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ACVECC boards: Journals and equations > Equations > Flashcards

Equations Flashcards

1
Q

Osmolality

Equation for calculated osmolality

A

number of solute particles (osmoles) in 1 kg of solvent
mOsm/kg

2xNa + BUN/2.8 + BG/18

  • 2x NA to account for Cl and HCO3
  • Divided to convert from mg/dL -> mmol/L
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2
Q

Osmolarity

A

number of solute particles (osmoles) per 1L of solvent

mOSm/L

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3
Q

Normal osmolarity in dogs and cats

A

Dogs: 290-3010 mOsm/L
Cats: 311-322 mOsm/L

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4
Q

Tonicity

Equation for calculated effective osmolality

A

Only accounts for effective osmoles, i.e. those that don’t freely permeate most cell membranes

2xNa + BG/18
(since BUN is an ineffective osmole)

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5
Q

Osmole gap equation

A

Osmole gap = measured - calculated osmolality

Gap > 10 mOsm/kg indicates presence of unmeasured solutes

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6
Q

Albumin deficit equation

A

albumin deficit (grams) = 10 x (desired-patient alb) x BW in kg x 0.3

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7
Q

FFP dose to increase albumin

A

22.5 mL/kg to raise albumin by 0.5 g/dL

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8
Q

Blood transfusion calculation (2)

A

90 ml x kg BW x ([desired PCV- patient PCV]/ PCV of donor blood)

1.5 ml x % PCV rise x kg BW

donor PCV usually 70-80%

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9
Q

Old and new Starling’s equation

A

Old: Jv = Kfc [( Pcap – Pint) – σ (πplasma – πint)]

New: Jv = Kfc [( Pcap – Pint) – σ (πplasma – πisg)]

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10
Q

What is:

  • Kf
  • σ
A

Kf= capillary filtration coefficient
-dictates membrane permeability (to water) and membrane surface area.

σ = reflection coefficient

  • describes the fact that a small amount of protein leaks from the capillary and depends on the interstitial protein content
  • Close to 1 (e.g. BBB) = impermeable to proteins
  • Close to 0 (e.g. liver sinusoidal) = freely permeable
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11
Q

reflection coefficient in:

  • liver
  • kidney
  • lungs
A

Liver: 0

Kidney, brain: 1

Lungs: ~0.5 due to significant leak of protein
-Protein leak decreases as interstitial oncotic pressure rises, limiting further edema formation

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12
Q

Normal Colloid osmotic pressure (COP) in dogs and cats

A

Dogs 15.3-26.3 mmHg
Cats: 17.6-33.1 mmHg
(20 average for both)

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13
Q

Henderson-Hasselback

A

pH = 6.1 x log [ (HCO3-) / (0.03 x PCO2)]

6.1 = pKa in body fluids
HCO3 in mEq/L or mmol/L
0.03 = solubility coefficient of CO2 in plasma
PCO2 in mmHg

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14
Q

Carbonic acid equation

A

CO2 + H2O H2CO3 H+ + HCO3-

Carbonic anhydrase catalyzes first half (intracellularly)

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15
Q

Anion gap

A

AG = (Na+K) - (Cl+HCO3-)

Not reliable if patient is hypoalbuminemic

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16
Q

Normal anion gap for dogs and cats

A

Dog: 12-24mEq/L
Cat: 17-31mEq/L

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17
Q

Expected compensation for metabolic disorders

A
  • Metabolic Acidosis ↓1mEq/L HCO3 = 0.7mmHg PCO2↓ +/-3

* Metabolic Alkalosis ↑1mEq/L HCO3 = 0.7mmHg PCO2↑ +/-3

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18
Q

Expected compensation for respiratory disorders

A

Acute Resp Acidosis ↑1mmHg PCO2 = 0.15mEq/L HCO3↑ +/- 2
Acute Resp Alkalosis ↓1mmHg PCO2= 0.25mEq/L HCO3 ↓ +/- 2
Chronic Resp Acidosis ↑ 1mmHg PCO2 = 0.35mEq/L HCO3 ↑ +/-2
Chronic Resp Alkalosis ↓1mmHg PCO2 = 0.55mEq/L HCO3↓ +/-2

