Measuring Cardiac Output:

A New Respiratory Method

David PreissInstitute for Biomaterials and Biomedical Engineering

University of TorontoDepartment of AnesthesiaUniversity Health Network

November 29, 2004

Introduction – Cardiac Output

Swan-Ganz Catheter

Non-Invasive: The Fick Equation

CvCO2 CaCO2

VCO2

22 COCO2CO

Ca-Cv

VC.O.

Fick Equation:

Change Ventilation to get CvCO2

Breathing Rate

Final Lung CO2

concentration

Mixed venous arterial

CO2 level

Time

Problem creating change in CO2

Time

Intubated, Ventilated

?

Time

Spontaneous Breathing

Change in CO2 in Awake Patients

• Must be independent of ventilation

• No physical manoeuvre

• Comfortable

Constant O2 flow

Exhaling…

Exhaling…

Exhalation ends

Inhalation starts…

Valve opens

Rebreathing

Rebreathing

Deeper breath

Problem Solved!

CO2 level

Time

Flow

Flow

Problem Solved!

Breathing Rate

Final Lung CO2

concentration

Mixed venous arterial

• Compare with direct measurements

• 3 pilot studies: – Jan, 2003 (32 patients)– June, 2003 (36 patients)– Feb, 2004 (37 patients)

• Patients were conscious and extubated

Evaluating the Method

Comparison with Invasive Methods

0

1

2

3

4

5

6

7

8

10 20 30 40 50 60

Time (min)

C.O

. (L

/min

) Catheter

Non-Invasive

Comparison with Invasive Methods

0

2

4

6

8

10

12

14

0 10 20 30 40 50

Time (min)

C.O

. L/m

in

Catheter

Non-Invasive

Results – 1st and 2nd cohorts

y = 1.0028x + 0.609

R2 = 0.7393

0

2

4

6

8

10

12

14

0 2 4 6 8 10 12 14

Catheter (L/min)

No

n-I

nv

as

ive

(L

/min

)

Results – 3rd cohort

y = 0.8367x + 0.4694

R2 = 0.8637

0

2

4

6

8

10

12

14

0 2 4 6 8 10 12 14

Catheter (L/min)

No

n-I

nva

sive

(L

/min

)

SD = 0.80 L/min

• Periodic breathing• Good seal around mouth required• Requires supply of compressed air• Pain for some patients – deeper breaths

Limitations

Future Work

• Larger range of cardiac outputs• Exercise

• Patients in poorer health• Alveolar deadspace• Shunt

Thanks!

Joseph Fisher MD

Arthur Slutsky MD

Jim Duffin PhD

Al Olszowka MD

Takafumi Azami MD

Cliff Ansel MBA

Ludwik Fedorko MD PhD

George Djaiani MD

Jo Caroll RN

Marat Slessarev

Steve Iscoe PhD

Ron Somogyi MSc

Hiroshi Sasano MD

CVICU Nursing StaffUniversity Health Network