Changes in arterial oxygen saturation during isotope perfusion scans using human macroaggregates of albumin

Sixty-three patients undergoing isotope ventilation/perfusion scintigraphy for suspected pulmonary embolism were monitored using pulse oximetry. Xenon inhalation had no adverse effect on arterial oxygen saturation. Fifty-seven per cent of patients demonstrated a drop in oxygen saturation of 2-10% within 5 min of injection of macroaggregates. Small changes in arterial oxygen saturation reflect larger changes in the arteriole partial pressure of oxygen. In 10 patients, oxygen saturation dropped to 91% and below, corresponding to an arterial pO2 of less than 60 mm Hg. The effect lasted up to 30 min and is thought unlikely to be simply due to arteriolar blockade. Falls in arterial oxygen saturation cannot be correlated with any specific pulmonary pathology and appear unlikely to be of any clinical significance in most patients.