Equations Flashcards
Arterial O2 Content
CaO2 = [Hg x 1.34 x SPO2] + [PaO2 x 0.003] = ml/dL
Normal = 19 - 21 mL/dL
Hg = 1/3 PCV
Cardiac Output (CO)
CO = SV x HR
100 - 200 mL/kg/min
Stroke Volume (SV)
SV = CI/HR (mL/beat/kg)
CI = CO/BSA
1.5 - 2.5 mL/beat/kg
or
EDV-ESV
Oxygen Delivery (DO2)
DO2 = CaO2 x CO
20-35 ml/kg/min
Critical DO2 = 9-10 mL/kg/min
O2 Consumption (VO2)
VO2 = CO x (CaO2 - CvO2)
4-11 ml/kg/min
CvO2 = [Hg x 1.34 x SvO2] + [PvO2 x 0.003]
Oxygen Extraction Rate (OER)
OER = VO2/DO2 x100
CO x (CaO2-CvO2)/ CO x CaO2 x 100
Cancel both CO
(CaO2-CvO2)/CaO2 x 100
Can also use SO2
(SaO2-SvO2)/SaO2 x 100
Normal = 25% (20-30)
Systemic Vascular Resistance (SVR)
(MAP-CVP)/CO (mmHg/mL/Kg/min)
0.5-0.8 mmHg/ml/kg/min
or - 1600-2500 dynes/sec/cm-5
Pulmonary Vascular Resistance (PVR)
(PAP - PAOP)/CO
mmHg/mL/kg/min
0.04-0.06 mm Hg/ml/kg/min
or - 125-250 dynes/sec/cm-5
Mean Arterial Pressure (MAP)
MAP = ((SAB-DAP)/3) + DAP
Dogs = 80-120 mm Hg
Cats = 100-150 mm Hg
or
BP = CO x SVR
Ejection Fraction (EF)
Fractional Shortening (FS)
EF = EDV-ESV / EDV (normal 70%)
FS = LVDd - LVDs / LVDd
Dog - 25-45
Cat- 30-55%
ECG
Instantaneous Heart rate
@ 50mm/sec = 3000/x
@ 25 mm/sec = 1500/x or use Square trick (image)
x = small boxes between R-R interval
Alveolar O2 content (PAO2)
PAO2 = [FiO2 x (BaroPressure - H2O pressure)] - [PaCO2/RQ]
PAO2 = [FiO2 x (760 - 47)] - [PaCO2/0.8-1]
(room air) PAO2 = [0.21 x (760 - 47)] - [PaCO2/0.8-1]
150 - [PaCO2/0.8]
A-a Gradient
PAO2 - PaO2
PAO2 (calculated) PaO2 (measured)
FiO2 x [760-47] - [PaCO2/0.8] - PaO2
< 15 is normal
P:F ratio (S:F)
PaO2:FiO2 = 500
or
SaO2:FiO2
P:F < 300 = ALI
P:F < 200 = ARDS
Respiratory Shunt Equation
Qs/Qt = [CcO2-CaO2/CcO2-CvO2] = < 5%
CcO2 (capillary O2 content) = [Hg x 1.34] + [PAO2 x 0.003]
CaO2 (arterial O2 content) = [Hg x 1.34 x SaO2] + [PaO2 x 0.003]
CvO2 (venous O2 content) = [Hg x 1.34 x SvO2] + [PvO2 x 0.003]
PAO2 - FiO2 x (760-47) - (PaCO2/0.8)
Normal is < 5%
10-20% minimaly affected
20-30% pulmonary disease
> 30% life threatning disease
or 1 - SaO2 / 1 - SvO2
Physiologic Dead Space
(Bohr’s Equation)
Vd/Vt = (PaCO2-PeCO2) / PaCO2
Can also use PetCO2 (end-tidal)
< 24%
Also PAO2-PEO2/PAO2 (alveolar)
Alveolar Ventilation (VA)
VA = TV - Vd
Fick Equation for CO
In a measurement of cardiac output using the Fick Principle, the oxygen concentration of mixed venous and arterial blood are 16 and 20 mL/100mL, respectively, and the O2 consumption is 300mL/min. The cardiac output in L/min is:
Fick Eq CO = Oxygen consumption/arteriovenous difference
CO = VO2/(CaO2-CvO2)
answer: 7.5.
Haldane effect and Bohr Effect
Haldane - offload of O2 allows more CO2 to be carried (Shift curve to the left)
Bohr effect - hemoglobin has decreased affinity for CO2 when O2 is bound (enhancement of CO2 dissociation and elimination in the lungs). A decrease in pH and increase CO2 will decrease affinity for O2 (shift curve to the right)
Henderson Hasselbalch Equation
pH = 6.1 + Log ([HCO3)]/[PaCO2 x 0.03]
Laplace Law
Pressure (P) = 2 x t / r
Wall tension (T) = P x r / 2h
P = pressure t = surface tension r = radius T = tension h = wall thickeness
Modified Bernoulli Equation
P = 4 x V(2) (power)
Used to estimate pulmonary artery pressure on echocardiography
Ohm’s Law
and
Poiseuille Equation
Q = P / R
or
P = Q x R
Q = Flow R = Resistance P = Pressure
Resistance comes from Poiseuille Equation
R = 8 x L x n / 2x(pi) x r(4)
Reynolds Number
Re = ( D x p x V ) / n
D = diameter p = Density V = velocity n = viscosity
< 2000 laminar
> 3000 turbulent
Ventilation Equation of Motion
Pressure = (TV/compliance) + (Resistence x Flow)
Lung compliance
Static and Dynamic
Compliance = DV/DP
Static compliance (remove interference of airway resistance, measure during vent. inspiratory hold.
Cstat = TV / (Pplat - PEEP)
Dynamic compliance (measured during airflow, might be less than static)
Cdyn = TV / (PIP - PEEP)