Calculations Flashcards
A-a Gradient
PAO2 - PaO2
[Alveolar oxygen pressure - arterial oxygen pressure]
Alveolar Gas Equation
PAO2 = FiO2 * (P atmosphere - P water vapor) - [PaCO2 / RQ]
PAO2 = FiO2 * (760 mmHg - 47 mmHg) - [PaCO2 / 0.8]
PAO2 = FiO2 * (713 mmHg) - [PaCO2 / 0.8]
Dynamic Compliance
Dynamic Compliance (Cdyn) = Tidal volume / [Peak Pressure - PEEP]
Minute Ventilation
MV = RR * TV
Calculation to predict PaO2 by age
110 - (age * 0.4)
Reynold’s Number
R = [Velocity * Density * Diameter] / Viscosity
Static Compliance
Static Compliance (Cstat) = TV / [Plateau Pressure - PEEP]
Transpulmonary Pressure
TPP = Alveolar Pressure - Pleural Pressure
Transthoracic Pressure
TTP = Pleural Pressure - Atmospheric Pressure
Dead Space to Tidal Volume Ratio
Vd / Vt Ratio
Vd / Vt
Cardiac Output
CO = HR * SV
Coronary Perfusion Pressure
CPP = DBP - LVEDP (or PAOP)
Ejection Fraction
EF = [End-Diastolic Volume - End-Systolic Volume] / End-Diastolic Volume
Fick Principle
CO = (VO2 / [CaO2 - CvO2]) * 100
Law of LaPlace (Cylinder)
Wall Tension (Cylinder) = [Pressure * Radius] / Wall Thickness
Law of LaPlace (Sphere)
Wall Tension (Sphere) = [Pressure * Radius] / [2 * Wall Thickness]
Maximum Allowable Blood Loss
ABL = EBV * ([starting HgB - target Hgb] / starting Hgb)
Mean Arterial Pressure
MAP = [SBP + (2*DBP)] / 3
Oxygen Carrying Capacity
CaO2
CaO2 = (Hgb * SaO2 * 1.34) + (PaO2 * 0.003)
Oxygen Delivery
DO2
DO2 = (Hgb * SaO2 * 1.34) + (PaO2 * 0.003) * CO * 10
Oxygen Extraction Ratio
ER
ER = Oxygen consumption / Oxygen delivery
Poiseuille’s Law
Flow
Flow = (pi * Radius^4 * deltaP) / (8 * viscosity * length)
Pulmonary Vascular Resistance
PVR = [(Mean PA Pressure - PAOP) / CO] * 80
PAOP = pulmonary artery occlusion pressure
Pulse Pressure
SBP - DBP
Systemic Vascular Resistance
SVR = [(MAP - CVP) / CO] * 80
Stroke Volume (2 equations)
SV = (CO * 1000) / HR
SV = End-Diastolic Volume - End-Systolic Volume
ETT Size for Children (Uncuffed)
uncuffed ETT size = [age / 4] + 4
ETT Size for Children (Cuffed)
cuffed ETT size = [age / 4] + 3.5
O2 Remaining in Oxygen E-Cylinder
2 Steps
Step 1
Tank Capacity (L) / Full Tank Pressure (psi) = Contents Remaining (L) / Gauge Pressure (psi)
660 L / 1900 psi = contents remaining (L) / gauge pressure (psi)
Step 2
Contents Remaining (L) / Flow Rate (L/min) = Minutes Left
Fraction of Inspired Oxygen
FiO2 = [(oxygen flow rate * 100) + (air flow rate * 21) / total flow rate]
3 Types of Gas Tanks
- air
- oxygen
- nitrous oxide
Air Gas Tank
volume / pressure / pin
Air Tank
volume = 625 L
pressure = 1900 psig
pin = 1-5
Oxygen Gas Tank
volume / pressure / pin
Oxygen Tank
volume = 660 L
pressure = 1900 psig
pin = 2-5
Nitrous Oxide Gas Tank
volume / pressure / pin
Nitrous Oxide Tank
volume = 1590 L
pressure = 745 psig
pin = 3-5
Cerebral Perfusion Pressure
CPP = MAP - ICP
CPP = MAP - CVP (or ICP, whichever is higher)
Anion Gap
Anion gap = [Na+] - ([Cl-] + [HCO3-])
Plasma Osmolarity
plasma osmolarity = (2 * [Na+]) + (glucose / 18) + (BUN / 2.8)
What are the 4 gas laws
- Boyle’s Law
- Gay Lussac’s Law
- Charles’ Law
- Ideal Gas Law
Boyle’s Law
P1 * V1 = P2 * V2
Gay Lussac’s Law
P1 / T1 = P2 / T2
Charles’ Law
V1 / T1 = V2 / T2
Ideal Gas Law
pressure * volume = # moles * 0.0821 * temperature
PV = nRT
pressure in atm * volume in L = # mol * 0.0821 * temp in K
Celsius
C = (F - 32) * (5/9)
Dalton’s Law
P total = P1 + P2 + P3 …
Farenheit
F = (C * 1.8) + 32
Henderson - Hasselbalch
pH = pK + log [HCO3- / (0.03 * PaCO2)]
Henry’s Law
PP = constant * concentration
Inverse Square Law
Intensity = 1 / Distance^2
Volume of Distribution
Vd = dose in mg / concentration in mg/L
Vd = amount of drug in the body / plasma drug concentration
Half Life
Half-life = Vd / rate of clearance
