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EQUATIONS Flashcards

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1
Q

Blood flow

A

Q (flow rate) =  P (pressure difference, Pi-Po) / R (resistance to flow)

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2
Q

Venous return

A

Venous return =
(Mean systemic filling pressure – right atrial pressure) / resistance to venous flow = (MSFP-RAP)/Rv

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3
Q

Poiseuille

A

R = 8Ln/pi x r^4

R = resistance to flow
r = inner radius
L = tube length
n = fluid viscosity

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4
Q

Starling

A

Jv = K[(Pc-Pi) - s(pc-pi)]

Jv = fluid movement (mL/min)
Kf = constant (filtration coefficient) (mL/min/mmHg)
Pc = capillary hydrostatic pressure (mmHg)
Pi = interstitial hydrostatic pressure
s = protein reflection coefficient (no unit)
pc = capillary oncotic pressure
pi = interstitial oncotic pressure

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5
Q

Fick principle

A

X (rate of transport) = Q (blood flow) x (Xa (arterial concentration) - Xv (venous concentration))

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6
Q

Oxygen delivery

A

DO2 (mL O2/min)
= CO (mL blood/min) x CaO2 (mL O2/mL blood)
= (HR (beats/min) x SV (mL)) x [(Hb (g/dL) x 1.34 (mL O2/g) x SaO2 (no units)) + (PaO2 (mmHg) x 0.003 (mL O2/mmHg/dL blood)]/100

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7
Q

Ejection fraction

A

(Stroke Volume/End Diastolic Volume) x 100 = (EDV-ESV)/EDV x 100

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8
Q

Conversion of mmHg into cmH2O

A

value in mmHg * 1.36 = value in cmH2O

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9
Q

Fractional shortening

A

(FS%) = [(LVIDd – LVIDs)/LVIDd] X100

Normal is > or = 40%

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10
Q

Bernoulli equation

A

Pressure gradient = 4 * velocity^2

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11
Q

O2 extraction ratio

A

O2ER = VO2/DO2 = (CaO2 - CmvO2)/CaO2

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12
Q

VO2 (oxygen consumption)

A

VO2 = CO*(CaO2-CvO2)

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13
Q

Equation of lymph flow

A

QL = (Pint + Pump - Psv)/RL

Pint = interstitial hydrostatic pressure
Ppump = driving pressure generated by intrinsic contraction and extrinsic compression of lymphatic vessels
Psv = systemic venous pressure
RL = resistance to lymph flow

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14
Q

Cardiac index

A

CO (ml/kg/min) / body surface area (m2)

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15
Q

SVR

A

(MAP - CVP)/CO

or

(MAP - right atrial pressure) / cardiac index

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16
Q

Pulmonary vascular resistance

A

(mean PAP - pulmonary wedge pressure) / cardiac output

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17
Q

Coronary perfusion pressure

A

CPP = ADP - RADP

(ADP = aortic diastolic pressure, RADP = right atrial diastolic pressure)

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18
Q

Free water deficit formula

A

Free water deficit (L) = [(current Na / normal Na)-1] * 0.6 * body weight (kg)

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19
Q

Sodium deficit formula

A

Sodium deficit (mmol) = (target Na+ - patient Na+) * 0.6 * body weight (kg)

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20
Q

Urinary free water clearance formula

A

Urinary free water clearance = Urine volume * [1-(urine Na + urine K) / serum Na]

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21
Q

Urinary fractional excretion of sodium (FeNa) formula

A

FeNa (%) = 100 * (urine Na * plasma creat) / (plasma Na * urine creat)

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22
Q

Bicarbonate deficit equation

Study These Flashcards
A

HCO3 deficit (mmol) = 0.3 * body weight (kg) * base excess (mmol/L)

or HCO3 deficit (mmol) = 0.3 * body weight (kg) * (normal HCO3 - patient HCO3) (mmol/L)

23
Q

General formula for SIG

Study These Flashcards
A

SIG = SID - (HCO3 + Atot)

