Ruppel Chapter 4 Flashcards

Closed Circuit CO2 Rebreathing Test

• Reservoir bag should contain 7% CO2 in O2 for the test setup.
• A variable CO2 scrubbing device is necessary in the breathing circuit for closed-circuit O2 response tests.

Respiratory Measurements

• Patient's respiratory dead space calculated at 0.3 L (BTPS), with a tidal volume (VT) of 0.7 L (BTPS) and a breathing rate of 22 bpm yields an alveolar ventilation (VA) of 8.8 L.
• In a COPD patient, effective tidal volume (VT) can be calculated using minute ventilation (VE) and respiratory rate (RR); example yields a VT of 0.42 L.
• Alveolar volume from tidal breathing of 720 ml and dead space of 150 ml results in an alveolar volume of 7.60 L.

Vd/Vt Ratio Calculation

• Noninvasive measurement of Vd/Vt ratio requires mixed expired PCO2 and PETCO2.
• Vd/Vt ratio estimation can mathematically illustrate the efficiency of ventilation; calculated from the formula VD/VT=(PaCO2-PeCO2)/PaCO2.

Hypoventilation Indicators

• Confirmed hypoventilation with a PAco2 of 48 mm Hg and a pH of 7.29.

Hyperventilation Criteria

• Defined by a PaCO2 less than 35 mm Hg, accompanied by a pH greater than 7.45.

P100 Measurement

• P100 (or P0.1) signifies the pressure developed during the first 100 milliseconds of an occluded breath in response testing.

Use of Sodium Hydroxide Crystals

• Sodium hydroxide crystals (sodasorb) used for CO2 scrubbing change color to violet when fully depleted.

VE and VT Calculations

• Subject's VE (minute ventilation) calculation requires BTPS correction factor; example results in 5.56 L.
• For the subject’s tidal volume (VT), a volume expired of 27L at a rate of 12 breaths per minute computes to 463 ml.
• Vd/Vt % calculated for the same subject is 25%.
• VA measurement for the same conditions results in 4.17 L/min.

Estimating Dead Space

• Dead space can be estimated at approximately 1 ml per pound of ideal body weight for patients.