Filtration dynamics and natriuretic response to volume expansion in humans

Role of albumin-induced volume expansion therapy for cerebral vasospasm in aneurysmal subarachnoid hemorrhage: A systematic review

Objectives

This study reviews the effect of albumin-induced volume expansion therapy on symptomatic vasospasm and clinical outcome in aneurysmal subarachnoid hemorrhage (aSAH).

Materials and Methods

Computer searches carried out from the Scopus, Medline, Embase, Web of Science, the Cochrane Library, and Internet documents; hand searching of medical journals; and review of reference lists. Randomized controlled trials (RCT) and observational studies (OSs) comparing albumin therapy in combination or alone with crystalloid therapy for the treatment of cerebral vasospasm in aSAH were included in the study. Risk-of-bias assessment was conducted using ROB2.0 and ROBINS-I tools for RCTs and Oss, respectively.

Results

Out of a total of 1078 searches, one RCT (published in two articles) and one observational (retrospective) study were included for final analysis. In RCT, albumin was used for volume expansion therapy with a baseline crystalloid regime and comparison made between hypervolemic and normovolemic groups and it showed no beneficial effects on symptomatic vasospasm and clinical outcomes based on the Glasgow outcome scale. Furthermore, the use of albumin showed a tendency for sodium retention with lowering of glomerular filtration rate, limiting the amount of total fluid required for targeted central venous pressure values, and thereby avoiding fluid overload manifestations. The retrospective study results between albumin versus non-albumin groups (crystalloids only) supported improved outcomes in the former group with lower in-hospital mortality. Cardiorespiratory complications were equivocal in RCT and increased in non-albumin group in the retrospective study. Risk-of-bias assessment analyses revealed "some concerns" in RCT and "serious" limitation in OS due to its retrospective design.

Conclusion

Albumin-induced volume expansion therapy for cerebral vasospasm does not have substantiative evidence to improve cerebral vasospasm and clinical outcomes in aSAH. Studies with well-designed RCTs are required to compare the use of albumin for volume expansion therapy versus standard fluid management using crystalloids to mitigate the scarcity of published data.

Longitudinal study of living kidney donor glomerular dynamics after nephrectomy

BACKGROUND

Over 5,000 living kidney donor nephrectomies are performed annually in the US. While the physiological changes that occur early after nephrectomy are well documented, less is known about the long-term glomerular dynamics in living donors.

METHODS

We enrolled 21 adult living kidney donors to undergo detailed long-term clinical, physiological, and radiological evaluation pre-, early post- (median, 0.8 years), and late post- (median, 6.3 years) donation. A morphometric analysis of glomeruli obtained during nephrectomy was performed in 19 subjects.

RESULTS

Donors showed parallel increases in single-kidney renal plasma flow (RPF), renocortical volume, and glomerular filtration rate (GFR) early after the procedure, and these changes were sustained through to the late post-donation period. We used mathematical modeling to estimate the glomerular ultrafiltration coefficient (Kf), which also increased early and then remained constant through the late post-donation study. Assuming that the filtration surface area (and hence, Kf) increased in proportion to renocortical volume after donation, we calculated that the 40% elevation in the single-kidney GFR observed after donation could be attributed exclusively to an increase in the Kf. The prevalence of hypertension in donors increased from 14% in the early post-donation period to 57% in the late post-donation period. No subjects exhibited elevated levels of albuminuria.

CONCLUSIONS

Adaptive hyperfiltration after donor nephrectomy is attributable to hyperperfusion and hypertrophy of the remaining glomeruli. Our findings point away from the development of glomerular hypertension following kidney donation.

TRIAL REGISTRATION

Not applicable. FUNDING. NIH (R01DK064697 and K23DK087937); Astellas Pharma US; the John M. Sobrato Foundation; the Satellite Extramural Grant Foundation; and the American Society of Nephrology.

Diuretic response to colloid and crystalloid fluid loading in critically ill patients

AIMS

In the critically ill patient, fluid loading is commonly done to stabilise hemodynamics and increase diuresis, whereas the absence of diuresis may predispose to harmful overloading. The goal of the current study was to evaluate the diuretic response and determinants thereof upon crystalloid and colloid fluid loading.

SUBJECTS AND METHODS

This is a substudy on 42 clinically hypovolemic, septic or non-septic patients without acute kidney injury, who were randomly assigned, after stratification for sepsis, to a 90-min fluid loading protocol with either 0.9% saline or a colloid solution (gelatin, hydroxyethyl starch 200/0.5 or albumin). Hemodynamics, biochemical parameters and diuresis were recorded. A response was defined by an increase in diuresis of >10% during fluid loading.

