Non-Anion Gap Metabolic Acidosis: A Clinical Approach to Evaluation

Anorexia Caused by Hyperchloremic Metabolic Acidosis Following Ileal Conduit Diversion: A Case Report

Hyperchloremic metabolic acidosis is a known complication following ileal conduit urinary diversion, often arising from urinary reabsorption in the ileum, which leads to chloride retention and bicarbonate loss and, though often asymptomatic, can produce clinically significant symptoms, particularly in patients with underlying renal impairment. A 75-year-old woman with a history of bladder cancer underwent cystectomy with ileal conduit diversion and presented on postoperative day 47 with anorexia, hypotension, and weight loss; laboratory findings revealed hyperchloremic metabolic acidosis with elevated serum chloride. The patient's acidosis gradually improved with sodium bicarbonate and Ringer's solution, stabilizing her blood pressure, creatinine, and acid-base balance, and she was discharged with outpatient follow-up. This case highlights the role of urinary reabsorption in the ileal conduit as a cause of bicarbonate loss and acidosis exacerbation, particularly in patients with renal impairment, while the sodium-chloride gap, although supplementary, provided additional insights into acidosis progression and facilitated early detection in this case. Hyperchloremic metabolic acidosis following ileal conduit diversion warrants vigilant monitoring and timely intervention, with bicarbonate supplementation playing a central role in treatment to optimize clinical outcomes in patients with compromised renal function.

A review of renal tubular acidosis

OBJECTIVE

To review the current scientific literature on renal tubular acidosis (RTA) in people and small animals, focusing on diseases in veterinary medicine that result in secondary RTA.

DATA SOURCES

Scientific reviews and original research publications on people and small animals focusing on RTA.

SUMMARY

RTA is characterized by defective renal acid-base regulation that results in normal anion gap hyperchloremic metabolic acidosis. Renal acid-base regulation includes the reabsorption and regeneration of bicarbonate in the renal proximal tubule and collecting ducts and the process of ammoniagenesis. RTA occurs as a primary genetic disorder or secondary to disease conditions. Based on pathophysiology, RTA is classified as distal or type 1 RTA, proximal or type 2 RTA, type 3 RTA or carbonic anhydrase II mutation, and type 4 or hyperkalemic RTA. Fanconi syndrome comprises proximal RTA with additional defects in proximal tubular function. Extensive research elucidating the genetic basis of RTA in people exists. RTA is a genetic disorder in the Basenji breed of dogs, where the mutation is known. Secondary RTA in human and veterinary medicine is the sequela of diseases that include immune-mediated, toxic, and infectious causes. Diagnosis and characterization of RTA include the measurement of urine pH and the evaluation of renal handling of substances that should affect acid or bicarbonate excretion.

CONCLUSIONS

Commonality exists between human and veterinary medicine among the types of RTA. Many genetic defects causing primary RTA are identified in people, but those in companion animals other than in the Basenji are unknown. Critically ill veterinary patients are often admitted to the ICU for diseases associated with secondary RTA, or they may develop RTA while hospitalized. Recognition and treatment of RTA may reverse tubular dysfunction and promote recovery by correcting metabolic acidosis.

Fluid management in hospitalized pediatric patients

The proper use of intravenous fluids has likely been responsible for saving more lives than any other group of substances. Proper use includes prescribing an appropriate electrolyte and carbohydrate solution, at a calculated rate or volume, for the right child, at the right time. Forming intravenous fluid plans for hospitalized children requires an understanding of water and electrolyte physiology in healthy children and how different pathology deviates from the norm. This review highlights fluid management in several disease types, including liver disease, diabetic ketoacidosis, syndrome of inappropriate antidiuretic hormone, diabetes insipidus, kidney disease, and intestinal failure as well as in those with nonphysiologic fluid losses. For each disease, the review discusses specific considerations, evaluations, and management strategies to consider when customizing intravenous fluid plans. Ultimately, all hospitalized children should receive an individualized fluid plan with recurrent evaluations and fluid modifications to provide optimal care.

