Norm of Oximetry (Pulse Oximetry, SpO2)
Adult arterial blood saturation is 94%–100%; newborn arterial blood saturation, 40%–92%, is dependent on lung development and altitude.
Usage of Oximetry (Pulse Oximetry, SpO2)
Any clinical situation in which adequate oxygenation is potentially compromised. Particularly helpful when used between arterial blood gas (ABG) determinations, to reduce both the number of blood draws and costs when the accuracy and correlation are known to the clinicians. Advantages: Is quick, noninvasive, and continuous; can detect variations in saturation that may not be noted with ABGs. Disadvantage: Provides only one of the determinants of the ABG and may be of only limited value when single readings are obtained. Must be carefully correlated with the clinical situation (see paragraph 8 under Factors That Affect Results). Conditions when it is used include acute myocardial infarction, acute respiratory distress syndrome (ARDS), anesthesia monitoring, asthma, cerebrovascular accident, chronic obstructive pulmonary disease, congenital heart defects, congestive heart failure, cor pulmonale, cystic fibrosis, emphysema, head trauma, intraoperatively, lung cancer, oxygen therapy, postoperatively, premature infant monitoring, pulmonary edema, pulmonary emboli, sickle cell anemia, tuberculosis, ventilator dependence, and weaning from mechanical ventilation.
Description of Oximetry (Pulse Oximetry, SpO2)
Pulse oximetry involves the spectrophotometric estimate of functional oxygen saturation of hemoglobin. This is a noninvasive measurement of oxygen saturation (see Blood gases, Arterial—Blood ), a percentage representing the ratio of arterial hemoglobin that is capable of transporting (saturated with) oxygen. Measurement is performed by means of a spectrophotometer probe connected to the adult's finger, temporal area, or bridge of the nose, or to an infant's foot or toe. The probe emits red and infrared light that passes through the body part and is directed at a photodetector that determines the amplitude of the transmitted light and isolates the blood's pulsatile flow. This enables calculation of SpO2 through measurement of light absorption based on known amounts absorbed by saturated and reduced hemoglobin. Pulse oximetry equipment is available with motion-resistant capabilities, which improves the consistency and accuracy of readings through reduction of motion artifact. The type of technology used in these pulse oximeters is called “3-wavelength reflectance.”
Professional Considerations of Oximetry (Pulse Oximetry, SpO2)
Consent form NOT required.
- Cleanse the area with water and dry it before attaching the probe.
- For clients with impaired tissue perfusion, use a nasal probe or a temporal probe. If a finger probe must be used, apply a warm pack around the hand and the extremity for 10 minutes before the probe application. The newest equipment uses centrally-placed forehead sensors that deliver improved sensitivity and rapid detection of hypoxemia.
- The skin should be clean and dry before placement. Attach the probe to the toe or foot for infants; the finger, temporal area, or bridge of the nose for adults; and the bridge of the nose for obese clients. Nasal probes should be placed over cartilage for best results.
- Activate the pulse oximeter and set low and high alarm limits according to the manufacturer's instructions.
- Note SpO2 after allowing at least 30 seconds for the reading to stabilize.
- For continuous or periodic oximetry, observe for downward trends in SpO2. Generally, decreased SpO2 below 90%–92% must be addressed by thorough assessment of the client and clinical status.
- Remove the probe. Clean nondisposable probes according to the manufacturer's instructions.
- Wash the area with soap and water.
Client and Family Teaching
- Results are normally available immediately.
- Alarms are normally set to sound for a trend downward in values. Keeping the probe covered with a cloth improves signal clarity.
- In cases of lung disease, discuss smoking cessation programs and strategies if applicable.
Factors That Affect Results
- Hyperbilirubinemia, hypotension, hypothermia, use of vasopressor medications, impaired tissue perfusion, or cold extremities may result in no reading or a falsely low reading, necessitating use of ABG SpO2. Desaturation by pulse oximetry may be used as a sign of severe hypotension, requiring evaluation.
- Failure to place the probe properly may result in no reading or a falsely low or high reading.
- Very bright light surrounding the probe may make obtaining a reading difficult. If so, cover the probe with a sheet or other opaque material.
- Falsely elevated results may occur in the presence of dyshemoglobins (carboxyhemoglobin, >3%; methemoglobin, 1.5 g/dL; sulfhemoglobin, 0.5 g/dL), necessitating periodic validation with ABG SaO2.
- Falsely decreased results may be caused by hyperbilirubinemia >20 mg%, necessitating periodic validation with ABG SaO2.
- Unreliable results may occur with the injection of radiographic dyes, necessitating periodic validation with ABG SaO2.
- Results may not be accurate in clients with rapid oxygen desaturation, low perfusion states, or hypothermia.
- Clients who are anemic may have misleadingly high saturation of hemoglobin and still be hypoxemic because of decreased oxygen-carrying capacity.
- Intra-arterial injection of Patent Blue lowers the pulse oximeter reading.
- Accurate between SaO2 levels of 85% and 100%.
- Some pulse oximeters give slightly false higher readings in dark-skinned clients, but use after validation with ABG is not affected.
- In healthy volunteers, significant delays in the detection of acute hypoxemia by pulse oximetry occur when pulse oximeters are placed at the toe as compared with probes at either the ear or the hand.
- Rosati et al. (2005) found routine pulse oximetry useful in screening asymptomatic newborns after the first 24 hours of life; they determined that an SpO2 less than 96% was indicative of critical congenital cardiovascular malformations (CCVMs) that require surgical correction. Follow-up cardiac ultrasonography revealed that the pulse oximetry screening had a 66.7% sensitivity and 100% specificity, a 50% positive predictive value, and a 100% negative predictive value for CCVMs.