Preop Eval vs ABG Acid
Price, ratings, monetisation and update history for both apps, side by side — with what reviewers say about each.
Preop Eval
This app provides guidance for evaluating and preparing adult patients for non-cardiac surgery. It includes algorithms and resources on medication management, cardiac event timing, and preoperative testing, serving as both a reference and a teaching tool for medical professionals.
- Cardiac evaluation algorithm
- Medication guidance (starting/stopping)
- Surgery timing after cardiac events
- Preoperative testing recommendations
- Review for students and residents
- Perioperative insulin management
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Preop Eval organizes and presents much of the guidance that one needs in order to evaluate and prepare adult patients for non-cardiac surgery. It is based upon the guidelines on this topic from the American College of Cardiology, the European Society of Anaesthesiology, the American Society of Anesthesiologists, the Institute for Clinical Systems Improvement, the American College of Chest Physicians, and more (full references in the app). The app contains 1 algorithm and 3 resources: the cardiac evaluation algorithm, guidance on starting and stopping key medications in the perioperative period, guidance on timing of surgery after cardiac events, and guidance on preoperative testing. It also contains a review of preoperative evaluation mainly for students and residents. The app addresses such common questions as: - who needs bloodwork before surgery? - who needs an EKG or a CXR? - how do I handle patients on warfarin, clopidogrel, and DOAC's? - which patients need adjustment of perioperative insulin and diabetic meds, and how? - which active cardiac conditions preclude surgery? - how long after MI or stent should a patient wait before surgery? - are there adjustments to make on psych meds, rheumatologic meds, ACE's and ARB's? This app is written and intended for practicing physicians like internists, family physicians, and hospitalists; for resident physician trainees; and for medical students. In addition to being a reference, the algorithm is written to be a teaching tool by not just delivering an answer, but instead walking a physician through the evaluation process so that one learns that process along the way. As an educator and clinician, I am interested in feedback and I would be grateful for guidance on improving the tool.
ABG Acid
This app guides clinicians through analyzing ABGs and electrolytes to identify acid-base disorders and diagnostic ideas for ill patients. It teaches a stepwise thinking process and provides differential diagnoses with explanations, aiding patient care and clinician learning.
- Stepwise ABG and electrolyte analysis
- Identifies acid-base disorders
- Provides diagnostic ideas
- Teaches critical thinking process
- Includes differential diagnoses mnemonics
- Calculates predicted pCO2 and corrected bicarbonate
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ABG Acid-Base eval walks a clinician through a stepwise approach to analyse ABG's and electrolytes in order to arrive at acid-base disorders and diagnostic ideas about ill patients. It is based mainly upon a worksheet developed by Dr. Erik Rupard from the medical literature. This tool not only yields answers, but just as importantly teaches the stepwise thinking process and the necessary concepts along the way. A clinician or learner will wind up with good information that assists patient care and should wind up a little smarter and more able to do it with less assistance the next time. It is a great support for those of us clinicians who use these tests only occasionally and don't have it memorized. The differential diagnoses include the classic mnemonics like MUDPILERS, CHAMPS, CLEVER PD, and HARDUPS, with explanations and examples. The app addresses such common questions as: * What are common causes of metabolic acidosis? respiratory alkalosis? * How do I calculate predicted pCO2? corrected bicarbonate? * What is the primary acid-base disorder? * Are additional acid-base disorders present, and if so, what are they? This app is written and intended for practicing clinicians like internists, family physicians, ER docs, cardiologists, pulmonologists, intensivists, and hospitalists; for resident physician trainees; for medical students; and of course for other clinician colleagues like NP's and PA's. As an educator and clinician, I am interested in feedback and I would be grateful for guidance on improving the tool. Notes of importance: - many thresholds and cutoffs are arbitrary and debatable, so you will have to use judgment to interpret which disorders are present and to what extent when suggested by the app - the app facilitates you to evaluate the data. If you make a mistake, the app will not argue with you. It will, at the end, offer to compare your work to the disorders that the app finds using the same algorithm - patients are more than the sums of their numbers and data, and they are often unique individuals. Use this information as a starting point in the evaluation of your patient and always do your own thinking!
Screenshots
Verdict
The clearest difference is monetization model: Preop Eval at free against ABG Acid's paid. Preop Eval also leads on rating (5.0 vs 4.6). ABG Acid's advantage is ratings volume (7 vs 2) and iOS requirement (13.0 vs 16.6). On price, review sentiment, update cadence and ads there is nothing between them.
Scored on Price · Rating · Positive reviews · Number of ratings · Update frequency · Ads · In-app purchases · Monetization · Best chart rank · Devices · Requires iOS
Both are free to download. Neither carries in-app purchases, so what you see is what you pay.
Preop Eval holds the better App Store score, 5.0 against 4.6. Both are backed by a comparable volume of ratings — 2 and 7 respectively. Written reviews point the same way: 67% of Preop Eval's written reviews are positive against 63% of ABG Acid's.
Preop Eval ships an update every 6 months, ABG Acid every 5 months. The most recent releases landed on September 30, 2026 and October 16, 2026 respectively.
| Parameter | Preop Eval | ABG Acid |
|---|---|---|
| Price | Free | Free |
| Rating | 5.0 (2 ratings) — better | 4.6 (7 ratings) |
| Positive reviews | 66.7% of reviews — better | 63.0% of reviews |
| Number of ratings | 2 | 7 — better |
| Update frequency | Every 6 months | Every 5 months — better |
| Ads | No | No |
| In-app purchases | No | No |
| Monetization | Free — better | Paid |
| Devices | iPhone | iPhone, iPod — better |
| Requires iOS | 16.6 | 13.0 — better |
| Further details — not scored | ||
| Size | 15 MB | 1 MB |
| Age rating | 17+ | 17+ |
| Developer | United Health Services, Inc. | Joshua D. steinberg |
Customer experience
Preop Eval
ABG Acid
In-app purchases
Preop Eval
No in-app purchases
ABG Acid
No in-app purchases









