Effect of tolvaptan on hyponatremia in a dog with syndrome of inappropriate secretion of antidiuretic hormone.

A 1-year-old spayed female Miniature Schnauzer had chronic hyponatremia, accompanied by polyuria and polydipsia. Blood tests and urinalysis revealed severe hyponatremia, low plasma osmolality with euvolemia, and increased sodium excretion in urine. Hypothyroidism and hypoadrenocorticism were ruled out as causes. These findings led to the diagnosis of syndrome of inappropriate secretion of antidiuretic hormone (SIADH). Magnetic resonance imaging (MRI) showed dilation of the lateral ventricles, indicating severe hydrocephalus. Tolvaptan, a vasopressin V2 receptor antagonist commonly used in human SIADH, was administered along with water restriction. This treatment resulted in a consistent increase in plasma sodium levels without any adverse effects. This case report represents the first documented evidence of the therapeutic efficacy of tolvaptan in treating SIADH in a dog.

Hematological differentiation of bladder rupture and complete/partial urethral obstruction in castrated Hanwoo (Korean indigenous cattle) with urolithiasis.

This case report describes the hematological and radiological examination of urinary bladder rupture and complete urethral obstruction. associated with urolithiasis in Hanwoo. Hyponatremia, hypochloremia, azotemia, and hyperglycemia were observed in both urethral obstruction and urinary bladder rupture. However, cattle with urethral obstruction showed hyperkalemia and mild hyperglycemia, whereas cattle with bladder rupture showed marked hyperglycemia and normal potassium levels. In ultrasonography, the urethral obstruction showed a dilated bladder with a thick bladder wall. In contrast to previous literature, in this study, severe electrolyte changes such as severe hyponatremia, hypochloremia, and hyperkalemia occurred in a case of complete urethral obstruction.

Clinicopathological and radiographic indicators for orogastric decompression in rabbits presenting with intestinal obstruction at a referral hospital (2015-2018).

BACKGROUND: Orogastric decompression is regularly recommended as a part of both medical and pre-surgical treatment for small intestinal obstruction in rabbits. However, guidelines as to when orogastric decompression is indicated are sparse. METHODS: The medical records of 35 rabbits diagnosed with gastrointestinal obstruction over a 3-year period were examined. Differences in presentation, clinicopathological and radiographic examination findings, treatments and outcome were evaluated. RESULTS: Approximately 49% of the cases evaluated were considered to have non-life-threatening disease, while 51% were considered to have life-threatening disease. The severity of gastric obstruction was correlated with the severity of hyperglycaemia (average 25.7 mmol/L; 463 mg/dl) and corresponding hyponatraemia (Na < 138 mmol/L; 138 mEq/L). These patients were treated with orogastric decompression and medical management only. LIMITATIONS: This is a retrospective study and there are inherent limitations involving the quality of the data and data collection. Additional studies should be completed that strive for larger sample sizes to compare the differences in outcome between surgical and medical management, as well as investigate the outcomes of rabbits with hyperglycaemia and hyponatraemia that did not have an orogastric decompression performed. CONCLUSIONS: Blood glucose and sodium concentrations, in combination with radiographic findings, may aid clinicians in determining if orogastric decompression is indicated to stabilise rabbits with small intestinal obstructive disorders.

Hyponatremia in horses with septic pneumopathy.

BACKGROUND: Hyponatremia is common in horses with bacterial pleuropneumonia, but no further characterization of this abnormality has been reported. OBJECTIVES: Describe admission plasma sodium concentration ([Na]) in horses with septic pneumopathy and evaluate any association of plasma [Na] with markers of systemic inflammation. ANIMALS: Medical records of horses >1 month of age that between 2008 and 2021 had a transtracheal aspirate (TTA) performed, abnormal TTA cytology, positive TTA culture, pulmonary disease on ultrasonography, radiography or both, and plasma [Na] assessed by direct ion-selective-electrode (dISE). Horses with concurrent diarrhea or azotemia were excluded. METHODS: Clinical and clinicopathological variables of interest between hypo- and normonatremic horses were compared. Spearman correlation and Fisher exact tests were used to identify significant associations (P < .05). RESULTS: Twenty of 35 horses had hyponatremia (median, 132 mmol/L; 25-75th interquartile range [IQR], 129.7-133.1 mmol/L; reference range, 134.2-138.4 mmol/L). A higher proportion of horses with systemic inflammatory response syndrome (SIRS) had hyponatremia (P = .01). Hyponatremic patients had higher mean plasma fibrinogen concentration (461 ± 160.5 mg/dL; P = .01) and higher rectal temperature (38.8 ± 0.7°C; P = .02) than normonatremic horses. Negative correlations were found between plasma [Na] and fibrinogen (P = .001; ρ = -0.57) concentrations and between plasma [Na] and rectal temperature (P = .001; ρ = -0.51). Presence or absence of pleural effusion did not influence severity of hyponatremia. Mean duration of hospitalization was longer (P = .04) in hyponatremic horses (9.8 ± 6.6 days). CONCLUSIONS AND CLINICAL IMPORTANCE: Hyponatremia at admission is associated with the presence of inflammation, SIRS, and with longer duration of hospitalization.

