Potassium

Axioms: K is abundant in all cells (~50mmol/kg body weight, ~3500mmol K adults), and is found in a much lower concentration in plasma. Acidaemia shifts K+ out of cells, Alkalaemia shifts K into cells. Cells also absorb K when they absorb glucose. Aldosterone causes Na retention and K excretion. K normal range is 3.5-5.0 mmol/l. Every 0.5 over/under means a ~150mmol extra/deficit. Hyper/Hypo's cause parasthesias and weakness.

• Hypokalaemic Patients: Cramps and apathy. ECG showing Saggy ST, Depressed T. Think urinary or GIT losses. Diuretics, NVD, laxitives and such. Eating too little? Anorexia. Remember aldosterone from the RAS system makes the body keep Na, in exchange for losing K. So hyperaldosteronism or mineralocorticoid excess causes it too. Consider axioms; insulin excess (eg after glucose load) will shift K into cells.

• Hyperkalaemic Patients: Hypotensive and bradycardic. ECG showing depressed P, peaked T (look for these in all ECGs as it is not well autodetected). Think renal failure, especially if older. Remember cells contain lots of K, so think about haemolysis, rhabdomyolysis, and tissue damage. Insulin deficiency means K accumulates in blood, causing mild hyperkalaemia. Drugs drugs drugs; NSAIDS, K sparing diuretics (spironolactone, amilioride), drugs that dampen the renin-angiotensin-aldosterone system (ACEi, ARBs. see axiom on aldo)

Low K Approach
Chlorvescent has 28mmol K per dose. SlowK has 600mg or 8mmol K. Infusion over 40mmol/L cannot be done peripherally. Infusion over 10mmol/hr is dangerous. Typical IV dose is 30mmol K over 6/24 (5mmol/hr), with 2/24 monitoring.

1. Slow release potassium. Target 16mmol per day. eg. 1 x SlowK (8mmol) BD
   
2. If severe: 10mmol/100ml premix infused 3/24.
3. Maintain with spironolactone 50mg po BD
   

High K General Approach:

• ALWAYS stabilize myocardium if severe: calcium gluconate 10% 10ml *large vein, slow 5min push.
• If severe: 10units Actrapid iv bolus + 50ml 50% Glucose over 5min. CI hypoaldosteronaemia as it precipitates refractory hypoglycaemia.
  
• If very severe: Consider dialysis. Short term salbutamol 0.5mg iv stat.
  
• Moderate: Sodium Polystyrene Sulfonate 15g po tid
  
• If applicable: Rehydrate patient to restore renal function. Consider Furosemide.
  
• Review meds.

High K + Chronic Renal Failure: As above. Review meds.

High K + Severe Metabolic Acidosis w Volume Depletion: Start with 50ml Sodium Bicarb 1mmol/mL iv over 10min w ECG monitoring. Repeat every hr as necessary. Aim to restore normal hydration.

High K + Adrenal Insufficiency: Seen in some CRF patients. Normal glucocorticoids but aldo deficient. Sole Mx if not acute is fludrocortisone 150mcg po sid.