Electrolyte imbalances

Barbara Skelly

doi:10.22233/9781910443255.8

British Small Animal Veterinary Association , 142 (2016); https://doi.org/10.22233/9781910443255.8

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Electrolyte imbalances

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Author: Barbara Skelly
From: BSAVA Manual of Canine and Feline Clinical Pathology
Item: Chapter 8, pp 142 - 164
DOI: 10.22233/9781910443255.8
Copyright: © 2016 British Small Animal Veterinary Association
Publication Date: March 2016

Abstract

The major electrolytes in the body are potassium, sodium, calcium and magnesium. Electrolyte concentrations are closely controlled by the action of multiple hormones and by the kidneys. Derangements affect many body organs including the nervous system and cardiac and skeletal muscle. Major imbalances can cause severe clinical signs and death. This chapter looks at measurement of electrolyte concentrations in serum and plasma, disorders of potassium homeostasis, disorders of sodium homeostasis, disorders of chloride homeostasis, disorders of magnesium homeostasis and disorders of calcium homeostasis. Case studies are included.

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Figures

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8.1

The main mechanisms leading to the development of hyper- or hypokalaemia. Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission. © 2016 British Small Animal Veterinary Association

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8.1 The main mechanisms leading to the development of hyper- or hypokalaemia. Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission.

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8.3

Factors affecting potassium movement into and out of the cell (represented by an oval in this diagram). The Na+/K+/ATPase pump mediates the movement of potassium into the cell whereas outward movement is caused by solvent drag or by displacement of potassium by other cations. Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission. © 2016 British Small Animal Veterinary Association

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8.3 Factors affecting potassium movement into and out of the cell (represented by an oval in this diagram). The Na+/K+/ATPase pump mediates the movement of potassium into the cell whereas outward movement is caused by solvent drag or by displacement of potassium by other cations. Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission.

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8.5

Young Burmese cat showing generalized weakness and cervical ventroflexion due to hypokalaemic myopathy. (Courtesy of ME Herrtage, University of Cambridge) © 2016 British Small Animal Veterinary Association

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8.5 Young Burmese cat showing generalized weakness and cervical ventroflexion due to hypokalaemic myopathy. (Courtesy of ME Herrtage, University of Cambridge)

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8.7

Activation of the renin–angiotensin system leading to aldosterone secretion and an increase in systemic blood pressure. When there is a significant drop in blood pressure, antidiuretic hormone (ADH) release is also stimulated. Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission. © 2016 British Small Animal Veterinary Association

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8.7 Activation of the renin–angiotensin system leading to aldosterone secretion and an increase in systemic blood pressure. When there is a significant drop in blood pressure, antidiuretic hormone (ADH) release is also stimulated. Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission.

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8.8

The relationship between osmoregulation and volume regulation. Although hyperosmolality is the primary stimulus for antidiuretic hormone (ADH) release and increase in thirst, severe hypovolaemia can also stimulate the same mechanisms. ANP = atrial natriuretic peptide; RAAS = renin–angiotensin–aldosterone system. Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission. © 2016 British Small Animal Veterinary Association

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8.8 The relationship between osmoregulation and volume regulation. Although hyperosmolality is the primary stimulus for antidiuretic hormone (ADH) release and increase in thirst, severe hypovolaemia can also stimulate the same mechanisms. ANP = atrial natriuretic peptide; RAAS = renin–angiotensin–aldosterone system. Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission.

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8.10

The cellular adaptation to hyponatraemia in the nervous system. (a) Cells within the nervous system are protected from dehydration by the presence of idiogenic organic osmoles (shown as small circles). (b) When hyponatraemia develops slowly, re-equilibration can occur and osmotic balance is maintained. However, when hyponatraemia develops rapidly, the intracellular space is hyperosmolar with respect to the extracellular fluid, water moves into the cells and cerebral oedema develops (c). Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission. © 2016 British Small Animal Veterinary Association

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8.10 The cellular adaptation to hyponatraemia in the nervous system. (a) Cells within the nervous system are protected from dehydration by the presence of idiogenic organic osmoles (shown as small circles). (b) When hyponatraemia develops slowly, re-equilibration can occur and osmotic balance is maintained. However, when hyponatraemia develops rapidly, the intracellular space is hyperosmolar with respect to the extracellular fluid, water moves into the cells and cerebral oedema develops (c). Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission.

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8.12

The mechanism of the development of hyponatraemia through volume depletion via renal and non-renal routes. ADH = antidiuretic hormone; Posm = plasma osmolality. Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission. © 2016 British Small Animal Veterinary Association

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8.12 The mechanism of the development of hyponatraemia through volume depletion via renal and non-renal routes. ADH = antidiuretic hormone; Posm = plasma osmolality. Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission.

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8.13

The basics of calcium homeostasis. The important hormones are parathyroid hormone (PTH) and 1,25-dihydroxyvitamin D. Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission. © 2016 British Small Animal Veterinary Association

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8.13 The basics of calcium homeostasis. The important hormones are parathyroid hormone (PTH) and 1,25-dihydroxyvitamin D. Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission.

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8.17

Algorithm illustrating the work-up of hypercalcaemia. ACTH = adrenocorticotropic hormone; CBC = complete blood count; iCa = ionized calcium; HHM = humoral hypercalcaemia of malignancy; PTH = parathyroid hormone; PTHrP = parathyroid hormone related peptide; tCa = total calcium. Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission. © 2016 British Small Animal Veterinary Association

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8.17 Algorithm illustrating the work-up of hypercalcaemia. ACTH = adrenocorticotropic hormone; CBC = complete blood count; iCa = ionized calcium; HHM = humoral hypercalcaemia of malignancy; PTH = parathyroid hormone; PTHrP = parathyroid hormone related peptide; tCa = total calcium. Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission.

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8.18

Ultrasonographic image of the ventral cervical area of a dog with primary hyperparathyroidism. A hypoechoic nodule (delineated by dotted lines) can be seen within the thyroid tissue (arrowed). © 2016 British Small Animal Veterinary Association

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8.18 Ultrasonographic image of the ventral cervical area of a dog with primary hyperparathyroidism. A hypoechoic nodule (delineated by dotted lines) can be seen within the thyroid tissue (arrowed).

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8.19

Intraoperative photograph of the removal of a parathyroid adenoma. The thyroid gland (dark red tissue) is visible overlying the trachea with a smaller, paler parathyroid gland associated (touching the cotton bud). (Courtesy of E Friend) © 2016 British Small Animal Veterinary Association

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8.19 Intraoperative photograph of the removal of a parathyroid adenoma. The thyroid gland (dark red tissue) is visible overlying the trachea with a smaller, paler parathyroid gland associated (touching the cotton bud). (Courtesy of E Friend)

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8.21

Algorithm illustrating the work-up of hypocalcaemia. CBC = complete blood count; GI = gastrointestinal; iCa = ionized calcium; PO4 = phosphate; PTH = parathyroid hormone; tCa = total calcium. Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission. © 2016 British Small Animal Veterinary Association

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8.21 Algorithm illustrating the work-up of hypocalcaemia. CBC = complete blood count; GI = gastrointestinal; iCa = ionized calcium; PO4 = phosphate; PTH = parathyroid hormone; tCa = total calcium. Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission.