Online Measurements of SaO₂, Ht and Hb Using a Micro Transmission Cell

Abstract

Oxygen saturation (SaO₂) and hemoglobin concentration (Hb) are important parameters for evaluation of oxygen transport in patient monitoring. Before the advent of noninvasive monitoring of SaO₂ with pulse oximetry (Yoshiya et al, 1980; Severinghaus and Honda, 1987) intermittent sampling of blood gases was the only reliable method of assessing arterial oxygenation and probably still is the most frequently used method. While intermittent sampling is satisfactory under most clinical conditions, this method does not give any indication of the oxygenation status between two samples (Lam, 1987). As shown by Thorson and colleagues (1983), considerable spontaneous variation in PaO₂ may occur in patients in the intensive care unit. Arterial hypoxaemia is often the cause of complications during anesthesia, resulting in for example neurological impairment and cardiac ischemia. The majority of incidents of severe hypoxaemia during anesthesia is the result of failure of oxygen delivery to the arterial blood. The common causes are mishaps reducing the inspired oxygen concentration, upper airway obstruction, misplacement of an endotracheal tube and hypoventilation (Knill, 1985). To prevent complications due to a failure of arterial oxygenation there is a strong need for continuous measurement of the arterial oxygenation status of the patient.