This is Stewart’s original piece and it’s a classic. It’s not an easy read but try to get through it at least once. It may be easier to understand after you have read through some of the other reviews.
Unfortunately, this is out of print. However, many medical libraries still have it on the shelf.
A concise summary of the major implications of the physical chemical approach to acid-base balance, focusing mainly on the clinical implications. The article probably lacks sufficient detail to allow you to fully understand this business but serves as an introduction.
A bit less concise, but more up to date. Available on line (subscription only) through Critical Care Forum http://ccforum.com.
The entire issue is devoted to Stewart’s approach to acid-base physiology.
Section 5; Chapter 1: Leblanc M, Kellum JA. Biochemical and Biophysical Principles of Hydrogen Ion Regulation. pp 261-277.
Section 5; Chapter 2: Magder S. Pathophysiology of metabolic acid-base disturbances in patients with critical illness. pp 279-296.
Chapter 75: Schlichtig R. Acid-Base Balance (Quantitation). pp 828-839
Chapter 76: Kellum JA. Diagnosis and Treatment of Acid-Base Disorders. pp 839-853.
Schlichtig R: Base excess vs strong ion difference: Which is more helpful? Adv Exper Med Biol 1997, 411:91--95.
Wooten EW: Analytic calculation of physiological acid-base parameters. J Appl Physiol 1999, 86:326--334.
This author has translated base-excess, standard bicarbonate and strong ion difference and shown that they are all mathematically equivalent and derived from the same basic principles. The simulations also support the premise that strong ion difference changes as ATOT changes.
Classification of acid-base disorders remains controversial. These authors argue for the use of three types of disorders based on the three independent variables identified by Stewart. However, there is little evidence that this approach to classification is logical or helpful (see 3 below and review 4).
These authors demonstrate how the anion gap must be corrected for changes in albumin concentration. Patients with severe disorders of phosphate will require additional correction not detailed by the authors but available in this review.
This excellent observational study details the changes in strong ion difference as a function of changes in ATOT. The study provides convincing evidence that the normal physiologic response to hypoalbuminemia is to reduce the strong ion difference, principally by increasing the plasma chloride concentration.
Experimental evidence of the effect of saline resuscitation on acid-base parameters in an endotoxic animal model.
A clinical study detailing the acidosis associated with saline vs. no change in pH with lactated Ringer’s solution in patient undergoing major abdominal/pelvic surgery.
Waters JH, Miller LR, Clack S, Kim JV. Cause of metabolic acidosis in prolonged surgery. Crit Care Med. 1999; 27:2142-6.
Liskaser FJ, Bellomo R, Hayhoe M, et al: Role of Pump Prime in the Etiology and Pathogenesis of Cardiopulmonary Bypass-associated Acidosis. Anesthesiology 2000; 93:1170-1173
Rehm M, Orth V, Scheingraber S, et al: Acid-Base Changes Caused by 5% Albumin versus 6% Hydroxyethyl Starch Solution in Patients Undergoing Acute Normovolemic Hemodilution: A Randomized Prospective Study. Anesthesiology 2000; 93:1174-1183
Waters JH, Bernstein CA: Dilutional Acidosis following Hetastarch or Albumin in Healthy Volunteers. Anesthesiology 2000; 93:1184-1187
These three studies published in the November, 2000 issue of the journal Anesthesiology provide conclusive evidence that the Chloride content of volume expanding solutions determines the degree of acidosis. In the study by Lisaker, two types of pump-priming solutions for cardiopulmonary bypass are compared. A hyperchloremic solution and a solution with acetate and gluconate as metabolizable anions are used. As predicted, both cause an acute acidosis but with the acetate/gluconate solution, it resolves quickly while the hyperchloremic solution causes a persistent hyperchloremic acidosis. The next two studies found that normovolumic hemodilution with HES or Albumin in saline (Rhem et al.) produced similar amounts of acidosis while Albumin in a normo-chloremic solution (Waters et al.) produced no acidosis at all. The accompanying editorial seemed to have missed this point.
This observational study argues for a re-classification of metabolic acid-base disorders into those that alter the SID and those that affect the ATOT. The controversy arises when a low ATOT and a low SID coexist with a normal pH and normal BE. This was a common occurrence in this study (1 out of 6 patients) and the authors classify it a mixed disorder.
Every new idea has it’s detractors…