Reflectance pulse oximetry in fetal lambs.

Transmission pulse oximetry is used for monitoring in many clinical settings. However, for fetal monitoring during labor and in situations with poor peripheral perfusion, transmission pulse oximetry cannot be used. Therefore, we developed a reflectance pulse oximeter, which uses the relative intensity changes of the reflected red and infrared light (red/infrared ratio) to measure the arterial oxygen saturation. The performance of the reflectance pulse oximeter was studied in acute experiments in fetal lambs. By stepwise reduction of the inspired oxygen concentration of the ewe, measurements were done at the fetal scalp at various arterial oxygen saturation levels (17-82%). Reflectance pulse oximeter readings were averaged over periods of 15 s and compared with simultaneously taken fetal arterial blood samples. A calibration curve for the relationship between red/infrared ratio and arterial oxygen saturation was obtained from 53 measurements in four fetal lambs, by linear regression analysis [red/infrared = 4.088-(0.038.SaO2), r = 0.96]. In these experiments, the pulse oximeter showed a precision of 4.7% oxygen saturation around the calibration curve, with a 95% confidence interval of +/- 9.4%.     

Morphine metabolism in acutely ill preterm newborn infants.

To examine the manner in which morphine is metabolized in acutely ill premature infants, we measured the levels of morphine, morphine-3- and -6-glucuronides, and codeine in timed urine specimens and paired plasma specimens at 4 hours and 24 hours after a single dose of morphine in 16 preterm infants (less than 32 weeks of gestational age). A large amount of unmetabolized morphine was found in the urine in 13 (81.2%) of the 16 infants at 4 hours; in 12 of them, morphine was excreted even at 24 hours. Urinary morphine levels varied greatly; the coefficient of variation was 130% at 4 hours and 118% at 24 hours. Codeine was not found in any of the infants. In 10 (62.5%) of the 16 infants, at least one metabolite was found in either plasma or urine. Plasma and urinary levels of morphine conjugates also varied greatly among these 10 infants (coefficient of variation: 109% to 317%). All six infants (37.5%) who had no metabolites excreted large amounts of unmetabolized morphine in the urine for up to 24 hours. Birth weight, gestational age, postnatal age, systemic blood pressure, and other clinical or physiologic variables did not differ significantly between the 10 infants who had morphine conjugates and the six who did not. We conclude that (1) nearly two thirds of acutely ill preterm infants born at less than 32 weeks of gestational age conjugate morphine; (2) irrespective of their ability to produce morphine conjugates, preterm infants excrete large amounts of morphine unmetabolized, as late as 24 hours after a single dose; (3) morphine handling patterns are highly variable among premature infants, and no obvious factors account for the variability; and (4) such variability in morphine handling in general, and the production of the highly potent morphine-6-glucuronide in particular, could explain the variance in morphine pharmacokinetic measures and in the clinical responses to morphine during the newborn period.     

Individualised pulse oximetry limits in neonatal intensive care.

AIM: To determine whether individualised limits for arterial oxyhaemaglobin saturation by pulse oximetry (SpO(2)) are more effective for detecting hypoxia and hyperoxia in sick newborn infants than setting fixed limits. METHODS: Six hundred and ninety two simultaneous measurements of SpO(2) and partial pressure of oxygen in arterial blood (PaO(2)) were made in 95 infants. The sensitivity and specificity for predicting hypoxia and hyperoxia using various fixed SpO(2) limits and also individualised SpO(2) limits, calculated using a standard equation, were determined and compared. RESULTS: None of the fixed limits for SpO(2) was both sensitive and specific for predicting hypoxia and/or hyperoxia. There was no difference between these and individualised limits. CONCLUSION: Individualised SpO(2) limits are no more effective than fixed SpO(2) limits for predicting hypoxia and/or hyperoxia in sick newborn infants. SpO(2) monitoring is not an ideal method for assessing PaO(2).     

The clinical utility of pulse oximetry in the pediatric emergency department setting.

