Respiratory Equations

NA (Sodium )

135 -145

K (Potassium)

3.5 - 4.5

Cl (Chloride)

85 - 100

RBC

5

Hb (Hemoglobin)

15

Hematocrit

45%

Vd/Vt

20-40%

CaO2

17-20%

CvO2

12-16%

C(a-v)O2

4-5%

Qs/Qt

5% normal
10-20% tolerable
20-30% life threatening

CVP

2-6 mmhg (4-12 cm H20)

PAP

25/8 mmhg (mean 14)

PCWP (Wedge=Left)

4-12 mmHg

CO

4-8 L/min

CI

2.5-4 L/min/m2

Unacceptable Vt

<5ml/kg

Unacceptable VC

<10ml/kg or (<2 x Vt)

Unacceptable RR

< 8 breaths or >20 breaths

Unacceptable Ve

>10 L/min

Unacceptable MIP (maximum inspiratory pressure

< - 20cmh20

Duration of flow for a liquid O2 system (formula)

344 (factor) x liquid wt (lbs)

80/20 heliox mixture: multiply flowmeter reading by

1.8

70/30 heliox mixyure:multiply flowmeter reading by

1.6

Absolute humidity is the amount of wtr in a given volume of gas, What is the fomula

RH = Absolute humidity/Capacity x 100
RAC = Real Active Children

Calculating Body Humidity (BH)

BH = Absolute Humidity/44mg/L x 100
BHA4 =

Calculating Humidity Deficit (HD)

HD = 44mg/L - absolute humidity
expressed as a percentage %= Humidity Deficit/44 mg/L

Calculating Alveolar PO2

PAO2 = (7 x FIO2) - (PaCO2 + 10)

Calculating P(A-a)O2

PAO2 - PaO2

Dynamic Compliance (air movement)

Exhaled volume/ PIP - PEEP

Static Compliance (no air movement)

Exhaled volume/Plateau - PEEP

VD/VT =

PaCo2 -PECO2/ PaCO2 x 100

SVR formula

(MAP - CVP/Cardiac Output
Convert to Dynes multiply by 80

PVR formula

(MPAP - PWP/Cardiac Output
convert to Dynes multiply by 80

Calculating ventilator tubing compliance (formula)

Tidal Volume/PIP

Calculating inspiratory flow rate

Tidal volume/inspiratory time

calculating I:E ratio

Inspiratory flow rate/Minute volume (Ve)

calculating Inspiratory Time

Total cycle Time/Sum of I:E ration parts

Calculating VD/VT ratio

PaCO2 - PECO2/PaCO2

Calculating airway resistance (Raw)

(PIP - Plateau pressure/Flow rate

Calculating desired ventilator rate

Rate(current setting) x PaCO2 (current value)/PaCO2 (desired value)

For Calibrating gases (For PCO2)

5% is commonly used for low value(balance) and 10% for the high (slope)

For calibrating gases (for PO20

0% for low and 12 or 20% for the high

PCO2 electrode

Severinghaus

PO2 electrode

Clark

Ph electrode

Sanz

Levey - Jennings Charts
"In Control

all the values are within 2 standard deviations of the mean

Levey - Jennings Chart
"Random Error

only 1 point falls outside the + or - standard deviation range

The A - a gradient
25-65 mm Hg on 100%

normal value
Treatment - None

The A - a gradient
66 - 300mm Hg

V/Q mismatch
Treatment -Give to 60% FIO2 only

The A - a gradient
>300

Shunting
Treatment - PEEP