Define the terms 'base excess' and 'standard base excess' (20% marks)
College Answer
Base excess is defined as the amount of acid or alkali that must be added to fully oxygenated blood to return the pH to 7.40 at a temperature of 37°C and a pCO2 of 40 mmHg.
Standard base excess is the amount of acid or alkali to return the ECF pH to 7.40 at a temperature of 37°C and a pCO2 of 40 mmHg and is calculated for blood at a Hb of 50 g/L.
Discussion
In brief:
Base excess definition
- Dose of acid or base required to return the pH of a blood sample
- Measured at standard conditions: 37°C and 40mmHg PaCO2
- Thus, isolates the metabolic disturbance from the respiratory
Standard base excess
- Dose of acid or base required to return the pH of an anaemic blood sample
- Calculated for a Hb of 50g/L
- Haemoglobin buffers both the intravascular and the extravascular fluid
- Thus, SBE assesses the buffering of the whole extracellular fluid, not just the haemoglobin-rich intravascular fluid
References
Reade, M. C. "Temporary epicardial pacing after cardiac surgery: a practical review." Anaesthesia 62.3 (2007): 264-271.
Reade, M. C. "Temporary epicardial pacing after cardiac surgery: a practical review: Part 2: Selection of epicardial pacing modes and troubleshooting."ANAESTHESIA-LONDON- 62.4 (2007): 364.
Gammage, Michael D. "Temporary cardiac pacing." Heart 83.6 (2000): 715-720.
Sanders, Richard S. "The Pulse Generator." Cardiac Pacing for the Clinician. Springer US, 2008. 47-71.