Measurement of aortal blood flow in supranormal cardiac output

Introduction

In order to minimize complications of invasive techniques for measurement of cardiac output, non-invasive methods will be of growing importance in anesthesiology and intensive care. The validity of non-invasive measurements has frequently been questioned. In our study the validity of non-invasive measurements was assessed in supranormal cardiac output.

Methods

In 12 patients, who underwent whole body hyperthermia (WBH) in general anesthesia, aortal blood flow was measured using an esophageal Doppler probe (DYNEMO 3000, Sometec, France). Measurements were performed at 37°C, 40°C, 42°C and 39°C body core temperature. At the same time cardiac output was determined by the invasive thermodilution method using a pulmonary artery catheter (Swan-Ganz-Catheter) as well an arterial catheter (PULSION COLD^®). Blood flow in the descending aorta is assumed to represent approximately 70% of total cardiac output, accordingly 70% of the value measured with the invasive technique was compared to the non-invasive measurement. For cardiac output measured by Doppler ultrasound median values were evaluated over a period of 5 min. Statistics were performed using the Mann-Whitney-U-Test.

Results

There were no significant differences between values obtained with the two different invasive techniques. Values measured with Doppler ultrasound were significantly lower at 40°C (P = 0.04) and 42°C (P = 0.01) compared to invasive measurements, despite a growing tendency with rising temperature (see Figure).

Conclusion

Under conditions with increasing supranormal cardiac output measurements with Doppler ultrasound do show a tendency, but absolute values are significantly underestimated with an increasing difference towards growing values.

Figure.

ABF and 70% CO during WBH.