Sodium-Based Osmotherapy in Continuous Renal Replacement Therapy: a Mathematical Approach

Prediction of end-dialysis serum sodium concentration in severely hyponatremic kidney failure patients undergoing conventional hemodialysis using sodium kinetic equation

Background and Objectives

Conventional hemodialysis (HD) for kidney failure patients with severe hyponatremia may be complicated by rapid correction of hyponatremia, which increases the risk of osmotic demyelination syndrome. A simple sodium kinetic equation was effective in prediction of end-dialysis serum Na+ in severely hyponatremic kidney failure patient treated with continuous venovenous hemofiltration, but was not tested in conventional HD. The aim of this study was to assess the validity of this equation when used in conventional HD.

Methods

Twenty conventional HD sessions were delivered to 12 kidney failure patients with severe hyponatremia (serum Na+  < 120 mEq/L). The target change in serum Na+ was 4 mEq/L. The DNa.t/V that obtained this change was predetermined according to the sodium kinetic equation and monitored in real time by online clearance monitoring software embedded in dialysis machine. The dialysis session was terminated once the target DNa.t/V was achieved.

Results

The mean observed and predicted serum Na+ were 119.80 ± 3.42 mEq/L and 119.45 ± 3.12 mEq/L, respectively. Bland–Altman plot analysis revealed a mean difference ± SD of 0.33 ± 1.26 mEq/L, and 95% limits of agreement of − 2.13 to 2.83. The imprecision in prediction of end-dialysis serum Na+ was 2.52 mEq/L. The small difference and clinically insignificant 95% limits of agreement indicate a good agreement between the observed and predicted serum Na+.

Conclusion

The sodium kinetic equation was effective in prediction of end-dialysis serum Na+ in kidney failure patients with severe hyponatremia.

Safely correct hyponatremia with continuous renal replacement therapy: A flexible, all-purpose method based on the mixing paradigm

Treating chronic hyponatremia by continuous renal replacement therapy (CRRT) is challenging because the gradient between a replacement fluid's [sodium] and a patient's serum sodium can be steep, risking too rapid of a correction rate with possible consequences. Besides CRRT, other gains and losses of sodium- and potassium-containing solutions, like intravenous fluid and urine output, affect the correction of serum sodium over time, known as osmotherapy. The way these fluids interact and contribute to the sodium/potassium/water balance can be parsed as a mixing problem. As Na/K/H₂ O are added, mixed in the body, and drained via CRRT, the net balance of solutes must be related to the change in serum sodium, expressible as a differential equation. Its solution has many variables, one of which is the sodium correction rate, but all variables can be evaluated by a root-finding technique. The mixing paradigm is proved to replicate the established equations of osmotherapy, as in the special case of a steady volume. The flexibility to solve for any variable broadens our treatment options. If the pre-filter replacement fluid cannot be diluted, then we can compensate by calculating the CRRT blood flow rate needed. Or we can deduce the infusion rate of dextrose 5% water, post-filter, to appropriately slow the rise in serum sodium. In conclusion, the mixing model is a generalizable and practical tool to analyze patient scenarios of greater complexity than before, to help doctors customize a CRRT prescription to safely and effectively reach the serum sodium target.

Management for Electrolytes Disturbances during Continuous Renal Replacement Therapy

Despite the lack of proven superiority in mortality compared to intermittent hemodialysis, continuous renal replacement therapy (CRRT) is the preferred renal replacement therapy modality for critically ill patients with acute kidney injury (AKI) due to better hemodynamic stability and steady correction of electrolytes disturbances and volume overload. Multiple and complex electrolyte disorders in patients with AKI can be managed effectively with CRRT because controlled and predictable correction is feasible. Thus, CRRT has an advantage with safety over conventional hemodialysis, especially in patients with both renal dysfunction and electrolyte disorder that require a sophisticated treatment with avoidance of rapid correction. On the contrary, CRRT can potentially lead to paradoxical disturbance of electrolytes such as hypokalemia or hypophosphatemia, especially in patients under high dose or prolonged duration of CRRT treatment. These electrolytes related complications can be prevented with close monitoring followed by the appropriate use of CRRT fluids. Although there is a lack of solid evidence and standardized guideline for CRRT prescriptions, optimal management of various electrolyte disturbances can be achieved with individualized and tailored dialysate and replacement fluid prescriptions. Several commercially available CRRT solutions with varying compositions provide flexibility to manage electrolyte disorders and maintain the stability of electrolyte. In this review, we discuss various prescription methods to manage common electrolyte imbalances as well as preventative strategies to maintain electrolyte homeostasis during CRRT providing detailed protocols used in our center. This review may contribute to future research that can lead to the development of clinical practice guidelines.

Successful treatment of acute encephalitis and hepatitis in a child with COVID-19 infection

We present the case of a 6-year-old Taiwanese boy with a fulminant course of COVID-19 manifesting as high fever, acute consciousness changes, and status epilepticus. Brain MRI showed restricted diffusion in the bilateral hemisphere. Electroencephalogram showed diffuse slow waves with few spikes. CSF study was clear without evidence of common pathogens. He received treatment with antiviral agents, corticosteroids, intravenous immunoglobulins, and anti-IL-6 monoclonal antibodies. However, progressive fulminant hepatitis, hyperammonaemia, and disseminated intravascular coagulopathy developed. Rescue therapy with hybrid continuous renal replacement therapy and plasma exchange were performed in the first 11 days. The patient improved and was extubated on the 11th day. After physical therapy, his neurological function improved significantly. The patient was discharged under rehabilitation after 1 month of hospitalization. Viral sequencing confirmed infection with the Omicron BA.2.3 variant, one of the dominant strains in Taiwan and Hong Kong. Whole-exome sequencing revealed heterozygous uncertain significance variants in <I>TICAM-1, RNF 31</I>, and mitochondrial <I>MT-RNR1</I>, which provide additional support for the fulminant course. To the best of our knowledge, this is the first reported case of COVID-19 in a child with a fulminant course of acute encephalitis and hepatitis who successfully recovered by hybrid continuous renal replacement therapy and plasma exchange.

