Physics & Equations Flashcards
(104 cards)
1
Q
Alveolar Oxygen Equation
A
PAO2 = FIO2 (PB-PAH2O) - (PACO2/R) - PAO2 = Alveolar Pressure of Oxygen FIO2 = 21% or 0.21 PB = 760mmHg PH2O = 47mmHg PACO2 = 40mmHg R = Quotient = 0.8 - Always assume STP unless otherwise stated
2
Q
Oxygen Consumption
A
(0.07) 7% consumption * 5,000mL/min = 350mL/min
-
Avg. for a 70K patient is about 250 mL a minute
3
Q
Minute Ventilation
A
VE = VT * f
Minute Ventilation = Tidal Volume * Breaths Per Minute
VE = Minute Ventilation VT = Tidal Volume f = Flow
4
Q
Oxygen Content Equation (CaO2)
A
CaO2 = 1.36 x Hb x Sat. + .0031 x PaO2
Sat. = %/100
PaO2 = variable provided in question
Hb = variable provided in question
CaO2 normal values are between 16 - 22 mlO2/dl
5
Q
Lung, Thorax Compliance Calculation
A
CLT = Delta V / Delta PAW
CLT - Compliance of the Lung and Thorax in ml/cmH2O
Delta V - Change in volume of Thorax
Delta PAW - Change in airway pressure
Normal Compliance is 200 for each CL and CT
6
Q
Individual Compliances
A
1/CLT = 1/CL + 1/CT
7
Q
Metabolic Jumping Off Point (oxygen consumption)
A
VO2 = Weight in Kg^0.75 * 10
10 is the assumed RR
8
Q
Respiratory Quotient
A
R = VCO2/VO2
VCO2 = VO2 * R
R = 0.8 for a metabolically normal euthermic patient VCO2 = 250ml/min in an euthermic patient
9
Q
Fractional Concentration
A
Fx = Px / Ptot
Fx = Fraction of Concentration Px = Partial Pressure Ptot = Pressure Total
10
Q
Ideal Alveolar Pressure for CO2 in a eucapnic patient
A
40mmHg
11
Q
Pressure of all gases in the Alveoli under dry conditions
A
Ptot = Pbar (dry)
737mmHg (Bar, Atlanta) - 47mmHg (PH2O @ 37°C)
12
Q
Alveolar Ventilation
A
Px/Ptot = Vx/Vtot or Paco2/Pbar = Vaco2/Va Partial Alveolar (CO2)/Pressure Total (atm) = Vol (CO2)/Vol total
13
Q
Pressure
A
P = F/a
F = Force a = area (pi * r^2)
14
Q
1 mmHg is equal to
A
1.36 cmH2O
15
Q
760 mmHg is equal to
A
101.33 Kpa
1013.3 mbar
1033.6 cmH2O
14.7 psi
1 atm
16
Q
1 atm is equal to
A
101.33 Kpa
1013.3 mbar
760 mmHg
1033.6 cmH2O
14.7 psi
17
Q
101.33 Kpa is equal to
A
1013.3 mbar 760 mmHg 1033.6 cmH2O 14.7 psi 1 atm
18
Q
14.7 psi is equal to
A
760 mmHg 101.33 Kpa 1013.3 mbar 1 atm 1033.6 cmH2O
19
Q
1033.6 cmH2O is equal to
A
1 atm 760 mmHg 101.33 Kpa 1013.3 mbar 14.7 psi
20
Q
Pressure in a tube (Laplace)
A
Ptube = T/r
T = Tension r = radius
21
Q
Pressure in a sphere (Laplace)
A
Psphere = 2T/r
T = Tension r = radius
22
Q
Equation for Flow
Equation for Resistance
A
F = Q/t
Q = Quantity (volume or mass) t = time
Flow is directly proportional to pressure. The ratio of pressure to flow is resistance, R = P/Q
23
Q
Mean Blood Pressure
A
(S-D)/3 + D
24
Q
Body Surface Area
A
Height^0.725 * Weight^0.425 * 0.007184
Height in cm
Weight in Kg
BSA in m^2
25
How is viscosity is measured
Pascal Seconds
26
How to calculate flow with viscosity variable
Q = [(pi)(r^4) (delta P)] / 8nL
Delta P = Pressure Loss
n = viscosity
Q = volumetric flow rate
L = Length of pipe
27
How to calculate pressure with viscosity variable
Delta P = 8QnL / (pi)(r^4)
Delta P = Pressure Loss
n = viscosity
Q = volumetric flow rate
L = Length of pipe
28
Reynolds Number
R = vpd / n
v = velocity
p (rho) = density
d = diameter
n = viscosity
If the Reynolds number is greater than 2000 turbulent flow is more likely to occur. Below 2000 results in more laminar flow.
