Useful Sites NBRC AARC ARC Foundation CDC NIH ARDSNet ASA American Lung Association American Heart Association American Thoracic Society Curriculm By Medtronic, Inc. Ventilator Training Alliance By Allego, Inc. Google Tutorials How to Take a Sim How to Sign up Mobile App Tutorial Job Analysis Correlations Terms of Service Register Gunderwoodsims Club Resp

Home Page tutorial was produced with OpenAI software.

Oxygenation

O2 Content (a = arterial; v = mixed venous; c = capillary/alveolar)
Equation / Formula	Normal Values (21% FiO2; 760 mmHg BP)	Comments
CaO2= Hb x 1.34 x SaO2 + (PaO2 x .003)	20 vol %	Oxygen content gives us an observation of the oxygen that is combined with hemoglobin (Hb * 1.34 * SaO2) as well as the amount dissolved in the plasma (PO2 * .003). Knowing the calculation(s) allows the practitioner to relate the hemoglobin carriage to partial pressure and express this observation succinctly. It is expressed as milliliters of oxygen/100 milliliters of blood... Commonly called volumes percent. It is a standard measure of oxygenation.
CvO2= Hb x 1.34 x SvO2 + (PvO2 x .003)	15 vol %
CcO2= Hb x 1.34 x SAO2 + (PAO2 x .003)	22 vol.%
CaO2 - CvO2	5 vol.%
O2 Delivery
DO2 = CaO2 x Q (Q = cardiac output)	1000 ml/min	Knowing the oxygen delivery formula and its value allows the practitioner to evaluate the oxygen delivered to the tissues. A person might have great oxygenation, but is it getting to where it needs to get? It is an excellent evaluative tool when titrating PEEP.
Alveolar Gas Equation
PAO2 = FiO2 (PB - PH2O) - (PaCO2 / R)	100 mm Hg	This calculation provides the means to determine the partial pressure of oxygen in the alveoli. The variety of factors that are involved in alveolar oxygen tension are brought to your attention when you perform this calculation.
Alveolar - Artierial Gradient
AaO2 = PAO2 - PaO2	5 - 25 mm Hg	This data tells us about the gradient between the oxygen tension in the lungs and that in the peripheral arterial system. Widened gradients indicate either a diffusion defect (rare) or a ventilation/perfusion imbalance (commonly of the shunt variety). This gradient also widens about 1 mmHg per decade; thus, it naturally widens with aging.
Estimation of shunt: AaO2 / 20	Less than 20%
Classic shunt: CcO2 - CaO2 / CcO2 - CvO2
Desired FiO2
DesFiO2 = DesPaO2 + KnoFiO2 / KnoPaO2		Calculating this equation successfully allows the practitioner to determine the appropriate FiO2 to change the PaO2.
Oxygen Index
OI = FiO2 x MPaw / PaO2 MPaw = mean airway pressure.	Greater than 40 may indicate ECMO	The calculation offers an opportunity to mathematically represent the clinical factors used to promote oxygenation in relation to the PaO2. It is often used in the neonatal intensive care setting to determine threshold criteria for instituting ECMO.
PaO2 / FiO2 ratio: (P/F ratio)
P/F = PaO2 / FiO2 (use decimal fractions)	Greater than 300	This equation prompts the user to consider the patient's oxygenation in relation to the FiO2 used. P/F of 200 - 300 indicates lung injury. Less than 200 indicates ARDS.

