occlusive disease involving the pararenal aorta. However, this may be accompanied a myriad of complications related to hemodynamic disturbances, cardiopulmonary compromise and hepatic ischemia. Supra-mesenteric aortic cross clamping may be an excellent option in selected patients with suitable anatomy to minimize or avoid these complications. Herein, the merits of and technical tips for supra-mesenteric aortic cross clamping are discussed.

Classic Papers Revisited: My Love Affair with the Venous System

The Pathophysiology of Aortic Cross-clamping and Unclamping. By Gelman S. ANesthesiology 1995; 82:1026–60. Reprinted with permission.

Aortic cross-clamping (AoX) and unclamping are associated with severe hemodynamic disturbances in virtually all organs and systems. The main hemodynamic changes induced by AoX result from an increase in impedance to aortic flow, an increase in systemic vascular resistance and afterload, blood volume redistribution caused by collapse and constriction of venous vasculature distal to the aortic clamp, and a subsequent increase in preload. Preload may not increase if the aorta is clamped distal to the celiac artery; in that case, blood volume from distal venous vasculature may be redistributed to the splanchnic vasculature without associated increases in preload. Increases in afterload and preload demand an increase in contractility, which results in an autoregulatory increase in coronary blood flow. Without increases in coronary blood flow and myocardial contractility, decompensation may occur. Aortic cross-clamping is associated with the formation and release of many mediators which constitute a double-edged sword: they may mitigate or aggravate the harmful hemodynamic effects of AoX and unclamping. Injuries to the lungs, kidneys, spinal cord, or abdominal viscera are caused mainly by ischemia and reperfusion of organs distal to aortic cross-clamping. A clear understanding of the pathophysiologic mechanisms involved in these processes should help to promote rational, well-focused, and effective measures to prevent and treat homeostatic disturbances occurring during AoX and unclamping.

Assessment of Blood Flow Patterns Distal to Aortic Occlusion Using CT in Patients with Resuscitative Endovascular Balloon Occlusion of the Aorta

BACKGROUND

Resuscitative endovascular balloon occlusion of the aorta (REBOA) is used to decrease hemorrhage below the level of aortic occlusion (AO); however, the amount of collateral blood flow below the level of occlusion is unknown. Our aim was to investigate blood flow patterns during complete AO in patients who underwent CT scan after REBOA.

STUDY DESIGN

Between February 2013 and January 2017, patients who received REBOA and underwent CT scan with intravenous contrast during full AO were included. Patients were excluded if they had a CT scan performed with the balloon partially or fully deflated.

RESULTS

Nine patients (8 men) were included; all had blunt trauma. Mean Injury Severity Score (±SD) was 48 ± 8 and mean age was 45 ± 19 years. Four had supra-celiac AO, and 5 had infra-renal AO. Arterial contrast enhancement was noted below the level of AO in all patients, and distal to REBOA sheath placement in 5. Collateralization from arteries above and below the AO was identified in all patients. Contrast extravasation distal to AO was identified in 4 patients, and hematomas in 8. Distal vascular enhancement patterns varied by level of AO and contrast administration site.

CONCLUSIONS

Aortic occlusion appears to dramatically decrease, but does not completely impede, distal perfusion during REBOA due to multiple pathways of collateralization. Active extravasation and hematomas can still be detected in the setting of full AO, with purposefully timed contrast and image acquisition. Blood flow persists below the level of both the AO and in-dwelling sheath. Dynamic flow studies are needed to determine the contribution of AO and sheath placement to distal tissue ischemia.

Cerebrospinal fluid drainage and thoracic endovascular aneurysm repair

Spinal cord complications including paraplegia and partial neurologic deficits remain a frequent problem during repair of descending thoracic or thoracoabdominal aortic aneurysms. Effective prevention of this dreaded complication is of paramount importance. Among the many adjuncts that have been proposed to prevent spinal cord complications, spinal fluid drainage is one that has been used by numerous teams. The aim of this review is to answer the following question: does spinal fluid drainage afford spinal cord protection during both open and endovascular repair of thoracic or thoracoabdominal aortic aneurysms?

Control of Left Ventricular and Proximal Aortic Dimensional Decompensation During Clamping of Descending Thoracic Aorta

