1. ABG book
Review by Oliver Walsh
What it is:
A series of brief lecture slides (visual only, no audio) and interactive tools about the biochemical basis of acid-base regulation, and interpretation of the arterial blood gas.
Pros
- Lots of diagrams and interactive tools (e.g. slide bars to select values for pH, pCO2 or HCO3-, then the other values are automatically calculated or graphed)
- A step-by step approach to acid-base interpretation
- Use of the Boston Rules (although an unconventional formula for expected PaCO2 in metabolic alkalosis)
- Single-page algorithms for alkalosis and acidosis are useful clinical aids
- Units can be displayed in mmHg or kPa
- Free, definitely FOAMed
- App support by developer
Cons
- No clinical cases
- Many diagrams and slide bar functions add little to the reader’s understanding and some are difficult to decipher, with too many colours and axes
- Specific causes for low and normal anion gap is discussed, however the well-known and arguably more important causes of a high AG are omitted.
- No mention of base excess (some argue this is a more accurate marker of metabolic acid-base status than HCO3-) nor the Copenhagen approach
- The physicochemical method (Stewart’s theory) isn’t included.
The bottom line
An overview of acid-base physiology that is a reasonable starting point for beginners. Unfortunately ABG Book doesn’t offer anything additional to most written, online or other app-based resources on this subject, has no clinical cases, and omits key concepts in advanced acid-base interpretation.
2. Complete ABG
What it is
An interactive tool that demonstrates the interplay between PaCO2, pH and HCO3- via the Henderson-Hasselbalch equation, including a diagnosis of the acid-base disorder and a list of causes.
Pros
- A simple tool where the reader enters the PaCO2 and pH, then the calculated HCO3- is displayed and the specific acid-base abnormality is diagnosed
- Also calculates the A-a gradient when PaO2 and FiO2 is entered
- The ‘extended ABG’ section includes the anion gap, delta-delta, osmolar gap, and urinary anion gap
- Single-page algorithms for alkalosis and acidosis are useful clinical aids
- Free, definitely FOAMed
- App support by developer
Cons
- No explanation of the basic biochemistry
- No clinical scenarios
- No mention of base excess, or the Copenhagen or physicochemical (Stewart’s) approach
- Includes anion gap, with differentials for low and normal AG, but omits the well-known and arguably more important causes of a high AG
The bottom line
A useful clinical aid to remind us of the wide differentials, especially the uncommon diagnoses.
For beginners without prior knowledge in this area, Complete ABG would need to be used in conjunction with another more didactic resource.
