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HLW
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What is the volume of gas per unit of time that reaches perfused alveoli?
Alveolar ventilation
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How can alveolar ventilation be indirectly measured?
Arterial partial pressure of PaCO2
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When PaCO2 is decreased, that means that the alveolar ventilation is increased and the patient is....? 3
- Hyperventilating
- Hypocapnia
- Hypocarbia
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When PaCO2 is increased, that means that the alveolar ventilation is decreased and the patient is....? 3
- Hypoventilating
- Hypercapnia
- Hypercarbia
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What is normal PaCO2?
35-45 mmHg
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What is acceptable PaCO2 under anesthesia (supplemented with O2)?
35-60 mmHg
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What is the definition of tachypnea?
Rapid respiratory rate
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What does a capnometer display? 3
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What does a capnograph display? 4
- iCO2
- ETCO2
- RR
- graph of CO2 partial pressure plotted against time
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Why is PaCO2 and EtCO2 not the same?
EtCO2 is lower than PaCO2 because of dead space ventilation
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How much is EtCO2 lower than PaCO2 in small animals? Large animals?
- Small - 5 mmHg
- Large - 10 mmHg
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What is hypercapnia?
PaCO2 >45 mmHg
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What are the effects of increased PaCO2? 3
- Peripheral vasodilation (Increased ICP, decreased BP
- Academia
- Sympathoadrenal responses (catecholamine release)
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What are the two ways to provide intermittent positive pressure ventilation?
- Manual - close the pop-off valve and squeeze reservoir bag
- Mechanical - replace reservoir bag with ventilator
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What are some reasons to use intermittent positive pressure? 4
- Constant delivery of inhalant
- Appropriate ventilation and PaCO2
- Improve arterial blood oxygenation
- Maintain ventilation in patients with decreased ability to expand chest/lungs
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What variable must be calculated for mechanical ventilation? 4
- Respiratory rate
- tidal volume (Vt)
- peak respiratory pressure (PIP)
- Inspiratory time or inspiratory time: expiratory time ratio (I:E)
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What is a good respiratory rate for mechanical ventilation of small animals? Large animals?
- Small - 8-12 bpm
- Large - 6-10 bpm
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What is a good tidal volume for patients under mechanical ventilation?
Vt = 10-20 ml/kg
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When can the demand valve be used?
Provide ventilation and oxygenation in large animals (not small animals)
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What are some disadvantages of intermittent positive pressure ventilation? 2
- Increase pressure inside the chest (decreased venous return)
- Lung injury (alveolar stretching and rupture)
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What is the accumulation of acid (H+) inside the body?
Metabolic acidosis
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What is the accumulation of base (HCO3) inside the body?
Metabolic alkalosis
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What is the result of hypoventilation (increase in PaCO2)?
Respiratory acidosis
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What is the result of hyperventilation (decrease in PaCO2)?
Respiratory alkalosis
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How are simple acid-base disturbances compensated?
- Fast - respiratory
- Slow - renal
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What are most acid-base disturbances in healthy anesthetized patients?
Respiratory acidosis
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For every 10 mmHg increase in PaCO2, how much will the pH decrease?
0.05 units
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When do you see severe acidosis?
- pH < 7.2
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- HCO3 < 10 mEq/L
- or
- PaCO2 > 80 mmHg
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