Makindo Medical Notes.com

Related Subjects: |Hyperkalaemia |ECG - Hyperkalaemia |Hypokalemia |Hyperkalaemic and Hypokalaemic Periodic Paralysis |Resuscitation - Advanced Life Support |Action Potential

Medical emergency as increased plasma [K⁺] leads to a partial membrane depolarization that may eventually cause cardioplegia and skeletal muscle paralysis and death. Calcium gluconate is preferred as less damaging to veins.

ECG changes

• Potentially lethal so act quickly if ECG changes or level > 6.5 mmol/L
• Tented T waves, Broad QRS, Bradycardia, Absent flat P waves, Sinewave, VT then treat

Physiology

• As the K⁺ level rises further, it inactivates too many Na⁺ channels to allow for an effective action potential. It is at this point that we see the QRS interval on the ECG begin to widen and start to take on a sine wave appearance.
• The benefit of administering IV calcium to patients with hyperkalemia is due to enhanced conduction through the L-type calcium channels and not due to membrane stabilization. The L-type calcium channels are much more resistant to hyperkalemia and are quite capable of initiating an action potential in the conducting tissue (His-Purkinje system) and the working myocytes.

Aetiology: Check all drugs in BNF or equivalent

• Chronic renal disease and perhaps failure to attend dialysis
• Causes (most commonly drugs check drug chart) [can get falsely high result: haemolysed sample, laboratory or sampling error]
• AKI, CKD, digoxin poisoning (poor prognostic sign).
• Rhabdomyolysis, tissue damage from trauma, burns, tumour lysis syndrome, vigorous exercise, haemolysis, blood transfusion.
• Drugs: ACE inhibitors, AT2 blockers, Spironolactone, Eplerenone, Amiloride, NSAIDs, Ciclosporin, depolarising muscle relaxants, Trimethoprim, Heparin/LMWH
• Metabolic acidosis, Addison's disease (pigmented, ?BP, fatigue),
• Type 4 RTA (diabetes) with low renin and low aldosterone and CKD
• Hyperkalaemic periodic paralysis (AD familial).
• Blood transfusion
• C-21 hydroxylase deficiency
• Congenital adrenal syndromes, e.g. 3-ß hydroxydehydrogenase deficiency

Causes

Clinical

• Asymptomatic, arrhythmias, muscle weakness, cramps, paraesthesia.
• Low BP, Low HR, cardiac arrest.

Severity

• Mild (K⁺ 5.5-5.9 mmol/L)
• Moderate (K⁺ 6.0-6.4 mmol/L)
• Severe (K⁺ >6.5 mmol/L) or if ECG changes or symptoms. Emergency treatment needed

Investigations

• FBC: low may suggest haemolysis. LDH also high
• Raised CK: rhabdomyolysis. LDH also high
• U&E, Ca, Mg: repeat it unexpected. Check ECG normal if high K⁺
• Venous blood gases: metabolic acidosis.
• ECG signs: peaked tented T waves, widened QRS, sine waves, agonal rhythm and V T/VF.

Generally Calcium Gluconate preferred when only a peripheral line is available for venous access.

ECG signs of Hyperkalaemia

• Peaked tented T waves, Absent P waves, Broad QRS, Sine waves, Bradycardia
• Agonal rhythm, Cardiac arrest with VT/VF.

Management

• ABC. Assess ECG changes. Stop all potentially offending drugs or infusions immediately. This is easily overlooked.
• Ensure IV access, repeat any sample if surprise result. Start IV fluids 0.9% Saline if not overloaded (consider Furosemide)
• If K⁺ >6.0 mmol/L or ECG changes needs telemetry and defibrillator are available.
• if K⁺ > 6.5 mmmol/L or ECG changes then IV 10-20 ml 10% Calcium Gluconate IV. Use a large vein. Give over 5-10 min and see ECG changes resolve. This intervention will not lower the potassium, but if ECG changes are present, there should be improvement seen within 1 to 3 minutes. If not consider repeating.
• Next give 10 units of Soluble Insulin with 50 ml of 50% Glucose or 100 ml of 20% Glucose to counteract the hypoglycaemia. Consider a 10% glucose infusion if higher doses of insulin are given.
• Consider Salbutamol 10 mg in 4 ml saline nebulised with caution in those with IHD/arrhythmias.
• Furosemide 20 mg IV may be considered if not dehydrated. Consider more if overloaded.
• U&E needs to be repeated every 2 h and blood gas, capillary blood glucose for 6-12 h. The remainder needs ECG and underlying cause to be found and close monitoring.
• These actions only lower K⁺ for 4 hours.
• If metabolic acidosis (low HCO₃) 15-19 then NaHCO₃ 1 g BD. If HCO₃ < 15 then 500 mls NaHCO₃ 1.26% over 6 hrs. In extremis pH < 6.9 consider IV 50 mL sodium bicarbonate 8.4% over 1 h. Take expert guidance. Can cause fluid overload.
• Exchange resins
  • Lokelma ( sodium zirconium cyclosilicate (SZC) for patients with moderate hyperkalaemia. ) 10 g 3 times a day, for up to 72 hours. It is a highly selective cation exchanger in the gastrointestinal tract, has been licensed for use in acute hyperkalaemia. 9
• AKI assess and manage cause: renal referral needed. If AKI/CKD and refractory/ severe hyperkalaemia despite treatment, then discuss suitability for haemodialysis/ haemoperfusion.
• Adopt a low potassium diet, e.g. avoid chocolate, fruit juices. Ensure that any amiloride, spironolactone, ACE inhibitor, ARB or similar has been stopped. See AKI, Section 10.4.

Hyperkalaemia and Cardiac arrest

• Confirm hyperkalaemia > 6.5 mmol/L on blood gas analyser
• Give 10 mL calcium chloride 10% IV by rapid bolus injection. Repeat if cardiac arrest is refractory or prolonged.
• Give 10 units soluble insulin and 25 g glucose IV by rapid injection. Monitor blood glucose. Start 10% glucose infusion guided by blood glucose to avoid hypoglycaemia.
• Give 50 mmol sodium bicarbonate (50 mL 8.4% solution) IV by rapid injection.
• Consider dialysis for refractory hyperkalaemic cardiac arrest.
• Consider mechanical chest compression device if prolonged CPR is needed. Consider ECLS or ECPR for patients who are peri-arrest or in cardiac arrest as a rescue therapy in those settings where it is feasible.

Reference

• Emergency Management of Hyperkalaemia in Adults
• Additional guidelines for hyperkalaemia