Physiology
Renal
Question 179 of 180
Which of the following is NOT an ECG change typically associated with hyperkalaemia:
Answer:
Hyperkalaemia causes a rapid reduction in resting membrane potential leading to increased cardiac depolarisation and muscle excitability. This in turn results in ECG changes which can rapidly progress to ventricular fibrillation or asystole. Classic ECG changes:- Tall peaked T waves
- Shortening of the QT interval
- Lengthening of the PR interval
- Widening of the QRS complex
- Loss of the S-T segment
- Loss of p waves
- Sine wave appearance
Hyperkalaemia
Physiology / Renal / Potassium Balance
Last Updated: 21st April 2019
RCEM defines normal values for total serum potassium as 3.0 - 4.5 mmol/L.
Causes
The causes of hyperkalaemia may be divided into:
- Renal retention
- Renal failure
- Hypoaldosteronism (e.g. Addison's disease)
- K+ sparing diuretics
- ACE inhibitors/ARBs
- NSAIDs
- Trimethoprim and pentamidine therapy
- Increased intake
- Excess dietary K+
- Transcellular shift of K+ out of cells
- Metabolic acidosis
- Insulin deficiency
- Beta-blockers
- Cellular injury/rhabdomyolysis
- Tumour lysis syndrome, trauma, burns, crush syndrome, chemotherapy
- Pseudohyperkalaemia
- Prolonged tourniquet time
- Difficulty collecting the sample
- Test tube haemolysis
- Length of storage of the specimen
- Sample from limb receiving IV fluids containing potassium
Clinical Features
Clinical features of hyperkalaemia may include:
- Asymptomatic
- Paraesthesia
- Muscle weakness or paralysis
- Cardiac conduction abnormalities and dysrhythmias
ECG Changes
Hyperkalaemia causes a rapid reduction in resting membrane potential leading to increased cardiac depolarisation and muscle excitability. This in turn results in ECG changes which can rapidly progress to ventricular fibrillation or asystole.
Classic ECG changes:
- Tall peaked T waves
- Shortening of the QT interval
- Lengthening of the PR interval
- Widening of the QRS complex
- Loss of the S-T segment
- Loss of p waves
- Sine wave appearance
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- Biochemistry
- Blood Gases
- Haematology
| Biochemistry | Normal Value |
|---|---|
| Sodium | 135 – 145 mmol/l |
| Potassium | 3.0 – 4.5 mmol/l |
| Urea | 2.5 – 7.5 mmol/l |
| Glucose | 3.5 – 5.0 mmol/l |
| Creatinine | 35 – 135 μmol/l |
| Alanine Aminotransferase (ALT) | 5 – 35 U/l |
| Gamma-glutamyl Transferase (GGT) | < 65 U/l |
| Alkaline Phosphatase (ALP) | 30 – 135 U/l |
| Aspartate Aminotransferase (AST) | < 40 U/l |
| Total Protein | 60 – 80 g/l |
| Albumin | 35 – 50 g/l |
| Globulin | 2.4 – 3.5 g/dl |
| Amylase | < 70 U/l |
| Total Bilirubin | 3 – 17 μmol/l |
| Calcium | 2.1 – 2.5 mmol/l |
| Chloride | 95 – 105 mmol/l |
| Phosphate | 0.8 – 1.4 mmol/l |
| Haematology | Normal Value |
|---|---|
| Haemoglobin | 11.5 – 16.6 g/dl |
| White Blood Cells | 4.0 – 11.0 x 109/l |
| Platelets | 150 – 450 x 109/l |
| MCV | 80 – 96 fl |
| MCHC | 32 – 36 g/dl |
| Neutrophils | 2.0 – 7.5 x 109/l |
| Lymphocytes | 1.5 – 4.0 x 109/l |
| Monocytes | 0.3 – 1.0 x 109/l |
| Eosinophils | 0.1 – 0.5 x 109/l |
| Basophils | < 0.2 x 109/l |
| Reticulocytes | < 2% |
| Haematocrit | 0.35 – 0.49 |
| Red Cell Distribution Width | 11 – 15% |
| Blood Gases | Normal Value |
|---|---|
| pH | 7.35 – 7.45 |
| pO2 | 11 – 14 kPa |
| pCO2 | 4.5 – 6.0 kPa |
| Base Excess | -2 – +2 mmol/l |
| Bicarbonate | 24 – 30 mmol/l |
| Lactate | < 2 mmol/l |
