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Snapshot
  • A 62-year-old man presents to the emergency department for increased confusion and a productive cough. He was found on the couch by his children and was only oriented to person but not place or time. Medical history is significant for chronic obstructive pulmonary disease and hypertension. He smokes approximately 1.5 packs of cigarettes a day for the past 35 years. His temperature is 101.4°F (38.5°C), blood pressure is 157/98 mmHg, pulse is 110/min, respirations are 17/min, and oxygen saturation is 83% on room air. An arterial blood gas is performed and demonstrates a pH of 7.21, PaCO2 of 99 mmHg, and PaO2 of 51 mmHg. (Chronic obstructive pulmonary disease exacerbation)
Introduction
  • Definition
    • an arterial blood test that effectively determines the patient's pH, PaCO2, PaO2, and HCO3
      • an arterial blood gas (ABG) should be performed in the following circumstances
        • determining and monitoring a patient's acid-base status
        • assessing treatment response (e.g., treated diabetic ketoacidosis with insulin)
  • Procedure
    • blood can be obtained via 
      • a percutaneous needle to the artery (e.g., radial artery, femoral artery, and brachial artery)
      • an indwelling arterial catheter
  • Interpretation
    • normal values
      • pH: 7.35-7.45
      • PaCO2: 35-45 mmHg
      • HCO3: 21-27 mEq/L
      • PaO2: > 80 mmHg
      • SaO2 > 95%
    • respiratory acidosis
      • characterized by a PaCO2 > 45 mmHg and a pH < 7.35
        • typically due to alveolar hypoventilation
          • the patient retains CO2 because the patient is not adequately expelling it
      • causes
        • sedative overdose (e.g., opiates and benzodiazepines)
        • obesity hypoventilation
        • brainstem disease
        • chronic obstructive pulmonary disease  
        • amyotrophic lateral sclerosis
        • kyphoscoliosis
        • asthma
        • heroin overdose 
    • respiratory alkalosis
      • characterized by a PaCO2 < 45 mmHg and a pH > 7.45 (this is true in acute cases, in chronic cases the pH can be close to normal due to renal compensation)
        • typically due to alveolar hyperventilation
          • the patient is effectively expelling too much CO2
      • can serve as a method to compensate for a metabolic acidosis  
      • examples
        • anxiety and panic attacks
        • fever
        • hyperventilation syndrome
        • pulmonary embolism
        • pneumonia
        • pregnancy
        • hyperthyroidism
        • aspirin overdose (recall that it causes both a respiratory alkalosis and metabolic acidosis)
    • metabolic acidosis
      • characterized by a pH < 7.35 and a serum bicarbonate < 22 mEq/L
      • examples
        • diabetic ketoacidosis
        • lactic acidosis
        • diarrhea
        • type 1, 2, and 4 renal tubule acidosis
    • metabolic alkalosis
      • characterized by a pH > 7.45 and a serum bicarbonate > 28 mEq/L
      • examples
        • primary mineralocorticoid excess
        • loop or thiazide diuretics
        • calcium-alkali syndrome
        • bicarbonate ingestion
 

