Saturday May 27, 2006
Room temperature or Iced Saline ?
Critical Care literature is not clear, actually controversial, regarding the suitable temperature of the solution use as injectable to measure cardiac output via thermodilution. Let see what is the major pro & con of iced saline.
Advantage: Iced injectate gives a higher signal/noise ratio and more reliability in the measured cardiac output. Signal-to-noise ratio is an engineering term for the power ratio between a signal (meaningful information) and the background noise.
Disadvantage: Iced injectate may affect heart rate and cardiodynamics 5.
But practically does it matter ?. Also, iced solution may not be as cold as we think after it passes through the operator's hand and long port.
Overall literature favours room temperature or atleast does not show any major advantage of using iced saline 1-4.
Related: Thermodilution Cardiac Output Measurement Protocol
(sample from Univ. of Carolina Hospitals)
1. Cardiac output measured by thermal dilution of room temperature injectate. - Evonuk E, Imig CJ, Greenfield W, et al: J Appl Physiol 1961; 16:271-275
2. Cardiac output by thermodilution technique. Effect of injectate's volume and temperature on accuracy and reproducibility in the critically Ill patient - Chest, Vol 84, 418-422, 1983
3. Effect of injectate volume and temperature on thermodilution cardiac output determination - Anesthesiology.1986 Jun;64(6):798-801.
4. Iced versus room temperature injectate for assessment of cardiac output, intrathoracic blood volume, and extravascular lung water by single transpulmonary thermodilution - J Crit Care. 2004 Jun;19(2):103-7.
5. The slowing of sinus rhythm during thermodilution cardiac output determination and the effect of altering injectate temperature. Anesthesiology 1985; 63:540-541