Syndrome of inappropriate antidiuretic hormone secretion secondary to trauma in a dog.

OBJECTIVE: To describe a case of inappropriate antidiuretic hormone (ADH) secretion in a dog secondary to trauma. CASE SUMMARY: A 14-year-old neutered female mixed breed dog presented for evaluation of bite wounds. The dog sustained multiple puncture wounds to the cervical area, stifle, and elbow. Treatment was initiated with isotonic crystalloid fluids, analgesia, broad-spectrum antimicrobials, and gastroprotectants. The dog developed hyponatremia with concurrent serum hypoosmolality and inappropriate urine hyperosmolality and urine sodium secretion, leading to a diagnosis of the syndrome of inappropriate ADH secretion. The hyponatremia improved, and the dog improved clinically and was discharged 3 days after admission. NEW OR UNIQUE INFORMATION PROVIDED: This is the first case description of the syndrome of inappropriate ADH secretion in a dog suffering from trauma. Inappropriate ADH secretion is largely under-recognized in veterinary patients. Increased awareness of this syndrome can lead to initiation of appropriate treatment and improved outcomes.

Koi sleepy disease as a pathophysiological and immunological consequence of a branchial infection of common carp with carp edema virus.

Gills of fish are involved in respiration, excretion and osmoregulation. Due to numerous interactions between these processes, branchial diseases have serious implications on fish health. Here, "koi sleepy disease" (KSD), caused by carp edema virus (CEV) infection was used to study physiological, immunological and metabolic consequences of a gill disease in fish. A metabolome analysis shows that the moderately hypoxic-tolerant carp can compensate the respiratory compromise related to this infection by various adaptations in their metabolism. Instead, the disease is accompanied by a massive disturbance of the osmotic balance with hyponatremia as low as 71.65 mmol L-1, and an accumulation of ammonia in circulatory blood causing a hyperammonemia as high as 1123.24 µmol L-1. At water conditions with increased ambient salt, the hydro-mineral balance and the ammonia excretion were restored. Importantly, both hyponatremia and hyperammonemia in KSD-affected carp can be linked to an immunosuppression leading to a four-fold drop in the number of white blood cells, and significant downregulation of cd4, tcr a2 and igm expression in gills, which can be evaded by increasing the ion concentration in water. This shows that the complex host-pathogen interactions within the gills can have immunosuppressive consequences, which have not previously been addressed in fish. Furthermore, it makes the CEV infection of carp a powerful model for studying interdependent pathological and immunological effects of a branchial disease in fish.

Clinical application of 2.16% hypertonic saline solution to correct the blood sodium concentration in diarrheic calves with hyponatremia.

The aim of this study was to examine whether 2.16% hypertonic saline solution (HSS) is useful for the treatment of diarrheic calves with hyponatremia. Eleven of 13 female Holstein calves exhibiting moderate diarrhea and hyponatremia received 1,250 ml of 2.16% HSS over 15 min regardless of body weight. The remaining two calves that were unable to stand and had severe hyponatremia received 2,500 ml of 2.16% HSS intravenously over 30 min. As a result, hyponatremia in all diarrheic calves was significantly improved by the administration of 2.16% HSS from 122.2 ± 7.0 mEq/l at pre to 134.8 ± 3.7 mEq/l at post, which was above the threshold of 132 mEq/l for hyponatremia. Therefore, 2.16% HSS may be useful for hyponatremia in calves with diarrhea.

Retrospective evaluation of the association between hyponatremia and neurological dysfunction in hospitalized foals (2012-2016): 109 cases.

