Potassium disorders Flashcards
What are the main roles of potassium
- Maintanence of the resting membrane potential
- Cell volume homeostasis
- Transmission of action potentials in muscle and nerve
What could cause falsely elevated potassium in a sample
- Hyperlipidaemia
- Hyperproteinaemia
- Contamination with EDTA
AT what level would hyperkalaemia be considered life threatening
> 7.5mmol/l
>5.5mmol/l is abnormal (RI 4- 5.5)
Categorise the main causes of hyperkalamia
- Impaired renal excretion
- Translocation from ICF to ECF
- Extra renal GI causes (more rare)
Summarise some differentials for reduced renal excretion of potassium
- anuric/Oliguric renal failure
- Urinary tract obstruction
- Uroabdomen
- Hypoadrenocortism
- GI disease
- Drugs
- Chylothorax/pleural effusion
- Thrombocytosis and leukocytosis
Summarise so differential for increased intake/extrarenal causes
- IV potassium fluids
- expired RBC transfusion
- Translocation from ICF to ECF
- insulin deficiency
- reperfusion injury
- Post CPA
- acute tumour lysis syndrome
What are the main ECG changes seen with hyperkalaemia
Flattened or absent p waves, widening of the QRS, tall peaked T waves
- idioventricular rhythmn
- can lead to atrial standstill
List the main treatment options for managing hyperkalaemia
- Fluid therapy with balanced crystalloid
- calcium gluconate 10%, 1ml/kg boulus diluted.
- Insulin 0.5IU/kg soluable insulin with 1-2g/kg dextrose IV bolus followed by 2.5% CRI.
- Glucose bolus alone to stimulate endogenous insulin.
- Terbulaline 0.01mg/kg IM
- sodium bicarbonate 1mmol/kg (intracellular drive).
- Dialysis in severe renal failure
- DEAL WITH THE UNDERLYING ISSUE
Which method do most reference labs use for measuring potassium and why is it advantageous
usinig ion selective elctrode. Less likely to be effected by by hyperlipidaemia or hyperproteinaemia
What levels classify hyperkalaemia as moderate or severe
- moderate 2.5 - 3mmol/l
- severe hypokalaemia <2.5mmol/l
list the extrarenal causes of hypokalaemia
- Decreased intake
- Vomiting and diarrhoea
- potassium translocation
- Aldosterone secreting tumour or other hyperaldosteronism
- DKA
- Steroid therapy
How can vomiting and diarrhoea cause hypokalaemia?
- through direct loss in diarrhoea and vomitus
- Activation of the RAAS through volume loss = increased aldosterone = increased urinary secretion
What are some causes of hypokalamia via translocation
- Glucose containing fluids or insulin therapy
- catecholamine release during stress
- Beta agonist therapy or intoxication
List some renal causes of hypokalaemia
- CKD, cats particularly = Polyuria.
- Renal tubular acidosis
- drug induced, loop and thiazide dieuretics
- post obstructive dieuresis
- osmotic dieuresis espec glucose
- other endocrine: cushings, hyperaldosteronism, hyperthyroidism.
What are the clinical signs of hypokalaemia
Muscle weakness, anorexia, polyuria, neck ventroflexion (cats), ventricular or supraventricular tachyarrthymias
What is the significance of the fractional excretion of potassium
It helps differentiate causes, less than 6% is likely due to extra renal causes such as GI loss
What is KMax
The maximum rate of potassium supplementation.
-0.5meq/kg/hr
- over this carries concerns for cardiotoxicity
When might you consider exceeding Kmax
- In patients with profound hypokalaemia ,2.5mmol/l and a normal urine output
- Continuous ECG monitoring needed to monitor for cardiotoxicity
what ECG changes could be seen with hypokalaemia
Flattened T waves, ST segment depression and u waves
These are less predictable than for hyperkalaemia
What are some practical considerations for potassium administration
- designated fluid line which is never flushed
- through bag mixing
- careful labelling to avoid accidental bolus
- avoid high concentrations due to phlebitis
make sure hypocalcaemia and hypomagnesia are also corrected for max effect
