“Our results suggest that a cut off of 92% for sending people home is much safer than has been appreciated in the past,” first authors Drs. Sumit R. Majumdar and Dean T. Eurich of University of Alberta in Edmonton, Canada wrote in an e-mail to Reuters Health.
Their study, they add, also confirms that hypoxemia is a powerful and independent predictor of an increased risk of illness and death in outpatients with pneumonia. “Rates of death or hospitalization for pneumonia, even in those deemed well enough to go home, are pretty high: by 30 days, almost one in 10 (9%) were dead or admitted to hospital,” Drs. Majumdar and Eurich point out.
As reported online December 10 in Clinical Infectious Diseases, the researchers assessed 30-day outcomes in 2,923 adults with pneumonia seen at any of seven emergency departments and discharged. Their mean blood oxygen saturation based on pulse oximetry at the time of presentation was 95%. In 126 patients (4%), blood oxygen saturation was less than 90% and 201 (7%) it was 90% to 92%.
Thirty days after the initial visit to the emergency department, 39 patients (1%) died and 224 (8%) were hospitalized; in all, 252 patients (9%) reached the composite end point of 30-day death or hospital admission.
The researchers found an inverse linear relationship between blood oxygen saturation and major adverse events, “with no inflection at the conventional definition of hypoxemia” (90% blood oxygen saturation).
Patients discharged with oxygen saturation less than 90%, relative to those discharged with higher saturations were more likely to die within one month of the initial ED visit (6% vs 1%), be hospitalized (18% vs 7%) or reach the composite outcome (21% vs 8%; P < 0.001 for all three comparisons).
Oxygen saturation less than 90% was independently associated with a 70% increased risk of 30-day mortality or hospitalization in analyses adjusting for relevant factors including pneumonia severity and receipt of appropriate antibiotics (adjusted odds ratio [aOR] 1.7; P = 0.032).
It was not until the admission-to-hospital threshold was raised to 92% that oxygen saturation was no longer significantly and independently associated with 30-day mortality or hospitalization (aOR 1.1; P = 0.48), the researchers say.
“Our results,” Drs. Majumdar and Eurich told Reuters Health, “suggest we might be sending too many people home from emergency departments using the usual cut off of 90%.”
They note that while a 2% shift upward in oxygen saturation “may seem inconsequential,” in absolute terms (in their population) it represented an additional 201 (7%) of outpatients being admitted to the hospital. Thus, raising the admission threshold to 92% means one additional hospitalization for every 14 patients discharged.
Oxygen Saturations Less than 92% Are Associated with Major Adverse Events in Outpatients with Pneumonia: A Population-Based Cohort Study
Clin Infect Dis 2010. Published online December 10, 2010.