OBJECTIVE: Hyponatremia and rapid correction of hyponatremia can lead to neurological abnormalities. The objective of the study was to determine whether plasma sodium concentrations (Na+ ) and speed of correction of hyponatremia are significantly associated with neurological abnormalities in foals. DESIGN: Retrospective cohort study 2012 to 2016. SETTING: Equine hospital. ANIMALS: One hundred and nine foals <6 months old with hyponatremia (Na+ concentration ≤125 mmol/L). INTERVENTIONS: Case records were reviewed for any foal with hyponatremia. Clinicopathological findings, presence or absence of neurological signs on the day of the lowest Na+ concentration measured and the following 5 days, diagnosis and outcome were recorded, and changes in Na+ concentration per hour were calculated for up to 5 subsequent days. Logistic regression was used to assess the association between presence or absence of neurological signs, Na+ concentration, other known risk factors for neurological dysfunction in foals, and possible confounders. MEASUREMENTS AND MAIN RESULTS: In the final multivariable model, only Na+ (odds ratio [OR]: 0.86; 95% CI 0.79-0.95; P = 0.002) and BUN concentrations (OR: 1.04; 95% CI: 1.02-1.06; P = 0.001) were significantly associated with neurological signs. Changes in Na+ concentrations per hour were not associated with neurological signs on any day after the lowest Na+ concentration had been measured (P = 0.18-0.82), and development of new neurological signs following correction of hyponatremia was not reported in any foal. CONCLUSIONS: Na+ concentrations were associated with the development of neurological signs in hyponatremic foals. Increased BUN concentrations might contribute to neurological dysfunction, but further studies are necessary to confirm or refute these findings.

Acid base disorders in hospitalized cattle / Distúrbios ácido-base em bovinos hospitalizados

The objectives of this retrospective study were to determine the main acid-base and electrolytes disorders in hospitalized cattle, using both Henderson-Hasselbalch and the physicochemical approach and to compare their diagnostic and therapeutic utility. A total of 31 medical records were reviewed of bovines admitted to the Large Animal Hospital at Universidad Nacional de Colombia, that met the inclusion criteria of the measurement of blood gases, blood electrolytes and plasma protein on admission before providing any treatment. Using the Henderson-Hasselbalch approach, acid base abnormalities were found in 83.3% of the patients, compared to 93.5% using the physicochemical approach. The principal acid-base disorders found were strong ion acidosis (61.29%) and weak acid acidosis (38.7%); strong ion gap (SIG) acidosis was found in 73.68% of cases showing strong ion acidosis. These results highlight the importance of the diagnosis of acid-base disorders in sick cattle for proper recognition of pathophysiological phenomena and its understanding to guide treatment decisions.(AU)

Os objetivos deste estudo retrospectivo foram determinar os principais distúrbios ácido-base e eletrolíticos em bovinos internados, utilizando a abordagem Henderson-Hasselbalch e a abordagem físico-química comparando a utilidade diagnóstica e terapêutica de tais procedimentos. Foram revisados 31 prontuários de bovinos admitidos no Hospital de Animais de Grande Porte da Universidad Nacional de Colombia, que preencheram os critérios de inclusão da medição de gases sanguíneos, eletrólitos sanguíneos e proteínas plasmáticas na admissão antes de fornecer qualquer tratamento. Com o emprego da abordagem de Henderson-Hasselbalch, as anormalidades da base ácida foram encontradas em 83,3% dos pacientes, enquanto com a abordagem físico-química o valor obtido foi de 93,5%. Os principais distúrbios ácido-base encontrados foram forte acidose iônica (61,29%) e acidose ácida fraca (38,7%). A acidose com Ion Gap Forte (SIG) foi encontrada em 73,68% dos casos com forte acidose iônica. Estes resultados destacam a importância do diagnóstico de distúrbios ácido-base em bovinos doentes para o reconhecimento adequado dos fenômenos fisiopatológicos e sua compreensão para orientar as decisões de tratamento.(AU)

Acute kidney injury, seizures, and hypertonic hyponatremia secondary to mannitol intoxication in a dog.

