Nephrology
Question 9 of 180
You have been asked to give a teaching session to a group of Physician Associate students. The topic of the session is hyperkalaemia. Which of the following drugs does NOT cause hyperkalaemia?
Answer:
Theophylline (methylxanthines) can cause hypokalaemia. Digoxin, ramipril (ACEi), suxamethonium and bisoprolol (beta-blocker) can all cause hyperkalaemia.Hyperkalaemia
Nephrology
Last Updated: 13th September 2022
Hyperkalaemia is the most common electrolyte disorder associated with cardiac arrest and occurs in up to 10% of hospitalised patients.
Definition
- Mild: 5.5 – 5.9 mmol/L
- Moderate 6.0 – 6.4 mmol/L
- Severe ≥ 6.5 mmol/L
Causes
- Excessive exogenous potassium load (increased intake)
- Potassium supplements
- Excess potassium in diet
- Excessive endogenous potassium load (increased production)
- Haemolysis
- Rhabdomyolysis
- Extensive burns
- Tumour lysis syndrome
- Trauma (especially crush injuries)
- Redistribution (intracellular to extracellular fluid shift)
- Metabolic acidosis (when serum pH decreases, serum potassium increases because potassium shifts from the cellular to the vascular space)
- Insulin deficiency e.g. DKA
- Drugs e.g. beta-blockers, digoxin, succinylcholine
- Decreased potassium excretion
- Renal failure
- Addison’s disease (mineralocorticoid deficiency)
- Drugs e.g. NSAIDs, ACE inhibitors, potassium-sparing diuretics
- Pseudohyperkalaemia (raised serum K+ value when actual value in plasma is normal)
- Haemolysis in test tube (prolonged transit time, poor storage conditions)
- Venepuncture technique
Clinical Features
- Muscle weakness/paralysis
- Paraesthesia
- Hypotonia
- Hyporeflexia
- Lethargy/confusion
- Cardiac arrhythmias
- Cardiac arrest
ECG Changes
In order of progression on ECG:
- Tenting (peaking) of T waves
- Widening and flattening of P waves
- Prolongation of P-R interval (first degree heart block)
- Widening of QRS complex
- Loss of P waves
- Progressive widening of QRS complex
- Merging of S and T wave (sine wave pattern)
- Cardiac arrest (PEA, VF/pVT, asystole)
Management
For patients not in cardiac arrest:
- Mild hyperkalaemia
- Address cause of hyperkalaemia to correct and avoid further rise in serum potassium
- If treatment is indicated, remove potassium from the body with potassium binders or cation-exchange resins
- Moderate hyperkalaemia without ECG changes
- Shift potassium intracellularly with glucose/insulin
- Remove potassium from the body (with potassium binders or cation-exchange resins)
- Severe hyperkalaemia without ECG changes
- Seek expert help
- Shift potassium intracellularly with glucose/insulin and salbutamol
- Remove potassium from the body (consider dialysis, sodium zirconium cyclosilicate and/or patiromer)
- Consider commencement of continuous cardiac monitoring
- Hyperkalemia with ECG changes
- Seek expert help
- Protect the heart with calcium chloride
- Shift potassium intracellularly with glucose/insulin and salbutamol
- Remove potassium from the body (see above - consider dialysis at outset or if refractory to medical treatment)
Five key steps:
- Cardiac protection (for patients with ECG changes)
- Calcium chloride: 10 mL 10% solution calcium chloride IV over 2 - 5 min (onset in 1 - 3 min)
- Shifting potassium into cells
- Salbutamol 10 - 20 mg nebulised (onset in 15 - 30 min; duration of action 4 - 6 h)
- Insulin/glucose: 10 units short-acting insulin and 25 g glucose IV over 15 - 30 min (onset in 15 - 30 min; maximal effect at 30 - 60 min; duration of action 4 - 6 h; monitor blood glucose)
- Sodium bicarbonate if severe acidosis or renal failure
- Removing potassium from the body
- Potassium binders or cation-exchange resins e.g. calcium resonium 15 - 30 g or sodium polystyrene sulfonate (Kayexalate) 15 - 30 g given either orally or by retention enema (onset in > 4 h)
- Sodium zirconium cyclosilicate (SZC, e.g. 5-10 g three times daily for up to 72 h) and/or patiromer
- Haemodialysis guided by clinical setting
- Monitoring serum potassium concentration
- Preventing recurrence
Modifications to CPR associated with severe hyperkalaemia
- Confirm hyperkalaemia using a blood gas analyser
- Protect the heart:
- Give 10 mL calcium chloride 10% IV by rapid bolus injection
- Shift potassium into cells
- Give 10 units short-acting insulin and 25 g glucose IV by rapid injection; monitor blood glucose
- Give sodium bicarbonate
- Give 50 mmol IV sodium bicarbonate by rapid injection (if severe acidosis or renal failure)
- Remove potassium from the body
- Consider dialysis for hyperkalaemic cardiac arrest resistant to medical treatment
Cardiac arrest during haemodialysis
- Call resuscitation team and seek expert help immediately
- Start resuscitation according to standard ALS protocols
- Assign a trained dialysis nurse to the dialysis machine, stop ultrafiltration and give a fluid bolus, return the patient's blood volume and disconnect from the dialysis machine
- Leave dialysis access open and use for drug administration
- Minimise delay in delivery defibrillation; VF/pVT is more common in dialysis patients than in the general population; disconnect from the dialysis equipment prior to defibrillation if recommended by manufacturer
- All of the standard reversible causes apply to dialysis patients; electrolyte disorders, particularly hyperkalaemia, and fluid overload are the most common causes
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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 |