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19
Q

Sodium bicarbonate dose

A

Sodium Bicarb dose (mmol/L) = 0.3 x BWkg x Base deficit (mmol/L)

Give a fraction to start
8.4%NaHCO3 is hyperosmolar (2000 mOsm/L) therefore must at least dilute 1:3

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20
Q

Stewart’s approach:

  • Apparent strong ion difference (SID)
  • Effective SID
  • Simplified SID
A

Apparent SID: (Na+ K+ Ca + Mg) – (Cl + other strong anions)

Effective SID: Atot- (albumin, phosphate) + HCO3

Simplified SID = (Na) – (Cl)

Normal: 38-40

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21
Q

Stewart’s approach:

-ATOT

A

ATOT = Alb + Phos

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22
Q

Stewart’s approach:

  • Strong ion gap (SIG)
  • Corrected AG for hyperPhos?
A

SIG = (Na+ K+ Cl + HCO3) – Atot
should be 0

SIG dogs = (alb x 4.9)- AG
SIG cats = (alb x 7.4) - AG

AG corrected = AG + (2.52 - 0.58xPhos)

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23
Q

Semi-quantitative approach:

5 effects

A

Free water effect, chloride effect, albumin effect, phosphate effect, lactate effect

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24
Q

Semi-quantitative approach:

Free water effect

A

Free water effect = (Nap - Nan) / 4

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25
Q

Semi-quantitative approach:

Chloride effect

A

Chloride effect = Cln – Clcorrected

Corrected Chloride = Clp x (Na normal /Na patient)

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26
Q

Semi-quantitative approach:

Albumin effect

A

Albumin effect = (Albn – Albp) x 4

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27
Q

Semi-quantitative approach:

Phosphate effect

A

Phosphate effect = (Phosn – Phosp) /2

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28
Q

Semi-quantitative approach:

Lactate effect

A

Lactate effect = Lact of patient x -1

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29
Q

Semi-quantitative approach:
final equations
what does + and - values mean

A

Add all effects together = sum

XA (unmeausred) = Base excess - Sum
+ = alkalosis
- = acidosis

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30
Q

Free water deficit

A

Free water deficit (L) = [ (current Na / normal Na) -1 ] x 0.6 x BWkg

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31
Q

Sodium deficit

A

Na deficit (mmol) = (Normal Na – Patients Na) x (0.6 x BWkg)

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32
Q

Pseudohyponatremia correction with hyperglycemia

A

Nacorrected = Nap + 1.6 [(Patient BG – Normal BG )/ 100]

BG>400:
Nacorrected = Nap + 2.4 [(Patient BG – Normal BG )/ 100]

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33
Q

Zinc toxicity

A
  • US pennies minted after 1982

- Canadian pennies minted between 1997-2001

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34
Q

Normals for intraabdominal pressure (IAP)

A

Normal less than 0-5 cm H2O (0-3.6mmHg)

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35
Q

Normal muscle pressures in dogs

A

5.7 +/- 5 mmHg

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36
Q

What is Kt/v

A

Describes efficacy of dialysis with 1.2 as a minimum recognized standard adequacy

K= dialyzer clearance of urea 
t= dialysis treatment time
v= volume of distribution of urea
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37
Q

Urea reduction ratio (URR)

A

URR = (BUNpre - BUNpost)/BUN pre x 100

URR in %

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38
Q

Extraction ratio in dialysis

A

ER (%) = (Conc In – Conc Out)/ Conc In

  • Percentage of a substance removed in a single pass through the dialyzer or device
  • Measure in blood entering and then leaving the system
39
Q

Clearance in dialysis

A

Clearance = Blood flow rate (Qb) x ER

volume of blood complete cleared of a certain solute during a single pass through the device (identical to concept of clearance in the kidney)

common substances used: urea, Cr, phos, viB12 and inulin

40
Q

urinary free water clearance (%)

A

only if urine Na >20 mEq/L

Urinary free water clearance = 1 – [(Urine Na + Urine K)/Urine Na]

41
Q

Fraction extraction of sodium (FENa)

