Indian J Pediatr DOI 10.1007/s12098-014-1381-z
ORIGINAL ARTICLE
Comparison of Two New Generation Pulse Oximeters with Arterial Oxygen Saturation in Critically Ill Children Bipin Jose & Rakesh Lodha & S. K. Kabra
Received: 21 September 2013 / Accepted: 17 February 2014 # Dr. K C Chaudhuri Foundation 2014
Abstract Objectives To compare the performance of two new generation pulse oximeters, one with enhanced signal extraction technology (SET) and other without enhanced SET in detecting hypoxemia and to correlate it with arterial blood gas analysis. Methods Forty-eight patients, admitted to pediatric intensive care unit (PICU) of a teritiary care teaching hospital in India for critical care and support during the study period, who had an arterial catheter in situ were included. Children with those disease conditions known to interfere with pulse oximetry and blood gas analysis were excluded.184 set of observations were made during the study period. Each set had oxygen saturation (SpO2) measured from both the pulse oximeters and the corresponding arterial oxygen saturation (SaO2). The values were compared for occurrence of true and false alarms during periods of normal BP, hypotension and varying degrees of hypoxia. Results The mean arterial SaO2 in the study was 94.4 %±4.9. The mean SpO2 recorded in conventional and enhanced signal extraction technology (SET) pulse oximeters were 94.9 %± 4.5 and 97.2 %±4.7 respectively. Enhanced signal extraction technology pulse oximeter detected 4/27 (15 %) of true hypoxemic events and 1 event was a false alarm. Conventional pulse oximeter detected 11/27 (41 %) true hypoxemic events but recorded 6 false alarms. Conclusions Both pulse oximeters were not found to be performing satisfactorily in picking up hypoxemia in the study. There was good correlation with mean SpO2 from pulse oximeters and arterial SaO2. The reliability of pulse oximetry decreases with worsening hypoxemia and hypotension, and the sensitivity for picking up hypoxemia can be as low as 15 %. B. Jose : R. Lodha (*) : S. K. Kabra Department of Pediatrics, All India Institute of Medical Sciences, Ansari Nagar, New Delhi 110029, India e-mail: [email protected]
Keywords Pulse oximetry . Children . Hypoxemia . Arterial blood gas analysis . Agreement
Introduction Pulse oximeters measuring saturation of oxyhemoglobin (SpO2) forms one of the core vital parameters in critically ill children admitted to intensive care unit (ICU) setting and elsewhere. Many patient and environment related factors can influence the accurate measurement of SpO2 in conventional pulse oximetry. Most of the inaccuracy in ICU setting, is related to patient movement [1, 2], poor peripheral perfusion, interference from other electro- surgical instruments, excess ambient light [3] and hyperbilirubinemia. Conventional pulse oximeters identify moving blood as arterial blood and measures oxygen saturation in this. Patient movement results in falsely lower values or signal dropouts in conventional pulse oximeters as deoxyhemoglobin in venous blood is also measured and interpreted as arterial blood. Newer generation pulse oximeters are to some extend motion resistant. In conventional pulse oximetry, differential absorption of infrared light (oxyhemoglobin) over red (deoxyhemoglobin) is measured and expressed as a percentage after comparing with a calibrated absorbance curve generated from healthy volunteers to give an estimation of arterial oxygen saturation (SaO2) [4]. An intensive care unit (ICU) is one of the most common settings where pulse oximetry is of immense use in monitoring sick children but at the same time the readings are most likely to be inaccurate, because of patient related issues like poor perfusion, irritability and interference from other electro surgical instruments. Pulse oximeters with enhanced signal extraction technology (SET) are claimed to be superior to other new generation pulse oximeters as it use adaptive filters with unique algorithms, along with conventional red over infrared algorithm to allow accurate readings through all patient
Indian J Pediatr
conditions [5] . The study is particularly important in an ICU setting where the occurrence of hypoxia episodes if missed by the pulse oximeter can harm a sick child. On the other hand frequent false alarms lead the treating team to increase the alarm limits which also may be catastrophic at times [6]. In this context an enhanced SET could decrease the occurrence of both missed events and false alarms. While multiple studies have compared the performance of enhanced SET with conventional pulse oximeter, comparison with arterial oxygen saturation in critically ill children are limited. The authors conducted this study to determine if the pulse oximeters with enhanced signal extraction technology (SET) are superior to other new generation pulse oximeters without SET in correlating better with the arterial blood gas analysis in critically ill children and to determine if enhanced SET has any advantage over other pulse oximeter during hypotension.
