Acid Base Cases Flashcards
what is the serum anion gap equation?
AG = Na - Cl - HCO3
normal AG = 12
largest contributor to the gap is albumin
what is the urine anion gap equation?
UAG = Na + K - Cl
it should be negative! UAG is a rough measure of NH4-
how does pCO2 compensate in metabolic acidosis?
pCO2 will decrease 1-1.5 for each decrease in HCO3
how does pCO2 compensate in metabolic alkalosis?
PCO2 increases 0.25-1 for each HCO3 increase
how does HCO3 compensate for respiratory acidosis?
in acute respiratory acidosis HCO3 increases 1 for each 10 pCO2 increase (+/-3)
in chronic respiratory acidosis HCO3 increases 4 for each 10 pCO2 increase (+/-4)
how does HCO3 compensate for respiratory alkalosis?
in acute respiratory alkalosis HCO3 decrease 1-3 for each 10 pCO2 (usually not less than 18)
in chronic respiratory alkalosis HCO3 decreases 2-5 for each 10 pCO2 decrease
(usually not less than 14)
A 57 year old man was admitted following three syncopal episodes. He complained of daily vomiting for one year with a 7 year history of intermittent vomiting episodes. Exam revealed a wasted man with a BP of 110/60, pulse 80. On standing BP was 75/60, pulse 116.
pH 7.47 pCO2 57 HCO3- 45 pO2 62;
Na 141; K 1.8; Cl 74; TCO2 (HCO3) 47
An upper gastrointestinal series demonstrated gastric outlet obstruction accompanying a duodenal ulcer. Gastric suction was instituted. Large volumes of normal saline containing KCl were administered over the first 5 days.
A. What acid-base disorder is present?
B. Is compensation appropriate?
A. metabolic alkalosis due to loss of H+ from vomitting
B. normally, PCO2 increases 0.25-1 for each HCO3 increase
HCO3 is 45 so it’s increased 21 which means PCO2 should increase 5.25-21
normal pCO2 is 40 so 40 + 5.25 to 21 = 45.25 to 61 if it’s compensating and in this case pCO2 is 57 so he’s definitely compensating because he’s in the range
use the serum HCO3, not the TCO2 in the ABG if you have it because the serum is more accurate
A 51 year old man was admitted from a boarding house in a semicomatose state. He was tachypneic, cyanotic, febrile and hypotensive. A barrel-shaped thoracic cage and “abdominal” respiratory pattern were noted. Sputum was purulent, but evidence for pneumonia was not found.
pH 7.29; pCO2 81; HCO3 38;
Na 138; K 5; CL 85; TCO2 (HCO3) 40
a. what acid-base disturbance is present?
b. is compensation appropriate
A. respiratory acidosis
B. in chronic respiratory acidosis HCO3 increases 4 for each 10 pCO2 increase (+/-4)
pCO2 is 81 and normally it’s 40 so it increased 41 which means HCO3 should increase 16 (range of 12-20)
normal HCO3 is 24 so it should be between 36-44 and he’s at 38 so he’s compensating
A 56 year old man was followed over a one-year period for increasing dyspnea, weakness and weight loss. Chest x-ray revealed evidence of diffuse interstitial pulmonary fibrosis.
Time 0:
pH 7.49; pCO2 24; HCO3 18; p O2 56
Time 12 month:
pH 7.47; pCO2 24; HCO3 17; p O2 52
What type of acid-base disturbance is present?
Is he compensating?
compensated respiratory alkalosis
chronic respiratory alkalosis: HCO3 decreases 2-5 for each 10 pCO2 decrease
CO2 is decreased 16 from normal so HCO3 should decrease 3-7.5 and be between 16.5-21 and HCO3 is 17 so yes he’s compensating
An 80 yom is brought from a nursing home unconscious. He has a blood pressure of 70/?, respirations of 34, temperature of 33oC rectally and a pulse of 130. He was well up until several days ago when he developed recurrent vomiting. During one of these vomiting episodes yesterday, he lost consciousness.
pH 7.40; pCO2- 20; HCO3- 12; pO2-44
Na- 133; K 3.3; Cl 77; T CO2 (HCO3) 13
What type of acid-base disturbance is present?