OBJECTIVE: To describe a case of mannitol overdose associated with acute kidney injury (AKI), hypertonic hyponatremia, and neurologic abnormalities in a dog. CASE SUMMARY: A 10-year-old intact male Shiba Inu dog was referred to the emergency service of a veterinary teaching hospital for inappetence and acute onset of seizures. The dog had received 2 IV boluses of 3 g/kg of mannitol in less than 24 hours for a glaucoma crisis. Twelve hours after the second injection, the dog became inappetant and developed 2 generalized seizures. Seizure activity was treated with diazepam (0.5 mg/kg IV). Serum biochemistry profile showed severe hyponatremia and hypochloremia, mild hypokalemia, marked increased creatinine (381 µmol/L [44-133 µmol/L]) and moderately increased BUN (13.8 mmol/L [1.6-10.9 mmol/L]). Urinalysis revealed a urine specific gravity of 1.018, glucosuria, proteinuria, pigmenturia and the presence of vacuolized tubular epithelial cells. A presumptive diagnosis of mannitol intoxication was made based on the high dose of mannitol, severe hyponatremia, neurological abnormalities suggestive of intracranial disease, AKI, and urine cytology. Initial calculated plasma osmolality was 263.4 mOsm/kg and measured plasma osmolality was 332 mOsm/kg with an osmolal gap of 68.6 mOsm/kg, confirming the presence of an unmeasured solute attributed to mannitol. Treatment consisted of fluid therapy and supportive care. On day 3, osmolal gap had resolved and serum creatinine concentration returned to normal within 12 days. NEW OR UNIQUE INFORMATION PROVIDED: Mannitol intoxication has been reported in human medicine. This case report is, to our knowledge, the first to describe AKI, hypertonic hyponatremia, and neurological abnormalities secondary to mannitol overdose in a dog.

Hyponatremia in dogs and cats.

OBJECTIVE: To review the pathophysiology, diagnostic approach, and treatment recommendations for hyponatremia in dogs and cats. ETIOLOGY: Hyponatremia almost always results from an increase in total body water (TBW), and not from loss of sodium. Abnormalities in antidiuretic hormone (ADH) are commonly part of the etiology of hyponatremia. DIAGNOSIS: Diagnosis of hyponatremia focuses on the cause of the increase of TBW. Assessment of the patient's volume status and measurement of urine sodium concentration are important factors. Measurement or calculated estimation of plasma osmolality can also guide the assessment of hyponatremia. THERAPY: Too rapid correction of serum sodium can precipitate osmotic demyelination syndrome. As a general rule, serum sodium concentration should be raised ≤10 mmol/L over 24 hours, but rapid increases in serum sodium are indicated if neurologic abnormalities are evident. Serum sodium can be increased using hypertonic saline, with dosing based on the patient's calculated sodium deficit. Treatment of the underlying cause of water ingestion or retention is also required to fully resolve hyponatremia. PROGNOSIS: Mortality rates are significantly higher in dogs and cats with hyponatremia compared to those with normal serum sodium concentrations, even in patients with mild hypontremia (<5 mmol/L below the lower value of the reference interval). Hyponatremia is also associated with increased risk of death if present during specific disease states in dogs.

Pharmacokinetic and pharmacodynamic properties of orally administered torsemide in healthy horses.

BACKGROUND: Diuretic treatment is the mainstay for management of congestive heart failure in horses, and its use has been restricted to injectable medications because no currently data supports the use of PO administered loop diuretics. OBJECTIVES: To determine the pharmacokinetic and pharmacodynamic properties of PO administered torsemide and, determine if PO administered torsemide, could be used as an alternative to injectable diuretics in the horse. ANIMALS: Six healthy adult mares. METHODS: A 2-phase, prospective study, that consisted of pharmacokinetic profiling of a single dose (6 mg/kg PO) and pharmacodynamic effects of long-term torsemide administration (2 mg/kg PO q12h) for 6 days in healthy horses. RESULTS: Pharmacokinetic analysis identified a peak concentration (Cmax ) of 10.14 µg/mL (range, 6.79-14.69 µg/mL) and elimination half-life (T1/2 ) 9.2 hours (range, 8.4-10.4 hours). The area under the plasma drug concentration over time curve (AUC) was 80.7 µg × h/mL (range, 56.5-117.2 µg × h/mL). A statistically significant increase in urine volume and decrease in urine specific gravity were found from day 0 (baseline) to day 6 (P < .0001). Significant alterations in biochemical variables included hyponatremia, hypokalemia, hypochloremia, and increased serum creatinine concentration. Mean arterial blood pressure significantly decreased on day 6 (57.7 ± 8.8 mm Hg, P = .001) as compared with baseline (78 ± 6.1 mm Hg). Serum aldosterone concentrations significantly increased after 6 days of torsemide administration (P = .0006). CONCLUSIONS AND CLINICAL IMPORTANCE: PO administered torsemide (4 mg/kg/day) successfully reached therapeutic concentrations in blood, induced clinically relevant diuresis, and resulted in moderate pre-renal azotemia and electrolyte disturbances.

