Accuracy of Pulse Oximeter on Newborn Wrist and Ankle
Accuracy of Pulse Oximeter on Newborn Wrist and Ankle
Objective: To compare the accuracy of pulse oximetry oxygen saturation (SpO2) measured on the wrist compared with the ipsilateral palm, and SpO2 measured on the ankle compared with the ipsilateral sole.
Study Design: In this prospective observational study, neonates admitted to the neonatal intensive care unit were enrolled. We recorded SpO2 (Masimo Radical-7 pulse oximeter) detected at the palm and ipsilateral wrist initially, then at 30 s, and at 1 min, and we repeated the same procedure over the sole and ipsilateral ankle. We recorded the time to obtain the SpO2 readings from all these sites. Regression analysis was performed to determine the relationship between paired SpO2 measurements. The mean difference (bias) and standard deviation of the paired SpO2 differences (precision) were calculated (Bland–Altman plots).
Result: A total of 150 patients (birth weight 2381±1020 g, gestational age 34.3±4.3 weeks, median postnatal age 3.5 days (25th–75th percentile 1–16 days)) were enrolled. There was a good correlation between SpO2 measured at the palm versus the wrist (r=0.95, P<0.001 (right); r=0.97, P< 0.001 (left)) and between SpO2 measured at the sole versus the ankle (r=0.92, P<0.001 (right); r=0.91, P<0.001 (left)). There was also a good agreement between paired SpO2 measurements from these sites. The bias and precision for SpO2 at the right palm and right wrist was 0.08±0.94% and for the left palm and left wrist 0.22±0.87%. Similarly, the bias and precision for SpO2 at the right sole and right ankle was −0.03±0.93% and for the left sole and left ankle was −0.01±0.93%.
Conclusion: Our results show that the wrist and ankle can be used as alternative sites to measure SpO2 in newborn infants in place of the routinely used palm or sole.
Arterial oxygen saturation measured by pulse oximetry is widely used as the fifth vital sign during monitoring of neonates in the intensive care unit. The most important advantage of pulse oximeters is the capability to provide continuous, safe and effective monitoring of blood oxygenation non-invasively at the patient's bedside without the need for caliberation. The accuracy of pulse oximeters is acceptable for a wide range of clinical applications. Most manufacturers claim that their instruments are accurate to within ±2% in the SpO2 range between 70 and 100% and ±3% for oxygen saturations between 50 and 69% and varies with the model of pulse oximetry. A number of studies also have verified the inaccuracies of pulse oximetry in certain clinical settings associated with decreased cardiac output, increased or decreased systemic vascular resistance, hypothermia, elevated or dependent limb position, venous engorgement and regional anesthesia even if the device is functioning properly and is free from external interference. Technical situations and subject motion may interfere with the proper acquisition of reliable data or the interpretation of pulse oximeter readings.
The choice of probe site may also affect accuracy; finger probes appear to be more accurate than forehead, nose or earlobe probes during low perfusion states. This can be a problem in newborn babies. Term as well as preterm infants tend to have poor peripheral perfusion (acrocyanosis) in the first few hours of life. Presence of acrocyanosis can result in low signal strength and affect the detection or processing of the biological signals thereby affecting the accuracy of pulse oximetry. This can result in inaccurate signal and false alarm. The choice of probe site may be difficult in sick preterm infants. These infant's have intravenous lines for fluid infusion, or heparin locks for medication infusions on the dorsum of the hands and the feet. Wrist or ankles have been an alternative site for pulse oximeter probe location in these infants requiring oxygen saturation monitoring. However, little is known about the accuracy and response time of pulse oximetry when the probe is placed at the wrist or the ankle of neonates during continuous pulse oximetry monitoring. Pulse oximeter response time depends on both inherent machine characteristics and circulation time and with pulse oximeter probe location. Furthermore, applying the sensor to the right hand or wrist before connection to the pulse oximeter has been shown to result in quicker acquisition of accurate heart rate data in infants compared with other techniques. This method of application should be preferred during resuscitation. Australian resuscitation guidelines recommend placing the sensor over the right wrist.
To date, no studies have specifically evaluated pulse oximetry at the wrist and the ankle compared with more commonly used sites, the palm and the sole in newborn infants, or determined if any significant differences in the time to detect hypoxemia exist among them. Because, in certain circumstances, the wrist and ankle are used as a site for peripheral pulse oximetry monitoring, we performed this study to see whether SpO2 measured on the wrist is comparable with SpO2 measured on the ipsilateral palm and to determine whether SpO2 measured on the ankle is comparable with SpO2 measured on the ipsilateral sole. We also wanted to compare the response time to get a valid reading from the pulse oximeter probes placed at different sites to detect changes in oxygen saturation compared with more usual monitoring sites.
