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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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Close correlation between glomerular filtration rate and renal oxygen consumption in uncomplicated post-cardiac surgery patients (controls, n = 37) and in patients with postoperative acute kidney injury (AKI). Note that the slope of the regression line is steeper in the AKI group. Thus filtration and reabsorbtion of sodium consumes approximately 2.5 times more oxygen in the AKI group. From [2] with permission.
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Figure 4: Close correlation between glomerular filtration rate and renal oxygen consumption in uncomplicated post-cardiac surgery patients (controls, n = 37) and in patients with postoperative acute kidney injury (AKI). Note that the slope of the regression line is steeper in the AKI group. Thus filtration and reabsorbtion of sodium consumes approximately 2.5 times more oxygen in the AKI group. From [2] with permission.

Mentions: Redfors et al. recently studied renal perfusion, filtration and oxygenation in patients with preoperative normal renal function developing early AKI (50-200% increase in serum creatinine) after complicated cardiac surgery [2]. Renal blood flow was measured by renal vein retrograde thermodilution and by infusion clearance of PAH corrected for renal extraction of PAH. 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). Thus, the renal VO2 of the AKI patients was 1.9 ml/mmol reabsorbed sodium, a value that was 2.4 times higher than in the uncomplicated control group (0.82 ml/mmol reabsorbed sodium). 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. According to the "acute renal success"- hypothesis [42-44], as put forward by several researchers, AKI patients should operate on the lower part of the regression line of the control patients. However, the regression line of the AKI patients is clearly shifted to the left, i. e., at a certain GFR, renal VO2 is higher, speaking against this hypothesis. On the contrary, the 40% decrease in renal DO2 in combination with a tubular sodium reabsorption at a high oxygen demand, suggests that renal hypoxia is present after the initiation phase of ischemic AKI.


Renal oxygenation in clinical acute kidney injury.

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

Close correlation between glomerular filtration rate and renal oxygen consumption in uncomplicated post-cardiac surgery patients (controls, n = 37) and in patients with postoperative acute kidney injury (AKI). Note that the slope of the regression line is steeper in the AKI group. Thus filtration and reabsorbtion of sodium consumes approximately 2.5 times more oxygen in the AKI group. From [2] with permission.
© Copyright Policy
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC3672481&req=5

Figure 4: Close correlation between glomerular filtration rate and renal oxygen consumption in uncomplicated post-cardiac surgery patients (controls, n = 37) and in patients with postoperative acute kidney injury (AKI). Note that the slope of the regression line is steeper in the AKI group. Thus filtration and reabsorbtion of sodium consumes approximately 2.5 times more oxygen in the AKI group. From [2] with permission.
Mentions: Redfors et al. recently studied renal perfusion, filtration and oxygenation in patients with preoperative normal renal function developing early AKI (50-200% increase in serum creatinine) after complicated cardiac surgery [2]. Renal blood flow was measured by renal vein retrograde thermodilution and by infusion clearance of PAH corrected for renal extraction of PAH. 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). Thus, the renal VO2 of the AKI patients was 1.9 ml/mmol reabsorbed sodium, a value that was 2.4 times higher than in the uncomplicated control group (0.82 ml/mmol reabsorbed sodium). 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. According to the "acute renal success"- hypothesis [42-44], as put forward by several researchers, AKI patients should operate on the lower part of the regression line of the control patients. However, the regression line of the AKI patients is clearly shifted to the left, i. e., at a certain GFR, renal VO2 is higher, speaking against this hypothesis. On the contrary, the 40% decrease in renal DO2 in combination with a tubular sodium reabsorption at a high oxygen demand, suggests that renal hypoxia is present after the initiation phase of ischemic AKI.

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