End-tidal carbon dioxide during extremely low cardiac output.
OBJECTIVE
A number of studies have shown that expired CO2 concentration is closely related to cardiac output, but that cardiac output was not controlled as an independent variable. In addition, the partial pressure of end-tidal CO2 (PETCO2) during extremely low cardiac output has not been reported. The objective of the present study was to measure PETCO2 during well-controlled, very low blood flow rates under conditions of constant minute ventilation.


METHODS
Ten anesthetized, intubated, and mechanically ventilated swine (weight, 43 to 102 kg) were placed on two ventricular assist devices in order to control cardiac output. Minute ventilation was measured and kept constant. Ventricular assist device output (measured with an ultrasonic flow probe); PETCO2; and aortic, pulmonary artery, and central venous pressures were recorded continuously.


METHODS
After electrical induction of ventricular fibrillation, pump output was decreased in steps.


RESULTS
Cardiac index ranged from 0 to 5,371 mL/min/m2; 59% of PETCO2 measurements were made at cardiac indexes of less than 1,313 mL/min/m2 (30 mL/min/kg). The relationship of PETCO2 levels to cardiac index was determined with linear regression analysis; P < .05 was statistically significant. PETCO2 correlated significantly with cardiac index (P < .0001). The best-fit line by least-squares analysis produced the equation: PETCO2 = 4.98 + 0.012 [cardiac index] (r2 = .82).


CONCLUSIONS
Under conditions of constant minute ventilation, PETCO2 correlated closely with cardiac index over a large range of blood flow rates, including extremely low rates.
Idris
A H
AH
Department of Internal Medicine, University of Florida College of Medicine, Gainesville.
Staples
E D
ED
O'Brien
D J
DJ
Melker
R J
RJ
Rush
W J
WJ
Del Duca
K D
KD
Falk
J L
JL
D000818:Animals; D001775:Blood Circulation; D001944:Breath Tests; D002245:Carbon Dioxide / Q000032:analysis*; D002302:Cardiac Output / Q000502:physiology*; D002303:Cardiac Output, Low / Q000503:physiopathology*; D012119:Respiration; D012121:Respiration, Artificial; D013552:Swine; D013990:Tidal Volume
D002245:Carbon Dioxide