Online Acid-Base

Introduction

Subsequently, American researchers in Boston and Danish physicians in Copenhagen waged the “Great Trans-Atlantic Acid-Base Debate” regarding the use of base excess as proposed by Copenhagen, or six acid-base rules based on measurement of the serum bicarbonate level as proposed by Boston.(3) The in-vitro base excess was dependent on the hemoglobin level–subsequently a source of criticism and debate. The entirety of this debate is beyond the scope of this introduction but has a page devoted to it in the first website detailed below. In general, most of the websites listed below use the serum bicarbonate as their arbiter of metabolic acid-base status. One of the last major changes to the landscape of clinical acid-base came in the early 1980s from Peter Stewart who focused on the contribution of the Strong Ion Difference to the acid-base status of a patient. Stewart’s approach is inherently different from previous paradigms in that it stresses the use of bicarbonate as a marker for acid-base disturbances rather than a causative factor. He analogized that assuming bicarbonate is the cause of an acid-base disorder is like blaming the chest radiograph for causing the pneumonia. His group has argued that the Strong Ion Difference is the best parameter for expressing acid-base derangements and has even suggested that the very concept of pH be abandoned. Several websites below have sections strictly dedicated to discussing Stewart’s approach. Finally, several sites are noted that have calculators to evaluate acid-base disturbances.

Last Update: October 2007 

Search

A Google® search for “acid base” returned 2.9 million hits, the first 300 of which were predominantly related to “hard” acid-base physiology. Adding “clinical,” “case example” or “human” to “acid base” shifts the number upward to 6 million-plus hits–the percentage of clinical websites in the first several hundred greatly increased. Searching through the first 150 of both “clinical acid-base” and “acid-base case example” produced several appropriate websites.

Best Websites

Anesthesiology Education Website

This primarily anesthesia-oriented site created by Kerry Brandis has a comprehensive tutorial composed of 11 chapters beginning with simple acid-base concepts which then segues to a lengthy discussion of each of the major acid-base disorders, finally ending with a case file series of 30-odd acid-base problems that are great for reproduction and teaching purposes.

1. Authority: Dr. Brandis is a clinical professor of anesthesiology at Gold Coast Hospital in Queensland, Australia. He compiled his lecture notes from decades of teaching medical students and residents and combined them into this website. Rating: 4

2. Currency: The discussion generally reflects current thinking about these diseases. The Bostonian method has been in place for decades, but the use of bicarbonate in metabolic acidosis covered here accurately reflects the controversial nature of its use in today’s clinical practice. The website has recently undergone a major renovation, the clinical cases that are added semi-regularly. Rating: 4

3. Accuracy: All formulae are referenced to their original publications. The history of acid-base is consistent with other texts’ accounts, as are the etiologies and treatments of above acid-base disorders. Rating: 5

4. Navigation & Readability: The website is user-friendly. The above link points to the main page listing the chapters, from which you can cycle through in order, or come back to the main menu for points of interest. Rating: 4

5. Utility: The site is extremely useful for students, fellows or practitioners needing a starting point, a refresher, or case examples for teaching Rating: 5

Summary: Overall, this is an excellent site, and should be a first stop for anyone interested in deepening their knowledge of acid-base disorders.

Acid-Base Tutorial from Tulane University Department of Anesthesiology

Authored by Alan Grogono, former chair of the Department of Anesthesiology at Tulane, this site explains the myriad aspects of acid-base physiology (using Flash animations to explain the more difficult concepts). Written in an entertaining manner, the history of acid-base is dissected thoroughly. Several cases are presented as well as many printable nomograms which can help to delineate acid-base problems on-the-go. Also discussed in detail is the base excess, (which is often underappreciated in Internal Medicine acid-base analysis). The Interactive Acid-Base Diagram allows one to drag a cursor around several axes comprised of PCO2, standard base excess and pH to determine a patient’s acid-base status in real-time.

1. Authority: Dr. Grogono is well-published in acid-base, was chair of anesthesiology at Tulane for decades, and holds several patents in Europe. He was instrumental in developing our currently used acid-base nomograms. See his website for his “Grogono nomogram”, published in 1976. Rating: 5

2. Currency: The discussion is about topics that are well-established, and as such, this website reflects current thinking about these subjects. It has recently undergone a major revision of the format and addition of content. Rating: 4

3. Accuracy: As with the above website, there is an impressively thorough index to reference its claims, the physiology and approach to acid-base. Rating: 5

4. Navigation & Readability: The website is user-friendly. The above link points to the main page listing the 20 major sections, which can be followed in logical order or skipped through as desired. Rating: 4

5. Utility: By lack of more clinical cases, this site veers more toward the theoretical, but the theory that is here is spectacularly presented. Rating: 4

Summary: Overall, this is the most cleverly written website on this list, and certainly the most graphically appealing. It’s great start to understand some difficult concepts.

Acid-Base Online Tutorial

The most accessible site on this list is aimed at medical students and internal medicine residents, and as such, is a great resource for teaching. The tutorial stems from an interesting collaboration between a fourth year medical student and his faculty mentor at the University of Connecticut. It explains the mechanisms of acid-base homeostasis with easy-to-follow diagrams and then finishes with eight well-explained clinical cases that will make a great transition to the chalkboard.