Ventilation

Alveolar Ventilation
Equation / Formula	Normal Values (21% FiO2; 760 mmHg BP)	Comments
VA = (Vt-VD) x f Vt = tidal volume VD = deadspace volume f = frequency	Greater than 300	Understanding this calculation promotes awareness of the relationship between tidal volume and deadspace volume... and then between this difference and respiratory rate. An interesting comparison is easily drawn when one compares the minute ventilation to the alveolar ventilation, (when tidal volume and respiratory rate are equal). By performing just a few problems (like try doubling the tidal volume... then separately doubling the respiratory rate), it becomes obvious that tidal volume has the greater effect on alveolar ventilation (gas exchange) than does respiratory rate. It might be quite easy to simply use a calculator or ventilator function for this one... But there is no substitute for going through the process of discovery that "doing it yourself" allows. Compare deadspace ventilation to tidal volume in order to observe the non-ventilating portion of the tidal volume.
Minute Ventilation: VE = Vt * f
Deadspace to tidal volume ratio: VD / Vt = PaCO2 - PECO2 / PaCO2	Less than 60%
Desired ventilation (in mechanical ventilation):
DesVE = KnoVE x KnoPaCO2 / DesPaCO2 DesVt= KnoVt x KnoPaCO2/ DesPaCO2 Desf = Knof x KnoPaCO2 / DesPaCO2 Des = "Desired"; Kno = "Known"		Calculating this simple formula allows the practitioner to determine the appropriate ventilation parameter given an undesirable PaCO2.
Flow, Time, and Volume
V = Vt/Ti Vt = Ti * V Ti = Vt / V V = VE * (I + E) V = Flow; Vt = Tidal Volume; Ti = Inspiratory Time) I and E are the parts of the I:E ratio;		These versions of the formula reveal the interaction between time, flow and volume. In order to produce a certain volume within a certain time, a precise minimum flow must occur. The last equation features a similar formula that involves minute ventilation and the I:E ratio parts. Again, the minimum flow is calculated.
Inspiratory time, Expiratory time, Total cycle time, I:E
Ti = TCT/ (I+E) Ti = TCT - TE TCT= 60/ f E = [TCT/ Ti] -1 Ti = Inspiratory Time; TE is Expiratory Time; E = expiratory portion of the total cycle		To understand and master these formulae, the practitioner will develop deeper understanding of the relationships between time, flow and volume, so essential to the operation of the mechanical ventilator system. The practitioner must carefully determine the inspiratory time. IT is NOT the same thing as the inspiratory portion of the breathing cycle. The former is measured in seconds, but the latter is simply "parts or portions" in a ratio.
Rapid Shallow Breathing Index
RSBI = f / Vt	Greater than 105	Both of these formulae are weaning indices. A RSBI greater than 105 is predictive of weaning success. A CROP index of less than 13 indicates success.
CROP index = Cdyn * Pmax * (PaO2/PAO2)/f Cdyn = Dynamic Compliance Pmax = Max Negative Inspiratory Pressure	Less than 13
Mechanical Ventilation Tidal Volume
Routinely, 5-8 ml/Kg BW(Predicted)		Lung protection for everyone!

Physiology and Facts

Predicted Body Weight
Equation / Formula	Normal Values (21% FiO2; 760 mm Hg BP)	Comments
Males: BW (Pred, kg) = 50 + 2.3 (height (inches) - 60) Females: BW (Pred, kg) = 45.5 + 2.3 (height (inches) - 60)
Anatomical Deadspace Estimate
VDan = 1 mL / lbs IBW VDan = Anatomical Deadspace IBW = Ideal Body Weight	150 ml
Lung Compliance
Cdyn = Vt / Pawp - PEEP Cdyn = Dynamic Compliance Cstat = Vt / Pplat - PEEP Pplat = Plateau Pressure Pstat = Static Compliance Pawp = Peak Airway Pressure	Cdyn: 30 - 40 ml/cm H2O Cstat 50 - 100 ml/cm H2O	Lung compliance formulae provide numerical description for the distensibility of the lung. The inverse relationship between compliance and pressure is evident, (decreased compliance will increase pressure) as well as the linear relationship between compliance and volume (as compliance increases, tidal volume increases).
Airway Resistance
Raw = Pawp - Pplat / Flow Raw = Airway Resistance Pawp = Peak Airway Pressure Pplat = Plateau Pressure	1-2 cmH20/L/sec	Airway resistance, often mathematically shortened to Pawp - Pplateau, describes the opposition to flow of the frictional forces of the airway. Remember as Pawp - Pplateau gradient widens, Raw increases. The math will set you free on this one!
Cardiac Output
Qt = HR x SV Qt = Total Cardiac Output SV = Stroke Volume Fick Equation for Qt: Qt = VO2/ CaO2 - CvO2 VO2 = Oxygen Consumption Cardiac Index: CI = Qt / BSA BSA = Body Surface Area	Qt: 5 L/min CI: 2.4 - 4 L/min/square meter	Fairly straight forward and simple math using stroke volume and heart rate. The tried and true Fick equation is the gold standard for cardiac output calculations. Current metabolic measuring devices enable the practitioner greater ease in determining oxygen consumption. Estimates of VO2 may be assumed using: VO2 = BSA x 1.25. The cardiac index allows height and weight (BSA) to be factored.
Deadspace to Tidal Volume Ratio
VD/Vt = PaCO2 - PECO2 / PaCO2	Approximately 30%	This equation determines the percentage of ventilation that may be attributed to deadsapce ventilation.