The dimensional changes (mea sured by ultrasonic miniaturized transducers) of the left ventricle (LV), and proximal aorta (PAo) that accompanied hemodynamic changes during a forty-minute period of cross-clamping of the descending tho racic aorta without (Group A, 5 dogs) or with (Group B, 5 dogs) controlled vasodilation with sodium nitroprus side (SNP) infusion were evaluated in 10 open-chest anesthetized dogs. In both groups, measurements were re peated for another thirty-minute pe riod after declamping. In Group A, during clamping, systemic vascular resistance (SVR), PAo pressure (PAoP), LV systolic pressure (LVSP), and PAo midwall stress increased sig nificantly (p < 0.001). LV end-diasto lic pressure (LVEDP), stroke volume (SV), cardiac output (CO), and coro nary blood flow (CBF) did not show major variations, whereas systolic and diastolic LV wall thickness were significantly reduced (p < 0.02). A re duction in systolic shortening and thickening was observed also (p > 0.05). In Group B, during the same period, CO and CBF increased substantially (p < 0.02). SVR, PAoP, LVEDP, PAo midwall stess, and SV remained close to baseline values, while systolic and diastolic (p < 0.05) segmental length and systolic short ening and thickening increased (p > 0.05). Furthermore, the velocity of systolic shortening in Group B was significantly higher (p<0.005) than in Group A. In conclusion, the data indicate that significant changes, as detected continuously by sonomicro metry, in LV wall geometry and PAo midwall stress were observed during aortic cross-clamping. SNP infusion appeared to be an effective pharma cologic intervention to control these changes and to preserve cardiovascu lar performance.

Bypass Techniques for Descending Thoracic Aortic Surgery

The conduct of partial left heart bypass or partial car diopulmonary bypass (CPB) during surgery involving the descending thoracic aorta or thoracoabdominal aorta is one of the most unappreciated and misunder stood extracorporeal circulation procedures in cardio vascular surgery. It is different from conventional CPB, and although some uninitiated practitioners consider it simpler, it is in fact more complicated than conven tional CPB and involves different concepts. It requires expertise and skill in regulating the flow, pressure, and oxygenation of blood going to both the proximal and distal parts of the body and management of the special bypass or shunt procedures used, specialized monitor ing, and knowledge about the protection and preserva tion of organs both proximal and distal to the aortic clamping. It demands exquisite communication and un derstanding of the unique problems faced by the sur geon, anesthesiologist, and perfusionist.

The pathophysiology of aortic cross-clamping

During open aortic surgery, interrupting the blood flow through the aorta by applying a cross-clamp is often a key step to allow for surgical repair. As a consequence, ischemia is induced in parts of the body distal to the clamp site. This significant alteration in the blood flow is almost always associated with hemodynamic changes. Upon release of the cross-clamp, the blood flow is restored, triggering an ischemia-reperfusion response, leading to many pathophysiological processes such as inflammation, humoral changes, and metabolite circulation that could lead to injury in many organ systems and may significantly influence the postoperative outcome. It is therefore important to understand these processes and how they can be treated in order to allow for safe surgical aortic repairs while ensuring the best possible outcomes.

Comparison of supramesenteric aortic cross-clamping with supraceliac aortic cross-clamping for aortic reconstruction

OBJECTIVE

Supraceliac aortic cross-clamping (SCXC) is routinely used during open aortic reconstruction (OAR) of pararenal aortic disease when suprarenal control is not feasible. On occasion, however, aortic control may be obtained at the supramesenteric level by supramesenteric cross-clamping (SMXC) between the superior mesenteric artery and the celiac axis. The purpose of this study was to compare outcomes between patients who had SMXC vs SCXC during OAR for both aneurysmal and occlusive diseases.

METHODS

A retrospective chart review identified 69 patients who underwent elective OAR requiring SMXC (n = 18) or SCXC (n = 51). All patients with thoracoabdominal aneurysms and those who had inframesenteric (suprarenal and infrarenal) aortic control were excluded. Propensity score-based matching was performed to adjust for confounding factors in a 1:1 ratio to compare outcomes. Late survival was estimated by Kaplan-Meier methods.

RESULTS

Propensity score-based matching was performed at a 1:1 ratio; 18 SMXC cases were matched with 18 SCXC cases. The average age was 66.7 years, and men constituted 72%. Baseline characteristics were matched, except for the incidence of peripheral vascular occlusive disease (72.2% in the SMXC group vs 33.3% in the SCXC group; P = .04). A majority (80.6%) of patients underwent OAR for aneurysmal disease (72.2% in the SMXC group, 88.9% in the SCXC group). Intraoperatively, there were no differences in operative times (325 minutes for SMXC vs 298 minutes for SCXC; P = .48), but the SMXC group had a longer renal ischemia time (40 minutes vs 28 minutes; P = .03). There were no significant differences in intraoperative blood loss (2.4 L vs 1.6 L; P = .2) or blood product transfusion requirements (packed red blood cells, 2.2 units vs 1.6 units [P = .5]; Cell Saver, 1.3 L vs 0.7 L [P = .09]). Overall complication rates did not differ significantly (27.8% for SMXC vs 44.4% for SCXC; P = .24). Thirty-day mortality rates did not differ between the two groups (0% for SMXC vs 5.6% for SCXC; P = 1).

CONCLUSIONS

In this study, there were no differences in early morbidity or mortality between SMXC and SCXC during aortic reconstruction. SMXC, however, can be performed safely and effectively in properly selected patients. A larger, multicenter prospective study would help elucidate the potential benefits.

