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20 Cards in this Set
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Determine whether the following blood gas and electrolyte panel represent a primary metabolic acidosis, metabolic alkalosis, respiratory acidosis, respiratory alkalosis, or if no disorder is present:
ABG: pH 7.27/pCO2 34/pO2 88 BMP: Na 138/K 4.4/Cl 99/HCO3 16/BUN 20/Cr 1.1/Glu 99 a). Metabolic acidosis b). Metabolic alkalosis c). Respiratory acidosis d). Respiratory alkalosis e). No acid/base disorder is present |
Answer A - Metabolic Acidosis. Serum pH is low, representing acidosis. Low serum bicarbonate is present, confirming the diagnosis of metabolic acidosis. The low pCO2 represents respiratory compensation.
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A 37-year-old male is hospitalized with pneumococcal pneumonia and sepsis. He has been in the ICU for four days, and has had multiple arterial blood gas samples. The team decides to use central venous blood gas samples to trend pH. Central venous blood gas pH is 7.26. This correlates with an arterial blood gas pH of:
a). 7.16 b). 7.21 c). 7.31 d). 7.36 |
Answer C - 7.31
Venous blood gas sampling should not replace arterial blood gas sampling, but may supplement arterial blood gas monitoring as a mechanism of trending results and minimizing arterial sampling. Central venous blood is preferable to peripheral venous blood, as it more accurately represents the arterial blood gas results. When using central venous blood to evaluate serum pH, note that venous blood is more acidemic than arterial blood, so venous pH is lower than arterial pH. To estimate arterial pH, we add 0.05 to central venous pH. |
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A 43-year-old man with type 2 diabetes comes to clinic for follow up of blood pressure after starting lisinopril 10mg daily. Before seeing you, he had the following fasting blood work done:
ABG: pH 7.33/pCO2 36/pO2 96 BMP: Na 136/K 5.0/Cl 107/HCO3 19/BUN 18/Cr 1.4/Glu 186 The most likely explanation of this patient's acid/base disorder is: a). Renal tubular acidosis b). Diabetic ketoacidosis c). Starvation ketosis d). Hypertension |
Answer A - Renal Tubular Acidosis
Serum pH is low, representing acidosis. Low serum bicarbonate is present, confirming a metabolic acidosis. The anion gap is 136-(107+19)=10, which is normal. Of the above possibilities, only renal tubular acidosis results in a normal anion gap metabolic acidosis. |
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A 46-year-old woman is brought into the Emergency Department after being found down in the street. She had a pulse and was breathing spontaneously, but was confused and unable to give a history. In the Emergency Department, she was no different. Physical examination was unremarkable. Blood work was as follows:
ABG: pH 7.20/pCO2 30/pO2 86 BMP: Na 140/K 5.4/Cl 106/HCO3 14/BUN 49/Cr 3.6/Glu 202 All of the following tests would be useful in diagnosing this patient except: a). Urine anion gap b). Serum lactate c). Serum salicylate level d). Serum ketones |
Answer A - UAG
This patient has an elevated anion gap metabolic acidosis. The differential diagnosis includes lactic acidosis, salicylate toxicity, as well as ketoacidosis (from diabetes, starvation, or alcohol). Urine anion gap is useful in evaluating a patient with a normal anion gap, which this patient does not have. |
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A 57-year-old woman with type 1 diabetes and hypertension presents to the Emergency Department with a three day history of malaise, fevers, and chills. Her daughter had visited last week, and was sick with similar symptoms. On physical examination, the patient appears acutely ill. She is febrile (temperature 38.5C), blood pressure is 92/50, but the remainder of the physical examination is unremarkable. Laboratory examination is as follows:
ABG: pH 7.20/pCO2 18/pO2 88 BMP: Na 125/K 6.8/Cl 97/HCO3 6/BUN 30/Cr 1.9/Glu 788 This patient has two acid/base disorders. Which of the following are suggested by this clinical picture? a). Elevated anion gap metabolic acidosis and normal anion gap metabolic acidosis b). Elevated anion gap metabolic acidosis and metabolic alkalosis c). Elevated anion gap metabolic acidosis and respiratory acidosis d). Elevated anion gap metabolic acidosis and respiratory alkalosis |
Answer A - AGMA + NAGMA
