Respiratory Therapy Formulas and normal values:
1. Ideal Body Weight (IBW):
- a. Female: 100 lb for 1st 5ft + 5lbs ea additional inch
- b. Male: 106 lb for 1st 5 ft + 6lbs ea additional inch
- a. Normal = 60-100
- b. less than 60 = lungs becoming less compliant
- c. greater than 25 is acceptable
- d. less than 25 is unacceptable
(Normal PaO2 on 21% or room air = 105)
4. Desired Ve= Known Ve*Known PaCO2 divided by desired PaCO2
5. Desired Vt = (Known PaCO2 x Known Vt)/Desired PaCO2
6. Desired f = (Known PaCO2 x Known f)/Desired PaCO2
7. RAW: PIP–Plateau/ Flow, or PIP–plateau
8. French size sx catheter = ETT size * 3/2
9. PAO2: (713 *Fio2 – PaCO2)/0.8or 0.1 if 100% O2
10. A-a gradient (ratio or A-ADO2): PAO2 – PaO2
- a. Normal on RA = 10-40 or on 100% = 25 – 70
- b. Increased 66-300 = acute lung injury
- c. greater than 300 = severe shunting, ARDS (unacceptable)
- a. If normal, hypoxia caused by hypoventilation,consider drug overdose, neuromuscular disorder.
- b. If abnormal & SpO2 improves with increased FiO2. Consider PE, pneumothorax, asthma,emphysema, pneumonia, bronchitis, heartfailure, congenital heart disease, aging.
- c. If abnormal & refractory hypoxemia occurs, hypoxia caused by shunting problem considerpneumonia, atelectasis, pulmonary edema or ARDS.
- if greater than 20 an increase in PEEP is indicated
- a. Normal = 80% (74% elderly)
- b. 60% = V/Q imbalance
- c. 15% = shunting
- a. Normal = 300 – 500
- b. Acute lung injury = 200 – 300
- c. less than 200 = ARDS (shunt)
Even though normal PaO2 is 105 on room air, a PaO2 of 200 on 100% FiO2 is not necessarily good. It should be 500. Therefore you know patient still not oxygenating effectively.
16. Actual PaO2/ Expected PaO2 = % of patient expected PaO2:
- a. Should be recorded daily
- b. Shows if patient is oxygenating better
- c. Better indicator than simply looking at actual PaO2 and FiO2
- d. Normal = zero (patient requiring no supplememtal oxygen)
- e. January 1 PaO2 40 on 100% FiO2 = 80%
- f. January 5 PaO2 60 on 40% FiO2 = 30%
- g. January 6 PaO2 55 on 50% FiO2 = 20%
- h. January 1 PaO2 200 on 100% FiO2 = 40%
- i. January 5 PaO2 100 on 100% = 20%
- j. January 6 PaO2 100 on 90% = 22%
- k. January 10 PaO2 55 on 80% = 13%
18. Oral intubation = 21-25cm @ lip.
19. Nasal intubation = 26-29cm
20. PEEP therapy = greater than 6-8 CWP
21. Humidity should be set at 37 degrees Celcius.
23. Patient WOB (available on newer microprocessor ventilators)
- a. Less than 0.8 = normal
- b. Measures effectiveness of rise time and sensitivity.
- c. Measured in spontaneous mode.
Note: There are other RT Formulas, yet these are the ones I have used on occasion while working. If you find another formula you find worthwhile, please email me with the formula and a note about when you would use it, and I will post it for others to use.