Dead Space to Tidal Volume

Normal value: 25-40%.   

VD/ VT =  Paco2  —  PĒco2

                  ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯

               Paco2

Oxygen Content Calculation

CaO2

CaO2 =

(Hb Concentration) (1.34) (Hb Saturation) + ( Po2) (0.003) )

P(A-a)O₂ Calculation

A a Gradient

A value that quantifies oxygen diffusion accross the alveolar mebrane and assess oxygenation status.

Generally >40 mm Hg @ 21%FIO2 require O2 and  > 350 on high flow O2 require positive pressure. 

PAO₂ - PaO₂

PAO₂

Partial Pressure of Oxygen in Alveolar Gas

PAO₂ = (P_B- P_H2O) FIO₂- P_aO₂ x 1.25

P_B = Barometric Pressure

P_H2O = Partial pressure of water vapor in the lungs

Qs/Qt = P(A-a) 02 x .003

                                C(a-v)02 + [P(A-a)02 x .003]

 or

Qs/Qt = (A-aDO₂) x .003

                                (A-aDO₂) x .003 + C(a-v)O₂

Classic

        Qs/Qt = Cc’02 – Ca02           

          Cc’02 – Cv02

a/A Ratio

Used to assess patient oxygenation. Values less than 0.60 are generally an indication for oxygen and less than 0.15 usually need PEEP or CPAP therapy.

a A Ratio =PaO₂

                PAO₂