Effect of left atrial to left femoral artery bypass and renin-angiotensin system blockade on renal blood flow and function during and after thoracic aortic occlusion

Endocrine Effects of Simulated Complete and Partial Aortic Occlusion in a Swine Model of Hemorrhagic Shock

INTRODUCTION

Low distal aortic flow via partial aortic occlusion (AO) may mitigate ischemia induced by resuscitative endovascular balloon occlusion of the aorta (REBOA). We compared endocrine effects of a novel simulated partial AO strategy, endovascular variable aortic control (EVAC), with simulated REBOA in a swine model.

MATERIALS AND METHODS

Aortic flow in 20 swine was routed from the supraceliac aorta through an automated extracorporeal circuit. Following liver injury-induced hemorrhagic shock, animals were randomized to control (unregulated distal flow), simulated REBOA (no flow, complete AO), or simulated EVAC (distal flow of 100-300 mL/min after 20 minutes of complete AO). After 90 minutes, damage control surgery, resuscitation, and full flow restoration ensued. Critical care was continued for 4.5 hours or until death.

RESULTS

Serum angiotensin II concentration was higher in the simulated EVAC (4,769 ± 624 pg/mL) than the simulated REBOA group (2649 ± 429) (p = 0.01) at 180 minutes. There was no detectable difference in serum renin [simulated REBOA: 231.3 (227.9-261.4) pg/mL; simulated EVAC: 294.1 (231.2-390.7) pg/mL; p = 0.27], aldosterone [simulated EVAC: 629 (454-1098), simulated REBOA: 777 (575-1079) pg/mL, p = 0.53], or cortisol (simulated EVAC: 141 ± 12, simulated REBOA: 127 ± 9 ng/mL, p = 0.34) concentrations between groups.

CONCLUSIONS

Simulated EVAC was associated with higher serum angiotensin II, which may have contributed to previously reported cardiovascular benefits. Future studies should evaluate the renal effects of EVAC and the concomitant therapeutic use of angiotensin II.

Heparin-Coated Left Heart Bypass: Renal Function and Hormonal Response

The effect of partial (50 mI/min/kg) left heart bypass (LHBP) on renal function, plasma renin activity (PRA), aldosterone, arginine vasopressin and atrial natriuretic peptide (ANP) response was studied in ten anesthetized, open-chested mongrel dogs (weight 23-50 kg) over a period of 6 h. Standard equipment with systemic heparinization (control), initially 300 IU/kg, was employed in five dogs, and heparin-coated equipment without additional heparin in the other five (heparin coated). Urine was continuously collected through a transurethral catheter. Urine samples and pulmonary artery blood samples for hormonal assays were taken at preset intervals before and during LHBP. The results in each group were summarized as median (25th-75th) and compared using the Mann-Whitney U test. In the control group higher blood loss required higher volume substitution. Urine output was maintained in heparin coated and slightly decreased at 3-4 h in control LHBP. Creatinine clearance at 3-5 h and free-water clearance at 3-6 h were significantly higher with heparin-coated LHBP. PRA, aldosterone and vasopressin peaked at 1-2 h of LHBP similarly in both groups, not exceeding the values before perfusion. PRA and aldosterone response was sustained during 6 h and the percentage changes corrected for hemodilution indicated a stronger response with standard equipment. Vasopressin concentrations were slightly but significantly higher in the control group at 1 and 6 h of perfusion. Corrected for hemodilution, vasopressin percentage changes were not different in the two groups. ANP, despite atrial unloading, rose similarly in both groups. There was a tendency to poorly sustained ANP response (control > heparin-coated) after 6 h of perfusion. In conclusion, preserved renal function and attenuated hormonal response during canine partial LHBP are results of better hemostasis and circulatory integrity of perfusion without systemic heparinization.

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.

Renal perfusion during thoracoabdominal aortic operations: cold crystalloid is superior to normothermic blood

BACKGROUND

Renal failure remains a common complication of thoracoabdominal aortic aneurysm repair. The purpose of this randomized clinical trial was to compare two methods of selective renal perfusion--cold crystalloid perfusion versus normothermic blood perfusion--and determine which technique provides the best kidney protection during thoracoabdominal aortic aneurysm repair.

METHODS

Thirty randomized patients undergoing Crawford extent II thoracoabdominal aortic aneurysm repair with left heart bypass had renal artery perfusion with either 4 degrees C Ringer's lactate solution (14 patients) or normothermic blood from the bypass circuit (16 patients). Acute renal dysfunction was defined as an elevation in serum creatinine level exceeding 50% of baseline within 10 postoperative days.

RESULTS

One death occurred in each group. One patient in the blood perfusion group experienced renal failure requiring hemodialysis. Ten patients (63%) in the blood perfusion group and 3 patients (21%) in the cold crystalloid perfusion group experienced acute renal dysfunction (p = 0.03). Multivariable analysis confirmed that the use of cold crystalloid perfusion was independently protective against acute renal dysfunction (p = 0.02; odds ratio, 0.133).

CONCLUSIONS

When using left heart bypass during repair of extensive thoracoabdominal aortic aneurysms, selective cold crystalloid perfusion offers superior renal protection when compared with conventional normothermic blood perfusion.

