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)
Daily Maintenance Fluid
Dehydration correction
Maintenance
(BW (kg) x 30) + 70
2-4 ml/kg/hr
Dehydration
BW(kg) x %(dehydration) / 1000 = mL/L
Calculated and Effective Osmolality
Calculated
2(Na + K) + GLU/18 + BUN/2.8
Effective
2(Na) + GLU/18
Normals (mOsm/L)
DOG - 290-310
CATS - 290 - 330
Osmol Gap
Difference between the calculated and measured Osmolality
OsmGap = Measured Osm - CalcOsm
DOG - 0 to 1
CAT = 2
Anion Gap
(Na + K) - (CL + HCO3)
DOG = 8-21 CAT = 12-16
Gen. < 25
Anion Gap with correction for Low Alb
AG = (Na + K) - (CL + HCO3)
If low ALB then;
DOG = AG + 0.42 (3.77 - ALB)
CAT = AG + 0.41 (3.3 - ALB)
Anion Gap corrected for Hyperphosphatemia
AG = (Na + K) - (CL + HCO3)
If high Phosphorus, then;
AG + [(2.52 - (0.58 x Pi)]
Total Body Water
TBW = Kg x 0.6
(60% of Body weight)
Free Water Deficit
FWD = TBW x (Nam / Nan -1)
TBW = kg x 0.6
so;
Kg x 0.6 x (Nam/Nan - 1)
Nam = Na measured
Nan = Na normal (145)
Traditional Acid-Base components
Non-traditional Acid-Base components
Traditional - PCO2, HCO3, pH, AG, BE
Non-Traditional - SID, Atot, SIG, pH, PCO2
Strong Ion GAP
DOG = (ALB x 4.9) - AG CAT = (ALB x 7.4) - AG
Correct AG for Phosphorus if needed;
AG + [2.52 - (0.58 x Pi)]
Normal SIG dog = −0.09 mEq/L (−0.82–0.65 mEq/L)
Normal SIG cat = ?
Corrected Na
Nac = Nam + [1.6 x (GLUm - GLUn)/100]
An Increase of 1.6 Na / 100 mg/dL GLU above normal
or
An increase of 1.0 Na / 62 mg/dL GLU above normal
Corrected CL
CLc = CLm x (Nan/Nam)
Note, Na is the inverse of Free water deficit.
Incr. CLc in renal CL retention, RTA, Chronic resp. alkalosis
Decr. CLc in GI diseaes (v/d), Loop diuretics, Hypoadre/steroids, chronic resp. acidosis
Corrected Calcium
Cac = Ca - ALB + 3.5
Na deficit
Nad = 0.6 x Kg (Nan - Nam)
Note, here you subtract and not divide Na.
Starling Law for fluids
Revised formula
Jv = KF x [(Pc - Pi) -o [(Oc - Oi) - Qlymph
Revised for Glycocalyx
Jv = KF x [(Pc - Pi) -o [(Oc - Osg)
Osg = sub-glycocalyx
Colloidal Osmotic pressure normals
DOG = 15 - 26
CATS = 17 -33
Target therapeutic ~ 16 mmHg
Cerebral Perfusion Pressure (CPP)
CPP - MAP - ICP
Coronary Perfusion Pressure (CoPP)
CoPP = DiastAorticP - RAp
Diastolic aortic pressure
Right atrial pressure
Normal circulating pressures
LA - 5-10 mmHg
LV - 125-10 mmHg
AO - 120-80 mmHg
RA - 0-5 mmHg
RV - 25-5 mmHG
PA - 25-10 mmHg
Albumin Deficit
ALBd = 0.3 x 10 x Kg x (desiredALB - pALB)
or
3 x Kg x (desALB - pALB)
Products
FFP - 3g/100mL
Whole Blood - 1.4g/100mL
HSA 25% - 25g/100mL
CSA - 5g/100mL
Blood transfusion Calculations
Rule - 1ml/kg of pRBC raise 1% - 10mL/kg raise 10%
2ml/kg of Whole Blood raise 1% - 20ml/kg raise 10%
Kg x 90 x (Desired PCV - Patient PCV) / Donor PCV
Example - 20kg dog with PCV 15%
pRBC PCV-80%
Want to increase to 28%
20 x 90 x (28 - 15)/80
20 x 90 x 0.162
20 x 14.62 = 292.4
Bicarbonate deficit
BD = 0.3 x kg x (HCO3n - HCO3m)
Give 1/4/-1/3
Simplified quantitative approach to acid-base analysis proposed by Hopper and Haskins
(list contribution to Acid-Base + formula)
Free water effect
FWE = (Nam - Nan) / 4
or
dog = 0.25 x (Nam - Nan)
cat = 0.22 x (Nam - Nan)
Decreased free water = increased sodium = leads to alkalosis
