Patient Controlled Analgesia (PCA) is used post operatively for pain management. Through the use of a PCA pump, patients, can self-administer a dose of pain medication with the push of a button. Although PCA usage is considered to be relatively safe, research shows the risk of patient harm is 3.5 times greater when a PCA pump is being used. The greatest risk to patients is that of respiratory depression, which can result in respiratory failure and death. Therefore careful monitoring of PCA patients' respiratory function is essential to prevent adverse events. PCA pump usage can either be monitored with pulse oximetry, or controlled through capnography. Pulse oximetry measures the patient's oxygenation status, which is an indirect measure of respiratory function. The pulse oximeter can be set to alarm the nure whenever a patient's oxygenation status dips below a certain percentage, usually 92%. Capnography controlled PCA pumps measure the amount of carbon dioxide expelled by the patient as a measure of respiratory function. If a patient's carbon dioxide measurements are not within normal limits, the capnography will alarm and will also lock-out the PCA pump thus preventing another dose of pain medication from being administered. Although some hsopitals use pulse oximetry, while others use capnography, new research suggests that pulse oximetry may not be the safest method for monitoring PCA patients.