Congress on Demand 2021: Internal Medicine

Making the diagnosis: Acute kidney injury (AKI) is a sudden fall in renal function and results in retention of uremic toxins and fluid, electrolyte, and acid-base imbalances. Classically AKI has been defined as a sudden (usually less than 1 week) increase in creatinine above the reference range, but because of the importance of obtaining an early diagnosis and the lack of sensitivity of creatinine in detecting a decline in GFR, more stringent criteria have been defined. AKI should be suspected in patients presenting with acute onset lethargy, anorexia, vomiting and diarrhoea regardless of their urine output. Critically ill and post-operative patients are at high risk and should monitored for AKI development. Physical exam findings often include dehydration and renal pain. Uremic halitosis, oral ulceration, hypothermia and bruising may also be present. The diagnosis is made based on an acute increase in creatinine and/or abrupt decline in urine output. Glucosuria (without hyperglycaemia), proteinuria, pyruria, microscopic haematuria and granular casts may be detected in on urinalysis. Further investigations should include a complete blood count, full biochemistry profile, urine culture, abdominal imaging and acid-base measurement (if possible). Other tests for underlying causes such as Leptospirosis, ethylene glycol toxicity and Lyme disease may be indicated.

Managing the patient: Acute kidney injury (AKI) is the rapid loss of kidney function leading to the accumulation of nitrogenous waste. AKI is potentially reversible either by resolution of the injury or by adaptation of the kidney or by both mechanisms. Management of the patient includes: correcting hypoperfusion, to the kidney, closely monitoring fluids ins and outs and adjusting intravenous fluid therapy as required, treating infections, such as pyelonephritis, leptospirosis and Lyme disease and alleviating blockages or repairing ruptures to the urinary tract. The holistic needs of the patient should be met: padded bedding in a warm, clean stress-free environment; time to rest and sleep; recumbency changed every four hours; water should be freely available, fresh and easily accessible; clinical examination at least twice a day; pain scores every four hours or as required; intravenous catheter care; consider a jugular catheter to facilitate fluid therapy and blood sampling; frequent toileting opportunity as likely high rates of fluid therapy. A urinary catheter would allow monitoring of urine output, oral hygiene, patients may develop painful ulcers on their tongue and oral mucosa. Suitable nutrition to meet the patients RER, a feeding tube should be considered.

Asymptomatic patients: I am hearing a heart murmur for the first time in an adult dog. What should I do? Incidentally discovered heart murmurs in adult dogs are common. Degenerative (myxomatous) mitral valve disease (DMVD) is by far the most common cause of acquired murmurs in dogs. Other possible causes would include dilated cardiomyopathy, bacterial endocarditis, previously undiscovered congenital heart disease and non-cardiac causes such as haemic murmurs and flow murmurs. In dogs with an appropriate signalment, a murmur with timing and location consistent with mitral regurgitation makes DMVD very likely. Factors that might make this less likely (or rule it out altogether) would include; the finding of a murmur that is audible continuously or in diastole, finding a murmur in a large breed dog or the presence of clinical signs indicative of significant systemic disease e.g. pallor or pyrexia. The single best diagnostic test to determine whether or not a murmur is caused by cardiac disease and to characterise the specific cause of a murmur is echocardiography. In some circumstances, echocardiography may not be possible due to cost or lack of access to appropriate equipment or expertise. In a patient suspected of having DMVD it is important to stage their disease as accurately as possible to ensure appropriate treatment can be instituted if appropriate.

Asymptomatic patients: I am hearing a heart murmur for the first time in an adult cat. What should I do? Cardiomyopathies are the most common heart diseases in cats with hypertrophic cardiomyopathy (HCM) being the most prevalent form. HCM affects 15% of apparently healthy cats. Cardiac auscultation in cats is challenging as it lacks both sensitivity and specificity. Cardiomyopathies may not cause a heart murmur, thus some cats with clinically significant heart disease have a normal cardiac auscultation. Conversely, a murmur may be present in some cats with structurally normal hearts. Thus, absence/presence of murmurs may not always help in determining which cats have heart disease. However, the majority of cats with a murmur do have structural heart disease, especially older cats with loud (≥3/6) murmurs. In HCM, murmurs are commonly caused by dynamic LV outflow tract obstruction. Normal cats can have murmurs due to dynamic RV outflow tract obstruction (clinically benign). NT-proBNP is increased in cats with moderate-severe asymptomatic cardiomyopathy, thus it may be used as a first-line test to assess the likelihood of heart disease in a cat with a murmur. But echocardiography is required to confirm the presence of heart disease, and most importantly to assess for risk factors associated with increased risk of CHF and ATE (e.g. left atrial size). Systemic diseases that may cause a murmur should also be excluded, i.e. check blood pressure, haematocrit and T4 (cats >6 years). Normal and HCM cats may have heart murmurs, but a loud murmur in a cat >6 years is more likely to be associated with HCM and further investigations are recommended. Early interventions in cardiomyopathic cats may reduce the risk of serious complications, thus early detection of occult cardiomyopathies is paramount.