Home Feedback Contents

Oesophageal Doppler

Up International consensus Oesophageal Doppler Figure 3 Table 1 Table 2 Table 3 Table 4 Table 5 Table 7 Table 8 Table 9

Asian Intensive Care: coming of age
International intensive care conference, Hong Kong, December 14th-15th
Register now!
Click here for details

 

Minimally invasive means of real time continuous cardiac output monitoring

Principle

When an ultrasound beam is directed at a column of flowing blood the reflected sound wave will shift in frequency (Doppler shift). The magnitude of this Doppler shift is directly proportional to the velocity of the blood flow. Stroke volume can be calculated by multiplying this average blood velocity during an ejection cycle by the ejection time (stroke distance) and by the cross-sectional area through which the blood flows (the cross-sectional area of the descending aorta which is obtained from nomograms based on age, weight and height). A correction factor is required to transform the blood flow measured in the descending aorta to a global CO


Insertion

Small (5-6mm) probe inserted via nasal or oral route. Advanced and rotated until characteristic descending aortic trace is obtained and optimized.

Additional information obtained from waveform

  • left ventricular ejection time (or flow time) corrected for heart rate provides an index of preload and is reflected by the waveform base. Typically corrected flow time (FTc) <330 ms in hypovolaemic patients. In normovolaemic patient FTc 330-360 ms

Narrow waveform base, decreased FTc characteristic of hypovolaemia

Image reproduced with the  permission of Prof. David Bennett

 

Same patient after fluid resuscitation

Image reproduced with the  permission of Prof. David Bennett

 

  • peak flow velocity (the peak of the waveform) is an indicator of myocardial contractility

  • afterload/SVR is represented by a combination of reduced waveform base and height.

 

Advantages

  • minimally invasive

  • real time measurement

  • rapid insertion. Results available within few minutes.

  • minimal technical skill required

  • short training period

  • good trend monitor

Disadvantages

  • interference by nasogastric tube

  • dislodgement by movement. This may result in loss of signal or may result in changes in monitored values

  • some patients contraindicated (eg post-oesophagectomy, oesophageal injuries)

  • absolute values of cardiac output not very accurate

© Sarah Ramsay December 2002, Sarah Ramsay & Charles Gomersall December 2003

©Charles Gomersall, October, 2009 unless otherwise stated. The author, editor and The Chinese University of Hong Kong take no responsibility for any adverse event resulting from the use of this webpage.
Copyright policy    Contributors