PURPOSE: In the intensive care setting accurate measurements of oxygenation are crucial to making therapeutic decisions. Unfortunately, invasive monitoring methods, such as central venous oxygen saturation, are prone to complications and not readily available. Although standard pulse oximetry is noninvasive and readily available, it may provide an erroneously high estimate of tissue oxygenation in peripheral vasodilated states. On the contrary, in the setting of vasopressor therapy, pulse oximetry often fails to obtain a reading secondary to vasopressor-mediated peripheral vasoconstriction. Our aim was to compare non-invasive NIRS tissue oximetry versus pulse oximetry for reliable measurements of oxygenation in septic patients.
METHODS: Patients undergoing vasopressor therapy in intensive care were monitored using both the pulse oximeter (SpO2, Agilent) and the In-Spectra NIRS tissue oximeter (StO2, Model 650, Hutchinson) device. Both of these obtained their readings from the same hand for close comparability. The pulse oximeter probe was fitted to the thumb and the tissue oxygen probe was fitted to the thenar eminence. Readings were obtained over 24 to 48 hours for each patient. Data with resolution of 1–5 minutes for SpO2 and 2 seconds for StO2 were downloaded into MS Excel for analyses.
RESULTS: At high dose vasopressor therapy the StO2 was consistent with the clinical picture of the patient whereas the SpO2 failed to pick up any signal. In one particular dying patient, the tissue oxygen monitor was able to generate readings till the moment of death and even beyond complete cessation of respiration to the point of zero tissue oxygenation.
CONCLUSION: Tissue oxygen monitoring based on the principle of Near Infrared Spectroscopy (NIRS) is a more sensitive non-invasive measure of oxygenation compared to conventional pulse oximetry.
CLINICAL IMPLICATIONS: In septic patients undergoing vasopressor therapy, continuous measurement of blood oxygenation by pulse oximetry becomes erroneous and unreliable. Tissue oxygen saturation measurement is a superior way to continuously monitor the patient's clinical status and guide therapeutic decisions.
DISCLOSURE: Parijat Joy, No Financial Disclosure Information; No Product/Research Disclosure Information