This patient has an acidosis based on a pH of 7.20. With the low serum bicarbonate, this is a metabolic acidosis. The anion gap is elevated at 22 (125 – 97 + 6). Therefore, we know that one of the disorders is an elevated anion gap metabolic acidosis (probably DKA, but her blood pressure is worrisome, so a lactate should be checked). Next, look for a coexisting normal anion gap metabolic acidosis by comparing the change in the bicarbonate with the change in the anion gap. The bicarbonate has dropped from 24 to 6, for a change of 18. The anion gap has increased from 12 to 22, for a change of 10. Therefore, the bicarbonate has dropped significantly more than the gap has elevated, suggesting that a normal anion gap metabolic acidosis is present (probably type 4 RTA, to go with her diabetes and what looks like chronic kidney disease). When assessing respiratory compensation for this woman's metabolic disorders, we use Winter's formula (1.5 x HCO3 + 8 +/- 2), and see that she has appropriate respiratory compensation for her metabolic disorder, with no evidence of respiratory acidosis or alkalosis. |
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A 19-year-old woman is admitted for evaluation of delirium. She is unable to provide a reliable history, but she appears intoxicated. Physical examination is notable for a strong chemical odor around the patient, but is otherwise unremarkable. Blood results are as follows:
ABG: pH 7.32/pCO2 35/pO2 99 BMP:Na 140/K 4.0/Cl 112/HCO3 18/BUN 14/Cr 0.6/Glu 90 Serum osmolality: 336 Serum ketones:negative A possible explanation of her presentation is: a). Alcohol b). Methanol c). Polyethylene glycol d). Isopropyl alcohol e). Toluene |
Answer E - Toluene
Serum osmolality can be estimated as 2[Na] + [glucose/18] + [BUN/2.8], or 280 + 5 + 5, or 290. Measured osmolality is 336, significantly higher than estimated osmolality, and thus an osmolar gap is present. A metabolic acidosis is also present, with a normal anion gap. Of the list above, only toluene causes a normal anion gap metabolic acidosis and an osmolar gap. The strong chemical odor is also suggestive of toluene. |
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A 57-year-old woman with hypertension presents for follow up. She feels generalized weakness, present for the past several days. Last month, she was started on HCTZ for blood pressure control. Physical examination is normal. She is not orthostatic. Blood work is as follows:
ABG:pH 7.48/pCO2 46/pO2 92 BMP: Na 132/K 3.1/Cl 93/HCO3 32/BUN 18/Cr 1.1/Glu 69 Which of the following acid/base disorders and potential etiologies is most likely? a). Respiratory acidosis due to CNS hypoperfusion b). Metabolic acidosis due to hypotension c). Metabolic alkalosis due to hypokalemia d). Respiratory alkalosis due to hypoventilation e). Two of the above |
Answer C - Metabolic Alkalosis due to Hypokalemia
Serum pH is elevated, representing alkalosis, which is explained by an elevated serum bicarbonate. Therefore, this patient has a metabolic alkalosis. Hypokalemia is a cause of metabolic alkalosis. Compensation is appropriate; only a single acid/base disorder is present. |
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A 48-year-old male with type 2 diabetes, hypertension and elevated cholesterol presents for routine follow up. Medications taken are metformin, lisinopril, HCTZ and atorvastatin. Blood work is as follows:
ABG: pH 7.34/pCO2 58/pO2 78 BMP: Na 138/K 4.4/Cl 108/HCO3 32/BUN 14/Cr 0.8/Glu 101 The most likely explanation of this patient's acid base disorder is: a). Obstructive sleep apnea b). Cushing's disease c). Restrictive lung disease d). Renal tubular acidosis e). Conn's syndrome |
Answer A - OSA
Serum pH is low, representing acidosis, which is explained by the elevated pCO2. Therefore, this patient has a respiratory acidosis. The elevated serum bicarbonate is compensatory. Of the disorders listed, only obstructive sleep apnea causes a respiratory acidosis. |
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A middle-aged male is rushed to the emergency department after being found down in the street. He is somnolent but easily aroused, yet incoherent when speaking. He smells of alcohol, and is jaundiced. Preliminary blood work shows the following:
ABG: pH 7.48/pCO2 26/pO2 80 BMP: Na 132/K 3.4/Cl 105/HCO3 17/BUN 12/Cr 0.3/Glu 57 Before further testing results are available, which of the following possible diagnoses is the most likely? a). Alcoholic ketoacidosis b). Renal tubular acidosis c). Methanol poisoning d). Cirrhosis e). Starvation ketosis |
