Thermodilution

When dye dilution is used, the graph of concentration versus time may show a second peak as dye recirculates to the measuring device. This is known as a recirculation hump and does not occur when thermodilution methods are used. 

The actual graph of temperature versus time for the thermodilution method would resemble the one below. 

Demonstrate that the thermodilution curve has no recirculation hump when compared with the dye dilution method. Otherwise the line should be drawn in a similar fashion. 

Cardiac output, pulmonary artery pressure (PAP) and stroke volume are measured by a thermodilution technique using a Cardiac Output Computer (Gould/Statham SP 1245) and a balloon-tip triple lumen catheter (Gould SP 5105, 5F) with the thermistor positioned in the pulmonary artery via the jugular vein. 

Alternatives to MRI include echo cardiography to measure LV wall thickness, lumen volume and cardiac output (Coatney 2001 Collins et al. 2003 de Simone et al. 1990 Zhou et al. 2004), dye-dilution techniques such as bolus thermodilution to measure cardiac output (Siren et al. 1990), and implanted pressure transducers and flow probes to measure left ventricular pressure... 

Biotrans II Transducer Kits, Thermodilution and Pulmonary Artery Cafiieters etc. 

Chilled 5% dextrose in water (D5W) or 0.9% NaCl can be used as indicators. The dilution curve represents a transient reduction in pulmonary artery blood temperature following injection of the indicator into the right atrium. Figure 13.2 illustrates the method and a typical thermodilution curve. Note that the indicator is really negative calories. The thermo dilution method is based on heat exchange measured in calories, and the flow equation contains terms for the specific heat (C) and the specific gravity (S) of the indicator (i) and blood b). The expression employed when a 7F thermistor-tipped catheter is used and chilled D5W is injected into the right atrium is as follows ... 

FIGURE 13.2 The thermodilution method (a) and a typical dilution curve (b). 

Martin RW, Bashein G (1989) Measurement of stroke volume with three-dimensional transesophageal ultrasonic scanning comparison with thermodilution measurement. Anesthesiology 70 470-476... 

Because ICG is a very simple and low-cost technique, very valuable applications may appear. It must be remembered that a gold standard method for SV and CO does not exist the intramethod variability may be larger than the intermethod variability. Reference methods have been thermodilution, dye dilution, oxygen Pick technique, radionuclear radiography, and transesophageal Doppler echocardiography. 

Suttner, S., ScholUiom, T., Boldt, J., Mayer, J., Rohm, K.D., Lang, K., Piper, S.N., 2006. Noninvasive assessment of cardiac output using thoracic electrical bioimpedance in hemod)mamically stable and unstable patients after cardiac surgery a comparison with pulmonary artery thermodilution. Intensive Care Med. 32, 2053-2058. 

A common cause of death in Western Europe is chronic heart failure. Measures for its severity are hemodynamic parameters, including stroke volume (SV). Until now, the gold standard for measuring these parameters is the thermodilution technique using pulmonary artery catheters. However, the risks of estimating cardiac output via catheters include infections, sepsis and arrhythmias, as well as increased morbidity and mortality. An alternative technique to assess SV easily and cost-effectively is the use of impedance cardiography (ICG). 

Firth BG, Dehmer Gl, Nicod P, WiUerson IT, Hillis LD. Effect of increasing heart rate in patients with aortic regurgitation. Effect of incremental atrial pacing on scintigraphic, hemodynamic and thermodilution measurements. Am J Cardiol 1982 49 1860-1867. 

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