Material and Methods The study was performed in the Pediatric Intensive Care Unit (PICU) of a tertiary care hospital, between January 2012 through July 2012. The 8 bedded pediatric ICU had an average admission rate of 20 patients a month. All patients admitted to PICU for critical care and support, who had an arterial catheter in situ were included. Children with those disease conditions known to interfere with pulse oximetry and blood gas analysis- met-hemoglobinemia [7], carbon monoxide poisoning [8], patients on nitroprusside infusion were excluded. A written consent was obtained from parents of all patients enroled in the study. Children were managed as per the PICU protocols existing at the time of study. After enrolment, patient related information including clinical diagnosis, vital signs and other relevant data were entered on a pre-designed proforma. Oxygen saturation values shown in a new generation pulse oximeter without SET (Mindray MPM module, Shenzhen Mindray, Bio-Medical Electronics CO, Ltd) and enhanced SET (Masimo Radical 7, Masimo Corporation, Irvine, CA 92618 USA) pulse oximeter were recorded. Both these pulse oximeters claim comparable accuracy (70–100 %: ±3 %) in neonates and children with motion. Each patient had a minimum 3 set of readings at least 12 h apart, with the first reading in the initial first hour of admission as per the PICU protocol existing at the time of study. No pulse oximeter reading or arterial blood gas analysis done on grounds of clinical suspicion of hypoxemia was recorded to avoid observer bias. Simultaneous recording of vital signs including heart rate, respiratory rate and invasive arterial blood pressure were done. It was ensured that the same devices were used on the same patient during the study period. Both the pulse oximeters with age appropriate fingertip probes were attached to the patient simultaneously on the same limb on different fingers for a period of atleast 5 min prior to
performing arterial blood gas (ABG) analysis. Before recording the SpO2 it was ensured that both the pulse oximeters had, adequate strength pleth wave forms and the heart rate corresponded to that in the precordial ECG leads. At the end of 5 min, the SpO2 and arterial blood pressure were recorded just before drawing 0.3 mL arterial blood sample from the indwelling arterial catheter for ABG analysis. Arterial blood gas analysis was performed using an automated ABG analyser ABL FLEX 800 (Radiometer Copenhagen), which was calibrated every day as per the manufacturer’s recommendations. The values were recorded on a pre-designed proforma against the time of obtaining sample. The study aimed to pick up the occurrence of true hypoxemic events and false alert events. True hypoxemia event was defined as one where ABG detected hypoxemia (SaO2 less than 90 %) and pulse oximeter also showed SpO2
ORIGINAL ARTICLE
Comparison of Two New Generation Pulse Oximeters with Arterial Oxygen Saturation in Critically Ill Children Bipin Jose & Rakesh Lodha & S. K. Kabra
Received: 21 September 2013 / Accepted: 17 February 2014 # Dr. K C Chaudhuri Foundation 2014
Abstract Objectives To compare the performance of two new generation pulse oximeters, one with enhanced signal extraction technology (SET) and other without enhanced SET in detecting hypoxemia and to correlate it with arterial blood gas analysis. Methods Forty-eight patients, admitted to pediatric intensive care unit (PICU) of a teritiary care teaching hospital in India for critical care and support during the study period, who had an arterial catheter in situ were included. Children with those disease conditions known to interfere with pulse oximetry and blood gas analysis were excluded.184 set of observations were made during the study period. Each set had oxygen saturation (SpO2) measured from both the pulse oximeters and the corresponding arterial oxygen saturation (SaO2). The values were compared for occurrence of true and false alarms during periods of normal BP, hypotension and varying degrees of hypoxia. Results The mean arterial SaO2 in the study was 94.4 %±4.9. The mean SpO2 recorded in conventional and enhanced signal extraction technology (SET) pulse oximeters were 94.9 %± 4.5 and 97.2 %±4.7 respectively. Enhanced signal extraction technology pulse oximeter detected 4/27 (15 %) of true hypoxemic events and 1 event was a false alarm. Conventional pulse oximeter detected 11/27 (41 %) true hypoxemic events but recorded 6 false alarms. Conclusions Both pulse oximeters were not found to be performing satisfactorily in picking up hypoxemia in the study. There was good correlation with mean SpO2 from pulse oximeters and arterial SaO2. The reliability of pulse oximetry decreases with worsening hypoxemia and hypotension, and the sensitivity for picking up hypoxemia can be as low as 15 %. B. Jose : R. Lodha (*) : S. K. Kabra Department of Pediatrics, All India Institute of Medical Sciences, Ansari Nagar, New Delhi 110029, India e-mail: [email protected]
Keywords Pulse oximetry . Children . Hypoxemia . Arterial blood gas analysis . Agreement
