Equations Flashcards by Meagan Goates

Altitude effect on PaO2

(Barometric pressure 1-47)(FiO2) =(barometric pressure 2-47 (FiO2)

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A-A gradient (pAO2-paO2)

[FiO2x (barometric pressure-47)- (paCO2/0.8)] -paO2

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Alveolar minute ventilation

(TV-dead space) x RR

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Anion gap

NA - (cl + bicarb)

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Cardiac output

HR x SV

SBP/ total peripheral vascular resistance

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Cerebral blood flow

Cerebral perfusion pressure /cerebral vascular resistance

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Cerebral perfusion pressure

Mean arterial pressure- intracranial pressure

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Conpliance

Change in Volume /change in pressure

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Physiologic dead space (Bohr)

[(Arterial CO2 -expired CO2)/arterial CO2] x TV

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Elastance

Change in pressure/change in volume

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FENa or urinary fractional secretion or Na:

[Urine Na] x [plasma creatinine] /
[urine creatinine] x [plasma Na]

X100

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Laminar flow

Change in pressure /Resistance

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Resistance

8 x viscosity x length / pie x radius^4

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Glomerular filtration rate

0.45 x height (cm) / plasma creatinine

(For premature infants use 0.33 instead of 0.45)

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Hardy Weingburg equilibrium

P + q =1

P^2 + 2pq + q^2 = 1

P = population frequency of dominant allele
q = population frequency of recessive allele

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Henderson- Hasselbach equation

[H+] = 24 x CO2 / bicarbonate

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Laplace law

Distending pressure = 2 x surface tension/ radius

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Mean Airway Pressure

K (PIP-PEEP) x [i-time / (I-time + e-time)] + peep

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Minute ventilation

TV x RR

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Osmolality

2(plasma Na) + (glucose/18) + (BUN/2.8)

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O2 content of blood

[1.34 x Hb x O2 sat] + [0.003 x PaO2]

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Oxygen consumption (Fick principle)

CO x (arterial O2 content - venous O2 content)
CO x (1.34) x Hb x (arterial O2 Sat -venous O2 Sat)

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Oxygen delivery

Cardiac output x O2 content

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Oxygenation index

MAP x FiO2 (full like 100)/
PaO2

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Ponderal index

Weight (grams)/ (Crown-heel^3) X100

Power

Work x frequency

Pulmonary to systemic blood flow ratio

Aorta O2 Sat - superior vena cava O2 Sat/ Pulm venous O2 Sat- pulm artery O2 sat

Pulmonary vascular resistance

Mean pulmonary pressure - mean left atrial pressure / Pulmonary blood flow

Renal clearance

Urinary concentration of solute x (urinary volume/ length of time collected)/ Plasma concentration of solute

Resistance

Change in pressure /change in flow

Saturation level for cyanosis

HbO2/ Reduced Hb + HbO2

Shortening fraction

LV diastolic dimension- LV systolic dimension / LV diastolic dimension x 100

Intrapulmonary shunt equation

O2 content pulm cap- O2 content systemic art/ O2 content pulm cap- O2 content mixed venous

Systemic vascular resistance

Mean aortic pressure -mean right atrial pressure / systemic blood flow

Na deficit

Na desired -Na current x 0.6 x weight

Time constant

Resistance x Conpliance

Work of breathing

Pressure x volume

Clearance of drug

Elimination rate constant x volume of distribution

Elimination half life

0.693 x Vd/ Clearance of drug

Elimination rate constant

Clearance of drug / Volume or distribution

Loading dose

Volume of distribution x plasma concentration/ Fraction of drug which is active x fraction of drug which is bioavailable

Steady state concentration

Infusion rate / Volume of distribution x elimination rate constant

Volume of distribution

Total amount of drug in body/ Plasma concentration of drug x weight

Attributable risk or risk difference

[A/a+b ] - [c/c+d]

Attributable risk%

Attributable risk / [a/ (a+b)] X 100

False negative

1- sensitivity

False positive

1- specificity

Incidence cumulative

# of new cases of disease in a given time period/ total population at risk

Incidence rate

# of new cases of disease in a give time period / person-time years of observation

Positive likelihood ratio

Sensitive / (1- specificity)

Negative likelihood

(1-sensitivity) / specificity

Mean

Sun of observations/ # of observations

Mortality rate , BW

Deaths in a specific BW category / # of births in same BW category x 100

Mortality rate fetal

Fetal deaths / Live births + fetal deaths X100

Mortality rate infant

Infant deaths / Live births x 100

Mortality rate, neonatal

Neonatal deaths (<28 days)/ Live births X100

Mortality rate perinatal

Fetal deaths greater or equal to 28 wks GA + neonatal deaths less than 7 days / Live births + fetal deaths greater than equal 28 wks gestation X 100

Negative predictive value

D/ (c+d) (true negative / false and true negative)

Number needed to treat

1 /[ c/ (c + d) - a/( a+b)]

Odds ratio

a x d/ b x c

Positive predictive value

a / (a+b) ( true positive / true and false positive)

Power

1- type II error (probability or rejecting the null hypothesis when the alternative hypothesis is true)

Prevalence

# of new cases at a point in time/ total population risk

Risk ratio or relative risk

[a/a+b] / [c/c+b]

Sensitivity

a / a+c (TP/ TP+ FN) Fan blows the toilet paper in denominator )

Specificity

D/ d+c ( true negative / (false positive + true negative) (tin man holds the flower pot in the denominator)

Standard deviation

Square root of variance

Standard error of the mean

Standard deviation / square root of number