DISORDERS OF POTASSIUM REGULATION

Dietary intake of potassium varies between 80 and 150 mmol daily, most of which is then excreted in the urine. Most of the body’s potassium (3500 mmol in an adult man) is intracellular (Table 8.2). Serum levels are controlled by:

■ Uptake of K+ into cells

■ Renal excretion - mainly controlled by aldosterone

■ Extrarenal losses, e.g. gastrointestinal.

Hypokalaemia

This is a serum potassium concentration of <3.5 mmol/L.

Aetiology

The most common causes of hypokalaemia are diuretic treatment and hyper-aldosteronism (Table 8.6). Blood taken from a drip arm may produce a spuri-ous result.

Clinical features

Hypokalaemia is usually asymptomatic, although muscle weakness may occur if it is severe. It results in an increased risk of cardiac arrhythmias, particularly in patients with cardiac disease. Hypokalaemia also predisposes to digoxin toxicity.

Management

The underlying cause should be identified and treated where possible. Usually withdrawal of purgatives, assessment of diuretic treatment, and replacement with oral potassium chloride supplements, preferably as a liquid or effervescent preparation (25-40 mmol/day in divided doses with monitor-ing of serum K+ every 1-2 days) is all that is required (p. 351). Serum magnesium concentrations should be normalized, as hypomagnesaemia makes hypokalaemia difficult or impossible to correct. Indications for the intravenous infusion of potassium chloride include hypokalaemic diabetic ketoacidosis and severe hypokalaemia associated with cardiac arrhythmias or muscle weakness. This should be performed slowly, and replacement at rates of greater than 20 mmol/h should only be done with electrocardio-graphic (ECG) monitoring and hourly measurement of serum potassium. Concentrations over 60 mmol/L should not be given via a peripheral vein because of local irritation. Ampoules of potassium should be thoroughly mixed in sodium chloride 0.9%; glucose solutions should be avoided as this may make hypokalaemia worse.

Table 8.6 Causes of hypokalaemia

Increased renal excretion

(spot urinary K+ >20 mmol/L)

Diuretics, e.g. thiazides, loop diuretics

Solute diuresis, e.g. glycosuria

Hypomagnesaemia

Increased aldosterone secretion
Liver failure
Heart failure
Nephrotic syndrome
Cushing’s syndrome
Conn’s syndrome

Exogenous mineralocorticoid
Corticosteroids
Carbenoxolone
Liquorice

Renal disease
Renal tubular acidosis: types 1 and 2
Renal tubular damage
Rare syndromes with renal potassium loss,
e.g. Liddle’s

Gastrointestinal losses

(spot urinary K+ <20 mmol/L)

Prolonged vomiting*, profuse diarrhoea, villous
adenoma, fistulae, ileostomies

Redistribution into cells

Increased activity of Na+/K+-ATPase
Alkalosis
β-Agonists
Insulin

  Hypokalaemic periodic paralysis (rare, episodic
K+ movement into cells leads to profound
muscle weakness)

Reduced intake

Severe dietary deficiency

Inadequate replacement in i.v. fluids

*Hypokalaemia primarily due to loss of gastric acid and associated metabolic alkalosis which leads to increased urinary loss of potassium and intracellular shift of potassium.

Hyperkalaemia

This is a serum potassium concentration >5.0 mmol/L. True hyperkalaemia must be differentiated from artefactual hyperkalaemia, which results from lysis of red cells during vigorous phlebotomy or in vitro release from abnormal red cells in some blood disorders, e.g. leukaemia.

Aetiology

The most common causes are renal impairment and drug interference with potassium excretion (Table 8.7). An elevated serum potassium in the absence of any of the listed causes should be confirmed before treatment, to exclude an artefactual result.

Clinical features

Hyperkalaemia usually produces few symptoms or signs, until it is high enough to cause cardiac arrest. Symptoms produced by hyperkalaemia are related to impaired neuromuscular transmission and include muscle weakness and paralysis. It may be associated with metabolic acidosis causing Kussmaul's respiration (low, deep, sighing inspiration and expira-tion). Hyperkalaemia may produce progressive abnormalities in the ECG (Fig. 8.3).

