Respiratory calculations and Vent Crap

Question 1

How do you calculate driving pressure?
- what does it represent?

Answer 1

ΔP = Pplat - PEEP

• Reps the pressure gradient responsible for gas flow during mechanical ventilation.

Question 2

How do you calculate static and dynamic compliance?

Answer 2

Cdyn = Change in Volume/ [PIP - PEEPtot]

Cstat = Change in Volume/ [Pplat - PEEPtot]

Question 3

What are the three categories of deadspace?

Answer 3

1. Anatomical deadspace (VDanat)

• Volume of gas in conducting airways

2. Alveolar deadspace (VDalv)

• volume of gas ventilating unperfused alveoli

3. physiological deadspace (VDphys)

• Total of [anatomical + alveolar] deadspace

Question 4

Normal anatomic deadspace (Vd) = 2.2 mL/lb ; what is the Vd/Vt ratio normal?

Answer 4

0.2 - 0.4

Question 5

How would you clinically calculate Vd/Vt?

Answer 5

[PaCO2 - PeCO2] / PaCO2

Question 6

Minute ventilation (Ve) RR x Vt
- what is alveolar minute ventilation (VA)?

Answer 6

VA = RR x (Vt - Vdphyslogical)

Question 7

How do you calculate anatomic deadspace?

Answer 7

Anatomic deadspace is 2.2mL/lb

• meaning; 2.2 x lb

Question 8

What is ROX index?

Answer 8

Ratio of oxygen saturation [(SpO2/FiO2)/RR]

• possible predictor if Pt needs intubation
• Calculated within the first 12 hours of HFNC therapy

Question 9

How do you calculate the ratio of oxygen saturation (ROX)

Answer 9

[(SpO2/FiO2)/RR]

> 4.88 after 2,6,12 hrs indicates high probability of therapy success

• Increased score = Increased outcome

Question 10

Predictors of Rate of oxygen saturation (ROX) failure?

Answer 10

• ROX < 2.85 at 2 hrs
• ROX < 3.47 at 6 hrs
• ROX < 3.85 at 12 hours

Increased score = Increased outcome