Answer D - Cirrhosis
Serum pH is elevated, representing alkalosis, which is explained by the low pCO2. Therefore, this patient has a respiratory alkalosis. The low serum bicarbonate is compensatory. Of the options listed, only cirrhosis causes respiratory alkalosis, and is consistent with the patient's presentation. |
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A 22-year-old woman with type 1 diabetes comes to the emergency department with a one-day history of nausea and vomiting. Past medical history is notable for gastroparesis. Blood work shows the following:
ABG: pH 7.40/pCO2 40/pO2 89 BMP: Na 134/K 3.2/Cl 90/HCO3 24/BUN 28/Cr 0.9/Glu 256 Which of the following explain her blood test results? a). Renal tubular acidosis and dehydration b). Diabetic ketoacidosis and vomiting c). Hypoalbuminemia and renal artery stenosis d). Hypotension and renal insufficiency e). Hyponatremia and hypokalemia |
Answer B - DKA and Vomiting
Serum pH is normal, which does not exclude an acid-base disorder. Serum bicarbonate and pCO2 are normal as well. The tip off that an acid/base disorder is present is that the patient has an elevated anion gap (which is 20). The only way that the serum bicarbonate can be normalized is if the patient had a metabolic acidosis and a metabolic alkalosis. This patient therefore has an elevated anion gap metabolic acidosis and a metabolic alkalosis. Of the options listed, only DKA and vomiting could result in such findings, and is consistent with the clinical picture. |
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A 49-year-old man with a 30-year history of type 1 diabetes presents to the emergency department with 2-3 days of nausea, malaise and fevers. He denies sick contacts, rash, headache, or localizing symptoms. He denies non-compliance with insulin, although he did not take his oral medications today due to nausea. Past history is notable for hypertension, diabetic neuropathy, and diabetic retinopathy. Medications include insulin, lisinopril, HCTZ, amlodipine and simvastatin. On physical examination, vital signs are: T38.2, P100, R20, BP 100/60. He is not orthostatic. No rash is noted, and the remainder of his physical examination is unremarkable. No foot ulcers are seen. Pertinent labs are as follows:
•Sodium 138mg/dl •Potassium 5.2mg/dl •Chloride 100mg/dl •Bicarbonate 12mg/dl •BUN 49mg/dl •Creatinine: 2.9mg/dl •Glucose: 180mg/dl •Serum ketones: negative •Urine ketones: positive •WBC: 18,700 •Urinalysis: TNTC WBC; TNTC RBC; 3+ protein; many bacteria •ABG: pH 7.27/pCO2 20/pO2 96 Of the following options, which one is the most likely explanation of the patient's clinical presentation? a). Uremia b). Diabetic ketoacidosis c). Pulmonary embolus d). Urosepsis |
Answer D - Urosepsis
This patient has a metabolic acidosis, an elevated anion gap of 26, and appropriate respiratory compensation. Serum ketones are negative; urine ketones most likely represent prior fasting state. Urinalysis suggests UTI. Although uremia can cause an anion gap metabolic acidosis, this febrile, hypotensive patient would not have the entire clinical picture explained by uremia. Ketoacidosis is not present. Pulmonary embolus causes respiratory acidosis, and does not cause an anion gap metabolic acidosis. The presentation described is most consistent with urosepsis. |
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A 59-year-old woman with diabetes, hypertension, and elevated cholesterol returns after obtaining pulmonary function tests performed because of a several year history of smoking. You also requested an ABG and basic metabolic panel to be done at the same time. Results are as follows:
· FVC 4.2L (90% predicted) · FEV1 3.36L (87% predicted) · FEV1/FVC 80% · Na 144mg/dl (normal 135-145) · K 3.3mg/dl (normal 3.5-5.0) · Cl 107mg/dl (normal 96-109) · Bicarbonate 30mg/dl (normal 21-29) · BUN 12mg/dl (normal 7-22) · Cr 0.9mg/dl (normal 0.5-1.3) · ABG: pH 7.48/pCO2 43/pO2 88 Of the following, which is the most likely explanation of her clinical presentation? a). Obstructive sleep apnea b). Renal artery stenosis c). COPD d). Renal tubular acidosis |
Answer B - RAS
This patient has a metabolic alkalosis with appropriate respiratory compensation. Of the options listed, only renal artery stenosis causes metabolic alkalosis. Obstructive sleep apnea and COPD cause respiratory acidosis, while RTA causes a normal anion gap metabolic acidosis. |
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Classic DDx for AGMA?
