Hyperventilation of the anaesthetised patient is common and preventable. Monitoring by capnography allows early recognition and correction. In major operations, serial arterial gases for assessment of oxygenation and ventilation is appropriate especially as the size of the endtidal-arterial pCO2 gradient can be determined and this is useful for determining ventilation settings between blood-gas analyses.
Summary of important aspects of Chapter Six: Respiratory Alkalosis
- Respiratory alkalosis is a primary acid-base disorder in which the pCO2 falls to a level lower than expected.
- All cases are due to increased alveolar ventilation
- The compensatory response is renal loss of bicarbonate which causes a fall in plasma bicarbonate
- The fall in bicarbonate can be predicted from a simple formula
- Metabolic effects include decreased cerebral blood flow, decrease in myocardial contractility and a shift of the oxygen dissociation curve to the left
- Hyperventilation is used to acutely decrease intracranial pressure as the onset is rapid. The effect on CBF is time-limited as equilibration of bicarbonate across the blood-brain barrier occurs over 4 to 6 hours and CBF and ICP return towards normal.