Hypoxemia 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 → ↑ PACO2 → ↓ 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
QUESTIONS 1 of 5 1 2 3 4 5 Previous Next Sorry, this question is for PEAK Premium Subscribers only Upgrade to PEAK Sorry, this question is for PEAK Premium Subscribers only Upgrade to PEAK Sorry, this question is for PEAK Premium Subscribers only Upgrade to PEAK Sorry, this question is for PEAK Premium Subscribers only Upgrade to PEAK (M1.PL.14.79) 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? QID: 106909 FIGURES: A Type & Select Correct Answer 1 Normal Aa gradient, decreased surface area for diffusion, normal diffusion distance 5% (8/157) 2 Decreased Aa gradient, decreased surface area for diffusion, normal diffusion distance 11% (17/157) 3 Decreased Aa gradient, increased surface area for diffusion, decreased diffusion distance 4% (7/157) 4 Increased Aa gradient, normal surface area for diffusion, increased diffusion distance 21% (33/157) 5 Increased Aa gradient, decreased surface area for diffusion, increased diffusion distance 55% (87/157) M 2 Question Complexity D Question Importance Select Answer to see Preferred Response SUBMIT RESPONSE 5 Review Tested Concept Review Full Topic
All Videos (1) Login to View Community Videos Login to View Community Videos Alveolar Gas equation 1 Keshav Mudgal Respiratory - Oxygen Deprivation E 10/29/2015 49 views 0.0 (0) Respiratory | Oxygen Deprivation Respiratory - Oxygen Deprivation Listen Now 13:30 min 11/14/2021 30 plays 5.0 (1)