Medical Gases

Heliox Factors
Equation / Formula	Normal Values (21% FiO2; 760 mmHg BP)	Comments
70/30 mix= 1.6 80/20 mix= 1.8		Multiplying the He/O2 factors by the liter flow set gives actual flow (L/min.) to the patient.
Compressed Oxygen Cylinder Duration
H Tanks: 3.14 x tank pressure / liter flow E Tanks: .28 x tank pressure / liter flow		Using the formula enables the practitioner to predict the duration of the tank at a given flow. Most practitioners use the safety practice of subtracting 500 from the pressure to give "reserve"". When questioned on examination one must be careful to answer the question asked... If you are requested to calculate duration, then do just that!
Liquid Oxygen Cylinder Duration
D = (860 x LOX in lbs. / 2.5) / Flow (L/m)		Simply calculate using the factor 860 (the volume of one pound of LOX) times the weight of the tank and divide by the factor 2.5 (each liter weighs 2.5 pounds). The solution will yield minutes. Divide by 60 to yield hours. Be sure to convert the fraction of hours to minutes by multiplying that by 60.
Air Entrainment Flows and Ratios
The "magic box method" 20            ??  40 100           ?? Start with 20 and 100 in the corners. Put FiO2 in the center. Next, subtract the left corners diagonally. The example gives 100 - 40 = 60 in the right upper corner; 40 - 20 = 20 in the lower right. 20            60  40 100           20 The result is 60:20 = 3:1 that is, 3 L/m air for each L/min O2 Total flow: Combine the ratios and multiply by liter flow.		The magic box is simple trick to figure the air entrainment ratio for a given FiO2. Use 20 in the upper left corner when FiO2 greater than 35% and use 21 when the FiO2 is less than 35%. You may compute total flow by combining both parts of the ratio and multiplying by the liter flow on the flowmeter. Given the total flow simply subtract the flow (from the O2 flowmeter) from it to determine the air flow. In the example on left total flow is 20. If 20 - 5 = 15, then there are 5 liters/min. oxygen plus 15 liters/min. of air. Or 3 liters of air for every 1 liter of oxygen!
Air Gas Laws
Boyle's Law P1V1 = P2V2 Charles' Law P1/T1 = P2/T2 Poiseuille's Law Q = pi*P*r4 / 8*n*l Q = Flow; P = Pressure; R = Radius n = Viscosity; l = Length (of tube) Laplace's Law P = 2T/r P = Transpulmonary Pressure T = tension in alveolar wall r = Radius Dalton's Law P1 + P2 ...		It is always useful to recall the relationships between pressure and volume, and pressure and temperature. Poiseuille's law determines the flow of a fluid / gas through a tube. It's most notable factor is the radius to the fourth power. This highlights the fact that the radius of a tube has the greatest effect on the flow within it. Laplace's law determines the effect of surface tension on flow. Dalton's Law states that the total pressure of a gas mixture is equal to the sum of the pressures of the individual gases that make up the mixture.