Respiratory Terminology & Equations

Resistance or Raw
Ppeak-Pplat/ flow in L per min
Static Compliance
Vte/Pplat-PEEP
Dynamic compliance
Vte/Ppeak-PEEP
Alveolar ventilation (Va)
(Vt-Vd weight in lbs) * f
Minute Ventilation (Ve)
Vt * f
Male:       4 * BSA
Female:   3.5 * BSA
Tidal Volume (Vt)
Flow * Ti
Convert flow to L /sec: divide by 60
Flow
Vt (L)/Ti sec
Convert to L/min; multiply by 60
Frequency or rate:
Ve/Vt
Apnea interval
TCT * 2
Rapid shallow breathing index RSBI
f/ Vte
Compliance
Change in Volume/Change in Pressure
Elastance
Change in Pressure/ Change in Volume
Arterial O2 content:
(hg * 1.34 * SaO2) + (Pao2 * 0.003)
Bound to hg                      in Plasma
Corrected Vt
Vt set – {(PIP – PEEP) * CF}
Total Cycle Time TCT
60/f  or  Ti + Te
Inspiratory Time Ti
Vt/ flow (in L per sec)
Expiratory Time Te
TCT- Ti
I:E ratio
Te/ Ti
A-a gradient
PAo2-Pao2
P- F ratio
Pao2/Fio2
Ideal Body Weight IBW
106 + 6(ht in inches- 60) male
105 + 5 (ht in inches-60) female
Multiply by 2.2 to convert to kg
Body Surface Area BSA
Square root of:
Ht inches – actual weight/
3131
Shunt equation
QS/QT= A-a gradient/
A-    Gradient (.003) + C-vO2
Short cut:
Take the A-a gradient and count # if hundreds
Multiply it by 5, add 5, and give as a %
Alveolar Air equation
(Pb – PH20)* FIO2- Pao2/0.8
Work of breathing WOB
Change in Pressure * change in volume
Desired Co2 from RR
PaC02 * f/ Desired PaC02
Oxygen Transport
Cardiac output * Pao2
Anion Gap
Na – (Cl + HCO2)
Cerebral perfusion pressure CPP
MAP- ICP