Page 733 - Clinical Application of Mechanical Ventilation

Appendix 1 699

P. VAsCulAr resistAnCe: systemiC

EQUATION
80
SVR = (MAP - R A) *
CO
SVR : Systemic vascular resistance in dyne sec/cm 5
MAP : Mean arterial pressure in mm Hg*
RA : Mean right atrial pressure in mm Hg
80 : Conversion factor from mm Hg/L/min to dynes sec/cm 5
#
CO : Cardiac output in L/min (Q )
T
NORMAL VALUE
SVR 5 800 to 1,500 dyne sec/cm 5

EXAMPLE
A patient has the following measurements. What is the calculated systemic vascular
resistance (SVR)?
MAP 5 70 mm Hg
RA 5 8 mm Hg
CO 5 5.0 L/min
80
SVR = (MAP - RA) *
CO
80
= (70 - 8) *
5.0
80
= 62 *
5.0
4,960
=
5
= 992 dyne.sec/cm 5

Q. VENTILATOR RATE NEEDED FOR A DESIRED PaCO 2

EQUATION 1
Rate * P CO
New Rate = a 2
Desired P CO 2
a
EQUATION 2
(Rate * P CO ) * (V - V )
New Rate = a 2 T D
Desired P CO * (New V - New V )
a
2
T
D
New rate : Ventilator rate needed for a desired PaCO 2
Rate : Original ventilator rate per minute
PaCO : Original arterial carbon dioxide tension in mm Hg
2
Desired PaCO : Desired arterial carbon dioxide tension in mm Hg
2
V : Original tidal volume
T
V : Original deadspace volume
D

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