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Online Acid-BaseJ.C. Michel, M.D. Fellow Pulmonary, Critical Care and Sleep Medicine University of Illinois at Chicago Chicago, IL IntroductionThe history of acid-base physiology is a long one, invoking memories of high school chemistry and names such as Arrhenius, Brønsted, and Lowry. Building on the work of these acid-base giants, the 1930s brought for the first time an increased understanding that physiological mechanisms (rather than solely physical and chemical) were responsible for the increase in plasma bicarbonate that accompanied increases in the partial pressure of CO2 in the blood.(1) At the height of the polio epidemic in the 1950s, Danish researchers began to measure pH and PCO2, with subsequent calculation of the serum bicarbonate concentration using the Henderson-Hasselbach equation(2). This marked the first period of determination of normal “compensations” for the independent movement of HCO3 and CO2 in relation to each other.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. SearchA 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. The sites varied from comprehensive explanations of acid-base physiology to solely clinical case examples to test acid-base acumen. Of note, most of the comprehensive discussion seemed to stem from anesthesiology-based websites. Both the classic Bostonian approach and the newer Stewart Strong Ion Difference approach are discussed at length. Also, included are several quick acid-base calculators that can be accessed via the web to check an interpretation of an arterial blood gas versus a computerized nomogram. The sites below are to be used for clinical teaching only, as some have some trademarked material.
Best WebsitesAnesthesiology Education WebsiteThis 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.
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 AnesthesiologyAuthored 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.
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 TutorialThe 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.
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-BaseThis 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.
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
DisclaimerThe author has no personal or financial interest in any of the websites discussed above. References
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