Calculations Flashcards by Diamond Ling

Altitude effect on paO2

=(pB#1 - pH2O) x FiO2#1
=(pB#2 - pH2O) x FiO2#2

B# - barometric pressure in location 1&2
pB at sea level = 760mmHg
pH2O = atmospheric pressure of water = 47mmHg

How well did you know this?

Not at all

Perfectly

Alveolar-arterial gradient of oxygen

=pAO2 - paO2
=[FiO2x(pB-pH2O)] - (paCO2/R) - paO2
R = 0.8
pB = 760mmHg @ sea level

How well did you know this?

Not at all

Perfectly

Alveolar gas equation

[FiO2(pB-pH2O)] - (paCO2/R)

How well did you know this?

Not at all

Perfectly

pH2O

47mmHg

How well did you know this?

Not at all

Perfectly

R - Respiratory Quotient

0.8 (usually)

How well did you know this?

Not at all

Perfectly

Alveolar minute ventilation (VA)

(tidal volume - dead space volume) x RR

How well did you know this?

Not at all

Perfectly

Cardiac Output

=Heart rate x SV
=SBP/Total peripheral vascular resistance

How well did you know this?

Not at all

Perfectly

Cerebral blood flow

=Cerebral perfusion pressure/
Cerebral vascular resistance

How well did you know this?

Not at all

Perfectly

Cerebral perfusion pressure

Mean arterial pressure - intracranial pressure

How well did you know this?

Not at all

Perfectly

Compliance

Change in volume (ml)/
Change in pressure (cmH2O)

How well did you know this?

Not at all

Perfectly

Dead space, physiologic
(Bohr equation)

=[(arterial CO2 - expired CO2)/
arterial CO2] x tidal volume

How well did you know this?

Not at all

Perfectly

Elastance (inverse compliance)

Change in pressure (cmH2O)/
Change in volume (ml)

How well did you know this?

Not at all

Perfectly

Urinary fractional excretion of Na(%)
(FENA)

(Urine [Na]x plasma [Cr]) x100/
(Urine [Cr] x plasma [Na])

How well did you know this?

Not at all

Perfectly

FENA interpretation

<1% = normal
1-2.5% = pre renal
>3% = intrinsic renal failure

How well did you know this?

Not at all

Perfectly

GFR

(0.45xheight(cm))/
Plasma Cr (mg/dl)
= ml/min

Preterm: change 0.45 to 0.33

How well did you know this?

Not at all

Perfectly

Hardy Weinberg Equilibrium

p + q = 1
p^2 + 2pq + q^2 = 1

Henderson - Hesselbach equation

[H+] = (24xpCO2)/[HCO3]

Laplace’s Law

Distending pressure =
2xsurface tension/radius

Mean Airway Pressure

K(PIP - PEEP)x[i-time/(i-time + E-time] + PEEP

K = constant (unspec)

Minute ventilation

Tidal volume x RR

Plasma osmolality

2x(plasma [Na+] + glucose/18 + BUN/2.8

Glucose mg/dl
BuN mg/dl

Normal 285-295 mOsm/kg

O2 content of blood

Bound to Hb + dissolved

Bound = [(1.34mlO2/gHb)xHb(g/dl)xO2 sat
Dissolved = [(0.003mlO2/mmHg/dl)xpaO2 (mmHg)]

Newborn Hb higher affinity - 1.37

Oxygen consumption
(Fick’s principle)

COx (arterial O2 content) - (venous O2 content)

CO = dl/min cardiac output
Hb g/dl

Oxygen Delivery
(ml/kg/min)

CO x O2 content

Oxygenation Index

(MAP x FiO2)x100/post ductal paO2

Poiseulle's law for laminar flow

[Change in pressure x (BIG π) x radius^4] / [8(length x viscosity)]

Ponderal index

Weight(g)x100/[(crown-heel)^3] Crown and heel in cm Low PI if asymmetric growth

Pulmonary to systemic blood flow ratio (Qp/Qs)

=PBF/SBF =[Aorta O2sat - mixed venous O2sat]/[left atrial or pulm venous O2sat - pulm artery O2sat] Pulse ox = aorta O2sat No lung disease, Pulm O2sat = 100%

Pulmonary vascular resistance

(Mean pulmonary artery pressure - mean left atrial pressure)/PBF

Renal clearance (ml/min)

(UxV)/P U = urinary [solute] (mg/dl) V = urinary volume/length of time collected (ml/min) P = plasma [solute] (mg/dl)

Resistance

Change in pressure (cmH2O)/ Change in flow (L/sec)

Saturation level for cyanosis

= % O2sat = HbO2/(reduced Hb + Hb O2)

Shunt equation, intrapulmonary

=Qs/Qtotal Qs = shunted blood Qs = O2 content pulm cap - O2 content systemic arterial Qtotal = O2 content pulm cap - O2 content mixed venous O2 content pulm cap: (Hbx1.34xSAlveolar)+(PAlv760x0.003)

Systemic vascular resistance

(mean aortic pressure - mean right atrial pressure)/SBF

Sodium deficit

[Na+ desired - current (mEq/L)] x 0.6 x weight (kg) 0.6 = volume distribution (L/kg)

Time constant

Resistance (cmH2O/ml/sec) x compliance (ml/cmH2O)

Free water deficit

4ml x weight x [desired change in serum Na]

Tubular reabsorption of phosphate

(1-[(urine Px serum Cr)/(serum Px urine Cr)])x 100

Volume transfusion

Desired ∆hct x 1.6 x weight (kg)