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M: methanol
U: uremia D: DKA*/Drugs (e.g., metformin, stavudine, topiramate) P: phosphate/paraldehyde I: ischemia/isoniazid (rare)/iron (rare) L: lactate E: ethylene glycol S: starvation/salicylates |
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What does the Anion Gap really mean?
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The differential diagnosis of a patient with a metabolic acidosis is broad and can be narrowed and further evaluated by calculating the anion gap. The anion gap is made of negatively charged phosphates, sulfates, organic acids and plasma proteins (including albumin). Rather than measure these on every patient, we calculate the difference between the dominant positive charge (i.e. sodium) and the dominant negative charges (i.e. chloride and bicarbonate), knowing that the difference is made up of these negative charges, and call them the anion gap. In other words, the anion gap is merely shorthand for the sum of those negative charges that we choose not to measure. The normal anion gap is 12, plus or minus 2.
Anion gap = Sodium – (Chloride + Bicarbonate) Some include the serum potassium, adding it to the serum sodium, when calculating the anion gap. In this instance, the normal anion gap is 16. Since the serum potassium often fluctuates from other causes that do not pertain to acid/base disorders, we will not use the serum potassium when calculating the anion gap in this module. The anion gap should be calculated on all patients who present with a metabolic acidosis (in fact, the anion gap should be calculated on all patients, including those with normal serum bicarbonate). The steps in evaluation would be as follows: 1. Evaluate the serum pH. a. In metabolic acidosis the pH is typically low. 2. Evaluate the pCO2 and serum bicarbonate a. In metabolic acidosis, the serum bicarbonate is typically low. b. In metabolic acidosis, the pCO2 is typically low as the body compensates with a respiratory alkalosis. 3. Calculate the anion gap. Note that low serum albumin will decrease the apparent anion gap. To correct the anion gap for low serum albumin, add 2.5 to the anion gap for every 1g/dl that serum albumin is decreased from the normal value of 4g/dl. |
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DDx of NAGMA?
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D: diarrhea
U: ureteral diversion R: renal tubular acidosis H: hyperalimentation A: Addison's disease/acetazolamide/ammonium chloride M: miscellaneous (chloridorrhea, amphotericin B, toluene*, others) *Toluene will initially result in an anion gap metabolic acidosis, but toluene causes a renal tubular acidosis, and a normal anion gap metabolic acidosis results. |
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DDx for Low anion gap metabolic acidosis
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B:Bromism (ingestion of bromo seltzer)
A:Albumin (low albumin) M:Multiple myeloma As stated previously, for every 1g/dl that serum albumin is below normal (i.e. below 4g/dl), correct the anion gap by adding 2.5. |
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What is meant by contraction alkalosis?
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In volume depletion, the kidney becomes Na+ avid (which will result in water resorption). As Na+ is resorbed, it will need a negatively charged ion to resorb along with it, maintaining electrical neutrality. Normally, chloride serves as the negative charge, but in volume depletion, chloride is typically very low. In this situation, HCO3, another negative charge, is resorbed at the expense of acid/base status, and alkalosis persists.
