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Renal oxygenation in clinical acute kidney injury.

Ricksten SE, Bragadottir G, Redfors B - Crit Care (2013)

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An increase in renal O2Ex means that renal DO2 has decreased in relation to renal VO2, i. e., renal oxygenation is impaired, and vice versa... Prasad et al. demonstrated in conscious volunteers that 20 mg of furosemide increased medullary oxygenation, using the blood oxygen level-dependent magnetic resonance imaging technique (BOLD MRI)... In contrast, acetazolamide, which inhibits tubular reabsorption of the proximal tubules in the cortex and which does not affect medullary PO2 in experimental studies, did not affect medullary oxygenation... Furosemide increased fractional excretion of sodium (excreted sodium/filtered sodium) from 2% to 25% and caused a 10-fold increase in urine flow because of a 28% decrease in tubular sodium reabsorption... These changes were in turn associated with a 23% decrease in renal VO2... Thus, furosemide decreased renal O2Ex and improved renal oxygenation as renal blood flow was not significantly affected by the diuretic... Redfors et al. recently studied the effects of low-dose (2-4 μg/kg/min) dopamine on renal blood flow, GFR, tubular sodium reabsorption, renal VO2 and the renal oxygen demand/supply relationship in post-cardiac surgery patients... Postoperative AKI in this group of patients is considered a consequence of impaired renal DO2, in turn caused by intra-operative hypotension and hemodilution-induced anemia, as well as perioperative low cardiac output... In spite of a normalization of cardiac index (CI) with inotropic treatment with or without intra-aortic balloon pump (IABP), renal oxygenation was severely impaired in patients with early AKI, as demonstrated by a 70% relative increase in renal O2Ex, compared to uncomplicated post-cardiac surgery patients with normal renal function This was, in turn, caused by a pronounced renal vasoconstriction and a 40% lower renal blood flow, in combination with a renal VO2 that was not significantly different from the control group, despite the 60% decrease in GFR and renal tubular sodium reabsorption (Table 3)... Figure 4 shows the close correlation between GFR and renal VO2 in patients with early AKI after cardiac surgery versus those undergoing uncomplicated surgery with no renal impairment... At a target MAP of 75 mm Hg, renal DO2 (13%), GFR (27%) and urine flow were higher and renal O2Ex was lower (7.4%) compared with a target MAP of 60 mm Hg... However, the renal variables did not differ when compared at target MAPs of 75 and 90 mm Hg (Figure 8)... ANP is ideally suited for treatment of ischemic AKI, as it preferentially dilates the preglomerular resistance vessels; this will increase GFR but also renal blood flow, meeting the increased oxygen demand of the medulla by an increase in renal DO2... Mannitol increases renal blood flow and GFR in clinical ischemic AKI most likely by endothelial and epithelial de-swelling effects.

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Effects of 2 and 4 μg/kg/min of dopamine (DA2, DA4) on renal blood flow (RBF), glomerular filtration rate (GFR), renal oxygen consumption (RVO2) and renal oxygen extraction (RO2Ex) in postoperative patients. RBF was measured by two independent techniques, retrograde renal vein thermodilution (RBF-TD) and infusion clearance for paraaminohippuric acid (PAH), with correction for renal extraction of PAH (RBF-IC). Note that low-dose dopamine improved renal oxygenation by a profound renal vasodilation with no changes in GFR or RVO2. From [23] with permission.
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Figure 3: Effects of 2 and 4 μg/kg/min of dopamine (DA2, DA4) on renal blood flow (RBF), glomerular filtration rate (GFR), renal oxygen consumption (RVO2) and renal oxygen extraction (RO2Ex) in postoperative patients. RBF was measured by two independent techniques, retrograde renal vein thermodilution (RBF-TD) and infusion clearance for paraaminohippuric acid (PAH), with correction for renal extraction of PAH (RBF-IC). Note that low-dose dopamine improved renal oxygenation by a profound renal vasodilation with no changes in GFR or RVO2. From [23] with permission.

Mentions: Redfors et al. recently studied the effects of low-dose (2-4 μg/kg/min) dopamine on renal blood flow, GFR, tubular sodium reabsorption, renal VO2 and the renal oxygen demand/supply relationship in post-cardiac surgery patients [23]. Renal blood flow was estimated by two independent techniques, the retrograde renal vein thermodilution technique and the paraaminohippuric acid (PAH) infusion clearance technique, with correction for renal extraction of PAH. Interestingly, low-dose dopamine induced pronounced renal vasodilation with a 45-55% increase in renal blood flow. One would expect that such a marked increase in renal blood flow would be accompanied by a proportional increase in GFR (Figure 3). However, GFR was not significantly affected by dopamine. Thus, because of the lack of effect of dopamine on GFR, renal VO2 was not affected and, consequently, renal oxygenation was improved (Figure 3). Thus, the hypothesis put forward by Jones and Bellomo [19], that dopamine may impair renal oxygenation is not supported by the data from Redfors et al. [23].


Renal oxygenation in clinical acute kidney injury.