Pulse oximetry provides a noninvasive, painless, accurate, and rapid method for measuring arterial oxygen saturation (SaO2). It has been shown to be valuable in anesthesia and critical care and recently has been used extensively in the outpatient setting. As is often the case with new technologies, little has been published on the basic issues of reliability, reproducibility, and effect on patient care. This prospective clinical study evaluated the basic principles of pulse oximetry in the pediatric emergency department setting and tested the hypotheses that pulse oximetry SaO2 measurements are reliable and provide valuable information, in addition to clinical and laboratory data which affect patient assessment and management. One hundred twenty patients were enrolled in phase 1 and 437 in phase 2 of the study. Pulse oximetry readings were reproducible with an intraclass correlation of 0.87. SaO2 measurements changed the assessed degree of illness in 188 (53%) patients; 47 (13%) were felt to be more ill and 130 (37%) to be less ill than at initial assessment. Sixty-nine (17%) patients were identified in whom SaO2 readings changed management plans; 27 (8%) were managed more aggressively (intubation, surgery, or admission), while 40 (11%) were managed less aggressively (discharged). In three cases, pulse oximetry was instrumental in the diagnosis of a serious illness. The results from this study indicate that pulse oximetry SaO2 readings are stable and reproducible and provide information which impacts significantly on patient assessment and management.     

Motion resistant pulse oximetry in neonates

BACKGROUND: Pulse oximetry is widely used in neonates. However, its reliability is often affected by motion artefact. Clinicians confronted with questionable oxygen saturation (SpO(2)) values often estimate the reliability by correlating heart rate (HR) obtained with the oximeter with that obtained by electrocardiogram. OBJECTIVE: To compare the effects of motion on SpO(2) and HR measurements made with Masimo signal extraction technology and those made with a Nellcor N-200. DESIGN: Continuous pulse oximetry and HR monitoring were performed in 15 healthy, term infants (mean (SD) birth weight 3408 (458) g) undergoing circumcision, using Masimo and Nellcor pulse oximeters and a standard HR monitor (Hewlett-Packard). Simultaneous minute by minute behavioural activity codes were also assigned. Baseline data were collected for 10 minutes when the infant was quietly asleep and then continued during and after circumcision for a total duration of one hour. The oximeter HR and SpO(2) values were compared and related to HR values obtained by ECG during all three periods. The effect of behavioural activity on SpO(2) and HR was also evaluated. RESULTS: When compared with results obtained with the Nellcor, the mean SpO(2) and HR were higher and the incidence of artefact lower with the Masimo during all three periods. Masimo HR more accurately predicted HR obtained with a standard monitor, with lower residual error. SpO(2) and HR values obtained with the Nellcor were lower and more variable during all behavioural states, especially crying, when excessive motion artefact was most likely. CONCLUSIONS: The data suggest that Masimo signal extraction technology may offer improvement in pulse oximetry performance, particularly in clinical situations in which extreme motion artefacts are likely.     

Making the most of pulse oximetry

A noninvasive device that gives continuous oxygenation readings has great appeal, and pulse oximetry has enjoyed wide acceptance. To use it most effectively, though, you need to understand the principles it's based on and know its limitations.     

Routine pulse oximetry in the asymptomatic newborn

OBJECTIVE: To assess the effect of routine measurement of postductal oxygen saturation as an adjunct to routine clinical examination in the asymptomatic newborn. DESIGN AND SETTING: Prospective study in a district general hospital. PATIENTS: All 6166 infants inborn between 1 April 1999 and 31 March 2001. INTERVENTION: Oxygen saturation was measured over two minutes, after the age of 2 hours and before discharge, in one foot of all babies not admitted directly to the neonatal unit. Babies with fractional (as opposed to functional) oxygen saturation (SaO(2)) below 95% were examined by the midwife. If this examination was abnormal or if normal but further measurements were below 95%, an echocardiogram was performed. All babies with cardiac malformations diagnosed by 1 year of age were identified from databases maintained at the regional cardiology referral unit and the regional congenital malformation survey. RESULTS: Measurements were made in 98% of eligible babies. A fractional SaO(2) less than 95% was found in 5% but persisted in only 1%. Structural cardiac malformations were found in 50 (8.1/1000), 26 of whom had isolated ventricular septal defects. Of the remaining 24 with other cardiac malformations, attention was first drawn to six by low SaO(2), and four more, first noticed for other reasons, also had low SaO(2). Low SaO(2) also first drew attention to 13 other babies ill for other reasons. CONCLUSION: Newborn babies with important cardiac malformations are often asymptomatic initially and the yield from clinical examination is poor. Measuring postductal saturation routinely in newborn babies before discharge is easy and can alert staff to ill babies.     

