Effects of vasodilation cardiac output measured by PulseCOTM

Introduction

PulseCOTM (LiDCO Ltd, London, UK) is a continuous cardiac output (CO) monitor using the pulse-contour method. The pulse-contour method was defined as the method to determine CO from characteristics of the arterial pressure waveform. However, the arterial pressure waveform often changes during surgery because of the arterial compliance changes using vasoactive drugs. These factors may induce miscalculation of the CO by PulseCOTM. In the present study, we investigated the effects of vasodilation induced by prostaglandin E₁ (PGE₁) on CO measured by PulseCOTM in comparison with CO measured by the bolus thermodilution method.

Patients and methods

Twelve patients who underwent off-pump coronary artery bypass grafting were enrolled in this study. Patients who suffered from aortic valve stenosis and regurgitation were excluded from the study. After premedication with oral diazepam 10 mg, anesthesia was induced and maintained with midazolam, fentanyl and vecuronium. After induction, radial artery and pulmonary artery catheters (Edwards Lifescience LLC, Irvine, CA, USA) were inserted. The CO and systemic vascular resistance (SVR) were measured after induction to calibrate the PulseCOTM and, subsequently, 10 min after PGE₁: (1) 0.01, (2) 0.02 and (3) 0.04 mg/kg/min infusion. CO by the standard thermodilution method was measured using the VigilanceTM system. PulseCOTM was initially calibrated with the value of CO measured by the thermodilution method and no recalibration was performed during the study. For the thermodilution method, the CO was measured three times by injection of 0.2 ml/kg saline of less than 5 degrees and the mean value was calculated.

Results

Patients were eight males and four females, 68 ± 7 years old, 156 ± 10 cm in height and 61 ± 7 kg in weight. SVR at concentrations (2) and (3) were significantly lower than the control value (Table 1). The correlation coefficient between the two techniques at each point was: (1) R² = 0.71, (2) R² = 0.18, (3) R² = 0.41. The limits of agreement (bias ± two standard deviations of bias) were: (1) 0.04 ± 0.91 l/min, (2) -0.31 ± 1.82 l/min, (3) -0.49 ± 1.33 l/min.

Table 1 (abstract P66)

Conclusions

PulseCOTM might underestimate the CO when the SVR is decreased significantly by infusion of PGE₁ 0.02 and 0.04 mg/kg/min in comparison with the CO measured by the bolus thermodilution method.