29
Entrainment Ratio
Entrained Flow / Driving Flow
30
Calculate FiO2 w/ Entrainment Ratio of 9:1 with 2L O2
FiO2 = [1 * 2 liters of O2 + .21 * 18 liters of air] / 20
31
FiO2 Equation
FiO2 = [1 * liters of O2 + .21 * liters of air] / total flow
32
What units are used to measure Tension?
newtons per square meter
33
Volume of Conducting Airways (Deadspace)
2.2 mL/Kg (or) 1 mL/lb
34
Ventilation of Anatomic Deadspace
Ventilation = Volume * f
f = respiratory rate
35
Minute Ventilation
MV = (Alveolar Ventilation) + (Deadspace Ventilation)
36
1 inch is equal to
2.54 cm
37
Charles' Law of Gas Constants
PV = nRT
(or)
V/T = nR/P ===> V1/T1 = V2/T2
38
Don's Law (barf)
P1/T1 = P2/T2
39
STP
Standard Temperature and Pressure
```
T = 273 K, 0°C
P = 760 mmHg
```
40
RTP
Room Temperature and Pressure
```
T = 293 K, 20°C
P = 760 mmHg
```
41
BTP
Body Temperature and Pressure
```
T = 310 K, 37°C
P = 760 mmHg
```
42
Volume and Pressure and Color of an O2 E-Cylinder
```
Volume = 660
Pressure = 2000psi
Color = Green
```
43
Volume and Pressure and Color of an N2O E-Cylinder
```
Volume = 1590
Pressure = 750
Color = Blue
```
44
Volume and Pressure Color of an Air E-Cylinder
```
Volume = 625
Pressure = 1800
Color = Yellow
```
45
Boyle's Law of Gas Constants
P1V1 = P2V2
Used to determine the remaining gas in a tank
46
Flow
Time Constants
Volume/Time
Volume/Flow
47
Hematocrit
Red Cell Volume/Blood Volume
Hematocrit of 40 means that 40% of the blood is red blood cells
48
Estimated Blood Volume (EBV) Constants
80-90 mL/Kg for Infants
70-75 mL/Kg for Males
60-65 mL/Kg for Females
49
Estimated Red Cell Volume (ERCVi)
= Estimated Blood Volume (EBV) x Hematocrit Initial (Hct(i))
50
Estimated Red Cell Volume Accepted (ERCVa)
= Estimated Blood Volume (EBV) x Hematocrit accepted (Hcta)
51
How to calculate Red Cell Volume Loss (RCVL)
ERCVi - ERCVa
52
How to calculate the Estimated Blood Loss Accepted (EBLa)
[(Hcti - Hcta)/Hct avg] * EBVi = EBLa
53
Blood Loss Replacement Values
Whole Blood, FFPs, RBCs = 1:1
Colloids [Albumin, Hydroxyethyl starch (Hespan, Hextend)] = 1:1
Crystalloids (NS, LR, D5W, Plasmalyte, etc.) = 3:1
54
Values for Time Constants
Each time constant will reduce the remaining amount to 36.78% of the previous value. After 2 time constants there will be a remainder of 13.52% of the initial value.
```
e^3 = 4.98% remaining or 95.02% complete
e^4 = 1.83% remaining or 98.17% complete
e^5 = 0.7% remaining or 99.3% complete
```
55
Circulatory Time Constants
Based on the fact that the heart can circulate TBV in 1 minute (blood volume/cardiac output) = 1, time constants can be represented in intervals of 1 minute
56
Pulmonary Time Constants
Pulmonary time constants are also 1 minute based on the fact that you are dividing the total volume by the minute ventilation, which comes out to 6/6 = 1
57
Circuit Time Constants
Circuit Volume = 5L
Time constant = Volume / Flow
At 1 L/min, time constant is 5/1 = 5 minutes
At 2 L/min, time constant is 5/2 = 2.5 minutes
Increasing sevo from 2% to 3% will give you a concentration of 2.63% of sevo in the circuit after 1 time constant
58
Pulmonary time constants with "wash in" curve function
1 - e^-x = 1 - (1/e^x)
59
Definition of Diffusion
The process by which the molecules of a substance transfer through a layer or area such as the surface of a solution. Diffusion can also refer to the spreading of gas molecules to evenly fill a space or container.
60
Fick's Law of Diffusion
States that the rate of diffusion of a substance across unit area (such as a surface or membrane) is proportional to the concentration gradient..
(larger gradient = faster diffusion)
61
Examples of conditions where the use of N2O might be hazardous
```
Air Embolism
Pneumothorax
Acute Intestinal obstruction
Intracranial Air
Pulmonary Air Cysts
Intraocular Air Bubbles
Tympanic Membrane Grafting
```
62
Graham's Law
States that the rate of diffusion of a gas is inversely proportional to the square root of its molecular weight.
Smaller molecular weight compounds diffuse faster
Larger molecular weight compounds diffuse slower
63
Henry's Law
States that at a particular temperature, the amount of a given gas dissolved in a given liquid is directly proportional to the partial pressure of the gas in equilibrium with the liquid.
64
Effect of Temperature on Solubility
As temperature increases, solubility decreases
65
Bunsen Solubility Coefficient
The volume of gas, corrected to STP, which dissolves 1 unit volume of the liquid at the temperature concerned, where the partial pressure of the gas above the liquid is 1 standard atmosphere pressure.
