COLD technique

Depending on the desired measurement, the COLD technique (circulation, oxygenation, lung water, and liver function diagnosis) utilizes cannulas placed in either the femoral or radial artery, the pulmonary artery, and/or a central vein. A bolus of cold fluid can be injected into any central vein enabling thermodilution cardiac output to be measured via a 3 French catheter placed in the femoral or radial artery. This catheter has an optional oximetry probe for continuous measurement of arterial oxygen saturation. A similar catheter can be placed in the pulmonary artery for cardiac output measurement and monitoring of mixed venous oxygen saturation. A new development allows continuous measurement of cardiac output by pulse contour analysis with automatic recalibration being performed by intermittent thermodilution injections.

The device is also geared for measurement of indocyanine green in the blood. Following injection of a bolus of indocyanine green into (preferably) a central vein, cardiac output can be computed from the dye dilution curve produced at the arterial catheter site. A fiber-optic reflectance densitometer built into this catheter measures the indocyanine green concentration. An additional advantage is that elimination of this dye is almost entirely via the liver. Thus the plasma disappearance rate can be used to assess hepatic function. With normal liver function only a tiny fraction of the injected indocyanine green is still detectable in the bloodstream after 10 min.

The device also purports to measure (i) global end-diastolic volume, i.e. the sum of the end-diastolic volumes of both left and right atria and ventricles, (ii) intrathoracic blood volume, and (iii) extravascular lung water. It has been suggested that intrathoracic blood volume can be used as an indicator of cardiac preload while cardiac performance can be derived from the ratio of cardiac output to global end-diastolic volume. Extravascular lung water measurement is purported to quantify acute lung injury and is claimed to enable appropriate therapy to shorten ventilation time and reduce complication rates such as pneumonia. Confirmatory studies to support these claims are scanty.

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