Primer On Clinical Acid-Base Problem Solving

Primer on clinical acid-base problem
solving
William L. Whittier, MD and Gregory W. Rutecki, MD
Acid-base problem solving has been an integral part
of medical practice in recent generations. Diseases
discovered in the last 30-plus years, for example,
Bartter syndrome and Gitelman syndrome, D-lactic
acidosis, and bulimia nervosa, can be diagnosed according to characteristic acid-basefindings. Accuracy
in acid-base problem solving is a direct result of a
reproducible, systematic approach to arterial pH, partial pressure of carbon dioxide, bicarbonate concentration, and electrolytes. The “Rules of Five” is one tool
that enables clinicians to determine the cause of simple
and complex disorders, even triple acid-base disturbances, with consistency. In addition, other electrolyteabnormalities that accompany acid-base disorders,
such as hypokalemia, can be incorporated into algorithms that complement the Rules and contribute to
efficient problem solving in a wide variety of diseases.
Recently urine electrolytes have also assisted clinicians
in further characterizing select disturbances. Acid-base
patterns, in many ways, can serve as a “common
diagnostic pathway” shared byall subspecialties in
medicine. From infectious disease (eg, lactic acidemia
with highly active antiviral therapy therapy) through
endocrinology (eg, Conn’s syndrome, high urine chloride alkalemia) to the interface between primary care
and psychiatry (eg, bulimia nervosa with multiple
potential acid-base disturbances), acid-base problem
solving is the key to unlocking otherwise unrelateddiagnoses. Inasmuch as the Rules are clinical tools,
Dis Mon 2004;50:117-162.
0011-5029/$ – see front matter
doi:10.1016/j.disamonth.2004.01.002
122 DM, March 2004they are applied throughout this monograph to diverse
pathologic conditions typical in contemporary practice.
A
strange thing happened to the art of acid-base problem solving
in the last decade. For some, the addition of a simpletool, the
pulse oximeter, or so-called fifth vital sign, seemed to relegate
blood gas values to unfamiliar territory. It seemed that monitoring of
oxygen saturation substituted for information obtained from arterial
blood gas values! In fact, since the advent of oximetry, to many senior
physicians (including the second author, G.W.R.), it appears that
blood gas values have been used lessfrequently. This primer has been
undertaken to prove that “reports of the demise of acid-base problem
solving have been greatly exaggerated”! As important as the noninvasive monitoring of oxygen saturation is, if the partial arterial oxygen
tension (PaO2
) is removed from the context of acid-base physiology,
the disease puzzle will not fit together successfully. Fluctuation in pH
and contingentcompensation by the kidneys and lungs are the
remaining pieces. Pulse oximetry, as important as it has been, has not
obviated the contribution of acid-base problem solving. As a group,
PaO2
or oxygen saturation, partial arterial carbon dioxide tension
(PaCO2
), bicarbonate concentration, and the many “gaps” (anion, delta
or 1:1, osmotic and urinary) complement one another. The skillsrequired to interpret blood gas values must remain in the repertoire of
practitioners everywhere, beginning with primary care and continuing
throughout subspecialty medicine.
The senior author (G.W.R.) had the benefit of experiencing the effect
of acid-base physiology on diseases that were part of his generationin-training. Phenformin-induced lactic acidemia, elevated urine chloride-metabolicalkalemia in Bartter syndrome and Gitelman syndrome,
and metabolic acidemia in ethylene glycol poisoning were all entities
to which the acid-base component contributed relevant information.
The junior author (W.L.W.) has been trained in a similar arena,
nephrology, but with the new additions of acid-base to his generation,
such as lactic acidemia during highly active antiviral therapy
(HAART),...