Pathophysiology of chronic kidney disease and the nursing care of cats

Kidneys play an important role in maintaining homeostasis (Lewis, 2012) being involved in the regulation of blood volume, pH, osmolarity, blood pressure and release of hormones (Breton, 2013). When kidneys start to fail this can lead to chronic kidney disease (CKD) where the kidneys irreversibly deteriorate (Somvanshi et al, 2012). CKD is a progressive loss of renal function due to nephron damage; these are the functional units of the kidneys where many homeostatic processes occur (Bartges, 2012). Signs of CKD include polyuria, polydipsia, vomiting and diarrhoea, anorexia and weight loss, dehydration, mucosal ulcers and uraemic breath.

One symptom of CKD is a rise in levels of blood urea nitrogen (BUN; normal reference range 17–29 mg/dl) (Brown, 2007) and creatinine (azotaemia being identified once the blood creatinine concentration >1.6 mg/dl) (Brown, 2007; Polzin, 2011). In healthy patients, urea is excreted in the urine but once kidneys begin to fail they are unable to remove the urea resulting in raised levels of BUN. Creatinine should be constantly filtered out through the kidneys but again when the kidneys begin to fail these levels also rise. These complications may show as typical gastrointestinal signs such as nausea, vomiting and diarrhoea (occasionally haemorrhagic) due to an increase in gastric acid where gastrin is not being metabolised within the kidneys as it once was. Mouth ulcers and a distinctive smell of ammonia on the breath occur due to nitrogenous waste such as ammonia and urea accumulating in the blood from the breakdown of proteins. Anorexia and subsequent weight loss and dehydration may then also be seen due to the build up of toxins in the blood combined with irritation and ulceration of the gastrointestinal tract making the patient feel unwell and painful (Acierno and Senior, 2011).