Electrolytes

Objectives

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Scope

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Audience

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Initial Assessment & Management

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Advanced Assessment & Management

 

Acute Renal Failure


Assess renal reserve
Estimated glomerular filtration rate (eGFR) can be derived from serum creatinine
(preferred to urea as it is independent of dietary protein intake) by the Cockcroft-Gault
equation:
• eGFR in males = [140 – Age(yrs)] x Wt(kg)/[serum creatinine (μmol/l) x
0.814]
• eGFR in females: multiply the result of the above equation by 0.85.
Normal eGFR is ~120mls/min. Critical minimum=20ml/min. A rising creatinine and falling
eGFR indicates a potential need for renal replacement treatment. Seek advice from a
nephrologist if management is uncertain.


Causes of impaired renal function


These are classified into three groups:
• Pre-renal = poor renal perfusion (best sign: hypotension especially if this
is postural)
• Renal = nephritis (best sign: urinary dipsticks show blood, protein or
both)
• Post-renal = obstruction (best sign: obstruction on ultrasound).


Indications for renal replacement treatment (haemofiltration, dialysis etc)
There are four indications for renal replacement. The presence of any one that fails to
respond to conservative measures qualifies:
• Fluid overload (pulmonary oedema)
• Hyperkalaemia ([K+]>6.5mmol/l)
• Urea>40mmol/l
• Metabolic acidosis ([HCO3-]<12mmol/l).


Diagnosis and treatment of oliguric acute renal failure


• Most causes are medical, usually due to reduced renal perfusion following
hypotension (secondary to absolute or relative hypovolaemia), but nephritis is
a possibility.


• Normal urine output is about 1500mls/24hrs = 60ml/hr
Acute renal failure = 400ml/24hrs = 18.5ml/hr
Hourly urine output and renal function tests (especially serum creatinine)
should be monitored regularly in seriously ill patients as soon as medical
assessment commences, especially in patients who have suffered trauma,
burns or infection who are at particular risk. In these patients, attention should
be paid to restoration of peripheral oxygen delivery (increasing pulmonary
arterial oxygenation and peripheral blood flow).

 

Paediatric Considerations

Basic Fluid Maintenance

Hyponatraemia

 

Diagnostic Features:
• Mild Hyponatraemia is commonly seen in soldiers excessively drinking
water.
• Confusion and irritability can occur with serum levels ~120mmol/L
• Coma, fits and death may occur with serum levels ~110mmol/L
Assessment of volume status may help in management but lacks sensitivity/specifity. If
time and resources allow, measure osmolality and urine sodium.


Management:
• Exclude pseudohyponatraemia. Seen in lipaemic serum,
hyperglycaemia, alcohol consumption, mannitol use and gives a falsely low
sodium reading. Will not occure on blood gas/I-Stat analysers due to the
measurement technique. If suspected and able to, measure serum
osmolality and liaise with laboratory early.

Hyperkalaemia

Hypocalcaemia

e.g. during Massive Transfusion

Arterial blood sample
• Consider the need for further calcium after each 4 units of stored red cells
transfused: determine the requirement by regular monitoring of ionized
clacium levels and clinical symptoms/signs


Cautions
• Undiluted calcium should not be used as it causes thrombophlebitis
• Calcium must not be given through the same line as NaHCO3 (sodium
bicarbonate) as this will result in precipitation of calcium carbonate


Monitor
• ECG
• Improvement in clinical signs and symptoms
• Serial blood levels (ionized calcium)

Hypokalaemia

Severe <2.5mmol/L

  • Replace intravenously
  • 40mmol/hour maximum, ideally via central line.
  • Use ECG monitoring
  • Continuing therapy will be determined by response


Moderate 2.5-3.0mmol/L

  • If receiving digoxin or ECG changes ('u' waves) replace intravenously
  • 40mmol/hour maximum
    • 40mmols in 100mls sodium chloride/dextrose over 1hour, ideally via central line)
  • Use ECG monitoring
  • If not receiving digoxin give Sando-K, 4 tablets stat
  • Continuing therapy will be determined by determined by response and estimation of ongoing losses


Mild >3.0mmol/L requiring replacement

  • Give Sando-K, 2 tablets stat
  • Continuing therapy will be determined by the response and estimation of ongoing losses

Approved By: DCA Emergency Medicine

References

Map of Medicine (dated 29 Jan 2009)