[Anesthesiologic procedure for elective aortic surgery]

Aortic aneurysms are frequent in the elderly who often suffer from relevant co-morbidities. In Germany it is estimated that approximately 250,000 patients suffer from an aortic aneurysm. Due to the high risk of cardiac or pulmonary complications operative management poses a challenge to the anesthesiologist. Especially hemodynamic management during aortic cross-clamping requires anesthesiologic know-how and an anticipatory use of vasodilators and catecholamines. Furthermore, the anesthesiologist has to protect renal function. In order to avoid paraplegia due to spinal ischemia cerebrospinal fluid drainage may be necessary in patients with aneurysms of the thoracic aorta. In recent years endovascular repair of aortic aneurysms has been established in addition to conventional open surgery. As a consequence in some patients aortic surgery can be performed under regional or local anesthesia. In special cases thoracic endovascular repair requires a medicinal induction of heart arrest or the reduction of aortic blood flow by overpacing.

Regional distribution of blood flow during proximal aortic cross‐clamping: An experimental study using coloured microspheres

OBJECTIVE

To investigate the effect of thoracic aortic cross-clamping on blood perfusion of the brain, spinal cord, heart, muscular tissue and visceral organs.

MATERIAL AND METHODS

Nine pigs underwent 30 min cross-clamping of the descending thoracic aorta. Multiple coloured microspheres (15.0 microm +/- 0.1) were infused into the left ventricle before and during aortic cross-clamping (XC) and after declamping (DC). Tissue samples were analysed by spectrophotometry.

RESULTS

Blood perfusion of the middle and lower segments of the spinal cord was significantly reduced during aortic XC. Perfusion of the brain was not significantly altered by aortic XC, while perfusion of myocardium increased 3-fold. During XC, perfusion of the deltoid muscle and diaphragm increased 5-fold and 13-fold, respectively, while a decrease was found in the gluteus muscle. Renal blood flow was significantly reduced during XC. Finally, XC induced a significant decrease of perfusion in the bowel, spleen, liver and pancreas.

CONCLUSION

During XC of the thoracic aorta, the perfusion of the muscular tissue was significantly increased proximal to the level of XC. The circulation of the brain was unchanged, probably because of autoregulatory mechanisms. Blood perfusion of the myocardium increased 3-fold during XC.

PANCREATIC INJURY AFTER THORACOABDOMINAL AORTIC OCCLUSION IN A PORCINE MODEL

BACKGROUND

The aim of this study was to investigate pancreatic injury after 45 min of thoracoabdominal aortic occlusion in a porcine model.

METHODS

Twenty-four pigs were used. Six pigs underwent sham operation and 18 intravascular balloon thoracoabdominal aortic occlusions for 45 min. The animals were randomly killed at 12, 48 and 120 h after reperfusion. After killing, all pancreata were examined macroscopically for any signs of acute pancreatitis, whereas gland specimens were harvested for histological study to evaluate pancreatic injury (haematoxylin and eosin staining) and acinar cell apoptosis (Terminal deoxynucleotidyl transferase mediated dUTP Nick-End Labelling staining).

RESULTS

Pancreatic injury severity score was mildly increased in terms of oedematous features at 12 h after reperfusion, but normalized to sham levels by the second day and thereafter. Necrotic injury was not statistically significant at any time point. Acinar cell apoptotic index was mildly increased at 12 and 48 h, but showed a tendency to decrease towards sham levels by the fifth day. One animal developed acute pancreatitis.

CONCLUSION

Acute pancreatitis is unlikely to occur after 45 min of thoracoabdominal aortic occlusion. However, an early, mild oedematous and apoptotic injury that occurs subclinically seems to be a constant event. This injury might have clinical significance when combined with pre-existent pancreatic pathologies.

Changes in hemodynamics and acid-base balance during cross-clamping of the descending thoracic aorta. A study in patients operated on for thoracic and thoracoabdominal aortic aneurysm

AIM OF THE STUDY

In the clinical situation there is discrepancy between various investigations regarding the cardiac response of thoracic aortic cross-clamping. The aim was therefore to investigate the hemodynamic response and blood gases during proximal aortic cross-clamping (XC) in patients operated for descending thoracic and thoracoabdominal aortic aneurysm without circulatory support.

PATIENTS AND METHODS

Altogether 51 patients operated on for thoracoabdominal (n=31) or descending thoracic aortic aneurysm (n=20) were included in the investigation. All patients were operated with aortic XC, but no circulatory support was applied. Hemodynamic variables and blood gases were recorded before and during XC.

RESULTS

A significant increase in cardiac output during XC from 4.7 to 6.0 liters/min was observed (p<0.01). There was a similar percentual increase in heart rate and also the proximal systolic blood pressure increased. A metabolic acidosis occurred during XC.

CONCLUSION

Cardiac output was significantly increased during XC in patients operated on for thoracoabdominal or descending thoracic aneurysm using direct aortic XC without circulatory support. Simultaneously, the heart rate was increased and there was a hyperdynamic circulatory state proximal to the aortic clamp. Redistribution of the blood volume in addition to catecholamine release may be responsible for the observed changes. These observations may influence the selection of operative strategy for some of these patients.