The use of pulse oximetry to detect congenital heart disease

OBJECTIVE: To evaluate whether pulse oximetry can be used as a screening test to detect congenital heart disease (CHD) in otherwise well newborns before nursery discharge. METHODS: Births at Lakeland Regional Medical Center (LRMC) who met inclusion criteria, had a single pulse oximeter reading before discharge. A normal reading was considered to be >94%. Abnormal readings were repeated on a different extremity and if still abnormal, an echocardiography was performed. The number of children with CHD and the number of echocardiograms were compared with the previous year at LRMC. RESULTS: There were 2114 infants enrolled, 88 echocardiograms (3.8%) were performed, and 43 were abnormal (yield = 48.9%), of which 12 required management (13.6%). The control group consisted of 2851 births, producing 108 echocardiograms (3.8%), 42 of which were abnormal (38.9%), and 13 required management (12.0%). No comparisons were significant. During both years, 3 children with cyanotic CHD were born. Routine pulse oximetry failed to detect a child with total anomalous pulmonary venous return. Not a single normal echocardiogram was generated by the study. CONCLUSION: Routine pulse oximetry was nearly 100% specific for detecting cyanotic CHD; as a result there was no increase in the number of echocardiograms. Routine pulse oximetry did detect a child who might not have been detected otherwise but failed to detect one that should have been detected.     

Oxygen saturation in pulse oximetry in hemoglobin anomalies

Pulse oximetry is an essential diagnostic method in pediatric emergency medicine and pediatric intensive care. However, if undetected hemoglobin anomalies are the underlying cause measurements of low oxygen saturation can be interpreted incorrectly or may lead to unnecessary examinations. In 2 recently discovered hemoglobin anomalies, Hb Bonn and Hb Venusberg, this resulted in extensive and repeat cardiopulmonary examinations. This review aims to provide an overview of hemoglobin anomalies causing low oxygen saturation.We describe the methods required for differential diagnosis of hemoglobin anomalies, such as hemoglobin electrophoresis, High Performance Liquid Chromatography, hemoglobin gene sequencing and spectral photometry, and the difficulties with the interpretation of results. Furthermore, with a review of the literature we provide an extensive overview of hemoglobin anomalies which result in low oxygen saturation measurement in pulse oximetry. With the examples of Hb Bonn, a novel hemoglobin mutation of the proximal α1-globin, which results in false low pulse oximetry measurements of oxygen saturation, and Hb Venusberg, a low oxygen-affine hemoglobin mutation of the β-globin, we highlight the difficulties arising from the respective case histories.In pediatric medicine, hemoglobin anomalies must be included in the diagnosis as a possible underlying cause of low oxygen saturation in case of ambiguous or conflicting pulse oximetry findings.     

The use of pulse oximetry in the prevention of hyperoxaemia in preterm infants

When deciding an appropriate upper limit for pulse oxygen saturation (SpO₂) in preterm infants the usefuleness of current data is limited by the fact that previous studies have examined a population of more mature infants and children or have applied various exclusion criteria which produce results unrepresentative of clinical practice. We tested the hypothesis of previous workers that maintaining the SpO₂ below 98% would ensure an arterial oxygen tension (PaO₂) less than 12 kPa. A total of 477 simultaneous measurements ofPaO₂ and SpO₂ were made using Ohmeda Biox oximeters on 43 infants who were less than 33 weeks gestation and receiving supplementary oxygen. Of 435 measurements performed when the SpO₂ was 97% or less, 26 (6%) had aPaO₂ greater than 12 kPa. Further examination of the data showed that of 108 estimations performed when the SpO₂ was less than 94%, none had aPaO₂ greater than 12kPa.Conclusion When using Ohmeda Biox pulse oximeters an upper limit of 97% for SaO₂ is not effective in preventing hyperoxaemia; however, a linit of 93% is likely to maintain thePaO₂ below 12 kPa.     

Apparent desaturation on pulse oximetry because of hemoglobinopathy

Hemoglobinopathies are an uncommon cause of cyanosis and low oxygen saturation on pulse oximetry. However, when they do occur, they can present a complex clinical scenario for the emergency physician. We report the index case of a previously undescribed hemoglobinopathy that presented to the pediatric emergency department. The evaluation and management of the cyanotic/hypoxic child and review of hemoglobinopathies are presented here.