A

FENa = 100 x [ (Urine Na x Plasma Creat) / (Plasma Na x Urine Creat)]

in %
Normal <1%, >2-5% in ATN

42
Q

What is urine specific gravity

A

= density (mass) urine compared to water (which has a SG of 1.000)

43
Q

Clearance (renal phys)

A

Cx = (Ux x V̇)/Pax

Cx = clearance of x
Ux = urinary concentration of x 
V̇ = urine flow rate
Pax = arterial plasma concentration of x

*Same equation for GFR except x is Cr

44
Q

Filtration fraction

A

Filtration fraction = GFR/RPF

Dogs: 32-36%
Cats: 22-42%

45
Q

Renal plasma flow equation

A

RPF = Ux x V̇ / Px

Dog: 7-20ml/min/kg
Cat: 8-22ml/min/kg

46
Q

Renal blood flow equation

A

RBF = RPF/(1-HCT)

47
Q

carry capacity of O2 (CaO2) equation

A

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

With units
CaO2 = (1.34ml O2/g x Hgb g/dl x SaO2 %) + (0.003 ml o2/dl/mmHg x PaO2 mmHg)

CaO2 units = mL O2/dL

48
Q

What is
-1.34
-0.003
in CaO2 equation

A
  1. 34 ml O2/g = normal oxygen carrying capacity of Hgb

0. 003 (ml O2/dl/mmHg) = solubility coefficient of oxygen at body temp

49
Q

cardiac output equation

A

CO =SV x HR

in L/min

50
Q

cardiac index equation

A

CO w.r.t. patient body surface area
CI = CO/BSA (m2)

Dogs: 3.5-5.5 L/min/m2

51
Q

Fick’s O2 consumption method of determining CO

A

CO = VO2 / (CaO2 – CvO2)

52
Q

Caudal vena cava collapsibility index (CVC-CI)

A

CVC-CI = (Max – Min)/Max x 100

< 20% variation then hypervolemic
If > 60% variation then hypovolemic

53
Q

Mean arterial pressure

A 
MAP = diastolic + [(SBP-DBP)/3)]
MAP = CO x SVR
54
Q

delivery of oxygen (DO2)

A

DO2 = CaO2 x CO

L/min

55
Q

O2 consumption (VO2)

A

VO2 = CO x (CaO2-CvO2)

L/min

56
Q

Oxygen extraction ratio (O2ER)

A

O2ER = VO2/ DO2

O2ER = (SaO2 – SvO2) / SaO2

O2ER = (CaO2 – CvO2)/ CaO2

Normal is about 25%

57
Q

Systemic vascular resistance (SVR)

A

SVR = (MAP-CVP)/CI

mL/kg/min

58
Q

Pulmonary vascular resistance (PVR)

A

PVR= (Mean PAP – PAOP)/CI

59
Q

Shock index (SI)

A

SI = HR/SBP

>0.9-1 consistent with shock

60
Q

Coronary perfusion pressure (CoPP)

A

CoPP = diastolic aortic pressure – right atrial pressure

61
Q

Ohm’s law

A

Change in pressure (P) = flow (Q) x resistance (R)

62
Q

Poiseuille’s law

A

Q = (πPr^4)/ (8ηl)

Q= flow
P = pressure
r= radius
η = fluid viscosity 
l = length of tubing
63
Q

Fractional shortening (FS)

A

FS % = [ (LVIDd- LVIDs)/LVIDd ] x 100

Normal: 35-45% dogs, 40% cats

64
Q

Ejection fraction (EF)

A

EF% = [(LVEDV- LVESV)/LVEDV ] x 100

65
Q

Modified Bernoulli equation

A

ΔP = 4 x velocity^2

The modified Bernoulli equation converts the measured velocity (m/s) of a jet of tricuspid or pulmonic insufficiency to an estimate of the pulmonary artery pressure in the absence of an outflow obstruction:

66
Q

Heart chamber pressures:

  • RA
  • RV
  • PA
  • LA
  • LV
  • Aorta
A
  • RA: mean 5mmHg
  • RV: 25/5
  • PA: 25/10
  • LA: mean 5-10
  • LV: 125/10
  • Ao: 125/80
67
Q