Introduction Pulse oximeters measuring saturation of oxyhemoglobin (SpO2) forms one of the core vital parameters in critically ill children admitted to intensive care unit (ICU) setting and elsewhere. Many patient and environment related factors can influence the accurate measurement of SpO2 in conventional pulse oximetry. Most of the inaccuracy in ICU setting, is related to patient movement [1, 2], poor peripheral perfusion, interference from other electro- surgical instruments, excess ambient light [3] and hyperbilirubinemia. Conventional pulse oximeters identify moving blood as arterial blood and measures oxygen saturation in this. Patient movement results in falsely lower values or signal dropouts in conventional pulse oximeters as deoxyhemoglobin in venous blood is also measured and interpreted as arterial blood. Newer generation pulse oximeters are to some extend motion resistant. In conventional pulse oximetry, differential absorption of infrared light (oxyhemoglobin) over red (deoxyhemoglobin) is measured and expressed as a percentage after comparing with a calibrated absorbance curve generated from healthy volunteers to give an estimation of arterial oxygen saturation (SaO2) [4]. An intensive care unit (ICU) is one of the most common settings where pulse oximetry is of immense use in monitoring sick children but at the same time the readings are most likely to be inaccurate, because of patient related issues like poor perfusion, irritability and interference from other electro surgical instruments. Pulse oximeters with enhanced signal extraction technology (SET) are claimed to be superior to other new generation pulse oximeters as it use adaptive filters with unique algorithms, along with conventional red over infrared algorithm to allow accurate readings through all patient
Indian J Pediatr
conditions [5] . The study is particularly important in an ICU setting where the occurrence of hypoxia episodes if missed by the pulse oximeter can harm a sick child. On the other hand frequent false alarms lead the treating team to increase the alarm limits which also may be catastrophic at times [6]. In this context an enhanced SET could decrease the occurrence of both missed events and false alarms. While multiple studies have compared the performance of enhanced SET with conventional pulse oximeter, comparison with arterial oxygen saturation in critically ill children are limited. The authors conducted this study to determine if the pulse oximeters with enhanced signal extraction technology (SET) are superior to other new generation pulse oximeters without SET in correlating better with the arterial blood gas analysis in critically ill children and to determine if enhanced SET has any advantage over other pulse oximeter during hypotension.
Material and Methods The study was performed in the Pediatric Intensive Care Unit (PICU) of a tertiary care hospital, between January 2012 through July 2012. The 8 bedded pediatric ICU had an average admission rate of 20 patients a month. All patients admitted to PICU for critical care and support, who had an arterial catheter in situ were included. Children with those disease conditions known to interfere with pulse oximetry and blood gas analysis- met-hemoglobinemia [7], carbon monoxide poisoning [8], patients on nitroprusside infusion were excluded. A written consent was obtained from parents of all patients enroled in the study. Children were managed as per the PICU protocols existing at the time of study. After enrolment, patient related information including clinical diagnosis, vital signs and other relevant data were entered on a pre-designed proforma. Oxygen saturation values shown in a new generation pulse oximeter without SET (Mindray MPM module, Shenzhen Mindray, Bio-Medical Electronics CO, Ltd) and enhanced SET (Masimo Radical 7, Masimo Corporation, Irvine, CA 92618 USA) pulse oximeter were recorded. Both these pulse oximeters claim comparable accuracy (70–100 %: ±3 %) in neonates and children with motion. Each patient had a minimum 3 set of readings at least 12 h apart, with the first reading in the initial first hour of admission as per the PICU protocol existing at the time of study. No pulse oximeter reading or arterial blood gas analysis done on grounds of clinical suspicion of hypoxemia was recorded to avoid observer bias. Simultaneous recording of vital signs including heart rate, respiratory rate and invasive arterial blood pressure were done. It was ensured that the same devices were used on the same patient during the study period. Both the pulse oximeters with age appropriate fingertip probes were attached to the patient simultaneously on the same limb on different fingers for a period of atleast 5 min prior to
performing arterial blood gas (ABG) analysis. Before recording the SpO2 it was ensured that both the pulse oximeters had, adequate strength pleth wave forms and the heart rate corresponded to that in the precordial ECG leads. At the end of 5 min, the SpO2 and arterial blood pressure were recorded just before drawing 0.3 mL arterial blood sample from the indwelling arterial catheter for ABG analysis. Arterial blood gas analysis was performed using an automated ABG analyser ABL FLEX 800 (Radiometer Copenhagen), which was calibrated every day as per the manufacturer’s recommendations. The values were recorded on a pre-designed proforma against the time of obtaining sample. The study aimed to pick up the occurrence of true hypoxemic events and false alert events. True hypoxemia event was defined as one where ABG detected hypoxemia (SaO2 less than 90 %) and pulse oximeter also showed SpO2
