Equations to know Flashcards
Fractional excretion (use Na as example but anything can be used) calculation
(UNa x PCr)/ (PNa x UCr) x 100
Renal clearance calculation
[Urine] x Urine flow rate / [Plasma]
Top should be in mg/min
Creatinine generally equals GFR
Renal blood flow calculation
Renal plasma flow / (1-HCT)
Filtration fraction calculation
GFR/ Renal plasma flow
Normal 20%
Excretion rate calculation
urine flow rate x [urine]
Reabsorption rate calculation
filtered load- excretion rate
filtered load calculation
GFR x [plasma]
secretion rate calculation
Excretion rate-filtered load
Protein requirements in dogs/cats
dog 4-5 g/ 100 Kcal
Cat 6-8 g/ 100 kcal
Fick’s law of gas diffusion
Volume of gas per unit time= area/ thickness x Diffusion constant x partial pressure difference
Calculate PAO2
FiO2 (PB - 47) - PaCO2/0.8
Generally considered at sea level and room air to be
150- PaCO2/0.8
Calculate A-a gradient
Should be done on room air
PAO2-PaO2
Normal < 15
> 15 implies V/Q mistmach
Calculate PF ration
Can be done with any FiO2 PaO2/Fio2 (decimal) Normal 5x FiO2--- 500 <300 vet ALI < 200 Vet ARDS
Calculate the shunt equation
Qs/Qt= (CcO2-CaO2) / (CcO2-CmvO2)
Normal < 5%
Calculate physiologic dead space
Bohr equation
Vd/Vt= (PaCO2- PETCO2)/PaCO2
<40% is normal with spontaneous breathing
What is lapace law
Pressure= (2 x wall thickness) / radius
Modified bernouli equation
Change in pressure= 4 x Velocity ^2
What is ohms law
Flow= change in pressure/ resistance
What is Poiseuilles law for flow
Flow= (Pi x pressure x radius^4)/ 8 x viscosisityx length
What is Poiseuilles law for resistance to flow
Resistance to flow = (8xviscosityx length) / (pi x radius^4)
Calculate Arterial oxygen content
CaO2= (Hgb x 1.34 x SaO2) + (PaO2 x 0.003)
Calculate oxygen delivery
DO2= cardiac output x CaO2
Normal 20-35 ml/kg/ min
Calculate oxygen consumption
VO2= CO x (CaO2 - CmvO2)
Normal 4-11 ml/kg/ min
Calculate oxygen extraction ratio
OER= (CaO2-CmvO2)/CaO2
Normal 20-30 %
Calculate systemic vascular resistance
(MAP-CVP)/ CO
Can put Cardiac index in for CO
Calculate pulmonary vascular resistance
PVR= (PAP-PAOP)/ CO
Normal 0.04-0.06
Calculate mean arterial pressure
[(Systolic-diastolic)/3] + Diasotolic
What is the fick principle for calculating CO
CO= VO2/ (CaO2-CmvO2)
Calculate cerebral perfusion pressure
CPP= MAP- ICP
Calculate coronary perfusion pressure
diastolic aortic pressure- right atrial pressure
What are the normal circulating pressures in the heart
RA: Mean 5 mmHg RV: 25/5 PA: 25/10 LA: 5-10 mmHg LV: 125/10 Aortic: 125/80
Calculate albumin deficit
grams= 3 x Kg x (desired albumin- actual albumin)
How much albumin is in FFP, whole blood and HSA`
FFP: 3 g/100 ml
Whole: 1.4 g/ 100 ml
HSA: 25 g/ 100 ml
Calculate pulse pressure
systolic- diastolic
changes with age
Calculate pulse pressure variation
When mecahnically venitilated
(PPmax - PP min)/ PP Mean = expressed as percentage
Max- inspiration, Min- expiration
Starling equation
Jv= K( Pc-Pi) - o ( Oncotic C - Oncotic Inter)
K= filtration coeffic
o= reflection coefficitient
P- hydrostatic pressure
Calculate shock index
Hr/ SBP
> 0.9-1 clinical diagnosis of shock
Not validated
Calculate a blood transfusion
Transfusion Amount for RBCS = [(PCV desired – PCV actual/PCV of donor/unit] x Body weight (kg) x blood volume
estimate 65% for Packed red cells if not labeled
Blood volume Dog 88 ml/kg Cats 66 ml/kg