Increased free water = decreased sodium = leads to acidosis
Simplified quantitative approach to acid-base analysis proposed by Hopper and Haskins
(list contribution to Acid-Base + formula)
Chloride effect
CLe = CLn - CLc
CLc = corrected CL
CLm x (Nan/Nam)
Low chloride promotes an alkalosis
High Chloride promotes Acidosis
Simplified quantitative approach to acid-base analysis proposed by Hopper and Haskins
(list contribution to Acid-Base + formula)
Phosphate effect
Phe = (Phn - Phm) / 2
or
0.58 x (Phn - Phm)
Increased phos promotes an acidosis
Decreased Ph promotes alkalosis
Simplified quantitative approach to acid-base analysis proposed by Hopper and Haskins
(list contribution to Acid-Base + formula)
Albumin effect
ALBe = (ALBn - ALBm) x 4
or
3.7 (ALBn - ALBm)
Low albumin promotes an alkalosis
High albumin promotes acidosis
Simplified quantitative approach to acid-base analysis proposed by Hopper and Haskins
(list contribution to Acid-Base + formula)
Lactate effect
Le = -1 x lactate
Hyperlactatemia promotes acidosis
Fractional Na Excretion
FNaE = (UNa x Pcr) / (PNa x Ucr) x 100
(UX x Pcr) / (PX x Ucr) x 100
Renal Clearance
A non-steroidal anti-inflammatory drug (X) given to a 50kg animal has a concentration of 0.05mg/mL in the plasma and 1.8mg/ml in the urine. Assuming this animal is producing 100ml of urine/hr, the renal clearance of the drug X per minute is…
(pay attention to the UNITS)
100mL/hr = 1.66 mL/min
Renal Clearance = Urine Flow x Urine [] / plasma []
1.66 x 1.8 / 0.05 = 60 mL/min
Renal Blood flow
RBF / (1 -HCT)
Renal Filtration Fraction
GFR / RBF
normal about 20%
Renal filtered load
GFR x [plasma]
Renal excretion rate
Urine flow rate x [Urine]
Renal reabsorption rate
Filtered load - excretion rate
Secretion rate
Excretion rate - filtered rate
Resting Energy Requirement
RER = (30 x kg) + 70
Total Parenteral Nutrition calculations
Dog protein required: 4-5g/100 Kcal
Cat protein requirement: 6-8g/100 Kcal
Dextrose for 30-50% remaining calories (50% dex has 1.7 Kcal/mL)
Lipid for 50-70% remaining calories (20% lipid has 2.0 Kcal/mL)
Acid-Base compensation for Metabolic Acidosis and Alkalosis
Metabolic Alkalosis (icr. HCO3) - expect resp. acidosis (icr. CO2) incr. CO2 by 0.7 mmHg for each icr. HCO3 of 1 mEq/L
Metabolic Acidosis (decr. HCO3) - expect resp. alkalosis (decr. CO2) decr. CO2 by 0.7 mmHg for each decr. in HCO3 of 1 mEq/L
Acid-Base compensation for Respiratory Acidosis and Alkalosis
Respiratory Acidosis (incr. CO2) - expect Metabolic Alkalosis (incr. HCO3)
Acute - incr of 0.15 mEq/L HCO3 for each incr CO2 of 1 mmHg
Chronic - incr. of 0.35 mEq/L HCO3 for each incr. CO2 by 1 mmHg
Respiratory Alkalosis (decr. CO2) - expect Metabolic acidosis (dedr. HCO3)
Acute - decr of 0.25 mEq/L of HCO3 for each decr. CO2 of 1 mmHg
Chronic - decr. 0.55 mEq/L og HCO3 for each decr. CO2 of 1 mmHg
Normal values for
CO
SV
DO2
VO2
CaO2
OER
SVR
PVR
MAP (dog/cat)
A-a
P:F
Qs/Qt
CO = 100-200 mL/Kg/min
SV = 9 mL/bet/min
DO2 = 20-35 mL/kg/min
VO2 = 4-11 mL/kg/min
CaO2 = 19-21 mL/dL
OER = 25%
SVR = 0.5-0.8 mmHg/mL/kg/min
PVR = 0.04 0.06 mmHg/mL/kg/min
MAP dog = 80-120 mmHg
cat = 100-150 mmHg
A-a = < 15
P:F - Normal 500
ALI < 300
ARDS < 200
Qs/Qt = <5%