Effects of furosemide, acetazolamide and amiloride on renal cortical and medullary tissue oxygenation in non-anaesthetised healthy sheep.

It has been proposed that diuretics can improve renal tissue oxygenation through inhibition of tubular sodium reabsorption and reduced metabolic demand. However, the impact of clinically used diuretic drugs on the renal cortical and medullary microcirculation is unclear. Therefore, we examined the effects of three commonly used diuretics, at clinically relevant doses, on renal cortical and medullary perfusion and oxygenation in non-anaesthetised healthy sheep. Merino ewes received acetazolamide (250 mg; n = 9), furosemide (20 mg; n = 10) or amiloride (10 mg; n = 7) intravenously. Systemic and renal haemodynamics, renal cortical and medullary tissue perfusion and P O 2 ${P_{{{\mathrm{O}}_{\mathrm{2}}}}}$ , and renal function were then monitored for up to 8 h post-treatment. The peak diuretic response occurred 2 h (99.4 ± 14.8 mL/h) after acetazolamide, at which stage cortical and medullary tissue perfusion and P O 2 ${P_{{{\mathrm{O}}_{\mathrm{2}}}}}$ were not significantly different from their baseline levels. The peak diuretic response to furosemide occurred at 1 h (196.5 ± 12.3 mL/h) post-treatment but there were no significant changes in cortical and medullary tissue oxygenation during this period. However, cortical tissue P O 2 ${P_{{{\mathrm{O}}_{\mathrm{2}}}}}$ fell from 40.1 ± 3.8 mmHg at baseline to 17.2 ± 4.4 mmHg at 3 h and to 20.5 ± 5.3 mmHg at 6 h after furosemide administration. Amiloride did not produce a diuretic response and was not associated with significant changes in cortical or medullary tissue oxygenation. In conclusion, clinically relevant doses of diuretic agents did not improve regional renal tissue oxygenation in healthy animals during the 8 h experimentation period. On the contrary, rebound renal cortical hypoxia may develop after dissipation of furosemide-induced diuresis.

Reversal of cerebral ischaemia and hypoxia and of sickness behaviour by megadose sodium ascorbate in ovine Gram-negative sepsis.

BACKGROUND: The mechanisms by which megadose sodium ascorbate improves clinical status in experimental sepsis is unclear. We determined its effects on cerebral perfusion, oxygenation, and temperature, and plasma levels of inflammatory biomarkers, nitrates, nitrites, and ascorbate in ovine Gram-negative sepsis. METHODS: Sepsis was induced by i.v. infusion of live Escherichia coli for 31 h in unanaesthetised Merino ewes instrumented with a combination sensor in the frontal cerebral cortex to measure tissue perfusion, oxygenation, and temperature. Fluid resuscitation at 23 h was followed by i.v. megadose sodium ascorbate (0.5 g kg-1 over 30 min+0.5 g kg-1 h-1 for 6.5 h) or vehicle (n=6 per group). Norepinephrine was titrated to restore mean arterial pressure (MAP) to 70-80 mm Hg. RESULTS: At 23 h of sepsis, MAP (mean [sem]: 85 [2] to 64 [2] mm Hg) and plasma ascorbate (27 [2] to 15 [1] µM) decreased (both P<0.001). Cerebral ischaemia (901 [58] to 396 [40] units), hypoxia (34 [1] to 19 [3] mm Hg), and hyperthermia (39.5 [0.1]°C to 40.8 [0.1]°C) (all P<0.001) developed, accompanied by malaise and lethargy. Sodium ascorbate restored cerebral perfusion (703 [121] units], oxygenation (30 [2] mm Hg), temperature (39.2 [0.1]°C) (all PTreatment<0.05), and the behavioural state to normal. Sodium ascorbate slightly reduced the sepsis-induced increase in interleukin-6, returned VEGF-A to normal (both PGroupxTime<0.01), and increased plasma ascorbate (20 000 [300] µM; PGroup<0.001). The effects of sodium ascorbate were not reproduced by equimolar sodium bicarbonate. CONCLUSIONS: Megadose sodium ascorbate rapidly reversed sepsis-induced cerebral ischaemia, hypoxia, hyperthermia, and sickness behaviour. These effects were not reproduced by an equimolar sodium load.

Differential responses of cerebral and renal oxygenation to altered perfusion conditions during experimental cardiopulmonary bypass in sheep.

