Osmotic diuretics and hemodilution in postischemic renal failure

Pathophysiology of Red Blood Cell Trapping in Ischemic Acute Kidney Injury

Red blood cell (RBC) trapping describes the accumulation of RBCs in the microvasculature of the kidney outer medulla that occurs following ischemic acute kidney injury (AKI). Despite its prominence in human kidneys following AKI, as well as evidence from experimental models demonstrating that the severity of RBC trapping is directly correlated with renal recovery, to date, RBC trapping has not been a primary focus in understanding the pathogenesis of ischemic kidney injury. New evidence from rodent models suggests that RBC trapping is responsible for much of the tubular injury occurring in the initial hours after kidney reperfusion from ischemia. This early injury appears to result from RBC cytotoxicity and closely reflects the injury profile observed in human kidneys, including sloughing of the medullary tubules and the formation of heme casts in the distal tubules. In this review, we discuss what is currently known about RBC trapping. We conclude that RBC trapping is likely avoidable. The primary causes of RBC trapping are thought to include rheologic alterations, blood coagulation, tubular cell swelling, and increased vascular permeability; however, new data indicate that a mismatch in blood flow between the cortex and medulla where medullary perfusion is maintained during cortical ischemia is also likely critical. The mechanism(s) by which RBC trapping contributes to renal functional decline require more investigation. We propose a renewed focus on the mechanisms mediating RBC trapping, and RBC trapping-associated injury is likely to provide important knowledge for improving AKI outcomes. © 2024 American Physiological Society. Compr Physiol 14:5325-5343, 2024.

Effect of anticoagulation on renal function and protein excretion in experimental acute ischemic renal failure

Female Sprague-Dawley rats underwent right nephrectomy and 40 min left renal artery occlusion (RAO). After 15 min of reflow, polyethylene glycol 1000 (PEG1000) was infused to induce osmotic diuresis and to enable glomerular filtration rate (GFR) measurements. Urine was collected during a 90 min period, and the concentrations of PEG1000, albumin, IgG, IgM and fibrin(ogen)/degradation products (FIB) were assessed both in plasma and urine by radial immuno diffusion technique Groups of rats were subjected to saline + RAO, warfarin + RAO or sham-operation. GFR as measured by PEG1000 clearance averaged 0.61, 0.036 and 0.094 mL/min/100g BW/kidney in sham-operated, saline + RAO and warfarin + RAO rats, respectively. Urinary excretion of albumin and IgG increased substantially in both ischemic groups. IgM was not detected in any of the urine samples. FIB excretion was lowest in the saline + RAO group, possibly due to retention of FIB-containing obstructions in the tubules. Rats subjected to warfarin + RAO had significantly higher excretion of FIB. This result suggests that warfarin does not prevent the glomerular sieving of macromolecules in the glomerular filter, but reduces tubular obstruction by preventing fibrin formation, which may explain its positive effect on GFR.

Effect of anticoagulation upon nephron obstruction in experimental acute ischaemic renal failure. A morphological study

Ischaemic-reperfusion injury as a model of acute renal failure (ARF) results in increased macromolecular permeability, tubular obstruction, and renal oedema. To investigate the role for coagulation in this model, anticoagulated and saline-pretreated rats were subjected to 60 min unilateral renal artery occlusion (RAO). After 15 min of reflow, specimens were collected for electron and light microscopic examination. Morphometry was employed to study podocyte changes and Bowman's space dilatation as measures of increased permeability and tubular obstruction, respectively. After 15 min of reflow, Bowman's space increased significantly and the podocytes were markedly widened and flattened. Rats pretreated with heparin or warfarin showed less widening of Bowman's space than saline-treated rats, whereas no significant difference was seen regarding the podocyte changes. In saline-treated rats, fibrin-positive material was seen in the tubules but not in the urine sediments collected after 90 min of reflow, either due to fibrinolysis or poor urinary elimination. The results suggest that anticoagulation does not preclude the glomerular sieving of macromolecules, but seems to reduce tubular obstruction, probably by preventing conversion of filtered fibrinogen into fibrin.

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.