A while back I asked the twitterverse whether anyone could recommend a good app for arterial blood gas (ABG) interpretation. The deafening silence showed me that (a) I have very few followers and (b) if I want an ABG app review, I have to write it myself. Hence this blog post. A few preliminary remarks are in order. If you don’t already know how to interpret tricky blood gases, go listen to the four-part podcast series by Scott Weingart part one can be found here
I used the same blood gas results to test every app – based on the gases provided in the post “A Really Tricky ABG?” (at LITFL). My reasoning is that this not only keeps the reviews fair, but it highlights the difference between mechanical apps and informed clinical judgement (a scan through the comments on that post is very instructive).
Finally, a disclaimer. I do not have any affiliation with any of these apps or their creators. I was not asked to do this review, and if an app cost money, I paid for it myself. Whenever there was a free “lite” version and a paid “pro” version, I chose to review the paid app. I downloaded 14 apps in total, that being all I could find in the iTunes store. Having said all that, on with the review!
ABG Acid-Base eval (free) = values for pH, pCO2, Na, HCO3 and Cl are input using scroll bars (good ranges available). The app steps the user through an analysis, requiring some (very) simple evaluation of results – a nice teaching feature not seen in other apps. After working through the steps and calculations (cheat option is provided for calculations if desired), the app compares your findings with the expected findings. Nice to see a reminder that “patients and their physiology are more than just numbers”. Provides email address for app creator. Includes list of references.
Graphical arterial BG ($0.99) = initially not intuitive to use. Separates gases from acid-base. Allows user to save patients’ values in a Patient List. Input values via sliders on sides of graph, with limited ranges. Includes a description of 6 diagnoses. Plots values on nomograms. Allows for trends to be plotted on nomogram for a particular patient. Creates PDF files of data in a graph (automatically) – which can then be printed or emailed. Can search for previous results by date. Can swap between mmHg and KPa.
PRETTY GOOD APPS:
Blood Gas ($0.99) = Asks for pH, PCO2, HCO3, Na, bicarb, chloride, albumin and anion gap. Input values by typing (no range limits). Able to leave blanks. Result “primary metabolic acidosis with normal anion gap, with superimposed respiratory acidosis”. Gives expected values for Pco2 (23-27), pH (7.12), CO2 (37) and HCO3 (11). Reset button. No further options, no further information provided.
Acid Plus ($4.49) = asks for input (via scroll bars) for pH, PCO2, Na, Cl, and HC. Result: primary non-gap metabolic acidosis, which is uncompensated (AG = 6; BE -17). Secondary concomitant respiratory acidosis. Right arrow provides more info about the analysis. Lists a variety of possible causes and the anion gap mnemonic (MUDPILES). Information is referenced. Preferences screen allows user to set upper limit for normal anion gap, enables base excess to be turned on or off, and allows selection between mmHg and kPa. Able to email feedback and visit the website. No ability to share or save information.
ABG Pro ($1.99. Free version – ABG Simple) = type in values for chosen calculation. Possible calculations: A-a gradient, osmolar gap, simple ABG, complex ABG, ABG & osmolar gap. Complex ABG asks for pH, pCO2, bicarb, Na, Cl, Alb (can leave blank), with result “Primary non-AG metabolic acidosis with secondary respiratory acidosis” – differential diagnoses provided for both. Lists expected pCO2 and bicarb. Able to set SI units (default is on), bicarb and pCO2 ranges, and whether problem is chronic or acute (default is acute). No options to share or save data. Reference provided.
Acidosis ($4.49. Lite version available) = asks for patient weight, gender. Options for total body water (child, adult, elder). Asks for input (via scroll bars, with good ranges) for pH, Co2, Na, K, Cl. Calculates bicarb (10.5), BE (- 17.1) and AG (6.5mmol). No chance to leave values blank. Result: severe acute metabolic acidosis. Click on arrow to obtain further information on the analysis and possible causes. No options provided to save or share information. Can change unit of measurement from mmHg/kPa and anion gap negative/positive. Provides option to email creator of app, has link to a website, and references provided.
APPS THAT DO THE JOB:
ABG (free) = input values for pH, pCO2, HCO3 and pO2 to get result “metabolic and respiratory acidosis”. Include Na, Cl and Alb to get gap calculations “anion gap 6, NI gap alb corrected 12, corrected bicarb 5”. Values are typed in with no limits to range. Includes screen to calculate FiO2, and another for haemodynamic calculations. Also includes a drip rate calculator. No further options available.
ABG Guide (free) = requests name, email and occupation before able to use. Option to get news and updates (default is off). Input values using sliders (with good ranges of values, some have to be rounded up or down). Gives results PER PARAMETER, not for the readings as a whole. Lists clinically significant features and possible underlying causes. Information button leads to screen where can choose to use SI units (off by default), parameter order, contact information, website, and an ‘account’ page.
ABG Stat ($1.99) = Input pH, pCO2 and HCO3 using scroll bars (good ranges). Result “uncompensated metabolic acidosis”. Button provides “more info” including causes. Can calculate ABG, anion gap, A-a gradient and CaO2. A “notes” tab provides graphs, nomograms and further information about the various calculations (includes references). No ability to choose different settings or to save/share information.
TOTALLY CRAP APPS:
iAcid (free) = starts with screen requesting cations Na, K, Ca and Mg, then asks for anions BE, HCO, CL, Alb and Lac. Input values via scroll screens, with limited ranges, and no option not to include a value/leave a value blank. Results screen gives anion gap (18.2), corrected gap (24.45), SID (25.7), Na/CL effect (-12), Albumin effect (0) and unmeasured effect (6.75). No further options or settings. To be fair, this is the only app that calculates strong ion difference.
Easy ABG ($0.99) = Can select between kPa and mmHg. Type values in (no limits to range). Asks for pH, PaO2, PaCO2 and HCO3. Result “metabolic acidosis”. No further information given. No other settings available. Don’t waste your money.
AciAlko ($1.99) = uses sliders to input values for pH, pCO2, HCO3. Limited ranges available. Gives a simple analysis. Website provided. No further options to customise settings. Wouldn’t recommend this even if it was free.
Smart Nurse ($1.99) = values typed in for pH, pCO2, HCO3. Gives a simple result “metabolic acidosis”. Can click tab at bottom to get a more detailed description of the result (definition, risk factors, symptoms, diagnostic tests, treatment). No further options. No mention of secondary or mixed disorders. This app also has sections for drip calculations, EKG interpretation, ACLS practice and nursing diagnosis > none of which this reviewer has used. This review only refers to the ABG interpretation tab.
Acid Base Disorders ($1.99) = Not very user-friendly for novice ABG interpretation. Excess anion gap and delta delta calculations only available when anion gap result is over 12. Describes 6 possible disorders and expected values. Has a screen for calculation of osmolar gap (requires Na, glucose, BUN). Values are input by typing. Includes a list of possible aetiologies divided into anion gap acidosis, non anion gap acidosis, acute respiratory acidosis, metabolic acidosis, respiratory alkalosis and chronic respiratory acidosis. No detail provided for these conditions. Has a link to website. No further options provided.