Abstract and Introduction
Abstract
Objective: To compare the accuracy of pulse oximetry oxygen saturation (SpO2) measured on the wrist compared with the ipsilateral palm, and SpO2 measured on the ankle compared with the ipsilateral sole.
Study Design: In this prospective observational study, neonates admitted to the neonatal intensive care unit were enrolled. We recorded SpO2 (Masimo Radical-7 pulse oximeter) detected at the palm and ipsilateral wrist initially, then at 30 s, and at 1 min, and we repeated the same procedure over the sole and ipsilateral ankle. We recorded the time to obtain the SpO2 readings from all these sites. Regression analysis was performed to determine the relationship between paired SpO2 measurements. The mean difference (bias) and standard deviation of the paired SpO2 differences (precision) were calculated (Bland–Altman plots).
Result: A total of 150 patients (birth weight 2381±1020 g, gestational age 34.3±4.3 weeks, median postnatal age 3.5 days (25th–75th percentile 1–16 days)) were enrolled. There was a good correlation between SpO2 measured at the palm versus the wrist (r=0.95, P<0.001 (right); r=0.97, P< 0.001 (left)) and between SpO2 measured at the sole versus the ankle (r=0.92, P<0.001 (right); r=0.91, P<0.001 (left)). There was also a good agreement between paired SpO2 measurements from these sites. The bias and precision for SpO2 at the right palm and right wrist was 0.08±0.94% and for the left palm and left wrist 0.22±0.87%. Similarly, the bias and precision for SpO2 at the right sole and right ankle was −0.03±0.93% and for the left sole and left ankle was −0.01±0.93%.
Conclusion: Our results show that the wrist and ankle can be used as alternative sites to measure SpO2 in newborn infants in place of the routinely used palm or sole.
Introduction
Arterial oxygen saturation measured by pulse oximetry is widely used as the fifth vital sign during monitoring of neonates in the intensive care unit. The most important advantage of pulse oximeters is the capability to provide continuous, safe and effective monitoring of blood oxygenation non-invasively at the patient's bedside without the need for caliberation. The accuracy of pulse oximeters is acceptable for a wide range of clinical applications. Most manufacturers claim that their instruments are accurate to within ±2% in the SpO2 range between 70 and 100% and ±3% for oxygen saturations between 50 and 69% and varies with the model of pulse oximetry. A number of studies also have verified the inaccuracies of pulse oximetry in certain clinical settings associated with decreased cardiac output, increased or decreased systemic vascular resistance, hypothermia, elevated or dependent limb position, venous engorgement and regional anesthesia even if the device is functioning properly and is free from external interference. Technical situations and subject motion may interfere with the proper acquisition of reliable data or the interpretation of pulse oximeter readings.
The choice of probe site may also affect accuracy; finger probes appear to be more accurate than forehead, nose or earlobe probes during low perfusion states. This can be a problem in newborn babies. Term as well as preterm infants tend to have poor peripheral perfusion (acrocyanosis) in the first few hours of life. Presence of acrocyanosis can result in low signal strength and affect the detection or processing of the biological signals thereby affecting the accuracy of pulse oximetry. This can result in inaccurate signal and false alarm. The choice of probe site may be difficult in sick preterm infants. These infant's have intravenous lines for fluid infusion, or heparin locks for medication infusions on the dorsum of the hands and the feet. Wrist or ankles have been an alternative site for pulse oximeter probe location in these infants requiring oxygen saturation monitoring. However, little is known about the accuracy and response time of pulse oximetry when the probe is placed at the wrist or the ankle of neonates during continuous pulse oximetry monitoring. Pulse oximeter response time depends on both inherent machine characteristics and circulation time and with pulse oximeter probe location. Furthermore, applying the sensor to the right hand or wrist before connection to the pulse oximeter has been shown to result in quicker acquisition of accurate heart rate data in infants compared with other techniques. This method of application should be preferred during resuscitation. Australian resuscitation guidelines recommend placing the sensor over the right wrist.
To date, no studies have specifically evaluated pulse oximetry at the wrist and the ankle compared with more commonly used sites, the palm and the sole in newborn infants, or determined if any significant differences in the time to detect hypoxemia exist among them. Because, in certain circumstances, the wrist and ankle are used as a site for peripheral pulse oximetry monitoring, we performed this study to see whether SpO2 measured on the wrist is comparable with SpO2 measured on the ipsilateral palm and to determine whether SpO2 measured on the ankle is comparable with SpO2 measured on the ipsilateral sole. We also wanted to compare the response time to get a valid reading from the pulse oximeter probes placed at different sites to detect changes in oxygen saturation compared with more usual monitoring sites.
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