Pulse Oximetry in Shock Management

Introduction to Pulse Oximetry Limitations

The American Thoracic Society recommends monitoring trends rather than absolute values with pulse oximeters, as they are better for monitoring trending phenomena than determining absolute magnitude of change, and notes that dark skin pigmentation, motion artifacts, carboxyhemoglobinemia, or methemoglobinemia may compound inaccuracy in shock states 1
Pulse oximetry has limitations, including inaccuracy in certain conditions such as cold extremities, Raynaud's phenomenon, skin pigmentation, nail varnish, and motion artifacts, which can lead to inaccurate measurements, as reported by the American Heart Association 2

The British Thoracic Society suggests aiming for SpO₂ of 94-98% in most patients, or 88-92% in those at risk of hypercapnic respiratory failure, and recommends using arterial blood gas analysis for initial assessment and when SpO₂ readings are questionable 3
Target saturation ranges for oxygen therapy are 94-98% for most patients and 88-92% for those at risk of hypercapnic respiratory failure, as recommended by the British Thoracic Society, with the goal of avoiding hypoxemia, which is strongly associated with mortality across various conditions, according to the World Health Organization 4, 3

Forehead reflectance sensors are significantly more accurate than finger transmission sensors in patients requiring high-dose vasopressors, and alternative sites such as the pharynx can be used in severe shock when finger oximetry fails, with readings only 0-2% lower than arterial samples, as noted by the American College of Emergency Physicians and the American Thoracic Society 1, 3

Clinical decisions should incorporate multiple parameters, including SpO₂ readings, rather than relying solely on pulse oximetry, which has limitations that must be recognized, as recommended by the American Thoracic Society and the European Respiratory Society 1, 3
Pulse oximetry serves several critical functions in shock management, including oxygen saturation monitoring, guiding oxygen therapy, and early detection of deterioration, and should be used in conjunction with other monitoring tools, such as arterial blood gases and capnography, as recommended by the Society of Critical Care Medicine and the American College of Cardiology 3
The strength of evidence for pulse oximetry as the "fifth vital sign" is not explicitly stated, but it is considered an invaluable tool in shock management, providing continuous assessment of oxygenation status that guides therapy and helps evaluate response to interventions, as recommended by the American College of Cardiology 1, 3
Documentation of SpO₂ readings, oxygen delivery method, and flow rate is essential, and clinicians should recognize limitations of pulse oximetry in severe shock states, as suggested by the European Society of Intensive Care Medicine and the National Institute for Health and Care Excellence 3