Flow dependency of error in thermodilution measurement of cardiac output during acute tricuspid regurgitation.
OBJECTIVE
To evaluate the effect of variable degrees of tricuspid regurgitation on thermodilution cardiac output measurements during changes in venous return.


METHODS
Prospective, controlled animal study.


METHODS
University laboratory.


METHODS
Eight anesthetized mongrel dogs instrumented for simultaneous measurement of cardiac output by thermodilution and ascending aortic electromagnetometry.


METHODS
Data were collected before and after induction of moderate and severe tricuspid regurgitation. Under each condition, measurements were obtained at baseline and after opening 2 peripheral arteriovenous shunts to increase venous return.


RESULTS
Baseline electromagnetic flow ranged from 1.74 to 3.62 L/min (median 2.73 L/min). Moderate and severe regurgitation reduced median electromagnetic flow values by 31% and 51%. Applying generalized estimating equations to model thermodilution cardiac output as a function of electromagnetic flow, arteriovenous shunt, and severity of tricuspid regurgitation revealed that (1) moderate and severe regurgitation changed the slope and intercept of the thermodilution/electromagnetic regression, but the differences between them were not significant, and (2) arteriovenous shunt alone had no effect under any condition. A simplified model independent of shunt and containing just 2 levels of tricuspid regurgitation (none or present) crossed with electromagnetic flow was applied. This analysis showed that regurgitation caused thermodilution to significantly underestimate electromagnetic flow at cardiac outputs > 2.27 L/min (99 mL/kg/min) and overestimate it at flows < 1.02 L/min (44 mL/kg/min).


CONCLUSIONS
These data show that acute tricuspid regurgitation may produce underestimation of cardiac output by thermodilution when flow is relatively high, produce overestimation when flow is relatively low, or have minimal effect when flow is in the midrange.
Heerdt
P M
PM
Department of Anesthesiology, New York Presbyterian Hospital-Weill Medical College at Cornell University, New York, NY, USA.
Blessios
G A
GA
Beach
M L
ML
Hogue
C W
CW
D000818:Animals; D001166:Arteriovenous Shunt, Surgical; D002302:Cardiac Output / Q000502:physiology*; D004285:Dogs; D004562:Electrocardiography; D013815:Thermodilution; D014262:Tricuspid Valve Insufficiency / Q000503:physiopathology*; D014682:Vena Cava, Inferior / Q000502:physiology