Hemodynamic monitoring in obese patients: the impact of body mass index on cardiac output and stroke volume.

OBJECTIVE: Interpreting hemodynamic parameters in critically ill obese patients can be difficult as the effects of body mass index (BMI) on cardiac output (CO) and stroke volume (SV) at the extremes of body size remains unknown. We examined the relationship between BMI and both CO and SV for patients with varying body sizes.
DESIGN: Retrospective cohort analysis.
SETTING: A large tertiary care academic medical center. PATIENTS: A total of 700 consecutive adults who were found to have disease-free coronary arteries and a cardiac output measurement (thermodilution or Fick method) during coronary angiography between July 1, 2000, and July 31, 2004. MEASUREMENTS AND
RESULTS: We examined the relationship between BMI (mean, 28 kg/m(2); range, 10.6-91.6 kg/m(2)) and cardiac hemodynamics after adjusting for demographic (age, sex) and clinical (diabetes, smoking status, valvular heart disease, medications, indications for catheterization) characteristics using multivariable regression. Body mass index was positively correlated with CO and SV. Each 1 kg/m increase in BMI was associated with a 0.08 L/min (95% confidence interval [CI], 0.06-0.10; p < .001) increase in CO and 1.35 mL (95% CI, 0.96-1.74; p < .001) increase in SV. There was no significant association between BMI and both cardiac index (0.003 L/min/m(2); 95% CI, -0.008-0.014; p = .571) and stroke volume index (0.17 mL/m(2); 95% CI, -0.03-0.37; p = .094).
CONCLUSION: Variations in BMI translate into predictable but only modest differences in CO and SV, even at the extremes of body size. Indexing hemodynamic measurements to body surface area attenuates the effects of BMI. Body habitus should not appreciably complicate the interpretation of hemodynamic measurements.