Is he compensating?
respiratory alkalosis and metabolic anion gap acidosis with hidden metabolic alkalosis
pCO2 is low = respiratory alkalosis
HCO3 is low = metabolic acidosis
AG = 133 - (77+12) = 43 and normal anion gap is 12 so this is a high anion gap –> if there is anion gap acidosis the extra anions should add to HCO3 to equal 24
deltaAG = 43 - 12 = 31 which means there are 31 extra anions in the HCO3 space!
the correct HCO3 = serum HCO3 + extra anions = 13 + 31 = 44 –> you have 44 bicarbonates!! the only way this happens with metabolic alkalosis
if the delta delta ratio is positive after determining that you have metabolic acidosis, then you will also have metabolic alkalosis. If the delta delta is negative, you only have metabolic acidosis
A 6 month old male child is brought into your office because of inadequate growth. He was found by his pediatrician to have metabolic acidosis (pHa = 7.32, HCO3- = 12, PCO2 = 24). Serum potassium is 2.5 meq/l and the serum anion-gap is normal. You are asked about the possibility of a renal tubular acidosis.
a. what is the acid base disorder?
b. what tests would help you in your evaluation
c. is the acidosis due to a renal cause or another cause like diarrhea?
a. metabolic acidosis
pCO2 decreases 1-1.5 for each HCO3 decrease in metabolic acidosis so pCO2 should decrease 12-18. it’s 24 in this case which is 16 decrease which means yes he’s compensated
b. urine anion gap
UAG = Na + K - Cl –> if it’s positive then there’s a kidney problem; if it’s negative it means the kidney is fine and we’re losing HCO3 somewhere else like diarrhea
A 45 yof develops acute cholecystitis complicated by septicemia and oliguric acute renal failure. For this she is treated with appropriate antibiotics and intermittent hemodialysis (every other day). Her predialysis blood gas is
pH 7.38; pCO2 34; HCO3 18; pO2 78
Na 135; K 4.3; Cl 97; T CO2 (HCO3)18
compensated metabolic acidosis
pCO2 will decrease 1-1.5 for each decrease in HCO3 so HCO3 decreased 6 which means pCO2 should decrease 6-9 and be 31-34 and it’s 34 so yes he’s compensating
AG = 135 - 97 - 18 = 20; high AG
deltaAG = 20-12 = 8 = 8 anions in the HCO3 space
18+8 = 26
Next, she is begun on total parenteral nutrition (TPN) with a regimen containing 100 gms of amino acids per day to assist in her recovery. Within 2 days, her predialysis blood gas becomes:
pH 7.26; pCO2 26; HCO3 12; pO2 98
Na 135; K 5.3; Cl 100; T CO2 (HCO3) 13
metabolic acidosis
pCO2 will decrease 1-1.5 for each decrease in HCO3 –> HCO3 decreased 11 so pCO2 should decrease 11-16 and it’s 26 which is within the range
AG = 22 and deltaAG = 22 - 12 = 10 extra anions in the HCO3 space
10 + 13 = 23 which is close to the normal 24 –> there’s an increase in the AG but the person is getting amino acids which is increasing the AG
Ms. H. is a 28 yof who works as a registered nurse. She complains of ankle swelling related to her menstrual cycle as well as intermittent dizziness. She denies taking any medications in the recent past but does state that a doctor had previously given her some diuretics to take “as needed” for the ankle swelling. She has also taken some diet pills in the past, On physical examination, the patient is appears to be normal. A routine chemistry panel is obtained and reveals:
Na 135; K 2.3; Cl 84; T CO2 (HCO3) 33
Because the TCO2 (HCO3) was so abnormal, an ABG is obtained which demonstrates:
pH 7.50; pCO2 46; HCO3 32; pO2 78
Na 135; K 2.3; Cl 84; T CO2 (HCO3) 33
A. what condition does she have?
B. what tests would further define her acid-base disturbance, and what would you expect them to show?
compensated metabolic alkalosis
PCO2 increases 0.25-1 for each HCO3 increase; HCO3 was increased 11 so pCO2 should increase 2.75-11 and be between 42.75 to 51 and it’s 46 so yes he’s compensating
AG = 135 - 84 - 33 = 18 so it’s a high anion gap due to conformational change of albumin
deltaAG = 18 - 12 = 6 which means there are 6 extra anions in the HCO3 space
6 + 33 = 39
Mr. S. is a 42 yom who is found unconscious in his garage near an empty bottle of Prestone Antifreeze (which contains ethylene glycol). His wife tells the interviewing physician in the Emergency Room that the patient was extremely depressed for the past several weeks. An initial blood gas is obtained and reveals:
pH 7.10; pCO2 20; HCO3 6; pO2 98
Na 135; K 4.3; Cl 100; TCO2 (HCO3) 6
A. what does she have?
compensated metabolic acidosis
pCO2 will decrease 1-1.5 for each decrease in HCO3 – HCO3 decreased 18 so pCO2 should decrease 18-27 and be 13-22 and he’s at 20 so yes he’s compensating
AG = 135 - 100 - 6 = 29 so high anion gap
deltaAG = 29 - 12 = 17 extra anions in the HCO3 space + the 6HCO3 already in the HCO3 space = 23 which means there isn’t a hidden metabolic alkalosis –> it’s just an anion gap respiratory acidosis