Urine sodium concentrations are predictive of hypoadrenocorticism in hyponatraemic dogs: a retrospective pilot study.

OBJECTIVES: To determine if a urine sodium concentration could be used to rule out hypoadrenocorticism in hyponatraemic dogs. MATERIALS AND METHODS: Medical records were reviewed for hyponatraemic dogs (serum sodium<135 mmol/L) that had recorded urine sodium concentrations. Twenty hyponatraemic dogs were included: 11 diagnosed with classical hypoadrenocorticism and nine with non-adrenal causes of hyponatraemia. A Wilcoxon rank-sum test was used to compare results between groups. RESULTS: No dog with hypoadrenocorticism had a urine sodium concentration less than 30 mmol/L. Urine sodium concentration in dogs with hypoadrenocorticism was significantly higher (median 103 mmol/L, range: 41 to 225) than in dogs with non-adrenal illness (median 10 mmol/L, range: 2 to 86) (P<0·0005). Serum sodium concentrations were not significantly different between dogs with hypoadrenocorticism and dogs with non-adrenal illness. CLINICAL SIGNIFICANCE: These results suggest that urine sodium concentrations can be used to prioritise a differential diagnosis of hypoadrenocorticism in hyponatraemic dogs. A urine sodium concentration less than 30 mmol/L in a hyponatraemic dog makes classical hypoadrenocorticism an unlikely cause of the hyponatraemia. Nevertheless, because of the small sample size our results should be interpreted with caution and a larger follow-up study would be valuable.

Elevated serum creatinine and hyponatraemia as prognostic factors in canine acute pancreatitis.

OBJECTIVE: To evaluate prognostic factors for canine acute pancreatitis (AP) based on clinical and laboratory data that can be easily assessed in veterinary practice. DESIGN: Retrospective study between January 2010 and December 2013. METHODS: The diagnosis of AP was based on clinical signs and an abnormal SNAP® cPL™ test result, concurrently with an ultrasound pattern suggestive of pancreatitis. Dogs were divided into survivors and non-survivors. We evaluated 12 clinical and laboratory parameters: respiratory rate, rectal temperature, white blood cells, haematocrit, total serum proteins, albumin, creatinine, cholesterol, total and ionised calcium, sodium and potassium. Clinical and clinicopathological data were statistically compared between survivors and non-survivors. A value of P < 0.05 was considered significant and P < 0.01 as highly significant. The odds ratio (OR) was calculated. RESULTS: The study enrolled 50 client-owned dogs with a diagnosis of AP. Serum creatinine (P = 0.017) and sodium (P = 0.004) correlated significantly with the outcome. Serum sodium < 139.0 mmol/L (139.0 mEq/L) and serum creatinine > 212 µmol/L (2.4 mg/dL) were associated significantly with poor prognosis. Azotaemia (OR 12.5; 95% confidence interval (CI) 1.32-118.48) and hyponatraemia (OR 4.9; 95% CI 1.36-17.64) were associated with increased risk of death. CONCLUSIONS: In dogs with AP, hyponatraemia and azotaemia seem to be significantly associated with an increased risk of death.

A Quick Reference on Hyponatremia.

The article focuses on causes of hyponatremia, including hypovolemia, diabetes mellitus and others. Hypovolemia is a major cause of hyponatremia in veterinary medicine. Hypovolemia causes a decrease in effective circulating volume, triggering antidiuretic hormone (ADH) secretion and free water retention, and develops after gastrointestinal losses, renal losses, hemorrhagic shock, hypoadrenocorticism, and other causes of hypovolemia. The article reviews the clinical approach to diagnosing the cause of hyponatremia in critically ill patients, including recognition of the syndrome of inappropriate ADH secretion (SIADH).

Maintenance Fluid Therapy: Isotonic Versus Hypotonic Solutions.

The goal of maintenance fluid therapy in small animals is to replace normal ongoing losses of water and salts when oral intake is withheld. Hospitalized dogs and cats may have multiple stimuli for antidiuretic hormone release that disrupt normal osmoregulation and predispose to water retention. Severe illness promotes retention of both sodium and water as edema. Commercially available fluids have electrolyte concentrations that are very different from dietary maintenance requirements, and potential consequences include development of hypoosmolality, edema, or both when excesses of water or sodium are administered. Suggestions for tailoring fluid administration toward specific goals are provided.

