Ventilation Flashcards
Where is dependent lung found? Where is non-dependent lung found? Which of West’s zones of the lung is dependent, and which is non-dependent? When are the lung bases dependent and the lung apices non-dependent?
Dependent lung is the region of lung that is closest to the ground and non-dependent lung is located farthest from the ground. West’s Zone I is non-dependent lung while Zone III is dependent lung. The bases of the lung are dependent in the upright (sitting or standing) individual. The apices of the lung are non-dependent in the upright (sitting or standing) individual. Dependent lung is dependent on gravity.
How is minute alveolar ventilation calculated? A healthy 65 kg 30-year-old has what alveolar ventilation if respiratory rate is 12 per minute and tidal volume is 450 ml?
Alveolar ventilation is minute ventilation minus dead space ventilation. Alveolar ventilation = (tidal volume - dead space) x ventilation rate. For a healthy patient, dead space is 2 ml/kg. Alveolar ventilation for the 65 kg 30-year-old is: (450 ml - 65 kg x 2 ml/kg) x 12/min = (450 ml - 130 ml) x 12/min = 320 ml x 12/min = 3,840 ml = 3.84 liters.
Increasing which component of minute ventilation
(ventilation rate or tidal volume) most improves alveolar ventilation? Why?
An increase in tidal volume will improve alveolar ventilation more than will an increase in ventilation rate. An increase in tidal volume increases alveolar ventilation without increasing dead space ventilation. An increase in ventilation rate increases both alveolar and dead space ventilation.
What happens to end-tidal CO2 if fresh gas flows and
minute ventilation are increased in a controlled ventilation patient?
End-tidal CO2 decreases. With high fresh gas flows, ETCO2 is dependent on minute ventilation.
What happens to tidal volume and minute ventilation with
high fresh gas flows in a controlled ventilation system?
Tidal volume and thus minute ventilation (respiratory rate x tidal volume) will increase due to high flows of fresh gas within the bellows and the anesthetic circuit to the patient.
Are PaCO2 and ETC02 directly or inversely proportional to alveolar ventilation?
PaC02 and ETCO2 are inversely proportional to alveolar ventilation. When alveolar ventilation increases, both PaC02 and ETCO2 decrease, and vice versa. Note: ETCO2 is average alveolar PCO2 (PACO2).
Explain what happens to PaCO2 and ETCO2 when deadspace increases if total minute ventilation is kept constant.
If deadspace ventilation increases without a change in total minute ventilation, alveolar ventilation decreases, and PaCO2 and ETC02 increase.
If you add dead space to a breathing circuit without changing the minute ventilation, state the changes that would occur in the arterial blood gas values.
Alveolar ventilation would decrease, so there would be increased PaC02 and decreased PaO2.
What are the two determinants of PaCO2? How may the anesthetist increase or decrease PaCO2?
Carbon dioxide production and alveolar ventilation are the two determinants of PaCO2. The anesthetist alters the patient’s PaC02 by decreasing or increasing ventilation (by changing tidal volume or ventilatory rate).
How does the alveolar partial pressures of O2 and CO2 vary from base to apex when the patient is upright?
The alveolar partial pressure of 02 (PAO2) is higher in the apex and lower in the base, and the alveolar partial pressure of C02 (PAC02) is lower in the apex and higher in the base.
Which zone of the lung (Zone I, Zone II, or Zone III) has the greatest alveolar oxygen partial pressure and which zone has the greatest alveolar carbon dioxide partial pressure when the patient is upright?
Zone I (non-dependent lung) has the highest PA02. Zone III (dependent lung) has the highest PAC02.
Which lung zone (Zone I, Zone II, or Zone III) has the most negative intrapleural pressure? Least negative?
The most negative intrapleural pressure is found in Zone I (non-dependent lung) and the least negative intrapleural pressure is found in Zone III (dependent lung).
Compared with ambient atmospheric air, the tracheal air during inspiration has a higher concentration of which substance?
Water has a higher concentration in the airway compared with atmospheric air. Alveolar air is 100% humidified at 37 degrees C. Air becomes 100% humidified as it flows into the respiratory tract. 02 and N2 are diluted slightly by the water vapor.
What is the relative humidity inside the alveoli?
The gas everywhere in the airway is saturated with water vapor (relative humidty = 100%).
Calculate the partial pressure of CO2 in expired gas if end- tidal CO2 (ETCO2) is 5%? What law permits this calculation to be made?
ETCO2 = 38 mmHg (0.05 x 760 mmHg). Note: % concentration/100 x atmospheric pressure yields the partial pressure. Dalton’s law of partial pressures permits this calculation to be made.