Ricksten SE, Bragadottir G, Redfors B - Crit Care (2013)

Effects of 2 and 4 μg/kg/min of dopamine (DA2, DA4) on renal blood flow (RBF), glomerular filtration rate (GFR), renal oxygen consumption (RVO2) and renal oxygen extraction (RO2Ex) in postoperative patients. RBF was measured by two independent techniques, retrograde renal vein thermodilution (RBF-TD) and infusion clearance for paraaminohippuric acid (PAH), with correction for renal extraction of PAH (RBF-IC). Note that low-dose dopamine improved renal oxygenation by a profound renal vasodilation with no changes in GFR or RVO2. From [23] with permission.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3672481&req=5

Figure 3: Effects of 2 and 4 μg/kg/min of dopamine (DA2, DA4) on renal blood flow (RBF), glomerular filtration rate (GFR), renal oxygen consumption (RVO2) and renal oxygen extraction (RO2Ex) in postoperative patients. RBF was measured by two independent techniques, retrograde renal vein thermodilution (RBF-TD) and infusion clearance for paraaminohippuric acid (PAH), with correction for renal extraction of PAH (RBF-IC). Note that low-dose dopamine improved renal oxygenation by a profound renal vasodilation with no changes in GFR or RVO2. From [23] with permission.
Mentions: Redfors et al. recently studied the effects of low-dose (2-4 μg/kg/min) dopamine on renal blood flow, GFR, tubular sodium reabsorption, renal VO2 and the renal oxygen demand/supply relationship in post-cardiac surgery patients [23]. Renal blood flow was estimated by two independent techniques, the retrograde renal vein thermodilution technique and the paraaminohippuric acid (PAH) infusion clearance technique, with correction for renal extraction of PAH. Interestingly, low-dose dopamine induced pronounced renal vasodilation with a 45-55% increase in renal blood flow. One would expect that such a marked increase in renal blood flow would be accompanied by a proportional increase in GFR (Figure 3). However, GFR was not significantly affected by dopamine. Thus, because of the lack of effect of dopamine on GFR, renal VO2 was not affected and, consequently, renal oxygenation was improved (Figure 3). Thus, the hypothesis put forward by Jones and Bellomo [19], that dopamine may impair renal oxygenation is not supported by the data from Redfors et al. [23].

View Article: PubMed Central - HTML - PubMed

AUTOMATICALLY GENERATED EXCERPT
Please rate it.

An increase in renal O2Ex means that renal DO2 has decreased in relation to renal VO2, i. e., renal oxygenation is impaired, and vice versa... Prasad et al. demonstrated in conscious volunteers that 20 mg of furosemide increased medullary oxygenation, using the blood oxygen level-dependent magnetic resonance imaging technique (BOLD MRI)... In contrast, acetazolamide, which inhibits tubular reabsorption of the proximal tubules in the cortex and which does not affect medullary PO2 in experimental studies, did not affect medullary oxygenation... Furosemide increased fractional excretion of sodium (excreted sodium/filtered sodium) from 2% to 25% and caused a 10-fold increase in urine flow because of a 28% decrease in tubular sodium reabsorption... These changes were in turn associated with a 23% decrease in renal VO2... Thus, furosemide decreased renal O2Ex and improved renal oxygenation as renal blood flow was not significantly affected by the diuretic... Redfors et al. recently studied the effects of low-dose (2-4 μg/kg/min) dopamine on renal blood flow, GFR, tubular sodium reabsorption, renal VO2 and the renal oxygen demand/supply relationship in post-cardiac surgery patients... Postoperative AKI in this group of patients is considered a consequence of impaired renal DO2, in turn caused by intra-operative hypotension and hemodilution-induced anemia, as well as perioperative low cardiac output... In spite of a normalization of cardiac index (CI) with inotropic treatment with or without intra-aortic balloon pump (IABP), renal oxygenation was severely impaired in patients with early AKI, as demonstrated by a 70% relative increase in renal O2Ex, compared to uncomplicated post-cardiac surgery patients with normal renal function This was, in turn, caused by a pronounced renal vasoconstriction and a 40% lower renal blood flow, in combination with a renal VO2 that was not significantly different from the control group, despite the 60% decrease in GFR and renal tubular sodium reabsorption (Table 3)... Figure 4 shows the close correlation between GFR and renal VO2 in patients with early AKI after cardiac surgery versus those undergoing uncomplicated surgery with no renal impairment... At a target MAP of 75 mm Hg, renal DO2 (13%), GFR (27%) and urine flow were higher and renal O2Ex was lower (7.4%) compared with a target MAP of 60 mm Hg... However, the renal variables did not differ when compared at target MAPs of 75 and 90 mm Hg (Figure 8)... ANP is ideally suited for treatment of ischemic AKI, as it preferentially dilates the preglomerular resistance vessels; this will increase GFR but also renal blood flow, meeting the increased oxygen demand of the medulla by an increase in renal DO2... Mannitol increases renal blood flow and GFR in clinical ischemic AKI most likely by endothelial and epithelial de-swelling effects.

Show MeSH
Related in: MedlinePlus