Acid-Base Physiology

7.4 - Metabolic Alkalosis - Metabolic Effects

7.4.1 Adverse effects of alkalosis

The effects of the alkalosis are often difficult to distinguish from the effects of associated problems such as hypovolaemia, potassium and chloride depletion.This makes it more difficult to characterise the effects of the alkalosis itself.

Adverse Effects of Alkalosis
  • decreased myocardial contractility
  • arrhythmias
  • decreased cerebral blood flow
  • confusion
  • mental obtundation
  • neuromuscular excitability
  • impaired peripheral oxygen unloading (due shift of oxygen dissociation curve to left).

The disorder is associated with significantly increased morbidity and mortality especially in critically ill patients. The compensatory rise in arterial pCO2 will tend to counteract some of these effects (eg the effect on cerebral blood flow)

7.4.2 Risk of Hypoxaemia

Hypoxaemia may occur and oxygen delivery to the tissues may be reduced. Factors involved in impaired arterial oxygen content are:

Peripheral oxygen unloading may be impaired because of the alkalotic shift of the haemoglobin oxygen dissociation curve to the left. The body’s major compensatory response to impaired tissue oxygen delivery is to increase cardiac output but this ability is impaired if hypovolaemia and decreased myocardial contractility are present.

Give oxygen!

The need for administration of supplemental oxygen to patients with metabolic alkalosis is a neglected part of therapy.