Total Oxygen Content Calculations

Total Oxygen Content - Arterial (CaO2)

• CaO2 formula: CaO2 = (1.34 x Hgb x SaO2) + (PaO2 x 0.003)
• Normal hemoglobin (Hgb): 12-16 g/dl
• Normal arterial Hgb saturation (SaO2): >92%
• Normal partial pressure of oxygen in arterial blood (PaO2): >80 mmHg (60-100 mmHg)

Total Oxygen Content Calculation Examples

• For Hgb = 15 g/dl, SaO2 = 97%, PaO2 = 100 mmHg, CaO2 = 19.8 vol%

Total Oxygen Content - Mixed Venous (CvO2)

• CvO2 formula: CvO2 = (1.34 x Hgb x SvO2) + (PvO2 x 0.003)
• Normal venous Hgb saturation (SvO2): 70-75%
• Normal partial pressure of oxygen in venous blood (PvO2): 37-43 mmHg

Mixed Venous Oxygen Content Calculation Example

• For Hgb = 15 g/dl, SvO2 = 75%, PvO2 = 40 mmHg, CvO2 = 15.2 vol%

Arterial-Mixed Venous Oxygen Content Difference (C(a-v)O2)

• C(a-v)O2 formula: C(a-v)O2 = CaO2 - CvO2

C(a-v)O2 Calculation Example

• Given CaO2 = 20 vol%, CvO2 = 15 vol%, resulting in C(a-v)O2 = 5 vol%

Deadspace/Tidal Volume Ratio (Vd/Vt)

• Vd/Vt ratio normal value: 33%
• Vd = deadspace; Vt = tidal volume

Bohr's Equation

• Bohr's Equation: Vd/Vt = (PaCO2 - PeCO2) / PaCO2
• Example calculation: Vd/Vt = 0.125 or 13%

Alveolar Air Equation (PAO2)

• PAO2 = (PB - PH2O)FIO2 - (PaCO2/RQ)
• Normal values: PAO2 = 99 mmHg, PB = 760 mmHg, PH2O = 47 mmHg, RQ = 0.8

PAO2 Calculation Example

• Given PB = 760 mmHg, PH2O = 47 mmHg, FIO2 = 21%, PaCO2 = 40 mmHg, PAO2 = 100 mmHg

Active Ingredient Concentration

• Relationship: mL active/mL total = mg active/mL total

Active Ingredient Example

• In a 1% solution, 10 mg is present in 1 cc (mL).

Active Ingredient Calculation Example

• In 0.7 mL of 1:200 Isuprel, there are 3.5 mg of active ingredient.

Concentration Calculation of Solutions

• Use V1C1 = V2C2 to find concentrations or volumes.

Dilution Calculation Example

• To dilute 15 mL of 20% Mucomyst to 15%, add 5 mL of diluent.

Alveolar Ventilation (VA)

• VA formula: VA = f(Vt - Vd)
• VA measures alveolar ventilation per minute using respiratory rate (f), tidal volume (Vt), and deadspace (Vd).

Ideal Body Weight (IBW) Formula

• For men: IBW = 106 + 6 for each inch over 5'
• For women: IBW = 100 + 5 for each inch over 5'

Classic Shunt Equation (Qs/Qt)

• Qs/Qt formula: Qs/Qt = (CcO2 - CaO2) / (CcO2 - CvO2)

When to Use Classic Shunt Equation

• Applicable when FIO2 ≥ 30%.

Modified Shunt Equation (Qs/Qt)

• Modified formula: Qs/Qt = (P(A-a)O2 x 0.003) / [(P(A-a)O2 x 0.003) + C(a-v)O2]
• P(A-a)O2 = alveolar-arterial oxygen tension gradient.

When to Use Modified Shunt Equation

• Relevant when PO2 ≥ 150 mmHg on any FIO2.

Static Compliance (Cst)

• Cst formula: Cst = corrected Vt / (Pplat - PEEP)

Cylinder Duration for Gas

• Calculation: PSI x tank factor / liter flow, with specific tank factors for different gases.

Cylinder Duration for Liquid

• Calculation: 3.44 x liquid weight / liter flow.

Percent Body Humidity Calculation

• Formula: Content / 44 mg/L x 100 = % Body Humidity.