Calculations

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1. Calculation of minutes remaining in an oxygen cylinder.	2. Calculating the duration of flow for a liquid O2 system.
3. Calculation of total arterial oxygen content (CaO2), total venous oxygen content (CVO2) and arterial venous oxygen content difference C(a-v)O2.	4. Calculating total flow delivered by a high flow oxygen delivery device.
5. Determining actual flow rate of He/O2 mixtures through an O2 flowmeter.	6. Calculating relative humidity (RH)
7. Calculating body humidity (BH)	8. Calculating humidity deficit (HD)
9. Calculating alveolar PO2 (PAO2) using the alveolar air equation.	10. Calculating P(A-a)O2
11. Calculating intrapulmonary shunt.	12. Calculating systemic vascular resistance (SVR).
13. Calculating pulmonary vascular resistance (PVR)	14. Calculating cardiac output (QT)
15. Calculating ideal body weight (lb)	16. Calculating ventilator tubing compliance.
17. Calculating actual ventilator tidal volume delivered.	18. Calculating dynamic and static lung compliance.
19. Calculating inspiratory flow rate.	20. Calculating I:E ratio.
21. Calculating inspiratory time.	22. Calculating VD/VT ratio
23. Calculating airway resistance (Raw)	24. Calculating desired O2 level.
25. Calculating desired ventilator rate.	26. Calculating desired minute ventilation (VE)
27. PaO2/FiO2 Ratio

1.    Calculation of minutes remaining in an oxygen cylinder.

Cylinder factors:

·         H cylinder: 3.14 L/psig

·         E cylinder: 0.28 L/psig

Calculate the Time Left in an E-Cylinder

2. Calculating the duration of flow for a liquid O₂ system.

Note: 1 liter of liquid oxygen weighs 2.5 lb (1.1 kg)

3. Calculation of total arterial oxygen content (CaO₂), total venous oxygen content (CVO₂) and arterial venous oxygen content difference C(a-v)O₂.

The sum total of oxygen bound to hemoglobin and dissolved in the plasma.

O₂ bound to Hb = 1.34 x Hb x SaO₂

O₂ dissolved in plasma = PaO₂ x .0003

· Add the answers to each to determine the CaO₂

· Use the same equation for calculating venous content but substitute SVO₂ for SaO₂, and PVO₂ for PaO₂

· Subtract the CVO₂ from the CaO₂ to determine the content difference

4. Calculating total flow delivered by a high flow oxygen delivery device.

Add the air/O₂ entrainment ratio parts together and multiply by the flowmeter setting.

Example: 40% air entrainment mask running at 8 L/min

40% air/O₂ ratio = 3:1; 3 + 1 = 4, 4 x 8 = 32 L/min

5. Determining actual flow rate of He/O₂ mixtures through an O₂ flowmeter.

· 80/20 heliox mixture: multiply flowmeter reading by 1.8

· 70/30 heliox mixture: multiply flowmeter reading by 1.6

To determine what to set the O₂ flowmeter on to deliver the ordered heliox flow, divide the factor 1.8 or 1.6 into the ordered flow.

6. Calculating relative humidity (RH)

· Absolute humidity is the amount of water in a given volume of gas

· Capacity is the total amount of water capable of being held in the gas at a given temperature

7. Calculating body humidity (BH)

8. Calculating humidity deficit (HD)

HD = 44 mg/L – absolute humidity

Expressed as a percentage:

9. Calculating alveolar PO₂ (PAO₂) using the alveolar air equation.

Shortcut equation for the exam when the barometric pressure is 747 torr:

PAO₂ = (7 x O₂%) – (PaCO₂ + 10)

10. Calculating P(A-a)O₂

(Referred to as the A-a gradient)

PAO₂ – PaO₂

Calculate A-a Gradient

11. Calculating intrapulmonary shunt.

12. Calculating systemic vascular resistance (SVR).

· QT = cardiac output

· MSAP = mean systemic arterial pressure

· Answer is in the units mmHg/L/min. Multiply by 80 to convert to dyne x sec x cm^-5

13. Calculating pulmonary vascular resistance (PVR)

· MPAP = mean pulmonary artery pressure

· PCWP = pulmonary capillary wedge pressure

· Answer is in the units mmHg/L/min. Multiply by 80 to convert to dyne x sec x cm^-5

14. Calculating cardiac output (QT)

(QT) = SV × HR

Hemodynamics Calculator

15. Calculating ideal body weight (lb)

Females: 105 + (height in inches – 60)

Males: 106 + 6 (height in inches – 60)

· To change from pounds to kilograms, divide your answer by 2.2

· This equation is commonly used to determine the appropriate ventilator tidal volume for a given body weight. Once the weight in pounds is calculated, simply divide the weight in half and add a zero to the end. This represents a VT of approximately 10 mL/kg of body weight.

· Example: ideal body weight is calculated to be 140 lb. divide by two (70) and add a zero (700). A 700 mL VT is appropriate for this body weight.

IBW & ABW calculator

Better Ideal Weight Body Calculations

16. Calculating ventilator tubing compliance.

Measured by occluding the ventilator Y adapter and dividing the peak pressure into the set tidal volume. (High pressure alarm must be adjusted to maximal level during the measurement)