Time to equilibration of oxygen saturation using pulse oximetry.

OBJECTIVE

To determine the time it takes for O2 saturation measured by pulse oximetry to equilibrate after a change is made in supplemental O2 administered by nasal cannula in patients with cardiac and pulmonary disease.

METHODS

A prospective, observational study of a convenience sample of 51 patients treated in a university-affiliated ED with nasal cannula O2. Patients were placed on and/or subsequently taken off O2 via nasal cannula set at 2 or 4 L/min based on clinical indications. Oxygen saturation was measured at 1-minute intervals over a 30-minute period using finger-probe pulse oximetry. Of the 51 patients in the study, 43 were monitored while O2 treatment was initiated and 18 were monitored when it was discontinued.

RESULTS

Most (95%) of the patients placed on O2 attained equilibration of O2 saturation within 3.5 minutes. Most (95%) of the patients taken off supplemental O2 attained equilibration of O2 saturation within 4.5 minutes.

CONCLUSION

The interval to equilibration of O2 saturation in patients receiving O2 by nasal cannula is considerably shorter than the 20-30 minutes generally suggested. Adequacy of O2 supplementation should be assessable much sooner than was previously taught.