66
Ostwald Solubility Coefficient
The volume of gas which dissolves in 1 unit volume of the liquid at the temperature concerned.
This is independent of pressure, unlike the Bunsen coefficient
67
Vapor pressure in mmHG of agents at 20°C
```
Nitrous Oxide = 38517
Halothane = 243
Isoflurane = 238
Desflurane = 664
Sevoflurane = 160
```
68
Vapor concentration in volume % of agents at 20°C
```
Nitrous Oxide = ( )
Halothane = 32
Isoflurane = 31
Desflurane = 87
Sevoflurane = 21
```
69
MAC of agents in 100% O2
```
Nitrous Oxide = 105
Halothane = 0.75
Isoflurane = 1.15
Desflurane = 6.0 - 7.25
Sevoflurane = 1.6 - 2.6
```
70
MAC Pressures
Take the MAC % and divide by 100, then multiply by 760
71
Blood/Gas Coefficients
```
Nitrous Oxide = 0.47
Halothane = 2.4
Isoflurane = 1.4
Desflurane = 0.42
Sevoflurane = 0.65
```
72
Three factors affecting anesthetic uptake in lungs
Solubility of agent in blood
Alveolar Blood Flow/Cardiac Output
Difference in partial pressure between venous blood and alveolar gas
73
Ways to increase the rate of induction
Increase concentration of agent
| Augmented inflow effect (second gas effect)
74
Potency
Potency is directly related to the fat/gas coefficient, however MAC% is also a relative indication of potency. The lower the MAC% the higher the potency will be.
75
MAC awake
0.3 - 0.4 MAC
76
MAC Bar (blocks adrenergic response)
1.5 - 2 MAC
77
MAC 1.3
ED95, which means that it will prevent response to stimuli in 95% of all patients in relation to volatiles
78
MAC (minimum alveolar concentration)
The alveolar concentration that prevents movement in 50% of patients (ED50) in response to a standardized stimulus (eg, surgical incision).
79
Water weight % at birth and 1 year
75% at birth
| 65% after 1 year
80
Water weight % of adult men and women
```
Men = 60%
Women = 50%
```
The higher fat content in females decreases water content. For the same reason, obesity and advanced age further decrease water content.
81
Adult daily water intake and output
Intake matches output
Intake = 2500 mL
Output = 1500 mL urine, 400 mL skin evaporation, 400 mL respiration, 100 mL sweat, 100 mL feces
82
Body fluid storage
Intracellular fluid = 40%
| Extracellular fluid = 20% (interstitial = 15%, Intravascular = 5%)
83
Exchange of fluid between compartments depends on
Permeability of that substance
Concentration gradient
Pressure difference
Electrical potential for charged substances
84
BMI
Weight in KG / Height in m^2
85
Scalar
Representable by position on a scale or line and only having magnitude
86
Vector
A quantity possessing both magnitude and direction, represented by an arrow. The arrow indicates the direction of the quantity. The length of the arrow is proportional to the magnitude.
87
Acceleration
delta V / delta T
Change in velocity over change in time
88
(Devine) Ideal Body Weight Male
W = 50 + (H (in) - 60) x 2.3
89
(Devine) Ideal Body Weight Female
W = 45.5 + (H (in) -60) x 2.3
90
(Broca) Ideal Body Weight
Height in cm - 100
91
Volume of a cylinder
pi * r^2 * length
92
Volts, Amps, Ohms
```
Volts = Unit of measure for driving force of electrons
Amps = Unit of measure for flow of electrons
Ohms = Unit of measure for resistance to flow of electrons
```
93
Ohms Law
V = I * R
94
Power
Measured in Watts
P = I * V = Watts
95
Cardiac Output
CO = Stroke Volume * Heart Rate
96
FiO2 with supplemental oxygen
0.21 + 3% per liter/min of supplemental oxygen
97
Half Life
equal to 0.69th of a time constant
half life = 50% wash out
time constant = 63% wash out
98
Pressure
P = Flow / Resistance
similarly, V = I * R (current * resistance)
99
Resistance
R = Pressure/Flow = Pressure/ (Volume/Time) = PT/V
100
Time Constant
Equal to volume undergoing washout / flow of perfusing fluid
101
BMI Classifications
```
Severe Starvation = less than 16
Under Weight = 16 - 18.49
Normal = 18.5 - 25
Over Weight = greater than 25 - 30
Obese = greater than 30 - 40
Morbidly Obese = greater than 40
```
102
Functional Residual Capacity (FRC)
35 ml/kg
103
I to E ratio calculations
Divide seconds in a minute (60) by breaths per minute to obtain the seconds per breath. Add the total units of the ratio (1:2 --> 1+2=3). Divide seconds per breath by the total of units to obtain the inspiration time. Multiply this value by the expiration ratio to get the expiration time.
104
Pleural Pressure equation
Pleural Pressure = AW pressure x CL/(CL + CT)
