Naoya Iguchi

Renal haemodynamics and oxygenation during and after cardiac surgery and cardiopulmonary bypass

Acute kidney injury (AKI) is a common complication following cardiac surgery performed on cardiopulmonary bypass (CPB) and has important implications for prognosis. The aetiology of cardiac surgery‐associated AKI is complex, but renal hypoxia, particularly in the medulla, is thought to play at least some role. There is strong evidence from studies in experimental animals, clinical observations and computational models that medullary ischaemia and hypoxia occur during CPB. There are no validated methods to monitor or improve renal oxygenation during CPB, and thus possibly decrease the risk of AKI. Attempts to reduce the incidence of AKI by early transfusion to ameliorate intra‐operative anaemia, refinement of protocols for cooling and rewarming on bypass, optimization of pump flow and arterial pressure, or the use of pulsatile flow, have not been successful to date. This may in part reflect the complexity of renal oxygenation, which may limit the effectiveness of individual interventions. We propose a multi‐disciplinary pathway for translation comprising three components. Firstly, large‐animal models of CPB to continuously monitor both whole kidney and regional kidney perfusion and oxygenation. Secondly, computational models to obtain information that can be used to interpret the data and develop rational interventions. Thirdly, clinically feasible non‐invasive methods to continuously monitor renal oxygenation in the operating theatre and to identify patients at risk of AKI. In this review, we outline the recent progress on each of these fronts.

Effects of low-dose atrial natriuretic peptide infusion on cardiac surgery–associated acute kidney injury: A multicenter randomized controlled trial

Purpose: To evaluate the effects of atrial natriuretic peptide (ANP) on renal function and medical costs in patients with acute kidney injury (AKI) associated with cardiac surgery. Materials and methods: The Japanese trial for AKI in Post‐cardiovascular surgery patients by ANP (JAPAN) was a prospective, multicenter, randomized, double‐blind, placebo‐controlled study conducted in 11 hospitals in Japan. Acute kidney injury was defined as an increase in serum creatinine of at least 0.3 mg/dL within 48 hours. The patients were randomly assigned to receive ANP (0.02 &mgr;g kg−1 min−1) or placebo. The primary end point was a change in renal function. The secondary end points were a need for renal replacement therapy, the lengths of intensive care unit and hospital stays, and medical costs incurred over the 90‐day follow‐up. Results: Of the 77 randomized patients, 37 were in the ANP group and 40 were in the placebo group. Although ANP significantly (P = .018) increased urine output, it did not significantly improve renal function compared with placebo. There were no significant differences between the groups in the renal replacement therapy rate, the lengths of the intensive care unit and hospital stays, or medical costs. Conclusion: Atrial natriuretic peptide infusion did not show a renoprotective effect or cost‐saving effect in the treatment of cardiac surgery–associated AKI. HighlightsANP was administered in patients with AKI associated with cardiac surgery.ANP significantly increased urine output.ANP did not significantly improve renal function.ANP did not significantly reduce the renal replacement therapy rate or medical costs.

Influence of Humidification on Comfort During Noninvasive Ventilation With a Helmet

OBJECTIVE: To evaluate optimal humidifier water temperature when using a helmet for noninvasive ventilation. METHODS: Twenty-eight healthy individuals underwent 8 cm H2O CPAP ventilation with FIO2 of 0.21 and 0.5. Each was sequentially tested in the following order: using the helmet without humidification at ambient temperature; with humidification with unheated chamber water; and with humidification with the chamber water at 31°C, 34°C, and 37°C. At each setting, after a 20 min stabilization period, measurements were taken. Comfort level at each setting was evaluated using a visual analog scale rated zero (least comfortable) to 10 (most comfortable). RESULTS: Temperature and relative and absolute humidity inside the helmet increased; however, the comfort scores significantly decreased as the humidification chamber water temperature increased. Regardless of the FIO2, statistically significantly highest comfort scores were obtained when humidification water, with and without active humidification, was at ambient temperature. Unacceptable absolute humidity was obtained only without humidification at room temperature when FIO2 was 0.5. CONCLUSIONS: With the clinical use of a helmet, for patient comfort and mucosal humidification during CPAP, the most desirable conditions are likely to be obtained by humidifying without heating, that is by leaving the water in the humidifier chamber at room temperature.

Plasma neutrophil gelatinase-associated lipocalin clearance during venovenous hemodiafiltration

