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Acid-Base Disorders

Acidosis; first we evaluate the primary disorder, and the definitions of the primary disorder. If you think about acid-base balance in a logical stepwise fashion, you may be able to remember it and figure it out. If you donít do it in a logical stepwise fashion you are almost for sure not going to be able to do it, and even if you do think about it in a logical stepwise fashion, a lot of people have problems with it - like me. So itís got to be logical and stepwise. So number one, we think of the primary disorder. What is the primary disorder? If there is metabolic acidosis.

Metabolic alkalosis; you are alkalotic, you have a high CO2 with retained bicarbonate. The compensation is low ventilation. You decrease your ventilation and you drive up your PCO2. The respiratory alkalosis, the PCO2 is low as you are blowing PCO2 off. The pH is high, the bicarbonate excretion is your compensation, so your CO2 will be low.

Okay, now, the next thing you do if you have an acidosis, and in particular is to determine the anion gap. The anion gap is the sodium minus the bicarbonate and chloride. Normally itís 9-12. An increase in the anion gap over normal represents unmeasured anions and those are usually things like lactate, beta-hydroxybutyrate, thatís the so-called gap acidosis. Where you are dumping acids into the blood. A gap acidosis, those include lactic acidosis, uremia, diabetic.

Renal tubular acidosis. How do we recognize renal tubular acidosis? Number one, what I said before; first have a blood pH. Youíve got to have acidosis. I canít tell you how often I have been consulted by some of you out there who will remain anonymous, in the audience, who say, "Low CO2, low bicarbonate, we obviously have an acidosis. Please evaluate the acidosis for us."

Now there are different types. We nephrologists have an incredible amount of imagination and wit, so we of course call them type I and type II, with our great creativity. Type I is called distal RTA. It is caused by a problem in the distal tubule with the inability to decrease the urine pH to 5.5 during acidosis. Because the kidney canít push out hydrogen ions out of the body. There is one of a number of molecular defects that cause the kidney to be unable to kick out hydrogen.

How do you evaluate these patients? They have a hyperchloremic metabolic acidosis and they have a positive urinary anion gap. Thatís because these patients donít make very much ammonia. The urine - a lot of the positives that are over here to balance out the chlorides, etc. - is ammonia and usually the sodium plus potassium minus chloride normally is a negative number. But in distal RTA the sodium plus the potassium minus the chloride is a positive number in distal RTA. Weíll get to proximal RTA in a minute. And in normals, itís a negative number.

Syndrome number one, which I donít have a picture of, is branchio-otorenal syndrome, BOR syndrome. You get dysplasia; unilateral renal agenesis is the renal anomalies, and other findings are branchial fistulas and in particular, preauricular pits and hearing losses. Those are underlined because those are the associations that you want to make. If you see somebody with a little pit in front of their ear and hearing loss, look for renal problems. Potterís syndrome: renal failure, oligohydramnios. Remember that oligohydramnios tends to be associated with pulmonary.

Prune-belly syndrome; the renal abnormalities, dilated urinary tract, dysplastic, aplastic, multicystic and hydronephrotic kidneys. Underline absence of abdominal musculature, cryptorchidism. Thatís called the triad because there are three of them. Cryptorchidism, absence of abdominal musculature, renal abnormalities. The triad.

Alportís syndrome has glomerular lesions, hematuria and decreased GFR. Underline anterior lenticonus, cataracts, sensorineural deafness. First, lets look at prune-belly syndrome. Here is the prune-belly. Lacks abdominal musculature. Testes are not palpable. Renal abnormalities. Prune-belly syndrome. By the way, what do you notice? Is this a boy or a girl? Boy. Prune-belly syndromes are almost always in boys. And we can talk at some point.

Tuberous sclerosis; youíve heard about tuberous sclerosis. The renal abnormalities, renal angiomyolipoma, cystic kidneys and renal cell carcinoma. An important clinical link and association. Other features, underline adenoma sebaceae, underline CNS tubers, retinal phacoma and of course some of the skin, the shagreen patches, the White Mountain ash spots.

Finally, what is this? Recognizable? Anaphylactoid purpura, right. Remember, it is usually classically over the lower limbs and buttocks. It is alliterative, palpable purpura. Write down, as a link and association, palpable purpura. Because you can feel it. Little lumps. Palpable purpura on the lower extremities, crampy abdominal pain, arthralgia, peak at 4-5 years of age. Itís mediated