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Questions (6)
Lab Values
Blood, Plasma, Serum Reference Range
ALT 8-20 U/L
Amylase, serum 25-125 U/L
AST 8-20 U/L
Bilirubin, serum (adult) Total // Direct 0.1-1.0 mg/dL // 0.0-0.3 mg/dL
Calcium, serum (Ca2+) 8.4-10.2 mg/dL
Cholesterol, serum Rec: < 200 mg/dL
Cortisol, serum 0800 h: 5-23 μg/dL //1600 h:
3-15 μg/dL
2000 h: ≤ 50% of 0800 h
Creatine kinase, serum Male: 25-90 U/L
Female: 10-70 U/L
Creatinine, serum 0.6-1.2 mg/dL
Electrolytes, serum  
Sodium (Na+) 136-145 mEq/L
Chloride (Cl-) 95-105 mEq/L
Potassium (K+) 3.5-5.0 mEq/L
Bicarbonate (HCO3-) 22-28 mEq/L
Magnesium (Mg2+) 1.5-2.0 mEq/L
Estriol, total, serum (in pregnancy)  
24-28 wks // 32-36 wks 30-170 ng/mL // 60-280 ng/mL
28-32 wk // 36-40 wks 40-220 ng/mL // 80-350 ng/mL
Ferritin, serum Male: 15-200 ng/mL
Female: 12-150 ng/mL
Follicle-stimulating hormone, serum/plasma Male: 4-25 mIU/mL
Female: premenopause: 4-30 mIU/mL
midcycle peak: 10-90 mIU/mL
postmenopause: 40-250
pH 7.35-7.45
PCO2 33-45 mmHg
PO2 75-105 mmHg
Glucose, serum Fasting: 70-110 mg/dL
2-h postprandial:<120 mg/dL
Growth hormone - arginine stimulation Fasting: <5 ng/mL
Provocative stimuli: > 7ng/mL
Immunoglobulins, serum  
IgA 76-390 mg/dL
IgE 0-380 IU/mL
IgG 650-1500 mg/dL
IgM 40-345 mg/dL
Iron 50-170 μg/dL
Lactate dehydrogenase, serum 45-90 U/L
Luteinizing hormone, serum/plasma Male: 6-23 mIU/mL
Female: follicular phase: 5-30 mIU/mL
midcycle: 75-150 mIU/mL
postmenopause 30-200 mIU/mL
Osmolality, serum 275-295 mOsmol/kd H2O
Parathyroid hormone, serume, N-terminal 230-630 pg/mL
Phosphatase (alkaline), serum (p-NPP at 30° C) 20-70 U/L
Phosphorus (inorganic), serum 3.0-4.5 mg/dL
Prolactin, serum (hPRL) < 20 ng/mL
Proteins, serum  
Total (recumbent) 6.0-7.8 g/dL
Albumin 3.5-5.5 g/dL
Globulin 2.3-3.5 g/dL
Thyroid-stimulating hormone, serum or plasma .5-5.0 μU/mL
Thyroidal iodine (123I) uptake 8%-30% of administered dose/24h
Thyroxine (T4), serum 5-12 μg/dL
Triglycerides, serum 35-160 mg/dL
Triiodothyronine (T3), serum (RIA) 115-190 ng/dL
Triiodothyronine (T3) resin uptake 25%-35%
Urea nitrogen, serum 7-18 mg/dL
Uric acid, serum 3.0-8.2 mg/dL
Hematologic Reference Range
Bleeding time 2-7 minutes
Erythrocyte count Male: 4.3-5.9 million/mm3
Female: 3.5-5.5 million mm3
Erythrocyte sedimentation rate (Westergren) Male: 0-15 mm/h
Female: 0-20 mm/h
Hematocrit Male: 41%-53%
Female: 36%-46%
Hemoglobin A1c ≤ 6 %
Hemoglobin, blood Male: 13.5-17.5 g/dL
Female: 12.0-16.0 g/dL
Hemoglobin, plasma 1-4 mg/dL
Leukocyte count and differential  
Leukocyte count 4,500-11,000/mm3
Segmented neutrophils 54%-62%
Bands 3%-5%
Eosinophils 1%-3%
Basophils 0%-0.75%
Lymphocytes 25%-33%
Monocytes 3%-7%
Mean corpuscular hemoglobin 25.4-34.6 pg/cell
Mean corpuscular hemoglobin concentration 31%-36% Hb/cell
Mean corpuscular volume 80-100 μm3
Partial thromboplastin time (activated) 25-40 seconds
Platelet count 150,000-400,000/mm3
Prothrombin time 11-15 seconds
Reticulocyte count 0.5%-1.5% of red cells
Thrombin time < 2 seconds deviation from control
Volume  
Plasma Male: 25-43 mL/kg
Female: 28-45 mL/kg
Red cell Male: 20-36 mL/kg
Female: 19-31 mL/kg
Cerebrospinal Fluid Reference Range
Cell count 0-5/mm3
Chloride 118-132 mEq/L
Gamma globulin 3%-12% total proteins
Glucose 40-70 mg/dL
Pressure 70-180 mm H2O
Proteins, total < 40 mg/dL
Sweat Reference Range
Chloride 0-35 mmol/L
Urine  
Calcium 100-300 mg/24 h
Chloride Varies with intake
Creatinine clearance Male: 97-137 mL/min
Female: 88-128 mL/min
Estriol, total (in pregnancy)  
30 wks 6-18 mg/24 h
35 wks 9-28 mg/24 h
40 wks 13-42 mg/24 h
17-Hydroxycorticosteroids Male: 3.0-10.0 mg/24 h
Female: 2.0-8.0 mg/24 h
17-Ketosteroids, total Male: 8-20 mg/24 h
Female: 6-15 mg/24 h
Osmolality 50-1400 mOsmol/kg H2O
Oxalate 8-40 μg/mL
Potassium Varies with diet
Proteins, total < 150 mg/24 h
Sodium Varies with diet
Uric acid Varies with diet
Body Mass Index (BMI) Adult: 19-25 kg/m2
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(M2.PL.17.14) A 19-year-old male college student with no significant medical history presents to the emergency department with altered mental status. His girlfriend said that he drank multiple shots of vodka and gin throughout the weekend and was found slumped on the couch with some vomit on his shirt. He is afebrile, with a blood pressure of 128/60 mmHg, pulse of 100/min, respirations at 25/min, and SpO2 of 95% on room air. His pupils are equal and reactive to light bilaterally. He exhibits no tremors or myoclonus. The remainder of the physical exam is unremarkable. His basic metabolic panel is displayed below:

Serum:
Na+: 138 mEq/L
Cl-: 90 mEq/L
K+: 4.0 mEq/L
HCO3-: 20 mEq/L
BUN: 30 mg/dL
Glucose: 100 mg/dL
Creatinine: 0.8 mg/dL

An arterial blood gas reveals the following:

pH: 7.32
pCO2: 34 mmHg
pO2: 89 mmHg

The girlfriend is concerned that the patient's breathing appears uncomfortable. How do you respond?
Review Topic | Tested Concept

QID: 104288
1

His breathing is concerning for hepatic encephalopathy

9%

(14/150)

2

His breathing requires evaluation for a pulmonary embolism

4%

(6/150)

3

His breathing suggests that he needs some fluids

58%

(87/150)

4

His breathing suggests that he has major depression disorder

3%

(5/150)

5

You are not his healthcare proxy and I cannot speak to you

25%

(38/150)

L 4 D

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(M2.PL.17.49) A 48-year-old woman is transferred from her primary care physician's office to the emergency department for further evaluation of hypokalemia to 2.5 mEq/L. She was recently diagnosed with hypertension 2 weeks ago and started on medical therapy. The patient said that she enjoys all kinds of food and exercises regularly, but has not been able to complete her workouts as she usually does. Her temperature is 97.7°F (36.5°C), blood pressure is 107/74 mmHg, pulse is 80/min, respirations are 15/min, and SpO2 is 94% on room air. Her physical exam is unremarkable. Peripheral intravenous (IV) access is obtained. Her basic metabolic panel is obtained below.

Serum:
Na+: 135 mEq/L
Cl-: 89 mEq/L
K+: 2.2 mEq/L
HCO3-: 33 mEq/L
BUN: 44 mg/dL
Glucose: 147 mg/dL
Creatinine: 2.3 mg/dL
Magnesium: 2.0 mEq/L

What is the next best step in management?
Review Topic | Tested Concept

QID: 104323
1

Obtain an electrocardiogram

47%

(20/43)

2

Administer potassium bicarbonate 50mEq per oral

2%

(1/43)

3

Administer potassium chloride 40mEq via peripheral IV

35%

(15/43)

4

Administer isotonic saline 1 liter via peripheral IV

12%

(5/43)

5

Obtain urine sodium and creatinine

5%

(2/43)

L 3 D

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(M2.PL.14.4) A 60-year-old homeless man presents to the emergency department with an altered mental status. He is not answering questions. His past medical history is unknown. A venous blood gas is drawn demonstrating the following.

Venous blood gas
pH: 7.2
PaO2: 80 mmHg
PaCO2: 80 mmHg
HCO3-: 24 mEq/L

Which of the following is the most likely etiology of this patient's presentation?
Review Topic | Tested Concept

QID: 104278
1

Aspirin overdose

69%

(55/80)

2

COPD

8%

(6/80)

3

Diabetic ketoacidosis

14%

(11/80)

4

Ethylene glycol intoxication

2%

(2/80)

5

Heroin overdose

6%

(5/80)

L 1 E

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