1. Authority: This site was authored by the collaborative efforts of a fourth year medical student, Timur Graham, and his faculty adviser, Dr. Steven Angus. Neither has any PubMed hit for publications relating to acid-base physiology, but Dr. Angus is part of a busy clinical practice as a hospitalist and internist at the University of Connecticut. Rating: 3

2. Currency: The discussion is about well-established topics, and as such, this website reflects current thinking about these subjects. It was created this year, and has a section labeled “pearls” (which has yet to be completed), promising more content to come. Rating: 5

3. Accuracy: The findings of the website are consistent with current thinking about acid-base physiology. There are no footnotes or references for their assertions, but their assertions are roughly the same as other sites being reviewed. Rating: 3

4. Navigation & Readability: The website is user-friendly. The front page linked above takes you through the entire tutorial and then the cases with just the press of the next button. Rating: 4

5. Utility: The site is a basic overview that may be the best starting off point for someone unfamiliar with acid-base concepts. Rating: 4

Summary: Overall, this is the most basic of all our listed websites, but the simplicity may be its actual strength. The cases are well-presented and explained.

The Worldwide Anesthetist Acid-Base

This is another anesthesiology-based website that attempts to explain both the traditional approach to acid-base physiology and the “physico-chemical” Stewart approach with several excellent sections explaining how the traditional method may fall short and how to reconcile the two in everyday clinical practice. From the very beginning, the narrative style of the prose is readily accessible, and several easily digestible mnemonics and tables are littered throughout the text. There are sections that are very dense from a chemistry standpoint (this is noted prior to these sections) but for those looking for an extremely thorough scientific dissection of the concepts underlying acid-base physiology, these are a treasure. Featured within these sections are some well-done interactive Java applets which help to explain the points. Most interestingly, the last section, “Acid-Base Balance – Finding Common Ground,” provides a great one-page review of acid-base full of great memory tricks and interesting paradigms for structuring one’s thinking about acid-base.

1. Authority: The web administrator was emailed and the address was no longer in service. It is, however, evidence-based and well-referenced. Rating: 3

2. Currency: The discussion is about well-established topics, and as such, this website reflects current thinking about these subjects. Its last update was in 2003. Rating: 3

3. Accuracy: This site is accurate and holds to classical thinking about traditional acid-base analysis. Rating: 4

4. Navigation & Readability: The website has a main page with six links that should be followed chronologically, as they build on each other. Each link has a quick link back to the main page. Rating: 4

5. Utility: There are no case examples, but the depth of discussion of the chemistry background underlying our practice of acid-base medicine is impressive. Rating: 3

Summary: For certain concepts, this is the most readable of any of the websites listed in the review. Overall, perhaps has too much general chemistry for the average practitioner. Certainly it has a balanced approach including Stewart’s work.

Other Important Sites

• VIN.com Acid-Base and Blood Gas Interpretation
  http://www.vin.com/WebLink.plx?URL=http://www.cvmbs.colostate.edu/clinsci/wing/fluids/bloodgas.htm

  This repository of 10 acid-base and arterial blood gas examples is for advanced practitioners only. At first glance, the diseases of the patients seem commonplace (pancreatic duct adenocarcinoma, mitral insufficiency, projectile vomiting), but the realization that the patients are from a veterinary website and mostly consist of Golden Retrievers and Great Danes quickly becomes apparent. Take a quick look at the normal blood gas values (which for dogs at altitude in Fort Collins, Colorado are quite hypocapnic). If one cannot suspend disbelief, multiply the ages of the dogs by seven and pretend they are human patients. The cases are well explained and the answers to the questions popup with a quick mouseover of the link called “answer.”

• Stony Brook Hospital Nephrology Website
  http://www.uhmc.sunysb.edu/internalmed/nephro/webpages/Part_E.htm

  This is a bare-bones review of traditional acid-base medicine filled with visual aids all in one consecutive page. This wins no points for frills, but certainly garners some for simplicity and accessibility. The numerous graphs, charts, figures and tables articulate the points and help to accentuate the anatomical physiology of acid-base perhaps better than any of the other websites listed here. The nephrological bent also provides a different viewpoint that complements the other different paradigms posted here. In general, it is a good starting point to become conversant with acid-base topics.

• MedCalc Acid-Base Calculator
  http://www.medcalc.com/acidbase.html
• Java Acid-Base Calculator
  http://www.health.adelaide.edu.au/paed-anaes/javaman/Respiratory/a-b/AcidBase.html
• Medcalc 3000
  http://www.medcalc3000.com/AnionGapDelta.htm

  The combination of these three websites afford the visitor a quick computerized interpretation of a given arterial blood gas using long-established equations, freeing white coat pockets from the burden of carrying laminated cards with the same information. The first acid-base calculator (MedCalc) requires the input of the pH, PCO2 and the bicarbonate from an arterial blood gas; it then gives a refreshingly thorough output of the various possibilities and normal compensations for that particular combination of labs. For those with a graphical penchant, the Java Acid-Base calculator automates the well-known acid-base nomogram and adds a visual flavor to the analysis. The last calculator helps to dissect one of the more difficult acid-base concepts for residents to grasp, the “delta-gap.” These are all free, and while they would be ideal for transfer to a PDA, they do not support this functionality at this time.

Disclaimer

The author has no personal or financial interest in any of the websites discussed above.

References

1. Peters JP, Van Slyke DD. Quantitative Clinical Chemistry: interpretations. Baltimore, MD: Williams and Wilkins; 1931
2. Story DA. Bench-to-bedside review: a brief history of clinical acid-base. In: Vincent JL, editor. Critical Care, Vol.8. Melbourne: BioMed Central ltd; 2004.p. 253-258.
3. Brandis K. The Great Trans-Atlantic Acid-base debate: acid-base physiology. Available from: http://www.anaesthesiamcq.com/AcidBaseBook/ab9_5.php