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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
Semi-quantitative approach: | Chloride effect
Chloride effect = Cln – Clcorrected Corrected Chloride = Clp x (Na normal /Na patient)
26
Semi-quantitative approach: | Albumin effect
Albumin effect = (Albn – Albp) x 4
27
Semi-quantitative approach: | Phosphate effect
Phosphate effect = (Phosn – Phosp) /2
28
Semi-quantitative approach: | Lactate effect
Lactate effect = Lact of patient x -1
29
Semi-quantitative approach: final equations what does + and - values mean
Add all effects together = sum XA (unmeausred) = Base excess - Sum + = alkalosis - = acidosis
30
Free water deficit
Free water deficit (L) = [ (current Na / normal Na) -1 ] x 0.6 x BWkg
31
Sodium deficit
Na deficit (mmol) = (Normal Na – Patients Na) x (0.6 x BWkg)
32
Pseudohyponatremia correction with hyperglycemia
Nacorrected = Nap + 1.6 [(Patient BG – Normal BG )/ 100] BG>400: Nacorrected = Nap + 2.4 [(Patient BG – Normal BG )/ 100]
33
Zinc toxicity
- US pennies minted after 1982 | - Canadian pennies minted between 1997-2001
34
Normals for intraabdominal pressure (IAP)
Normal less than 0-5 cm H2O (0-3.6mmHg)
35
Normal muscle pressures in dogs
5.7 +/- 5 mmHg
36
What is Kt/v
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 ```
37
Urea reduction ratio (URR)
URR = (BUNpre - BUNpost)/BUN pre x 100 | URR in %
38
Extraction ratio in dialysis
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
Clearance in dialysis
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
urinary free water clearance (%)
only if urine Na >20 mEq/L Urinary free water clearance = 1 – [(Urine Na + Urine K)/Urine Na]
41
Fraction extraction of sodium (FENa)
FENa = 100 x [ (Urine Na x Plasma Creat) / (Plasma Na x Urine Creat)] in % Normal <1%, >2-5% in ATN
42
What is urine specific gravity
= density (mass) urine compared to water (which has a SG of 1.000)
43
Clearance (renal phys)
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
Filtration fraction
Filtration fraction = GFR/RPF Dogs: 32-36% Cats: 22-42%
45
Renal plasma flow equation
RPF = Ux x V̇ / Px Dog: 7-20ml/min/kg Cat: 8-22ml/min/kg
46
Renal blood flow equation
RBF = RPF/(1-HCT)
47
carry capacity of O2 (CaO2) equation
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
What is -1.34 -0.003 in CaO2 equation
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
cardiac output equation
CO =SV x HR | in L/min
50
cardiac index equation
CO w.r.t. patient body surface area CI = CO/BSA (m2) Dogs: 3.5-5.5 L/min/m2
51
Fick's O2 consumption method of determining CO
CO = VO2 / (CaO2 – CvO2)
52
Caudal vena cava collapsibility index (CVC-CI)
CVC-CI = (Max – Min)/Max x 100 < 20% variation then hypervolemic If > 60% variation then hypovolemic
53
Mean arterial pressure
``` MAP = diastolic + [(SBP-DBP)/3)] MAP = CO x SVR ```
54
delivery of oxygen (DO2)
DO2 = CaO2 x CO | L/min
55
O2 consumption (VO2)
VO2 = CO x (CaO2-CvO2) | L/min
56
Oxygen extraction ratio (O2ER)
O2ER = VO2/ DO2 O2ER = (SaO2 – SvO2) / SaO2 O2ER = (CaO2 – CvO2)/ CaO2 Normal is about 25%
57
Systemic vascular resistance (SVR)
SVR = (MAP-CVP)/CI | mL/kg/min
58
Pulmonary vascular resistance (PVR)
PVR= (Mean PAP – PAOP)/CI
59
Shock index (SI)
SI = HR/SBP | >0.9-1 consistent with shock
60
Coronary perfusion pressure (CoPP)
CoPP = diastolic aortic pressure – right atrial pressure
61
Ohm's law
Change in pressure (P) = flow (Q) x resistance (R)
62
Poiseuille's law
Q = (πPr^4)/ (8ηl) ``` Q= flow P = pressure r= radius η = fluid viscosity l = length of tubing ```
63
Fractional shortening (FS)
FS % = [ (LVIDd- LVIDs)/LVIDd ] x 100 Normal: 35-45% dogs, 40% cats
64
Ejection fraction (EF)
EF% = [(LVEDV- LVESV)/LVEDV ] x 100
65
Modified Bernoulli equation
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
Heart chamber pressures: - RA - RV - PA - LA - LV - Aorta
* RA: mean 5mmHg * RV: 25/5 * PA: 25/10 * LA: mean 5-10 * LV: 125/10 * Ao: 125/80
67
Boyle's law
Pressure x volume is constant (at constant temperature) P1 x V1 = P2 x V2 (temperature constant)
68
Bohr's equation
Vd / Vt = (PACO2 – PECO2) / PACO2 Normal Vd/Vt around 0.2-0.35
69
Fick's law of diffusion
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
Fick's principle
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
Alveolar gas equation
PAO2 = FiO2(Pbarometric-Pwatervapor) - (PACO2/R) PAO2 = 0.21(760-49) - (PACO2/0.8)
72
A-a gradient
PAO2-PaO2 Normal <10 Abnormal >20 A-a gradient increase w/ age
73
Henry's Law
Amount dissolved is proportional to the partial pressure
74
Bohr Effect
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
Haldane Effect
Deoxygenation of the blood (low PaO2, or offloading of O2) increases Hgb’s ability to carry CO2
76
Compliance
change in volume/change in pressure L/cm H20
77
Elastance
Change in pressure / Change in volume opposite of compliance
78
Reynold's number (Re)
Re = (2rvd)/n r=radius v= average velocity d= density n= viscosity
79
Law of LaPlace
P = (2T)/r
80
PaO2/FiO2 ratio (PF ratio)
PaO2 should be approximately 5 x FiO2 Normal patient on room air 100/0.21 = 500
81
Airway pressure during inspiration: Equation of motion
Equation of motion Pvent + Pmuscle = (Δ Tidal volume/ Compliance) + (Resistance X Δ Flow)
82
Equation of motion (mechanical ventilation)
Pressure = (TV/Compliance) + (resistance x flow)
83
Dynamic compliance (mechanical ventilation)
Tidal volume/PIP - PEEP
84
Static compliance (mechanical ventilation)
Tidal volume/Pplat - PEEP
85
Resting energy requirement (RER)
RER= 70 x BWkg^0.75
86
TPN protein requirement
Dog: 15-20% or 4-6g protein/100kcal Cat: 25-30% or 6+ g protein/100kcal
87
TPN variables - Protein - Lipid - Dextrose
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
Specificity
ability to correctly ID those without disease | true neg/all without disease = true neg/(true neg + false pos)
89
Sensitivity
ability to correctly ID those with disease | true pos/all with disease = true pos/(true pos + false neg
90
Positive predictive value
Likelihood that patient with positive result has the disease | True pos/all test pos = true pos/(true pos + false pos)
91
Negative predictive value
Likelihood that patient with negative result doesn't have the disease True neg/all test neg = true neg/(true neg + false neg)
92
Cerebral perfusion pressure (CPP)
CPP = MAP - ICP Normal ICP = 5-12 mmHg Normal CPP = 50-90 mmHg
93
Inhibitory Quotient
Cmax / MIC

ACVECC boards: Journals and equations (15 decks)

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