Nephrology
Question 22 of 52
A 27 year old woman is asked to present to the Emergency Department by her General Practitioner (GP). She had seen the GP earlier that day complaining of lethargy. The GP had arranged for several blood tests including renal function. This has shown the patient is mildly hyperkalaemic. Which of the following serum potassium results equates to "mild" hyperkalaemia?
Answer:
- Mild: 5.5 – 5.9 mmol/L
- Moderate 6.0 – 6.4 mmol/L
- Severe ≥ 6.5 mmol/L
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 |