Disorders of Sodium and Water Homeostasis.

This review article discusses normal and abnormal sodium balance in small animals. The terms and concepts central to understanding normal sodium and water balance are presented as well as of the physiology of body fluid compartments and the movement of fluid between those compartments. As dysnatremia is a very common disorder across the spectrum of critically ill patients, the main focus of the article is to present several clinical examples of both acute and chronic hypernatremia and hyponatremia and their practical, clinical management.

Syndrome of Inappropriate Antidiuretic Hormone Secretion in a Mini-Breed Puppy Associated With Aspiration Pneumonia.

A 3-month-old intact male Prague ratter was presented to the emergency service for evaluation of progressive lethargy, weakness, coughing and labour breathing after an episode of resistance to oral deworming. The patient exhibited depression, increased respiratory effort and cyanosis at initial presentation. Results of first diagnostic work-up (complete blood cell count, biochemistry panel and thoracic x-rays) were all consistent with aspiration pneumonia. The puppy was initially treated with balanced isotonic crystalloids, broad spectrum antibiotics, nebulization with thoracic coupage and was transferred to an infant incubator with a sustained FiO2 of 40-50%. Twenty-four hours after ICU admission the patient's condition suffered a worsening and the dog was orthopneic, severely depressed with episodes of intermittent dysphoria and seizuring. New thoracic radiographs and several samples of blood and urine were collected to go further in the diagnostic workup revealing severe hyponatremia, severe plasma hypotonicity, high natriuresis and metabolic acidosis with a worsening of the radiological pulmonary pattern. Based on these new clinical findings a diagnosis of SIADH was established. Emergency treatment with hypertonic 3% saline solution and loop diuretics was started like a sodium supplement and to inhibit water resorption in renal tubules, thus reducing the volume overload. The goal of this treatment was to achieve a progressive and controlled increase of plasma sodium concentration and promoting the excretion of positive body water imbalance. The patient's condition improved clinically over the following days, treatment was progressively discontinued and the dog was discharged 7 days after admission. To the author's knowledge this is the first report of a puppy younger than 12 weeks with respiratory distress developing SIADH associated to aspiration pneumonia.

Water intoxication in adult cattle.

Water intoxication is a common disorder in calves and is usually characterized by transient hemoglobinuria. In contrast, the condition is very rare in adult cattle, with few reports on naturally occurring cases. In the present report, four female Japanese Black cattle, aged 16-25 months, showed neurological signs when they drank water following a water outage. Hemoglobinuria was not grossly observed, while severe hyponatremia was revealed by laboratory tests. Autopsy indicated cerebral edema with accumulation of serous fluid in expanded Virchow-Robin spaces. These results indicate the possibility of water intoxication associated with cerebral edema due to severe dilutional hyponatremia in adult cattle.

Severe hyponatraemia in foals: clinical findings, primary diagnosis and outcome.

OBJECTIVE: To evaluate severe hyponatraemia in foals presenting as medical emergencies to an intensive care unit (ICU) in order to determine the prevalence, clinical findings, primary diagnosis and outcome. DESIGN: Retrospective case study of records from Thoroughbred foals aged less than 3 months presenting to an ICU as medical emergencies in 2002-12; foals with severe hyponatraemia (serum sodium <122 mmol/L) on admission laboratory data were identified. Data retrieved included signalment, clinical findings, laboratory results, primary diagnosis, treatment and outcome. RESULTS: Severe hyponatraemia was identified in 69/1718 Thoroughbred foals (4%) presenting to the ICU during the study period. Of the 69 foals, 11 (15.9%) presented with neurological signs attributable to hyponatraemic encephalopathy and 7 of these foals had seizures; other neurological signs included obtundation, ataxia and apparent blindness. The three most common primary diagnoses of the 69 foals with severe hyponatraemia were renal disease (18/69, 26.1%), enterocolitis (16/69, 23.2%) and uroperitoneum (15/69, 21.7%). Treatment was directed at the primary disease and correction of the hyponatraemia. A total of 50 of the 69 foals (72.5%) with severe hyponatraemia survived to hospital discharge and 38 of them (76%) survived at least 12 months following discharge. CONCLUSION: The prevalence of severe hyponatraemia in this study population was 4%. The majority of foals with severe hyponatraemia did not demonstrate direct clinical manifestations as a result of the low serum sodium concentration. The outcome of foals with severe hyponatraemia was mostly favourable.