Equations to know

Question 1

Fractional excretion (use Na as example but anything can be used) calculation

Answer 1

(UNa x PCr)/ (PNa x UCr) x 100

Question 2

Renal clearance calculation

Answer 2

[Urine] x Urine flow rate / [Plasma]
Top should be in mg/min
Creatinine generally equals GFR

Question 3

Renal blood flow calculation

Answer 3

Renal plasma flow / (1-HCT)

Question 4

Filtration fraction calculation

Answer 4

GFR/ Renal plasma flow

Normal 20%

Question 5

Excretion rate calculation

Answer 5

urine flow rate x [urine]

Question 6

Reabsorption rate calculation

Answer 6

filtered load- excretion rate

Question 7

filtered load calculation

Answer 7

GFR x [plasma]

Question 8

secretion rate calculation

Answer 8

Excretion rate-filtered load

Question 9

Protein requirements in dogs/cats

Answer 9

dog 4-5 g/ 100 Kcal

Cat 6-8 g/ 100 kcal

Question 10

Fick’s law of gas diffusion

Answer 10

Volume of gas per unit time= area/ thickness x Diffusion constant x partial pressure difference

Question 11

Calculate PAO2

Answer 11

FiO2 (PB - 47) - PaCO2/0.8
Generally considered at sea level and room air to be
150- PaCO2/0.8

Question 12

Calculate A-a gradient

Answer 12

Should be done on room air
PAO2-PaO2
Normal < 15
> 15 implies V/Q mistmach

Question 13

Calculate PF ration

Answer 13

Can be done with any FiO2
PaO2/Fio2 (decimal)
Normal 5x FiO2--- 500 
<300 vet ALI
< 200 Vet ARDS

Question 14

Calculate the shunt equation

Answer 14

Qs/Qt= (CcO2-CaO2) / (CcO2-CmvO2)

Normal < 5%

Question 15

Calculate physiologic dead space

Bohr equation

Answer 15

Vd/Vt= (PaCO2- PETCO2)/PaCO2

<40% is normal with spontaneous breathing

Question 16

What is lapace law

Answer 16

Pressure= (2 x wall thickness) / radius

Question 17

Modified bernouli equation

Answer 17

Change in pressure= 4 x Velocity ^2

Question 18

What is ohms law

Answer 18

Flow= change in pressure/ resistance

Question 19

What is Poiseuilles law for flow

Answer 19

Flow= (Pi x pressure x radius^4)/ 8 x viscosisityx length

Question 20

What is Poiseuilles law for resistance to flow

Answer 20

Resistance to flow = (8xviscosityx length) / (pi x radius^4)

Question 21

Calculate Arterial oxygen content

Answer 21

CaO2= (Hgb x 1.34 x SaO2) + (PaO2 x 0.003)

Question 22

Calculate oxygen delivery

Answer 22

DO2= cardiac output x CaO2

Normal 20-35 ml/kg/ min

Question 23

Calculate oxygen consumption

Answer 23

VO2= CO x (CaO2 - CmvO2)

Normal 4-11 ml/kg/ min

Question 24

Calculate oxygen extraction ratio

Answer 24

OER= (CaO2-CmvO2)/CaO2

Normal 20-30 %

Question 25

Calculate systemic vascular resistance

Answer 25

(MAP-CVP)/ CO | Can put Cardiac index in for CO

Question 26

Calculate pulmonary vascular resistance

Answer 26

PVR= (PAP-PAOP)/ CO | Normal 0.04-0.06

Question 27

Calculate mean arterial pressure

Answer 27

[(Systolic-diastolic)/3] + Diasotolic

Question 28

What is the fick principle for calculating CO

Answer 28

CO= VO2/ (CaO2-CmvO2)

Question 29

Calculate cerebral perfusion pressure

Answer 29

CPP= MAP- ICP

Question 30

Calculate coronary perfusion pressure

Answer 30

diastolic aortic pressure- right atrial pressure

Question 31

What are the normal circulating pressures in the heart

Answer 31

``` RA: Mean 5 mmHg RV: 25/5 PA: 25/10 LA: 5-10 mmHg LV: 125/10 Aortic: 125/80 ```

Question 32

Calculate albumin deficit

Answer 32

grams= 3 x Kg x (desired albumin- actual albumin)

Question 33

How much albumin is in FFP, whole blood and HSA`

Answer 33

FFP: 3 g/100 ml Whole: 1.4 g/ 100 ml HSA: 25 g/ 100 ml

Question 34

Calculate pulse pressure

Answer 34

systolic- diastolic | changes with age

Question 35

Calculate pulse pressure variation

Answer 35

When mecahnically venitilated (PPmax - PP min)/ PP Mean = expressed as percentage Max- inspiration, Min- expiration

Question 36

Starling equation

Answer 36

Jv= K( Pc-Pi) - o ( Oncotic C - Oncotic Inter) K= filtration coeffic o= reflection coefficitient P- hydrostatic pressure

Question 37

Calculate shock index

Answer 37

Hr/ SBP > 0.9-1 clinical diagnosis of shock Not validated

Question 38

Calculate a blood transfusion

Answer 38

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