Effects of dopexamine in a rat model of supracoeliac aortic cross-clamping and declamping

This experimental study in rats was designed to demonstrate effects of dopexamine (3 microg kg(-1) min(-1), n = 6) or physiologic saline solution (n = 6) on systemic as well as regional perfusion during 30 min of supracoeliac aortic cross-clamping and during 180 min of reperfusion following declamping. Rats were surgically instrumented with arterial, right atrial and portal venous catheters, ultrasonic flow probes around the abdominal aorta, superior mesenteric and carotid artery, and a paediatric tonometer for intestinal mucosal PCO(2) measurement. During 120 min of reperfusion, fluid resuscitation was titrated to keep abdominal aortic blood flow above 80% of baseline values. We found that during cross-clamping, values of arterial lactate (p = 0.002) and intestinal tonometric PCO(2) (p = 0.018) were higher in the dopexamine group than in the control group.

The Effects of L-Arginine on Neurological Function, Histopathology, and Expression of Hypoxia-Inducible Factor-1 Alpha following Spinal Cord Ischemia in Rats

The aim of this study was to investigate the effects of L-arginine (L-Arg) on neurological function, histopathology, and expression of hypoxia-inducible factor-1 alpha (HIF-1alpha) following spinal cord ischemia in rats, and the interaction between therapy with the nitric oxide donor L-Arg and up-regulation of the expression of HIF-1alpha. Thirty Wistar rats weighing between 200 and 250 g were divided into three groups, each containing 10 rats: group 1, sham operation; group 2, untreated ischemia-reperfusion (I-R); group 3, I-R plus L-Arg treatment. Spinal cord ischemia was applied for 20 min. There were no significant differences in mean arterial pressures, temperatures, and blood gas levels among the groups. In group 2, malondialdehyde values were significantly increased compared with groups 1 and 3. The rats with aortic occlusion in group 2 had paraplegia or paraparesis. In group 3, all animals were neurologically intact. In group 3, spinal motor neurons did not decrease significantly, and little proliferation of microglia was observed compared with those in group 2. In group 2, spinal motor neurons in ventral gray matter decreased significantly compared with those in groups 1 and 3. HIF-1alpha-positive immunostaining was mildly detected in group 2 animals. The expression of immunoreactive cells was intensely increased in spinal cord tissue from I-R/L-Arg rats. In conclusion, our findings suggest that HIF-1alpha-positive immunostaining may be critical factors in the pathophysiology of inflammatory spinal cord injury induced by I-R. Nitric oxide may play an important role in the immunohistochemical expression of these molecules, and the neuroprotective benefit of L-Arg may be attributed to preventing neural cell necrosis.

The effects of intraoperative fenoldopam on renal blood flow and tubular function following suprarenal aortic cross-clamping

This study evaluated the effect of fenoldopam, a selective dopamine (DA1) agonist, on renal blood flow and renal tubular function following renal ischemia induced by suprarenal aortic cross-clamping. Twenty anesthetized research pigs received either fenoldopam (10 micro g/kg/min; n = 10) or saline ( n = 10) beginning 20 min before suprarenal aortic cross-clamping and continuing for 20 min after clamp release, for a total infusion time of 160 min (120-min cross-clamp). Recordings of renal blood flow, mean arterial pressure, and heart rate were taken at baseline, during cross-clamping, and immediately postclamp. Ischemic renal injury was evaluated by serum creatinine and by histologic grading of acute tubular necrosis. Treatment with fenoldopam increased renal blood flow in comparison to that in the control group ( p = 0.03). The mean creatinine increase from baseline at 6 hr and 18 hr after cross-clamp removal for the fenoldopam-treated group was significantly less than that in the control group ( p < 0.001). On histologic evaluation, the mean score for the degree of tubular necrosis was significantly higher in the control group ( p = 0.02), indicating less derangement of tubular morphology in the fenoldopam group. This study demonstrated that the intraoperative use of a continuous infusion of fenoldopam during suprarenal aortic cross-clamping results in increased renal blood flow, less postoperative rise in creatinine, and better preservation of tubular histology in the pig model.

[Subdural haemorrhage following lumbar spinal drainage during repair of thoraco-abdominal aneurysm]

Physicians in charge of patients undergoing thoracic or thoraco-abdominal aneurysmectomy, frequently use lumbar spinal drainage of the cerebrospinal fluid (CSF) to prevent paraplegia. Whereas the profit of this technique is a much debated question, we report 2 case reports of delayed sub-dural hemorrhage, after lumbar spinal drainage of CSF. Cross clamping of the aorta decreases the spinal cord artery pressure, increases the cerebral pressure and by alterations of distribution of the venous return, is responsible for an increase of the CSF pressure. This increase of the CSF pressure decreases the spinal cord driving pressure. Lumbar spinal drainage of CSF aims to improve the spinal cord driving pressure close to the normal (where driving pressure = aortic pressure - CSF pressure). The two case reports have to be added to the liability of a method of prevention that, as attractive that it is, did not give the proof of its efficiency to decrease the frequency and/or the severity of paraplegia after thoracic or thoraco-abdominal aneurysmectomy. At this time, this technique should be reserved to the patients with documented risk, as it is possible using preoperative spinal cord arteriography. The insertion and the withdrawal of the catheter must be done in the usual conditions of medullar puncture with regard to anticoagulant and antiplatelet agents

