We investigated the relationship of oxygen saturation by the invasive method in pulmonary artery (mixed venous oxygen saturation, SmvO2), liver tissue (StLO2) and deltoid muscle tissue (StDO2). SmvO2 is known to represent the body’s total balance of O2 supply/demand. SmvO2 is measured in critically-ill patients since it has the ability to reflect a threat against patient’s physiology. However SmvO2 measurement requires invasive techniques such as a pulmonary artery catheter (PAC), which can pose significant risks. Near-infrared spectroscopy (NIRS) offers a safe and noninvasive monitoring method for tissue oxygenation (StO2). A diode emits infrared light into the tissue beneath the skin surface resulting in the measurement of oxygen saturation of the tissue of interest. We hypothesized that a correlation could exist between a total summation of oxygen delivery vs consumption (SmvO2) and local tissue oxygenation in liver (StLO2) or deltoid muscle (StDO2) since the SmvO2 is dependent on oxygenation in local tissues.
Our study was performed among critically ill patients with a PAC. We designed a customized graphic user interface (GUI) to collect parameters simultaneously from 1) invasive SmvO2 by the Edwards Vigilance monitor by PAC, and 2) non-invasive Hutchinson InSpectra monitor (BioMeasurement Division, Hutchinson, MN 55350) with two separate NIRS probes for deltoid muscle and liver, respectively. Data was collected on individuals continuously over the course of several hours to days. StO2 from healthy subjects were also measured for comparison.
StO2 of liver and deltoid muscle among healthy subjects showed a range of 70-90% and 60-80% repectively. However range of StO2 was larger among critically-ill patients studied. The StLO2 and StDO2 both followed the trends of SmvO2 over time. If there was a deterioration in patient status as per the SmvO2, such a change was also evident with a simultaneous drop in the StLO2 and StDO2.
Data showed a promising correlation between SmvO2 and StLO2 and StDO2 in critically-ill patients.
In the future, SmvO2 may be easily estimated by non-invasive StO2 measurements in selected patients.
Y. Kwon, Hutchinson Technology, Edwards Lifesciences LLC