Should the Pulse Oximetry be an A or A+?
A patient has arrived with increased work of breathing, hypoxia, and altered mental status requiring intubation. After intubation, the patient stabilizes and their oxygenation improves. You know that both hypoxia and hyperoxia are bad for patients and that initial ED mechanical ventilation strategies are often continued after admission1. How can you titrate the patient’s fraction of inspired oxygen (FiO2) to keep them safe from both hypoxia and hyperoxia?
While an ABG is the gold standard for measuring the partial pressure of arterial oxygen (PaO2), pulse oximetry (SPO2) has a role as well. Pulse oximetry is non-invasive, continuous, and can be remotely monitored. It can show hypoxia fairly easily, but once the SPO2 reads 100%, the bedside clinician can’t know if that means there’s just enough oxygen to bring the hemoglobin saturation to 100% or there’s excessive PaO2 which could cause vasoconstriction or free radical damage.
A recent database analysis2 showed that patients whose SPO2 was maintained between 94-98% had an association with increased survival. This is congruent with previous data showing that mindful titration of FiO2 using SPO2 lower than 100 but generally above 94, is associated with improved outcomes. Of course, this is not universally applicable. Lower SPO2 targets may be acceptable in other disease states such as COPD exacerbations.
This information tells us we probably don’t need to shoot for an A+ on our patients’ SPO2. Rather, let's aim for a solid A, and target 94-98%.
1. Fuller BM, Mohr NM, Dettmer M, et al. Mechanical Ventilation and Acute Lung Injury in Emergency Department Patients With Severe Sepsis and Septic Shock: An Observational Study. Jones A, ed. Academic Emergency Medicine. 2013;20(7):659-669. doi:10.1111/acem.12167.
2. van den Boom W, Hoy M, Sankaran J, Liu M. The Search for Optimal Oxygen Saturation Targets in Critically Ill Patients: Observational Data From Large ICU Databases. CHEST. October 2019:1-8. doi:10.1016/j.chest.2019.09.015.