Updated: 10/16/2017

Oxygen Deprivation

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Hypoxemia

Alveolar Gas Equation

A-a Gradient

  • Alveolar gas equation
    • predicts the change in PAO2 that will occur for a given change in PACO2
    • PAO2 = alveolar PO2
    • PIO2 = PO2 in inspired air
      • normally, PIO2 = 150 mm Hg
    • PACO2 = alveolar PCO2
    • R = respiratory exchange ratio = (CO2 production) / (O2 consumption)
      • normally, R = 0.80
  • A-a Gradient
    • alveolar PO2 (PAO2) - systemic arterial PO2 (PaO2)
    • normal A-a gradient = 15 mm Hg (~Age/4 +4)
      • equilibration of O2 across alveolar gas and pulmonary capillary blood
        • pulmonary capillary blood becomes systemic arterial blood
      • increases with age
    • hypoxemia↑ A-a gradient
      • e.g., shunt, V/Q mismatch, pulmonary fibrosis (diffusion defect)
  • Causes of Hypoxemia (↓ PaO2)
    • High Altitude (normal A-a gradient) 
      • a decrease in barometric pressure (PB) decreases the PIO2 of inspired air
        • FiO2 doesn't change (21%)
        • ↓ PB → ↓ PIO2  ↓ PAO2 → ↓ PaO2
    • Hypoventilation (normal A-a gradient)  
      • a decrease in minute ventilation (respiratory rate x tidal volume) decreases PAO2
        • ↓ ventilation → PACO→ ↓ PAO2
        • FiO2 and PB don't change in alveolar gas equation
    • V/Q Mismatch (↑ A-a gradient)
    • Diffusion Limitation (↑ A-a gradient)
      • e.g., pulmonary fibrosis
        • ↑ diffusion distance for diffusion
      • e.g., pulmonary edema
        • ↓ surface area for diffusion, ↑ diffusion distance
    • Right-to-Left Shunt (↑ A-a gradient)
      • low O2 shunted blood mixes with and dilutes high O2 non-shunted blood
Hypoxia
  • Decreased Oxygen Delivery to Tissues
    • O2 content of blood = (O2 binding capacity) x (% saturation) + dissolved O2
      • (O2 binding capacity) x (% saturation) = O2 bound to hemoglobin
    • O2 delivery = (cardiac output) x (O2 content of blood)
  • Causes of Hypoxia (↓ O2 Delivery to Tissues)
    • circulatory (↓ Cardiac Output)
      • ↓ blood flow
    • hypoxemic
      • ↓ PaO2 → ↓ % saturation → ↓ O2 content of blood
    • anemic (see CO poisoning below)
      • ↓ concentration of hemoglobin→ ↓ O2 content of blood
    • histotoxic (example: cyanide poisoning)
      • ↓ O2 utilization by tissues (mitochondrial poison)
    • CO Poisoning
      • ↓ O2 bound to hemoglobin → ↓ O2 content of blood, ↓ O2 delivery to tissues
        • CO binds to hemoglobin with 200x greater affinity than O2
          • oxygen-hemoglobin dissociation curve left shift
      • early sign of exposure is headache; significant exposure causes coma, death
      • classical presentation at autopsy is cherry-red appearance of skin
        • not common in living patients
Ischemia
  • Causes of Ischemia (↓ Blood Flow)
    • ↓ arterial blood flow
      • e.g., atherosclerosis
    • ↓ venous return
      • e.g., Budd-Chiari syndrome
 

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Questions (5)
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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(M1.PL.79) A 64-year-old male with a past medical history of two myocardial infarctions presents to the emergency room with shortness of breath. He notes that he stopped taking his furosemide two weeks prior, because he ran out of pills. On exam, his oxygen saturation is 78%, his lungs have crackles throughout, and jugular venous pulsation is located at the earlobe. EKG and troponin levels are normal. Which of the following is consistent with this man's pulmonary physiology? Review Topic

QID: 106909
FIGURES:
1

Normal Aa gradient, decreased surface area for diffusion, normal diffusion distance

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Decreased Aa gradient, decreased surface area for diffusion, normal diffusion distance

8%

(1/12)

3

Decreased Aa gradient, increased surface area for diffusion, decreased diffusion distance

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4

Increased Aa gradient, normal surface area for diffusion, increased diffusion distance

8%

(1/12)

5

Increased Aa gradient, decreased surface area for diffusion, increased diffusion distance

75%

(9/12)

M1

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