24
Q

What weight loss is expected in an anorexic patient

Study These Flashcards
A

0.1-0.5 kg/d/1000 kcal of energy requirements

25
Osmolality
2 (Na+) + (BUN / 2.8) + (Glu / 18) mmol/L (when BUN and glu are in mg/dL)
26
Effective osmolality/tonicity
2 (Na+) + (Glu / 18) (when glu is in mg/dL)
27
Physiologic dead space
Vd = Vt x [(PACO2 - PECO2)/PACO2] PACO2 = PCO2 of alveolar gaz PECO2 = PCO2 of expired air
28
Laplace's law
Pressure = (2 x surface tension) / alveolar radius
29
Henry's Law
Partial pressure = concentration of dissolved gas / solubility coefficient * Solubility coefficient = 0.024 (O2) & 0.57 (CO2)
30
A-a gradient
A-a gradient = PAO2 - PaO2 Long version: PAO2 (mmHg) = [FiO2 (no unit) x (Pb-Pwater vapor) (mmHg) - PACO2 (mmHg) / R (no unit))] = [0.21 x (760-47) - (PACO2/R)] = 150 - (PACO2/R) Short version: A-a gradient = [150 - (PACO2/R)] = PaO2 * R = respiratory coefficient - normal 0.8
31
Oxygenation index
OI = 100 * (MaP * FIO2)/PaO2 Where MaP = mean airway pressure Lower number indicates better lung function Can use oxygen saturation index where PaO2 is replaced by SpO2
32
Venous admixture calculation ("shunt fraction")
Qs/Qt = (CcO2 - CaO2) / (CcO2 - CvO2) Qs = "shunt fraction" Qt = cardiac output (Qs/Qt = venous admixture) CcO2 = oxygen content of end-capillary blood (calculated from PcO2 which is estimated to be the same as PAO2, needs to be calculated depending on FiO2 - ScO2 is then determined based on dissociation curve) CaO2 = oxygen content of arterial blood CvO2 = oxygen content of mixed venous blood (can be estimated with central venous blood) Should be less than 5% ; greater than 10% indicates venous admixture issues (low V/Q or zero V/Q or anatomic shunt)
33
Alveolar minute ventilation
RR * (Vt - Vd) Vt = tidal volume Vd = dead space
34
Equation of motion
Pvent + Pmuscles = elastance * volume + resistance *flow + PEEP
35
Dynamic and static compliance formulas
Cdyn = Vt/(PIP-PEEP) Cs = Vt/(Pplat-PEEP)
36
Corrected chloride
Measured Cl x (normal Na/measured Na)
37
Corrected Na
Measured Na + [1.6 x (Glu (mmol/L) – 5.6)/5.6] --> using mmol/L Measured Na + [1.6 x (glu - 100)/100] --> using mg/dl
38
CVC collapsibility equation
CVCcl = (CVCd max - CVCd min) / CVCd max
39
Albumin deficit
Albumin deficit (g) = 10 * 0.3 * BW (kg) * (desired albumin - patient albumin) (g/dL)]
40
What is the formula for urinary clearance of free water
Cfw = Vu * [1 - (urine Na + urine K) / plasmaNa]
41
Formula for Se, Sp, PPV, NPV
- Sensitivity = True positives / All positives = True positives / (True positives + False negatives) - Specificity= True negatives / All negatives = True negatives / (True negatives + False positives) - PPV = True Positives / (True positives + False positives) - NPV = True negatives / (True negatives + False negatives)
42
Formula for positive likelihood ratio and negative likelihood ratio
Positive Likelihood Ratio = Sensitivity / (1-Specificity) Negative Likelihood Ratio = (1- Sensitivity) / Specificity
43
Formula for the accuracy of a binary test
Accuracy = (True positive + True negative) / (True positive + False positive + True negative + False negative)
44
Cerebral perfusion pressure Cerebral blood flow Cerebral vascular resistance
CPP = MAP - ICP CBF = CPP/CVR CVR = 8Ln/(pi)r4 (Poiseuille)
45
What is the formula to calculate volume of pRBC to transfuse based on the desired PCV
V (mL) = [(desired PCV - patient PCV) / donor unit PCV] * blood volume (L/kg) * BW (kg) (Or V = desired PCV rise * 1.5 * BW)
46
What is the formula to calculate dose of canine albumin to transfuse based on the desired albumin
Dose (g) = 10 * (desired albumin - patient albumin) * BW (kg) * 0.3
47
Formula for % hemolysis of a blood unit
% hemolysis = (100 - Hct) * (plasma Hb / total Hb)
48
Fick's law of diffusion
Diffusion rate ~ (surface area * gas solubility * pressure gradient) / (membrane thickness * molecular weight's square root)
49
Formula for renal clearance of a substance
Clearance (mL/min) = [urine concentration (mg/mL) * urine output (mL/min)] / plasma concentration (mg/mL)
50
How to calculate urine volume based on bladder measurement
Vurine (mL) = [L * W * (dl + DT)/2] * 0.52 L = length in longitudinal W = width in transverse dl = depth in longitudinal DT = depth in transverse
51
A patient is on the ventilator in volume control with Vt 250 mL, RR 20 brpm, I:E 1:2, PEEP 5 cmH2O. His PIP is 12 cmH2O and his Pplat is 11 cmH2O. What is his resistance and compliance?
1. Resistance R = (PIP-Pplat) / flow Flow = Vt / Tinsp Tinsp = (60/RR) / 3 = 1 sec -> R = (12-11)/0.25 = 4 cmH2O/L/s 2. Compliance C = Vt / (Pplat - PEEP) -> C = 0.25/(11-5) = 0.042 L/cmH2O = 42 mL/cmH2O
52
You have the following patient data: - SaO2 = 96% - PaO2 = 99 mmHg - HR = 160 bpm - SV = 20 mL - Hct = 40% - BW = 30 kg Calculate DO2
DO2 = (HR (beats/min) x SV (mL)) x [(Hb (g/dL) x 1.34 (mL O2/g) x SaO2 (no units)) + (PaO2 (mmHg) x 0.003 (mL O2/mmHg/dL blood)]/100 DO2 = 3200 mL blood / min x 18 mL O2 / dL blood = 3200 mL blood / min x 0.18 mL O2 / dL blood = 576 mL O2 / min (= 19.2 mL O2 / min / kg)
53
How to calculate pulse pressure variation? What value is associated with fluid responsiveness?
PPV (%) = 100*(PPmax-PPmin)/[(PPmax + PPmin)/2] Values >10% associated with fluid responsiveness, values >13% correlate with hypotension and fluid responsiveness

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