To the Editor Plasma neutrophil gelatinase-associated lipocalin (NGAL) levels are predictors of acute kidney injury (AKI) severity [1, 2]. NGAL may also limit kidney injury [3]. Hemodiafiltration (HDF) may affect plasma NGAL levels because NGAL is probably filtered and absorbed by the filter membrane. We investigated the effect of HDF on plasma NGAL levels in eight AKI patients undergoing intermittent HDF (Osaka University Hospital Ethics Committee No. 9024). HDF by the post-dilution method was performed using an EXCELFLO AEF-10 filter (Asahi Kasei Kuraray Medical Co., Ltd., Tokyo, Japan). The blood flow rate was 80 mL/min. Plasma NGAL levels were measured using the CircuLex NGAL/Lipocalin-2 ELISA Kit (CycLex Co., Ltd. Ina, Japan) before, during, and after HDF. NGAL clearance (ClNGAL) was determined as ClNGAL = (Cpre Cpost)/Cpre 9 80 (mL/min) and the sieving coefficient (SC) as SC = 2 9 Cfil/(Cpre ? Cpost), where Cfil is the concentration in filtered fluid and Cpre and Cpost are the concentrations in preand post-filtered plasma, respectively. The interval between initial HDF and the study was 21.4 ± 24.6 days. Within this period, continuous HDF was applied for 10.1 ± 11.8 days. The total flow rate of the replacement and dialysis fluids was 21.8 ± 2.3 mL/kg/h. Plasma NGAL levels decreased significantly to 83.6 ± 5.6% (percentage of NGAL level at HDF initiation) at the end of HDF (P \ 0.001, repeated measures ANOVA) (Fig. 1). Discontinuation of HDF increased plasma NGAL levels which returned to 90.8 ± 6.3% at 17.5 ± 4.7 h.

Pulse oximetric thresholds for tonsillectomy and adenotomy in children: significance of 1–2% decline in oxyhemoglobin saturation

Objectives:  We aimed to establish optimal overnight pulse oximetric thresholds for determining the indication of tonsillectomy and adenotomy (TA) in children by revising the definition of ‘desaturation’.

Sepsis-induced acute kidney injury: A disease of the microcirculation

AKI is a common complication of sepsis and is significantly associated with mortality. Sepsis accounts for more than 50% of the cases of AKI, with a mortality rate of up to 40%. The pathogenesis of septic AKI is complex, but there is emerging evidence that, at least in the first 48 hours, the defects may be functional rather than structural in nature. For example, septic AKI is associated with an absence of histopathological changes, but with microvascular abnormalities and tubular stress. In this context, renal medullary hypoxia due to redistribution of intra‐renal perfusion is emerging as a critical mediator of septic AKI. Clinically, vasopressor drugs remain the cornerstone of therapy for maintenance of blood pressure and organ perfusion. However, in septic AKI, there is insensitivity to vasopressors such as norepinephrine, leading to persistent hypotension and organ failure. Vasopressin, angiotensin II, and, paradoxically, α2‐adrenergic receptor agonists (clonidine and dexmedetomidine) may be feasible adjunct therapies for catecholamine‐resistant vasodilatory shock. In this review, we outline the recent progress made in understanding how these drugs may influence the renal microcirculation, which represents a crucial step toward developing better approaches for the circulatory management of patients with septic AKI.

Alterations in regional kidney oxygenation during expansion of extracellular fluid volume in conscious healthy sheep

Expansion of extracellular fluid volume with crystalloid solutions is a common medical intervention, but its effects on renal cortical and medullary oxygenation are poorly understood. Therefore, we instrumented sheep under general anesthesia to enable continuous measurement of systemic and renal hemodynamics, global renal oxygen delivery and consumption, and intrarenal tissue perfusion and oxygen tension (Po2) in conscious animals ( n = 7). The effects of three sequential intermittent infusions of 500 ml of compound sodium lactate solution, administered at hourly intervals, were determined. Volume expansion induced transient increases in mean arterial pressure (+7 ± 2%), central venous pressure (+50 ± 19%), and cardiac output (+15 ± 3%). There were sustained increases in renal medullary tissue Po2 (+35 ± 10%) despite increases in global renal oxygen consumption (+66 ± 18%) and renal oxygen extraction (+64 ± 8%). Volume expansion did not significantly alter renal blood flow, renal oxygen delivery, or medullary perfusion. The sustained increase in medullary Po2 was paralleled by increased bladder urine Po2 (34 ± 4%). Cortical perfusion and Po2 did not change significantly. Our findings indicate that extracellular fluid volume expansion can increase renal medullary oxygenation, providing a potential mechanistic basis for its use as prophylaxis against iatrogenic acute kidney injury. They also indicate that continuous measurement of bladder urine Po2 could be used to monitor the effects of volume expansion on medullary oxygenation. However, the mechanisms mediating increased medullary oxygenation during volume expansion remain to be determined.

Rhabdomyolysis induced by Pseudomonas aeruginosa sepsis

We describe advanced hemodynamic insufficiency and remarkably high myoglobinemia in a 77-year-old man who was admitted to the intensive care unit after total aortic arch replacement. Serum myoglobin showed an unusually high value (peak value, 155 030 ng·ml−1). The patient died of sepsis and untreatable metabolic acidosis. Pseudomonas aeruginosa was detected in blood culture specimens after his death. On histopathological examination, dense congregations of gramnegative bacilli were present in clots in blood vessels, while congregations of gram-negative bacilli around the circumference of small blood vessels were particularly apparent in every specimen examined. Moreover, a generalized breakdown of muscle fibers, consistent with findings of rhabdomyolysis, was observed in muscle tissue throughout the body.