Continuous Renal Replacement Therapy in Acute Brain Injury

Acute brain injury is the sudden and reversible loss of brain self regulation capacity as a disruption of the blood-brain barrier that conditions metabolic and inflammatory disorders that can exacerbate acute kidney injury in a critical setting; specifically it has been described that the alterations of the internal environment that come from the severity of the acute kidney injury increases the risk of endocranial hypertension and cerebral edema; in this context, injuries should be identified and treated in a timely manner with a comprehensive approach. Continuous renal replacement therapy is an extracorporeal purification technique that has been gaining ground in the management of acute kidney injury in critically ill patients. Within its modalities, continuous venous venous hemofiltration is described as the therapy of choice in patients with acute brain injury due to its advantages in maintaining hemodynamic stability and reducing the risk of cerebral edema. Optimal control of variables such as timing to start renal replacement therapy, the prescribed dose, the composition of the replacement fluid and the anticoagulation of the extracorporeal circuit will have a significant impact on the evolution of the neurocritical patient with acute kidney injury. There are limited studies evaluating the role of hemofiltration in this context.

Sodium-based osmotherapy for hyponatremia in acute decompensated heart failure

Acute decompensated heart failure (ADHF) accounts for more than 1 million hospital admissions annually and is associated with high morbidity and mortality. Decongestion with removal of increased total body sodium and total body water are goals of treatment. Acute kidney injury (AKI) or chronic kidney disease (CKD) is present in two-thirds of patients with ADHF. The pathophysiology of ADHF and AKI is bidirectional and synergistic. AKI and CKD complicate the management of ADHF by decreasing diuretic efficiency and excretion of sodium and water. Among patients hospitalized with ADHF, hyponatremia is the most common electrolyte abnormality and is classically encountered with volume overload. ADHF represents an additional therapeutic challenge particularly when oligoanuria is present. Predilution continuous venovenous hemofiltration with sodium-based osmotherapy can safely increase plasma sodium concentration without deleteriously increasing total body sodium. We present a detailed methodology that addresses the issue of hypervolemic hyponatremia in patients with ADHF and AKI.

A mathematical approach to severe hyponatremia and hypernatremia in renal replacement therapies

Severe dysnatremias are perplexing problems in patients undergoing renal replacement therapy on a chronic or acute basis. The ability to manipulate sodium concentration in the dialysate or replacement solutions is limited. Compounding dialysate or replacement fluids to alter sodium concentration could result in errors. Rapid correction of hyponatremia or hypernatremia due to equilibrium with dialysate or replacement solutions could lead to osmotic demyelination syndrome or cerebral edema respectively. Continuous renal replacement therapy is the preferred dialysis modality in patients with severe dysnatremias. In this article, we present simple formulas to determine the rate of hypotonic or hypertonic solutions needed to mitigate rapid correction of dysnatremias. These formulas can be used readily by the clinician at bedside.

Severe Hyponatremia and Continuous Renal Replacement Therapy: Safety and Effectiveness of Low-Sodium Dialysate

RATIONALE & OBJECTIVE

In patients with severe hyponatremia in the setting of acute kidney injury or end-stage kidney disease, continuous renal replacement therapy (CRRT) using standard-sodium (140 mEq/L) fluids may lead to excessively rapid correction of plasma sodium concentration. Use of dialysate and replacement fluids with reduced sodium concentrations can provide a controlled rate of correction of plasma sodium concentration.

STUDY DESIGN

We performed a single-center retrospective analysis of the safety and effectiveness of this approach in patients with plasma sodium concentrations ≤ 126 mEq/L who underwent CRRT for 24 or more hours using low-sodium (119 or 126 mEq/L) dialysate and replacement fluids. Change in plasma sodium level was assessed at 24 and 48 hours after initiation of low-sodium CRRT and at the end of treatment.

SETTING & PARTICIPANTS

Between January 2016 and June 2018, a total of 23 hyponatremic patients underwent continuous venovenous hemodiafiltration using low-sodium dialysate and replacement fluids; 4 patients were excluded from analysis because of CRRT duration less than <24 hours.

RESULTS

The 19 patients included in the study had a mean age of 56 years, 11 (58%) were men, and 15 (79%) were white. The initial mean plasma sodium level was 121 mEq/L and the initial CRRT effluent dose was 27 mL/kg/h. Only 2 (11%) patients had an increase in plasma sodium concentration > 6 mEq/L at 24 hours. Mean changes in plasma sodium levels at 24 and 48 hours and at the time of CRRT discontinuation were 3, 3, and 6 mEq/L, respectively. None of the patients developed osmotic demyelination syndrome.

LIMITATIONS

Key limitations were small sample size and lack of a control group.

CONCLUSIONS

Use of low-sodium dialysate and replacement fluids is a safe strategy for the prevention of overly rapid correction of plasma sodium levels in hyponatremic patients undergoing CRRT.