Systemic and mesenteric hemodynamics, metabolism, and intestinal tonometry in a rat model of supraceliac aortic cross-clamping and declamping

OBJECTIVE

To describe systemic and mesenteric hemodynamics, metabolism, and intestinal tonometry in a rat model of supraceliac aortic cross-clamping and declamping.

DESIGN

Prospective, randomized, experimental study.

SETTING

University cardiovascular research laboratory.

PARTICIPANTS

Twelve male anesthetized and ventilated Sprague-Dawley rats.

INTERVENTION

Supraceliac aortic cross-clamping was performed for 30 minutes, followed by declamping and reperfusion for 180 minutes or sham clamping and sham declamping.

MEASUREMENTS AND MAIN RESULTS

Mean arterial blood pressure; abdominal aortic, superior mesenteric, and carotid artery blood flow; intestinal mucosal tonometry; hemoglobin; lactate; and blood gases were measured before and after 30 minutes of aortic cross-clamping and 15, 30, 60, 120, and 180 minutes after declamping during reperfusion. Aortic cross-clamping induced an increase in mean arterial pressure (117+/-20 mm Hg to 147+/-12 mm Hg), an increase in right atrial hemoglobin saturation(66%+/-11% to 81%+/-6%), an increase in lactate levels (1.7+/-0.7 mmol/L to 4.3+/-1.3 mmol/L), and an increase in tonometric PCO2 (49.6+/-5.0 mm Hg to 75.6+/-8.6 mm Hg). Three hours of reperfusion after declamping resulted in significantly decreased mean arterial pressure (38+/-10 mm Hg); decreased aortic (101+/-12 mL/min/kg to 57+/-32 mL/min/kg), mesenteric (19+/-4 to 13+/-6 mL/min/kg), and carotid (12+/-4 mL/min/kg to 5+/-3 mL/min/ kg) blood flows; and elevated lactate levels (4.2+/-2.0 mmol/L). Tonometric PCO2 had normalized to baseline levels (51.9+/-3.8 mm Hg), but PCO2 gap was significantly higher than in sham clamped rats (17.9+/-7.8 mm Hg v. 7.0+/-2.6 mm Hg).

CONCLUSIONS

Hemodynamic and metabolic effects of aortic cross-clamping and declamping known from large animal models are reproducible using a rat model. Intestinal tonometry indicated mesenteric ischemia during aortic cross-clamping, which was reversible to preclamp values within 30 minutes of reperfusion after declamping.

Hemodynamic changes during a new procedure for regional chemotherapy involving occlusion of the thoracic aorta and inferior vena cava

STUDY OBJECTIVE

To describe the hemodynamic consequences of a regional chemotherapy procedure involving occlusion of the thoracic aorta and inferior vena cava (IVC) by intraluminal balloons.

DESIGN

Prospective study.

SETTING

Operating rooms of an academic hospital.

PATIENTS

10 patients with inoperable intraabdominal malignancy.

INTERVENTIONS

After the induction of general anesthesia and the insertion of a pulmonary artery catheter the patients underwent the regional chemotherapy procedure.

MEASUREMENTS AND MAIN RESULTS

Occlusion of the thoracic aorta induced an increase in blood pressure (BP) and systemic vascular resistance (SVR) (41% +/- 8% and 80% +/- 15% from baseline, respectively), and a 30% +/- 7% decrease in cardiac output (CO). After aortic balloon deflation at the end of the procedure, we observed a decrease in BP to baseline values, decrease in SVR (to 62% +/- 12% below baseline), and increase in CO (to 80% +/- 15% above baseline). Those changes resemble those described during vascular surgery. Isolated occlusion of the IVC before aortic occlusion caused hemodynamic deterioration in only three of 10 patients, suggesting incomplete obstruction or collateral blood flow in others. Occluding the IVC while the aorta was occluded, caused minimal hemodynamic changes.

CONCLUSIONS

Independent inflation of the IVC balloon should not be performed routinely because of possible unpredicted hemodynamic instability. Inferior vena cava occlusion should always be performed after complete aortic occlusion, because it is then that it produces negligible hemodynamic consequences. It is possible that a better assessment of IVC occlusion after balloon inflation needs to be done by contrast injection to prevent a possible leak of chemotherapeutic drugs.