Association of dietary acid load with serum bicarbonate in chronic kidney disease (CKD) patients

BACKGROUND/OBJECTIVES

Diet can affect the acid-base status depending on the balance between the intake of acid-inducing foods and base-inducing foods. The purpose of this study was to estimate the dietary acid load and evaluate its association with serum bicarbonate in patients with stages 3 and 4 chronic kidney disease.

SUBJECTS/METHODS

One hundred adults (aged ≥ 20 years) with chronic kidney disease (CKD) stages 3 and 4 were enrolled in a cross-sectional study. A food diary was used to estimate the animal and plant protein intakes, which were used in the potential renal acid load (PRAL) formula described by Remer and Manz. PRAL was divided into quartiles. Regression models unadjusted and adjusted for age, gender, body mass index, diabetes, systolic and diastolic blood pressure, creatinine clearance were performed using the stepwise regression method.

RESULTS

The median level (25th, 75th percentiles) of PRAL was 8.3 mEq/day (1.6, 15.6). The highest quartile of PRAL had a higher consumption of animal protein (77.8 ± 10.9%) and a reduced consumption of plant protein (22.2 ± 10.9%), compared to the lowest quartile (59.5 ± 18.6% animal protein, 40.5 ± 18.6% plant protein), p for trend <0.0001. In the adjusted analysis, a significant association was observed between the highest quartile of PRAL and serum bicarbonate in CKD patients compared to the lowest quartile (β: 2.07, 95% CI: 0.21-3.92). According to the multiple linear regression, for each increase of 1 unit of PRAL there was a reduction of 0.25 mmol/L in serum bicarbonate (HCO₃). Using the stepwise method, animal protein intake and PRAL were determinants of HCO₃ (r = 0.49).

CONCLUSIONS

In CKD patients of stages 3 and 4, the dietary acid load was associated with HCO₃. Limiting dietary acid load could be a complementary approach in the dietary treatment of CKD. In addition, studies are needed to analyze the effect of replacing animal protein with plant protein.

Diagnostic et Prise en Charge de l’Acidose Métabolique Recommandations formalisées d’experts communes Société de réanimation de langue française (SRLF) – Société française de médecine d’urgence (SFMU)

L’acidose métabolique est un trouble fréquemment rencontré en médecine d’urgence et en médecine intensive réanimation. La littérature s’étant enrichie de nouvelles données concernant la prise en charge de l’acidose métabolique, la Société de Réanimation de Langue Française (SRLF) et la Société Française de Médecine d’Urgence (SFMU) ont élaboré des recommandations formalisées d’experts selon la méthodologie GRADE. Les champs de la stratégie diagnostique, de l’orientation et de la prise en charge thérapeutique ont été traités et vingt-neuf recommandations ont été formulées : quatre recommandations fortes (Grade 1), dix recommandations faibles (Grade 2) et quinze avis d’experts. Toutes ont obtenu un accord fort. L’application des méthodes d’Henderson-Hasselbalch et de Stewart pour le diagnostic du mécanisme de l’acidose métabolique est discutée et un algorithme diagnostique est proposé. L’utilisation de la cétonémie et des lactatémies veineuse et capillaire est également traitée. L’intérêt du pH, de la lactatémie et de sa cinétique pour l’orientation des patients en pré-hospitalier et aux urgences est envisagé. Enfin, les modalités de l’insulinothérapie au cours de l’acidocétose diabétique, les indications de la perfusion de bicarbonate de sodium et de l’épuration extra-rénale ainsi que les modalités de la ventilation mécanique au cours des acidoses métaboliques sévères sont traitées dans la prise en charge thérapeutique.

