Continuous monitoring of oxygen saturation in prehospital patients with severe illness: The problem of unrecognized hypoxemia

Abstract

The continuous measurement of arterial oxygen saturation using pulse oximetry (SpO2) has become popular for critically ill hospitalized patients. Its use in the ambulance transfer of similarly ill patients has been infrequently documented. This study examines the use of prehospital pulse oximetry, with special reference to the ability of ambulance attendants to recognize hypoxemia. Using a prospective single-blind case series method, a convenience sample of adult patients transferred by ambulance designated Code 3 (serious but not life threatening) or Code 4 (serious and life threatening) to a regional base hospital were examined for the presence of hypoxemia. An Ohmeda finger pulse oximeter probe was attached to all patients. Prior to the study, oxygen treatment was reviewed and ambulance personnel were instructed on the use of the instrument. The continuous oxygen saturation record was not revealed to the attendant(s) during the call. Administration of oxygen was monitored, and a study form was completed by the attendant at the completion of the call. Overall, 50 patients were included in the study. The most common complaints were chest pain 21 (37%) and shortness of breath 15 (27%). The average age was 64 years, with a range of 32–82. Hypoxemia, defined as SpO2 of less than 90% for more than 1 minute, was detected in 14 patients. Attendants recognized hypoxemia on clinical grounds in only 4 patients (sensitivity = 28%). Forty-one (82%) patients received various amounts of supplemental oxygen; many patients remained hypoxemic despite therapy. To supplement hypoxemia detection, the addition of vital sign criteria to patient assessment would have improved the sensitivity (93%), however, many patients would receive oxygen without need (specificity = 39%). We conclude that clinical recognition of hypoxemia by ambulance attendants is difficult. The use of a pulse oximeter can assist ambulance attendants to identify hypoxemia in the prehospital setting.