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A 58-year-old woman is admitted with a diagnosis of pyelonephritis. Past medical history is notable for obesity, type 2 diabetes and hypertension. She has been nauseated due to her pyelonephritis, and did not take her medications today. On physical exam, she appears acutely ill. She is febrile (temperature 39.6C). Blood pressure is normal (106/56). Lungs are clear, and cardiac exam is normal. There is moderate costovertebral angle tenderness, but the remainder of the physical exam is normal. Blood work is as follows:
ABG: pH 7.33/pCO2 32/pO2 80 BMP:Na 137/K 4.0/Cl 101/HCO3 16/BUN 12/Cr 0.8/Glu 136 Which of the following is the most likely explanation of her clinical presentation? a). Obstructive sleep apnea b). Diabetic ketoacidosis c). Pulmonary embolus d). Renal tubular acidosis e). Sepsis |
Answer E - Sepsis
Serum pH is low, representing an acidosis, which is explained by the low serum bicarbonate. The low serum pCO2 is compensatory. This patient therefore has a metabolic acidosis. The anion gap is 137-(101+16)=20, which is elevated. Both DKA and sepsis can cause an elevated anion gap metabolic acidosis, but plasma glucose is normal, making sepsis the likely diagnosis, and is consistent with the clinical presentation. |
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A 57-year-old man is brought in to the Emergency Department by his partner after several days of malaise. The patient has HIV, with his most recent CD4=11 and a viral load of 342,000 after failing multiple antiretroviral regimens due to HIV resistance. Past medical history also includes CMV retinitis, disseminated histoplasmosis, and benign prostatic hypertrophy. On exam the patient is febrile. Blood pressure is 87/40. Respirations are 16, with an oxygen saturation of 96%. He appears chronically ill, but the physical exam is non-focal. Initial blood work is as follows:
ABG: pH 7.20/pCO2 18/pO2 92 BMP: Na 129/K 5.6/Cl 100/HCO3 8/BUN 12/Cr 1.1/Glu 67 Which of the following combinations of diagnoses are possible in this patient? a). Dehydration and cirrhosis b). Salicylate toxicity and narcotic overdose c). Ethylene glycol poisoning and hyperthyroidism d). Urosepsis and Addison disease |
Answer D - Urosepsis and Addison's Disease
This patient has both an elevated anion gap metabolic acidosis and a normal anion gap metabolic acidosis (note that his bicarbonate has dropped by 16 and his anion gap of 21 is up by 9). Only urosepsis (which causes an elevated anion gap metabolic acidosis) and Addison disease (which causes a normal anion gap metabolic acidosis) would explain this. Dehydration causes a metabolic alkalosis; cirrhosis causes a respiratory alkalosis. Salicylate toxicity causes an elevated anion gap metabolic acidosis, but narcotic overdose causes a respiratory acidosis. Ethylene glycol causes an elevated anion gap metabolic acidosis, but hyperthyroidism causes (rarely) a respiratory alkalosis. |
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You are evaluating a 23-year-old woman for a 3-month history of malaise and fatigue. Past history is notable only for vitiligo. She recalls no precipitating event to her fatigue, and screens negative for depression. Blood work is as follows:
· CBC: normal · TSH 3.3mg/dl (normal 0.5-4.5) · Na 137mg/dl (normal 135-145) · K 5.2mg/dl (normal 3.5 – 5.0) · Cl 107mg/dl (normal 96-109) · Bicarbonate 18mg/dl (normal 21-29) · BUN 14mg/dl (normal 7-22) · Cr 0.8mg/dl (normal 0.5-1.3) · Glucose 54mg/dl (normal 60-100) · ABG: pH 7.34/pCO2 37/pO2 96 · Serum osmolality: 280 · Urine anion gap: +10 Of the following choices, which is the most likely explanation of her presentation? a). Surreptitious isopropyl alcohol ingestion b). Renal tubular acidosis c). Starvation ketosis d). Addison disease |
Answer D - Addison's Disease
This patient has a metabolic acidosis with a normal anion gap of 12. Important clinical clues include hyperkalemia, hypoglycemia, a normal serum osmolality, and a history of vitiligo. Isopropyl alcohol ingestion would elevate serum osmolality, and does not cause a metabolic acidosis. Renal tubular acidosis causes a normal anion gap metabolic acidosis, but alone does not explain her symptoms. Starvation ketosis causes an elevated anion gap metabolic acidosis. Addison disease explains all the clinical findings and causes at Type IV RTA, resulting in a positive urine anion gap. |