Thoracoabdominal aortic aneurysm repair in patients with single kidney

Data were analyzed from 581 consecutive cases of thoracoabdominal aortic aneurysm (TAAA) repairs. Preoperatively, 32 patients (6%) had only one functioning kidney (single-kidney group), and 549 patients (94%) had tow functioning kidneys (reference group). The patients' mean age was higher in the reference group (64.9 years, range: 21-85) than in the single-kidney group (63.2 years, range: 38-79); p < 0.05. However, there was a significantly higher incidence of hypertension (97% versus 78%), coronary artery disease (50% versus 34%), and renal artery stenosis ipsilateral to functioning kidneys (88% versus 26%) in the single-kidney group than in the reference group; p < 0.05. Preoperatively, renal insufficiency (serum creatinine > or = 2.5 mg/dl or patients on dialysis) was present in four patients (13%) in the single-kidney group and in 21 patients (4%) in the reference group; p < 0.05. In the former group, the unilateral loss of kidney function was secondary to atrophy in 30 patients (94%) and agenesis in two patients (6%). The simple clamp-open distal anastomosis technique was employed in the majority of the cases in the single-kidney group (91%) and in the reference group (83%); p > 0.05. Renal artery endarterectomy or bypass ipsilateral to functioning kidneys was performed on 18 patients (56%) in the single-kidney group and 68 patients (12%) in the reference group; p < 0.05. Renal perfusion with cold Ringer's lactate solution was done in 18 cases (56%) in the single-kidney group and 228 cases (42%) in the reference group; p > 0.05. There was no difference in the operative mortality (9% versus 7%) and the incidence of paraplegia/paraparesis (6% versus 5%) between the single-kidney group and the reference group; p > 0.05. Postoperatively, new onset renal insufficiency developed in 10 patients (31%) in the single-kidney group, and 58 patients (11%) in the reference group; p < 0.05. In the single-kidney group, four patients (13%) had mild renal dysfunction (serum creatinine > or = 2.5 mg/dl), and two patients (6%) were on dialysis on discharge. Notably, there was no significant difference in the incidence of renal insufficiency on admission compared to the incidence of renal insufficiency on discharge in the single-kidney group (13% versus 19%; p > 0.05). TAAA repair in patients with one functioning kidney can be performed safely. Postoperative renal insufficiency can be managed successfully in the majority of patients.

Predictive factors for acute renal failure in thoracic and thoracoabdominal aortic aneurysm surgery

PURPOSE

The purpose of this study was to analyze the factors associated with acute renal failure in total descending thoracic and thoracoabdominal aortic aneurysm surgery.

METHODS

A total of 234 patients underwent thoracoabdominal aortic aneurysm or total descending thoracic aneurysm repair between January 1991 and January 1994. Eighty-five women and 149 men were evaluated. The median age was 67 years (range 8 to 88 years). Seventy-seven patients had type I thoracoabdominal aortic aneurysm, 99 had type II, 51 had type III or IV, and 7 had total descending thoracic aneurysm. Factors such as age, sex, aneurysm type, and visceral and distal aortic perfusion were examined with univariate fourfold table and multivariate logistic regression analysis.

RESULTS

Acute renal failure, defined as an increase in serum creatinine by 1 mg/dl per day for two consecutive days after surgery, occurred in 41 (17.5%) of 234 patients. Thirty-six (15%) of 234 patients required dialysis. Twenty (49%) of 41 patients with acute renal failure died. Of the 21 survivors with renal failure, renal failure resolved in 18 (86%) within 30 days of surgery. The univariate odds ratio of death, given acute renal failure, was 6.7 (95% confidence interval [CI] 3.2 to 14.2, p < 0.0001). No significant association was found between the probability of acute renal failure and age, sex, hypertension, right renal artery reattachment, or renal bypass. Factors associated with increased risk of acute renal failure in multivariate analysis were visceral perfusion (odds ratio [OR] = 3.6 95%, CI 1.2 to 11.0, p < 0.02), left renal artery reattachment (OR = 4.4 95%, CI 1.6 to 11.9, p < 0.004), preoperative creatinine > or = 2.8 mg/dl (OR = 10.3, 95% CI 12.0 to 411.8, p < 0.0001), and simple clamp technique (OR = 3.4 95%, CI 1.07 to 10.76, p < 0.04). Direct univariate correlation was seen between preoperative creatinine and acute renal failure (OR = 3.2 per mg/dl increase, 95% CI 2.7 to 10.1, p < 0.0001).

CONCLUSION

Postoperative acute renal failure after thoracoabdominal and total descending thoracic aortic aneurysm surgery is associated with preoperative creatinine level, visceral perfusion, left renal artery reattachment, and simple cross-clamp technique.

Abdominal aortic aneurysmectomy in a renal transplant patient

Standard surgical techniques were modified to allow continued perfusion of a renal allograft during resection of a large symptomatic abdominal aortic aneurysm. Neither hypothermic perfusion nor temporary bypass were employed. No alteration in renal function was observed and the patient remains well. Complex methods of renal allograft protection are probably unnecessary when transplant recipients undergo aortic reconstruction. However simple modifications or technique can substantially reduce renal ischaemic time and further add to the safety of the procedure.