Diagnosis and management of metabolic acidosis: guidelines from a French expert panel

Metabolic acidosis is a disorder frequently encountered in emergency medicine and intensive care medicine. As literature has been enriched with new data concerning the management of metabolic acidosis, the French Intensive Care Society (Société de Réanimation de Langue Française [SRLF]) and the French Emergency Medicine Society (Société Française de Médecine d’Urgence [SFMU]) have developed formalized recommendations from experts using the GRADE methodology. The fields of diagnostic strategy, patient assessment, and referral and therapeutic management were addressed and 29 recommendations were made: 4 recommendations were strong (Grade 1), 10 were weak (Grade 2), and 15 were experts’ opinions. A strong agreement from voting participants was obtained for all recommendations. The application of Henderson–Hasselbalch and Stewart methods for the diagnosis of the metabolic acidosis mechanism is discussed and a diagnostic algorithm is proposed. The use of ketosis and venous and capillary lactatemia is also treated. The value of pH, lactatemia, and its kinetics for the referral of patients in pre-hospital and emergency departments is considered. Finally, the modalities of insulin therapy during diabetic ketoacidosis, the indications for sodium bicarbonate infusion and extra-renal purification as well as the modalities of mechanical ventilation during severe metabolic acidosis are addressed in therapeutic management.

The role of the clinical laboratory in diagnosing acid-base disorders

Acid-base homeostasis is fundamental for life. The body is exceptionally sensitive to changes in pH, and as a result, potent mechanisms exist to regulate the body's acid-base balance to maintain it in a very narrow range. Accurate and timely interpretation of an acid-base disorder can be lifesaving but establishing a correct diagnosis may be challenging. The underlying cause of the acid-base disorder is generally responsible for a patient's signs and symptoms, but laboratory results and their integration into the clinical picture is crucial. Important acid-base parameters are often available within minutes in the acute hospital care setting, and with basic knowledge it should be easy to establish the diagnosis with a stepwise approach. Unfortunately, many caveats exist, beginning in the pre-analytical phase. In the post-analytical phase, studies on the arterial reference pH are scarce and therefore many different reference values are used in the literature without any solid evidence. The prediction models that are currently used to assess the acid-base status are approximations that are mostly based on older studies with several limitations. The two most commonly used methods are the physiological method and the base excess method, both easy to use. The secondary response equations in the base excess method are the most convenient. Evaluation of acid-base disorders should always include the assessment of electrolytes and the anion gap. A major limitation of the current acid-base laboratory tests available is the lack of rapid point-of-care laboratory tests to diagnose intoxications with toxic alcohols. These intoxications can be fatal if not recognized and treated within minutes to hours. The surrogate use of the osmolal gap is often an inadequate substitute in this respect. This article reviews the role of the clinical laboratory to evaluate acid-base disorders.

Pseudo-Renal Tubular Acidosis: Conditions Mimicking Renal Tubular Acidosis

Hyperchloremic metabolic acidosis, particularly renal tubular acidosis, can pose diagnostic challenges. The laboratory phenotype of a low total carbon dioxide content, normal anion gap, and hyperchloremia may be misconstrued as hypobicarbonatemia from renal tubular acidosis. Several disorders can mimic renal tubular acidosis, and these must be appropriately diagnosed to prevent inadvertent and inappropriate application of alkali therapy. Key physiologic principles and limitations in the assessment of renal acid handling that can pose diagnostic challenges are enumerated.

Review of the Diagnostic Evaluation of Normal Anion Gap Metabolic Acidosis

Background

Normal anion gap metabolic acidosis is a common but often misdiagnosed clinical condition associated with diarrhea and renal tubular acidosis (RTA). Early identification of RTA remains challenging for inexperienced physicians, and diagnosis and treatment are often delayed.

Summary

The presence of RTA should be considered in any patient with a high chloride level when the CL^-/Na⁺ ratio is above 0.79, if the patient does not have diarrhea. In patients with significant hyperkalemia one should evaluate for RTA type 4, especially in diabetic patients, with a relatively conserved renal function. A still growing list of medications can produce RTA.

Key Messages

This review highlights practical aspects concerning normal anion gap metabolic acidosis.