Hypo- and Hyperkalaemia Flashcards
What are some causes of hyperkalaemia?
CARED:
- Cell lysis (haemolysis, burns, surgery, rhabdomyolysis etc); cirrhosis and CCF
- Adrenal insufficiency/Addison’s disease; Acidosis
- Renal failure (AKI, chronic)
- Excessive intake (PO, IVI, blood products)
- DKA; Dehydration; Drugs
(BADHAN = Betablockers, ARBs, Digoxin, Heparin, ACEi’s, NSAIDs, Steroid)
How does hyperkalaemia present?
Asymptomatic, incidental finding on U+E
MURDER:
- Muscle weakness + cramps
- Urine output = decreased
- Reduced = cardiac output
- ECG changes
- Reflexes = decreased
What are the different grades of hyperkalaemia?
Mild = 5.5-5.9 Moderate = 6-6.4 Severe = >6.5
What ECG changes do you see in hyperkalaemia?
K >5.5: repolarisation abnormalities:
- Peaked T waves (usually the earliest sign of hyperkalaemia)
K >6.5: progressive paralysis of the atria
- Flattening then absent P waves
- Prolonged PR segment
K >7: conduction abnormalities and bradycardia
- Prolonged QRS, potentially bizarre morphology
- Any kind of conduction block e.g. BBBs, fascicular blocks
- Sinus bradycardia or slow AF
- Development of a sine wave appearance = pre-terminal rhythm
K >9: causes cardiac arrest
- V fib
- Asystole
The concentrations here are just guides, individual variation is common
Changes are usually across all leads
After ECG shows changes will need continuous 3 lead cardiac monitoring + repeat ECG after interventions
What drugs do you give to treat acute hyperkalaemia?
Usually used in moderate-high hyperkalaemia; for a mild-moderate, you might want to change diet (if chronic) or stop medicines (if acute)
Calcium gluconate/chloride:
- 10% by slow IVI
- Given when plasma-potassium concentration above 6.5 mmol/litre OR in the presence of ECG changes
- Titrated to ECG improvement
- To chelate K in the blood - Immediately cardioprotective
- If the patient is taking digoxin, rapid administration of calcium gluconate may precipitate myocardial digoxin toxicity. The 10 ml of calcium gluconate 10% solution should be mixed with 100ml of glucose 5% and administered slowly over 20 minutes
Insulin + dextrose/glucose:
- IV injection of 5-10 units with 50ml of 50% glucose over 5-15 mins
- Repeated as necessary or IVI set up
- K is taken up alongside sugar into cells in the presence of insulin, will reduce plasma concentration acutely
- (salbutamol NEB or IVI may accomplish same job but is not preferred)
Sodium bicarbonate:
- Should be considered for correction of causal or compounding acidosis
- SHOULD NOT BE ADMINISTERED IN THE SAME LINE AS CALCIUM SALTS - as risk of precipitation
Med review:
- Stop causal/exacerbating agents
Calcium resonium (calcium polystyrene sulfonate):
- It is given orally at a dose of 15 g three to four times a day (short-term only)
- To reduce GI absorption
- Administration of the resin should stop when the serum potassium falls to 5 mmol/litre or below
- Monitor closely to avoid hypokalaemia
- Can cause constipation therefore consider co-prescribing laxatives as appropriate
What are the indications for renal replacement therapy in hyperkalaemia?
Severe hyperkalaemia that is unresponsive 2-3 rounds of normal measures (??)
What are the causes of hypokalaemia?
c. 3% are hypokalaemic on admission to hospital for anything
- This rises to >20% in hospital due to iatrogenic causes e.g. drugs; 1/5 will have severe hypokalaemia
DITCH (the k):
- Drugs = (LADS) Laxatives, Antibiotics (penicillins and aminoglycosides), Diuretics (loop + thiazides), Steroids
- Inadequate K+ intake
- Too much water intake
- Cushing’s and Conn’s syndromes
- Heavy fluid losses (NG tube suction, ileostomy, diarrhoea, vomiting, wound drainage etc)
- Metabolic acidosis
- Mg depletion
What are the different grades of hypokalaemia?
Mild - 3.1-3.5 mmol/L
Moderate - 2.5-3.0 mmol/L
Severe - <2.5 mmol/L
How does hypokalaemia present?
Asymptomatic, incidental blood finding
- Often associated with hypomagnesaemia as well
7 L’s:
- Lethargy
- Lots of urine
- Leg cramps
- Limp muscles
- Low, shallow breathing
- Low BP (severe)
- Lethal cardiac dysrhythmias
What are the ECG features of hypokalaemia?
Start occurring when K <2.7mmol/L
- Increased amplitude + width of P wave
- Prolongation of PR interval
- T wave flattening and inversion
- ST depression
- Prominent U waves (best seen in V1-3)
- Apparent long QT due to fusion of T and U waves
In severe:
- Frequent supraventricular and ventricular ectopics
- Supraventricular tachyarrhythmias e.g. AF, flutter and atrial tachycardia
- Potential to develop malignant ventricular rhythms e.g. VT , VF and Torsades de Pointes
How do you manage hypokalaemia?
Treat underlying cause e.g. reduction of/withdrawal of diuretics
Dietary change - more fruits/veg, legumes, potatoes, milk, yogurt, nuts
PO supplementation - e.g. Sando-K; regimen depends on extent of deficiency, monitor K daily and adjust accordingly
IV fluids with K+ - if severe deficiency/symptomatic, monitor and titrate accordingly
- Do give K at a rate exceeding 10mmol/h outside of ICU (as can precipitate arrhythmias)
If Mg deficient: you will have to correct this prior to correcting K, else treatment with IV K may appear to improve temporarily but will not last - this is due to Mg being required for co-transport of K
What are some key features of potassium physiology?
Mostly intraellular
Vast majority ( >90%) is excreted in the urine
The electrical properties of excitable cells is dependent on the concentration gradient of potassium:
- Therefore, abnormalities may manifest in cell hyperpolarisation or increased duration of the action potential or refractory period
Na/K-ATPase:
- ATP hydrolysis leads to ADP+Pi+ energy
- Beta-1 and -2 adrenoreceptors stimulate ATPase, leading to hypokalaemia (low K in serum)
Renal:
- K absorption in thick ascending limb of LoH
- Na/K channels in late DCT + collecting duct - K excretion with Na reabsorption; stimulated by aldosterone
Hormonal control:
- Insulin + catecholamines responsible for driving into cells
Acidaemia:
- May result in hyperkalaemia as H+ and K+ are exchanged in tissues
What are some spurious causes of hyperkalaemia?
Hemolysis - most common cause of falsely elevated potassium, largely due to pressure gradients created during blood draws performed via syringe or an indwelling cannula
Cold weather/environment, or keeping blood samples in fridge overnight:
- As K leaks out of RBCs into serum)
Thrombocytosis:
- As K can leach from platelets and megakaryocytes during the clotting process
- Can use a green top tube instead (?) in these cases, to get a more accurate K