Boyle’s law

A

Pressure x volume is constant (at constant temperature)

P1 x V1 = P2 x V2 (temperature constant)

68
Q

Bohr’s equation

A

Vd / Vt = (PACO2 – PECO2) / PACO2

Normal Vd/Vt around 0.2-0.35

69
Q

Fick’s law of diffusion

A

V̇gas = (A/T) x D x (P1-P2)

D (diffusion constant) = Solubility / (square root of the MW)
Vgas = movement of volume of gas per unit

70
Q

Fick’s principle

A

Q̇ = V̇O2 / (CaO2 - CVO2)

-Used to calculate the volume of blood passing through the lungs each minute (what all the cardiac output measurements are ultimately derived from)

71
Q

Alveolar gas equation

A

PAO2 = FiO2(Pbarometric-Pwatervapor) - (PACO2/R)

PAO2 = 0.21(760-49) - (PACO2/0.8)

72
Q

A-a gradient

A

PAO2-PaO2

Normal <10
Abnormal >20
A-a gradient increase w/ age

73
Q

Henry’s Law

A

Amount dissolved is proportional to the partial pressure

74
Q

Bohr Effect

A

Increased CO2 (PaCO2) will decrease the affinity of hemoglobin for O2 (right-shifted) and oxygen will more easily be unloaded at the capillaries

-Effect of PCO2 attributed to its action on [H+]

75
Q

Haldane Effect

A

Deoxygenation of the blood (low PaO2, or offloading of O2) increases Hgb’s ability to carry CO2

76
Q

Compliance

A

change in volume/change in pressure

L/cm H20

77
Q

Elastance

A

Change in pressure / Change in volume

opposite of compliance

78
Q

Reynold’s number (Re)

A

Re = (2rvd)/n

r=radius
v= average velocity
d= density
n= viscosity

79
Q

Law of LaPlace

A

P = (2T)/r

80
Q

PaO2/FiO2 ratio (PF ratio)

A

PaO2 should be approximately 5 x FiO2

Normal patient on room air 100/0.21 = 500

81
Q

Airway pressure during inspiration:

Equation of motion

A

Equation of motion

Pvent + Pmuscle = (Δ Tidal volume/ Compliance) + (Resistance X Δ Flow)

82
Q

Equation of motion (mechanical ventilation)

A

Pressure = (TV/Compliance) + (resistance x flow)

83
Q

Dynamic compliance (mechanical ventilation)

A

Tidal volume/PIP - PEEP

84
Q

Static compliance (mechanical ventilation)

A

Tidal volume/Pplat - PEEP

85
Q

Resting energy requirement (RER)

A

RER= 70 x BWkg^0.75

86
Q

TPN protein requirement

A

Dog: 15-20% or 4-6g protein/100kcal
Cat: 25-30% or 6+ g protein/100kcal

87
Q

TPN variables

  • Protein
  • Lipid
  • Dextrose
A

1) Protein: 4 kcal/g
Protein: 8.5% aa solution = 0.085g/ml
= 0.34kacl/ml

2) Lipid: 20% Lipid emulsion = 2kcal/ml
3) Dextrose: 50% dextrose solution = 1.7 kcal/ml

88
Q

Specificity

A

ability to correctly ID those without disease

true neg/all without disease = true neg/(true neg + false pos)

89
Q

Sensitivity

A

ability to correctly ID those with disease

true pos/all with disease = true pos/(true pos + false neg

90
Q

Positive predictive value

A

Likelihood that patient with positive result has the disease

True pos/all test pos = true pos/(true pos + false pos)

91
Q

Negative predictive value

A

Likelihood that patient with negative result doesn’t have the disease
True neg/all test neg = true neg/(true neg + false neg)

92
Q

Cerebral perfusion pressure (CPP)

A

CPP = MAP - ICP

Normal ICP = 5-12 mmHg
Normal CPP = 50-90 mmHg

93
Q

Inhibitory Quotient

A

Cmax / MIC

ACVECC boards: Journals and equations (15 decks)

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