Use of Non-invasive Tissue Oxygen Saturation Monitoring to Assess Cardiovascular Insufficiency

Abstract

Cardiovascular insufficiency is characterized by an inadequate oxygen delivery (DO₂) relative to metabolic demands. In the early stages of shock, compensatory autonomic mechanisms, such as vasoconstriction of muscles and skin and eventually lesser vital organs, are activated in an attempt to maintain central blood pressure and vital organ perfusion above an anaerobic threshold. Because in this stage of compensated shock macrocirculatory measures, like arterial pressure or cardiac output, are often inside the range of values defined as normal, these traditional measures of circulatory shock are insensitive as early predictors of subsequent decompensation. Patients in these states of compensated shock are at increased risk of tissue ischemia and subsequent development of multi-organ failure and death. Although macrocirculatory assessments are usually insensitive to assess compensated shock states, microcirculation alterations in muscle and skin blood flow already occur. Thus, measures of tissue cardiovascular reserve should be a sensitive early warning measure of impending cardiovascular collapse due to progressive hemorrhage presenting as compensated shock. In that regard, we present published and preliminary data demonstrating that the non-invasive measurement of tissue oxygen saturation (StO₂) when coupled to a functional hemodynamic monitoring test, such as the vascular occlusion test, may allow early identification of compensated circulatory shock and thus guide initial resuscitation efforts.