We tested whether the brain and kidney respond differently to cardiopulmonary bypass (CPB) and to changes in perfusion conditions during CPB. Therefore, in ovine CPB, we assessed regional cerebral oxygen saturation (rSO2 ) by near-infrared spectroscopy and renal cortical and medullary tissue oxygen tension (PO2 ), and, in some protocols, brain tissue PO2 , by phosphorescence lifetime oximetry. During CPB, rSO2 correlated with mixed venous SO2 (r = 0.78) and brain tissue PO2 (r = 0.49) when arterial PO2 was varied. During the first 30 min of CPB, brain tissue PO2 , rSO2 and renal cortical tissue PO2 did not fall, but renal medullary tissue PO2 did. Nevertheless, compared with stable anaesthesia, during stable CPB, rSO2 (66.8 decreasing to 61.3%) and both renal cortical (90.8 decreasing to 43.5 mm Hg) and medullary (44.3 decreasing to 19.2 mm Hg) tissue PO2 were lower. Both rSO2 and renal PO2 increased when pump flow was increased from 60 to 100 mL kg-1 min-1 at a target arterial pressure of 70 mm Hg. They also both increased when pump flow and arterial pressure were increased simultaneously. Neither was significantly altered by partially pulsatile flow. The vasopressor, metaraminol, dose-dependently decreased rSO2 , but increased renal cortical and medullary PO2 . Increasing blood haemoglobin concentration increased rSO2 , but not renal PO2 . We conclude that both the brain and kidney are susceptible to hypoxia during CPB, which can be alleviated by increasing pump flow, even without increasing arterial pressure. However, increasing blood haemoglobin concentration increases brain, but not kidney oxygenation, whereas vasopressor support with metaraminol increases kidney, but not brain oxygenation.

Effects of sodium-glucose transporter-2 inhibition on systemic hemodynamics, renal function, and intra-renal oxygenation in sepsis-associated acute kidney injury.

BACKGROUND: People with type 2 diabetes mellitus treated with sodium-glucose transporter-2 inhibitors (SGLT2i) have lower rates of acute kidney injury (AKI). Sepsis is responsible for the majority of AKI in critically ill patients. This study investigated whether SGLT2i is renoprotective in an ovine model of Gram-negative septic AKI. METHODS: Sixteen healthy merino ewes were surgically instrumented to enable measurement of mean arterial pressure, cardiac output, renal blood flow, renal cortical and medullary perfusion, and oxygenation. After a 5-day recovery period, sepsis was induced via slow and continuous intravenous infusion of live Escherichia coli. Twenty-three hours later, sheep were randomized to receive an intravenous bolus of 0.2 mg/kg empagliflozin (n = 8) or a fluid-matched vehicle (n = 8). RESULTS: Empagliflozin treatment did not significantly reduce renal medullary hypoperfusion or hypoxia, improve kidney function, or induce histological changes. Renal cortical oxygenation during the intervention period was 47.6 ± 5.9 mmHg in the empagliflozin group compared with 40.6 ± 8.2 mmHg in the placebo group (P = 0.16). Renal medullary oxygenation was 28.0 ± 18.5 mmHg in the empagliflozin compared with 25.7 ± 16.3 mmHg (P = 0.82). Empagliflozin treatment did not result in significant between-group differences in renal blood flow, kidney function, or renal histopathological changes. CONCLUSION: In a large mammalian model of septic AKI, a single dose of empagliflozin did not improve renal microcirculatory perfusion, oxygenation, kidney function, or histopathology.

Cerebrospinal fluid and plasma ascorbate concentrations following subarachnoid haemorrhage.

Background: Ascorbate, the biologically active form of vitamin C, is the primary neural anti-oxidant. Ascorbate concentrations have never been quantified following aneurysmal subarachnoid haemorrhage (aSAH). Objective: To quantify plasma and cerebrospinal fluid (CSF) ascorbate concentrations in patients following SAH. Design Setting Participants Main Outcome Measures: Cohort study in which plasma and CSF ascorbate concentrations were measured longitudinally in 12 aSAH patients admitted to a quaternary referral intensive care unit and compared to one-off samples obtained from 20 pregnant women prior to delivery in a co-located obstetric hospital. Data are median [interquartile range] or median (95 % confidence intervals). Results: Forty-eight plasma samples were obtained from the 12 aSAH patients (eight females, age 62 [53-68] years). Eight participants with extra-ventricular drains provided 31 paired CSF-plasma samples. Single plasma and CSF samples were obtained from 20 pregnant women (age 35 [31-37] years). Initial plasma and CSF ascorbate concentrations post aSAH were less than half those in pregnant controls (plasma: aSAH: 31 [25-39] µmol/L vs. comparator: 64 [59-77] µmol/L; P < 0.001 and CSF: 116 [80-142] µmol/L vs. 252 [240-288] µmol/L; P < 0.001). Post aSAH there was a gradual reduction in the CSF:plasma ascorbate ratio from ∼4:1 to ∼1:1. Six (50 %) patients developed vasospasm and CSF ascorbate concentrations were lower in these patients (vasospasm: 61 (25, 97) vs. no vasospasm: 110 (96, 125) µmol/L; P = 0.01). Conclusion: Post aSAH there is a marked reduction in CSF ascorbate concentration that is most prominent in those who develop vasospasm.