Clinical decision making and operative approaches to thoracic aortic aneurysms

The care of the patient with thoracic aneurysms is quite complicated. The decision to treat an aneurysm must be based on the risk of rupture and the patient's life expectancy. The preoperative evaluation must include detailed imaging to allow proper preoperative planning. This is especially important to determine the need for hypothermic circulatory arrest or the potential to treat a descending aneurysm with an endovascular approach. Thorough preoperative preparation and intraoperative care are as important as surgical decision making and meticulous technique. Although significant advances have been made in operative approaches, cerebral and myocardial preservation, and postoperative care, the management of complicated aneurysms of the thoracic aorta is frequently a humbling experience.

Fractured cervical spine and aortic transection

A 17-year-old victim of a road traffic accident presented. Following investigation diagnoses of fractured first cervical vertebra, aortic transection, diffuse cerebral oedema, fractured right ribs 2-4 and pubic rami were made. Management of this case presented a number of anaesthetic dilemmas: management of the airway, use of cross-clamp vs. shunting or heparinization and bypass, cardiovascular and neurological monitoring, maintenance of cardiovascular stability during and post cross-clamp, minimizing the risk of post-operative renal and neurological dysfunction.

Descending thoracic aorta aneurysmectomy: left-left centrifugal pump versus simple clamping technique

Forty-six patients who had had an elective repair of a descending thoracic aortic aneurysm were reviewed, in order to investigate the efficacy of support by a centrifugal pump on distal organ perfusion and spinal cord protection during cross-clamping of the thoracic aorta. Two concurrent groups were analysed: 36 patients (78%) were supported by left atriofemoral arterial bypass with a centrifugal pump and 10 (22%) had no distal circulatory support. No patient was fully heparinized. The demographic data and preoperative characteristics of the groups, including location and type of aneurysm, were similar. The mean(s.d.) duration of cross-clamping was 37.8 (16) min in the centrifugal pump group and 42.3(21) min in the simple clamping group. Preoperative haemodynamic and laboratory data were similar in both groups. During cross-clamping, parameters of pH and blood urea varied but were better in the centrifugal pump group; changes from pre-intervention to early aortic cross-clamping time were not significant (pH, P < 0.0006; bases, P < 0.0003). Differences in creatinine values were caused mainly by the change from pre-intervention to the first postoperative day (P < 0.03); this continued throughout the hospital stay. The cerebrospinal fluid pressure measurement indicated a significant difference in time change (P < 0.0001) and mean level over time (P < 0.0002): levels were significantly lower in the centrifugal pump group throughout aortic cross-clamping. Three patients in the simple clamping group and none in the centrifugal pump group (P < 0.02) required cerebrospinal fluid drainage.(ABSTRACT TRUNCATED AT 250 WORDS)

Sodium nitroprusside: twenty years and counting

SNP remains an effective, reliable, and commonly used drug for the rapid reduction of significant arterial hypertension regardless of the etiology, for afterload reduction in the face of low CO when blood volume is normal or increased, and for intraoperative induced hypotension. After establishing indwelling arterial monitoring, an initial infusion rate of 0.3-0.5 micrograms.kg-1.min-1 is begun with titration as needed up to 2.0 micrograms.kg-1.min-1. Higher rates for brief periods of time (10 min) are acceptable. The use of alternative drugs to reduce the dose or shorten the duration of infusion should be considered when the 2.0 micrograms.kg-1.min-1 range is exceeded (Table 1). SNP should not be used by individuals unfamiliar with its potency and metabolic pathways, as the many reports of adverse reactions testify. Careful attention to infusion rates, particularly in patients at risk for depleted thiosulfate stores, is mandatory, and the use of other drugs in conjunction with or instead of SNP should always be considered. As with many therapeutic interventions, SNP requires careful administration to appropriately selected patients by a clinician who knows its inherent hazards. Despite its toxicity, SNP is popular because it is often the most (in some cases, the only) effective drug in some difficult clinical circumstances.

Use of left heart bypass in the surgical repair of thoracoabdominal aortic aneurysms

The purpose of this study was to assess the usefulness of left heart bypass in thoracoabdominal aortic aneurysm surgery. Data from 50 patients who underwent thoracoabdominal aortic aneurysm repair between July 1987 and October 1993 were retrospectively reviewed. In all of them a left heart bypass (left atrium to left femoral artery) with a centrifugal pump (without systemic heparinization) was used. Patient-, disease-, and operation-related variables were analyzed using univariate methods. There were no intraoperative deaths. The in-hospital mortality rate was 8% (n = 4). Survival rates were 77% (+/- 6.5) at 2 years and 62% (+/- 8.7) at 5 years. Renal failure requiring dialysis occurred in five (10%) patients and paraplegia in five (10%). Sixteen (32%) patients had respiratory insufficiency requiring prolonged (> 8 days) ventilation. After univariate analysis, the risk factors for developing a need for postoperative dialysis were found to be the preoperative creatinine level (p = 0.002) and the presence of preoperative arterial hypertension (p = 0.018). A history of peripheral vascular occlusive disease (p = 0.008) was an important risk factor for predicting late death. No factors retained significance in the univariate analysis of hospital deaths and postoperative paraplegia. Renal and spinal ischemic times were substantially reduced in comparison to the theoretic times calculated if cross-clamping had been used. Bypass-related complications were completely absent. The use of a left heart bypass during thoracoabdominal aortic aneurysm surgery may not reduce the global complication rate; the results were similar to those achieved using simple cross-clamping. However, this technique appears to be the method of choice for protecting organ systems at risk during difficult repairs.