RESULTS

Diuresis increased more during saline than colloid infusion, together with a decline in colloid osmotic pressure (COP) of plasma and less increase in plasma volume and global hemodynamics with saline, at similar fluid balance. Nine patients (82%) receiving saline had a diuretic response, compared to 13 patients (42%) receiving colloids (P = 0.04), and the response was not predicted by underlying condition, global hemodynamics, volume of fluid infused and COP.

CONCLUSION

In critically ill patients with clinical hypovolemia, diuresis increases more during saline than colloid fluid loading, only partly dependent of a fall in plasma COP.

Glomerular function, structure, and number in renal allografts from older deceased donors

The 5-yr survival rate of renal allografts is significantly lower for grafts from older deceased donors than from younger deceased donors. For evaluation of the potential contribution of renal senescence in this shortened graft survival, glomerular function and structure were analyzed in allografts from deceased donors older than 55 yr ("aging") or younger than 40 yr ("youthful"). Aging donors had a significantly higher prevalence of sclerotic glomeruli (P < 0.002), and their nonsclerotic glomeruli tended to be larger, had a larger filtration surface area (P = 0.02), and had a higher single-nephron ultrafiltration coefficient (K(f); P = 0.07), suggesting a compensatory response to functional loss of glomeruli. After serum creatinine reached a stable nadir in the transplant recipients, GFR and its hemodynamic determinants were evaluated and the whole allograft K(f) was computed. Compared with the allografts from youthful donors, allografts from aging donors exhibited a 32% lower GFR, which was exclusively attributable to a 45% reduction in allograft K(f) (both P < 0.001). In addition, the number of functioning glomeruli per allograft was profoundly lower in grafts from aging donors than from youthful donors (3.6 +/- 2.1 x 10(5) versus 8.5 +/- 3.4 x 10(5); P < 0.01), and this could not be explained by the relatively modest 17% prevalence of global glomerulosclerosis in the aging group. The marked reduction in overall glomerular number in many aging donors may lead to a "remnant kidney" phenomenon, potentially explaining the shorter mean survival of these allografts.

Course of preeclamptic glomerular injury after delivery

We evaluated the early postpartum recovery of glomerular function over 4 wk in 57 women with preeclampsia. We used physiological techniques to measure glomerular filtration rate (GFR), renal plasma flow, and oncotic pressure (πA) and computed a value for the two-kidney ultrafiltration coefficient ( Kf). Compared with healthy, postpartum controls, GFR was depressed by 40% on postpartum day 1, but by only 19% and 8% in the second and fourth postpartum weeks, respectively. Hypofiltration was attributable solely to depression, at corresponding postpartum times, of Kf by 55%, 30%, and 18%, respectively. Improvement in glomerular filtration capacity was accompanied by recovery of hypertension to near-normal levels and significant improvement in albuminuria. We conclude that the functional manifestations of the glomerular endothelial injury of preeclampsia largely resolve within the first postpartum month.

A genetic model defines the importance of the atrial natriuretic peptide receptor (guanylyl cyclase-A) in the regulation of kidney function

Disruption of the atrial natriuretic peptide (ANP) receptor [guanylyl cyclase-A (GC-A)] gene yields mice with a salt-resistant form of hypertension, raising fundamental questions on the role of ANP in acute regulation of the kidney. Here, we show that water intake, food consumption, stool weight, urine volume, and sodium excretion are not significantly different between wild-type and GC-A null mice on standard rodent chow (0.7% NaCl) or a high-salt diet (8% NaCl). In conscious mice with an indwelling catheter, the infusion of a physiological saline solution containing 4% BSA resulted in a marked natriuresis/diuresis in wild-type mice but no response in GC-A null animals. When physiological saline was given by gavage, however, the kidney response of wild-type and null mice was equivalent, raising the possibility that the gastrointestinal tract can directly regulate kidney function. However, administration of 0.9% saline through an intraperitoneal route also resulted in equal kidney responses in wild-type and null mice. When 0.9% NaCl lacking protein was infused i.v., wild-type and null mice both responded at the kidney level. Thus, GC-A appears dispensable for regulation of sodium/water excretion in response to changes in dietary sodium concentration, but likely becomes critical in volume expansions where the isooncotic pressure remains constant, such as head-out immersion or the initial and correctable stages of congestive heart failure.