Table 8.7 Causes of hyperkalaemia
Decreased excretion
Acute kidney injury/acute renal failure
Drugs (potassium-sparing diuretics, ACE inhibitors, NSAIDs, ciclosporin,
heparin)
Addison’s disease
Hyporeninaemic hypoaldosteronism (type 4 renal tubular acidosis)
Redistribution (intracellular to extracellular fluid)
Diabetic ketoacidosis
Metabolic acidosis
Tissue necrosis or lysis (rhabdomyolysis, tumour lysis syndrome, severe burns)
Drugs (suxamethonium, digoxin toxicity)
Hyperkalaemic periodic paralysis
Increased extraneous load
Potassium chloride
Salt substitutes
Transfusion of stored blood
ACE, angiotensin-converting enzyme; NSAID, non-steroidal anti-inflammatory drug.

 

Progressive electrocardiographic changes with increasing

Fig. 8.3 Progressive electrocardiographic changes with increasing
hyperkalaemia.

Management

In the absence of any underlying cause (Table 8.7) the serum potassium should be rechecked to rule out spurious hyperkalaemia unless ECG changes are present (Fig. 8.3) that warrant emergency treatment. Mild to moderate hyperkalaemia can be managed by dietary potassium restriction, restriction of drugs causing hyperkalaemia and a loop diuretic (if appropriate) to increase urinary potassium excretion. Severe hyperkalaemia (>6.5 mmol/L) or hyper-kalaemia (>6.0 mmol/L) with ECG changes (Fig. 8.3) is a medical emergency (Emergency Box 8.2).

Ebook Essentials of Kumar and Clark's Clinical Medicine, 5e

1. Ethics and communication

Ethics and communication

2. Infectious diseases

Infectious diseases

3. Gastroenterology and nutrition

Gastroenterology and nutrition

4. Liver, biliary tract and pancreatic disease

Liver, biliary tract and pancreatic disease
LIVER BIOCHEMISTRY AND LIVER FUNCTION TESTS
SYMPTOMS AND SIGNS OF LIVER DISEASE
JAUNDICE
HEPATITIS
NON - ALCOHOLIC FATTY LIVER DISEASE (NAFLD)
CIRRHOSIS
COMPLICATIONS AND EFFECTS OF CIRRHOSIS
LIVER TRANSPLANTATION
TYPES OF CHRONIC LIVER DISEASE AND CIRRHOSIS
PRIMARY SCLEROSING CHOLANGITIS
BUDD - CHIARI SYNDROME
LIVER ABSCESS
LIVER DISEASE IN PREGNANCY
LIVER TUMOURS
GALLSTONES
THE PANCREAS
CARCINOMA OF THE PANCREAS
NEUROENDOCRINE TUMOURS OF THE PANCREAS

5. Haematological disease

Haematological disease
ANAEMIA
Assessment and treatment of suspected neutropenic sepsis
HAEMOLYTIC ANAEMIA
INHERITED HAEMOLYTIC ANAEMIAS
ACQUIRED HAEMOLYTIC ANAEMIA
MYELOPROLIFERATIVE DISORDERS
THE SPLEEN
BLOOD TRANSFUSION
THE WHITE CELL
HAEMOSTASIS AND THROMBOSIS
THROMBOSIS
THERAPEUTICS

6. Malignant disease

Malignant disease
MYELOABLATIVE THERAPY AND HAEMOPOIETIC STEM CELL TRANSPLANTATION
THE LYMPHOMAS
THE PARAPROTEINAEMIAS
PALLIATIVE MEDICINE AND SYMPTOM CONTROL

7. Rheumatology

Rheumatology
COMMON INVESTIGATIONS IN MUSCULOSKELETAL DISEASE
COMMON REGIONAL MUSCULOSKELETAL PROBLEMS
BACK PAIN
OSTEOARTHRITIS
INFLAMMATORY ARTHRITIS
THE SERONEGATIVE SPONDYLOARTHROPATHIES
Clinical features, Investigations
INFECTION OF JOINTS AND BONES
AUTOIMMUNE RHEUMATIC DISEASES
SYSTEMIC INFLAMMATORY VASCULITIS
DISEASES OF BONE
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8. Water, electrolytes and acid–base balance

