Emergency Medicine

Electrolyte Disorders

Acid–Base, Electrolyte and Renal Emergencies 131

(b) pain, fear, stress, psychogenic, voluntary

(c) fever (cytokines), pregnancy (progesterone), thyrotoxicosis,

liver disease

(d) drugs, e.g. salicylate poisoning.

(iv) Iatrogenic from excessive artificial ventilation.

3 Clinical manifestations are secondary to hypocapnoea, hypokalaemia and
hypocalcaemia. Look for the specific effects of hypocapnoea:
(i) Circumoral paraesthesia, carpopedal spasm and tetany from
neuromuscular irritability.
(ii) Light-headedness and confusion from cerebral vasoconstriction
(usually adapts in 6–8 h).
(iii) Cardiac arrhythmias and decreased myocardial contractility.

4 The body compensates to reduce alkalaemia by excreting or buffering
bicarbonate ions.
(i) A moderate compensatory response via a non-renal-mediated
buffering process can reduce plasma bicarbonate levels to
18–20 mmol/L in an acute respiratory alkalosis within hours.
(ii) The kidneys increase the rate of bicarbonate excretion in chronic
respiratory alkalosis, and reduce serum bicarbonate levels to as
low as 12–15 mmol/L returning the pH towards normal
(a) this renal compensatory response is slow. The maximal effect
takes 2–3 days to occur.
(iii) The expected compensatory fall in plasma bicarbonate in acute and
chronic respiratory alkalosis may be calculated (see Table 3.2, p. 127).

MANAGEMENT

1 Give oxygen to treat any coexistent hypoxia.

2 Look for and correct any reversible underlying disorder.

3 Never diagnose ‘hysterical’ hyperventilation until subtle presentations of
pneumonia, pulmonary embolism, pneumothorax, fever, etc., have been
actively excluded.

4 Otherwise if no significant underlying cause for hyperventilation is likely,
reassure the patient and/or ask them to rebreathe into a paper bag.

ELECTROLYTE DISORDERS

Electroly te disturbances are commonly associated with cardiovascular emergen-
cies and may cause cardiac arrhythmias and cardiopulmonary arrest. Prompt
recognition and immediate treatment of electrolyte disorders can prevent cardiac
arrest.