Combined use of cerebral spinal fluid drainage and naloxone reduces the risk of paraplegia in thoracoabdominal aneurysm repair

PURPOSE

This report summarizes our experience with the use of cerebral spinal fluid drainage (CSFD) and naloxone for prevention of postoperative neurologic deficit (paraplegia or paraparesis).

METHODS

We reviewed 110 consecutive patients with 86 thoracoabdominal aneurysms and 24 thoracic aneurysms. The status of 47 patients (43%) was acute (rupture or dissection), and the status of 52 (47%) was Crawford type I or II. None of the patients had intercostal artery reimplantation. There were two patient groups for analysis of neurologic deficit risk. Group A (61 patients) received naloxone and CSFD, and group B (49 patients) did not.

RESULTS

One deficit occurred in group A and 11 deficits occurred in group B (p = 0.001). By multiple logistic regression analysis, the variables acute status, Crawford type II, or group B classification were significant factors for deficit risk. Use of the same logistic regression analysis on the subgroup of 47 patients with acute aneurysms and 33 patients with Crawford type 2 aneurysms confirmed the protective effect of combined CSFD and naloxone (group A) and that clinical presentation and extent of aorta replaced are the primary risk factors for development of deficit. To test this conclusion we developed a highly predictive model (correlation coefficient 0.997 with 16 series of thoracoabdominal aneurysms) for neurologic deficit. We applied our data to this model. Group B had the predicted number of deficits, and group A had substantially fewer deficits than predicted.

CONCLUSIONS

We conclude that the combined use of CSFD and naloxone offers significant protection from neurologic deficits in patients undergoing thoracoabdominal and thoracic aortic replacement.

Effect of sodium nitroprusside on paraplegia during cross-clamping of the thoracic aorta

Sodium nitroprusside (SNP) is usually used to control excessive proximal pressure after aortic cross-clamping. To assess the effect of SNP on circulatory dynamics, somatosensory evoked potentials, and neurologic outcome, 10 adult mongrel dogs that underwent 45 minutes of cross-clamping of the thoracic aorta were randomly assigned to receive either 50 mg/kg of SNP or no treatment for excessive proximal hypertension. There was a statistically significant difference noted between the SNP-treated animals and the control animals in terms of the proximal mean arterial pressures (112 +/- 13 versus 142.2 +/- 15 mm Hg, respectively; p < 0.05) and the mean distal arterial pressures (15 +/- 3 mm Hg versus 23 +/- 1 mm Hg; p = 0.04). However, the electrical activity of the spinal cord, as indicated by the somatosensory evoked potentials, returned significantly faster in the nontreated group than in the SNP-treated group (15 +/- 9 versus 44 +/- 13 minutes; p < 0.05). Control animals exhibited a significantly better neurologic outcome and no paraplegia 24 hours postoperatively. We conclude that the use of SNP to treat excessive proximal hypertension may be detrimental to the spinal cord during cross-clamping of the thoracic aorta, resulting in a decline in the ischemic tolerance.

Changes in cerebrospinal fluid pressure and spinal cord perfusion pressure prior to cross-clamping of the thoracic aorta in humans

Little is known about what influences cerebrospinal fluid pressure (CSFP) during anesthesia prior to aortic cross-clamping (AXC). Therefore, this study measured the effect of anesthetic induction, of various drugs administered during the course of surgery prior to AXC, and of hemodynamic changes on CSFP, and calculated spinal cord perfusion pressure (SCPP = mean arterial pressure [MAP] - CSFP) in 11 patients undergoing surgery on the descending thoracic aorta. A lumbar drainage catheter was placed to facilitate drainage of CSF and to measure CSFP. Anesthesia was induced with fentanyl, 50 micrograms/kg, and midazolam, 1 mg, using a pancuronium-metocurine mixture for neuromuscular blockade. Data were collected prior to and after (1) anesthetic induction, (2) mannitol to augment diuresis, (3) sequential use of sodium nitroprusside (SNP) and isoflurane (ISO) to lower MAP by 20%, (4) drainage of spinal fluid, (5) intrathecal injection of papaverine (IP), and (6) AXC. Statistical comparisons of recorded data were made using the least squares mean method and Friedman test. Linear regression was used to test for correlation between CSFP and hemodynamics. Anesthetic induction affected neither hemodynamics nor CSFP. Mannitol significantly increased heart rate, central venous pressure (CVP), pulmonary capillary wedge pressure (PCWP), cardiac output (CO), and CSFP (P less than 0.05). SNP or ISO altered neither CVP, PCWP, CO, nor CSFP, which remained elevated at the postmannitol infusion level. ISO, unlike SNP, caused a significant decrease in SCPP (P less than 0.005). Subsequent drainage of 20 mL of CSF improved SCPP (P less than 0.05). IP did not have any effect on hemodynamics or CSFP. CSFP showed a strong correlation with CVP (r = 0.86).(ABSTRACT TRUNCATED AT 250 WORDS)