WATER AND ELECTROLYTE REQUIREMENTS
BODY FLUID COMPARTMENTS
REGULATION OF BODY FLUID HOMEOSTASIS
PLASMA OSMOLALITY AND DISORDERS OF SODIUM REGULATION
DISORDERS OF POTASSIUM REGULATION
DISORDERS OF MAGNESIUM REGULATION
DISORDERS OF ACID - BASE BALANCE
THERAPEUTICS

9. Renal disease

Renal disease
INVESTIGATION OF RENAL DISEASE
GLOMERULAR DISEASES
NEPHROTIC SYNDROME
URINARY TRACT INFECTION
TUBULOINTERSTITIAL NEPHRITIS
HYPERTENSION AND THE KIDNEY
RENAL CALCULI AND NEPHROCALCINOSIS
URINARY TRACT OBSTRUCTION
ACUTE RENAL FAILURE/ACUTE KIDNEY INJURY
CHRONIC KIDNEY DISEASE
RENAL REPLACEMENT THERAPY
CYSTIC RENAL DISEASE
TUMOURS OF THE KIDNEY AND GENITOURINARY TRACT
DISEASES OF THE PROSTATE GLAND
TESTICULAR TUMOUR
URINARY INCONTINENCE

10. Cardiovascular disease

COMMON PRESENTING SYMPTOMS OF HEART DISEASE
INVESTIGATIONS IN CARDIAC DISEASE
CARDIAC ARRHYTHMIAS
HEART FAILURE
ISCHAEMIC HEART DISEASE
RHEUMATIC FEVER
VALVULAR HEART DISEASE
PULMONARY HEART DISEASE
MYOCARDIAL DISEASE
CARDIOMYOPATHY
PERICARDIAL DISEASE
SYSTEMIC HYPERTENSION
ARTERIAL AND VENOUS DISEASE
ELECTRICAL CARDIOVERSION
DRUGS FOR ARRHYTHMIAS
DRUGS FOR HEART FAILURE
DRUGS AFFECTING THE RENIN - ANGIOTENSIN SYSTEM
NITRATES, CALCIUM - CHANNEL BLOCKERS AND POTASSIUM - CHANNEL ACTIVATORS

11. Respiratory disease


Respiratory disease
TUBERCULOSISnd
DIFFUSE DISEASES OF THE LUNG PARENCHYMA
OCCUPATIONAL LUNG DISEASE
CARCINOMA OF THE LUNG
DISEASES OF THE CHEST WALL AND PLEURA
DISORDERS OF THE DIAPHRAGM

12. Intensive care medicine

Intensive care medicine

13. Drug therapy, poisoning, and alcohol misuse

Drug therapy, poisoning, and alcohol misuse

14. Endocrine disease

Endocrine disease
PITUITARY HYPERSECRETION SYNDROMES
THE THYROID AXIS
MALE REPRODUCTION AND SEX
FEMALE REPRODUCTION AND SEX
THE GLUCOCORTICOID AXIS
THE THIRST AXIS
DISORDERS OF CALCIUM METABOLISM
DISORDERS OF PHOSPHATE CONCENTRATION
ENDOCRINOLOGY OF BLOOD PRESSURE CONTROL
DISORDERS OF TEMPERATURE REGULATION
THERAPEUTICS

15. Diabetes mellitus and other disorders of metabolism

DIABETES MELLITUS
DIABETIC METABOLIC EMERGENCIES
COMPLICATIONS OF DIABETES
SPECIAL SITUATIONS
HYPOGLYCAEMIA IN THE NON - DIABETIC
DISORDERS OF LIPID METABOLISM
THE PORPHYRIAS

16. The special senses

THE EAR
THE NOSE AND NASAL CAVITY
THE THROAT
THE EYE

17. Neurology

COMMON NEUROLOGICAL SYMPTOMS
COORDINATION OF MOVEMENT
THE CRANIAL NERVES
COMMON INVESTIGATIONS IN NEUROLOGICAL DISEASE
UNCONSCIOUSNESS AND COMA
STROKE AND CEREBROVASCULAR DISEASE
EPILEPSY AND LOSS OF CONSCIOUSNESS
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HYDROCEPHALUS
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SPINAL CORD DISEASE
DEGENERATIVE NEURONAL DISEASES
DISEASES OF THE PERIPHERAL NERVES
MUSCLE DISEASES
MYOTONIAS
DELIRIUM
THERAPEUTICS

18. Dermatology

Dermatology

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