Basic Concepts of Fluid and Electrolyte Therapy

Existing respiratory disease may be exacerbated perioperatively by
atelectasis, respiratory infection, retained sputum, abdominal distension,
splinting of the diaphragm, pain from the wound or high doses
of opiates. Epidural analgesia may be advantageous in these respects.
In severe cases, particularly those with prior lung disease, bronchial
suction and mechanical ventilation may be necessary. Chest physiotherapy
is also vital in many cases.
Respiratory alkalosis – is due to hyperventilation, causing a low Pco 2
and in chronic cases, some compensatory reduction in HCO 3 – . It may
be iatrogenic due to deliberate or mistakenly overenthusiastic artificial
ventilation, or secondary to anxiety or distress. It may be associated
with paraesthesiae, tetany and chest pain.
Management
The principles of management involve correcting any abnormalities of
fluid and electrolyte balance (e.g. hypovolaemia, salt and water
deficit). The underlying cause for the acid-base disorder (e.g. ketoacidosis,
acute kidney injury, sepsis) must be diagnosed and managed
promptly. In general, specific therapy to correct the HCO – 3
or Pco 2
should only be contemplated if the acid-base disorder is affecting
organ function or if the pH is 7.6.
Patients identified as having a metabolic acidosis secondary to ethylene
glycol or methanol intoxication need immediate referral to the
renal team for consideration for intermittent haemodialysis to remove
the toxin. Additional management should be guided by advice from a
poisons centre, but will include the intravenous infusion of alcohol to
prevent the breakdown of ethylene glycol and methanol to their toxic
metabolites by alcohol dehydrogenase. If available fomepizole, an
alcohol dehydrogenase inhibitor is the preferred first line therapy.
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