Using Willie's acid-base box for blood gas analysis.

Many years ago, I was asked to evaluate a method developed by Dr. William T. Lipscomb for teaching blood gas analysis of acid-base status. Dr. Lipscomb was a Professor in the Department of Physiology of the University of Nebraska College of Medicine during my graduate student days and served as a teaching mentor to myself and several other graduate students for our first physiology lectures. Dr. Lipscomb went on to teach anatomy and physiology at Costal Georgia Community College for 18 yr and after retiring and served as Secretary for the Glynn Environmental Coalition until his death in 2005. Glynn Environmental Coalition named a science award in his honor as he was a much-loved teacher. When I first examined this approach, it seemed much too simplistic for medical students, but I decided to try it in my lectures. First, I present the standard Henderson-Hasselbalch equation and apply this to some simple patient problems but then reexamine the patient cases using Willie’s acid-base box. Invariably, some of the students find it silly at first, but every single year I have some more senior students who come back to this method. For example, a recent second-year medical class tackling acid-base cases in a course titled “EvidenceBased Medicine” contacted me to review “Willie’s box.” Even third-year medical students have found the method useful to prepare for an Internal Medicine Shelf exam. Also, students have e-mailed me after exams attesting that this method was helpful in securing correct answers on various board-style tests. Before dismissing this method, give it a try, as I’m sure many of your students will enjoy it and benefit in the long run. The box is constructed using three of the parameters of standard arterial blood gas analysis: pH, bicarbonate, and CO2. Therefore, it depicts the Henderson-Hasselbalch equation in a simple visual form that requires no calculations. The top value depicts the pH with the normal range of 7.35–7.45 and is considered inside the box. Anything below that range is outside the box and identifies acidosis, whereas any value above the range is outside the box to the right and depicts alkalosis. The middle line represents the metabolic component of the acidbase system, which is measured clinically as bicarbonate. I took the liberty of broadening the normal range for this value from Dr. Lipscomb’s original to account for the immediate changes in bicarbonate that result from CO2 conversion to bicarbonate by buffering from hemoglobin (1). The first case (Fig. 1) shows a patient who is experiencing an acute asthma attack with the following blood gas values: pH 7.27, bicarbonate 26 meq/l, and CO2 60 mmHg. Willie’s