Right ventricular function assessed by thermodilution technique during apnea and mechanical ventilation.

OBJECTIVES

To evaluate strategies for thermodilution-based measurement of cardiac output and right ventricular (RV) ejection fraction and to assess the effects of controlled mechanical ventilation in patients. Furthermore, to compare strategy-associated reproducibility with reference values obtained during long-term apnea.

DESIGN

Crossover trial in patients; reference values from apneic animals.

SETTING

University ICU and physiology laboratory.

PATIENTS

Six consecutive male ICU patients (48 to 70 yrs) after major abdominal vascular surgery.

ANIMALS

two adult female sheep.

INTERVENTIONS

Three ventilatory rates (8, 16, and 24 cycles/min) and 15-sec periods of apnea were selected for measurements in patients. In animals, continuous apnea was achieved with extracorporeal CO2 removal and apneic oxygenation.

MEASUREMENTS

Measurements were performed using an appropriate pulmonary artery catheter and an ejection fraction/cardiac output computer prototype. The thermal indicator was injected automatically at four defined points of the ventilatory cycle, but triggered manually during apnea.

MAIN RESULTS

At 8 cycles/min, there was a wide mean range of cyclic variable modulation, with a coefficient of variation of 11.6% and 23.2% for cardiac output and RV ejection fraction, respectively. Allowing for ventilatory phase or changing from 8 to 16 cycles/min reduced errors by half. Combining both procedures resulted in a coefficient of variation of 4.7% and 6.6% for cardiac output and RV ejection fraction, respectively. The best coefficient of variation values obtained during 15 secs of apnea in patients approached those variations in experimental apnea (coefficient of variation of 2.1% and 4.5% for cardiac output and RV ejection fraction, respectively).

CONCLUSIONS

At low ventilatory rates, best results are achieved by averaging four phase-selected measurements. One-point measurements were less accurate and random point measurements less reproducible.