Cerebral haemodynamics during proximal aortic cross-clamping

This study was carried out to examine cerebral blood flow, including the microcirculation and intracranial pressure during cross-clamping (XC) of the thoracic aorta in pigs. Blood flow in the internal carotid artery was measured by electromagnetic flowmetry. Cerebral microcirculation was studied by the laser Doppler technique, and intracranial pressure measured by applying a fibre optic pressure monitoring catheter in the same craniotomy. Maximal and mean blood flow velocity of the middle cerebral artery was recorded using a transcranial Doppler and cardiac output measured by thermodilution. The thoracic aorta was cross-clamped distal to the left subclavian artery for 30 min. During aortic XC the internal carotid artery blood flow increased 191% (p less than 0.05). Simultaneously mean and maximal blood flow velocity of the middle cerebral artery both increased 125% (p less than 0.01). Intracranial pressure increased 163% (p less than 0.05), and there was an increase in cerebral flux of 23% (p less than 0.05). Within the first minutes following the release of XC, all values decreased to preocclusive values. In conclusion, we observed a significant increase in cerebral blood flow during XC of the thoracic aorta. This is in accordance with the finding of a simultaneous increase in cardiac output. These haemodynamic changes support the theory that an increased blood flow via the proximal feeding system to the anterior spinal artery might be important in avoiding neurological sequelae following proximal aortic XC.

Distal aortic pressure during coarctation operation

Mean distal aortic pressure (DAP) was monitored continuously during operative repair of coarctation of the aorta in 67 children more than 1 year of age between 1982 and 1987. At initial test clamping a DAP of 45 mm Hg or more was considered adequate. In 42 patients (group A), DAP exceeded 45 mm Hg and the operation proceeded. In 25 patients (group B) the DAP was less than 45 mm Hg, and adjustments were made to the position of the proximal and distal clamps and in the use of hypotensive agents. After these adjustments in group B, DAP rose from 34.7 to 50.6 mm Hg (p less than 0.001), achieving the desired level in all but 5 patients, who required temporary shunts to support the distal circulation. The adjustments were as follows: the left subclavian artery was open in 28% of patients before and 60% after (p less than 0.02); no more than one pair of intercostal arteries was clamped in 64% before and 88% after (p less than 0.05); and no hypotensive agents were used in 56% before and 80% after (p = 0.07). During the first ten minutes of cross-clamping the DAP rose by 5.5 mm Hg (p less than 0.01, n = 52). It is concluded that continuous monitoring of DAP contributed to the operative management of these patients by indicating when adjustments in the position of the clamps or in the use of hypotensive agents were needed. The use of hypotensive agents should be reduced to achieve a higher DAP.

Sodium nitroprusside decreases spinal cord perfusion pressure during descending thoracic aortic cross-clamping in the dog

Paraplegia is a devastating complication of surgery on the descending thoracic aorta. During surgical repair, the aorta is cross-clamped, and nitroprusside is often used to treat arterial hypertension that can occur above the cross-clamp. Twenty-one dogs were studied to determine the effects of nitroprusside on intraspinal pressures, mean aortic pressures below the cross-clamp, and spinal cord perfusion pressure. Perfusion pressure in spinal radicular arteries originating below the aortic cross-clamp was estimated as the distal aortic pressure minus intraspinal pressure. Nitroprusside was used to return the mean arterial pressure above the cross-clamp to values similar to the pre-cross-clamp levels in 7 dogs. Fourteen animals did not receive sodium nitroprusside. Aortic cross-clamping resulted in small but significant increases in intraspinal pressure (4.3 +/- 0.8 to 7.5 +/- 0.9 mm Hg in non-nitroprusside-treated dogs, and 3.4 +/- 1.0 to 5.6 +/- 1.5 mm Hg in the nitroprusside group before nitroprusside). Nitroprusside caused a further increase in intraspinal pressure (5.6 +/- 1.5 to 8.3 +/- 2.2 mm Hg) and a decrease in aortic pressure below the cross-clamp (26 +/- 5 to 18 +/- 4 mm Hg). The increase in intraspinal pressure and the decrease in aortic pressure below the cross-clamp after nitroprusside resulted in a decrease in spinal cord perfusion pressure from 19 +/- 5 mm Hg to 11 +/- 4 mm Hg. Because nitroprusside decreases spinal cord perfusion pressure and may increase the risk of spinal cord ischemia, the avoidance of large doses of nitroprusside to arbitrarily return mean arterial pressure above the cross-clamp to pre-cross-clamp levels is recommended.