Failure of loop diuretics to improve the long term outcome of ischaemic damage in rat kidneys

Fluid management and use of diuretics in acute kidney injury

Critically ill adult patients at risk for or with acute kidney injury (AKI) require careful attention to their hemodynamic status because hypotension and hypovolemia may contribute to or worsen kidney injury. Increasing evidence suggests that isotonic crystalloids should be used instead of colloids for initial expansion of intravascular volume in patients at risk for AKI or with AKI, such as those with sepsis, septic shock, or trauma. The timing and amount of volume to be administered to prevent AKI and other organ damage is still debated, but an aggressive fluid repletion in the early setting is probably beneficial. However, fluid overload has also been associated with increased mortality and reduced rate of kidney recovery in observational studies in critically ill patients with AKI. Diuretics may prevent or treat fluid overload and may also affect kidney function. The efficacy of these procedures in critically ill AKI patients need to be confirmed with randomized controlled trials. This review focuses on early volume resuscitation, overall fluid management, and use of diuretics in critically ill adult patients at risk for or with AKI and their effect on mortality and kidney function in this setting.

Benefits and risks of furosemide in acute kidney injury

Furosemide, a potent loop diuretic, is frequently used in different stages of acute kidney injury, but its clinical roles remain uncertain. This review summarises the pharmacology of furosemide, its potential uses and side effects, and the evidence of its efficacy. Furosemide is actively secreted by the proximal tubules into the urine before reaching its site of action at the ascending limb of loop of Henle. It is the urinary concentrations of furosemide that determine its diuretic effect. The severity of acute kidney injury has a significant effect on the diuretic response to furosemide; a good 'urinary response' may be considered as a 'proxy' for having some residual renal function. The current evidence does not suggest that furosemide can reduce mortality in patients with acute kidney injury. In patients with acute lung injury without haemodynamic instability, furosemide may be useful in achieving fluid balance to facilitate mechanical ventilation according to the lung-protective ventilation strategy.

Renal endothelial dysfunction and impaired autoregulation after ischemia-reperfusion injury result from excess nitric oxide

Endothelial dysfunction in ischemic acute renal failure (IARF) has been attributed to both direct endothelial injury and to altered endothelial nitric oxide synthase (eNOS) activity, with either maximal upregulation of eNOS or inhibition of eNOS by excess nitric oxide (NO) derived from iNOS. We investigated renal endothelial dysfunction in kidneys from Sprague-Dawley rats by assessing autoregulation and endothelium-dependent vasorelaxation 24 h after unilateral (U) or bilateral (B) renal artery occlusion for 30 (U30, B30) or 60 min (U60, B60) and in sham-operated controls. Although renal failure was induced in all degrees of ischemia, neither endothelial dysfunction nor altered facilitation of autoregulation by 75 pM angiotensin II was detected in U30, U60, or B30 kidneys. Baseline and angiotensin II-facilitated autoregulation were impaired, methacholine EC(50) was increased, and endothelium-derived hyperpolarizing factor (EDHF) activity was preserved in B60 kidneys. Increasing angiotensin II concentration restored autoregulation and increased renal vascular resistance (RVR) in B60 kidneys; this facilitated autoregulation, and the increase in RVR was abolished by 100 microM furosemide. Autoregulation was enhanced by N(omega)-nitro-l-arginine methyl ester. Peri-ischemic inhibition of inducible NOS ameliorated renal failure but did not prevent endothelial dysfunction or impaired autoregulation. There was no significant structural injury to the afferent arterioles with ischemia. These results suggest that tubuloglomerular feedback is preserved in IARF but that excess NO and probably EDHF produce endothelial dysfunction and antagonize autoregulation. The threshold for injury-producing, detectable endothelial dysfunction was higher than for the loss of glomerular filtration rate. Arteriolar endothelial dysfunction after prolonged IARF is predominantly functional rather than structural.